Ecological Effects of the Moss Landing Powerplant Thermal Discharge 

A report submitted to the Monterey Bay National Marine Sanctuary 

Sanctuary Integrated Monitoring Network (SIMoN) 

and 

Monterey Bay Sanctuary Foundation 

June 2006 

Moss Landing Marine Laboratories 

8272 Moss Landing Road 

Moss Landing CA 95039 
 Moss Landing Powerplant Thermal Discharge Effects 2 

Moss Landing Marine Laboratories 

Table of Contents 

Executive Summary........................................................................................................4

1 Introduction..............................................................................................................6

2 Plankton ...................................................................................................................8

2.1 Introduction ...........................................................................................................................8

2.2 Previous Studies.....................................................................................................................9

2.3 Objectives .............................................................................................................................10

2.4 Methods.................................................................................................................................11

2.4.1 Sampling........................................................................................................................................11

2.4.2 Bacterial analysis ..........................................................................................................................11

2.4.3 Phytoplankton analysis.................................................................................................................12

2.4.4 Production and Respiration ..........................................................................................................13

2.4.5 Statistical analysis.........................................................................................................................13

2.5 Results ...................................................................................................................................14

2.5.1 Temperature ..................................................................................................................................14

2.5.2 Bacteria..........................................................................................................................................14

2.5.3 Phytoplankton ...............................................................................................................................15

2.5.4 Gross Primary Production and Community Dark Respiration...................................................16

2.6 Discussion .............................................................................................................................16

2.7 Literature Cited...................................................................................................................19

2.8 Tables and Figures ..............................................................................................................22

3 Benthos...................................................................................................................34

3.1 Introduction .........................................................................................................................34

3.2 Objectives .............................................................................................................................35

3.3 Background ..........................................................................................................................36

3.3.1 Intertidal Ecological Background ................................................................................................36

3.3.2 Shallow Subtidal Ecological Background...................................................................................37

3.4 Methods.................................................................................................................................38

3.4.1 Intertidal Methods.........................................................................................................................38

3.4.2 Subtidal Methods ..........................................................................................................................40

3.5 Results ...................................................................................................................................41

3.5.1 Intertidal Results ...........................................................................................................................41

3.5.2 Subtidal Results.............................................................................................................................44

3.6 Discussion .............................................................................................................................47

3.6.1 Results of Study Objectives .........................................................................................................47

3.6.2 Discussion of Thermal Impacts....................................................................................................48

3.6.3 Intertidal Ecological Discussion ..................................................................................................50

3.6.4 Subtidal Ecology Discussion........................................................................................................54

3.7 Historical Data .....................................................................................................................58

3.8 Literature Cited...................................................................................................................60

3.9 Tables and Figures ..............................................................................................................65
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4 Fish.........................................................................................................................95

4.1 Introduction .........................................................................................................................95

4.2 Historical Data .....................................................................................................................95

4.3 Bat Ray Observations .........................................................................................................97

4.4 Discussion .............................................................................................................................97

4.5 Literature Cited...................................................................................................................98

4.6 Tables and Figures ..............................................................................................................99

5 Birds ..................................................................................................................... 100

5.1 Introduction .......................................................................................................................100

5.1.1 Resident seabirds ........................................................................................................................100

5.1.2 Wintering birds ...........................................................................................................................100

5.1.3 Migratory seabirds ......................................................................................................................101

5.2 Methods...............................................................................................................................101

5.3 Results .................................................................................................................................102

5.3.1 Migratory season (May/June) ....................................................................................................102

5.3.2 Summer season (September)......................................................................................................103

5.3.3 Winter season (January/February) .............................................................................................103

5.4 Discussion ...........................................................................................................................104

5.5 Historical Database ...........................................................................................................106

5.6 Literature Cited.................................................................................................................106

5.7 Tables and Figures ............................................................................................................107

6 Acknowledgements ............................................................................................... 112
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Moss Landing Marine Laboratories 

Executive Summary 

During the period 2002-2005 a study of the Moss Landing Power Plant was undertaken 

by Moss Landing Marine Laboratories under the auspices of the Sanctuary Integrated 

Monitoring Network (SIMoN) of the Monterey Bay National Marine Sanctuary. The 

study focused on plankton, sand beach and shallow subtidal benthos, and birds. The 

primary goals of the study were to identify if changes in the distribution or community 

structure of the plankton, benthos, and birds could be correlated with the thermal plume 

from the powerplant outfall, and in the case of benthos, to set a long-term baseline of the 

invertebrate fauna near the outfall and to compare beach fauna to a study done in 1975. In 

addition a database of previously performed studies on fish and benthos was compiled. 

The study was not designed to determine the causal factors of any observed distributional 

or community changes. 

The mean temperature of water exiting the Moss Landing Power Plant (MLPP) outfall was 

22.3 o

C and dropped to 14.5 oC 100 m from the discharge site and 14.1 oC 500 m from the 

discharge site. Sample design of the plankton investigations provided measurements along 

the cooling-water flow-path, such that conditions before intake, during entrainment and after 

discharge into Monterey Bay could be assessed. Bacterial growth was enhanced as a result of 

passage through the MLPP cooling system, as evidenced from increases in bacterial colony 

growth, increases in the frequency of dividing cells, and increased dark respiration in water 

sampled at the immediate exit from the power plant. Phytoplankton were negatively 

impacted after passage through the MLPP cooling system as shown by reductions in 

photochemical quantum efficiency (Fv/Fm), increases in pheopigment/chl a ratios, and 

decreases in phytoplankton gross primary productivity at the power plant exit station. Thus, 

bacteria and phytoplankton were differentially impacted by once-through cooling transport. 

However, differential enhancement and inhibition effects on bacteria and phytoplankton, 

respectively, could not be detected after discharge and dilution into local Monterey Bay 

waters. 

There were no detectable significant impacts of the MLPP outfall on intertidal and shallow 

subtidal faunal communities. The Outfall and MBARI intertidal stations had significantly 

more polychaete worms, however the total number of individuals, species, and biomass were 

similar along the exposure gradient (in and outside the canyon). There was no significant 

difference in the abundance of the intertidal total fauna, crustaceans, or polychaetes between 

1975-76 and 2003-05. There were, however, significantly fewer species in 2003-05. Since 

the sea otters arrived in the central bay in the mid 1970’s, Pismo clams have been rare on the 

regional beach and populations continue to be suppressed. Faunal community patterns 

demonstrated the depth zonation of key species within the surf zone and also an increase in 

the density of species from 1 m to 4 m depth. 

No negative impacts on seabird abundance and distribution as a direct result of the thermal 

plume were observed (e.g., no species were observed actively avoiding the thermal plume). 

Seasonal abundance of locally resident, migratory, and wintering seabirds common in the 

nearshore environment of Monterey Bay was reflected in the species composition observed at 
 Moss Landing Powerplant Thermal Discharge Effects 5 

Moss Landing Marine Laboratories 

both the Plume and Reference survey sites. Some seabird species, especially cormorants, 

showed an increased occurrence at the Plume site, indicating potential utilization of the 

plume for foraging on small schooling or benthic fishes. Sea otters were regularly observed 

utilizing the thermal plume for grooming, resting, foraging, and interacting with other sea 

otters. The reasons for the otter utilization of the plume are uncertain, but may have to do 

with the relatively warmer water at the plume. Bat Rays (Myliobatis californica) aggregate at 

the surface in the powerplant outfall plume mostly in winter months. The reason for the 

aggregations is unknown, but may relate to thermoregulation. 
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Moss Landing Marine Laboratories 

1 Introduction 

The Moss Landing power plant is California’s largest power plant. It is located in Moss 

Landing, CA, roughly midway between Santa Cruz and Monterey (Fig. 1-1). Cooling 

water for the power plant is taken up within Moss Landing Harbor and discharged into 

Monterey Bay 200 m from shore and approximately 7 m below the sea surface. The 

thermal effluent temperature is approximately 13 o

C higher than the intake cooling water. 

Both the entrainment process and the discharge of the heated water have the potential to 

impact benthic and pelagic ecosystems, although these effects have never before been 

quantitatively evaluated. 

We have targeted several types of short-term and long-term indicator communities. 

Because of their relative lack of mobility, benthic invertebrates living in the intertidal 

sand beach and shallow surf zone are the best long-term indicators of potential negative 

impacts to the nearshore ecosystem. In contrast, marine birds are the best short-term 

indicators because of their ability to respond to negative impacts by changing location, 

while the short turnover time in the planktonic community also gives it the ability to 

respond quickly to change and thus act as a short-term indicator of ecosystem change. 

All of these communities, benthic infauna, plankton, and marine birds, were sampled at 

the thermal plume and at control sites outside the plume. 

The sampling design permitted us to resample benthic communities that were sampled in 

the 1970’s at the end of a cold, productive period in the CA current system. The inner, 

wave-exposed shelf ecosystem, which is highly sensitive to a wide variety of natural and 

anthropogenic disturbances, is a prime target for exploring future, long-term changes in 

ecosystem dynamics. We have provided the first complete baseline on nearshore 

planktonic communities at Moss Landing, which are likely to change as the extremely 

high rates of habitat erosion in Elkhorn Slough accelerate. We have also extended the 

first quantitative survey of nearshore marine birds from 2 to 5 years, again providing a 

solid baseline for assessing future ecosystem changes. We have compiled all historical 

community data on benthic invertebrates, plankton, marine birds, fishes, and related 

physical and chemical habitats conditions into the project database. Most of these 

historical data were collected by students and staff at Moss Landing Marine Laboratories 

(MLML). Since the marine lab overlooks the study site, most of the future work is also 

likely to be done by MLML. 
 Moss Landing Powerplant Thermal Discharge Effects 7 

Moss Landing Marine Laboratories 

Figure 1-1. Maps showing location of study area on Monterey Bay in central California. Inset shows close-up of Moss Landing vicinity with the powerplant outfall. 
 Moss Landing Powerplant Thermal Discharge Effects 8 

Moss Landing Marine Laboratories 

2 Plankton 

Prepared by Gala Wagner and Dr. Nick Welschmeyer 

2.1 Introduction 

Electric power plants account for 75 – 80% of the thermal pollution in the U.S. (Laws 2000). 

The increased use of cooling water in the electricity generating industry leads to potential 

impacts on estuarine and marine resources since cooling water is largely of marine origin 

(Laws 2000, Turnpenny and Coughlan 2003). This report describes experiments that were 

designed to measure impacts, if any, on planktonic organisms that are entrained and 

ultimately heated in cooling water that is pumped through the recently modernized Moss 

Landing Power Plant (MLPP) currently operated by LS Power. 

Moss Landing Power Plant is the largest energy producing plant (2545 megawatts) in 

California (Commission 2004); it is located in Moss Landing, CA roughly midway between 

Santa Cruz and Monterey. Cooling water for the facility is drawn from two separate intake 

structures within Moss Landing harbor. Historically, cooling water from five units was 

discharged directly into Elkhorn Slough, one of California’s largest estuaries, but this 

practice was discontinued in 1995 (Tenera 2000). Currently MLPP discharges thermal 

effluent into Monterey Bay through two subsurface conduits 200 m from shore and 

approximately 7 m below the sea surface ( Tenera 2000, Paduan 2002). The discharge into 

Monterey Bay is estimated at 4.56 billion liters per day, equivalent to half the volume of 

Elkhorn Slough (Genz 2003). The average temperature of the intake water is 13.9 oC with a 

range of 12.9 oC to 18.6 oC. After a residence time of approximately 30 minutes in the power 

plant (Genz 2003), the temperature of the discharged water is elevated to an average of 22.3 

oC with a range of 17.9 oC to 27.2 oC (Tenera 2000). Moss Landing Power Plant is permitted 

by the Monterey County Water Quality Resources Control Board to increase the ambient 

(intake) water temperature by 14.3 oC daily (Tenera 2000). Most power plants in the United 

States operate so that the effluent water is between 5 oC and 15 oC above ambient (Laws 

2000). However, the EPA criteria specifies that the maximum acceptable increase in the 

weekly average temperature resulting from artificial sources is 1.0 oC during all seasons of 

the year (EPA 1986). The discharge plume is turbulent, producing rapid mixing with 

surrounding seawater, and therefore rapid cooling of the discharge water (Paduan 2002). 

In 2001 the MLPP upgraded its energy production capacity to 2545 MW, compared to 1250 

MW in 2000. This doubling of electrical output has doubled the volume of thermal effluent 

into Monterey Bay. The maximum heat loading for the modernized facility increased about 

41% over present conditions to 182 million BTU/min, although the addition of the new units' 

cooling water to the existing discharge lowered the maximum temperature by about 2.4 °C 

(Paduan 2002). The present report provides an analysis of entrainment effects to lower 

trophic level organisms, bacteria and phytoplankton, which were not considered in previous 

studies of the MLPP (Tenera 2000, Paduan 2002). Recent concerns over pathogenic bacteria 

and harmful algal blooms provide motivation for analysis of entrainment effects on these 

organisms (Horner et al. 1997). 
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Moss Landing Marine Laboratories 

2.2 Previous Studies 

Planktonic organisms entrained in power plant cooling water are exposed to initial thermal 

increase within the power plant condenser coils and may be affected (Clark 1989; Langford 

1990; Laws 2000; Turnpenny and Coughlan 2003). The resulting thermal effluent that enters 

the surrounding marine environment may also affect planktonic and benthic organisms in the 

vicinity of the discharge site (Clark 1989; Langford 1990; Laws 2000). 

The 1970s brought significant scientific focus to entrainment in power plant cooling water 

systems, subsequent thermal discharge and the potential negative effects on commercially 

important fish larvae, marine invertebrates, and the environment (Capuzzo 1980). From the 

late 1970s the number of publications declined, though the amounts of heat discharged 

increased, and there continues to be an increase in the building of power plants to meet new 

demand and replace older power plants (Langford 1990). 

Studies focusing on entrainment of zooplankton and commercially important larvae found 

reduced survival of organisms after entrainment in the cooling system of power plants 

(Carpenter et al. 1974; Davies and Jensen 1975; Heinle 1976). Zooplankton losses have been 

reported to range from 0% - 100% loss (Clark and Brownell 1973; Langford 1983). At four 

power plants along the California coast, zooplankton losses were related positively with 

temperature increase (Icanberry and Adams 1974). 

The impact of entrainment on phytoplankton is generally negative and appears to result from 

thermal stress and/or chlorination, but it is unclear whether cells have actually been killed or 

just temporarily stressed (Laws 2000). Several studies have shown that primary productivity 

decreases 2 to 80 % in thermal effluent from power plants (38 %, Morgan and Stross (1965); 

2 – 37 %, Fox and Moyer (1973); 26 %, Suchanek (1975); 30 %, Bienfang and Johnson 

(1980); 22 %, Miller et al. (1976); 20 -80 %, Chang and Rossman (1985); 60 %, Servais and 

Billen (1989); 36 %, Martinez-Arroyo et al. (1999); 38 %, Guseva and Chebotina (2000)). 

Others found that entrainment of phytoplankton had minimal impact on phytoplankton 

productivity (Dunstall 1985; Hirayama and Hirano 1970; Socal et al. 1999). Thus, the effects 

of thermal discharge on phytoplankton appear to vary widely. 

The impact of heated discharge water on phytoplankton seems dependent on both ambient 

sea temperature and the subsequent increase in temperature from the power plant (i.e. the 

overall effect is not dependent on delta o

T alone). In the temperate northeastern Pacific and 

northwestern Atlantic oceans it was reported that an increase in temperature of 8 – 11 oC 

stimulated photosynthesis when ambient water temperatures were 16 oC or cooler, and 

inhibited photosynthesis when ambient water temperatures were 17 oC or warmer ( Morgan 

and Stross 1965; Briand 1975). These findings were supported by Chang and Rossmann 

(1985) who found variable effects of temperature increase on phytoplankton related to the 

temperature differential relative to ambient natural temperature. 

Temperature increases may also affect the phytoplankton assemblage by eliminating 

stenothermal forms and increasing remaining eurythermal species (Naylor 1965) thereby 

altering phytoplankton community structure. Briand (1975) found that in two southern 
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Moss Landing Marine Laboratories 

California coastal power plants passage through the condenser tubes enhanced the dominance 

of two heat tolerant phytoplankton species (Asterionella japonica and Gonyaulaux polyedra) 

while killing less heat tolerant diatoms (45.7 % decrease in cell numbers) and dinoflagellates 

(32.8 % decrease in cell numbers). Rossmann et al. (1980) found that at elevated 

temperatures, phytoplankton assemblages exhibited a decrease in species diversity, seen as a 

shift from a diatom dominated assemblage to one dominated by green algae. Saravanane et 

al. (1998) found increased dominance of Thalassiosira, a diatom genus, after passage 

through a power plant cooling system. Touliabah and Taylor (2004) also found dominance 

of Thalassiosira in effluent at 45 oC and domoic acid producing Pseudonitzschia

pseudodelicatissima in effluent at 50 oC. This finding is particularly relevant to the Monterey 

Bay ecosystem since Pseudonitzschia blooms are well documented locally (Scholin et al. 

2000). However, it is unknown if the MLPP will affect harmful algal blooms in Monterey 

Bay. Corroborating laboratory studies (Ukeles 1961; Goldman and Ryther 1976) indicate 

that the maximum temperature for normal growth is variable among phytoplankton groups, 

therefore supporting the notion that temperature may result in preferential selection of 

tolerant species. However, field studies have also been completed showing no significant 

change in phytoplankton assemblages caused by thermal stress in discharged cooling water 

(Suchanek 1975; Martinez-Arroyo et al. 1999). 

Bacteria are generally regarded as the organisms most tolerant of temperature (Brock 1985). 

Mesophilic bacteria have an optimal growth range of temperature between 20 and 45 oC, and 

thermophilic bacteria have an optimal growth range of temperature between 45 and 70 oC 

(Brock 1985). Shiah and Ducklow (1994) found that bacterial growth rates were positively 

correlated with incubation temperatures between 3 and 25 oC; they argued that marine 

bacterial production rates may in fact be temperature limited, not necessarily nutrient and/or 

food limited. At higher temperature increases the literature results are variable. High 

temperature (40 oC) was shown to decrease bacterial production by 9 to 39 % (Choi et al. 

2002). Miller et al. (1976) and Fox and Moyer (1973) found that the numbers of bacteria 

increased in the discharge of power stations. Suzdaleva (1998) found bacterial populations 

from the intake water were significantly reduced when heated to temperatures higher than 50 

oC, while others found that bacterial populations from the discharge water were not 

significantly reduced when heated to temperatures up 70 oC (Rankin et al. 1974). Solski 

(1974) found no difference in the abundance of bacterial populations at thermal discharge 

sites compared with intake waters. 

Clearly the expected effects of entrainment on bacteria and phytoplankton may be site 

specific and attempts to assess impacts may differ if assays for standing crops alone are not 

augmented by complementary assays for productivity and growth. Snapshot comparisons of 

organism concentrations before and after cooling water entrainment may be an appropriate 

metric to measure effects on larger organisms trapped on filters or macerated by pumps, but 

standing crops of smaller organisms may appear to remain relatively unchanged using 

conventional counting techniques while viability per se may be quite different. 

2.3 Objectives 

The following objectives were addressed in this study: 
 Moss Landing Powerplant Thermal Discharge Effects 11 

Moss Landing Marine Laboratories 

Determine the impact of the thermal increase and entrainment on the biomass and 

productivity of bacteria. 

Determine the impact of the thermal increase and entrainment on the biomass, physiology, 

and productivity of phytoplankton. 

Assess the spatial extent of the area impacted surrounding the discharge plume within 

Monterey Bay, California. 

2.4 Methods 

2.4.1 Sampling 

Surface water samples were collected in triplicate in darkened 1.0 L polycarbonate bottles 

(rinsed three times at each station before filling) at five sites chosen to represent the path 

traveled from the intake source in Moss Landing Harbor to the discharge site in Monterey 

Bay (Fig. 2-1). The station sequence was as follows: Station 1 (Moss Landing Harbor 

directly in front of intake chambers), Station 2 (the surge chamber on MLPP property that 

represented the closest access to heated water immediately leaving the plant), Station 3 

(Monterey Bay, directly over the thermal discharge site located 200 m from shore), Station 4 

(Monterey Bay, 100 m west of the discharge site) and Station 5 (Monterey Bay, 500 m west 

of the discharge site). Temperature was measured at each sampling site using a digital 

thermometer (Hanna instruments) accurate to ± 0.2 oC. Samples were collected and analyzed 

at least monthly from March 2004 to November 2005. 

2.4.2 Bacterial analysis 

Biomass 

The standing crop biomass of bacteria was measured using two techniques, direct bacterial 

counts and colony growth. For direct bacterial counting, sample water (15 ml) from each site 

was preserved with 1% gluteraldehyde and 1-5 ml was quantitatively filtered onto 0.02 μm 

Anodisc filter, backed with 0.45 μm Millipore filter. The sample was filtered to dryness and 

removed while the vacuum was on. The dry filter was placed on top of 100 μl of working 

stock SYBR Gold nuclear stain solution (Molecular Probes/Invitrogen, Inc.) on a sterile Petri 

dish and stored in the dark for 15 minutes (working stock was a 400-fold dilution of the 

10,000x SYBR Gold concentrate distributed by Invitrogen). After the staining period, the 

filter was placed back on the filtration rack and rinsed with 0.02 μm filtered de-ionized 

water. The filter was placed on a microscope slide with one drop of Slow Fade and a glass 

cover slip was placed over the filter. Slides were stored in the freezer (Noble 2001) until 

bacteria cells could be enumerated using an epifluorescent microscope under blue light 

excitation (Hagstrom et al. 1979; Sherr et al. 2001); at least 100 bacterial cells were 

enumerated per counting grid using 1250x magnification. 

Bacterial colony growth was measured using unpreserved sample water. A quantitative 

volume of sample (10-25 l) was streaked onto Difco marine agar plates in triplicate with 
 Moss Landing Powerplant Thermal Discharge Effects 12 

Moss Landing Marine Laboratories 

sterile transfer loops and incubated at 25 oC for 24 hrs in the dark. The bacterial colonies 

were counted at the end of the incubation time (Wood 1965). 

Productivity 

Relative productivity of bacteria was estimated by determining the frequency of dividing 

cells (FDC) as described by Hagstrom et al. (1979) and Sherr et al. (2001). Bacterial cells 

were enumerated as explained previously, noting paired cells and single cells, to calculate 

FDC as a percentage. The technique provides a means to estimate relative growth rates 

without the need for incubations. 

2.4.3 Phytoplankton analysis 

Biomass and degradation 

Biomass and potential degradation of the phytoplankton was measured by fluorometric 

chlorophyll analysis using an acidification protocol on acetone pigment extracts. 

Quantitative volumes of sample water (100 ml to 500 ml) from each site were filtered onto a 

Whatmann glass fiber filter (GF/F; 0.7 m nominal pore size). Phytoplankton pigments were 

extracted by placing the filter in a 2.0 ml micro-centrifuge tube with 1.2 ml of 90 % acetone 

stored at -20 oC for a minimum of 24 hours in the dark. After extraction, the samples were 

vortexed, the filters were compressed to the bottom of the tube with a stainless steel spatula 

and centrifuged for approximately 1 minute in a microfuge to remove debris. The extract 

was quantitatively sub-sampled (100 to 500 l) and diluted in 5 ml of acetone in a glass 

culture tube for biomass and degradation pigment analysis. Fluorescence was measured 

using a Turner Designs 112 and/or a Turner 10AU fluorometer to determine chlorophyll a

(chl a) and pheophytin a concentrations (Strickland and Parsons 1972). The remaining 

extract volume was retained for later HPLC analysis of pigments to corroborate data 

generated by fluorescence acidification protocol. 

