OCS Study 

•

MMS 2006-055 

Population Trends and Trophic 

Dynamics in Pacific OCS Ecosystems: 

What Can Monitoring Data Tell Us? 

Final Technical Summary 

Final Study Report 

U.S. Department of the Interior 

Minerals Management Service

Pacific OCS Region 

OCS Study 

MMS 2006-055 

Population Trends and Trophic 

Dynamics in Pacific OCS Ecosystems: 

What Can Monitoring Data Tell Us? 

Final Technical Summary 

Final Study Report 

Authors 

Russell J. Schmitt 

Andrew Brooks 

Sally J. Holbrook 

Principal Investigators 

Prepared under MMS Cooperative 

Agreement No. 14-35-0001-30758 

by 

Coastal Marine Institute 

Marine Science Institute 

University of California 

Santa Barbara, CA 93106-6150 

U.S. Department of the Interior 

Minerals Management Service Camarillo

Pacific OCS Region October 2006
Disclaimer 

This report has been reviewed by the Pacific Outer Continental Shelf Region, Minerals Management 

Service, U.S. Department of the Interior and approved for publication. The opinions, findings, 

conclusions, or recommendations in this report are those of the authors, and do not necessarily reflect 

the views and policies of the Minerals Management Service. Mention of trade names or commercial 

products does not constitute an endorsement or recommendation for use. This report has not been 

edited for conformity with Minerals Management Service editorial standards. 

Availability of Report

Extra copies of the report may be obtained from: 

U.S. Dept. of the Interior 

Minerals Management Service 

Pacific OCS Region 

770 Paseo Camarillo 

Camarillo, CA 93010 

Phone: 805-389-7621 

A PDF file of this report is available at: 

http://www.coastalresearchcenter.ucsb.edu/CMI/ 

Suggested Citation 

The suggested citation for this report is: 

Schmitt, R.J., S.J. Holbrook, A. Brooks. Population Trends and Trophic Dynamics in Pacific OCS 

Ecosystems: What Can Monitoring Data Tell Us? MMS OCS Study 2006-055. Coastal Research 

Center, Marine Science Institute, University of California, Santa Barbara, California. MMS 

Cooperative Agreement Number 14-35-0001-30758. 65 pages. 
Table of Contents 

FINAL TECHNICAL SUMMARY........................................................................ 1 

FINAL STUDY REPORT....................................................................................... 7 

 Chapter 1........................................................................................................ 7 

 Abstract.................................................................................................... 7 

 Introduction.............................................................................................. 7 

 Methods.................................................................................................... 8 

 Results...................................................................................................... 13 

 Discussion................................................................................................ 19 

 Acknowledgements.................................................................................. 23 

 Chapter 2........................................................................................................ 24 

 Abstract.................................................................................................... 24 

 Introduction.............................................................................................. 24 

 Materials and Methods............................................................................. 26 

 Results...................................................................................................... 27 

 Discussion................................................................................................ 30 

 Acknowledgements.................................................................................. 32 

 Chapter 3........................................................................................................ 33 

 Abstract.................................................................................................... 33 

 Introduction.............................................................................................. 33 

 Materials and Methods............................................................................. 35 

 Results...................................................................................................... 37 

 Temporal Patterns at Santa Cruz Island............................................. 37 

 Temporal Patterns in the Southern California Bight.......................... 41 

 Evidence for response of trophic groups ........................................... 41 

 Discussion................................................................................................ 42 

 Acknowledgements.................................................................................. 44 

REFERENCES......................................................................................................... 45

APPENDIX I ............................................................................................................ 57 

 
List of Tables 

CHAPTER 1 

Table 1. Criteria used to classify species and abundance ........................................ 15 

Table 2: Values of the computed cross-correlation coefficients.............................. 17 

CHAPTER 3 

Table 1: Mean proportional change in abundance ................................................... 41 

Table 2: Mean proportional change among trophic groups ..................................... 41 

 

 

List of Figures 

CHAPTER 1 

Figure 1. Map of the Southern California Bight ...................................................... 9 

Figure 2. Time series of standardized temperatures and zooplankton .................... 10 

Figure 3. Relationship between abundances ........................................................... 14 

Figure 4. Time series of the average deviation in standardized abundance ............ 16 

Figure 5. Values of the cross-correlational coefficient............................................ 18 

Figure 6. Values of the cross-correlational coefficient............................................ 19 

CHAPTER 2 

Figure 1. The pattern of co-variation in magnitudes of temporal variability........... 28 

Figure 2. The relationships between the magnitudes of inter-annual variability..... 29 

Figure 3. The pattern of co-variation in magnitudes of inter-annual variability...... 30 

CHAPTER 3 

Figure 1. Density of kelp bass over time ................................................................. 37 

Figure 2. Densities of surfperch at Santa Cruz Island.............................................. 38 

Figure 3. Abundance of the food base for surfperch at Santa Cruz Island .............. 39 

Figure 4. Trends in algal biomass and cover over time ........................................... 40 

 

 

 
Population Trends and Trophic Dynamics 

1

FINAL TECHNICAL SUMMARY 

STUDY TITLE: Population Trends and Trophic Dynamics in Pacific OCS Ecosystems: 

What Can Monitoring Data Tell Us? 

REPORT TITLE: Population Trends and Trophic Dynamics in Pacific OCS Ecosystems: 

What Can Monitoring Data Tell Us? 

CONTRACT NUMBER: 14-35-0001-30758 

SPONSORING OCS REGION: Pacific 

APPLICABLE PLANNING AREA(S): Southern California 

FISCAL YEAR(S) OF PROJECT FUNDING: FY 97, FY 98, FY 99, FY 00, FY 01 

COMPLETION DATE OF REPORT: October 2006 

COSTS: FY 97-01 - $195,000 

CUMULATIVE PROJECT COST: $195,000 

PROJECT MANAGER: Russell J. Schmitt

AFFILIATION: Coastal Research Center, Marine Science Institute, University of 

California, Santa Barbara, CA 93106 

ADDRESS: University of California, Santa Barbara, CA 93106 

PRINCIPAL INVESTIGATORS: Russell J. Schmitt1,2 and Andrew J. Brooks1,3

ADDRESSES: 1

Coastal Research Center, 2 Department of Ecology, Evolution and Marine 

Biology, 3

Marine Science Institute, University of California, Santa Barbara, CA 93106-6150 

KEY WORDS: Trophic dynamics; climate change; food web ecology; PDO; Southern 

California bight

BACKGROUND: A number of entities (including MMS) have devoted considerable effort and 

resources to the long-term monitoring of various components of the coastal marine ecosystems in 

the Southern California outer-continental shelf (OCS) region. The primary goals of such 

monitoring programs are to estimate the current state of the biota and to identify long-term trends 

in population demographics. Data from such studies are vital to resource and regulatory 

agencies as they provide critical baseline information needed for accurate assessment of potential 

effects arising from such particular activities as offshore oil and gas production. The 
Final Technical Summary – Schmitt and Brooks 

2

fundamental need for such information is evidenced by the growing number of coastal marine 

monitoring programs that have been implemented in Southern California. 

The vast amount of long-term data on nearshore biota collected by a large number of separate 

monitoring programs in the Southern California OCS region represents a relatively untapped 

“gold mine” of information for environmental managers. The occurrence of a regime shift in the 

ocean climate in the North Pacific (PDO) in the past two decades provides a unique opportunity 

to determine whether and how various components of the biota have responded to this natural 

perturbation. Data from long-term monitoring programs not only indicate the current state and 

recent history of the biota, they can reveal much about the ecological structure of various coastal 

ecosystems, including the dynamical behavior and regulation of different food webs. Such 

knowledge provides managers with better understanding and enhanced predictive ability 

regarding the potential impacts to these ecosystems from other potential sources of disturbance. 

Further, analyses of existing data sets can expose whether and how our ability to estimate or 

interpret responses of the biota may be constrained by present monitoring practices. 

OBJECTIVES: Our MMS-UC CMI funded research encompassed two separate objectives: (1) 

the analysis and synthesis of existing monitoring data for long-term trends in the biota of the 

Southern California Bight and (2) the continued annual surveys of subtidal reef communities at 

Santa Cruz Island.

DESCRIPTION: We initially obtained data from 5 separate monitoring programs enumerating 

the flora and fauna of southern California nearshore marine communities in three different 

ecological systems, subtidal rocky reef, kelp bed, and open ocean/pelagic, between 1977 and 

2006. These datasets included the CalCOFI monitoring program, King Harbor monitoring data 

collected by John Stephens Jr., Occidental College, Southern California Edison NPDES 

monitoring data for the San Onofre Nuclear Generating Station and the Huntington Beach, 

Redondo Beach and Ormond Beach Steam Electrical Generating Stations, National Park Service 

Kelp Forest Monitoring Program data for the northern Channel Islands, and data collected by 

Russell Schmitt and Sally Holbrook, University of California, Santa Barbara as part of their 

ongoing monitoring of subtidal communities around Santa Cruz Island. Subsequent to our initial 

analyses, we also obtained data collected by the National Marine Fisheries Services during their 

triennial surveys of west coast groundfishes. This last dataset covered roughly the same time 

period as our original datasets, 1977-2001, but concentrated on fish species inhabiting the deeper 

waters of the continental shelf (55-500m) along the west coast of the United States from 

Monterey Bay, California to Alaska. 

Data were standardized between studies by re-expressing data on population densities as the 

percent change in initial population density over the time period 1977 through 1999-2000 and 

then again over the time period 1999-2000 through 2005-2006. Organisms within a given 

community were assigned to one of four trophic categories, primary producer, primary, 

secondary, or tertiary consumer, mode of reproduction, extent of geographic range, association 

with benthic or pelagic food webs, and habitat based on published life history information. 

Time-series analyses were performed on these data sets to describe temporal trends and explore 

the timing and magnitude of the observed changes. 
Population Trends and Trophic Dynamics 

3

STUDY RESULTS: (1) The analysis and synthesis of existing monitoring data for long-term 

trends in the biota of the Southern California Bight: 

Trends in population abundances following the regime shift of the PDO to a warm water phase in 

1977 show consistent declines in all three ecological systems, subtidal rocky reef, kelp bed, and 

open ocean/pelagic, between 1977 and 2001. Within each system examined, trends for each 

component trophic level showed approximately the same magnitude of decline. This pattern 

held across spatial scales ranging from a single island (Santa Cruz Island) within the northern 

Channel Islands group to the entire Southern California Bight suggesting genuine regional 

declines in abundances rather than a redistribution of individuals in response to changing 

environmental conditions. Also interesting is the fact that data collected using extremely 

different methodologies, e.g., coastal power plant impingement studies versus diver visual 

surveys, provide similar estimates of the magnitudes of these declines. Beginning in 2001 and 

following a reversal in the PDO to a cold water phase, some of these species, e.g., foliose algae, 

mesocrustaceans and surfperches, have begun to increase in abundance. 

While observed declines in fishes inhabiting open ocean/pelagic communities occurred almost 

simultaneously with declines in pelagic zooplankton populations, declines in fishes associated 

with nearshore subtidal rocky reefs and kelp beds lagged one to two years and declines in fishes 

associated with soft bottom habitats lagged two to three years behind declining zooplankton 

populations. These patterns are consistent with an explanation that a regional decline in 

productivity was responsible for the regional declines observed in fish stocks within the southern 

California Bight. Differences in response times probably represent the effects of species being 

longer lived in rocky reef and kelp bed communities when compared with species in 

pelagic/open water communities, i.e., storage effects. Comparisons with changes in the 

population abundances of deeper water species indicated that even though many species, most 

notably several species of rockfishes, exhibited declines consistent with those observed in 

nearshore fish communities, certain species, particularly flatfishes, actually increased in 

abundance during the period 1977-2001. 

(2) The continued annual surveys of subtidal reef communities at Santa Cruz Island: 

Our detailed examinations of a simple food web indicated that for two species of viviparous 

surchperches examined (black surfperch Embiotoca jacksoni; striped surfperch E. lateralis), 

recruitment of new individuals varied comparatively little through time on some reefs while it 

fluctuated substantially on others. These fishes harvest invertebrate prey from specific benthic 

foraging microhabitats (algal turf for black surfperch; the red alga Gelidium robustum for striped 

surfperch), and these microhabitats showed a range in dynamics among the reefs examined over 

a 12 yr period. Interannual fluctuations in foraging microhabitat were a strong predictor of the 

extent to which the abundance of young-of-year surfperches fluctuated. However, the foraging 

microhabitat for black surfperch (algal turf) on a reef fluctuated independently of that for striped 

surfperch (Gelidium). As a consequence, the extent to which the abundance of young of one 

surfperch varied on a given reef was unrelated to that of its congener. These data show that the 

magnitude of temporal variation in year-class strength of reef-associated fishes was related to the 

magnitude of variation in the forage base, reefs in close proximity can show a range in resource 
Final Technical Summary – Schmitt and Brooks 

4

dynamics that can affect reproductive output, and the reproductive output of even closely-related 

species can fluctuate independently on the same reef. 

