INTRA-ANNUAL CHANGES IN BENTHIC FORAMINIFERAL ASSEMBLAGES INHABITING THE SHELF OF THE WESTERN ANTARCTIC PENINSULA

Intra-annual changes in most deep-sea ecosystems are dependant on organic flux from the sea surface. Changes in sea surface conditions can thereby cause temporal and spatial variations in seafloor communities. In an effort to gain a better understanding of seasonal changes in benthic ecosystems of the Antarctic, the SEASONS (Seasonal Ecological Analysis of Seafloor Organic Nutrient Supplies) project examined living (Rose Bengal stained) benthic foraminiferal assemblages in surface sediments (0-1cm) from seven (7) sites (~600m and 1200m) along a surface productivity gradient in the northern Gerlache/southern Bransfield straits region of the Western Antarctic Peninsula. Samples were collected in April 2008 (during a period of high surface productivity bloom) and again in July 2008 (during a period of lower surface productivity). Dominant species (>63 micron size fraction) found in this region include: Bolivina pseudopunctata, Pullenia spp., Reophax spp., Astrononion echolsi, and Globocassidulina biora. B. pseudopunctata is the dominant taxon in all the sites examined thus far and, like most of the other common calcareous taxa observed in this study, decreased in abundance from April to July. In contrast, Reophax spp. increased in abundance in July. This agglutinated taxon may be able to thrive on degraded organic matter. Changes in benthic foraminiferal assemblages in surface sediments at these sites appear to be positively related to organic input over space and time. Additional work is needed to evaluate responses of infauna living in sediments below 1cm. Results from this study will generate modern analogs for regional reconstructions of ancient trends in seasonality and will provide much needed information about the influences of intra-annual environmental changes on foraminiferal assemblages of the past and present.