Phytoplankton Physiology 

Instantaneous measurements of photochemical efficiency based on variable fluorescence 

were made with a pulse amplitude modulated (PAM) fluorometer (Water PAM, H. Walz, 

Germany). The fluorescence ratio, Fv/Fm corresponding to photochemical efficiency, was 

determined using the saturation pulse technique (Schreiber et al. 1998) on dark-adapted 

samples. The technique is rapid, sensitive and density-independent, allowing quantitative 

assessment of algal physiological status from variable fluorescence properties of photosystem 

II (Genty 1989). Fluorescence measurements were made on triplicate samples (3 ml) from 

each site; sample water was returned to the laboratory for measurements within three hours 

of collection. The saturation pulse method provides quantitative information on 

photochemical efficiency (also termed photochemical yield, the fraction of absorbed photons 

utilized in photochemical energy conversion) calculated as: 

 YIELD = (Fm’ – F)/Fm’ = Fv/Fm’ where, 

Fm’= maximum fluorescence 
 Moss Landing Powerplant Thermal Discharge Effects 13 

Moss Landing Marine Laboratories 

F = minimum fluorescence 

Fv = variable fluorescence 

Fv/Fm’= unitless ratio 

The variable fluorescence ratio, Fv/Fm, produces values ranging from 0.0 to 0.7 (Genty 

1989, Schreiber at al. 1998). Exponentially growing phytoplankton usually exhibit higher 

dark-adapted Fv/Fm values from 0.55-0.70. Decreases from the highest possible values of 

Fv/Fm have been shown to indicate physiological stress to the photoautotroph in both higher 

land plants and algae. 

2.4.4 Production and Respiration 

On three sampling dates (6/15/05, 9/14/05, and 11/1/05) gross primary production and dark 

respiration of samples from Stations 1, 2, 3 and 4 were determined using light-dark bottle 

incubations analyzed for oxygen exchange rates with high precision potentiometric Winkler 

titrations (Furuya and Harada 1995). Duplicate surface water samples were collected in 2 L 

clear polycarbonate bottles. Sample water from each 2 L bottle was distributed to three 300 

mL biological oxygen demand (BOD) bottles with polypropylene tubing to reduce oxygen 

introduction. One bottle was immediately fixed with manganese chloride and alkaline iodide 

to determine the initial oxygen content, one bottle was wrapped in aluminum foil (dark 

bottle), and the third bottle was left uncovered (light bottle). The light and dark bottles were 

placed in an outdoor incubation tank with continuous seawater flow at 25 % irradiance for a 

24 hr incubation. At the end of 24 hr each bottle was fixed with manganese chloride and 

alkaline iodide. Algal gross primary production rate was determined from the light bottle 

minus dark bottle; dark community respiration was determined from the initial oxygen level 

minus final dark bottle. 

2.4.5 Statistical analysis 

An Analysis of Covariance with a Tukey’s pairwise comparisons test was used to detect 

differences among the stations for the following parameters: temperature, bacterial biomass, 

FDC, phytoplankton biomass, degradation pigments (pheopigments), photochemical yield, 

gross production, and community respiration (Zar 1999). Normality, equality of variances, 

and independence were confirmed by analysis of residuals. The correlative relationship 

between temperature and the above parameters were analyzed. 

Absolute values of parameters on any given date provided useful comparisons of biological 

conditions among stations. However, during the sampling period (3/4/04 – 11/1/05) seasonal 

variation in biomass and production confounded useful comparisons among sampling dates. 

In order to remove seasonal variations in biomass and production among sampling dates, the 

results were normalized to Station 1 (the intake source water) for each biological parameter 

measured on a given date. Normalized values were scaled to 1.0 for Station 1 providing a 

‘snapshot’ of the relative variation in parameters measured at all five stations for a given day; 
 Moss Landing Powerplant Thermal Discharge Effects 14 

Moss Landing Marine Laboratories 

mean values of the relative changes in specific parameters could then be summarized for all 

sampling dates. 

2.5 Results 

2.5.1 Temperature 

The mean temperature of source water entering MLPP (Station 1) was 15.1±1.8 oC (3/4/04 – 

11/1/05). The power plant increased the cooling water temperature to a mean of 22.3±2.3 oC 

in the surge chamber (Station 2), the sampling location with the highest water temperatures 

and most reflective of conditions at the immediate exit of the power plant. The mean 

temperature at the surface of the discharge site in Monterey Bay (Station 3) was 18.4±2.1 oC, 

the mean temperature 100 m from the discharge site (Station 4) was 14.5±2.0 oC, and the 

mean temperature 500 m from the discharge site (Station 5) was 14.1±1.9 oC (Figs. 2-2 and 

2-3). The maximum temperature measured at the power plant surge tank (Station 2) was 

27.2 oC and at Station 3 was 24.6 oC (Fig. 2-2). The mean temperatures at Stations 2 and 3 

were significantly higher (p < 0.0001) than all other stations and significantly different (p < 

0.001) from each other. Due to the tidal influence of warmer shallow waters from Elkhorn 

and Tembladero Sloughs the source water (Station 1) was on average 0.8 oC warmer than the 

outer bay stations (Stations 4 and 5) but Stations 1, 4, and 5 did not differ significantly (p 

0.127). The typical range of coastal sea surface water temperature in Monterey Bay is 10 – 

18 oC, during an El Niño event the typical range is increased by 2.7 oC, and during a La Niña 

event the typical range is lowered by 1.8 oC. 

2.5.2 Bacteria 

Biomass 

Mean bacterial biomass from epifluorescence direct counts at the surge tank (Station 2) was 

significantly greater (mean = 4.2 x 105

 cells/mL) than at the intake site (Station 1) (mean = 

3.1 x 105

 cells/mL) (p = 0.001) (Figs. 2-4 and 2-5). Bacterial biomass at station 2 was also 

significantly higher than Stations 3 (p < 0.001) and 4 (p = 0.019) but not Station 5 (p = 

0.530). Stations 1, 4, and 5 (intake water and two outer Monterey Bay stations) did not differ 

significantly (p 0.803). There was no relationship (r2 = 0.099, p = 0.090) between average 

bacterial biomass and temperature (Fig. 2-6). Generally, the levels of direct count total 

bacteria among stations on any given date did not differ by more than a factor of two. 

The colony growth assessments on bacterial agar plates showed much larger ranges in 

bacterial activity among stations. On average the bacterial colony biomass at the surge tank 

(Station 2) was more than ten times higher than at the intake site (Station 1)(Figs. 2-7 & 2-8). 

This indicates a significant increase in cultivable bacterial cells originating after passage 

through the power plant. Inactive cells could have been induced into a higher rate of 

reproduction as a result of temperature increases and/or a higher population of cultivable 

cells could have been scavenged from conduit walls within the circulation system. The surge 

tank (Station 2) was significantly different (p  0.001) from all other stations. Station 3 did 

not significantly differ from the remaining stations (p 0.567). Stations 1, 4, and 5 did not 

differ significantly from each other (p 0.547). There was a positive relationship (r2

 = 

0.7806, p < 0.001) between source temperature and cultivable bacterial colony counts (Fig. 
 Moss Landing Powerplant Thermal Discharge Effects 15 

Moss Landing Marine Laboratories 

2-6). No attempt was made to identify the bacterial taxa present in the grow-out colonies, but 

it is well recognized that cultivable bacteria constitute much less than 10% of the total 

bacterial cell population in natural marine samples (Azam 2001). The results above indicate 

that increases in cultivable bacteria were detectable at the immediate exit from the MLPP 

cooling system; however, this bacterial signal was not detectable at the Monterey Bay 

stations per se. 

Bacterial Productivity 

Frequency of dividing cells (FDC) provides another indicator of bacterial productivity 

(Newell 1981) based on total bacteria enumeration, which can be contrasted to colony 

growth, which only reflects activity of those cells capable of cultivation on agar growth 

media (Azam 2001). The results indicated by percentage that the surge tank (Station 2; mean 

= 29.7±3.6 %) had twice as many dividing (productive) cells as the intake site (Station 1; 

mean = 12.9±2.4 %) (Figs. 2-10 and 2-11). The FDC of Station 2 was significantly greater 

than all other stations (p  0.005). The FDC of Station 3 was 18.2 ± 8.6 %, which was 

significantly different from Station 1 (p = 0.003), but did not differ significantly from 

Stations 4 and 5 (p 0.744). The FDC of Station 4 was a 15.1±7.4 %, and Station 5 was 

14.3 ± 7.3 %; Stations 1, 4, and 5 did not differ significantly (p 0.810). There was a 

positive relationship (r2

 = 0.579 p = 0.000) between temperature and FDC (Fig. 2-12). The 

results of bacterial productivity from FDC generally parallel those from colony growth. Both 

methods indicate enhanced bacterial growth by thermal increase and entrainment in the 

MLPP. 

2.5.3 Phytoplankton 

Biomass and Degradation 

Relative standing stocks of phytoplankton, estimated from chl a determinations, were 

variable and indicated no clear trend among stations, possibly a result of patchy 

phytoplankton distributions. There was not a significant relationship (r2 = 0.007, p = 0.408) 

between phytoplankton biomass (chl a) and temperature (data not shown). 

The relative ratio of pheopigments to chl a, determined by the routine fluorescence 

acidification protocol (Strickland and Parsons 1972), did show repeatable trends along the 

sampling grid. The ratio of pheopigments to chl a represents degradation of chl a by 

phytoplankton cell death and/or grazing of cells, relative to algal cellular chl a; it may also 

indicate the presence of sediment-derived particles that are dominated by pheopigments 

degradation products. High pheo/chl a ratios can also result as an artifact of chl b

contamination using fluorescence acidification protocol (Welschmeyer 1994); however, 

corroborating HPLC assays did not show relative increases in chl b concentrations at the 

surge tank (Station 2). The mean pheopigment to chl a ratio was 2.5 times greater at Station 

2 (mean = 1.32) than at Station 1 (mean = 0.47)(Figs. 2-13 and 2-14). The surge tank 

(Station 2) was significantly different (p  0.002) from all other stations. The mean ratio of 

pheopigments to chl a at Station 3 (mean = 0.77) was 1.6 times greater than Station 1 (Figs. 

2-13 and 2-14). Station 3 was significantly different (p  0.007) from Stations 1 and 4, but 

did not differ significantly (p = 0.576) from Station 5. Stations 1, 4, and 5 did not differ 
 Moss Landing Powerplant Thermal Discharge Effects 16 

Moss Landing Marine Laboratories 

significantly (p  0.956). There was a positive relationship (r2 = 0.301, p < 0.001) between 

the pheopigments-to-chl a ratio and temperature (Fig. 2-15). These results indicate 

significant phytoplankton cell death and/or the entrainment of substantial quantities of 

sediment that are typically dominated by pheopigments relative to chl a. Quantification of 

sediment concentration should be considered in future analyses. 

Phytoplankton Physiology 

The photochemical yield (Fv/Fm) measured by variable fluorescence was significantly higher 

(p < 0.001) at the intake site (Station 1; mean = 0.45 ± 0.07) than at the surge tank (Station 2; 

mean = 0.27 ± 0.11), indicating high stress in the phytoplankton at Station 2 (Figs. 2-16 and 

2-17). The mean photochemical yield at Station 2 was significantly lower (p < 0.001) than 

all other stations. Station 3 had a higher average yield than Station 1 (mean = 0.49 ± 0.09) 

though not significantly different (p  0.971) from the other bay samples (Station 4 mean = 

0.52 ± 0.07 and Station 5 mean = 0.52 ± 0.08) (Figs. 2-16 and 2-17). Stations 4 and 5 did not 

differ significantly (p = 0.907). The results indicate that the physiology of the phytoplankton 

(photochemical energy conversion efficiency) was negatively affected by thermal stress 

and/or entrainment in the MLPP and could easily be detected at the surge tank exit site. 

2.5.4 Gross Primary Production and Community Dark Respiration 

Oxygen exchange determined in light-minus-dark experiments provides unambiguous 

determination of gross primary production specific to phytoplankton, while the 

corresponding dark oxygen depletion indicates respiration of the bulk planktonic community. 

On three sampling dates the chl-specific gross production rate (mg O2 μg chl a L-1 d-1) and 

bulk dark respiration (O2 mg L-1 d-1) was determined using the Winkler titration method. 

Average gross production was 8 times lower at the surge tank (Station 2; mean (± S.D.) = 

0.01±0.009 mg O2 μg chl a L-1 d-1) than at the intake site (Station 1; mean (± S.D.) = 

0.08±0.01 mg O2 μg chl a L-1 d-1) and, correspondingly, average respiration was 9 times 

higher at Station 2 (mean (± S.D.) = 3.13±1.52 O2 mg L-1 d-1) than Station 1 (mean (± S.D.) = 

0.35±0.18 O2 mg L-1 d-1)(Figs. 2-18 and 2-19). The average gross primary production for 

Station 2 was significantly lower than all other stations (p<= 0.001) and average respiration 

at Station 2 was significantly higher than all other stations (p < 0.001). Gross primary 

production at Station 3 was 0.08±0.04 mg O2 μg chl a L-1 d-1, and at Station 4 was 0.07±0.04 

mg O2 μg chl a L-1 d-1. The mean (± S.D.) respiration at Station 3 was a -0.28±0.13 O2 mg 

L-1 d-1, and at Station 4 was -0.35 ± 0.40 O2 mg L-1 d-1. Neither gross primary production nor 

community respiration at Stations 1, 3, and 4 were significantly different (p  0.129). The 

significant increase in respiration at the surge chamber (Station 2) corroborates results of 

enhanced bacterial growth while the significant decrease in gross production at the surge 

chamber (Station 2) suggests negative effects on phytoplankton by thermal stress and/or 

entrainment in the MLPP. 

2.6 Discussion 

The first objective of this study was to determine the impact of thermal increase and 

entrainment on the biomass and productivity of bacteria. Bacterial growth was enhanced as a 
 Moss Landing Powerplant Thermal Discharge Effects 17 

Moss Landing Marine Laboratories 

result of passage through the MLPP cooling system, as evidenced from 1) increases in 

bacterial colony counts (Fig. 2-8), 2) increases in the frequency of dividing cells (Fig. 2-11), 

and 3) increased dark respiration in the surge chamber (Fig. 2-19). These results are 

supported by Miller et al. (1976) and Fox and Moyer (1973) who found that the numbers of 

bacteria increased in the discharge effluent of power stations. Shiah and Ducklow (1994) 

also observed increased bacterial productivity with increasing temperature between 3 and 25 

oC in incubation experiments. In the present study, bacteria biomass as total direct 

epifluorescent counts was not a good indicator for assessing the impact of thermal stress and 

entrainment on bacteria, as would be expected given the short residence time (<1h) of 

entrained water within the power plant. We cannot reject the possibility that bacteria 

associated with wall growth within the conduit system contributed to the signals we detected 

at the surge site (Station 2). However, since significant increases in bacterial abundance at 

the surge site were not evident in total direct counts we must assume that total contribution of 

such cells was relatively small. 

The second objective of this study was to determine the impact of the thermal increase and 

entrainment on the biomass, physiology, and productivity of phytoplankton. Phytoplankton 

was negatively impacted after passage through the MLPP cooling system as shown by 

reductions in photochemical yield (Fig. 2-14), increases in pheopigment/chl a ratios (Fig. 2-

17), and decreases in phytoplankton gross primary productivity in the surge chamber (Fig. 2-

18). Suchanek (1975) also observed an increase in pheophytin as a result of thermal increase 

at a power plant in Long Island. Several previous studies have shown that primary 

productivity decreased 2-80 % in thermal effluent from power plants (38 %, Morgan and 

Stross (1965); 2–37 %, Fox and Moyer (1973); 26 %, Suchanek (1975); 30 %, Bienfang and 

Johnson (1980); 20-80 %, Chang and Rossman (1985); 60 %, Servais and Billen (1989) and 

36 %, Martinez-Arroyo et al. (1999)); our results corroborate those findings. In the present 

study we found roughly a five-fold decrease in chl-specific primary production determined 

from water samples immediately exiting the power plant at the surge tank. Phytoplankton 

biomass, as chl a, was not a good indicator for assessing the impact of thermal stress and 

entrainment on phytoplankton; this finding is supported by other studies which found no 

significant differences in phytoplankton biomass (Bienfang and Johnson 1980, Briand 1975, 

Chang and Rossman 1985, Martinez-Arroyo et al. 1999, Servais and Billen 1989, Suchaneck 

1975). To our knowledge, this is the first study to utilize PAM fluorometry to assess 

physiological effects of once-through cooling on phytoplankton. The technique was rapid, 

sensitive and density-independent; it clearly identified negative impacts of thermal stress on 

phytoplankton photochemical efficiency, Fv/Fm, which presumably were manifested in 

reduced photosynthetic rates as also found here. The fact that PAM fluorometers can be 

plumbed for flow-through analysis (rather than discrete cuvet sampling) suggests this method 

may provide a cost-effective means for monitoring biological impacts of once-through 

cooling flow on a continuous basis. 

A fundamental objective of this study was to determine the effects, if any, of thermal 

increase and entrainment on bacteria and phytoplankton passing through the Moss Landing 

Power Plant. Our results indicate that differential effects were indeed in place; bacteria 

appeared to be enhanced as a result of entrainment while phytoplankton was negatively 

impacted. Measurements supporting these conclusions were all based on indicators of 
 Moss Landing Powerplant Thermal Discharge Effects 18 

Moss Landing Marine Laboratories 

physiological condition and rate processes. Measurements of bulk concentrations, e.g., total 

direct bacteria counts and chl a, provided relatively little indication of impacts. This is not 

surprising given the potentially short (<1 h) residence time of cooling water within the power 

plant. 

The final objective of this study was to assess the spatial extent of the area impacted 

surrounding the discharge plume within Monterey Bay, California. In spite of the fact that 

differential biological enhancement and inhibition effects were clearly evident in the cooling 

water flow measured at the surge tank (Station 2), the corresponding impacts in Monterey 

Bay (Stations 3-5) were much more difficult to detect. It appears that even at the high 

discharge rates that result in measurable surface temperature increases at the discharge site in 

Monterey Bay, the apparent biological effect is dissipated quickly within 100-500 m of the 

site by dilution in surrounding waters (Figs. 2-5, 2-8, 2-11, 2-14, 2-18 and 19). It is possible 

that bacteria and phytoplankton experienced physiological recovery back to the native 

biological state after reintroduction to normal ambient temperature. However, our results on 

negative rates of primary production do not support this possibility since the experimental 

productivity incubations were conducted under normal cool temperatures (13 o

C) for all 

samples. 

We generally conclude that bacterial enhancement and phytoplankton inhibition are expected 

to occur as a result of entrainment through the Moss Landing Power Plant. However, we 

were not able to document perceptible biological impacts after discharge and dilution in 

surrounding Monterey Bay waters. 
 Moss Landing Powerplant Thermal Discharge Effects 19 

Moss Landing Marine Laboratories 

2.7 Literature Cited 

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Paul [ed.], Methods in Microbiology. Academic Press. 

BIENFANG, P., and W. JOHNSON. 1980. Response of subtropical phytoplankton to power 

plant entrainment. Environmental Pollution (Series A) 22: 165-178. 

BRIAND, F. 1975. Effects of power-plant cooling system on marine phytoplankton. Marine 

Biology 33: 135-146. 

BROCK, T. 1985. Life at high temperatures. Science 230: 132-138. 

CAPUZZO, T. M. 1980. Impact of power-plant discharges on marine zooplankton: A review 

of thermal, mechanical and biocidal effects. 14th European marine biological 

symposium on protection of life in the sea. 33: 422-433. 

CARPENTER, E., B. PECK, and S. ANDERSON. 1974. Survival of copepods passing through a 

nuclear power station on Northeastern Long Island Sound, USA. Marine Biology 24: 49-

55. 

CHANG, W., and R. ROSSMANN. 1985. Effects of power plant entrainment on 

phytoplankton response. Applied Limnology: 2493-2497. 

CHOI, D., J. PARK, C. HWANG, S. HUH, and B. CHO. 2002. Effects of thermal effluents 

from a power station on bacteria and heterotrophic nanoflagellates in coastal waters. 

Marine Ecology Progress Series 229: 1-10. 

CLARK, J., and W. BROWNELL. 1973. Electric Power Plants in the Coastal Zone: 

Environmental Issues. American Littoral Society Special Publication. 

CLARK, R. 1989. Marine Pollution. Oxford University Press. 

COMMISSION, C. E. 2004. California Energy Commission Power Plant Database. 

DAVIES, R., and L. JENSEN. 1975. Zooplankton entrainment at three mid-Atlantic power 

plants. Journal of Water Pollution 47: 2130-2142. 

DUNSTALL, T. 1985. Effects on entrainment on phytoplankton primary production at four 

thermal electric generating stations on the Laurentian Great Lakes. Int. Revue ges. 

Hydrobiol. 70: 247-257. 

EPA. 1986. Quality Criteria for Water. In Environmental Protection Agency [ed.]. 

FOX, J., and M. MOYER. 1973. Some effects of a power plant on marine microbiota. 

Chesapeake Science 14: 1-10. 

FURUYA, K., and K. HARADA. 1995. An automated precise winkler titration for determining 

dissolved oxygen on board ship. Journal of Oceanography 51: 375-383. 

GENTY, B., J. BRIANTAIS, and N. BAKER. 1989. The relationship between the quantum 

yield of photosynthetic electron transport and quenching of chlorophyll fluorescence. 

Biochim Biophys Acta 990: 87-92. 

GENZ, L. 2003. Personal communication. 

GOLDMAN, J., and J. RYTHER. 1976. Temperature-influenced speciescompetition in mass 

cultures of marine phytoplankton. Biotechnology and Bioengineering 18: 1125-1144. 
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GUSEVA, V., and M. CHEBOTINA. 2000. Changes in plankton abundance, biomass, and 

chemical compostition under the influence of the cooling system of the Beloyarsk 

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HAGSTROM, A., U. LARSSON, P. HORSTEDT, and S. NORMARK. 1979. Frequency of 

dividing cells, a new approach to the determination of bacterial growth in aquatic 

environments. Applied and Environmental Microbiology 37: 805-812. 

HEINLE, D. R. 1976. Effects of passage through power plant cooling systems on estuarine 

copepods. Environmental Pollution 11: 39-58. 

HIRAYAMA, K., and R. HIRANO. 1970. Influences of high temperature and residual chlorine 

on marine plankton. Marine Biology 2: 205-213. 

HORNER, R., D. GARRISON, and F. PLUMLEY. 1997. Harmful algal blooms and red tide 

problems on the U.S. west coast. Limnology and Oceanography 42: 1076-1088. 

ICANBERRY, J., and J. ADAMS. 1974. Zooplankton survival in cooling water systems of four 

thermal power plants on the California Coast. In J. Gibson and R. Sharitz [eds.], 

Thermal Ecology. 

LANGFORD, T. 1983. Electricity Generation and the Ecology of Natural Waters. Liverpool 

University Press. 

LANGFORD, T. 1990. Ecological Effects of Thermal Discharges. Elsevier. 

LAWS, E. 2000. Aquatic Pollution., Third ed. John Wiley and Sons, Inc. 

MARTINEZ-ARROYO, A., S. ABUNDES, E. GONZALES, and I. ROSAS. 1999. On the 

influence of hot water discharges on phytoplankton communities from a coastal zone of 

the Gulf of Mexico. Water, Air and Soil Pollution 119: 209-230. 

MILLER, M., G. HATER, T. FEDERLE, and J. REED. 1976. Effects of power plant operation 

on the biota of a thermal discharge channel., p. 251-258. In Esch and McFarlane [eds.], 

Thermal Ecology II. 

