Regional Patterns in Invertebrate Assemblages on Offshore Oil Platforms Along the Pacific Outer Continental Shelf

Susan Zaleski, Department of Interior, Bureau of Ocean Energy Management, Camarillo, CA, United States, Henry Mark Page, Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA, Robert J. Miller, University of California Santa Barbara, Marine Science Institute, Santa Barbara, CA, United States, Brandon Doheny, Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA, United States, Jenifer Dugan, University of California, Santa Barbara, Marine Science Institute, Santa Barbara, CA, United States and Donna M Schroeder, U.S. Department of the Interior, Bureau of Ocean Energy Management, Camarillo, CA, United States
Abstract:
Twenty-seven oil and gas platforms are arrayed offshore California from north of Point Conception south to San Pedro Bay (a coastline distance of >300 km). To test the hypothesis that variability in the structure of sessile invertebrate communities on the platforms is associated with regional differences in sea surface temperature, we sampled space-holding invertebrate taxa photographically on 23 platforms and compared the composition and cover of invertebrates among and within regions using multivariate analyses. To explore temporal variability in invertebrate assemblages, we also compared the cover and composition of invertebrates on a subset of platforms in the Santa Barbara Channel (SBC) where data were collected over ten years previously. The composition of invertebrate assemblages differed significantly among regions, and was driven by variation in the relative abundance of certain anemone, bryozoan, tubiferous annelid, sponge, and bivalve taxa. The presence of non-native bryozoan and anemone taxa on some platforms in the south (San Pedro Bay) and southeast SBC contributed to the distinction of these assemblages from the others. Comparison of survey data on the subset of platforms in the SBC surveyed over ten years apart revealed little change in the cover of major space-holding taxa (e.g., anemones Metridium, Corynactis) across platforms, although there was an increase in cover of the non-native bryozoan Watersipora subtorquata between surveys. The existence of geographical patterns in the composition of platform invertebrate assemblages suggests that these assemblages may be useful as barometers of short and longer-term environmental change. For biogeographic transition zones, such as the SBC, monitoring of platform invertebrate assemblages could permit an evaluation of the concept that these zones are particularly susceptible to shifts in the composition of marine species driven by ocean climate.
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