PRESERVATION POTENTIAL AND CARBONATE BIOMASS OF EPIBIOTA: PROTIST COMMUNITIES FROM SUBTROPICAL AND POLAR SHELLY HABITATS

With increasing global climate change, organisms that depend on calcium carbonate to build their skeletons are in peril, and it is not just the corals that will be affected. Benthic foraminiferans too, may be at risk. These protists are vital in most marine communities, recycling carbon from phytoplankton, and in tropical regions of the world, they can form vast carbonate sediments. In contrast, encrusting foraminiferans are just beginning to be studied. Here, we present results obtained, in part, from field experiments to: 1) determine species and family diversity of foraminiferans that encrust molluscan shells; 2) approximate the amount of carbonate they may produce per square meter of habitat space; and, 3) compare these attributes between a subtropical and polar environment. Twenty-seven calcareous foraminifera species representing 13 families were present on experimental shells deployed after eight years in the subtropics (Bahamas, Shelf-Slope Experimental Taphonomy, SSETI, data). Of these, three families (Planorbulinidae, Acervulinidae, and Nubeculariidae) were the most common carbonate producers. In the Antarctic (Explorers Cove, McMurdo Sound), only four species of foraminifera representing three families (Trochamminidae, Rosalinidae, Cibicididae) encrusted the shells of the scallop, Adamussium colbecki. The dominant carbonate producer, unlike in the subtropics, is represented by only one family (Cibicididae). Foraminiferans on the SSETI subtropical shells deployed for eight years produce approximately 0.10g CaCO3/dm2 (1 g/m2 at 15 m water depth) in contrast to Antarctic encrusting foraminiferans that produce approximately 0.013 g/dm2 (0.13 g CaCO3/m2 at 18 m water depth). Solubility of CaCO3 in polar waters is great, with the majority of carbonate locked up in the living community rather than preserved in the benthos; in tropical regions, carbonate is preserved both in the benthos and living community. Any small change in geochemistry that reduces carbonate biomineralization will have a disproportionately larger affect on polar encrusting foraminifera because of their carbonate biomass. Therefore, global climate change may have a great effect on both these regions, but for different physical, chemical and biological reasons.