MORGAN, R., and R. STROSS. 1965. Destruction of phytoplankton in the cooling water 

supply of a steam electric station. Chesapeake Science 10: 165-171. 

NAYLOR, E. 1965. Effects of heated effluents upon marine and estuarine organisms. 

Advances in Marine Biology 3: 63-103. 

NOBLE, R. 2001. Enumeration of viruses. Methods in Microbiology. 30: 43-51. 

PADUAN, J. 2002. Moss Landing power plant post-modernization thermal plume evaluation 

plan. Duke Energy Moss Landing. 

RANKIN, J., J. BUCK, and J. FOERSTER. 1974. Thermal effects of the microbiology and 

chemistry of the Connecticut River., p. 350-355. In Gibbons and Sharitz [eds.], ? 

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SARAVANANE, N., K. SATPATHY, K. NAIR, and G. DURAIRAJ. 1998. Preliminary 

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SCHREIBER, U., H. HORMANN, C. NEUBAUER, and C. KLUGHAMMER. 1995. Assessment of 

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SHERR, B., E. SHERR, and P. DEL GIORGIO. 2001. Enumeration of total and highly active 

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SOCAL, G., F. BIANCHI, and L. ALBERIGHI. 1999. Effects of thermal pollution and nutrient 

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 Moss Landing Powerplant Thermal Discharge Effects 22 

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2.8 Tables and Figures 
 Moss Landing Powerplant Thermal Discharge Effects 23 

Moss Landing Marine Laboratories 

0

5

10

15

20

25

30

1/14/04 4/23/04 8/1/04 11/9/04 2/17/05 5/28/05 9/5/05 12/14/05

Date

Temperature (C)

Source (1)

Surge (2)

Discharge (3)

100m (4)

500m (5)

Figure 2-2. Temperature (C) for each sampling date between 3/4/04 – 11/1/05 

at sampling stations (1 - 5). 

0

5

10

15

20

25

012345

Station

Temperature (C)

a a a

b

c

Figure 2-3. Mean temperature (C) ± SD for all sampling dates 3/4/05 – 11/1/05 (n = 20) 

at sampling stations (1 - 5) and results of an ANCOVA with multiple comparison Tukey 

tests. Different letters above symbols indicate significant differences (p  0.05). 
 Moss Landing Powerplant Thermal Discharge Effects 24 

Moss Landing Marine Laboratories 

0

100000

200000

300000

400000

500000

600000

700000

800000

1/14/04 3/4/04 4/23/04 6/12/04 8/1/04 9/20/04 11/9/04 12/29/04

Date

Bacteria (cells/ml)

Source (1)

Duke Surge (2)

Discharge (3)

100m West (4)

500m West (5)

Figure 2-4. Bacteria biomass (cells/mL) for each sampling date between 3/4/04 – 11/16/04 

(n = 6) at sampling stations (1 - 5). 

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

12345

Station

Bacterial biomass (cells/mL)

(Normalized to Station 1)

a

a

a

b

a,b

Figure 2-5. Bacteria biomass (cells/mL) ±SD at sampling stations (1 - 5) for each sampling 

date between 3/4/04 – 11/16/04 (n = 6). All values normalized to 1.0 in reference to the 

intake site at Station 1 (identified by arrow) and results of an ANCOVA with multiple 

comparison Tukey tests. Different letters above symbols indicate significant differences (p 

0.05). 
 Moss Landing Powerplant Thermal Discharge Effects 25 

Moss Landing Marine Laboratories 

0

100000

200000

300000

400000

500000

600000

700000

800000

10 12 14 16 18 20 22 24 26

Temperature (C)

Bacteria Biomass (cells/mL)

y = 16298x + 16298

 r

2

 = 0.099

p = 0.090

Figure 2-6. Relationship between bacteria biomass (cell/mL) and temperature. Linear 

regression equation is given and plotted (n = 6). 
 Moss Landing Powerplant Thermal Discharge Effects 26 

Moss Landing Marine Laboratories 

0

10000

20000

30000

40000

50000

60000

2/3/04 3/24/04 5/13/04 7/2/04 8/21/04 10/10/04 11/29/04

Date

Bacteria colony growth (cols/ml)

Source (1)

Surge (2)

Discharge (3)

100m (4)

500m (5)

Figure 2-7. Bacteria colony growth (cols/mL) for each sampling date between 3/4/04 – 

11/16/04 (n = 12) at sampling stations (1 - 5). 

0

2

4

6

8

10

12

14

16

18

20

12345

Station

Bacteria colony growth (cols/ml) 

(Normalized to Station 1)

b

a

a

a a

Figure 2-8. Bacteria colony growth (cols/mL) ± SD at sampling stations (1 - 5) 3/4/04 – 

11/16/04 (n = 12). All values normalized to 1.0 in reference to the intake site at Station 1 

(identified by arrow) and results of an ANCOVA with multiple comparison Tukey tests. 

Different letters above symbols indicate significant differences (p  0.05). 
 Moss Landing Powerplant Thermal Discharge Effects 27 

Moss Landing Marine Laboratories 

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

10 12 14 16 18 20 22 24 26 28

Temperature (C)

Bacteria Colony Growth (cols/mL)

y = 1282x - 16285

 r

2

 = 0.231

p = 0.000

Figure 2-9. Relationship between bacterial colony growth (cols/mL) and temperature. 

Linear regression equation is given and plotted (n = 12). 
 Moss Landing Powerplant Thermal Discharge Effects 28 

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0

5

10

15

20

25

30

35

40

1/14/2004 3/4/2004 4/23/2004 6/12/2004 8/1/2004 9/20/2004 11/9/2004 12/29/200

4

Date

FDC (%)

Source (1)

Duke Surge (2)

Discharge (3)

100m West (4)

500m West (5)

Figure 2-10. Frequency of dividing cells (FDC %) for each sampling date between 3/4/04 – 

11/16/04 (n = 6) at sampling stations (1 - 5). 

0

0.5

1

1.5

2

2.5

3

12345

Station

FDC (%)

(Normalized to Station 1)

a

c

a,c a,c

b

Figure 2-11. Frequency of dividing cells (FDC %) ± SD at sampling stations (1 - 5) 3/4/04 – 

11/16/04 (n = 6). All values normalized to 1.0 in reference to the intake site at Station 1 

(identified by arrow) and results of an ANCOVA with Tukey’s multiple comparisons test. 

Different letters above symbols indicate significant differences (p  0.05). 
 Moss Landing Powerplant Thermal Discharge Effects 29 

Moss Landing Marine Laboratories 

0

5

10

15

20

25

30

35

40

10 12 14 16 18 20 22 24 26

Temperature (C)

FDC (%) 

y = 1.996x - 13.084

 r2

 = 0.579

p = 0.000

Figure 2-12. Relationship between frequency of dividing cells (FDC %) and temperature. 

Linear regression equation is given and plotted (n = 6). 
 Moss Landing Powerplant Thermal Discharge Effects 30 

Moss Landing Marine Laboratories 

0

0.5

1

1.5

2

2.5

3

3.5

4

1/14/2004 4/23/2004 8/1/2004 11/9/2004 2/17/2005 5/28/2005 9/5/2005 12/14/2005

Date

Pheo/Chl a

Source (1)

Duke Surge (2)

Discharge (3)

100m West (4)

500m West (5)

Figure 2-13. Degradation pigment ratio (pheopigment/chl a) for each sampling date between 

3/4/04 – 11/1/05 (n = 20) at sampling stations (1 - 5). 

0

1

2

3

4

5

6

7

12345

Station

Pheopigment/ Chla

(Normalized to Station 1) 

a

b

c

a

a,c

Figure 2-14. Degradation pigments (pheopigment/chl a) ± SD at sampling stations (1 - 5) 

3/4/04 – 11/1/05 (n = 20). All values normalized to 1.0 in reference to the intake site at 

Station 1 (identified by arrow) and results of an ANCOVA with Tukey’s multiple 

comparisons test. Different letters above symbols indicate significant differences (p  0.05). 
 Moss Landing Powerplant Thermal Discharge Effects 31 

Moss Landing Marine Laboratories 

0

0.5

1

1.5

2

2.5

3

3.5

4

10 12 14 16 18 20 22 24 26 28

Temperature (C)

Pheopigment/Chla 

y = 0.088x - 0.821

r

2

 = 0.301

p = 0.001

Figure 2-15. Relationship between degradation pigment ratio (pheopigment/chl a) ± SD and 

temperature. Linear regression equation is given and plotted (n =20). 
 Moss Landing Powerplant Thermal Discharge Effects 32 

Moss Landing Marine Laboratories 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1/14/04 3/4/04 4/23/04 6/12/04 8/1/04 9/20/04 11/9/04 12/29/04

Date

Photochemical Yield 

(Fv/Fm)

Source (1)

Duke Surge (2)

Discharge (3)

100 m West (4)

500 m West (5)

Figure 2-16. Photochemical yield (Fv/Fm) for each sampling date between 3/4/04 – 11/1/05 

(n = 20) at sampling stations (1 – 5). 

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

12345

Station

Photochemical Yield 

(Fv/Fm) 

(Normalized to Station 1)

a

c c

b

a,c

Figure 2-17. Photochemical yield (Fv/Fm) ± SD at sampling stations (1 - 5) 3/4/04 – 11/1/05 

(n = 20). All values normalized to 1.0 in reference to the intake site at Station 1 (identified 

by arrow) and results of an ANCOVA with Tukey’s multiple comparisons test. Different 

letters above symbols indicate significant differences (p  0.05). 
 Moss Landing Powerplant Thermal Discharge Effects 33 

Moss Landing Marine Laboratories 

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

1234

Station

Gross Primary Production

(mg O2/ug Chla L -1 day-1 )

6/15/05

9/14/05

11/1/05

a

b

a a

Figure 2-18. Average gross primary production (mg O2/μg chl a) ± SD at sampling stations 

(1 - 4) for each sampling date between 6/15/05 – 11/1/05 (n = 3) and results of an ANCOVA 

with Tukey’s multiple comparisons test. Different letters above groups indicate significant 

differences (p  0.05). 

-6

-5

-4

-3

-2

-1

0

1

1234

Station

Community Respiration

(O2 mgL-1 day-1

)

6/15/05

9/14/05

11/1/05

a

b

a a

Figure 2-19. Average community respiration (O2 mg/L) ± SD at sampling stations (1, 2, 3, 4) 

for each sampling date between 6/15/05 – 11/1/05 (n = 3) and results of an ANCOVA with 

Tukey’s multiple comparisons test. Different letters above groups indicate significant 

differences (p  0.05). 
 Moss Landing Powerplant Thermal Discharge Effects 34 

Moss Landing Marine Laboratories 

3 Benthos 

Prepared by Dr. John Oliver, James Oakden, and Kamille Hammerstrom 

3.1 Introduction 

Moss Landing Power Plant has had a thermal discharge at the head of Monterey Canyon 

since the 1960’s (Figs. 1-1 and 3-1). The warm water plume is generally 2-4° C above 

ambient surface water temperatures, with a maximum of 7°C above ambient at the hottest 

spot. The highest rise recorded at the intertidal beach has been 2°C above ambient, directly 

inshore from the outfall (Tenera 2000a,b). Most of the past work around the thermal 

discharge has been to characterize the thermal structure of the plume (Tenera 2000a,b). At 

high tide, the warm water from the outfall plume is a distinct feature that can be detected 

from the air. There are also distinct pockets of warm water in the south and north sections of 

Moss Landing Harbor. At low tide, these warm surface-water features are highly obscured by 

the extensive outflow of water from Elkhorn Slough into Monterey Bay. The outfall is 

adjacent to the main tidal flow from the slough. The thermal plume is a small feature 

compared to the turbid plume from Elkhorn Slough, which often extends over a kilometer 

into the bay at low tides. Both the outfall and slough plumes are present all year long. There 

are also net up-canyon currents that pulse deeper, colder water into the same shallow region 

as the thermal discharge (Breaker and Broenkow 1994). Within one day, the temperature 

around the canyon head, including the adjacent sand flats, can plummet from 15 to 9 °C from 

the surface to the sea floor in over 10 m of water. Larger scale currents sweep through the 

entire bay episodically during the year (Breaker and Broenkow 1994). 

Longshore water currents commonly flow towards Moss Landing both from the north and 

more strongly from the south, especially during storms and high winds (Arnal et al. 1973). 

Every winter the muddy, relatively warm-water runoff from the Salinas River and other 

watersheds covers the near shore region around Moss Landing. This giant turbid plume 

spreads offshore and alongshore into the northern coast of Santa Cruz towards San Francisco. 

Therefore, Moss Landing is a region of dynamic natural water flow, modified by the 

tremendous tidal flow in and out of Elkhorn Slough through the man-made entrance channel 

for Moss Landing Harbor. The thermal plume is subjected to mixing events tidally, 

seasonally, and episodically throughout the year (Tenera 2000 a,b). This is only a brief 

summary of the dynamic, extensive mixing processes around the head of Monterey Canyon. 

There are many more observations, particularly from investigators at MBARI and NPGS 

(See Section 2). However, this summary is adequate to set the physical stage for interpreting 

the ecological data from the benthos. 

The intertidal beach is exposed to air temperature at low tides. On the high beach, organic 

debris or wrack (mostly drifting macroalgae and eel and sea grass) accumulates and harbors a 

unique community of beach hoppers (talitrid amphipods), insects, and worms (oligochaetes, 

nematodes, and insect larvae). These patches can become very warm from decay and 

elevated air temperatures. They are usually above the water line, and therefore they were not 

the focus of our benthic sampling. Our sampling began just below the wrack zone where the 

beach isopod, Excirolana, is the most abundant animal. However, the intertidal beach harbors 
 Moss Landing Powerplant Thermal Discharge Effects 35 

Moss Landing Marine Laboratories 

a group of animals subjected to more extreme temperature fluctuations (warm and cold) than 

those in seawater. Stress from exposure to extreme air temperatures obviously increases with 

higher elevation on the beach. 

Moss Landing is located in the center of a coastal upwelling system, extending from Point 

Conception in the south to just beyond Cape Mendocino in the north (Huyer 1983). This 

biogeographic region has a benthic diversity hotspot along the shelf edge (at 100-200 m 

depth), containing the highest density of macrofaunal invertebrate species discovered so far 

on the planet (Oliver et al. in prep.). The high diversity is probably fueled by high primary 

production caused by upwelling; strong bottom currents at the shelf-slope boundary; and 

mixing of southern and northern species in the California current system. Just inshore of the 

diversity center there is a fine sediment sink from 60-100 m depth. The inner shelf (< 40 m) 

is heavily impacted by wave disturbance (Oliver et al. 1980). Monterey Bay is a semiprotected coastal environment with smaller waves compared to the open coast. In addition, 

wave disturbance increases from California to Washington, where the inner shelf ecosystem 

(wave-disturbed) extends to the shelf edge and there is no fine sediment sink or diversity 

center along the outer shelf (Lie and Kisker 1970, Oliver et al. 1980). The present study was 

conducted along the wave-exposed inner shelf around Moss Landing (Figure 1). 

Moss Landing beach is in the center of Monterey Bay at the head of Monterey Canyon 

(Figure 1). The canyon head is flanked by extensive, gently sloping sand flats. Wave energy 

is refracted away from the canyon head and intensified along the sandflats (Oliver et al. 

1980). Since waves usually arrive from the northwest, the northern sandflat has larger waves 

than the sandflat south of the canyon (Arnal et al. 1973, Oliver et al. 1980). Longshore 

currents often move towards the canyon, dumping sediment and organic debris into the 

canyon axis, which is flushed each year by winter storms (Oliver and Slattery 1976, Okey 

1993, 1997). The thermal discharge is located along the shallow, sandy canyon wall (in about 

16 m of water) between the northern and middle branches of the canyon head. The southern 

branch is directly off the old pier site, the middle branch is off the Monterey Bay Aquarium 

Research Institute (MBARI), and the northern branch is off the harbor mouth (Shepard 1948, 

Okey 1997). There is also a relatively flat, shallow bench (< 20 m) between the southern and 

middle branch of the canyon head. Although the warm water plume covers a portion of the 

canyon axis and deeper walls (> 20 m), potential impacts should be highest in the intertidal 

and shallow subtidal beach because the warm water concentrates near the sea surface. 

3.2 Objectives 

The following objectives were addressed in the benthic portion of this study: 

1) Determine whether the thermal outfall is having a measurable impact on the sand 

beach and shallow subtidal communities in the outfall vicinity. 

2) Determine whether significant changes in the beach community at Moss Landing 

have occurred since it was last sampled in 1975-76. 
 Moss Landing Powerplant Thermal Discharge Effects 36 

Moss Landing Marine Laboratories 

3) Characterize the previously-unsampled shallow subtidal community in the outfall 

vicinity and nearby areas. 

4) Compile a historic database of previous benthic work that has been performed on the 

Moss Landing beach and nearby areas. 

3.3 Background 

3.3.1 Intertidal Ecological Background 

Wave-exposed sandy beaches are often classified by morphodynamics along gradients of 

wave disturbance and sediment availability from dissipative to reflective (Short and Wright 

1983, McLachlan 1990, Defeo and McLachlan 2005). Reflective beaches are narrow and 

steep with coarse sediment, and swept by smaller waves. They generally harbor invertebrate 

communities with lower diversity, abundance, and biomass. Dissipative beaches have the 

opposite characteristics (Defeo and McLachlan 2005). Many of these patterns depend on 

large-scale geographic comparisons from tropical to temperate latitudes, but also 

morphodynamic variations among beaches. There are also mesoscale patterns that occur 

within a single uninterrupted beach. Zonation of the fauna across the shore is well known 

(Ricketts and Calvin 1985, McLachlan and Jaramillo 1995), but there are significant 

variations at several spatial scales along shore, including animal responses to swash 

circulation in cusps and bays at a finer level to impacts from river outflows and differences 

between the central beach and the ends (McArdle and McLachlan 1992, Degraer et al. 2003, 

Defeo and McLachlan 2005). 

Some submarine canyons cut through the continental shelf and head at sandy beaches with 

dramatic impacts on along shore wave energy and sediment availability. Wave energy is 

refracted away from the canyon head and intensified along the adjacent sand flats; beach 

sand is captured and transported into deeper water at the canyon head (Bascom 1964, 

Shepard and Dill 1966). Moss Landing Beach is in the center of Monterey Bay at the head of 

Monterey Canyon (Fig. 1-1), where waves are always smaller than they are along the 

extensive, gently sloping sand flats to the north and south (Arnal et al. 1973, Oliver et al. 

1980). Beach sand is transported towards the canyon from the north and south, and into the 

north and south branches of the deeper canyon head (Arnal et al. 1973). The beaches at the 

head of the canyon receive little transported sand. They are narrow and steep, while the 

beaches directly adjacent to the north and south canyon rims are sand transport corridors and 

are broader and flatter. The exposed sandy beaches in Monterey Bay are intermediate 

between the reflective and dissipative beaches. However, the canyon morphology creates a 

distinct, persistent wave-disturbance and sediment availability gradient from more dissipative 

outside to more reflective beaches within the canyon head. 

The Moss Landing Beach fauna is similar to sandy beach fauna throughout central California 

(Ricketts and Calvin 1985), and in many other parts of the world (Brown and McLachlan 

1990, Peterson 1991, McLachlan and Jaramillo 1995, Dugan et al. 1999). Throughout 

California, there is distinct faunal zonation with tidal elevation on the beaches (Dahl 1952, 

Ricketts and Calvin 1985), large seasonal pulses of animal recruitment (Barnes and Wenner 

1968), and considerable geographic variation from beach to beach (Dugan et al. 1999). In 
 Moss Landing Powerplant Thermal Discharge Effects 37 

Moss Landing Marine Laboratories 

general, relatively little is known about longer-term decadal variations in beach communities 

(but see Arntz et al. 1997, Lima et al. 2000, Defoe 2003), although these fluctuations are 

profound in other marine ecosystems (e.g., Dayton 1989, Roemmich and McGowan 1995, 

Tegner and Dayton 1996, McGowan et al. 1998, Francis et al. 1998, Chavez et al. 2003, 

Ainley et al. 2005). Just 25 km south of the sandy beach at Moss Landing, the rocky 

intertidal community at Hopkins Marine Station changed significantly since the early 1930’s. 

In particular, there was an increase in the abundances of species ranging more to the south, 

and a decrease in those ranging to the north as sea surface temperatures increased (Barry et 

al. 1995, Sagarin et al. 1999). 

This study was designed specifically to detect potential impacts of the thermal plume on the 

sand beach community. This was done by comparing beach species composition along four 

transects at increasing distances from where the thermal plume could impinge on the 

intertidal zone. The study design also allows the examination of several subsidiary ecological 

questions. This study presents a unique opportunity to explore how the sandy beach 

community changed since the 1970’s because of a historical quantitative survey of the fauna 

on Moss Landing Beach (Nybakken et al. 1977). The four sites sampled for this plume study, 

including the historical one, are along the wave-disturbance and sediment availability 

gradient on the south side of Monterey Canyon (Fig. 1-1). Therefore, another study objective 

is to explore how sandy beach communities are structured along a canyon-head exposure 

gradient. 

3.3.2 Shallow Subtidal Ecological Background 

Intertidal sandy beaches harbor a distinct invertebrate macrofauna that often live in welldefined zones (Dahl 1952, Ricketts and Calvin 1985, Brown and McLachlan 1990, Peterson 

1991, McLachlan and Jaramillo 1995). In central California, three zones are generally 

recognized: the supralittoral zone above the wrack line where air breathing talitrid amphipods 

and insects are common; the midlittoral zone characterized by cirolanid isopods; and the 

sublittoral fringe with mole crabs, mysids, amphipods, polychaetes, and other marine 

invertebrates (Ricketts and Calvin 1985). Unlike the intertidal beach, only a few studies 

document the structure of benthic communities through the subtidal surf zone, especially 

along high-energy beaches; and these investigations were primarily done in South Africa 

(Field 1971, Christie 1976, McLachlan et al. 1984). McLachlan et al. (1984) provide the 

most comprehensive zonation scheme for this wave-controlled environment, both for 

intertidal and subtidal habitats. They define an inner turbulent zone including the intertidal 

sublittoral fringe that extends to the outer edge of the breaker zone in 2-4 m; a transition zone 

from here to 5-12 m around the outer limit of surf circulation cells; and an outer turbulent 

zone that extends into 20-40 m of water. These zones also have distinct faunal patterns 

(McLachlan et al. 1984). Coincidentally, the deeper limit of their outer turbulent zone (20-40 

m) corresponds to the transition between the shallow crustacean and deeper polychaete zone 

in Monterey Bay (Oliver et al. 1980). 

There are no comparable benthic studies through the subtidal surf zone in the Pacific Ocean. 

Just seaward of the surf zone on many high-energy beaches along the California coast, sand 

dollars form dense beds that move seaward with winter waves and shoreward again during 
 Moss Landing Powerplant Thermal Discharge Effects 38 

Moss Landing Marine Laboratories 

the calmer months of summer and fall (Oliver et al. 1980, Morin et al. 1985). In contrast to 

the subtidal surf zone, there have been a number of ecological studies of sand dollar beds 

(Fager 1964, Merrill and Hobson 1970, Kastendiek 1982, Cameron and Rumrill 1982, Morin 

et al. 1985) and the nearby, offshore sandy bottoms in the outer turbulent zone (Barnard and 

Ziesenhenne 1961, Barnard 1963, Fager 1968, Hodgson and Nybakken 1973, Davis and 

VanBlaricom 1978, VanBlaricom 1982, Oliver et al. 1980, 1982, in preparation, Hulberg and 

Oliver 1980, Slattery 1985). There are also many studies of intertidal sandy beaches in 

California (Nybakken et al. 1977, Ricketts and Calvin 1985, Dugan et al. 1999, 2004). 

