The infaunal benthos of a natural oil seep in the Santa Barbara channel

We are studying a diverse infaunal benthic community that exists in the fine sand sediments of a shallow (16 m) natural oil seep near Santa Barbara, California, USA. The study area and sampling methods are described in this introductory paper. Data presented indicate the adequacy of sampling in revealing horizontal patchiness and vertical faunal distributions. The infauna of the seep and of a nearby comparison area, without seepage but of similar depth and sediment type, are compared. The data indicate a consistently larger but fluctuating density of organisms at the seep station. However, Shannon-Weaver diversity (H=1.6 to 1.7), Peilou's evenness (J=0.80 to 0.81), and measures of dominance-diversity with estimates of graphical skewness (0.66 to 0.68) and kurtosis (1.2 to 1.4) are all similar for the two stations. The rank correlation of common species at the stations is significant according to Spearman's rho. Species common to both stations account for 85 to 95% of the individuals, further indicating the high degree of similarity between stations. Denser populations of oligochaetes and the maldanid polychaete Praxillella affinis pacifica suggest some advantages for deposit feeders at the seep station. Mats of the bacterium Beggiatoa sp. are associated with localized intense oil seepage. Hypotheses suggesting trophic enrichment and biochemical adaptation at the seep are presented.