SIGNIFICANT CONCLUSIONS: A primary goal of environmental assessments is to quantify 

trends in species responses following a perturbation. Evaluation or predictions of the effects of 

anthropogenic perturbations typically are made based upon the observed or hypothesized 

magnitude and direction of these trends. To be valid, however, trends observed to occur at small 

spatial scales, e.g., around an offshore oil production platform, must be placed within a larger 

regional context. In the case of predicted trends, these changes should reflect not only the 

hypothesized effects due to the perturbation, but also those effects likely to occur as a 

consequence of unrelated, natural changes in regional environmental conditions. Studies 

examining long-term or large scale spatial or temporal gradients in productivity provide both a 

regional context within which observed trends may be placed and an opportunity to explore 

responses of food webs to environmental perturbations. 

STUDY PRODUCTS: 

Published works: 

Brooks, A.J., R. J. Schmitt and S. J. Holbrook. 2002. Declines in regional fish populations: 

have different species responded similarly to environmental change? Marine and Freshwater 

Research 53(2):189-198. 

Schmitt, R.J. and S.J. Holbrook. 2006. Predicting the magnitude of temporal variation in youngof-year class strength of surfperch (Teleostei: Embiotocidae). Raffles Bulletin of Zoology. 

In Press. 

Holbrook, S.J., A.J. Brooks and R.J. Schmitt. Temporal variation in temperate reef assemblages: 

have trophic levels responded similarly to environmental change? To be submitted 

December, 2006. 

Presentations: 

Brooks, A.J., R.J. Schmitt and S.J. Holbrook. “Population Trends and Trophic Dynamics, the 

Use of Long-term Datasets.” 5th Temperate Reef Symposium, Capetown, S.A., January, 

2000. 

Brooks, A.J., R.J. Schmitt and S.J. Holbrook. “Population Trends and Trophic Dynamics, the 

Use of Long-term Datasets.” American Society for Ichthyology and Herpetology, La Paz, 

Mexico, June, 2000. 

Brooks, A.J. “Declines in Regional Fish Populations: Species Responses to Environmental 

Change and the Nature of Community Organization.” Western Society of Naturalists, 

Ventura, CA, November 2001. 

Brooks, A.J. “Declines in Rocky Reef Fish Populations: Have Different Species Responded 

Similarly to Environmental Change.” Southern California Academy of Sciences, Claremont, 

CA, June, 2002. 
Population Trends and Trophic Dynamics 

5

Brooks, A.J., H.S. Lenihan and S. Lester. “Temporal Trends in Shallow Nearshore and Deeper 

Continental Shelf Fishes Since 1977: Do Similar Responses Suggest a Common Mechanism 

Behind Observed Declines?” Southern California Academy of Sciences, Northridge, CA, 

May 2003. 

Brooks, A.J., R.J. Schmitt and S.J. Holbrook. “Population Trends and Trophic Dynamics – 

What Can Be Learned from Long-term Monitoring.” The Nature Conservancy, Santa 

Barbara, CA, October, 2003. 

Schmitt, R.J. and S.J. Holbrook. “Predicting the magnitude of temporal variation in youngof-year class strength of surfperch (Teleostei: Embiotocidae).” 7th Indo-Pacific Fish 

Conference, Taipei, Taiwan, May, 2005.
Final Study Report – Schmitt and Brooks 

6
Population Trends and Trophic Dynamics 

7

FINAL STUDY REPORT 

CHAPTER 1 

This Chapter was published in Marine and Freshwater Research with the following citation: 

Brooks1, A.J., R. J. Schmitt1,2 and S. J. Holbrook2. 2002. Declines in regional fish 

populations: have different species responded similarly to environmental change? Marine 

and Freshwater Research 53(2):189-198. 

1

Coastal Research Center, Marine Science Institute, and 

2

Department of Ecology, Evolution, and Marine Biology 

University of California, Santa Barbara, CA 93106, USA 

Abstract 

Abundances of many coastal species off southern California have undergone dramatic declines 

over the past two decades concurrent with a regional climate shift. This shift in climatic 

conditions represents a natural, large-scale perturbation and provides an opportunity to 

understand whether and how various components of coastal ecosystems respond. We conducted 

time-series analyses on long-term data sets of non-exploited fish populations from the Southern 

California Bight to describe their temporal trends and explore the timing and magnitude of 

change. The species examined were classified as to trophic level, mode of reproduction, extent 

of geographic range, association with benthic or pelagic food webs, and habitat. In general, the 

magnitude of decline was similar for all species, regardless of classification. Trends were similar 

at all locations examined within the Bight, suggesting regional declines in abundances rather 

than redistribution of individuals. These patterns are consistent with the explanation that a 

regional decline in productivity associated with the shift to an alternate climatic regime is 

responsible for regional decline in fish stocks. 

Introduction 

Understanding the processes that link and/or limit component populations within aquatic 

communities represents a significant ecological challenge. This understanding is essential, 

however, for predicting how perturbations to populations at one trophic level might be 

propagated throughout the rest of the community (Wootton 1994; Albritton et al. 2001). Current 

models predicting the responses of populations to “top down” or “bottom up” effects often differ 

widely in their estimates of the magnitude of change expected by species at other trophic levels 

(Hairston et al. 1960; Menge and Sutherland 1976; Fretwell 1977, 1987; Oksanen et al. 1981; 

Carpenter and Kitchell 1993; Estes and Duggins 1995; Hairston and Hairston 1997; see Sinclair 

et al. 2000 for a review). Attempts to experimentally test predictions of these models in 

temperate marine systems have been hindered by the logistical difficulties inherent in conducting 

long-term manipulative studies encompassing multiple levels of community organization at 

meaningful spatial scales. 
Final Study Report – Schmitt and Brooks 

8

Increasingly, marine ecologists are turning to observational studies of the responses of 

communities to environmental changes to gain insight into the mechanisms structuring marine 

communities (Carpenter 1990; Corten 1990; Aebischer et al. 1990; Barry et al. 1995; Holbrook 

and Schmitt 1996; Veit et al. 1996; Beamish et al. 2000). We use such an approach here. The 

behavior of the California Current system is one of the most important determinants of 

environmental conditions in the nearshore marine environment off Southern California (Brodeur 

et al. 1996). The typically high productivity of this system is attributed to coastal upwelling, 

which brings deeper, nutrient-rich waters to the surface near shore. This high supply rate of 

nutrients enhances primary productivity, which, in turn, drives the secondary productivity of 

nearshore benthic and pelagic food webs. Oceanographic conditions within the California 

Current system underwent a substantial shift in the late 1970s when there was a rapid, large, and 

persistent increase in seawater temperature (Miller et al. 1994; Minobe 1997; but see Mantua et 

al. 1997; Beamish et al. 1998). Between 1976 and 1977, recorded seawater temperatures within 

the Southern California Bight rose an average of 1-20

C above the mean for the previous two 

decades (Roemmich 1992). Associated with this warming event was a decrease in upwelling 

intensity and productivity of nearshore surface waters (Roemmich and McGowan 1995; 

McGowan et al. 1996). 

Numerous studies have documented decreases in the abundances of various nearshore species 

within the California Current region since the regime shift of the late 1970s. While these 

declines are often cited as evidence of a tight linkage between large scale changes in 

oceanographic circulation patterns and the productivity of nearshore marine ecosystems, few 

studies have attempted to compare observed trends in the magnitude and timing of these declines 

among species with differing life histories, geographical ranges, or trophic status (but see Barry 

et al. 1995; Veit et al. 1996; Holbrook et al. 1997). Such comparisons could provide useful 

insight into whether and how various components of the nearshore coastal ecosystem respond to 

the same disturbance. 

We use data collected from fish impingement studies conducted at coastal electrical generating 

stations located throughout the Southern California Bight to describe trends over a 17 year period 

and establish the timing and magnitudes of change in the abundances of 37 species of nearshore 

fishes. These data thus provide a long-term estimate of fish abundances that is both integrated 

through time and spatially extensive. Specifically, we explore the extent to which responses 

(i.e., effect sizes and response times) were manifested similarly between pelagic and benthic 

ecosystems, among various habitat types (pelagic vs. reef associated vs. benthic), among 

different trophic levels, and among species that vary in life history attributes (e.g. reproductive 

mode and geographic range). 

Methods 

Coastal electrical generating stations entrain a wide variety of fishes in their cooling waters 

during the course of normal operating activities. We obtained data from the Southern California 

Edison Company’s (SCE) Biological Monitoring Program on the numbers of fishes impinged at 

four coastal electrical generating stations located over a 200 km stretch of coastline throughout 

the Southern California Bight (Figure 1). Although the four plants differ somewhat in their 

designs (three are conventional fossil fuel fired and one is nuclear powered) all possess intake 
Population Trends and Trophic Dynamics 

9

structures that are surrounded by rock rubble and situated on sandy bottoms in depths ranging 

from 8-14m (Love et al. 1998). Temperature records for the southern and northern portions of 

the Southern California Bight indicate that an abrupt increase in surface water temperature 

occurred in 1977 concomitant with the 1976-1977 regime shift in the north Pacific (Figure 2a). 

We were able to obtain data from the beginning of this period in 1977 through the end of 1993. 

While impingement data have been collected through the present, data after 1993 were not 

available. 

Figure 1. Map of the Southern California Bight showing the locations of the four coastal electrical generating 

stations providing impingement data used in this study. San Onofre is a nuclear powered plant. Huntington Beach, 

Redondo Beach, and Ormond Beach are all conventional fossil fuel fired. 
Final Study Report – Schmitt and Brooks 

10

Year

1970 1975 1980 1985 1990 1995 2000

Standarized zooplankton anomaly -3

-2

-1

0

1

2

3

Standardized temperature anomaly

-3

-2

-1

0

1

2

3

(a)

(b)

Figure 2. (a) Time series of standardized surface water temperatures as recorded off San Diego, CA (closed bars) 

and Santa Barbara, CA (open bars). Temperature values were standardized to a mean of zero and a standard 

deviation of one by subtracting the 25 year mean (1972-1997) and dividing by the standard deviation of the 25 year 

mean for each location. Positive values represent years with surface water temperatures that were above the 25 year 

mean, while negative values indicate years that were colder than the long term mean. The arrow indicates the onset 

of the 1977 climate shift. (b) Time series of the standardized zooplankton anomaly within the Southern California 

Bight for the years 1972-1997 (data from the California Cooperative Oceanic Fisheries Investigations). Positive 

values represent years with zooplankton abundances that were above the long-term mean, while negative values 

indicate years below the long run average. The arrow indicates the onset of the 1977 climate shift.
Population Trends and Trophic Dynamics 

11

Raw data consisted of the counts of all fishes impinged within each generating station during a 

24 hour period of normal power plant operations. Counts were made at least monthly at each 

plant and of the 112 species entrained during this period, 37 occurred with a great enough 

frequency, i.e. were present in samples collected from at least two of the four plants in at least 

half of the years sampled, to permit inclusion in this study (Appendix I). With few exceptions, 

notably Sardinops sagax, Paralichthys californicus, Atractoscion nobilis, Paralabrax clathratus, 

and the two species of Sebastes, none of these species are heavily targeted by either commercial 

or recreational fishers. Before being used in any analyses, raw data first were standardized by 

dividing the counts for each species averaged within a month if necessary by the appropriate 

average monthly flow rate (gallons*106/day) to account for potential plant effects due to 

differences in the designs of the intake structures and in the amount of cooling water flowing 

through them from month to month. 

Standardized impingement values calculated for most species demonstrated a high degree of both 

spatial (between generating stations) and temporal (between consecutive months) variability. To 

minimize the possibility that our estimate of the proportional change in the abundances of a 

species within the Southern California Bight was driven by extreme changes observed at only 

one or two of the four coastal generating stations included in this study, we first transformed the 

data series obtained from each station for a given species by calculating the natural logs (ln) of 

the standardized count data. The transformed values were averaged across the four power plants 

within a given month for each species to yield a single data series for that species. Because we 

primarily were interested in long-term changes in abundance, i.e. changes occurring over time 

spans of up to a decade or more rather than those occurring over a single year, data were 

smoothed using a three month moving average in an attempt to reduce the fine scale seasonal 

variability still present in each averaged series. 

