FORAMINIFERAL DISTRIBUTIONS ON A SUB-MILLIMETER SCALE IN METHANE SEEP CLAM BEDS

Most studies using stained or labeled benthic foraminifera to assess distribution patterns of living specimens within sediments are based on analyses obtained from sections of sediment cores. However, individual foraminiferans may not be distributed homogenously within sediments at the scale of the sampling intervals, which are typically 1 cm. With the aim of evaluating the life positions and distributions of individual foraminifera within methane seep sediments, which have very steep geochemical gradients, push cores were collected with the ROV Jason in 2007 from seep (clam bed) and non-seep habitats in the Clam Flats area (~1000m water depth) of Monterey Bay, California. Cores were prepared using the Fluorescently-Labeled Embedded Core method (FLEC) that allows specimens to be examined in life position (Bernhard et al. 2003, L&O). The life position of individual foraminifera within the top 20-60mm of 33 cores showed that the foraminifera were distributed heterogeneously in both seep and non-seep habitats. More specifically, observations indicate that live specimens were not distributed within a thin layer of surface sediments, that specimens were sometimes intimately associated with bacteria, and that apertures were often oriented downward. Results from this study provide the first life-position data of seep foraminifera, and yield important insights into the ecology and geochemistry of methane seep species.