Because no studies are available for comparison, detection of possible thermal plume effects 

will rely on detection of changes in community structure and species composition along 

transects at increasing distances from the plume, and an examination of the communities 

nearest the outfall for signs of warm-water species. An examination of data from nearby 

deeper water areas and a discussion of regional climatic trends are necessary to put the 

results of this study into a broader ecological perspective. 

3.4 Methods 

3.4.1 Intertidal Methods 

A quandary presented itself in trying to determine the sampling design. It was not possible 

logistically to collect more than about 70 samples over two days in the short sampling 

windows allowed by the tides, even with large field crews (our crews ranged from 9-18 

people per day). When determining how to allocate these samples, we were driven by two 

opposing desires. In order to get an idea of within-elevation variability, and particularly to be 

able to locate rare species that might only be found at a particular tidal height, it was 

necessary to take more replicates at a fewer number of stations. On the other hand, in order to 

get a more complete representation of the zonation, and to have data comparable to the 

historical study, it was necessary to have fewer replicates at more stations. 

We solved this dilemma by using two different sampling designs over the course of the study 

to maximize the information gained. During the first two years of the study, at each of the 

four locations, 6 replicates were taken at four stations corresponding to the high, mid, low, 

and lowest intertidal (stations A, B, C, and D). During the last year of the study, we collected 

3 replicates at a larger number of stations spaced at regular (5 m or 10 m) intervals down the 

beach. Different transects had different numbers of samples because of variations in the 

width of the beach and the degree of the low tide. 

Four sites were chosen to give a representative picture of the beach and nearshore subtidal 

(Figs. 1-1 and 3-1). These sites are located at increasing distances from the Moss Landing 

Power Plant thermal discharge at the canyon head. They also fall along a wave exposure 

gradient caused by the bathymetry of Monterey Canyon and the direction of wave arrival, 

and thus represent the beach conditions around the head of a submarine canyon. The 4 

locations and their reference points are (from north to south): 

Outfall (OF): transect starts at the final fencepost on the north side of the public access 

walkway by Phil’s Fish Market, with a bearing directly west towards the powerplant outfall 
 Moss Landing Powerplant Thermal Discharge Effects 39 

Moss Landing Marine Laboratories 

plume and inside the canyon head. This spot is the closest point on the beach to the outfall, 

and presumably would be where any outfall effects would be seen if present. 

MBARI (MB): starts on the edge of the sidewalk directly under the MBARI seminar room 

and bears due west, inside the canyon head. 

Shore Lab (SL): starts at the fencepost at the south end of the former Moss Landing Lab 

property and bears due west, on the south rim of the canyon head within the beach transport 

corridor but protected from the prevailing northwest ocean swell by the canyon bathymetry. 

This is the same location used in Oakden and Nybakken (1976). 

Potrero Rd. (PR): starts at the Hazardous Surf Warning sign near the Potrero State Beach 

parking lot, and bears west towards the closest surf line, outside the canyon’s impact on local 

wave climate and representative of the sandy beaches throughout central Monterey Bay. 

For each site, a permanent reference point was surveyed near the sand dunes using an RTK 

GPS system, which gives both horizontal and vertical accuracy to a few centimeters. 

Sampling dates were determined by good (minus) low tides, which severely limited the 

months that could be sampled. During the first two years (Surveys 1-6), 6 replicate samples 

were taken at four stations along an elevational gradient across the beach (stations A, B, C, 

and D) at each of the four sites (OR, MB, SL, PR). The highest station (A) was below the 

strand line in the mid-littoral zone, where cirolanid isopods are common. Station B was at the 

interface between the mid-littoral and the top of the sublittoral fringe, where stations C and D 

were located. D was closest to the water in each survey. We did not survey the supralittoral 

zone, which is above the high tide and includes the stand zone, because this region was not 

sampled well in the 1970’s survey; there is little potential for impacts from the thermal 

discharge; and this zone is unlikely to respond to decadal variations in oceanographic 

climate. During the last year (Surveys 7-8), we modified the sampling to allow more detailed 

comparisons with the 1970’s survey (Nybakken et al. 1977). We collected 3 replicate 

samples at a larger number of stations spaced at regular (5 m or 10 m) intervals down the 

beach. Different sites had different numbers of samples because of site variations in beach 

width and tide level at sampling. 

At the beginning of each sampling session, a theodolite was set up at the reference point and 

used to measure relative elevations of the 4 stations during the first portion of the study. 

During the third year of the study, a meter tape was used to position the stations at 5 m or 10 

m intervals along each transect, and elevations were taken at each station using the 

theodolite. The station intervals were determined by the width of the beach, with steeper 

beaches having stations closer together. A core of the top 5 cm of sand was taken for grainsize analysis at each station. Replicate faunal samples from each station were taken at 

random within 10 m on either side of the station marker. Each sample was a 0.25 m2

 quadrat 

excavated to a depth of 10 cm. Samples were sieved on the beach, using 1 mm (Shore Lab) 

or 1.5 mm (other 3 stations) nylon-mesh sieves, then placed in Ziplock bags. The smaller 

sieve size was used for consistency with the 1976 study. Samples were preserved in buffered 

formalin, and transferred to isopropyl alcohol for sorting. Animals were separated from the 

sand in the preserved samples using an elutriation technique, followed by a quality assurance 
 Moss Landing Powerplant Thermal Discharge Effects 40 

Moss Landing Marine Laboratories 

examination of the residue. All animals were identified to the lowest possible taxon, 

generally species. Grain-size distribution was measured using a Beckman-Coulter LS 13 320 

laser particle size analyzer. 

Data were square-root transformed to meet assumptions of normality and variance 

homogeneity. For the first 6 surveys, a three-way analysis of variance (ANOVA) was 

conducted testing the main effects of survey time, site, and elevation (A, B, C, D), as well as 

all main effects interaction terms, on the total number of crustaceans, polychaetes, Emerita 

analoga, selected crustaceans (no Emerita included) and selected crustaceans and stations 

(no Emerita and no Shore Lab data included). Additional one-way ANOVAs examined the 

effect of site on elevation for each survey time. Tukey’s studentized range test was utilized to 

test all pair-wise comparisons among sites. All analyses were performed in SAS v.9.1 (SAS 

Institute 2003). 

In order to obtain estimates of the numbers of two large, rare species, the Pismo clam (Tivella 

stultorum) and the spiny sand crab (Blepharipoda occidentalis), we used a wheeled sieve cart 

that was 0.5 m high with a screen surface of 0.75 m2

, equipped with a nylon mesh with 2.5 

mm square openings. This mesh size allowed most of the sand to move through the sieve 

rapidly while retaining larger animals. Samples were collected in the lowest tidal elevation 

(D) from 0.5 m2

 to 20 cm depth and placed in the cart, which was rolled into the water to 

wash the sand away. The screen was then examined, and the individuals rapidly counted and 

other observations recorded such as gravid females and clam size. Cart samples were 

collected on 4 June 2004 (2 at OF, 4 at MB, and 15 at SL); on 25 May 2005 (17 at SL); and 

on 27 May 2005 (15 at PR). The Shore Lab and Potrero sites were primary site targets 

because of a long history of Pismo clam collection here before the sea otters arrived 

(Stephenson 1977). 

3.4.2 Subtidal Methods 

Four sampling sites were established on the wave-exposed, sandy beach around the head of 

Monterey Canyon (Figs. 1-1, 3-1). They were located along a gradient away from the warm 

water discharge of the Moss Landing Power Plant, which is also a natural environmental 

gradient related to canyon bathymetry and wave disturbance (Arnal et al. 1973). Three water 

depths (1, 2, 4 m) were sampled at each site in the shallow subtidal zone where waves break. 

Historical sampling was done in the deeper subtidal environment (6 m to >20 m) directly 

offshore of the Shore Lab (Oliver et al. 1977, 1980), Potrero Road sites (Oliver et al. 1980, 

Oliver et al. in preparation), and also in the intertidal zone at the Shore Lab site (Nybakken et 

al. 1977). The new stations were positioned to fill in the sampling gap between the intertidal 

and shallow subtidal beach (6 m). Each water depth (1, 2, 4 m) was sampled at all four sites 

during the summer or early fall for three years (5, 30 June 2003; 5, 14 October 2004; 20, 21 

October 2005). The summer and early fall were selected because this is a period of high 

abundance, species density, and biomass, with relatively low seasonal fluctuations from 

recruitment, which are greatest in the spring (Oliver et al. 1980). In addition, this is a period 

of lower wave action, which is critical for gaining sampling access to the surf zone. Even so, 

we were unable to sample from the two shallowest depths at Potrero Road in 2005 because of 

high wave action limiting boat operations and scuba diving. Our boat was swamped by a 
 Moss Landing Powerplant Thermal Discharge Effects 41 

Moss Landing Marine Laboratories 

large wave set, leading to the loss of the sediment sample from the 4 m station here. At each 

sampling period, scuba divers qualitatively surveyed the depth transect and deeper water to 

search for larger benthic animals such as crabs, sand dollars, and patches of gastropods 

(Olivella spp.). 

Six replicate diver-held cores (area= 180 cm2, 15 cm deep) were taken at each depth and 

time, and were washed over a 0.5 mm screen. Invertebrates were sorted from the screen 

residues; identified to the lowest possible taxon; and the number of individuals per taxon 

recorded with qualitative observations of size and reproductive condition. Surface sediments 

(top 2 cm) were also collected for measuring grain size distribution. 

Patterns in species composition and relative abundance were displayed using a cluster 

analysis from PRIMER v.5 (Clarke and Gorley 2001). In addition, data were square-root 

transformed to meet assumptions of normality and variance homogeneity, and a three-way 

analysis of variance (ANOVA) was conducted testing the main effects of survey time, site, 

and depth, as well as all main effects interaction terms, on the total number of crustaceans, 

polychaetes and molluscs. Additional one-way ANOVAs examined the effect of site on 

depth for each survey time. Tukey’s studentized range test was utilized to test all pair-wise 

comparisons among sites. These analyses were performed in SAS v.9.1 (SAS Institute 2003). 

3.5 Results 

3.5.1 Intertidal Results 

Surveys 1-6 

The number of individuals of macrofaunal invertebrates fluctuated by more than ten times 

among the sites at the highest elevation (A) and by more than 5 times at the lowest (D) (Fig. 

3-2). The crustaceans dominated the variation, with polychaetes producing three significant 

peaks. The fluctuations among the crustaceans were caused by the sand crab Emerita at the 

three lower elevations (B-D) and by the isopod Excirolana at the highest elevation (Fig. 3-3). 

These were the two most abundant macrofauna on the beach (Table 3-1). As a result, the total 

number of crustaceans largely reflected the abundances of these two species, particularly 

Emerita because Excirolana was only abundant at A stations (Figs. 3-2 and 3-3). Since 

Emerita was abundant at all sites and at all beach elevations (Table 3-2 and Fig. 3-3), its 

dominance obscured site and elevation patterns that were present for the polychaetes as a 

group and for most of the other numerically dominant animals (Figs. 3-2 and 3-3). 

Excirolana was the only numerical dominant that was most abundant at the highest elevation 

(station A) at each site (Fig. 3-3). It was frequently encountered at the next highest elevation 

as well (station B), but was not nearly as abundant here (Table 3-2, Fig. 3-3). Excirolana and 

the other numerically dominant crustaceans were most abundant at the Shore Lab site, where 

we collected the fauna with a 1 mm screen in contrast to a 1.5 mm screen used at the other 

three sites (Fig. 3-3). While Emerita occurred at all tidal elevations and Excirolana primarily 

at the highest, the other three numerically dominant crustaceans were most abundant at the 

two lowest intertidal stations (Fig. 3-3, Table 3-2). The peaks in abundance of the crustacean 

species were often in the spring, but not limited to this season (Figs. 3-4 and 3-5, Table 3-1). 

Individuals were present throughout the year. 
 Moss Landing Powerplant Thermal Discharge Effects 42 

Moss Landing Marine Laboratories 

In contrast to the crustaceans, the polychaetes generally increased in abundance from the 

Potrero site to the Outfall site (Fig. 3-2). They were also more abundant and frequently 

encountered at the lower intertidal stations (C and D) (Figs. 3-2 and 3-6, Table 3-2). Every 

major abundance peak in the numerically dominant polychaetes occurred at one sampling 

time and at one site (Fig. 3-6). The polychaetes were thus more restricted in their temporal 

occurrence compared to the crustaceans (Table 3-1). At these peaks (Fig. 3-6), individuals 

were spread throughout the replicate samples with the exception of the peak in Nephtys

(MBARI site), which was 21 animals in on quadrat, and the secondary peak in Saccocirrus

(MBARI site), 62 animals in one quadrat. Despite the smaller screen size used at the Shore 

Lab site, only one polychaete species was most abundant here, Archiannelid sp. B (Fig. 3-6). 

There was a general increase in species from the high to the low intertidal beach at the 

Outfall and Shore Lab sites, but the trend was less distinct at Potrero, and not present at 

MBARI (Fig. 3-7). 

Unlike the number of species, there were highly significant variations in the number of 

individuals on the beach (Figs. 3-2 and 3-7). We examined the variation in individuals using 

ANOVAs (Tables 3-3 and 3-4) for crustaceans, polychaetes, the most abundant animal, 

Emerita, and the other four numerically dominant crustaceans, excluding Emerita

(Excirolana, Archaeomysis, Americelidium, Mandibulophoxus). These four crustaceans had 

similar patterns of abundance among the four sites, which were different from the pattern in 

Emerita (Figs. 3-4 and 3-5). Since these four species were also most abundant at the Shore 

Lab site, where we used a finer sampling screen throughout the study (1 mm compared to 1.5 

mm at the other three sites), we also tested for site differences among only the three sites, 

excluding the Shore Lab (labeled selected crustacean and site in Tables 3-3 and 3-4). The 

three-way ANOVA showed significant variation by site, time of survey, and tidal elevation. 

However, all interaction terms were also highly significant (Table 3-3: the last 4 rows). 

Therefore, we used one-way ANOVAs to test for differences among the four sites at each 

time and tidal elevation (A-D). We sampled at all elevations, except D, at all six time 

periods. 

Table 3-4 shows the number of significant ANOVAs for each metric by tidal elevation. The 

number of significant analyses decreased from total crustaceans, Emerita, the other four 

numerically dominant crustaceans, to the polychaetes. There was a similar pattern in the 

number of significant analyses when the Shore Lab site was excluded from the fourcrustacean metric (compare selected crustaceans to selected crustaceans and site in Table 3-

4). We did pair-wise tests on each significant ANOVA to see which sites were significantly 

different from each other. There was no trend for greater significance at the Outfall site, or 

one of the other three sites. However, there was a trend towards significant differences in 

pair-wise tests where there were peaks in abundance. For example, for the 23 ANOVA’s 

done on total crustaceans (Table 3-4), 18 were significant. The Shore Lab was significantly 

different from all the other sites in seven tests: six times it had the highest number of 

crustaceans, probably because of the large number of Excirolana here (Figs. 3-2 and 3-3). 

The Outfall site was significantly different from all other sites five times: four times it was 

the lowest, apparently because of the low numbers of Excirolana and Emerita at the highest 
 Moss Landing Powerplant Thermal Discharge Effects 43 

Moss Landing Marine Laboratories 

elevation (station A)(Figs. 3-2 and 3-3). The MBARI and Potrero sites were each 

significantly different from all the other sites in three tests. They had the highest abundance 

in five of these six tests. The distribution of significant tests among the sites for total 

crustaceans was similar to that for Emerita and the four other numerical dominants. In 

contrast to the crustaceans, only 10 of the 23 tests were significant for the polychaetes (Table 

3-4). Here the link to abundance peaks is easiest to show. The Outfall site was significantly 

different from all the other sites in six tests (always highest). The MBARI and Shore Lab 

sites were both significantly different from all the other sites in one test (highest), and the 

Potrero site in none. Each significant test for polychaetes corresponded to the peak 

abundances and times shown in Fig. 3-6. We only present the patterns in pair-wise tests when 

a site was significantly different from all of the other sites in the test. There are other 

combinations such as one site being different from only one or two of the others and so on. 

However, our primary purpose here is to show that the frequency of occurrence of 

significance in the pair-wise tests was highest at the Shore Lab and Outfall sites, where there 

were generally the greatest lows and especially peaks in abundance (Fig. 2-6). 

Grain size shows a general gradient from the Outfall to the Potrero site (Table 3-4). The 

Outfall had the least fine-grained sand and the most coarse-grained sand. MBARI was 

similar. The Shore Lab and Potrero sites had more fine sand and less coarse. These patterns 

persisted along the entire elevation gradient from A-D among the sites. Within each site, 

there was a weaker trend for decreasing coarse sand from the high (A) to lower beach (D). 

The Shore Lab had the finest deposit among the four sites with the highest percentage of fine 

sand at every elevation, the highest silt fraction at 3 elevations, and the lowest quantity of 

coarse sand at 3 of the 4 elevations (Table 3-4). The Shore Lab and Potrero beaches were 

twice as wide as the Outfall and MBARI beaches, which were the steepest (Fig. 3-8: note the 

horizontal scale changes). March and April usually had the lowest beach profile after the 

winter storms. 

Sieve Cart Samples 

We found two immature Pismo clams at the Shore Lab in the 2004 cart samples (shell 

lengths: 63 and 69 mm). We collected seven invertebrate species at the Shore Lab. The olive 

snail Olivella biplicata was present in all 15 samples (mean= 5, range 1-18/sample). We 

collected one spiny mole crab Blepharipoda occidentalis in two samples. Only Emerita and 

Nephtys californiensis were collected at the MBARI and Outfall sites. These species were 

frequently collected at all sites, but were not the focus of the cart sampling. The pattern was 

similar at the Shore Lab in 2005, when we collected one Pismo clam (29 mm); Olivella in 10 

of 17 samples (mean=1, range 1-3); and Blepharipoda in 7 of 17 samples (range 1-3). We 

found one Pismo clam (56 mm) and Blepharipoda at Potrero in 2005; and Olivella in 5 of 15 

samples (range 1-7). 

1975-76 vs 2003-05 

For the comparison with the 1975-76 samples, we used the data collected in all the surveys 

(1-8) from 2003-05. The 1970’s data are from Oakden and Nybakken (1977), and were 

taxonomically updated for comparison with the 2003-05 community data. A primary 

objective in sampling at the three additional sites in 2003-04 was to increase the mesoscale 

sampling along the beach to help evaluate differences between the decadal samples. Using 
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Moss Landing Marine Laboratories 

the entire data sets for both decades, all the species shown in Table 3-6 are significantly 

different between the decades in t-tests and Wilcoxon rank sum tests (p<0.05), with the 

exception of Excirolana and Nephtys. There are also no significant differences among the 

decades for the total number of species, total individuals, and crustacean and polychaete 

individuals (Table 3-6). 

Table 3-6 also shows data from only the Shore Lab site in 2003-05, which is the same beach 

site sampled in the 1970’s. The entire data set from 2003-05 gives a better view of the 

community patterns along the larger beach for comparing with the 1970’s. For example, 

Excirolana was most abundant at the Shore Lab site in 2003-05 (Fig. 3-3), so Excirolana

differences between the decades are highly significant comparing just the Shore Lab sites 

between decades (p<0.0001). However, they are not different when the others sites along the 

beach are considered in 2003-05 (Table 3-6). Archaeomysis and Mandibulophoxus also had 

abundance peaks at the Shore Lab (Fig. 3-3), so when only the Shore Lab sites are compared 

they are not significantly different (p<0.05) between the decades, reversing the pattern when 

the entire 2003-05 data set is used (Table 3-6). In 2003-05, there were also highly significant 

variations in time and along shore in the abundances of polychaete worms (Fig. 3-6). The 

polychaete differences between the decades fall within the variation along the beach in 2003-

05. Therefore, for the these three numerically dominant crustacean species and the 

polychaetes, there is no compelling evidence that there were significant differences in 

abundance between the decades, when the site variations along the beach in 2003-05 are 

considered. 

On the other hand, Emerita was abundant at all sites in 2003-05, so along shore patterns 

support the conclusion that there are significant differences between the decades for Emerita

(Table 3-6). This is also true for Grandifoxus, Americhelidium, and nemertean worms (Table 

3-6). In the 1970’s, 103 Grandifoxus were captured. Only 22 were captured in 2003-05 with 

five times the sampling effort (equivalent to 4 instead of 103 individuals if the sampling area 

is adjusted to the 116 samples in 1975-76). There were no Americhelidium in the 1970’s 

samples, and 353 in 2003-05 (71 adjusted to 116 samples in 1975-76). The changes in 

frequency of occurrence generally coincided with abundance. Grandifoxus decreased from 

34 to 3%; and the nemerteans from 43 to 9%; while Emerita occurred in almost twice as 

many samples as it became more abundant (Table 3-6). 

The species composition changed little between the two decades. There were no warm water 

species extending their range into the Monterey Bay. With one exception, the species that 

were not common to each sampling effort live in deeper water. Only a few individuals of 

each species were in the beach samples. Therefore, the differences in species composition 

between the decades can be explained by chance capture of relatively rare animals. The 

exception was Archiannelida B, which is a beach animal and was abundant in 2003-05, but 

not found in the 1970’s. 

3.5.2 Subtidal Results 

Cluster analysis is effective at grouping samples with similar species composition and 

relative abundance patterns based on Bray-Curtis similarity coefficients, and graphically 
 Moss Landing Powerplant Thermal Discharge Effects 45 

Moss Landing Marine Laboratories 

displaying the patterns. However, the cluster analysis showed no patterns in species 

assemblages grouping by depth, site, or year of sampling (Fig. 3-9). The sample from the 

Outfall site at 1 m in 2005 (2005OF1) clustered uniquely from all other samples, because of 

the very high abundance of a small phyllodocid polychaete worm, Hesionura sp., which had 

a mean abundance of 96 animals per core. Five of the remaining samples from the 1 m 

stations closest to the canyon head clustered together (OF, MB, and SL), but three others did 

not, in addition to the unique sample from OF-1 m in 2005. That’s only five out of nine 1 m 

samples in a distinct cluster, and one other sample in this 1 m dominant cluster was from a 2 

m depth (2005OF2). The two samples from 1 m at Potrero Road also did not cluster with the 

larger group of 1 m stations (Fig. 3-9). In general, the sites, depths, and years were mixed 

together, indicating significant spatial and temporal variation in species composition and 

relative abundance as they define assemblages. 

There were also significant variations in the numbers of individuals. Figure 3-10 combines 

the three annual samples and shows fluctuations in number of individuals at each water depth 

and site. The total fauna is compared to the abundance of crustaceans and to the most 

abundant genus of crustacean, the oedicerodid amphipods, Americhelidium spp. (Fig. 3-10). 

The error bars partially reflect large temporal variations at some depths and sites. 

Nevertheless, much of the general pattern in the total fauna was present in just the 

crustaceans; and much of the crustacean pattern was reflected in the abundance of the 

numerically dominant genus, Americhelidium. When the two species of Americhelidium were 

combined, they were more than twice as abundant as the next numerical dominant ranked for 

the entire data set (Table 3-7: overall). The abundance of polychaetes generally increased 

around the canyon head, but this pattern largely reflected the high abundance of Hesionura at 

the Outfall site (Fig. 3-11). Mollusca showed the opposite pattern, primarily because of 

Olivella increasing at Potrero Road (Fig. 3-11, Table 3-7). 

