ECOLOGY AND PALEOECOLOGY OF BENTHIC FORAMINIFERA ASSOCIATED WITH METHANE SEEPS ON THE NORTHERN CALIFORNIA MARGIN

As part of a program designed to characterize the ecology, geochemistry, and paleontology of methane seeps, ROV cores were taken from bacterial mats and clam beds associated with active methane seeps off the northern California coast. An examination of the living (Rose Bengal stained) benthic foraminifera from these cores reveals assemblage differences between seep subenvironments. Assemblages are dominated by agglutinated taxa. In bacterial mat environments, low diversity calcareous assemblages, when present, are dominated by Uvigerina peregrina. Calcareous assemblages at clam bed environments generally have higher diversities and abundances than those of bacterial mats. Despite the low oxygen availability and relatively high concentration of sulfide present in subsurface microhabitats of bacterial mats at seeps, infaunal densities of living agglutinated foraminifera are, in some cases, higher than densities near the sediment-water interface. Comparisons of these data with those of previously published seep data from Eel River and Monterey Bay also suggest variability of foraminifera assemblages associated with methane seeps; no single species or assemblage characterizes all methane seeps. Results from this study suggest that the variability of seep microenvironments are reflected in the distributional composition of foraminiferal assemblages, and that it is imperative to study a wide range of seeps in order to understand the factors that control seep ecosystems.