Standing Crop versus Sediment Assemblages of Large Benthic Foraminifera in Sea-Grass Habitats at San Salvador, Bahamas

Olivia Claire Buchan
Auburn University, Department of Geology and Geography
Auburn, AL
[email protected]

The purpose of the present study is to investigate the relationship between large (> 1 mm) foraminifera living on vegetation and those found (live and dead) in the sea-floor sediment. One objective was to establish substrate preference for the dominant foraminiferal taxa. Furthermore, we hypothesized that, because most taxa are phytal, both species composition and relative abundance of foraminifera in the sediment would correspond to the types and overall density of the vegetation.

Six localities, representing a range of vegetation densities, water depths, and water-energy conditions were selected. Algae and sea-grass densities were recorded in 50x50 cm grids located at 10m intervals along transects. Sediment and vegetation samples were collected for each locality and were preserved in buffered formalin. Sediment samples and vegetation were examined for foraminifera. Live specimens were recognized by the presence of colored protoplasm. Total foraminiferal density was recorded as the number of individuals per plant and per gram of sediment picked.

Preliminary results show that Thalassia and Halimeda are the favored substrates for the dominant phytal foraminifera: Cornuspiramia, Sorites, and Planorbulina. Archaias and Cyclorbiculina are rarely attached to vegetation but are the most plentiful taxa in the sediment, even as live individuals. Thus, the assemblages do not match. Cornuspiramia, Sorites, and Planorbulina are susceptible to breakage and therefore less likely to be preserved in the sediment, whereas Archaias is more durable. Foraminiferal density in the sediment corresponds to vegetation density to some degree, but other factors (possibly water energy and nutrient supply) also play a role.

AAPG Search and Discovery Article #90033©2004 AAPG Foundation Grants-in-Aid