Structure of a northwest Atlantic Shelf macrofaunal assemblage with respect to seasonal variation in sediment nutritional quality

We examined temporal variation in the relationship between benthic macrofaunal assemblage structure and sediment nutritional quality using core samples taken seasonally from a 232-m deep site in Wilkinson Basin, Gulf of Maine, from October 2003 through August 2004. The benthic assemblage was dominated by deposit-feeding polychaetes of the families Cirratulidae, Paraonidae, and Cossuridae. Assemblage composition and abundance remained relatively constant over the course of the study, despite seasonal changes in sediment nutritional quality. Constant seawater temperatures and/or relatively long species generation times may account for this pattern. Sediment depth-frequency distributions of cirratulid and paraonid polychaetes varied temporally and exhibited subsurface abundance peaks; depth-frequency distributions of cossurid polychaetes, in contrast, were temporally stable. Subsurface peaks of plant pigment concentrations matched those of the cirratulid and cossurid polychaetes, suggesting that these groups transport and cache recently deposited phytodetritus below the sediment surface. This subsurface caching may ameliorate the effects of a seasonally variable food supply, damping any seasonal response of the fauna.