We estimated the magnitude of the long-term change in the average abundance for each species 

by calculating the proportional change in abundance using the equation (NFinal-NInitial)/NInitial. 

Inspection of the standardized data series for each species indicated that the standardized number 

of individuals for most species sampled during impingement surveys increased slightly from 

1977 until 1979 or 1980 when they began slowly decreasing to a minimum in 1991 before 

increasing again in 1992 and 1993. Given this pattern in the standardized data, we used the 

average of the maximum smoothed monthly ln (abundance) observed within each year during the 

period 1978-1980 as an estimate of NInitial and those observed during the years 1990-1992 as an 

estimate of NFinal. All statistical analyses were conducted using SAS (SAS v.8.1, SAS Institute 

2001). 

Implicit in all of our analyses was the assumption that changes in the number of fishes impinged 

by coastal electrical generating stations serve as a meaningful index of changes occurring in the 

abundances of these species within the Southern California Bight. To test this assumption, we 

correlated species specific values for the proportional change observed in the abundance of 17 

species calculated using impingement data obtained from SCE’s Redondo Beach plant with 

values calculated for the same species using a second, independently collected data set: a longterm study of the abundances of reef associated fishes within King Harbor, a small boat harbor 

and marina immediately adjacent to the cooling water intakes for the SCE Redondo Beach 

electrical generating station. In the King Harbor study, divers using SCUBA visually censused 
Final Study Report – Schmitt and Brooks 

12

juvenile and adult fishes within a series of 50 x 2 m band transects and hence, these data 

provided a different estimate of abundance for these species (see Terry and Stephens 1976; 

Stephens 1983; Holbrook et al. 1994; Holbrook et al. 1997 for details of the survey design). 

To test for differences in the magnitude of the proportional response between species exhibiting 

different life history characteristics or habitat affinities, we used the criteria presented in Table 1 

to establish several subcategories within the broader ecological categories of habitat, trophic 

level, geographic range, reproductive mode, and primary food web. Species were classified and 

placed within each sub-category based on dietary and life history information obtained from 

Cailliet et al. (2000) (see Appendix I for classifications). Values for the long-term proportional 

change in the ln (abundance) of each species were arcsine, squareroot transformed to meet the 

underlying assumptions of parametric statistics, and then comparisons between the various subcategories present in each category were made using a one factor generalized linear model with 

species serving as replicates. 

To explore possible links between the timing of aggregated species responses to long-term 

changes in secondary productivity (Figure 2b) associated with increased water temperatures and 

decreased levels of upwelling throughout the Southern California Bight (Roemmich and 

McGowen 1995; McGowen et al. 1996), we employed standard correlation analyses to compute 

cross-correlation coefficients between the California Cooperative Oceanic Fisheries 

Investigations (CalCOFI) bight-wide annual time series of mesozooplankton volumes (cubic 

centimeters per 1000 m3

 of water sampled) and time series for the aggregated abundances of 

planktivores (those species feeding largely on zooplankton or small microinvertebrates), primary 

macrocarnivores (species feeding on polycheates, small crustacea and molluscs) and secondary 

macrocarnivores (species feeding on large crustaceans, molluscs, and other fishes) as estimated 

by the SCE impingement data. In order to meet the assumptions of stationarity required by this 

type of analysis (Chatfield 1984), time series of the standardized abundances for each fish 

species, as well as the CalCOFI zooplankton series, first were converted to an annual series of 

standard deviates (mean 0, standard deviation 1) by subtracting the 17 year mean (1977-1993) 

from each yearly averaged standardized abundance estimate and then dividing this result by the 

standard deviation of the 17 year series mean. Average annual standard deviates for each trophic 

level were calculated by averaging across all species assigned to a given trophic level category 

and cross-correlation coefficients then were computed between each of the three aggregated 

trophic level standard deviate series and the standard deviate time series for mesozooplankton 

volume. Similar analyses were performed to examine relationships between long-term changes 

in secondary productivity and the responses of fishes occupying positions within benthic versus 

pelagic food webs and between long-term changes in secondary productivity and the responses 

of fishes occupying benthic, pelagic, and reef habitats. 

It is well known that the use of correlational analysis to explore relationships between time series 

of data that exhibit strong within series levels of autocorrelation is problematic. The presence of 

autocorrelation within the two data series violates the assumption of serial independence 

underpinning correlation analysis and results in an overestimation of the number of degrees of 

freedom that should be employed in statistically evaluating calculated cross-correlation 

coefficients. Consequently, failure to correctly account for significant autocorrelation present 

within each series can lead to an increase in the Type I error rate above that specified by α and 
Population Trends and Trophic Dynamics 

13

thus, the probability of erroneously concluding that a given correlation is statistically significant 

(Kope and Botsford 1988; Jassby and Powell 1990; Bence 1995; Pyper and Peterman 1998). 

To account for the autocorrelation present in our data, we calculated an “effective” number of 

degrees of freedom, N*

, using the formula 1/N* = 1/N + {2/N*ΣρXXj)*ρYY(j)} over N/5 lags 

where N represents the sample size and ρXX(j) and ρYY(j) represent the autocorrelations present 

in the two series, X and Y, at lag j (Chelton 1984). This value of N* was then used to calculate 

an adjusted critical value for the cross-correlation coefficient, rcrit, using the expression rcrit = sqrt 

(t2

α, N*-2/( t2α, N*-2 + N*

) (see Pyper and Peterman 1998 for a thorough review of methods). 

Results 

Thirty five of the 37 species examined in this study exhibited proportional declines in abundance 

between the initial period (1978-1980) and the final period (1990-1992) (Appendix I) as 

estimated using impingement data. Taken together, the abundances of the 37 species declined by 

an average (± 1 SE) of 41% ± 5 over an approximately 15 year period. Values for calculated 

declines ranged from 2% for the clinid, Heterostichus rostratus, to 89% for the elasmobranch, 

Myliobatus californica. Of the remaining two species, one species, Sphyraena argentea, was 

essentially unchanged (~ 1% increase) while the other, Sardinops sagax, increased by 37%. 

Comparison of Impingement Data with Other Estimates of Population Abundances

We found a significant and positive relationship between calculated declines in standardized 

abundances for 17 species common to both the King Harbor diver surveys and the SCE 

impingement surveys (r=0.66, p=0.004) (Figure 3). Although the estimates of population 

declines obtained using data collected from diver surveys had a tendency to underpredict those 

calculated from impingement data (slope=0.59, intercept=0.02), estimates obtained using 

impingement data did appear to be relatively unbiased with nine of the 17 species representing 

underestimates and eight representing overestimates. In general, estimates of population 

declines based on diver survey data for schooling species such as the pomacentrid Chromis 

punctipinnis tended to exceed that estimated from impingement data, while those obtained for 

benthic or cryptic species such as the flatfish, Hypsopsetta guttulata, or the kelp associated 

Heterostichus rostratus, tended to be less. 
Final Study Report – Schmitt and Brooks 

14

Comparisons of Proportional Changes in Abundance 

Proportional decline based on diver transect data

0.0 0.2 0.4 0.6 0.8 1.0

Proportional decline based on impingement survey data

0.2

0.4

0.6

0.8

1.0

Figure 3. Relationship between the proportional decline in the abundance of 17 species of fishes as estimated by 

diver visual surveys conducted in King Harbor, Redondo Beach, CA and the proportional decline in the abundance 

of these same species as estimated using impingement data. Solid line represents the least squares fit to these data 

(p=0.004, r2

=0.44).

The magnitude of the proportional change in abundance displayed by the majority of species 

included in this study was extremely uniform regardless of classification. Although it appeared 

that primary macrocarnivores experienced larger declines than either planktivores or secondary 

macrocarnivores (Table 1), we found no statistically significant differences in the average 

proportional change in standardized abundance among species occupying different trophic levels 

(F2,34=1.01, p=0.37), exhibiting different modes of reproduction (F1,35=2.00, p=0.17), or 

associating within different food webs (F1,35=0.67, p=0.42). Unlike results presented by 

Holbrook and Schmitt (1996) and Holbrook et al. (1997) who found that species with more 

northerly limits to their geographical ranges exhibited greater declines in abundance than more 

southern species, we found no difference between species with differing distributions (F2,34=2.26, 

p=0.12). We did find that species occurring in benthic habitats experienced significantly larger 

declines (F2,34=5.52, p=0.008) than species occupying either pelagic or reef associated habitats. 
Population Trends and Trophic Dynamics 

15

Comparisons of the Timing of Observed Changes 

Table 1. Criteria used to classify species into functional groups and the mean change (± 1 SE) in proportional 

abundance exhibited by each group. N equals the number of species assigned to each group. (* indicates subcategories that differ significantly from one another within a category at the α = 0.05 level). 

Category Mean Change 

 Sub-category Criteria in Abundance N 

Habitat 

 Pelagic Found predominantly in water column -0.32 (0.08) 13 

 Benthic Found predominantly on benthos; not reef associated -0.62 (0.08)* 11 

 Reef Found in close association with rocky reefs or outcrops -0.32 (0.06) 13 

Trophic Level 

 Planktivore Feeds predominantly on zooplankton or other small invertebrates -0.38 (0.08) 14 

 10

 Macro. Feeds predominantly on small macroinvertebrates -0.50 (0.07) 13 

 20

 Macro. Feeds predominantly on large macroinvertebrates and fishes -0.34 (0.09) 10 

Geographic Range 

 Southern Northern range limit is approx. Pt. Conception, Calif. -0.35 (0.07) 13 

 Central Northern range limit is approx. Calif./Oregon border -0.55 (0.08) 13 

 Northern Northern range limit is approx. N. Canada or Alaska -0.32 (0.08) 11 

Reproductive Mode 

 Eggs Oviparous species -0.38 (0.06) 29 

 Live Ovoviviparous or viviparous species -0.54 (0.07) 8 

Food Web 

 Pelagic Feeds primarily in water column -0.30 (0.10) 10 

 Benthic Feeds primarily from benthos -0.45 (0.05) 27 

As with the magnitude of observed changes in the proportional abundances, we found a high 

degree of similarity in the timing of the responses exhibited by the various levels within each of 

our functional categories (Figure 4). All calculated cross-correlation coefficients between the 

average deviates of the standardized abundances showed significant correlations at a lag of zero 

(Table 2) indicating that each level of species aggregations responded simultaneously to changes 

in the environment. Within the habitat association category, the average abundance of reef 

associated species also showed significant correlations with the abundances of both benthic 

(r=0.73, p<0.05) and pelagic (r=0.68, p<0.05) species one year earlier suggesting that the timing 

of the response by reef associated species lagged slightly behind that of the other two groups. 
Final Study Report – Schmitt and Brooks 

16

Average deviation in standardized abundance

-1

0

1 (b)

-1

0

1

(a)

Year

1977 1981 1985 1989 1993

-1

0

1 (c)

(d)

Year

1977 1981 1985 1989 1993

(e)

Figure 4. Time series of the average deviation in standardized abundance for fish species by (a) habitat type: 

Benthic (closed circle), Pelagic (square), and Reef Associated (open circle); (b) trophic level: Planktivore (closed 

circle), Primary Macrocarnivore (square), and Secondary Macrocarnivore (closed circle); (c) geographic range: 

Southern (open circle), Central (closed circle), Northern (square); (d) reproductive mode: Egg bearers (circle) and 

Live bearers (square); and (e) food web: Benthic derived (circle) and Reef derived (square). Data were first 

standardized to a mean of zero and a standard deviation of one by subtracting the 17 year (1977-1993) mean and 

dividing by the overall standard deviation for each species. Data were then averaged across all species within a 

functional group by year.
Population Trends and Trophic Dynamics 

17

Table 2. Values of the computed cross-correlation coefficients between members of each functional group for a lag 

of 0 years. All values are statistically significant at the 0.05 level after adjustment for the within series 

autocorrelation. 