The sample variation was reduced when the data were presented separately for each year 

(Figs. 3-12 and 3-13). The most abundant taxa accounting for significant peaks in the data 

were listed near the respective abundance peaks with the mean abundance shown in 

parentheses. The largest peak in abundance was caused by Hesionura at the 1 m Outfall 

station. The mean abundance of Hesionura (96/core) here was twice as much as the next 

most abundant taxa accounting for a large peak in the data: the phoxocephalid amphipod 

crustacean, Mandibulophoxus (46/core). With the exception of Hesionura and the olive snail, 

Olivella biplicata, crustaceans caused the major peaks in abundance: primarily the 

amphipods, Americhelidium spp. and Mandibulophoxus, but also in one case the cumacean, 

Cyclaspis sp. (Figs. 3-12 and 3-13). The six species accounting for the highest peaks in 

abundance were also the numerical dominants for the entire data set (Tables 3-7 and 3-8). 

There were distinct changes in abundance with water depth among the numerical dominants. 

Americheldium micropleon was most abundant at 1 m, and A. shoemakeri was more 

abundant at 2 and 4 m (Fig. 3-14). Along with A. micropleon, Hesionura was the only other 

numerical dominant that was clearly most abundant at the 1 m depth. However, nemertean 

worms were most abundant at the two shallowest depths (Table 3-7). Mandibulophoxus and 

Olivella increased in abundance with increasing water depth, similar to A. shoemakeri (Table 

3-7). All the common polychaete worms, excluding Hesionura, increased with water depth, 
 Moss Landing Powerplant Thermal Discharge Effects 46 

Moss Landing Marine Laboratories 

including Apoprionospio pygmaea, Nephtys caecoides, Armandia brevis, Scoloplos armiger, 

and Dispio uncinata, although none were abundant (Table 3-7). 

Several animals known primarily from the intertdial beach occurred in the subtidal surf zone. 

Only 7 individuals of the sand crab, Emerita analoga, were found at the 1 m stations, one 

animal occurred at 2 m, and none at 4 m. Nine individuals of the intertidal beach polychaete, 

Nephyts californiensis, occurred in the surf zone samples; compared with 120 N. caecoides, 

the deeper water species. We captured two of the beach mysids, Archaeomysis graebnitski, in 

addition to Metamysidopsis elongata, Holmesmysis sculpta, and H. costata, which were not 

encountered on the intertidal beach or the deeper subtidal sandflat (Oliver et al. 1980). 

There were several distinct abundance patterns among the four sites. First, Hesionura only 

dominated at 1 m at the Outfall site in 2005 (Fig. 3-11 and 3-12). There were more 

polychaetes at all three canyon head stations compared to Potrero Road (Fig. 3-11). The total 

number of individuals was lowest at the Shore Lab site, particularly because of the low 

numbers of crustaceans (Fig. 3-10 and Table 3-7). And finally, Mandibulophoxus and 

Olivella were most abundant at Portrero Road (Table 3-7); and the total abundance of 

molluscs increased from the Outfall to Potrero Road (Fig. 3-11). 

The relatively sparse nature of much of the fauna is illustrated by the number of times that no 

animals were collected at a station (i.e. water depth), where six replicate cores were collected 

each year (Table 3-8). The most frequent means were zero and one animal per core. The 

extreme variation was in Hesionura, where there was a mean of 96/core at 1 m at the Outfall 

in 2005; 3/core at the closest station at the same time (OF 2m); and only a few individuals at 

the next site (MBARI). At the spatial scale of single cores, the nemertean worms showed the 

greatest variation. In five single cores from three of the sites, there were more than 40 

individuals/core. No other taxa showed this much variation among the six cores taken at a 

depth station. On the other hand, the Americhelidium spp., Mandibulophoxus, and 

nemerteans had the least number of stations with no animals present (Table 3-8). 

We examined the variation in individuals using ANOVAs (Tables 3-9 and 3-10) for 

crustaceans, polychaetes, and molluscs. The three-way ANOVA showed significant variation 

by site, time of survey, and water depth. However, all interaction terms were also highly 

significant (Table 3-9: the last 4 rows). Therefore, we used one-way ANOVAs to test for 

differences among the four sites at each of the three times and water depths. Table 3-10 

shows the number of significant ANOVAs for each metric for the three water depths. The 

number of significant analyses was greatest for the crustaceans, and was the same for the 

polychaetes and molluscs. We did pair-wise tests on each significant ANOVA to see which 

sites were significantly different from each other. There was no trend for greater significance 

at the Outfall site, or one of the other three sites. However, there was a trend towards 

significant differences in pair-wise tests where there were peaks in abundance. For example, 

when we consider cases where one site was significantly different from all of the other three 

sites, this occurred for the peaks at Potrero at 2 m and 4 m for June 2003; and at MBARI at 2 

m for Oct 2004 and at 1 m for Oct 2005 (Fig. 3-13). For the polychaetes, several peaks are 

significant including the largest at the Outfall at 1 m in Oct 2005 (Fig. 3-12) and for the 

molluscs at Potrero 4 m (Fig. 3-11) in the first year. 
 Moss Landing Powerplant Thermal Discharge Effects 47 

Moss Landing Marine Laboratories 

The density of species showed a relatively consistent pattern of increasing with increasing 

water depth at all sites (Fig. 3-15 and 3-16). In addition, species number was lowest at 1 m 

and 2 m in 2005, but was not lowest at 4 m in 2005 (Fig. 3-16). 

Qualitative observations by scuba divers revealed a bed of sand dollars (Dendraster 

excentricus) just offshore of the 4 m station at Potrero Road each year. The inshore edge of 

the bed was sparse (only a few animals/m2); and the first individuals were encountered about 

20 m from the 4 m station. Only a few sand dollars were observed offshore from the Shore 

Lab site, and no distinct bed. None were observed at the two sites within the canyon head 

(OF, MB). On 5 June 2003, we observed a dense band of juvenile cancer crabs around the 

canyon head (OF, MB, SL) within the depth range of the sampling (2-4 m), but not in deeper 

water (6-8 m) or at any depth at Potrero Road. On 20 June 2003, we returned to the canyon 

head area and found no crabs in the surf zone, but many in the deeper canyon between 10-15 

m. This was at the base of a steep sandy slope within the rim of the canyon where there was 

no wave swell. The juvenile crabs were mainly Cancer magister and some C. gracilis, with a 

carapace width of around 1 cm, but not greater than 2 cm. At the highest density, there were 

50 to over 100 small crabs/m2

. We did not see any at Potrero Road or in October 2004 and 

2005. 

The grain size distributions were similar among sites and along the depth gradient (Fig. 3-17 

and Table 3-11), with one obvious exception. The sample from 1 m at MBARI had a much 

larger percentage of sediment volume in the coarse sand fraction in 2004: 25% compared to 

less than 10% at all other stations (Table 3-11). This shows up clearly in the 2004 graph of 

the sample grain size (Fig. 3-17). The sediment at all the other stations was dominated by 

fine and medium sand, with almost no silt or clay (< 1%) at any station (Table 3-11). The 

percentages in fine and medium sand shifted in time and by site. The Outfall and MBARI 1 

m stations had a consistently higher percentage of medium sand, with somewhat less at the 2 

m stations. The Shore Lab site showed the greatest variation between the medium and fine 

sand fractions over time. By the 4 m depth, the percentage of fine sand was higher than 

medium sand at the three sites nearest to the canyon (OF,MB,SL). This pattern may be 

related to the canyon head topography and its impact on damping wave energy. In contrast, 

the most wave-exposed site at Potrero had similar percentages in fine and medium sand 

categories at all three depths (Table 3-11). 

3.6 Discussion 

3.6.1 Results of Study Objectives 

1) The thermal plume had no detectable impact on the intertidal or shallow-subtidal 

benthos. See section 3.6.2: Discussion of Thermal Impacts 

2) Significant changes in the intertidal beach community have occurred since it was 

last sampled in 1975-76. See section 3.6.3: Intertidal Ecology Discussion. 

3) The shallow subtidal community was characterized. This is the first central 

California study to examine the shallow subtidal community. See section 3.6.4: 

Subtidal Ecology Discussion 
 Moss Landing Powerplant Thermal Discharge Effects 48 

Moss Landing Marine Laboratories 

4) A historical database of previous benthic work was compiled. See section 3.7. 

3.6.2 Discussion of Thermal Impacts 

In order to put the potential thermal impacts on the beach fauna in context, it is necessary to 

examine the temperature ranges to which the beach organisms are normally exposed, and 

compare that range to the maximum temperature increases that could be expected from the 

plume. The intertidal beach is exposed to air temperature at low tides that can range in 

central California from -2°C to 30°C. Stress from exposure to extreme air temperatures 

obviously increases with higher elevation on the beach. On the high beach, organic debris or 

wrack (mostly drifting macroalgae and eel and sea grass) accumulates and harbors a unique 

community of beach hoppers (talitrid amphipods), insects, and worms (oligochaetes, 

nematodes, and insect larvae). These patches can become very warm from decay and 

elevated air temperatures. They are usually above the water line, and therefore they were not 

the focus of our benthic sampling. The high intertidal animals have wider tolerances for a 

variety of physical parameters, including temperature and salinity, than the more strictly 

marine animals in the lower intertidal. Our sampling began just below the wrack zone where 

the beach isopod, Excirolana, is the most abundant animal. 

The highest temperate increase caused by the warm-water discharge observed bathing the 

beach is 2°C (Tenera 2000). The seasonal sea surface temperature range in the offshore 

waters of Moss Landing is 9-17°C. Most of the animals that live on the beach have 

geographic ranges that extend into southern California, where the temperature range is 

broader. At the beach, we can add breaking waves to the other regional mixing processes. 

The presence of the warm-water plume at the beach is an infrequent event (Tenera 2000 a,b). 

We found no evidence of a biological response to a persistent or regular elevation of 

temperature on the beach from the outfall. 

In the following section we consider a hypothetical worse case situation, where the warmwater plume is always at the beach and the water temperature is therefore consistently 2°C 

above the ambient temperature of the surrounding waters. A persistent 2°C change in 

temperature is unlikely to degrade the beach community, because all the beach species 

experience much greater temperature ranges under natural conditions throughout the year. In 

addition, dynamic local currents and nearshore mixing will limit drastic temperature 

increases. In this hypothetical case, the most likely impact of this persistent, slightly elevated 

local beach temperature would be a shift towards a higher frequency of warm-water species 

or a higher abundance of species that have distinct southern (warmer) ranges, and perhaps a 

decrease in species with more northerly ranges. For example, just 20 km south in the rocky 

intertidal habitat at the Hopkins Marine Station in Pacific Grove, as sea surface temperatures 

increased since the early 1930’s there was an increase in the abundances of invertebrate 

species ranging more to the south, and a decrease in abundances of those ranging to the north 

(Barry et al. 1995, Sagarin et al. 1999). This is an unlikely result at Moss Landing due to the 

infrequent arrival of the warm-water plume at the beach. Moreover, it is much more difficult 

to find species with distinct northern and southern ranges in the sandy beach community (See 

Section 3.2). Nevertheless, this is the first potential impact to explore. The next impact 

concerns the degradation of the community, which might start with the loss of a temperaturesensitive species or degradation of local population structure and dynamics. Although we 
 Moss Landing Powerplant Thermal Discharge Effects 49 

Moss Landing Marine Laboratories 

cannot identify local species that are more temperature sensitive than the others, particularly 

to the slight increase posited here, we have looked for evidence of negative community 

change. 

The first benthic area to explore for potential impacts from the thermal discharge is the 

Outfall site. This beach station was placed as close as possible to the discharge plume based 

on the observations from past plume monitoring. If we can detect an impact here, then we 

can investigate how far it might spread by looking at the other stations starting with the 

MBARI site. Our beach and subtidal surf zone sampling at the four sites revealed no arrival 

of a warm-water species assemblage at the Outfall or any of the more distant sites. In fact, no 

warm-water species has invaded the beach since the first quantitative surveys in 1975-76. All 

the species are members of the regional intertidal and subtidal fauna of central California. 

We were also unable to distinguish species with distinct southern and northern ranges in the 

sandy beach community (intertidal or subtidal) to determine if abundances changed in a 

manner similar to the rocky shore study to the south (Barry et al. 1995, Sagarin et al. 1999). 

Therefore, the most likely effects to manifest in the beach community due to the warm-water 

discharge were not detected in over 500 0.25m2

 samples taken on the beach and over 200 

0.02m2

 cores from the subtidal surf zone. This is a large sample area, so the possibility of 

missing the new arrival of a warm-water species is low, unless it is extremely rare. 

We found no abnormally low numbers of beach animals at the Outfall site compared to the 

other beach sites. For both the beach and surf zone, we performed a series of statistical 

analyses to determine if there was any trend towards greater population or community 

differences at the Outfall compared to the other sites. It was clear from examining the tables 

and figures that there was no trend. The statistical analysis reinforces this observation, and 

permits more comparisons. We did a series of three-way ANOVAs, which indicated highly 

significant interactions among sites, survey times, and water depths (surf zone) or tidal 

elevations (beach). As a result, we did one-way ANOVAs for each time and water depth or 

tidal elevation to evaluate just differences among the four sites. This avoids the significant 

interactions from the three-way test. When a one-way ANOVA was significant, we then did 

pair-wise tests to determine which sites were different from the others. This is a lot of 

multiple testing, even though all the tests were based on the starting hypothesis for the study 

that the Outfall site would not be different from the other sites along the beach (and further 

from the thermal discharge). The statistical exercise was done to look for trends in 

significance. The trend we observed for both the beach and surf zone was that significant 

differences in pair-wise tests were mostly related to peaks in abundance, and less often to 

lows. These peaks occurred at different sites, survey times, and water depths or tidal 

elevations as indicated in the figures and tables. There was no trend for the Outfall site to 

have significantly fewer species or individuals, which is one expectation if the site were 

degraded by the thermal discharge. 

Although the abundances of several numerically dominant crustaceans were lowest at the 

Outfall along the intertidal beach (Fig. 3-3), this was not an abnormally low pattern. The total 

number of crustaceans, on the other hand, was similar among the four sites (Fig. 3-2). In fact, 

some of the crustacean species that were relatively sparse at the intertidal Outfall site were 

more abundant in the subtidal surf zone at the Outfall compared to the other sites, particularly 
 Moss Landing Powerplant Thermal Discharge Effects 50 

Moss Landing Marine Laboratories 

the most abundant surf zone animal, Americhelidium mircopleon (Fig. 3-14). The most 

common pattern at the Outfall site was the high number of polychaete worms, in both the 

intertidal (Fig. 3-6) and subtidal beach (Fig. 3-11). This is not a negative community pattern. 

It is positive and probably related to the changes in beach morphology in the canyon head, 

which creates a better interstitial habitat for interstitial polychaetes (i.e. small worms) that 

live in the spaces between coarse sand grains. None of the abundant polychaetes in the beach 

or surf zone are indicators of anthropogenic environmental stress, such as thermal stress or 

pollution (Grassle and Grassle 1974, Weisberg et al. 1997, Maurer et al. 1999, Karr and Chu 

1999). They are more indicative of unpolluted benthic habitats. 

The total number of species was the same at all sites, in the intertidal (Fig. 3-7) and subtidal 

habitats (Figs. 3-15 and 3-16). The density of species is the best measure of species diversity, 

an excellent indicator of community degradation (Weisberg et al. 1997, Maurer et al. 1999, 

Karr and Chu 1999, Hunt et al. 2001). It is not low at the Outfall. Although we observed no 

population or community impacts that can be related to the thermal discharge, there are 

distinct faunal patterns related to beach elevation (Figs. 3-3 and 3-6, Table 3-2), subtidal 

water depth (Figs. 3-14 and 3-15, Table 3-7), and the wave exposure and sediment 

availability gradient from Potrero Road to the canyon head and Outfall site (Fig. 3-2; Figs. 3-

11 and 3-14, Table 3-7). We even found very significant differences in the beach fauna 

between our recent samples (2003-05) and samples collected from Moss Landing Beach in 

1975-76 (Table 3-6). So the lack of ecological patterns related to the thermal discharge 

cannot be attributed to a general lack of faunal patterns and linkage to important processes on 

the beach. In summary, as might be expected from the infrequent interaction of the thermal 

discharge with the adjacent beach, we found no evidence of outfall thermal impacts to the 

beach and surf zone community nearest to the power plant discharge. 

3.6.3 Intertidal Ecological Discussion 

There were great spatial and temporal variations in the beach fauna, and yet distinct patterns 

as well. In space, there were persistent patterns across (elevation) and along the beach (site). 

The zonation patterns we observed with elevation have been documented before (Dahl 1952, 

Nybakken et al. 1977, Ricketts and Calvin 1985, Peterson 1991, McLachlan and Jaramillo 

1995). Our sampling started just below the supralittoral zone, where wrack debris 

accumulates and talitrid amphipods and insects are common (Ricketts and Calvin 1985). The 

beach isopod, Excirolana, characterizes the high beach stations (A) of the midlittoral zone, 

where our sampling started (Fig. 3-3, Table 3-2). Emerita (mole crab) epitomizes extreme 

variation on the beach (Dugan et al. 1999). It can occur in narrow, dense aggregations often 

in response to wave wash patterns (McArdle and McLachlan 1992); had large seasonal 

pulses of recruitment (Fig. 3-4); and occurred at all elevations in our samples (Fig. 3-3). It 

was in 57% of the samples from the high beach (A), and over 80% of the samples from the 

three lower elevations (B-D)(Table 3-2). In contrast, the polychaete worms, mysid 

crustaceans, and phoxocephalid amphipods were mostly in the lower beach (Figs. 3-3 and 3-

6), with the Pismo clams, Blepharipoda (sand crab), and Olivella (olive snail) that we 

captured with the large-area cart sampling. This is the classic zonation pattern on the highenergy sandy beaches in Central California (Ricketts and Calvin 1985). 
 Moss Landing Powerplant Thermal Discharge Effects 51 

Moss Landing Marine Laboratories 

There were also distinct faunal patterns along the beach. The four sampling sites were 

established along a wave-exposure and sediment availability gradient caused by the 

Monterey Canyon (Fig. 3-1). This is also the most well-defined gradient away from the warm 

water discharge from Moss Landing Power Plant (see Thermal Impacts to Benthos). Because 

of the steep canyon bathymetry, the canyon head beaches at the Outfall (OF) and MBARI 

(MB) sites are narrow and steep. These beaches also receive little long-shore sand transport, 

because sand moves off the beach and into the offshore canyon head to the north and south. 

As a result, the canyon head sites (OF, MB) have the most poorly consolidated deposits with 

the lowest fine sediment fractions (Table 3-5). On the other hand, in the subtidal surf zone, 

these same sites have the largest fraction of fine sands (See Surf Zone Section), and just 

beyond the surf zone the sea floor slopes steeply into the canyon where there are seasonal 

accumulations of muddy sediments (Oliver et al. 1980, Okey 1997, 2003). Wave energy and 

therefore disturbance to the intertidal beach is dramatically reduced in the canyon head 

(Bascom 1964, Shepard and Dill 1966, Arnal et al. 1973, Oliver et al. 1980). The Shore Lab 

site has a broader, less steep beach, which is still within the wave-energy shadow created by 

the canyon and the general northwest direction of wave arrival. Sand transport from the south 

moves across the Shore Lab beach into the canyon head, not onto the MBARI and Outfall 

sites (Arnal et al. 1973). The Shore Lab site is uniquely positioned for maximum sand 

transport and minimal wave disturbance. It therefore had the highest percentage of fine 

sediments among the sites (Table 3-5). The Potrero site is swept by large winter waves like 

most of central Monterey Bay; the intertidal beach (Fig. 3-8) and subtidal surf zone are the 

widest and the sediments in the subtidal surf zone are coarser as a result (See Surf Zone 

Section). 

The abundance of polychaete worms increased significantly and dramatically as wave 

exposure decreased around the canyon head (Fig. 3-3). This is the same pattern seen along 

many wave-exposure gradients moving from more exposed open coastal environments to 

protected embayments (Ricketts and Calvin 1985, Brown and McLachlan 1990). However, 

along these gradients there is also a corresponding gradient in sediment grain size, from 

coarse to finer deposits. There is a similar wave exposure gradient along the deeper sand flat 

(Oliver et al. 1980). Crustaceans dominate the inner wave-swept zone, and polychaete worms 

characterize the deeper zone, where sediment is finer. The entire wave-exposure and 

sediment availability gradient around the canyon head is an exposed sandy beach; so the 

gradient in sediment size is more subtle than the offshore-depth and open coast to 

embayment exposure gradients. Moreover, instead of finer, the beach deposit is coarser 

because of low sediment availability and moderate wave action (Table 3-5). The polychaetes 

increasing along the canyon gradient are among the interstitial fauna, living in the spaces 

between coarse sand grains. The canyon head beach (OF & MB) has less fine sand to fill the 

interstitial spaces and lower wave action to disrupt them. 

Apparently, the exposure gradient was not extreme enough to impact crustaceans nearly as 

much as the polychaetes (Fig. 3-3). The numbers of beach crustaceans were dominated by the 

mole crab Emerita, which was abundant at all sites, but is least abundant at the high elevation 

(A) at the Outfall (Figs. 3-2 and 3-3). The numerical dominance of Emerita is common on 

many exposed beaches (Dugan et al. 1999). Since this was also the largest abundant animal 

on the beach, it dominated the biomass. The numbers of Olivella, Blepharipoda, and Pismo 
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Moss Landing Marine Laboratories 

clams in cart samples were similar from the Shore Lab and Potrero sites. These species were 

not captured at the canyon head sites (MB & OF), probably because the beaches are too steep 

and narrow (Fig. 3-8). The other numerically dominant crustaceans, excluding Emerita, were 

all most abundant at the Shore Lab site (Fig. 3-3). These increases are expected in a more 

dissipative beach, broader with finer sand. However, the pattern also may reflect the finer 

screen size used at the Shore Lab, but the screen size change had no obvious effect on the 

larger Emerita or the large or smaller polychaetes (Figs. 3-2 and 3-6). 

So, despite the tremendous variations in the beach fauna, the samples show the wellestablished zonation by tidal elevation as well as a distinct pattern related to wave exposure. 

However, the canyon head exposure gradient is unique, because it is not linked to a 

corresponding coarse to fine sediment gradient. Instead, there appears to be a gradient in the 

quality of interstitial habitat on the beach, and the polychaetes are likely responding to this 

structure. The gradient does fit the general physical pattern of change from dissipative to 

reflective beaches. The canyon head beach (OR, MB) is more reflective and is thus narrower, 

steeper, and coarser than the southern beach (SL, PR). However, we did not observe a 

decrease in faunal diversity (Fig. 3-7), or abundance (Fig. 3-2) at the reflective end of the 

gradient, the canyon head. Since Emerita dominated the biomass at all stations, there was no 

decrease in biomass as well. However, before the sea otters ate most of the Pismo clam 

population in the mid 1970’s, this large clam dominated the beach biomass and was never 

abundant at the canyon head. The commercial fishery started on the north and south sides of 

the canyon (Stephenson 1977). On the other hand, the historically high biomass of Pismo 

clams was linked to extreme human exploitation of sea otters in the 1800’s; and American 

Indians periodically captured sea otters and other coastal marine mammals for thousands of 

years along the beach, where they also collected Pismo clams (Gordon 1996). 

We observed three distinct temporal patterns on the beach: seasonal, episodic, and decadal. 

The seasonal pattern of recruitment is exemplified best among the abundant crustaceans, 

particularly the mole crab Emerita (Figs. 3-4 and 3-5, Table 3-1). Pulses of spring 

recruitment are common in many benthic invertebrates (Coe 1956), and especially crustacean 

populations along the subtidal and intertidal beach (Barnes and Wenner 1968, Oliver et al. 

