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DETECTING LONG‐TERM CHANGE IN COMPLEX COMMUNITIES: A CASE STUDY FROM THE ROCKY INTERTIDAL ZONE
Author(s) -
Steinbeck John R.,
Schiel David R.,
Foster Michael S.
Publication year - 2005
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/04-1046
Subject(s) - intertidal zone , environmental science , intertidal ecology , ecology , invertebrate , sampling (signal processing) , abundance (ecology) , community structure , biology , filter (signal processing) , computer science , computer vision
Despite the recognition of the usefulness of BACI designs for assessing environmental impacts, there are few examples because of the need for repetitive sampling over long time periods. Our examination of the application of a BACI design to detect the impacts of elevated seawater temperature from the Diablo Canyon Power Plant in central California on rocky intertidal communities showed statistically significant changes in a large percentage of the species analyzed. The statistical power of the analysis resulted from both the large numbers of surveys before and during plant operation and from other design features that made the study resilient to the effects of two “100‐year” storms, several ENSO warming events, and the highly variable nature of the impacts. The large data set from the study required the development of decision rules for determining the appropriate surveys, stations, and species to analyze. BACI analyses were used to test the effects of the thermal plume on 47 algal and 50 invertebrate data sets. There were statistically significant effects for 79% of the algal and 60% of the invertebrate data sets. At the impact sites, there was a loss of cover by foliose algae and increases in crustose forms. Many invertebrates, particularly grazing gastropods, increased in abundance. Multivariate analysis of the community showed that there was continual change in impact sites that lasted throughout the study. The nature, magnitude, and spatial extent of the effects identified from the study are being used to determine appropriate plant modifications or mitigation for the effects of discharge. This study illustrates many of the problems in analyzing environmental effects and clearly demonstrates the need for long‐term monitoring. This was especially true for this study, where storms and ENSO events affected our ability to analyze data from some of the stations, and points out the importance of having redundancies built into monitoring programs. The complex interactions among the direct effects of the discharge, indirect community‐level effects, and variation due to oceanographic conditions provide useful insights for planning impact assessments and other ecological studies, and help contribute toward science‐based regulation and management.