Category Category 

 Sub-category Sub-category 

Habitat Benthic Reef 

 Pelagic 0.86 0.59 

 Benthic 0.75 

Trophic Level 10

 Macrocarnivore 20 Macrocarnivore 

 Planktivore 0.90 0.75 

 10

 Macrocarnivore 0.81 

Geographic Range Central Northern 

 Southern 0.89 0.88 

 Central 0.96 

Reproductive Mode Live 

 Eggs 0.92 

Food Web Benthic 

 Pelagic 0.77 

Cross-correlations between the CalCOFI mesozooplankton time series and the abundances of 

species feeding within pelagic food webs showed a higher degree of synchrony as measured by 

the magnitude of the cross-correlation coefficient than did species feeding within benthic food 

webs (pelagic: rmax=0.54, benthic: rmax=0.45). Significant correlations at lags of two and three 

years indicated that the decline in the abundance of both pelagic and benthic feeding species 

occurred approximately two to three years following the observed decline in mesozooplankton 

abundance (Figure 5a and 5b). Species occupying different trophic levels differed slightly but 

systematically in the timing of their response to decreasing zooplankton abundance. While 

abundances of planktivores showed a significant correlation (r=0.49, p<0.05) with measured 

abundances of mesozooplankton only at a lag of two years (Figure 6a), secondary 

macrocarnivores showed significant correlations at lags of both two (r=0.50, p<0.05) and three 

(r=0.47, p<0.05) years (Figure 6c) suggesting that these species responded more slowly to 

changes in secondary productivity than did planktivores. Primary macrocarnivores, having a 

significant correlation at a lag of two years (r=0.54, p<0.05) and a marginally significant (r=0.54, 

p~0.06) correlation at a lag of three years (Figure 6b), appeared to have responded at a rate 

intermediate to that exhibited by planktivores and secondary macrocarnivores. 
Final Study Report – Schmitt and Brooks 

18

-1

0

1

Lag (Years)

02468

Crosscorrelation coefficent

-1

0

1

(a)

(b)

Figure 5. Values of the cross-correlational coefficient between the standardized zooplankton anomaly, expressed as 

deviations from the 25 year mean, and the average deviation in the standardized abundance of those species feeding 

(a) largely in the pelagic zone or (b) from the benthos for lags ranging from zero to eight years. Dashed horizontal 

line represents the value of the cross-correlation coefficient which is significant at p=0.05. Values lying on or above 

this line indicate a significant correlation between the standardized zooplankton anomaly and the average 

standardized abundance of fishes feeding in the pelagic zone or from the benthos at some time in the future.
Population Trends and Trophic Dynamics 

19

-1

0

1

Crosscorrelation coefficent

-1

0

1

Lag (Years)

02468

-1

0

1

(a)

(c)

(b)

Figure 6. Values of the cross-correlational coefficient between the standardized zooplankton anomaly and the 

average deviation in the standardized abundance of those species feeding largely on (a) zooplankton and other 

microcrustacea, (b) species feeding largely on mesocrustaceans and other small invertebrates, and (c) species 

feeding largely on macrocrustacea and fishes for lags ranging from zero to eight years. Dashed horizontal line 

represents the value of the cross-correlation coefficient which is significant at p=0.05. Values lying on or above this 

line indicate a significant correlation between the standardized zooplankton anomaly and the average standardized 

abundance of primary consumers at some time in the future.

Discussion 

The ability to accurately predict whether and how rapidly changes manifested at one level of a 

biological community will be transmitted to other members of the community requires some 

mechanistic understanding of the linkages between the component species. Whether these 

predictions can be generalized from one system to the next will depend on the equivalency and 

consistency of the mechanisms operating within differing communities. One commonly held 

theory predicts that species ranges should shift poleward in response to increasing temperatures 
Final Study Report – Schmitt and Brooks 

20

(Lodge 1993; Lubchenco et al. 1993). As a result, community composition at a regional scale 

should become increasingly dominated by more warm-adapted species. This has been observed 

in several temperate marine communities over the last 30 years (intertidal invertebrates-Barry et 

al. 1995; subtidal fishes-Stephens et al. 1994). Our results contrast with these findings because 

with only two exceptions, Sardinops sagax and Sphyraena argentea, the abundances of all 

species included in our study declined regardless of their pre-1977 geographical distribution. We 

found no evidence that the magnitude of a species’ decline was related to the extent of its 

geographical range. 

These results do not appear to reflect inadequacies or systematic biases inherent in our use of 

impingement data to estimate abundances, as estimates derived from impingement surveys were 

significantly and positively correlated with those obtained directly using more traditional visual 

surveys. Holbrook et al. (1997) estimated that the average decline exhibited by populations of 

75 species of fishes observed in King Harbor and the offshore waters near Palos Verdes, 

California between 1975 and 1993 was approximately 69%. Application of the fitted 

relationship we obtained from comparing diver survey estimates to those obtained from the 

impingement study to this value yields an estimate of the predicted average decline based on 

impingement data of approximately 43%. This value is statistically indistinguishable from our 

calculated average value of 41% based on the average declines observed among the 37 species 

included in the SCE impingement surveys. 

The similarity in the population responses and their consistency among the sites we examined 

point to a regional decline in productivity as the underlying explanation. There are several lines 

of evidence for this. First, numerous authors have reported declines of similar magnitudes for a 

diverse array of species occupying a range of habitats and trophic levels (including primary 

producers) within both benthic and pelagic food webs throughout the Southern California Bight. 

The timing of these declines appears to be strongly correlated with the onset of a period of 

decreased upwelling and a lessening in the supply of nutrient-laden water to surface waters. 

Tegner et al. (1996) reported declines of 60% in stands of giant kelp, Macrocystis pyrifera, off of 

San Diego, while Holbrook et al. (1997) found that several species of foliose macroalgae off of 

Santa Cruz Island had decreased by approximately 80%. Roemmich and McGowan (1995) 

reported that the average biomass of macrozooplankton in surface waters throughout Southern 

California decreased by approximately 80% and a comparable decrease in the abundance of 

mesocrustaceans has occurred on understory algae at sites around Santa Cruz Island (Holbrook 

and Schmitt 1996). Veit et al. (1996) and Oedekoven et al. (2001) examined temporal patterns 

in the abundances of seabirds feeding on pelagic fishes and found that, on average, populations 

of species that fed over Southern California shelf and slope waters had declined by almost 40%. 

Finally, our finding of an average decline of approximately 41% in the abundance of nearshore 

fishes is comparable (when corrected for differences due to sampling methodologies) to reported 

declines of 70-90% for other populations of reef associated fishes throughout the Bight 

(Stephens 1983; Holbrook and Schmitt 1996; Holbrook et al. 1997; Love et al. 1998). As in 

previous studies, the magnitude of the declines observed in this study appeared to be independent 

of life history and we found no evidence of an effect that could be attributed to either trophic 

level or association with either benthic or pelagic food webs. 
Population Trends and Trophic Dynamics 

21

The second line of evidence that declining regional productivity underlies the observed changes 

is the similarity in the responses of species producing planktonic eggs and larvae relative to those 

giving birth to live, largely non-dispersing, young. It is well known that several large scale 

oceanographic features, e.g. fronts, jets, and eddies, acting on the dispersive larval phase of many 

marine species can introduce significant spatial and temporal variation in population abundances 

(Roughgarden et al. 1987; Kingsford 1990; Swearer et al. 1999; reviewed in Underwood and 

Keough 2001). The strength, timing, and magnitude of many of these oceanographic features are 

altered following a regime shift such as the one that occurred along the western coast of North 

America during 1977 (Chelton 1981; Chelton et al. 1982). As such, it is possible that the 

declines in the abundances of fishes possessing dispersive eggs and larvae may be due to the 

effects of altered current patterns or shifts in the locations of oceanic fronts leading to a 

redistribution or loss of eggs from the California Current region. This is not likely to be the case, 

however, for those species that lack a dispersive planktonic larval phase. The production of 

offspring by adult livebearing surfperches responds directly to changes in the amount of 

secondary productivity available to the adults on a reef and offspring rarely disperse from their 

natal reef (Holbrook and Schmitt 1996). Thus, it is unlikely that the declines we observed in live 

bearing species resulted directly from the redistribution of offspring, but rather resulted from a 

decrease in secondary productivity which led to lower birth rates and ultimately smaller 

population sizes (Holbrook et al. 1997). The similarity in the magnitudes of the response 

exhibited by species with dispersing larvae and those with non-dispersing young is suggestive of 

a common regional response by all species to decreased productivity. 

We did find a significant difference in the magnitude of the decline exhibited by species that 

occupy benthic habitats versus those in pelagic or reef associated habitats. This might represent 

a simple shift in the distribution of benthic species into deeper, colder waters following the 

increase in seawater temperature. Such a behavioral response is less likely to be effective for 

pelagic species that are restricted to surface waters or even possible for reef associated species 

that are tied to areas possessing reef habitat. A perhaps more parsimonious explanation is that all 

three groups have responded to a regional decrease in productivity, but that benthic species, by 

virtue of their association with a lower productivity habitat, are more sensitive to this decrease. 

Lastly, our data exhibited strong patterns of temporal coherency as measured by the crosscorrelation coefficients in the responses of the different levels of geographic range, habitat, 

reproductive mode, food web, and trophic level. All component levels of the fish assemblage 

showed significant correlations at a lag of zero indicating synchrony in the timing of changes in 

abundance. In addition, the abundances of reef associated species also were significantly 

correlated with the abundances of pelagic and benthic associated species in the previous year, 

suggesting that reef associated species may have experienced a slightly delayed response relative 

to the other two groups. This could be due to the large standing stocks of foliose macro-algae 

present on many Southern California reefs which could have partially buffered the initial decline 

in pelagic primary productivity associated with the regime shift. With regard to coherencies 

between the observed declines in fish abundance and those observed for zooplankton, the fact 

that we found no difference in the response times of species assigned to either benthic or pelagic 

food webs in relation to the onset of the decline in pelagic zooplankton abundance indicates that 

the productivity of both pelagic and benthic food webs may have declined synchronously 

throughout the Southern California Bight. Species in both food webs began declining two years 
Final Study Report – Schmitt and Brooks 

22

following the initial decline in zooplankton abundance, suggesting some degree of inertia in the 

response of the higher trophic levels in both webs. 

We also discovered lags in the response times of planktivores, and primary and secondary 

macrocarnivores to the decline in zooplankton abundance. While all three trophic levels 

displayed significant correlations between their abundances and the abundance of zooplankton 

two years earlier, there was a tendency for successively higher levels to display significant 

correlations at even longer lags. This is not the pattern expected if the declines were due strictly 

to climatic forcing, but it is consistent with a hypothesis involving the effects of decreased 

productivity and the propagation of those effects up the food chain (Aebischer et al. 1990). 

That the declines in the abundances of nearshore fishes described here occurred simultaneously 

and were of approximately similar magnitudes across species groups possessing differing 

geographic ranges, reproductive modes, and habitat affinities as well as between species 

occupying different trophic levels within benthic and pelagic food webs suggests a common 

mechanism for the decline. Our results point to a concurrent decline in the regional productivity 

of the Southern California Bight as that mechanism. If this decrease in productivity is, in fact, 

the result of altered oceanographic conditions due to interdecadal fluctuations in atmospheric 

circulation patterns as has been suggested (Hayward 1996), then our results predict that 

abundances of nearshore fishes should increase when the current climate regime returns to one 

characterized by cooler surface waters and more pronounced upwelling leading to increased 

levels of productivity within the Bight. Several authors (Mantua et al. 1997; Beamish et al.

1998) have suggested that such a regime shift did take place toward the end of the 1980s and our 

data do indeed show a slight increase in the abundances of the nearshore species beginning in the 

early 1990s; a lag of approximately two to three years consistent with our earlier findings related 

to the timing of the initial declines. Recent data on global climate change (Smith and Lazo 

2001) suggest, however, that sea surface temperatures may continue to increase well into the 

next century. If so, and if these changes are of sufficient magnitude to prevent or override the 

effects of the recent regime shift, our results predict continued declines in the abundances of 

most nearshore fishes regardless of their habitat, geographic range, or life history. 
Population Trends and Trophic Dynamics 

23

Acknowledgements 

We thank K. Herbinson of the Southern California Edison Company for providing us with access 

to the data collected by the Southern California Edison’s Biological Monitoring Program and J. 