1980, Slattery 1985). All the numerically dominant crustaceans were present throughout the 

year on the beach (Figs. 3-4 and 3-5, Table 3-1). As a result, the major peaks in abundance 

shown in Fig. 3-3 contain animals from most, if not all, of the 6 sampling periods. This is in 

stark contrast to the polychaetes, where every major peak in abundance represents a large 

number of animals present at only one sampling period (Fig. 3-6). Their numbers were thus 

patchy in both space and time. Since these individuals occurred in most, if not all, of the 

replicate samples from each time period when they were abundant, these peaks may be 

related more to episodic recruitment rather than spatial patches. Although variations in 

polychaete abundance among sites displayed extreme mesoscale patchiness along the beach 

(Fig. 3-6), one-time recruitment events within a site were more common among the 

polychaetes than the crustaceans. The most extreme example was the small phyllodocid 

polychaete, Hesionura, which occurred at the highest abundance recorded for any species 

almost exclusively at a depth of 1 m in the surf zone of the Outfall site (See Surf Zone 

Section). 
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Moss Landing Marine Laboratories 

Sea otters invaded the central bay area in the mid 1970’s. A year later no large Pismo clams 

could be found on the beach, after decades of sport fishing here (Stephenson 1977). Four 

small clams were collected in the quantitative surveys in 1975-76. We collected four small 

Pismo clams in the large-area cart sampling targeted for this species, and another four small 

individuals in over 500 of the 0.25 m2

 samples. Similar sized shells broken by otters were 

seen on the intertidal beach throughout the study period. In a section of beach 100 m long, 

we found as many as 5 otter-cracked Pismo shells at low tides, but only several times in a 

year. Fresh large shells are very rare. There is thus no evidence of the recovery of the Pismo 

clam population on the beach, and evidence of continuing otter predation on relatively rare, 

small individuals. 

There are no significant differences between 1975-76 and 2003-05 in the density of species 

and the number of individuals of the entire fauna, crustaceans or polychaetes (Table 3-6). On 

the other hand, abundance differences for most of the numerically dominant species are 

statistically significant between the decades (Table 3-6). For about half of these species, the 

differences between the decades can be seen in mesoscale variations along the beach in 2003-

05. This is not true for Emerita, Grandiphoxus, Americhelidum and nemertean worms. 

Emerita, however, is known to vary tremendously over seasons and among years and also 

among beaches (Barnes and Wenner 1968, Wenner et al. 1987, Ricketts and Calvin 1985, 

Dugan et al. 1999). Therefore, although there are distinct differences between 1975-75 and 

2003-05, these are likely to be short-term annual variations on Moss Landing Beach, and less 

likely to represent differences that persisted over decades. We know too little about the 

nemertean worms to say any more. However, there is evidence that the changes in 

Grandifoxus and Americhelidium may be linked to interdecadal regime shifts in the 

California Current. 

The decadal change in abundance and frequency of occurrence of the giant phoxocephalid 

amphipod, Grandifoxis, is related to a regional pattern for this family. Throughout the 

1970’s, this species could be readily collected on the regional beaches, and not since then. 

None of the other numerically dominant beach species showed a similar qualitative trend. In 

addition, the subtidal populations of phoxocephalids decreased by a factor of ten from 1971-

75 compared to 1997-98 (Oliver et al. in preparation). Coincidentally, so did Grandifoxus

from 1975-76 to 2003-05 (Table 3-6). Phoxocephalids are voracious predators (Oliver et al. 

1982). In the offshore benthos, there were dramatic decadal decreases in the number of 

individuals, diversity (species density), biomass, and population size of many higher trophic 

level consumers like the phoxocephalids. Oliver et al. argue that these changes are related to 

the regime shift in the California Current. The 1971-75 samples were taken after 25 years of 

high production in a cold regime, and the 1997-98 samples at the end of a low production, 

warm regime. After over two decades of significantly less planktonic production, the 1997-

98 subtidal community was highly degraded compared to the 1970’s. 

As the phoxocephalids declined, the abundance of Americhelidium shoemakeri increased 

dramatically (also by 10 times) in the same offshore habitats (Oliver et al. in preparation). 

We have no long-term qualitative observations on Americhelidium in the intertidal beach, 

because both species are small enough to escape detection in classroom field trips and 

qualitative surveys for Pismo clams and Grandifoxus. Nevertheless, the quantitative and 
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Moss Landing Marine Laboratories 

qualitative sampling in the adjacent offshore extends throughout the two regimes, and 

suggests that the beach may change in a similar manner. There were no A. microplean in the 

1975-76 beach samples and hundreds in the 2003-05 samples. 

 

In contrast to Grandifoxus, the abundance of another, much smaller phoxocephalid 

amphipod, Mandibulophoxus, did not change between the decades on the beach (Table 3-6). 

This species primarily lives in the subtidal surf zone, not the intertidal beach (See Surf Zone 

Section). There is another pattern in the offshore benthos related to the oceanographic regime 

shift. This is an expansion of the zones of certain shallow water species into deeper water as 

the numbers of potential predators and competitors decreased. Mandibulophoxus showed this 

pattern. It was never encountered at offshore stations (6 and 9 m) in the 1970’s, and was 

there in the 1990’s. Perhaps it expanded into or at least persisted in the intertidal as the 

Grandiphoxus decreased. As longer-term (decadal) patterns become better known, we can 

evaluate and either refute or accept hypotheses about regimes shifts and decadal fluctuations 

in plankton production and food for the benthos, expansion and contraction of faunal zones 

in different regimes, physical disturbance, recruitment, and key ecological indicators of these 

and other potentially important processes. 

Finally, no warm-water invertebrates colonized the sandy beach at Moss Landing since the 

first quantitative sampling in 1975-76. There is also no evidence of the arrival of warm-water 

species before the 1970’s, since the present list of species is characteristic of the sandy beach 

fauna observed throughout central California for many decades (Ricketts and Calvin 1985). 

There is also no evidence of trends in abundance for species with ranges extending more to 

the south or north of Monterey Bay. This result is dramatically different from the pattern 

documented along the rocky intertidal shore just 25 km south of Moss Landing. At Hopkins 

Marine Station, the abundances of southern species increased and northern species decreased 

between 1931-33 and 1993-94 (Barry et al. 1995, Sagarin et al. 1999). The sandy beach has 

many fewer species than the rocky shore, and a fauna that cannot be as easily divided into 

those with greater northern and southern ranges. We can also show that many of the decadal 

variations can be seen along the beach in a much shorter time period (2003-05). The rocky 

shore may simply be a better system to explore patterns related to geographical range. 

3.6.4 Subtidal Ecology Discussion 

This is the first quantitative study of the structure of macrofaunal invertebrate communities 

living in the subtidal surf zone of a high-energy sandy beach in the Pacific Ocean. The most 

distinct community patterns are the faunal zonation with water depth. Two groups of species 

are characteristic of the subtidal surf zone (Table 3-12). The first group lives almost 

exclusively here, but also much less abundantly in the low intertidal zone (sublittoral fringe). 

It has a relatively narrow zonation. The second group has a broader zonation, living primarily 

in the subtidal surf zone but also on the low intertidal beach and especially in deeper water. 

There are two other groups of relatively transient species that live in the subtidal surf zone, 

but primarily inhabit either the intertidal beach or deeper water, where they are much more 

characteristic community members (Table 3-12). The local subtidal surf zone community fits 

into the well-known zonation of intertidal beach fauna (Ricketts and Calvin 1985, Nybakken 

et al. 1977) and subtidal species just beyond the surf zone (Oliver et al. 1980). 
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Moss Landing Marine Laboratories 

The most characteristic macrofaunal species inhabiting the subtidal surf zone is the 

odecerodid amphipod crustacean, Americhelidium micropleon (Fig. 3-14, Tables 3-7 and 3-

8). This species is most abundant at 1 m, but occurs at 2 m and 4 m. It was never encountered 

at stations sampled in 6 m and deeper along the sand flat (Oliver et al. 1980 in preparation, 

Slattery 1985, Table 3-13), but does occur much less abundantly in the low intertidal zone 

(See Beach Section). It is thus a surf zone species with a narrow zonation pattern (Table 3-

12). Americhelidum is an active swimmer, a small animal about 4-5 mm long with a slender 

body. It burrows only into superficial sediments, and is a scavenger and predator here and in 

near-bottom waters (Oliver et al. 1980 in preparation). In Korea, a closely related species 

(Synchelidium) mainly eats harpacticoid copepods, while the juveniles also eat copepod 

nauplii and nematodes (Yu et al. 2003). The other common amphipod groups (haustoriids 

and phoxocephalids) on the local intertidal and subtidal beach are larger with wider bodies 

that are more adapted for burrowing in sediment(Slattery 1985). The other animals that are 

most characteristic of the subtidal surf zone are also crustaceans and fit the narrow zonation 

pattern (Table 3-12). They include the mysids, Holmesmysis sculpta and H. costata, and a 

cumacean Cyclaspsis sp. These crustaceans and the little phyllodocid polychaete worm, 

Hesionura sp., have been found primarily in the subtidal surf zone and much less in the lower 

intertidal beach, but not in deeper water. 

The phoxocephalid amphipod, Mandibulophoxus gilesi, (Figs. 3-12 and 3-13; Table 3-7) is 

also characteristic of the subtidal surf zone, but occurs on the low intertidal beach and along 

the deeper sand flat (Table 3-12). It is a surf zone species with a broad zonation pattern. 

Several other species have this zonation pattern as well, including Metamysidopsis elongata, 

the Pismo clam Tivella stultorum, and the sand crab Blepharipoda occidentalis (Ricketts and 

Calvin 1985). Pismo clams are now rare on the low intertidal and subtidal beach because of 

predation by sea otters (Stephenson 1977). 

There are several species that are characteristic of the intertidal beach and only occur in the 

surf zone infrequently and in low numbers as transients. These include the sand crab Emerita 

analoga, Archaeomysis grebnitski, and the polycheate worm Nephtys californiensis (Ricketts 

and Calvin 1985). There are more species that are abundant in deeper water, but also occur as 

surf zone transients, particularly polychaete worms (Table 3-12) with relatively opportunistic 

life histories (Oliver et al. 1977, in preparation, Grassle and Grassle 1974); but crustaceans as 

well such as Americhelidium shoemakeri (Fig. 3-14) and haustoriid amphipods (Table 3-12). 

In the present study, these deeper-water species generally increase in abundance from the 1 

to 4 m depths (Fig. 3-14), but are more abundant in deeper water (Tables 3-12 and 3-13). 

The faunal zonation we observe also fits the general zonation scheme proposed by 

McLachlan et al. (1984). Their inner turbulent zone includes the sublittoral intertidal beach 

and the subtidal surf zone to 2-4 m. Americhelidium micropleon is abundant to 1-2 m (Fig. 3-

14). It is the most characteristic species of the subtidal surf zone. Offshore of our sampling 

area, the inner edge of the sand dollar (Dendraster excentricus) bed is around 5 m. It can be 

several meters deeper on the northern side of Monterey Canyon where wave energy increases 

(Oliver et al. 1980). The inner edge of the sand dollar bed is highly dispersed: the outer edge 

is a dense band that often ends in a sharp boundary (Merrill and Hobson 1971, Morin et al. 
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Moss Landing Marine Laboratories 

1985). The dense sand dollar bed defines the beginning of the outer turbulent zone, and A. 

microplean defines the offshore side of the inner turbulent zone. This leaves a narrow 

transition area between 1-2 m and 5-8 m. 

This general agreement in zonation is remarkable considering the large differences between 

the fauna found in Monterey Bay and the fauna of South Africa. Monterey Bay subtidal 

beaches are numerically dominated by pericarid crustaceans: cumaceans, and especially 

ostracods and haustoriid, phoxocephalid, and oedeceroid amphipods (Table 3-13). 

Polychaetes become more abundant and diverse with depth (Oliver et al. 1980). There is a 

dense, narrow sand dollar bed. The South African benthos includes relatively large bivalves 

and gastropods; many heart urchins and brittle stars; and high densities of Callianassa

(crustaceans), which live in relatively stable burrows. All of these groups are abundant as 

shallow as 5 m. Sipunculid and echiuroid worms and aplacophoran molluscs are abundant at 

some stations (McLachlan et al. 1984). In Monterey Bay, the later groups are found only 

along the outer continental shelf. Tube and burrow dwellers are rare until 15-20 m at the edge 

of the outer turbulent zone, where polychaetes become more abundant. Monterey Bay has 

nothing like the high numbers of Callianassa found in South Africa. And the only abundant 

bivalves are juvenile Tellina modesta (several mm), which are also mostly in the polychaete 

zone (Oliver et al. 1980). Despite these striking faunal differences between South Africa and 

Monterey Bay, the wave climate divides the communities into similar physical zones. 

 

There are numerous groups of closely related species that replace each other along the beach 

from the intertidal into the subtidal sand flat. Nephtys californiensis is most abundant in the 

intertidal zone (See Beach Section), N. caecoides peaks in 6-9 m, and N. cornuta is most 

abundant deeper than 15 m (Oliver et al. 1980, Tables 3-12 and 3-13). Among the 

phoxocephaid amphipods, Grandifoxus grandis is on the intertidal beach (Beach Section); 

Mandibulophoxus peaks in the surf zone and occurs shallower and deeper (Tables 3-7, 3-12 

and 3-13); and Rhepoxynius lucubrans is replaced by R. fatigans and then by R. abronius

with increasing water depth (Slattery 1985, Table 3-13). Among the haustoriid amphipods, 

Eohaustorius washingtonianus is on the intertidal and shallow subtidal beach, and is replaced 

by E. sawyeri and then E. sencillus with increasing depth (Slattery 1985, Table 3-13). The 

olive snail Olivella biplicata is in the low intertidal beach and subtidal surf zone and is 

replaced by O. pycna in deeper water (Tables 3-12 and 3-13). Sand crabs (Ricketts and 

Calvin 1985, Table 3-12), mysids, and cumaceans (Cyclaspsis species) show similar depth 

replacement patterns or zonation (Oliver et al. 1980, Tables 3-12 and 3-13). Finally, although 

there are more examples, Americhelidium micropleon and A. shoemaker co-occur in the surf 

zone (Fig. 3-14, Table 3-7), but only A. shoemaker lives along the deeper sand flat, where it 

is more abundant (Table 3-13). In contrast, A. micropleon occurs in the low intertidal zone, 

but in lower numbers than it does in the subtidal surf zone. 

The zonation patterns presented here can change with wave exposure and other factors. For 

example, Olivella biplicata can be more characteristic of the intertidal flats that are more 

protected from wave exposure. Ricketts and Calvin (1985) provide a number of similar 

examples of the zonation of local species changing with wave exposure. Oliver et al. (1980) 

document a major offshore shift in the crustacean zone with an increase in wave exposure 
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Moss Landing Marine Laboratories 

along the subtidal sand flats on the north side of Monterey Canyon compared to the south 

side. 

The four sampling sites were selected along a gradient away from the warm-water discharge 

from the Moss Landing Power Plant (Fig. 3-1). The Outfall site was closest and the Potrero 

site was furthest from the discharge. Potential impacts from the warm-water discharge are 

considered in another section. 

There are few differences among the four subtidal sites we sampled, but two patterns may be 

related to the wave exposure gradient created by the canyon bathymetry and the direction of 

wave arrival (Bascom 1964, Shepard and Dill 1966, Arnal et al. 1973). Mandibulophoxus

and Olivella are most abundant at Potrero Road (Fig. 3-12, Table 3-7), where the impacts of 

wave action are clearly the highest (Oliver et al. 1980). Compared to the other numerical 

dominants in the subtidal surf zone (Tables 3-7 and 3-12), these two species occur in deeper 

water along the subtidal sand flat, and thus may be able to move seaward more easily to 

avoid extreme wave disturbance. Seaward and shoreward movement in response to changes 

in wave action has been documented for sand dollars (Oliver et al. 1980, Morin et al. 1985), 

which are also more abundant at Potrero Road (Oliver et al. 1980). Although Hesionura

dominates the polychaete abundance patterns, there is a general tendency for higher 

polychaete abundance at the three canyon head sites, which may be related to lower wave 

exposure here (Fig. 3-11). This polychaete abundance pattern is more pronounced on the 

intertidal beach along the same canyon-exposure gradient (See Section 3.2-) and along the 

wave disturbance gradient in deeper water, where a shallow crustacean zone is replaced by a 

deeper polychaete zone (Oliver et al. 1980). 

In addition, the shallow canyon head appears to be an important recruitment region for 

juvenile cancer crabs, both Cancer gracilis and C. magister. We observed a narrow band of 

many young crabs in the surf zone, and then again two weeks later in the deeper canyon head 

in June 2003 (about 50-100/m2). Water clarity is low in the canyon head compared to the 

flanking sand flats, and the numbers of predacious fishes are lower as well. There are also 

patches of drift algae that can provide refuge from predators as well as prey for the young 

crabs (Okey 1997, 2003). 

Benthic communities living in the intertidal beach and shallow subtidal habitats, including 

the subtidal surf zone and deeper, may be strongly limited by physical disturbance from 

wave-generated bottom disturbance (Oliver et al. 1980, McLachlan et al. 1984, Defeo and 

McLachlan 2005). Where the sediments are more stable, food may be more important in 

community organization (Oliver et al. in preparation). In the present study, the number of 

species increased at all sites with increasing water depth in the surf zone (Figs. 3-15 and 3-

16). This pattern was also observed along the deeper sand flat, where the density of species 

increased from 6 m to 24 m (Oliver et al. 1980, in preparation). The 6 m depth has a higher 

number of species per core than any of the 4 m stations sampled in the present study (<10 

species/core compared to >10). Therefore, the depth patterns along the sand flat suggest that 

wave disturbance plays an increasingly important role in controlling the density of species 

with decreasing water depth (Oliver et al. 1980). The pattern of increasing diversity with 
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Moss Landing Marine Laboratories 

depth has been documented in other sampling efforts through the wave-controlled subtidal 

beach (Day et al. 1971, Fields 1971, Masse 1972, Christie 1976, McLachlan et al. 1984). 

In addition to wave disturbance, regional patterns of planktonic production also appear to 

have an important impact along the deeper sand flat, where there were radically different 

communities at the end of a warm, low production regime in the California Current 

compared to a cold, high production regime (Oliver et al. in preparation). Species density 

decreased significantly at all water depths (6, 9, 18, and 24 m) by the end of the warm 

regime, after the benthos was poorly fed for over two decades. We apparently entered into 

another cold regime in 1999, so the data collected in this study provide an opportunity to 

observe how diversity changes in the surf zone compared to deeper water, where we expect it 

to increase during the new high-production cold regime. In contrast, we predict that diversity 

will not change in the surf zone, where wave disturbance probably plays the dominant role in 

controlling species richness. 

Another change between the cold and warm regimes was in animal zonation. By the end of 

the warm regime, the distribution of a number of species extended into deeper water (Oliver 

et al. in preparation, Table 3-13). Americhelidium shoemakeri is an excellent example. It was 

only abundant at the 6 m station in the 1970’s at the end of the last cold regime. It was ten 

times more abundant at 6 m in the 1990’s, and was also abundant at 9 m for the first time 

(Table 3-13). Rhepoxynius lucubrans characterized the 6 m station in the 1970’s, and was 

more abundant at 9 m by the 1990’s (Table 3-13). Mandibulophoxus occurred at the offshore 

stations only in the 1990’s (Table 3-13). It is most abundant in the subtidal surf zone (Fig. 3-

13 and Table 3-7). If these zones contract again by the end of the present cold regime, we 

may see this reflected in the surf zone as well, particularly in the zonation of Americhelidium 

micropleon, which may be the most characteristic macrofaunal species in the surf zone only 

during periods of low planktonic production in the California Current. Perhaps another 

species dominates when production is greater. We predict this will be Mandibulophoxus, 

since phoxocephalid amphipods were much more abundant in deeper water during the last 

cold regime (Table 3-13, Oliver et al. in preparation). 

3.7 Historical Data 

For the invertebrate fauna, reports and papers of surveys in intertidal and shallow subtidal 

sandy habitats hear Moss Landing have been collected. The data have been entered in 

electronic form, and the taxonomy has been updated in some cases. 

Keeping the taxonomy of historical databases up to date is a significant problem in benthic 

ecology, because the taxonomy is constantly changing. It can be very time consuming, and in 

many cases requires a bit of detective work. However, if realistic long-term comparisons are 

to be made, it is necessary to keep the taxonomy up to date. This is immeasurably easier if 

the original researchers are still alive and active (as is the case with the data presented 

below). We recommend updating all datasets listed below that were not updated as part of 

this study. There are also a number of deeper-water datasets from the Monterey Bay area that 

need to be compiled and updated as well. 
 Moss Landing Powerplant Thermal Discharge Effects 59 

Moss Landing Marine Laboratories 

1. “P-Data” 

These were large coffee can cores from 3 depth stations (15 ft, 30 ft, and 60 ft), with 6 

replicates per station. They were collected by John Oliver and Peter Slattery from 1971 

through 1975. The data have been recovered and entered into the database. The taxonomy 

has not been updated. 

2. Narine, Vidya. 1976. The Vertical and Horizontal Distribution Of the Meiofauna and 

some Physical Factors in a Sandy Beach in Monterey, California. Masters Arts Thesis, 

CSUS. 243 p. 

These are meiofaunal data from the Salinas River Mouth, collected in 1974 and 1975. Data 

were identified to major taxonomic groups (Gastroticha, Ostracoda, Copepoda, Nematoda, 

Turbellaria, Nemertina, Polychaeta, Archiannelida, Oligochaeta). 

3. "Preliminary Baseline Studies of the Intertidal Sandy Beach at Moss Landing" By James 

Oakden and James Nybakken, 1975-1976. 

This is the original dataset collected from in front of the old Moss Landing Marine Labs by 

Jim Oakden in 1975. Two 0.25 m2

 replicates per station were collected at 5 m intervals along 

1 transect. Samples covered most low tides (13 dates) from October 1975 through June 1976. 

We have updated the species names and have used these data extensively as a comparison to 

the data collected as part of this study. 

4. Kaiser/National Refractories Outfall data 

These data are from several stations around the Kaiser/National Refractories outfall as part of 

their NPDES monitoring program from 1971 through 1989. The data were compiled by ABA 

Consultants in 1994, and the names were updated then. 

Another dataset from the Moss Landing beach (Steve Locey’s MLML MS thesis) has no raw 

data, only graphs, and we were unable to figure a way to utilize it. There is also a great deal 

of deeper-water data from the canyon and vicinity, but it is beyond the scope of this project. 

There was monitoring done around the PG&E outfall, but it seems to have been only 

photographs, with no usable data. 

The available raw data have been entered into electronic format. The historical benthic data 

will be included on a CD prepared for this project. 
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Moss Landing Marine Laboratories 

3.8 Literature Cited 

Ainley, D.G., Clarke, E.D., Arrigo, K., Fraser, W.R., Kato, A., Barton, K. & Wilson, P.R. 

2005. Decadal-scale changes in the climate and biota of the Pacific sector of the 

Southern Ocean, 1950s to the 1990s. Antarctic Science 17(2), 171-182. 

Arnal, R.E., E. Dittmar, and E. Shumaker. 1973. Sand transport studies in Monterey Bay, 

California. Moss Landing Marine Laboratories Technical Publication, 73-5, 71 p. 

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Grassle, J.F. and J.P. Grassle. 1974. Opportunistic life histories and genetic systems in 

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Hulberg, L.W. and J.S. Oliver. 1980. The exclusion of demersal fish from a soft-bottom 

community: the role of biological interactions or sedimentary habitat modifications. 

