PALEOENVIRONMENTAL POTENTIAL OF ENCRUSTING FORAMINIFERA ON EXPERIMENTALLY-DEPLOYED MOLLUSC SHELLS, SHELF/SLOPE SETTINGS, BAHAMAS

Sediment-inhabiting foraminifera (forams) are known for their biostratigraphic and paleoenvironmental utility, while little is known about the diversity, relative abundance, and depth distributions of foraminifera that encrust carbonate hardparts. Indeed, results show that experimentally-deployed shells harbored a high diversity of forams at all depths compared to metazoan encrusters (e.g., bryozoans, annelids): up to 40 foram species were present during the first and second year at shelf (15-70 m) and slope (88m to 262 m) depths, AA transect, Lee Stocking Island, Bahamas. Although diversity remained similar during the first two years, relative abundance of certain species had a distinct temporal component. Within the first year, over 2000 forams encrusted the shells (n=32 shells), but 95% of these forams were from shallow (<30 m) water; outer shelf and slope shells had limited numbers of forams. After two years, forams occurred in greater numbers at outer shelf depths (70-88 m) with high relative abundance; at the deepest depths, foram abundance was higher than the first year. After six years, relative abundance of shallow shelf forams was greatly affected by Gypsina planawhich completely encrusted many of the experimental shells and "overgrew" metazoan encrusters. Encrusting forams also appear to be excellent depth indicaters, albeit temporally affected: within the first year, calcareous forams (Acervulina,Planorbulina) and agglutinated Cornuspiramiawere abundant at 15 m; Planorbulina,Cibicides, and Tritaxis-likeagglutinated forams were common between 30-70 m; below 70 m, agglutinated taxa were rare. After two years, Gypsina spp., Homotrema rubrum,and Planorbulinawere common to abundant at shallow shelf depths; agglutinated Placopsilinaand Tritaxis-likeforams were common in the outer shelf and a diverse agglutinated assembage occurred at slope depths. Because many of these encrusting forams have a fossil record (but imperfectly known), we posit that these often overlooked protists would make excellent paleoenvironmental and temporal indicators in regard to paleobathymetry and retention time above the sediment-water interface.