S. Stephens Jr. of Occidental College for providing us with the King Harbor and Palos Verdes 

survey data. J. Lawyer and K. Seydel provided valuable logistical support and proved 

remarkably adapt at the collection of additional data. B. Williamson provided additional 

logistical support. This paper benefited from the comments of two anonymous reviewers. This 

research was supported by the UC-MMS Coastal Marine Institute Program, Minerals 

Management Service, U.S. Department of the Interior, under MMS Agreement No. 14-35-0001-

30758 (Task No. 14181). The views and conclusions contained in this document are those of the 

authors and should not be interpreted as necessarily representing the official policies, either 

express or implied, of the U.S. Government. 
Final Study Report – Schmitt and Brooks 

24

CHAPTER 2 

This Chapter is in press in Raffles Bulletin of Zoology with the following citation: 

Schmitt1, 2, R.J. and S.J. Holbrook1, 2. 2006. Predicting the magnitude of temporal variation 

in young-of-year class strength of surfperch (Teleostei: Embiotocidae). Raffles Bulletin of 

Zoology. In Press. 

1

Coastal Research Center, Marine Science Institute, and 

2

Department of Ecology, Evolution, and Marine Biology 

University of California, Santa Barbara, CA 93106, USA 

Abstract 

Members of the fish family Embiotocidae (surfperches) are viviparous and give birth to fully 

developed, non-dispersing juveniles. We explored (a) whether fluctuations in recruitment of 

young-of-year surfperches were similar among a series of shallow rocky reefs off southern 

California, USA, and (b) whether spatial variation in recruitment fluctuations mapped onto 

spatial differences in how much the local forage base on a reef fluctuated. For both surchperches 

examined (black surfperch Embiotoca jacksoni; striped surfperch E. lateralis), recruitment varied 

comparatively little through time on some reefs while it fluctuated substantially on others. These 

fishes harvest invertebrate prey from specific benthic foraging microhabitats (algal turf for black 

surfperch; the red alga Gelidium robustum for striped surfperch), and these microhabitats showed 

a range in dynamics among the reefs examined over a 12 yr period. Interannual fluctuations in 

foraging microhabitat were a strong predictor of the extent to which the abundance of young-ofyear surfperches fluctuated. However, the foraging microhabitat for black surfperch (algal turf) 

on a reef fluctuated independently of that for striped surfperch (Gelidium). As a consequence, 

the extent to which the abundance of young of one surfperch varied on a given reef was 

unrelated to that of its congener. These data show that (1) the magnitude of temporal variation in 

year-class strength of reef-associated fishes was related to the magnitude of variation in the 

forage base, (2) reefs in close proximity can show a range in resource dynamics that can affect 

reproductive output, and (3) the reproductive output of even closely-related species can fluctuate 

independently on the same reef. 

Introduction 

Subtidal marine reefs are subjected to considerable variation in environmental conditions that 

can influence the abundance and dynamics of such reef-associated organisms as benthic fishes, 

and there is growing interest in understanding how fishes will respond to disturbances and 

climate forcing (Holbrook et al., 1997; Jenkins, 2005). Many studies have explored spatial covariation between attributes of reefs and of the associated fish assemblage (e.g., Sale & Dybdahl, 

1975; Gladfelter et al., 1980; Anderson et al., 1981; Ogden & Ebersole, 1981; Choat & Ayling, 

1987; Choat et al., 1988; Tolimieri, 1995; Caley & St John, 1996; Ault & Johnson, 1998; 

Holbrook et al., 1990, 1993, 1994, 2000, 2002; Holbrook & Schmitt, 2003; Schmitt & Holbrook, 
Population Trends and Trophic Dynamics 

25

2000). By contrast, there have been comparatively few explorations of whether or how the 

temporal dynamics of reef resources impinge on the structure or dynamics of associated fishes 

(e.g., Ault & Johnson, 1998; Schmitt & Holbrook, 1990a; Holbrook & Schmitt, 2003). When 

examined, the reef resource more often explored has involved structural attributes of the 

environment that might serve as refuge space from predators (e.g., Hixon & Beets, 1989, 1993; 

Holbrook & Schmitt, 2002). For example, Syms and Jones (2000) altered physical structure and 

habitat complexity of the reef to varying degrees, which was crossed with different levels of 

pulsed mortality on fish, to determine resilience of the fish community. 

A critical reef resource that can fluctuate on a relatively fast time scale is the food supply of 

benthic fishes (e.g., Schmitt & Holbrook, 1986). With one exception, we know comparatively 

little about the demographic or population-level consequences of variation in the food supply of 

reef fishes. The exception concerns body growth - numerous studies have shown that the 

individual growth rate of fishes is plastic and can absorb some variation in per capita availability 

of prey (e.g., Doherty, 1982, 1983; Jones, 1984, 1987a, 1987b, 1988; Forrester, 1990; Anderson 

& Sabado, 1995; Booth, 1995, 2004). Fluctuations in food also should influence directly 

fecundity of individuals and thus subsequently their recruitment (e.g., McCauley et al., 1990), 

although this aspect is difficult to assess in reef fishes because most species produce dispersing 

larvae. Further, the dispersal of locally produced propagules decouples local variation in 

reproductive output from subsequent recruitment to that population (Shulman, 1985). 

Surfperches in the family Embiotocidae offer an unparalleled opportunity to explore the effect of 

fluctuations in the food supply on demographic and population-level attributes because these 

species are viviparous and give birth to fully-developed, non-dispersing juveniles (Baltz, 1984). 

Since adult surfperch convert food to young that are born into the parental population, it may be 

possible to determine the extent to which fluctuations in food affect reproductive output (here 

estimated as young-of-year class strength) and, for this type of life history, recruitment 

dynamics. 

Here we explore the influence of temporal variation in the forage base of two species of 

surfperches, the black surfperch (Embiotoca jacksoni) and the striped surfperch (E. lateralis) that 

co-occur on shallow rocky reefs off the Pacific coast of North America. These species consume 

small invertebrates such as amphipods from benthic substrata (Schmitt & Coyer, 1982; Schmitt 

& Holbrook, 1984). The two species concentrate their foraging activities on different reef 

substrata: black surfperch primarily feed on crustaceans harbored in turf, a low-dimensional 

mixture of debris, colonial animals, turf algae and surfperch food, whereas striped surfperch 

harvest crustaceans on foliose algae, primarily from the red alga Gelidium robustum (Holbrook 

& Schmitt, 1989, 1996). While the density of surfperch prey contained on these foraging 

microhabitats can fluctuate substantially (Schmitt & Holbrook, 1986), observational and 

experimental evidence has shown that the abundance of black surfperch or striped surfperch on a 

reef is positively and strongly related to the amount of turf or Gelidium present (Holbrook et al., 

1990, 1994). These foraging microhabitats are biogenic in nature and therefore have dynamics 

of their own (Schmitt & Holbrook, 1990a; Holbrook et al., 1994); much of the dynamics are 

caused by disturbances that range from local (e.g., sea urchin grazing, storm wave exposure; 

Schmitt & Holbrook, 1990a) to larger scales (e.g., climatic regime; Holbrook et al., 1997). Since 

the crustaceans that reside on turf and Gelidium are the food of these surfperches, these particular 

substrata represent a major component of the forage base of black surfperch and striped 
Final Study Report – Schmitt and Brooks 

26

surfperch respectively. This suggests that fluctuations in turf and Gelidium potentially could 

have substantial influences on local reproductive output and recruitment of young, thereby 

driving dynamics of local surfperch populations. Because surfperches do not consume their 

foraging substrata, there likely is no direct feedback between surfperches on the abundance of 

either turf or Gelidium. 

The purposes of this study were: (1) to evaluate whether inter-annual variation in the abundance 

of young-of-year surfperch on a reef are correlated with fluctuations in the cover of turf and 

Gelidium, and (2) to determine the extent to which the dynamics of the forage base and youngof-year class strength of black surfperch and striped surfperch co-vary among reefs. Because all 

of the reefs examined occur within a 15 km stretch of shore, the study also indicated whether reef 

populations behave independently or coherently at this spatial scale. 

Materials and Methods 

Field work was conducted on a series of reefs along a 15 km stretch of Santa Cruz Island, 

(34o

05’N:119o45’W), which is located in the Santa Barbara Channel of southern California, 

USA. Reefs consisted of algae-covered bedrock that sloped from above the tide mark to sand at 

~ 12 m depth. At each reef, permanent 40 x 2 m horizontal band transects were established at the 

3, 6, and 9 m depth contours. The transects delineated a rectangular shaped study site on each 

reef that was similar in area among the reefs sampled. Study sites were established at 6 reefs in 

1982, and sites at 5 additional reefs were established in 1986; data reported here were collected 

annually, except for 1984 and 1985, for a 12 year period beginning in 1982. Only reefs where 

young-of-year surfperch were observed were included in these analyses, which reduced the 

number of reefs to 9 for black surfperch and 8 for striped surfperch. 

The number of young-of-year surfperch at each study site was estimated from visual counts 

along the permanent transects in August to September each year. Young-of-year surfperch are 

easily distinguished from older conspecifics by their size, morphology and behavior, and the 

newborn cohort was up to 3 months old at the time they were counted. Fish on transects were 

counted repeatedly over multiple days, and the number of counts ranged between 4 and 8 each 

year. For each survey date, the number of young-of-year for each species was summed across 

the transects to yield a site-wide estimate of young-of-year abundance, and the number of young 

seen per survey within a year was calculated. 

For years when surfperch were counted, the percent cover of benthic substrata also was 

estimated within the study site of each reef using four 50 m lines per depth zone that were 

centered around the 3, 6 and 9 m fish transects. The substratum under 100 randomly selected 

points per line was identified (yielding N = 400 points per depth zone per reef per year). 

Previous work indicated that turf was the critical foraging microhabitat for black surfperch and 

the red alga Gelidium robustum was that for striped surfperch (Schmitt & Holbrook, 1986; 

Holbrook & Schmitt, 1989). To explore patterns of co-variation in the amount of variation in 

foraging habitats and young-of-year abundance, we calculated the temporal (inter-annual) 

variability in percent cover of these microhabitats separately for each reef sampled. Our main 

goal was to see if differences among reefs in the extent to which the forage microhabitat 

fluctuated were a good predictor of the spatial differences in the extent to which surfperch year-
Population Trends and Trophic Dynamics 

27

class strength varied among years. A secondary goal was to explore whether the two species of 

surfperches showed spatial coherence (i.e., same patterns among reefs) in the amount of temporal 

variation in the abundance of young-of-year. The measure of temporal variability used was the 

Coefficient of Variation (CV), which is the (standard deviation x 100) / mean. Similarly, 

temporal variability in the number of young-of-year of each surfperch was estimated, again using 

the CV, for each reef. To determine how well temporal variation in the forage base (turf or 

Gelidium) predicted the pattern of temporal variation in abundance of young-of-year, we 

regressed the CV for black surfperch or striped surfperch young for each site against the CV for 

turf or Gelidium at that reef. We also calculated the correlation between CV for turf against CV 

for Gelidium to explore spatial co-variation in the dynamical pattern of the foraging 

microhabitats. Finally, we calculated the correlation between CV in black surfperch young 

against that for striped surfperch young to explore whether there was spatial co-variation in the 

dynamical pattern of abundance of (locally produced) young-of-year among the reefs sampled. 

Results 

Turf and Gelidium robustum, the foraging microhabitats for black surfperch and striped 

surfperch respectively, did not remain constant over the 12 yrs of the study. The difference 

between the maximum and minimum availability of these microhabitats, averaged across the 

reefs examined, was ~ 2-fold for turf and ~ 4-fold for Gelidium. The amount of temporal 

variability in these foraging microhabitats differed among the reefs, with some showing 

relatively little variability in the cover of turf or Gelidium while other reefs showed substantially 

greater fluctuation (Figure 1). However, the degree to which turf fluctuated at a given site was 

independent of the magnitude of the temporal variability in Gelidium on that reef (Figure 1; r = -

0.09; P > 0.8). 
Final Study Report – Schmitt and Brooks 

28

Temporal Variability (CV) in Gelidium

0 10 20 30 40

Temporal Variability (CV) in Turf

0

10

20

30

40

Figure 1. The pattern of co-variation in magnitudes of temporal variability (measured by the coefficient of variation 

CV), between turf and Gelidium robustum, the foraging microhabitats for black surfperch and striped surfperch 

respectively (correlation coefficient r = - 0.09; P > 0.8). Each point represents a reef followed for either 8 or 12 yrs.

