Effect of Temporal and Spatial Separation of Samples 

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 FINAL TECHNICAL SUMMARY 

STUDY TITLE: Effect of Temporal and Spatial Separation of Samples on Estimation of 

Impacts 

REPORT TITLE: Effect of Temporal and Spatial Separation of Samples on Estimation 

of Impacts 

CONTRACT NUMBER: 14-35-0001-30758 

SPONSORING OCS REGION: Pacific 

APPLICABLE PLANNING AREA(S): Southern and Central California 

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

COMPLETION DATE OF REPORT: April 2005

COSTS: FY 99/00 - $34,293; FY 00/01 - $34,293 

CUMULATIVE PROJECT COST: $68,568 

PROJECT MANAGER: Russell J. Schmitt

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

California, Santa Barbara, CA 93106 

PRINCIPAL INVESTIGATORS: 1Todd E. Minchinton, 2Peter T. Raimondi 

ADDRESSES: 1Department of Biological Sciences, University of Wollongong, 

Wollongong NSW, 2522 Australia; 2Department of Ecology and Evolutionary Biology, 

University of California, Santa Cruz, CA 95064

KEY WORDS: Abalone, Anemone, BACI design, Barnacle, Baseline data, Before-After 

design, California, El Niño, Environmental impacts, Intertidal, Limpet, Marine algae, 

Marine invertebrates, Monitoring, Mussel, Power analysis, Rockweed, Seasonal trend, Sea 

star, Surfgrass, Temporal Trend, Turfweed, Withering Syndrome

BACKGROUND: Since 1991 the Minerals Management Service has funded a monitoring 

program for Santa Barbara County, California, U.S.A, called the “Shoreline Inventory”. The 

inventory was to provide baseline data on rocky intertidal communities that could be used in 

the event of an oil spill to calculate losses due to the impact. The main logistical task of the 

inventory was to set-up and sample at regular intervals 9 permanent sampling sites in the 

rocky intertidal zone of Santa Barbara County. At each site species assemblages dominated 

by 13 species were targeted and sampled in permanent plots in spring and autumn of each 
Final Technical Summary – Minchinton and Raimondi 

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year. From 1991 to 1995 the Shoreline Inventory was expanded to 18 mainland sites across 4 

counties (San Luis Obispo County, Santa Barbara County, Ventura County, Los Angeles 

County) and 8 offshore sites on two islands (Catalina Island, Santa Cruz Island). This report 

summarizes the spatial and temporal trends in abundance for the 13 target species at the 18 

mainland sites and assesses using power analysis the ability of the Shoreline Inventory 

monitoring program to detect changes in the abundance of the target species. 

OBJECTIVES: The primary objective of this study was to use the database of the Shoreline 

Inventory to test quantitatively the critical assumption that estimation of consequences after 

an impact is possible for sites that were monitored before the impact. Specifically, we answer 

the following two questions: 

1. What are the spatial and temporal patterns of abundance for the 13 target species at 

the 18 mainland sites?

2. Based upon power analyses following simulated impacts to target species at each 

site, should there be any modifications to the sampling design of the monitoring 

program?

DESCRIPTION: The Shoreline Inventory includes 18 mainland sites extending from central 

to southern California. Five sites were established in autumn 1995 in San Luis Obispo 

County (Point Sierra Nevada, Piedras Blancas, Cayucos Point, Hazards, Shell Beach), 9 sites 

in spring 1992 in Santa Barbara County (Occulto, Purisima Point, Stairs, Boathouse, 

Government Point, Alegria, Arroyo Hondo, Coal Oil Point, Carpinteria), 2 sites in autumn 

1994 in Ventura County (Mussel Shoals, Old Stairs), and 2 sites in autumn 1994 in Los 

Angeles County (Paradise Cove, White’s Point). The Shoreline Inventory includes 13 key 

target species comprising both sessile and mobile macroinvertebrates and macroalgae that are 

generally the dominant occupiers of primary space at particular heights and exposures in the 

intertidal zone. Four target species (or species groups) are sessile or sedentary 

macroinvertebrates: (1) barnacles (the acorn barnacles Chthamalus fissus/dalli and Balanus 

glandula), (2) the gooseneck barnacle Pollicipes polymerus, (3) mussels (primarily Mytilus 

californianus), and (4) the sea anemones Anthopleura elegantissima and A. sola. Six target 

species are macroalgae: (5) the brown fucoid alga or rockweed Silvetia compressa (formerly 

Pelvetia compressa, Pelvetia fastigiata), (6) the brown fucoid alga or rockweed 

Hesperophycus californicus (formerly H. harveyanus), (7) the red alga Mastocarpus 

papillatus, (8) the red alga or turfweed Endocladia muricata, (9) the “rainbow” alga 

Mazzaella spp. (formerly Iridaea spp.), and (10) the marine angiosperm or surfgrass 

Phyllospadix torreyi/scouleri. Three target species are mobile invertebrates: (11) the ochre 

sea star Pisaster ochraceus, (12) the giant owl limpet Lottia gigantea, and (13) the black 

abalone Haliotis cracherodii. At each site permanent areas were established where target 

species were the dominant organisms, and then their abundances were sampled in spring and 

autumn of each year. 