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sites in San Francisco Bay, USA, based on the sediment quality triad, toxicity 

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macroinfauna to physical factors over a range of exposed sandy beaches in South-central 

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a subtidal sand-bottom habitat. Oecologia (Berl.) 52: 340-347. 

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McLachlan, A. 1990. Dissipative beaches and macrofauna communities on exposed intertidal 

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dollar of western North America. American Midland Naturalist 83: 595-624. 
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Morin, J.G., J.E. Kastendiek, A. Harrington, and N. Davis. 1985. Organization and patterns 

of interactions in a subtidal sand community on an exposed coast. Marine Ecology 

Progress Series 27: 163-185. 

Nybakken, J. W., G. M. Cailliet, and W. W. Broenkow. 1977. Ecological and hydrographic 

studies of Elkhorn Slough, Moss Landing Harbor and nearshore coastal waters. Moss 

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community changes in Monterey Canyon head. Continental Shelf Research 17: 877-897. 

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drift algae: partitioning multidimensions. Ecological Monographs 73:415-440. 

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predators on larvae and juveniles in marine soft-bottom communities. Marine Ecology 

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Oliver, J.S., P.N. Slattery, L.W. Hulberg and J.W. Nybakken. 1977. Patterns of succession in 

benthic infaunal communities following dredging and dredge spoil disposal in Monterey 

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wave disturbance and zonation of benthic invertebrate communities along a high-energy 

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Monterey Bay, California. Journal of Crustacean Biology 5: 635-649. 

Stephenson, M.D. 1977. Sea otter predation on Pismo clams in Monterey Bay. California 

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Duke Energy Moss Landing LLC. 109 pp. 

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316(b) Resource Assessment. Prepared for Duke Energy Moss Landing LLC. 

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community exposed to oceanic swell. Ecological Monographs 52: 283-305. 

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availability on pacific shorelines. Bull Mar Sci 4:221–233 

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Synchelidium lenorostralum, S. trioostegitum and Gitanopsis japonica in the surf zone of 

a sandy shore. Mar. Ecol. Prog. Ser. 258: 189-199. 
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3.9 Tables and Figures 

Table 3-1. Percentage of individuals (N) of the 10 most abundant species sampled in each of the 

first six sampling periods. 

 Percent of N 

Species Apr 03 May 03 Aug 03 Oct 03 Mar 04 May 04 N 

Spionid 100 184 

Pisione remota 43 57 449 

Saccrocirrus sp. 32 42 25 1 281 

Archiannelid 1 7 92 988 

Hemipodus borealis 73 6 1 5 6 9 902 

Nephtys californiensis 2 6 18 28 40 6 65 

Emerita analoga 44 18 3 3 8 24 6085 

Excirolina chiltoni 42 6 13 10 26 3 4518 

Archaeomysis grebnitskii 39 9 34 9 4 5 568 

Americhelidium micropleon 18 13 20 36 5 8 97 
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Table 3-2. Frequency of occurrence percentage of the 10 most abundant species, along 

with the mean number of individuals, the standard error and the number of samples, in 

the four elevations from the high (A) to the low (D) intertidal beach. (for example, 88% 

of the samples at Elevation A contained Excirolana). 

Elevation Species Mean SE N 

Freq of 

Occurrence 

(%) 

A Excirolana chiltoni 33.21 5.80 129 88 

Emerita analoga 8.54 1.73 129 57 

Hemipodus borealis 0.22 0.10 129 9 

 Archiannelid 0.14 0.07 129 5 

Megalorchestia columbiana 0.12 0.04 129 6 

Megalorchestia sp. 0.11 0.04 129 8 

Megalorchestia benedicti 0.06 0.03 129 4 

 Nemertea 0.05 0.03 129 2 

 Hesionid 0.04 0.03 129 2 

Saccocirrus sp. 0.03 0.02 129 2 

 

B Emerita analoga 16.43 5.62 121 81 

Excirolana chiltoni 1.69 0.37 121 47 

Hemipodus borealis 1.44 0.36 121 31 

 Spionid 1.10 0.71 121 4 

 Archiannelid 0.79 0.41 121 10 

 Nemertea 0.34 0.16 121 9 

Pisione remota 0.34 0.11 121 12 

Archaeomysis grebnitskii 0.28 0.10 121 13 

Nephtys californiensis 0.28 0.18 121 9 

Saccocirrus sp. 0.21 0.10 121 7 

 

C Emerita analoga 15.63 2.38 115 80 

 Archiannelid 7.14 2.84 115 21 

Hemipodus borealis 5.75 1.90 115 36 

Archaeomysis grebnitskii 3.50 0.76 115 44 

Pisione remota 1.97 0.56 115 14 

Saccocirrus sp. 0.85 0.26 115 14 

 Spionid 0.42 0.23 115 5 

Mandibulophoxus gilesi 0.37 0.11 115 16 

Americhelidium micropleon 0.33 0.10 115 16 

Excirolana chiltoni 0.19 0.06 115 13 

 

D Emerita analoga 15.96 3.69 75 85 

Pisione remota 2.43 1.43 75 5 

Saccocirrus sp. 2.05 1.11 75 7 

Archaeomysis grebnitskii 1.72 0.36 75 48 

 Archiannelid 0.72 0.31 75 17 

Americhelidium micropleon 0.67 0.31 75 16 

Hemipodus borealis 0.51 0.20 75 16 

Mandibulophoxus gilesi 0.51 0.19 75 20 

Nephtys californiensis 0.24 0.08 75 15 
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Table 3-9. Three -way ANOVAs testing effect of survey date, site and depth on square -

root transformed total numbers of crustaceans, polychaetes, and molluscs . 

 Total Crustaceans Total Polychaetes Total Molluscs 

Source of variability df F P value df F P value df F P value 

 Overall Model 33 17.08 0.0001 33 16.19 0.0001 33 17.98 0.0001 

 Survey 2 26.29 0.0001 2 34.37 0.0001 2 5.16 0.0067 

 Site 3 34.13 0.0001 3 7.16 0.0001 3 19.45 0.0001 

 Depth 2 8.22 0.0001 2 7.06 0.0001 2 64.49 0.0001 

Interact ion terms 

 Survey*Site 6 25.59 0.0001 6 22.50 0.0001 6 13.18 0.0001 

 Survey*Depth 4 19.52 0.0001 4 19.07 0.0001 4 10.62 0.0001 

 Site*Depth 6 8.30 0.0001 6 15.51 0.0001 6 16.08 0.0001 

 Survey*Site*Depth 10 11.09 0.0001 10 12.57 0.0001 10 17.77 0.0001 
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Table 3-10. Summary of individual ANOVAs testing differences among sites for total numbers 

of individuals (as in Table 3) at each water depth and for each survey date. Significance was 

defined as any analysis with a p -value of < 0.05. 

 Total Crustaceans Total Polychaetes Total Molluscs 

 

Depth (m) 

Total 

Analyses 

Significant 

Analyses 

Total 

Analyses 

Significant 

Analyses 

Total 

Analyses 

Significant 

Analyses 

1 3 3 3 2 3 2 

2 3 2 3 2 3 1 

4 3 3 3 2 3 3 
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Table 3-13. Ten most abundant invertebrate species at 6m and 9m just offshore of the 

Potrero Road site at the end of a high production, cold regime in the 1970’s and at the end of 

a low production, warm regime in the CA Current in the 1990’s (mean per core, n = number 

of core samples). Major taxonomic groups are crustaceans (C), polychaetes (P), molluscs 

(M), and echinoderms (E). From Oliver et al. in preparation. 

1971-75 1997-98 

6 m Group n=139 6 m Group n=6 

Euphilomedes longiseta C 14.77 Americhelidium shoemakerC 32.25 

Olivella pycna M 5.43 Dendraster excentricus E 6.25 

Rhepoxynius lucubrans C 5.30 Eohaustorius sawyeri C 4.50 

Eohaustorius sencillus C 5.21 Scoloplos armiger P 2.75 

Eohaustorius sawyeri C 4.09 Mandibulophoxus gilesi C 2.50 

Americhelidium shoemakerC 2.49 Syllis sp. P 1.50 

Apoprionospio pygmaea P 1.88 Lamprops sp. C 1.00 

Scoloplos armiger P 1.67 Armandia brevis P 0.75 

Foxiphalus obtusidens C 1.01 Hemilamprops californica C 0.75 

Rhepoxynius fatigans C 0.96 Pacificulodes spinipes C 0.75 

 

9 m Group n=111 9 m Group n=30 

Rhepoxynius fatigans C 28.65 Zeugophilomedes oblongusC 10.52 

Rhepoxynius abronius C 28.62 Eohaustorius sencillus C 8.87 

Eohaustorius sencillus C 22.60 Americhelidium shoemakerC 4.27 

Zeugophilomedes oblongusC 18.56 Eohaustorius sawyeri C 4.17 

Dendraster excentricus E 14.35 Dendraster excentricus E 3.04 

Tellina modesta M 13.54 Rhepoxynius abronius C 2.75 

Euphilomedes longiseta C 9.48 Apoprionospio pygmaea P 2.63 

Rochefortia tumida M 6.96 Mediomastus californiensisP 2.15 

Armandia brevis P 4.92 Rhepoxynius lucubrans C 2.08 

Magelona sacculata P 4.40 Armandia brevis P 1.38 
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Figure 3-1. Location map. Stations for intertidal and shallow subtidal sampling are along 

transects indicated by the symbols. The thermal outfall plume is indicated. 
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Figure 3-2. Variations in the number of individuals of all benthic invertebrates, crustaceans, 

and polychaete worms at the four sampling sites from the high (A) to the low intertidal (D) 

beach. Means and standard errors (SE) based on the following sample sizes listed by station 

and from high (A) to low (D) elevation: OF – 6, 6, 6, 2; MB – 5, 4, 3, 2; SL – 6, 6, 6, 5; and 

PR – 6, 6, 6, 5. 
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Figure 3-3. Abundance changes for the five most abundant crustacean species at the four 

sites from the high to low intertidal beach. Means and SE based on same sample sizes as 

Figure 3-2. 
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Figure 3-4. Temporal variations in Emerita collected during each of the first six sampling 

dates at the four sites from the high (A) to the low (D) intertidal beach. Asterisk indicates no 

samples collected. At each station, collection date, and elevation n = 6 samples, except for 

the following: May 2003 n = 3 samples for each station and elevation; Oct 2003 n = 5 

samples for OFB, OFC, and SLC, and Mar 2004 n = 5 samples for OFB. 
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Figure 3-5. Temporal variations in Excirolana on the high intertidal beach (A) and 

Archaeomysis on the low beach (C, D). Asterisk indicates no samples collected. Means and 

SE based on same sample sizes as in Figure 3-4. 
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Figure 3-6. Abundance changes for the six most abundant polychaete species at the four sites 

from the high (A) to the low (D) intertidal beach. Means and SE based on same sample sizes 

as in Figure 3-2. Each major peak is from a single time period as indicated in the graph. 
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Figure 3-7. Variations in the number of species of all benthic invertebrates, crustaceans, and 

polychaete worms at the four sampling sites from the high (A) to the low (D) intertidal 

beach. Means and SE based on same sample sizes as in Figure 3-2. 
 Moss Landing Powerplant Thermal Discharge Effects 85 

Moss Landing Marine Laboratories Figure 3-8. Changes in beach elevation for the first six sampling periods at each site. The Shore Lab 

and Potrero beaches are twice as wide as the other two and less steep. 
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Figure 3-9. Cluster analysis showing no distinct assemblages grouping by water depth, site, or time of sampling. 
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Figure 3-10. Number of individuals of all infauna, crustaceans, and Americhelidium spp. at 

the three water depths for each site (means and SE; n = 18 samples for each mean except for 

PR 1 m and PR 2 m where n = 12). 
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Figure 3-11. Number of individuals of polychaete worms and molluscs at the three water 

depths for each site (means and SE; sample sizes as in Figure 3-10). 
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Figure 3-12. Annual changes in the total number of individuals in the shallow subtidal beach 

(means and SE; n = 6 samples for each mean). There were no samples taken at PR 1 m and 

PR 2 m in October 2005. Means of selected taxa are shown in parentheses for major peaks. 
 Moss Landing Powerplant Thermal Discharge Effects 90 

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Figure 3-13. Annual changes in the number of crustacean individuals in the shallow subtidal 

beach (means and SE; n = 6 samples for each mean). There were no samples taken at PR 1 

m and PR 2 m in October 2005. Means of selected taxa are shown in parentheses for peaks. 
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Figure 3-14. Abundance patterns in the two species of Americhelidium, the numerically 

dominant amphipod crustacean, at the three water depths for each site (means and SE; same 

sample sizes as Figure 3). 
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Figure 3-15. Number of species at the three water depths for each site (means and SE; same 

sample sizes as Figure 3). 
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Figure 3-16. Annual changes in the number of species in the shallow subtidal beach (means 

and SE; n = 6 samples for each mean). There were no samples taken at PR 1 m and PR 2 m 

in October 2005. 
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Fig

ure 3-17. Changes in grain size patterns among water depths, sites, and years. 
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4 Fish 

Prepared by James Oakden 

4.1 Introduction 

The only fish study proposed for inclusion in this project was the creation of a historical 

database of unpublished reports from the Moss Landing vicinity. Several fish studies have 

already been done on the outfall (Tenera 2000), mostly related to larval fish and entrainment. 

It was thought that no further fish studies were warranted at this time due to the extreme 

difficulty in relating fish distributions to the outfall. However, during the period of this study 

Bat Ray (Myliobatis californica) aggregations were observed in the outfall plume. It was felt 

that this observation should be reported, so a list of the recent bat ray observations were 

compiled for inclusion in this report. 

4.2 Historical Data 

As part of this study, a database was prepared by Aaron Carlisle and Gregor Cailliet of Moss 

Landing Marine Laboratories which compiles a number of unpublished studies on fish from 

Elkhorn Slough and the Monterey Bay waters near Moss Landing. The data were not 

previously collated, have generally not been included in previously published databases, and 

are often not in easily located archives. The main sources were Master’s thesis and uncataloged reports in the MLML library, the personal archive of Gregor Cailliet, who has been 

the ichthyology professor at MLML since 1973, and through personal interviews with former 

MLML students and other Monterey Bay researchers who performed the research. The 

database will be included on the CD for this project. The database includes a detailed 

appendix which allows interpretation of the metadata associated with each entry. 

Sources of Data in the Database: 

The original data from the following projects have been entered into the Elkhorn Slough 

Historical Fish Database: 

• Barry, J., 1983. Utilization of shallow marsh habitats by fishes in Elkhorn Slough, 

California. MS Thesis, San Jose State University. 95 pp. 

• Bennett, T., 1993. Resource partitioning of two fish ectoparasites, Lironeca vulgaris and 

Lironeca california (Class Isopoda, Family Cymothoidae). MS Thesis, San Jose State 

University. 46 pp. 

• Brown, J., 2003. An evaluation of the nursery role of estuaries for flatfish populations 

 in central California.. PhD Thesis, University of California Santa Cruz. 97p. 

• Creel Census (funded by Pacific Gas and Electric), 1974-1976. 
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• Hall, M.A., 2000. Species composition and temporal and spatial characteristics of 

fish assemblages surveyed at Old Salinas River and Bennett Slough, California. Senior 

Thesis, Southampton College, Long Island University. 54 pp. 

• Lindquist, D., 1998. The effects of erosion on the trophic ecology of fishes in Elkhorn 

Slough, California. MS Thesis, California State University Hayward. 65 pp. 

• Moss Landing Marine Laboratories records of class field trips, class projects, and visiting 

groups (1964-present) 

• Oxman, D., 1995. Seasonal abundance, movements, and food habits of harbor seals 

(Phoca vitulina richardsi) in Elkhorn Slough, California. MS Thesis, California State 

University Stanislaus. 125 pp. 

Unobtained Data: 

There were a number of additional studies that could potentially have sampling data that 

could be entered into the database. It has been very problematic to get the original data from 

many studies despite many attempts. Unfortunately, we were unable to obtain the original 

data from the following projects. It should be out there somewhere, and while we were 

unable to get it, it may be possible to input the original data at some point in the future. 

• Ackerman, L.T., 1971. Contributions to the biology of the leopard shark, Triakis

semifasciata (Girard) in Elkhorn Slough, Monterey Bay, California. MS Thesis, Sacramento 

State College, CA. 54 pp. 

• Antrim, B, 1981. Habitat and food resource utilization of three species of in Elkhorn 

Slough, Monterey Bay, California. California State University Fresno. 83 pp. 

• Appiah, J.C., 1977. Species composition and abundance of fish populations in Bennett 

 Slough, Monterey Bay, California. MS Thesis, California State University Fresno, 

 63 pp. 

• Cailliet, G., Species composition, abundance and ecological studies of fishes, larval fishes, 

and zooplankton in Elkhorn Slough. In: Ecologic and hydrographic studies of Elkhorn 

Slough, Moss Landing, and nearshore coastal waters, July 1974-June 1976. Moss Landing 

Marine Laboratories, Moss Landing, CA. 1977. 462 pp. 

(The original data from the study above appear to be lost, hopefully it will turn up in the 

future) 

• Kao, J., 2000. Diet, daily ration and gastric evacuation of the leopard shark (Triakis 

semifasciata). MS Thesis, California State University Hayward. 96 pp. 

• Martin, L.K., 1982. Growth and reproduction of the bat ray Myliobatis californica Gill, in 

California. MS Thesis, San Jose State University, San Jose, CA. 87 pp. 
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• Ruagh, A., 1976. Feeding habits of silversides (family Atherinidae) in Elkhorn Slough, 

Monterey Bay, California. MS Thesis California State University Fresno. 60 pp. 

• Talent, L, 1973. The seasonal abundance and food of elasmobranchs occuring in Elkhorn 

Slough, Monterey Bay, California. MS Thesis, California State University Fresno. 58 pp. 

4.3 Bat Ray Observations 

Jim Oakden observed aggregations of Bat Rays (Myliobatis californica) at the surface of the 

power plant outfall plume on 5 January 2004, as did Gala Wagner a few days later while 

doing plankton tows as part of this project. During the winter bird surveys in 2005 Elizabeth 

Phillips observed ray congregations from shore through a spotting scope. 

Diana Steller, the current diving officer at MLML, observed the bat ray aggregation during a 

dive trip in late January 2004: 

“January 2004 - we saw ~15-20 rays swimming in the outflow. Most of them were ~ 3-4' in 

'wing' span. This observation was based on driving a whaler through the outflow and then 

snorkeling over the outflow numerous times for about 15 minutes. The rays were definitely 

actively swimming round and round to stay within the warm outflow because as we swam 

across the outflow, it was so strong that it pushed us out of the main path. These surface 

sightings occurred while motoring by the outflow for approx. 15 minutes at mid-day.” 

Sporadic reports of such aggregations have been received in the past (Greg Cailliet, pers 

comm.), but no one has followed up on them. Table 4-1 is a compilation of the information 

gathered in a rapid informal survey at MLML. 

4.4 Discussion 

The congregation of bat rays in the outfall plume appears to be a relatively new phenomenon. 

John Heine, former dive officer at MLML, and John Oliver, PI on this project and longtime 

researcher at MLML, have made hundreds of trips over the area over the past 30 years, and 

did not ever observe aggregations. Jim Oakden has passed by the outfall monthly for the past 

15 years, and first noticed the rays in 2004. The surface aggregations are visible from some 

distance away (>100 m), so it seems unlikely they would have gone unnoticed had they been 

present. 

Bat rays are bottom feeders, which excavate clams, echinoderms, and crustaceans from sandy 

bottoms. The pits they leave during these excavations have been well documented, and are 

one of the major disturbances and causes of small-scale habitat heterogeneity in some sandy 

nearshore areas of California. 

It seems possible that the aggregations in the warm water (up to 8°C above ambient) of the 

outfall plume may be related to thermoregulation. Bat rays in Tomales Bay exhibit diurnal 

movements that have been linked to thermoregulatory efficiency (Matern et al. 2000). In 

elasmobranchs, metabolic rates tend to increase with increasing ambient temperature. In 

Tomales Bay the rays move to the warmer areas of the bay to feed, taking advantage of their 
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higher metabolic rates in the energetically-demanding food excavating, then move to cooler 

areas of the Bay to rest. The situation at the power plant outfall is a bit different, in that the 

bottom-feeding rays seem to be resting in the warm water in winter months. 

A thermoregulatory explanation similar to the Tomales Bay situation could apply at the 

power plant outfall. When the ambient water temperature is low (12°C) bat rays may go into 

the warm water to elevate their body temperatures so that they can then forage more 

effectively on the bottom away from the plume. This hypothesis could be tested with a 

straightforward series of experiments and field observations. The aggregations could also 

relate to reproduction, about which little is known. 

4.5 Literature Cited 

Matern, S., Cech, J. and T. Hopkins. 2000. Diel movements of bat rays, Myliobatis 

californica, in Tomales Bay, California: evidence for behavioral thermoregulation? 

Environmental Biology of Fishes 58: 173–182. 

Tenera, C. (2000). Moss Landing Power Plant Modernization Project 316(b) Resource 

Assessment, Prepared for Duke Energy Moss Landing. 
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4.6 Tables and Figures 

Table 4-1: Observations of Bat Rays (Myliobatis californica) at the surface in the Moss 

Landing power plant outfall plume. P=present, NP=not present 

Date Time Present? source Date Time Present? source 

1/5/04 900 P Oakden 2/7/05 840 P Phillips 

1/7/04 P Wagner 2/7/05 1215 P Phillips 

1/04 P Steller 2/7/05 1610 P Phillips 

2/5/04 P Wagner 2/7/05 1750 P Phillips 

2/17/04 900 P Oakden 2/15/05 900 P Oakden 

3/4/04 P Wagner 3/14/05 900 NP Oakden 

3/8/04 900 NP Oakden 3/24/05 P Wagner 

4/12/04 900 NP Oakden 3/05 P Steller 

10/04 NP Phillips 4/4/05 1000 NP Hansen 

10/04 NP Oakden 5/9/05 1000 NP Hansen 

10/04 NP Wagner 5/31/05 all day NP Phillips 

11/20/04 NP Oakden 6/1/05 all day NP Phillips 

1/18/05 900 P Oakden 6/4/05 all day NP Phillips 

1/22/05 820 P Phillips 6/6/05 1000 NP Oakden 

1/22/05 1130 NP Phillips 6/9/05 all day NP Phillips 

1/22/05 2535 P Phillips 7/7/05 1100 P Steller 

1/22/05 1720 P Phillips 7/18/05 1000 NP Oakden 

1/25/05 735 P Phillips 8/8/05 1000 NP Oakden 

1/25/05 950 P Phillips 9/12/05 1000 NP Oakden 

1/25/05 1345 P Phillips 10/3/05 1000 NP Oakden 

1/25/05 1715 P Phillips 11/7/05 1000 NP Oakden 

2/4/05 715 P Phillips 12/12/05 1000 NP Oakden 

2/4/05 1015 P Phillips 1/9/06 1000 P Oakden 

2/4/05 1320 P Phillips 2/6/06 1000 P Oakden 

2/4/05 1720 P Phillips 3/13/06 1000 P Oakden 

2/5/05 900 P Oakden
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5 Birds 

Prepared by Elizabeth M. Phillips, James Oakden, and James T. Harvey 

5.1 Introduction 

The waters within Monterey Bay support an incredible abundance and diversity of marine 

life, including 90 seabird species (Ainley and Terrill 1996). Strong upwelling events and 

subsequent primary production, in combination with the central location of Monterey Bay 

between arctic and tropical habitats, and the variety of habitats and prey available, attract 

large amounts of marine vertebrates. Monterey Bay has been identified as an area of 

biological importance for seabirds, primarily because of the strong upwelling and subsequent 

primary production (Ainley 1976, Briggs et al. 1987, Benson 2002). The unique bathymetry 

of Monterey Bay includes a deep submarine canyon that bisects the continental shelf and 

attracts species to the shallow, nearshore habitat, the productive shelf-edge habitat, and the 

deep water habitat, all within a few kilometers of shore (Ainley and Terrill 1996). 