For both surfperches, there was considerable variation among reefs in the magnitude of 

interannual variation in recruitment of young-of-year (Figure 2). The extent to which the 

abundance of young-of-year varied from year to year on a reef was positively related to the 

dynamics of their foraging microhabitat (Figure 2). The degree of fluctuation in turf predicted 

almost two-thirds of the among-reef variance in the amount of temporal variability in the 

abundance of young-of-year black surfperch (Figure 2a; r2 = 0.64; P < 0.01). The amount of 

temporal variability in Gelidium predicted even more of the among-reef difference in temporal 

variability in abundance of young-of-year striped surfperch (Figure 2b; r2

 = 0.72; P < 0.01). 

However, there was no relationship between the two species in the degree of temporal variation 

in the abundance of their young on a reef (Figure 3; r = + 0.30; P > 0.4). Thus, while 

microhabitat and young-of-year dynamics were tightly coupled for each surfperch species, there 

was no spatial co-variation between the species. 
Population Trends and Trophic Dynamics 

29

(a) Black Surfperch

Temporal Variability in Forage Base 

(CV for Turf)

0 10 20 30 40

Temporal Variability (CV) 

in Abundance of Young

0

100

200

300

(b) Striped Surfperch

Temporal Variability in Forage Base 

(CV for Gelidium)

0 10 20 30 40

Temporal Variability (CV) 

in Abundance of Young

0

100

200

300

Figure 2. The relationships between the magnitudes of inter-annual variability in abundances of young-of-year 

surfperch and in the forage base for: (a) black surfperch young and turf (r2

 = 0.64; P < 0.01), and (b) striped 

surfperch young and Gelidium robustum (r2

 = 0.72; P < 0.01). 
Final Study Report – Schmitt and Brooks 

30

Temporal Variability (CV) in Abundance 

of Striped Surfperch Young

Temporal Variability (CV) in Abundance

0 100 200 300

of Black Surfperch Young

0

100

200

300

Figure 3. The pattern of co-variation in magnitudes of inter-annual variability in abundances of black surfperch and 

striped surfperch young-of-year (correlation coefficient r = 0.30; P > 0.4).

Discussion 

Understanding processes that influence abundance and dynamics of marine reef fishes has been a 

central focus in marine ecological research. Much effort has been devoted to understanding 

whether and how local dynamics of reef fish are coupled to processes that occur in other 

locations, which reflects the fact that most species have dispersing larvae (Doherty, 1991). To 

the extent that the influence of variation in abundance of a reef resource on local dynamics of 

reef fishes has been explored, the main thrust has been to understand the nature of loss rates after 

larval recruitment (see reviews by Hixon & Webster, 2002; Osenberg et al., 2002), again 

reflecting the notion that variation in mortality is expressed locally while that for fecundity 

probably is not (Shulman, 1985). Because local populations typically are connected via 

exchange of reproductive output, local events that affect fecundity surely will be expressed 

‘downstream,’ giving rise to the need to consider metapopulation dynamics and connectivity 

(e.g., Armsworth, 2002). However, there is growing evidence of relatively localized retention of 

larval fishes (e.g., Jones et al., 1999), suggesting that local fecundity and local recruitment may 

not be as decoupled as once believed. Despite the relevance, there has been little attention paid 

to whether and how fluctuations of reef resources affect reproductive output and recruitment of 

marine reef fish. Further, there have been extremely few long-term studies that have 

simultaneously estimated demographic rates and resources in assemblages of marine reef fish, 

adding to the difficulties in evaluating this important but under-studied issue (Holbrook & 

Schmitt, 1996). 

The surfperch system provides an excellent model to explore the link between variability of reef 

resources and demographic and population-level responses because fecundity is expressed 
Population Trends and Trophic Dynamics 

31

locally and newborn fish do not disperse from the parental population (Baltz, 1984). Our longterm study revealed that the degree to which the forage base on a reef fluctuated predicted 

around two-thirds of the inter-annual variation in recruitment of young-of-year surfperch; the 

greater the variation in the forage base of a reef, the more the abundance of young varied from 

year to year. While previously published experiments confirmed the importance of turf and 

Gelidium robustum to the local abundance of adult black surfperch and striped surfperch 

respectively (Holbrook et al., 1990, 1994), the present findings strongly suggest that the 

availability of these foraging microhabitats influences the production of young-of-year surfperch 

on a reef. Further, there was considerable variation among the study sites in the dynamics of the 

forage base and hence in the production / recruitment of young surfperch. The spatial scale of 

this heterogeneity was highly localized as all reefs were situated along a 15 km stretch of the 

same shore. 

The current study further revealed that the different forage bases of the two surfperch species 

varied independently among the sites. As a result, recruitment dynamics of the co-occurring 

surfperch also were independent. Given that these species of fish compete with one another 

(Hixon, 1980; Schmitt & Holbrook, 1986, 1990b), the independent responses to environmental 

fluctuations may be a mechanism that helps promote their coexistence (Chesson, 1994, 2000a, 

2000b). At the very least, the results imply that the local dynamics of these surfperch species 

need not be similar. 

The results reported here may shed insight into species of reef fishes that have the more typical 

life history where dispersing larvae are produced. In these cases the demographic or populationlevel consequences of a fluctuating food supply may not be easily discerned. Since mature fish 

convert food to reproductive products, fluctuations in the supply of food over an appropriate time 

scale should not only affect individual growth rates (Anderson & Sabado, 1995), but also should 

produce temporally varying size-specific fecundity relationships. Further, the surfperch system 

revealed considerable asynchrony in resource dynamics over relatively short distances. While 

connectivity and retention are now being included as potentially important aspects in 

metapopulation models of reef fishes (e.g., Armsworth, 2002), resource dynamics and its effect 

on fecundity also need to be incorporated if we are to fully understand effects of environmental 

fluctuations on reef fishes. 
Final Study Report – Schmitt and Brooks 

32

Acknowledgements 

We thank D. Canestro, K. Seydel, W. Douros, K. Collins, M. Carr, M. Anghera, and M.M. Perez 

for assistance in the field. The work was funded by the U.S. National Science Foundation (OCE 

99-10677, OCE 99-82105, OCE 04-17412 and earlier awards), the W.M. Keck Foundation and 

the Minerals Management Service, U.S. Department of the Interior (MMS agreement no.14-35-

0001-30758). The views and conclusions contained in this paper are those of the authors and 

should not be interpreted as necessarily representing the official policies, either expressed or 

implied, of the U.S. government. This is a contribution of the Santa Barbara Coastal LTER Site. 
Population Trends and Trophic Dynamics 

33

CHAPTER 3 

Temporal variation in temperate reef assemblages: have trophic levels responded similarly to 

environmental change? 

Sally J. Holbrook1,2, Andrew J. Brooks1 and Russell J. Schmitt1,2

1

Coastal Research Center, Marine Science Institute, and 

2

Department of Ecology, Evolution and Marine Biology 

University of California, Santa Barbara, CA 93106, USA 

Abstract 

Spatial or temporal gradients in productivity provide an opportunity to explore responses of food 

webs to environmental perturbations. Such variation is particularly marked in coastal marine 

environments, where climate-driven oceanographic processes drive the supply of nutrients and 

potentially can have profound effects on benthic and pelagic productivity. Oceanographic 

conditions in the California Current system underwent a substantial shift during the mid 1970s to 

the warm water, low productivity phase of the Pacific Decadal Oscillation (PDO) which 

persisted until the late 1990s. We assessed temporal patterns of abundance within two food 

pathways of the benthic food web at several locations in the Southern California Bight during the 

past two decades to explore responses to the bottom-up effects of lowered productivity during 

the warm phase, and assess evidence that the food chain is responding to the shift in the late 

1990s to cooler, more productive ocean conditions. Abundances of all trophic levels of the two 

food pathways examined (kelp bass, surfperches, understory algae, mesocrustaceans; sheephead, 

urchins, edible algae) declined dramatically during the warm phase of the PDO. Within each 

pathway, the magnitude of the declines of the trophic levels was similar. In addition, the patterns 

of decline appeared consistent at several different locations within the Southern California Bight. 

By the final years of the warm phase, proportional declines from abundances documented earlier 

in the phase were on the order of 0.8 for one of the food pathways and 0.6 for the other. Since 

2000, populations of kelp bass, surfperch, and foliose algae have increased modestly from the 

very low levels reached at the end of the warm phase of the PDO, consistent with predictions of 

bottom-up forcing of the effects of the rising nutrient supply associated with cooler 

oceanographic conditions. 

Introduction 

Ecologists have long sought to understand mechanisms that link trophic levels in order to predict 

whether effects of perturbations to populations in one portion of the food web will be propagated 

through the community. Models that predict reactions to variation in top-down or bottom-up 

forces differ greatly in their estimates of the magnitude of change of populations at different 

trophic levels (Hairston et al. 1960, Hairston and Hairston 1977, Menge and Sutherland 1976, 

Fretwell 1977, Oksanen et al. 1981, Carpenter and Kitchell 1993, Nisbet et al. 1997, Sinclair et 

al. 2000, Diehl et al. 2000, Shurin et al. 2002, Borer et al. 2005). Empirical studies have sought 

to resolve these differences by exploring the existence and strength of trophic cascades, which 
Final Study Report – Schmitt and Brooks 

34

involve indirect positive effects of predators on plant biomass, as well as potential effects of 

bottom-up forcing through alteration of primary production. Numerous investigations in both 

terrestrial and aquatic ecosystems have been conducted, and specific predictions of various 

trophic models have been tested (Menge 2000, Schmitz et al. 2000, Halaj and Wise 2001, Shurin 

et al. 2002, Bell et al. 2003, Borer et al. 2005). 

A recent meta-analysis of field experiments from several ecosystems revealed that trophic 

cascades were common but tended to be strongest in the lentic and marine benthos and weakest 

in the marine plankton and terrestrial systems (Shurin et al. 2002). Trophic responses often have 

been estimated during relatively short experimental manipulations, often at small spatial scales in 

the field or in laboratory mesocosms (Bell et al. 2003) and increasingly ecologists have turned to 

longer-term studies, sometimes carried out at relatively large spatial scales, to explore effects of 

food web perturbations (Menge 2000, Ripple and Beschta 2004, Findlay et al. 2005, Frank et al. 

2005, Terborgh et al. 2006). Frequently these datasets involve cases where abundances of 

predators vary, following reduction in their previously-abundant populations (northwest Atlantic 

cod; Frank et al. 2005), reintroduction following a period of absence (wolves; Ripple and 

Beschta 2004), or introduction of a non-native predator species (northern pike; Findlay et al. 

2005). In studies such as these evidence for trophic cascades is sought by examining the patterns 

of population sizes in low trophic levels, with high abundances of predators resulting in an 

indirect positive effect on primary producers. 

Spatial or temporal gradients in productivity provide another context for exploring responses of 

food webs to perturbations (Holbrook et al. 1997, Menge 2000, Brooks et al. 2002, Chase 2003, 

Daskalov 2003, Hunt and McKinnell 2006). In studies of benthic food webs in ponds, Chase 

(2003) found that predator effects on prey biomass were strongest and cascaded to plants only 

under low productivity regimes; under conditions of moderate to high productivity predator 

effects on prey were weak and there was no trophic cascade. Similarly, the strength of top-down 

processes in marine rocky intertidal communities appears to be strongly impacted by 

oceanographic conditions that alter primary productivity (Menge 2000). These findings suggest 

that the magnitude and existence of trophic cascades could vary with productivity. 

In coastal marine environments, productivity is heavily influenced by climate-driven 

oceanographic processes. For example, the behavior of the California Current system has a 

profound effect on nearshore conditions in Southern California (Brodeur et al. 1996, Hayward 

1997, Peterson and Schwing 2003). Coastal upwelling, which brings deeper, nutrient-laden 

waters to the surface, enhances primary productivity, which in turn drives the secondary 

productivity of the benthic and pelagic food webs. Oceanographic conditions in the California 

Current system underwent a substantial shift in the late 1970s when there was a rapid, persistent 

increase in seawater temperature (Miller et al. 1994, Minobe 1997, Hayward 1997, Mantua and 

Hare 2002, Peterson and Schwing 2003, Chavez et al. 2003). Associated with this warming 

event was a decrease in upwelling intensity and productivity of nearshore surface waters 

(Roemmich and McGowan 1995, McGowan et al. 1996). By the middle 1990s, abundances of 

organisms representing several trophic levels in nearshore reef food webs in the Southern 

California Bight all had declined on the order of eighty percent, with no evidence of alternating 

control by trophic level (Holbrook and Schmitt 1996, Holbrook et al. 1997, Brooks et al. 2002). 