To examine variation in the abundance of target species in space and time, summary statistics 

(mean and standard error of the mean) for all sites and sample periods were calculated and 

plotted graphically. Analyses of covariance (ANCOVA) procedures were used to assess 

seasonal and temporal patterns of abundance for each of the target species at each site. The 
Effect of Temporal and Spatial Separation of Samples 

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ability of the monitoring program to estimate the effects of impacts was done using power 

analyses. Impacts to the abundance of target species were simulated and then the ability to 

detect these impacts was assessed under a before-after design. Based on these results, we then 

determined whether there should there be modifications to the sampling design of the 

Shoreline Inventory monitoring program. 

STUDY RESULTS AND SIGNIFICANT CONCLUSIONS: The Shoreline Inventory 

monitoring program has produced what is, in terms of its spatial and temporal extent, one of 

the most comprehensive sets of data ever collected for species living in rocky intertidal 

communities. Visual inspection of graphs and statistical analyses of the data reveal that the 

current sampling design and monitoring protocols have a great ability to show the natural 

limits of variation and to detect trends in the abundance of target species. Three types of 

temporal trends were clear: (1) short-term seasonal trends, (2) intermediate-term fluctuations 

on time scales ranging from one to several years, and (3) long-term changes for five or more 

years due to changes in abundance over the entire sampling period. First, short-term seasonal 

trends were apparent at a minority of sites for the acorn barnacles, the gooseneck barnacle 

Pollicipes and the sea star Pisaster, with abundances greater in autumn than in spring. The 

macroalgae exhibited more pronounced seasonal trends than the macroinvertebrates. At most 

sites, the cover of Silvetia, Mastocarpus and Phyllospadix was greater in autumn than in 

spring, whereas Endocladia was more abundant in spring than in autumn. A second striking 

and common trend in the data were intermediate-term fluctuations in abundance where there 

were relatively rapid declines sometimes followed by more gradual increases. These 

relatively rapid and common declines occurred from 1997 to 1998, which corresponds to the 

1997-98 El Niño event, which was the strongest of the century. Many target species 

experienced declines at some sites during the 1997/98 El Niño event, including barnacles, 

mussels, Endocladia, Silvetia, Phyllospadix, Anthopleura and Haliotis. The third obvious and 

consistent trend was the long-term declines in abundance over the entire monitoring period for 

some target species at several sites, including Haliotis, which experienced population crashes 

due to the fatal disease, withering syndrome. Detection of these temporal trends in abundance 

(seasonal, El Niño, disease) highlights the efficacy and utility of the current Shoreline 

Inventory monitoring program. 

For all target species that met assumptions of statistical tests (10 of 13 species; see section 

3.2.2), there was 80% power to detect 50% changes in abundance at α = 0.05. Indeed, for the 

majority of species and sites, changes in abundance of only 20% could be detected with 80% 

power at α = 0.05. Power to detect change varied among target species (but not among sites) 

and was greatest for mussels and least for Pisaster. Some species (Silvetia, Hesperophycus, 

Haliotis) and sites (e.g., Stairs) could not be assessed through power analysis because they 

failed to meet the assumptions of statistical tests. Alternative means should be considered to 

determine whether impacts could be detected for these species and sites should they occur. 

Indeed, additional more sophisticated analyses and designs should be explored to make 

greater use of the entire range of data. No changes should be made to the current monitoring 

program, but additional sites and target species, including means to monitor recruitment, 

should be added as resources permit. 
Final Technical Summary – Minchinton and Raimondi 

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STUDY PRODUCTS: 

Publications: 

Wilson, C. T., P. T. Raimondi, J. A. Altstatt, and T. E. Minchinton. Changes in intertidal 

community structure following mass mortality of the black abalone, Haliotis 

cracherodii, and implications for abalone recovery. Conservation Biology. In Review. 

Raimondi, P. T., C. M. Wilson, R. F. Ambrose, J. M. Engle and T. E. Minchinton. 2002. 

Continued declines of black abalone along the coast of California: are mass mortalities 

related to El Niño events? Marine Ecology Progress Series 242:143–152. 

Minchinton, T. E. and P. T. Raimondi. 2001. Long-term Monitoring of Rocky Intertidal 

Communities at the Channel Islands National Park: Summary of Spatial and Temporal 

Trends and Statistical Power Analysis. Report and presentation for the Scientific and 

Management Review of Monitoring Protocols for the Channel Islands National Park. 

29 pp. 

Research Presentations:

Minchinton, T. E. and P. T. Raimondi. 2001. Long-term Monitoring of Rocky Intertidal 

Communities at the Channel Islands National Park: Summary of Spatial and Temporal 

Trends and Statistical Power Analysis. Report and presentation for the Scientific and 

Management Review of Monitoring Protocols for the Channel Islands National Park. 

29 pp. 

Minchinton, T. E., P. T. Raimondi, D. V. Richards, G. E. Davis and K. D. Lafferty. 2001. 

Detecting Environmental Impacts: Monitoring Programs and Power Analysis. Poster 

presented at UC Toxic Substances Research & Training Program 14th Annual 

Research Symposium. Lake Tahoe, California. 

Minchinton, T. E., P. T. Raimondi, M. Wilson, R. F. Ambrose and J. M. Engle. 2000. 

Continued Declines of Black Abalone due to Withering Syndrome along the Coast of 

California. Poster presented at UC Toxic Substances Research & Training Program 

13th Annual Research Symposium. San Diego, California. April 2000. 

Becker, B. J. and MARINE members. 2001. MARINE (Multi-Agency Rocky Intertidal 

Network): Coordinated ecological monitoring on a regional scale. Displayed at various 

symposia.