Some species of seabirds use Monterey Bay as a foraging area during winter (e.g. surf 

scoters), some migrate to Monterey Bay in the summer and fall to take advantage of the high 

productivity (e.g. sooty shearwaters), and some reside in the area year round (e.g. Brandt’s 

cormorants). Nearly one half of the seabirds nesting in California and millions more seasonal 

migrants are observed in Monterey Bay at various times of the year (Briggs et al. 1987). 

Mean densities of birds in Monterey Bay are approximately 172.5 birds/km2

 and average 

approximately 20.5 species/month (Mason 1997). Greatest numbers of seabirds are observed 

nearshore in mid-fall and early spring, when there is an overlap between wintering birds and 

the arrival or departure of migratory species (Benson 2002, Henkel 2003). The strong 

upwelling events in early spring, combined with the unique bathymetry of Monterey Bay 

provide excellent habitat for seabirds (Ainley and Terrill 1996). Generally, seabirds in 

Monterey Bay can be divided into three categories, including Resident, Wintering, and 

Migratory species. 

5.1.1 Resident seabirds 

Resident seabirds are defined here as those species that breed within Monterey Bay, as well 

as those that breed in the areas surrounding Monterey Bay, and are present throughout the 

majority of the seasons. Commonly occurring resident seabirds include the Western gull, 

Caspian tern, pigeon guillemot, common murre, and Brandt’s and Double crested cormorants 

(Baltz and Morejohn 1977, Ainley and Hunt 1991, Roberson 2002). The Brandt’s cormorant 

breeds on piers, rocks and other structures and is commonly seen throughout Monterey Bay 

(within 50 km). The Western gull also breeds coastally on cliffs, islets and rooftops and is 

one of the most common and conspicuous species in Monterey Bay (Roberson 2002). 

Common murres breed on islands to the north and south of Monterey Bay, and are observed 

year round offshore (Mason 1997). 

5.1.2 Wintering birds 

A number of seabirds migrate to Monterey Bay in the early fall and remain through the 

winter, using Monterey Bay as a rest stop and foraging area. Common species include surf 
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scoters, Western/Clark’s grebes, California brown pelicans and Common and Pacific loons. 

Most of these species are much more abundant in the nearshore waters of the Bay (within 5 

km), and commonly feed in shallow nearshore waters, either plunge or pursuit diving for 

prey (Henkel 2003). 

5.1.3 Migratory seabirds 

Many species of seabirds migrate to Monterey Bay in the late summer and early fall to take 

advantage of the high productivity in the region. Some species, such as the sooty shearwater, 

occur in incredibly large numbers in late summer and make up the majority of the birds 

encountered in Monterey Bay (Briggs et al. 1987, Ainley and Terrill 1996). Common 

migratory species include the shearwaters, Northern fulmars, and Heermann’s gulls. 

Typically these birds arrive and remain in Monterey Bay for a couple of months, then make 

the long migration back to their breeding areas in late fall and winter. 

The purpose of this study was to assess the utilization and distribution of seabirds in and 

around the power plant’s thermal outfall just offshore of Moss Landing, California, in 

Monterey Bay. The study focused on quantifying bird distribution around the thermal plume 

in comparison to a control site. We set out to study all seabird species potentially present in 

Monterey Bay throughout the year, including resident, migratory, and wintering birds. In 

addition, data on marine mammal and other marine vertebrate (e.g. bat ray) occurrences at 

the two study sites were noted. 

5.2 Methods 

Surveys were conducted at both the thermal outfall plume (“Plume site”), readily visible 

from shore, and at a reference site (“Reference site”) approximately 1,000 meters south of the 

Plume site. To minimize confounding variables, the plume and reference survey sites were of 

equal area (determined by the size of the thermal plume), and were equidistant from shore. 

Surveys were conducted 3 times per year and corresponded to the 3 general bird 

assemblages, as follows: May/June surveys quantified the migratory assemblage, September 

surveys quantified the summer assemblage, and January/February surveys quantified the 

winter assemblage. Surveys were conducted on 4 randomly selected days for each of the 3 

sample periods. Each daily survey consisted of 4 survey intervals corresponding to different 

tidal regimes: high tide, low tide, flood tide, and ebb tide. Each of the 4 daily survey periods 

comprised a snapshot of all of the birds and other animals present in the 2 survey areas at the 

survey time. The surveys occurred only during daylight hours, thus the high and low tides 

were either the low low tide or the high low tide, for example, depending on what low tide 

occurred during daylight hours. 

All surveys were conducted from the second-level balcony at the Monterey Bay Aquarium 

Research Institute (MBARI) in Moss Landing, CA. A spotting scope and tripod was set at a 

known height on the balcony and leveled (tripod had internal level). Once the Plume site was 

found in the scope’s view, the scope angle was set to that point. The center of the thermal 

plume was the center of the Plume site survey area, and an offshore buoy (M0) was used as a 

reference for the location of the Reference site, because it was approximately 90° to the south 

of the Plume site when the scope was swung around. The angle of the scope was not changed 
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when scanning between the Reference and Plume sites, to ensure that the distance from shore 

remained the same (Figure 5-1). 

All birds within the scope’s view were counted and identified to species level. In some cases 

when species could not be determined, the genus was noted (e.g. Gavia spp.). If birds entered 

the scope’s view after surfacing from a dive, they were included in the count. Birds in flight 

were generally not included in the count, unless it was determined that they were interacting 

with the survey site (e.g. circling over the thermal plume, or landing on the surface of the 

water within the survey area). Marine mammals and other marine vertebrates were also 

identified and counted. The surveys took place for approximately 10 minutes at each site 

during 4 daily intervals to ensure adequate enumeration and identification of species. 

Analyses focused on differences between the number and assemblage of birds and marine 

mammals present at the Reference and Plume sites, in addition to any patterns associated 

with changing tidal cycle or season. Species richness, diversity, and evenness were 

calculated for both sites and each season. Additionally, Chi-square analyses were conducted 

to quantify expected and observed proportions of birds at each site and in each season. 

5.3 Results 

Surveys were completed between May 2004 and September 2005 (Table 5-1). On a few 

occasions, all four daily surveys could not be completed, due to foggy weather. In general, all 

surveys were conducted in clear, relatively calm weather, and weather was not considered a 

factor in determining the number of birds sighted at either survey site. The general shape and 

width of the thermal plume varied with swell height and wind, but because the area of the 

plume was incorporated into the survey area for the reference site, this was not an issue. The 

thermal plume was detectable during all surveys, and tidal height did not affect our ability to 

locate the plume. We occasionally noted that the thermal plume was more “frothy” and the 

water in the plume seemed more turbulent, but whether this was due to changes in the current 

patterns and swell height or actual volume of water coming out of the plume is unknown. 

During these observations, we did not note any changes in behavior of any of the animals 

related to the turbulence of the plume. 

5.3.1 Migratory season (May/June) 

A total of 30 surveys were completed over the course of two migratory seasons (Table 5-1). 

Brandt’s and Double crested cormorants were regularly seen at the Plume site (mean = 0.73 

per survey; Fig. 5-2), and were often observed diving repeatedly within the plume (Table 5-

3). Brandt’s and Double crested cormorants were also the most common species observed at 

the Reference site during the Migratory period, although in fewer numbers (mean = 0.37 

birds per survey) and were generally not observed actively diving. California brown pelicans, 

Caspian terns, cormorants, and grebes were seen at both study sites, but were sighted more 

frequently at the Plume site. Common murres, Pigeon guillemots, and surf scoters were seen 

in low numbers at both sites, whereas greater numbers of gulls were sighted at the Reference 

site during the Migratory period. 

A total of 42 seabirds were sighted during the surveys at the Plume site, in comparison to a 

total of 29 seabirds at the Reference site (Table 5-2). Total species richness was greater at the 
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Plume site (9 species), in comparison with 6 species at the reference site. Additionally, the 

Shannon-Weaver Diversity Index (S) was greater at the plume site (1.96), in comparison to 

the reference site (1.44). However, a Chi square analysis of the six most common species 

indicated that there was not a significant difference between expected and observed 

proportions of birds at the two study sites (2

(5, n=59) = 11.00, p > 0.05), and species evenness 

(H’) was not different between sites (0.89 vs. 0.80). 

A total of five sea otters were observed at the Plume site over the course of the surveys 

during the Migratory period (Table 5-2), but never in high numbers (mean = 0.17 otters per 

survey). No other marine mammal species were observed. 

5.3.2 Summer season (September) 

A total of 30 surveys were completed over the course of two summer survey seasons (Table 

5-1). Brandt’s and Double crested cormorants were still common at the Plume site during the 

summer monitoring period (mean = 1.1 birds per survey, Fig. 5-2), in addition to California 

brown pelicans (mean = 0.13 birds per survey) and gulls (mean = 0.53 birds per survey). 

Other species sighted at the Plume site included Caspian terns and Heermann’s gulls. Equal 

numbers of common murres were observed at each site (2 total per site). Gulls were the most 

common species sighted at the Reference site, and their numbers were more than double 

those observed at the Plume site. 

In total, 63 seabirds were counted at the Plume site during summer surveys, in comparison 

with 54 seabirds at the Reference site (74% of which were gulls; Table 5-2). The species 

richness at the Plume site was double that of the Reference site (8 species vs. 4 species). 

Additionally, the Shannon-Weaver Index of Diversity (S) at the Plume site was 1.65, in 

contrast to 0.37 at the Reference site. Similarly, species evenness (H’) was also greater at the 

Plume site (0.79) in comparison with the Reference site (0.27). A Chi square analysis of the 

six most common species indicated a significant difference between observed and expected 

proportions of seabirds at the two sites (2

(5, n=113) = 28.21, p < 0.05). 

Sea otters were common in the plume, and a total of 30 otters were counted during surveys 

(mean = 1.0 per survey), actively foraging, grooming, fighting and resting (Table 5-3). 

Additionally, four California sea lions were observed (mean = 0.13 per survey). As expected, 

no winter species were observed. 

5.3.3 Winter season (January/February) 

A total of 16 surveys were completed over the course of one winter survey season (Table 5-

1). Brandt’s and Double crested cormorants were regularly seen at Plume site (mean = 0.44 

birds per survey), in addition to high numbers of gulls (mean = 0.56 birds per survey). Surf 

scoters were present at both sites in low numbers, and a mean of 0.25 birds per survey were 

sighted at the Reference site, in comparison with 0.06 birds per survey at the Plume site. 

Other seabird species seen at the Plume site included a single Caspian tern, a single Common 

murre, and one Western grebe (Table 5-2). Three Common murres and one loon were sighted 

at the Reference site. 
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In total, 20 seabirds were counted at the Plume site, in comparison with 16 seabirds at the 

Reference site during winter surveys. The species richness at the Plume site was 9 species, in 

comparison with 5 at the Reference site. However, the Shannon-Weaver Index of Diversity 

was 0.44 at the Plume site, compared with 1.20 at the Reference site. The species evenness 

was also lower at the Plume site in contrast with the Reference site (0.20 vs. 0.74). A Chi 

Square analysis also indicated that there were no significant differences between species 

assemblages at either site (2

(5, n=34) = 3.75, p > 0.05). 

Sea otters continued to occur commonly in the Plume site, and a mean of 0.81 otters were 

sighed per survey. One harbor seal was sighted in the Plume site, and no California sea lions 

were sighted in either survey site. 

Interestingly, bat rays were observed in very high numbers at the Plume site during almost all 

of the winter surveys (mean = 1.9 bat rays per survey). A total of 31 bat rays were counted 

over the course of the 16 surveys (Table 5-2, Fig. 5-2). The bat rays were seen swimming at 

the surface of the thermal plume, and seemed to be actively remaining within the plume’s 

area (Table 5-3). 

5.4 Discussion 

It is apparent from the data that the outfall is having an effect on local bird and mammal 

distribution. Some seabird species, especially cormorants, showed an increased occurrence at 

the Plume site, indicating potential utilization of the plume for foraging on small schooling or 

benthic fish. Sea otters showed an increased abundance in the plume versus the control site. 

In addition, no negative impacts on seabird abundance and distribution as a direct result of 

the thermal plume were observed (e.g. no species were observed actively avoiding the 

thermal plume). These observations lead us to believe that although the plume is having an 

effect on distribution, there is no reason to suspect that the impact is negative. However, the 

study was not designed to show the causal factors influencing the observed distributions. 

Potential causal factors could include prey distribution, thermal benefits, and/or mechanical 

stimulation (turbulence). 

Based on our observations, seasonal abundance of local seabird species was well reflected in 

both the Plume and Reference study sites. Brandt’s cormorants, Double crested cormorants, 

Western gulls, and Caspian terns are all resident seabirds that nest near Moss Landing harbor 

or in Elkhorn Slough. They are year-round residents commonly seen throughout the year in 

the nearshore environment (Baltz and Morejohn 1977, Ainley and Hunt 1991, Roberson 

2002). Cormorants, gulls, and terns were observed in nearly all surveys, reflecting their local 

abundance in Monterey Bay. Additionally, Common murres, which nest to the north and 

south of Monterey Bay (Mason 1997), were also seen during all of the study periods, 

reflecting their common occurrence in the bay. 

Heermann’s gulls were one of the most conspicuous migratory species seen in the summer 

surveys, reflecting their seasonality here. They generally arrive in the mid-summer months 

and remain until late fall, at which point they migrate back to Baja California to breed. The 

winter assemblage of birds in the surveys reflected the seabird species commonly arriving in 
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Monterey Bay in the late fall and early winter, including surf scoters, Western/Clark’s 

grebes, and Common and Pacific loons. Most of these species were not common in the 

survey sites themselves, but were locally abundant in the nearshore waters around the survey 

areas, reflecting their nearshore distribution and also the small area that the plume actually 

occupies in the nearshore environment off Moss Landing, CA. Small numbers of surf scoters 

and grebes were seen at the Plume and reference sites, but our analyses did not indicate a 

significant change in the proportions of these species at either study site, also indicating the 

nearshore habitat of these birds. 

Monterey Bay is host to a great diversity of seabirds throughout the year, making it a 

biologically important area. In spite of this fact, our surveys do not indicate any sort of 

negative impacts on any seabird species related to the presence of the thermal plume. Most 

wintering and migratory seabirds were observed in low numbers at both sites, and did not 

appear to actively avoid the thermal plume’s area. In contrast, our surveys indicate that some 

of the locally occurring resident seabird species may actually be utilizing the plume for 

foraging. Cormorants were regularly observed foraging within the Plume site. Especially 

during the summer survey season, we observed a significant increase in the proportion of 

birds at the Plume site. This is likely due to an increase in total numbers of birds within the 

nearshore environment, in combination with high productivity throughout Monterey Bay. Sea 

otters were commonly sighted in the plume, although it is unclear how they may be utilizing 

the plume. 

Cormorants are diving seabirds, using their feet to propel them underwater and capture fish at 

depth before returning to the surface to consume it. We often observed them repeatedly 

diving within the plume site, and returning to the surface with a fish in their mouth. It is 

unknown which fish species the cormorants consume within the plume, but they are 

generally opportunistic, and will take a variety of locally abundant fish species. Although 

cormorants were observed repeatedly diving at both the Reference and Plume sites, the fact 

that on average more cormorants were seen in the Plume in all survey seasons indicates that 

they were utilizing the plume specifically to forage. Other seabird species were also observed 

foraging within the plume site, including Caspian terns and California brown pelicans, which 

occasionally circled above the plume and plunged into the water to capture a fish. These 

seabird species were probably taking advantage of fish species that became concentrated in 

the plume. With the exception of the cormorants, we did not observe any obvious feeding 

behavior by any seabirds at the Reference site. 

Additionally, the regular occurrence of sea otters occupying the plume site indicated that 

they, too, were utilizing the thermal plume in some way. We observed nearly all of the 

different types of sea otter behavior commonly noted in Elkhorn Slough, including grooming, 

feeding, resting and fighting with other otters. Thus, it is not clear what the exact role of the 

plume is in the sea otter’s occurrence there, but the numbers of otters concentrated in this 

small area suggests that it is an important area for them. 

As earlier noted, bat rays were regularly noted at the surface within the plume during the 

winter surveys. They were discussed previously in Section 4. 
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5.5 Historical Database 

The only significant historical bird data from the plume vicinity was collected by Laird 

Henkel as part of his thesis project (Henkel, L.A. 2003). The data are available from the 

author. 

5.6 Literature Cited 

Ainley, D.G. 1976. The occurrence of seabirds in the coastal region of California. W.Birds 

7(2): 33-68. 

Ainley, D.G. and G.L. Hunt, Jr. 1991. Status and conservation of seabirds in California. In

Seabird Status and Conservation: A supplement, edited by J.P Croxall. International 

Council for Bird Preservation, Cambridge: Tech. Pub. No. 11. 

Ainley, D.G and S.B. Terrill. 1996. Site characterization of MBNMS: Seabirds & shorebirds. 

http://www.mbnms.nos.noaa.gov/sitechar/bird.html (17 July 2004). 

Baltz, D.M. and G.V. Morejohn. 1977. Food habits and niche-overlap of seabirds wintering 

on Monterey Bay, California. Auk 94: 526-543. 

Benson, S.R. 2002. Ecosystem studies of marine mammals and seabirds in Monterey Bay, 

CA, 1996-99. Moss Landing Marine Laboratories, SJSU. 

Briggs, K.T., W.B. Tyler, and D.B. Lewis. 1987. Bird communities at sea off California: 

1975-1983. Stud. Avian Biol. 11: 1-74. 

Henkel, L.A. 2003. The distribution and abundance of marine birds in nearshore waters of 

Monterey Bay, California. Moss Landing Marine Laboratories, CSU Monterey Bay. 

Mason, J.W. 1997. Distribution and abundance of seabirds in Monterey Bay, California. 

Moss Landing Marine Laboratories, CSU Fresno. 

Roberson, D. 2002. Monterey Birds, 2nd Edition. Monterey Peninsula Audubon Society, 

Carmel, CA. 
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Moss Landing Marine Laboratories 

5.7 Tables and Figures 

Date Season

Number of 

daily surveys 

completed

Mean 

duration of 

survey (min)

Total number of 

animals counted

5/27/2004 Migratory 4 0:13 16

5/28/2004 Migratory 4 0:11 14

6/3/2004 Migratory 4 0:16 5

6/4/2004 Migratory 4 0:11 6

9/18/2004 Summer 4 0:12 26

9/20/2004 Summer 4 0:10 17

10/8/2004 Summer 4 0:10 36

10/11/2004 Summer 4 0:09 16

1/22/2005 Winter 4 0:10 28

1/25/2005 Winter 4 0:09 30

2/4/2005 Winter 4 0:10 16

2/7/2005 Winter 4 0:10 6

5/31/2005 Migratory 4 0:09 9

6/1/2005 Migratory 3a 0:10 15

6/4/2005 Migratory 3a 0:10 6

6/9/2005 Migratory 4 0:09 5

9/6/2005 Summer 4 0:10 16

9/13/2005 Summer 3a 0:10 25

9/16/2005 Summer 3a 0:10 9

9/26/2005 Summer 4 0:09 13

a

 Surveys were completed for three of the four daily intervals, due to foggy conditions

Table 5-1. Summary of survey effort including dates of all surveys, survey season, total number of 

surveys completed, survey duration, and total number of seabirds and marine mammals counted. 
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Moss Landing Marine Laboratories 

Table 5-2. Summary of total number of animals counted during each survey period: 

Migratory (M), Summer (S), and Winter (W) at the Plume and Reference sites. 

Plume site Reference site

Species M S W Total M S W Total

Brown pelican 3 4 7

Caspian tern 5 5 1 11 1 1

Common murre 1 2 1 4 2 3 5

Cormorant spp. 22 32 7 61 11 12 3 26

Gull spp. 3 16 9 28 9 40 5 54

Heermann's Gull 4 4

Loon spp. 2 1 3

Pigeon guillemont 5 5 4 4

Surf scoter 2 1 3 2 4 6

Western/Clark's 

grebe 1 1 2

Sea otter 5 30 13 48 1 1

CA sea lion 4 4

Harbor seal 1 1

Bat rays 31 31

47 97 65 209 29 55 16 100
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Moss Landing Marine Laboratories 

Plume site Reference site

Species Behavior Behavior

Brown pelican circle overhead, dive; sit -

Caspian tern hover and dive hover and dive

Common murre sit, dive sit, preen

Cormorant spp. dive, sit dive, sit

Gull spp. sit, circle overhead sit

Heermann's Gull sit -

Loon spp. - dive, preen

Pigeon guillemont sit, dive, eat fish sit

Surf scoter sit sit

Western/Clark's grebe dive -

Sea otter eat, groom, rest, fight eat

CA sea lion swim, bask -

Harbor seal swim through -

Bat rays swimming at surface -

Table 5-3. Description of most commonly observed behavior of each seabird and marine mammal 

species at the Plume and Reference sites. 
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Moss Landing Marine Laboratories 

Figure 5-1. Map of Moss Landing vicinity showing location of the two bird study sites and 

the location where the spotting scope was set up at MBARI. 
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Moss Landing Marine Laboratories 

a) Reference site

b) Plume site

Figure 5-2. Mean number of seabirds and marine mammals occurring at the a) Reference 

site, and b) Plume site for each of the three sampling periods (Migratory, Summer, and 

Winter).
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Moss Landing Marine Laboratories 

6 Acknowledgements 

This work was supported by a contract from the Monterey Bay Sanctuary Foundation 

through the Sanctuary Integrated Monitoring Network (SIMoN) program to Moss Landing 

Marine Laboratories. We would like to thank the staff, faculty, and students of Moss Landing 

Marine Labs for their assistance with this project, and the SIMoN staff for their support and 

encouragement. 

We would like to thank the staff of the Moss Landing Power Plant for allowing us access to 

the outfall pipeline and for providing records and logistical support. 

Benthos field sampling and sorting would not have been possible without the enthusiasm and 

good humor of a large group of staff and students. We would like to thank Alta Anzalone, 

Lewis Barnett, Luie Camilli, Aaron Carlisle, Stepheni Ceperley, Jesse Christiansen, Cara 

Clark, Eric Cronk, Jenny Erbes, Daphne Gehringer, Andy Hansen, Scott Hansen, Brent 

Hughes, Kambiz Kamrani, Stacy Kim, Rob Leaf, Lyndsey Lefebvre, Dan Malone, Aroon 

Melwani, Niko Oliver, Chelsea Phillips, Alex Ponik, Catalina Reyes, Gene Ruff, Rhea 

Sanders, Jayna Schaaf, Sue Shaw, Peter Slattery, Rachael Spencer, Dawn Tanner, Andrew 

Thurber, Brad Travers, Tonatiuh Trejo, Kristy Uschyk, Gabby Vega, Jared Von Schell, Jon 

Walsh, Megan Wehrenberg, and last, but not least, Bob Zook. Alta Anzalone, Stepheni 

Ceperley, Gene Ruff and Peter Slattery identified infauna. 

We also thank MBARI for providing a shore-based research platform to the conduct bird 

surveys. Moss Landing Marine Laboratories’ Vertebrate Ecology Lab provided the survey 

equipment, including the spotting scope and tripod.