The warm, low productivity phase of the Pacific Decadal Oscillation (PDO) persisted until the 
Population Trends and Trophic Dynamics 

35

late 1990s, when a shift to the cool phase began (Peterson and Schwing 2003, Goericke et al. 

2004, 2005). Both the declining productivity during the warm phase and the recent trend toward 

a higher productivity regime afford opportunities to explore the responses of the ecosystem to 

changes in bottom-up forcing. 

Here we assess temporal patterns of abundance within two food pathways of the benthic food 

web in the Southern California Bight during the past two decades. Our goals are to explore the 

whether the two sets of linked trophic groups showed similar responses to the bottom-up effects 

of the warm phase of the Pacific Decadal Oscillation and if there was coherency in the regional 

scale of responses during that period. In addition, in light of predictions from trophic theory, we 

investigate the trophic responses to the recent apparent shift to the more productive cool 

oceanographic phase. 

Materials and Methods 

Temporal patterns in abundances of communities on shallow (<20 m depth) rocky reefs were 

established using three studies that assess long-term population trends in the Southern California 

Bight, USA. We focused on two sets of linked trophic groups that comprise different portions of 

the benthic food web: (1) kelp bass – surfperches – benthic crustaceans – understory algae and 

(2) California sheephead – urchins – edible understory algae. The three studies provided data on 

abundance of each trophic group during the recent warm phase of the Pacific Decadal Oscillation 

(i.e., from the onset of sampling in the 1970s or 1980s until the late 1990s). This enabled us to 

explore the magnitude of responses of species in different trophic levels to conditions during the 

warm phase at several different locations – a single island (Santa Cruz Island), the northern 

Channel Islands (situated in the northern region of the Southern California Bight), and a coastal 

reef near Los Angeles in the southern portion of the Southern California Bight. The consistency 

of trophic responses to declining productivity could thus be assessed over increasingly broad 

spatial scales. Recent data (since the late 1990s) from two of the datasets also provided insight 

into possible patterns of change in one of the food pathways in response to the shift to the cool, 

higher productivity phase of the Pacific Decadal Oscillation that now appears to be occurring 

(Goericke et al. 2004, 2005). 

The first dataset is a long-term study of surfperches (Embiotocidae) and their associated reef 

resources at 11 reefs on Santa Cruz Island (35o

5’ N, 119o45’ W) in the northern part of the 

Southern California Bight (see Schmitt and Holbrook 1986, 1990a, 1990b, in press; Holbrook 

and Schmitt 1989, 1996; Holbrook et al. 1994, 1997). At the beginning of the study in 1982, the 

study reefs were covered with foliose macroalgae and turf, a low-growing, debris-laden mixture 

of small animals and algae. Giant kelp, Macrocystis pyrifera, has occurred intermittently on 

some of the reefs during the past two decades but is generally absent. Estimates of abundances 

of three species of surfperch (black surfperch, Embiotoca jacksoni; striped surfperch, Embiotoca

lateralis; and pile surfperch, Damalichthys vacca) are obtained from visual counts made by 

divers along 40 x 2 m isobathic transects ranging from 3 to 9 m bottom depth annually during 

September – November. Bottom cover on the reefs is characterized at the time fish are counted 

using a random point contact (RPC) method (see Schmitt and Holbrook 1986), to obtain 

estimates of the percent cover of turf and the common species of understory macroalgae. When 

present, the abundance of giant kelp is estimated in band transects (Schmitt and Holbrook 
Final Study Report – Schmitt and Brooks 

36

1990a). Abundance of crustaceans used by the surfperch as food is assessed during the fall 

months (a period of seasonally high crustacean abundance; see Schmitt and Holbrook 1986) by 

collecting prey in ten randomly placed 0.1 m2 quadrats at three depths (3, 6 and 9 m). Preyladen substrates are collected, placed in plastic bags underwater; in the laboratory prey are 

removed, counted and identified. Substrates in each sample are sorted taxonomically and 

weighed damp to provide estimates of algal biomass. An estimate of the food base in a given 

year was computed from the product of the substrate cover used by fishes as foraging 

microhabitat in shallow reef zones (Gelidium robustum) and in deep reef zones (turf) as 

estimated by the RPC transects and respective prey densities estimated from 0.1 m2 quadrats 

from each depth; these two values were averaged to yield the food base estimate for a site during 

a year. 

The second dataset used in this study is the ongoing Kelp Forest Monitoring Program conducted 

by the Channel Islands National Park (Davis et al. 1997). In this effort, which was initiated in 

1985 following a several year long design phase, population abundances of a wide variety of reef 

organisms are assessed annually during summer months at sites on 5 northern Channel Islands 

(San Miguel, Santa Rosa, Santa Cruz, Anacapa, Santa Barbara) using a total of 12 sampling 

techniques. Visual transects (100 x 2 m until 1995; 50 x 2 m since 1996) by divers are used to 

assess abundances of 13 species of fish, several of which [kelp bass (Paralabrax clathratus), 

California sheephead (Pimelometopon pulchrum) and three species of surfperch (E. jacksoni, E. 

lateralis, and D. vacca)] are pertinent to this study. Abundance of benthic algae, red sea urchins 

(Stronglyocentrotus franciscanus) and purple sea urchins (S. purpuratus) are estimated in 1 m2

quadrats placed along transect lines. Additional information on abundance of algae is obtained 

by random point contact sampling on the transect lines. Techniques are fully described in Davis 

et al. 1997. Here we present data from three islands (Santa Cruz, Anacapa and Santa Rosa). 

The third dataset is the long term study conducted by J.S. Stephens and colleagues at King 

Harbor along the mainland coast off Los Angeles County in the southern part of the Bight 

(33o51’ N, 118o24’ W; see Terry and Stephens 1976, Stephens 1983, Stephens et al. 1984, 1994, 

Holbrook et al. 1997 ). Estimates of fish species occurrence and densities are obtained from 

visual counts made by divers along isobathic transects ranging from 3 to 20 m bottom depth. 

Multiple counts of different-staged fish (usually adult, sub-adult and young-of-year) were made 

four times each year starting in 1974. We include here analyses of data for the time period 1974 

to 1993. 

Abundances of all of trophic groups that we examined declined during the warm phase of the 

PDO. To quantify this change for each trophic group, we calculated the mean proportional 

decline between abundances during the initial two-year period in each dataset (1982-1983 for 

Santa Cruz Island, 1985-1986 for Channel Islands National Park, and 1974-1975 for King 

Harbor) and the last two years of the warm phase (1998-1999). 
Population Trends and Trophic Dynamics 

37

Results 

Temporal Patterns during the Warm Phase of the PDO at Santa Cruz Island 

Abundances of all four trophic levels of the Santa Cruz Island food chain – kelp bass, 

surfperches, mesocrustaceans and understory algae – declined during the warm phase of the PDO 

(Figs. 1-4, Table 1). By the final years of the warm phase, the proportional decline of all four 

trophic groups from abundances documented earlier in the phase (early 1980s) was on the order 

of 0.8. Abundances of kelp bass, surfperch, mesocrustaceans and algae fell steadily beginning in 

the middle of the 1980s, reaching their lowest points between 1995 and 2001. Species within a 

trophic level (e.g., the three species of surfperch) showed similar patterns of abundance over 

time (Figure 2). The decline in total biomass of understory algae at all depths was mirrored by 

the pattern in percent cover of the red alga that is the most productive feeding habitat for 

surfperch (Gelidium robustum). Taken together, the results indicate that all of the trophic levels 

displayed similar population responses to the declining productivity associated with the warm 

phase of the Pacific Decadal Oscillation. 

Year

1980 1985 1990 1995 2000 2005 2010

Kelp Bass Density

(no per 300 m

3)

0

1

2

3

4

5

6

7

Figure 1. Density of kelp bass (Paralabrax clathratus) over time at Santa Cruz Island. Given is the mean number 

of individuals seen on visual transects at 3-10 monitoring sites on the island per year. 
Final Study Report – Schmitt and Brooks 

38

Year

1980 1985 1990 1995 2000 2005 2010

Black Surfperch Density

(no per 240 m2)

0

10

20

30

40

50

60

Year

1980 1985 1990 1995 2000 2005 2010

Striped Surfperch Density

(no per 240 m2)

0

5

10

15

20

25

30

35

Year

1980 1985 1990 1995 2000 2005 2010

Pile Surfperch Density

(no per 240 m2)

0

2

4

6

8

10

12

Figure 2. Densities of black surfperch (Embiotoca jacksoni, top), striped surfperch (E. lateralis, middle) and pile 

surfperch Damalichthys vacca, bottom) at Santa Cruz Island. Given is the mean total number of individuals seen on 

visual transects per day per site (N = 6-11 sites monitored 2 to 8 times per year). 
Population Trends and Trophic Dynamics 

39

Year

1980 1985 1990 1995 2000 2005 2010

Food Base

(mean crustaceans per 0.1 m2

)

0

200

400

600

800

1000

1200

Figure 3. Abundance of the crustacean food base for surfperch at Santa Cruz Island. Given is the estimated food 

supply based on abundance of crustaceans in 0.1m2

 quadrats (N = 30 per year) as well as the supply of the red alga 

Gelidium robustum and of algal turf, key foraging substrates for surfperch. 
Final Study Report – Schmitt and Brooks 

40

Year

1980 1985 1990 1995 2000 2005 2010

Algal Biomass

(mean grams per 0.3 m2

)

0

200

400

600

800

1000

1200

Year

1980 1985 1990 1995 2000 2005 2010

Proportion Cover of 

Gelidium robustum

0.0

0.1

0.2

0.3

0.4

Figure 4. Trends in algal biomass (top) and in the cover of Gelidium robustum (bottom) over time at Santa Cruz 

Island. Algal biomass is estimated in 0.1m2

 quadrats (N = 30 per year). Cover of Gelidium is estimated on RPC 

transects at 3m and 6m water depths.
Population Trends and Trophic Dynamics 

41

Table 1. Mean proportional change (+1 SE) in abundance during the warm phase of the Pacific Decadal Oscillation 

of four linked trophic groups at 3 different spatial scales: SCI = Santa Cruz Island; CINP = Channel Islands National 

Park; Redondo = King Harbor, Redondo Beach. See Methods for time frames of declines. 

SPATIAL SCALE 

SCI CINP Redondo 

TROPHIC GROUP 

Understory Algae -0.78 (0.02) -0.60(0.14) 

Meso-crustaceans -0.80 (0.02) 

Surfperch -0.79 (0.06) -0.68 (0.06) -0.75 (0.07) 

Kelp bass -0.78 (0.12) -0.60 (0.15) -0.62 (0.20) 

Temporal patterns during the warm phase of the PDO in the Southern California Bight 

The decline in abundance in the kelp bass–surfperch–algae–mesocrustacean trophic set that 

occurred on Santa Cruz Island starting in the 1980s also took place at other locations in the 

Southern California Bight (Table 1). On three northern islands, the mean proportional decline in 

abundances of these groups was about 0.6 from the mid 1980s until the late 1990s, and the 

magnitude of the change was similar among the trophic levels. A comparable decline occurred 

for kelp bass and surfperch populations at King Harbor (Table 1), consistent with a regional 

phenomenon of declining populations of reef organisms. In addition, on the northern Channel 

Islands, populations of species in the second reef-based trophic set we examined (California 

sheephead – urchins – edible algae) also experienced steep declines over the same time period 

(Table 2). 

 

Table 2. Mean proportional change (+1 SE) among three linked trophic groups within a benthic food web surveyed 

at the Channel Islands National Park from the mid 1980s to the late 1990s. 

Proportional 

Trophic Group Change 

 

Edible Algae -0.60 (0.14) 

Urchins -0.62 (0.05) 

Sheephead -0.45 (0.07) 

Evidence for response of trophic groups to shift to cool phase of the PDO 

Data on species abundances for the few years that have elapsed since the onset of cool 

oceanographic conditions indicate some modest increases in several trophic levels at Santa Cruz 

Island (Figs. 1-4). Only one group, pile surfperch, which reached their low in the mid-1990s, has 

regained abundances similar to those of the early 1980s (Figure 2). By contrast, kelp bass, 

striped surfperch and black surfperch show much smaller recent increases (Figs. 1 and 2), as do 

the biomass of algae and cover of Gelidium robustum (Figure 4). In addition, the data also 

suggest that most groups did not experience an immediate change in abundance at the end of the 
Final Study Report – Schmitt and Brooks 

42

warm phase of the PDO (1999). Rather, evidence for rising abundance does not become 

apparent for one to two years. 

