INVESTIGATING THE PRESERVATION POTENTIAL OF LOCAL-SCALE BIOTIC GRADIENTS USING BENTHIC FORAMINIFERA

Biotic gradients are a ubiquitous feature of ecosystems at all spatial scales, and can be used to infer a wealth of information about ecosystem structure, organization, and health. Studying how local scale biotic gradients change through time, especially in response to environmental change, has enormous potential to help us understand how communities may respond in the future to global change and anthropogenic impacts. Although regional-scale (10-100 km) biotic gradients have been heavily studied, and are generally thought to have high preservational potential in shallow marine settings, relatively few studies have investigated the preservation potential of local-scale (< 10 km) gradients. This project investigates whether (and how faithfully) local scale biotic gradients can be preserved in the rock record by performing a live-dead analysis on populations of recent benthic foraminifera collected from along a strong local-scale (~ 1km) energy gradient in Graham's Harbor on San Salvador Island, The Bahamas. To analyze the living community, we counted all living foraminifera found attached to Thalassia seagrass and Halimeda algae from 6 locations (with 3 collections made from each location) along a transect matching the orientation of the energy gradient. To analyze the dead community, we identified and counted 100 dead foraminifera from sediment surface assemblages corresponding to each living collection. Within the living community, the energy gradient (weak to strong from the interior of Graham’s Harbor up towards North Point) produces a biotic gradient in the changing ratios of Sorites to Planorbulina foraminifera. The extent to which these ratios are recorded in the dead community therefore indicate how well the fossil record may preserve this community information. Here, I present the preliminary results of live-dead analyses, which include over 1800 individual foraminifera across 37 genera. These results will provide new data on the quality of the spatial fossil record in marine environments, as well the potential for using benthic foraminifera to study the responses of local-scale biotic gradients to environmental change.