Discussion 

Ecologists have long sought to understand the responses of ecosystems to trophic perturbations, 

and in recent decades, there has been increasing interest in determining how food webs are 

controlled. A large number of studies have explored top-down and bottom-up processes, and 

how various perturbations such as removal of top predators or increase in nutrient supply to the 

bottom of the food chain affects both structure (e.g., abundance, species diversity) and function 

(e.g., productivity, reproduction). Currently, there is abundant evidence that in many systems, 

both top-down and bottom-up processes operate; the challenge is to determine under what 

conditions one type of control predominates. This issue has been addressed in a few 

experimental studies where the relative importance of and potential interaction between topdown and bottom-up effects were explicitly tested. For example, top-down and bottom-up 

processes both contributed to control of the structure of stream communities studied by Nystrom 

et al. (2003), but the effects were largely independent. In contrast, the processes interacted to 

produce effects on plant growth in an old field food web. Stronger top-down forcing occurred 

under conditions of higher productivity (Moral and Schleider 2002), suggesting that the strength 

of top-down forcing can be mediated by the resource base. 

Strong top-down forcing has been experimentally demonstrated in a variety of benthic marine 

communities, both in the rocky intertidal and the subtidal (Menge 2000, Shurin et al. 2002). 

However, marine populations are known to respond to large scale physical change in the 

environment that can greatly alter productivity. Temporal phenomena including short-term (e.g., 

El Nino events) and longer term decadal-scale processes (e.g., the Pacific Decadal Oscillation) 

drive changes in oceanic primary production and have been identified as important influences in 

fisheries production (Hunt and McKinnell 2006). Indeed, bottom-up forcing has been argued to 

be the predominant environmental force affecting commercially harvested fish stocks in the 

Northeast Pacific Ocean (Ware and Thompson 2005). In addition, spatial variation in physical 

processes such as currents and upwelling regimes can result in alterations in primary productivity 

at scales of tens to thousands of kilometers (Menge 2000). At these spatial scales, oceanographic 

influences help explain variation in the structure of rocky intertidal food webs, despite the fact 

that these communities have a rich history of studies demonstrating top-down effects operating at 

very small spatial scales (Menge 2000). 

If it is true that bottom-up factors resulting from changing productivity regimes could reduce or 

even eliminate the potential for top-down control, evidence for declines (or increases) in 

productivity should be apparent at temporal and spatial scales that reflect the scale of ocean 

processes that influence nutrient availability. The results we report here are consistent with the 

idea that population abundances in the nearshore food webs of the Southern California Bight are 

driven by variation in oceanographic processes that influence productivity for several reasons. 

First, the magnitude of declines in abundance during the warm phase of PDO were similar for 

organisms on several different trophic levels within each food chain. Second, the patterns were 

consistent among the three data sets that represented sites in different portions of the Southern 

California Bight, indicating spatial coherence in the underlying mechanism. Third, the dramatic 
Population Trends and Trophic Dynamics 

43

declines in population sizes that we report are concordant to those described previously for other 

organisms in the Southern California Bight during the two decades following the onset of the 

warm phase of the Pacific Decadal Oscillation in 1976, including giant kelp, Macrocystis 

pyrifera, off San Diego (Tegner et al. 1996), macrozooplankton in surface waters of the 

California Current (Roemmich and McGowan 1995), seabirds (Veit et al. 1996, Oedekoven et al. 

2001), over 50 species of reef fishes sampled near Los Angeles (Holbrook et al. 1997), and a 

group of 37 species of fish from reef, pelagic and benthic habitats in the southern portion of the 

Bight (Brooks et al. 2002). 

Earlier we documented declines for some of the groups in one of the Santa Cruz Island food 

webs described here that had taken place between the early 1980s and 1995 (Holbrook et al. 

1997). If changing ocean productivity regimes and the associated bottom-up effects underlie the 

patterns of abundances in our dataset, we would predict continued low abundance until the next 

regime shift to the cool water, productive PDO phase. Indeed, the time series of data (Figs. 1-4) 

reveal low abundances for these groups on Santa Cruz Island persisted in most cases until 2000 

or 2001. Although only a few years have elapsed since the reported end of the warm phase of 

the PDO in the late 1990s, the Santa Cruz Island data suggest that the food web there is perhaps 

responding to increasing supply of nutrients associated with cooler ocean conditions. 

Interestingly, most groups show a lag in response of approximately two years in that their 

populations remained low or declined further during the first years of the cool phase. Brooks et 

al. (2002) reported a two to three year lag in abundance responses of 37 species of fish in the 

Southern California Bight to declines in mesozooplankton abundances in the California Current. 

This result was argued to be consistent with the effects of decreased primary and secondary 

productivity in the pelagic nearshore ecosystem propagating (rapidly) up the benthic food chain. 

The patterns that hint of increasing abundances of groups in our data set during the past several 

years are also consistent with reports regarding responses of the pelagic ecosystem on the West 

Coast to recent higher oceanic productivity. For example, beginning in 2000, zooplankton 

abundances in the California Current and biomass of cold-water species of copepods off Oregon 

both increased markedly, as did the number of adult Chinook salmon returning to the Columbia 

River system (Peterson and Schwing 2003). 

Ecologists have long recognized impacts on populations and communities to short term climate 

events (ENSO), but in the past decade increasing attention has been paid to the effects of lowfrequency climate change events like the Pacific Decadal Oscillation. Retrospective analyses 

have been hampered by a paucity of datasets of multidecadal length and longer for most 

organisms. Such datasets are more common for exploited species like marine fish, but 

interpretation of temporal patterns is confounded by exploitation pressure. 
Final Study Report – Schmitt and Brooks 

44

Acknowledgements 

We thank the Channel Islands National Park and J.S. Stephens Jr. for providing us with access to 

the data collected in their monitoring programs. We are very grateful to K. Seydel and the many 

field and laboratory assistants who have worked with us over the years to collect the long time 

series of data at Santa Cruz Island. Research at Santa Cruz Island was supported by grants from 

the National Science Foundation (OCE 9503305, OCE 0620276 and earlier awards), and the UCMMS Coastal Marine Institute Program, Minerals Management Service, US Department of the 

Interior, under MMS Agreement No. 14-35-0001-30758 (Task No. 14181). The views and 

conclusions contained in this document are those of the authors and should not be interpreted as 

necessarily representing the official policies, either expressed or implied, of the US Government. 
Population Trends and Trophic Dynamics 

45

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57

APPENDIX I 

Species and classifications (after Cailliet et al. 2000, Table 1) used in the analysis of the proportional change in 

population abundance from 1977 to 1993 as estimated from monthly fish impingement surveys conducted by the 

Southern California Edison Company. Species marked with a *

 were used in the comparison of the proportional 

changes in abundance estimated from impingement data with that from diver visual surveys. (P = Planktivore, 10

 M 

= Primary Macrocarnivore, 20

 M = Secondary Macrocarnivore 

Family 

 Species Habitat 

Trophic 

Level 

Geographic 

Range 

Reproductive

Mode 

Food 

Web 

Proportional

Change 

Atherinidae 

 Atherinops affinis Pelagic P Northern Eggs Pelagic -0.69 

 Atherinopsis californiensis Pelagic P Northern Eggs Pelagic -0.39 

 Leuresthes tenuis Pelagic P Central Eggs Pelagic -0.42 

Carangidae 

 Trachurus symmetricus Pelagic P Northern Eggs Benthic -0.43 

Clinidae 

 Heterostichus rostratus* Reef 10

 M Central Eggs Benthic -0.02 

Clupeidae 

 Sardinops sagax Pelagic P Northern Eggs Pelagic 0.37 

Cottidae 

 Scorpaenichthys marmoratus* Reef 20

 M Northern Eggs Benthic -0.24 

Dasyatididae 

 Urolophus halleri Benthic 10

 M Central Live Benthic -0.47 

Embiotocidae 

 Brachyistius frenatus* Reef P Northern Live Benthic -0.45 

 Damalichthys vacca* Reef 10

 M Northern Live Benthic -0.39 

 Embiotoca jacksoni* Reef 10

 M Central Live Benthic -0.32 

Engraulididae 

 Anchoa compressa Pelagic P Southern Eggs Pelagic -0.31 

 Engraulis mordax Pelagic P Central Eggs Pelagic -0.83 

Haemulidae 

 Anisotremus davidsonii* Pelagic 10

 M Southern Eggs Benthic -0.23 

 Xenistius californiensis* Pelagic P Southern Eggs Pelagic -0.29 

Kyphosidae 

 Girella nigricans* Reef P Southern Eggs Benthic -0.38 

Labridae 

 Oxyjulis californica* Reef P Central Eggs Benthic -0.12 

Myliobatididae 

 Myliobatis californica Benthic 10

 M Central Live Benthic -0.89 

Ophidiidae 

 Ophidion scrippsae Benthic P Southern Eggs Benthic -0.85 

Paralichthidae 

 Paralichthys californicus* Benthic 20

 M Central Eggs Benthic -0.82 

Pleuronectidae 

 Hypsopsetta guttulata* Benthic 10

 M Central Eggs Benthic -0.85 

 Pleuronichthys verticalis Benthic 10

 M Central Eggs Benthic -0.70 

Pomacentridae 

 Chromis punctipinnis* Reef P Southern Eggs Pelagic -0.22 

Rhinobatidae 

 Platyrhinoidis triseriata Benthic 10

 M Central Live Benthic -0.47 
58

Sciaenidae 

 Atractoscion nobilis Pelagic 20

 M Northern Eggs Pelagic -0.26 

 Cheilotrema saturnum* Reef 10

 M Southern Eggs Benthic -0.50 

 Genyonemus lineatus Benthic 10

 M Central Eggs Benthic -0.80 

 Menticirrhus undulatus Benthic 10

 M Southern Eggs Benthic -0.55 

 Seriphus politus Pelagic P Central Eggs Benthic -0.36 

 Umbrina roncador Benthic 10 M Southern Eggs Benthic -0.24 

Scorpaenidae 

 Sebastes paucispinis* Pelagic 20

 M Northern Eggs Benthic -0.38 

 Sebastes serranoides* Reef 20

 M Central Live Benthic -0.82 

Serranidae 

 Paralabrax clathratus* Reef 20

 M Southern Eggs Benthic -0.15 

 Paralabrax nebulifer* Reef 20

 M Southern Eggs Benthic -0.11 

Sphyraenidae 

 Sphyraena argentea Pelagic 20

 M Southern Eggs Pelagic 0.01 

Synodontidae 

 Synodus lucioceps Benthic 20

 M Northern Eggs Benthic -0.18 

Torpedinidae 

 Torpedo californica Reef 20

 M Northern Live Benthic -0.51 
59

The Department of the Interior Mission

As the Nation's principal conservation agency, the Department of the Interior has responsibility for most 

of our nationally owned public lands and natural resources. This includes fostering sound use of our 

land and water resources; protecting our fish, wildlife, and biological diversity; preserving the 

environmental and cultural values of our national parks and historical places; and providing for the 

enjoyment of life through outdoor recreation. The Department assesses our energy and mineral 

resources and works to ensure that their development is in the best interests of all our people by 

encouraging stewardship and citizen participation in their care. The Department also has a major 

responsibility for American Indian reservation communities and for people who live in island territories 

under U.S. administration. 

The Minerals Management Service Mission 

As a bureau of the Department of the Interior, the Minerals Management Service's (MMS) primary 

responsibilities are to manage the mineral resources located on the Nation's Outer Continental Shelf 

(OCS), collect revenue from the Federal OCS and onshore Federal and Indian lands, and distribute 

those revenues. 

Moreover, in working to meet its responsibilities, the Offshore Minerals Management Program

administers the OCS competitive leasing program and oversees the safe and environmentally sound 

exploration and production of our Nation's offshore natural gas, oil and other mineral resources. The 

MMS Royalty Management Program meets its responsibilities by ensuring the efficient, timely and 

accurate collection and disbursement of revenue from mineral leasing and production due to Indian 

tribes and allottees, States and the U.S. Treasury. 

The MMS strives to fulfill its responsibilities through the general guiding principles of: (1) being 

responsive to the public's concerns and interests by maintaining a dialogue with all potentially affected 

parties and (2) carrying out its programs with an emphasis on working to enhance the quality of life for 

all Americans by lending MMS assistance and expertise to economic development and environmental 

protection.