Distribution of Encrusting Foraminifera At San Salvador, Bahamas: a Comparison By Reef Types and Onshore−offshore Zonation

Abstract

Foraminifera attached permanently to hard substrates have received relatively little research attention in distributional studies compared to free-living specimens. Because attached (encrusting) species are commonly found on hard substrata, such as coral rubble, and they are sensitive to environmental variables controlled by water depth and distance from shore, these species can be useful in paleoecologic research. This study examined the distribution of encrusting foraminifera found at the outer Bahamian island of San Salvador to describe onshore-to-offshore zonation and to characterize foraminiferal assemblages found in different reef types. Cobbles were collected along two transects on the leeward side of the island and at numerous locations on the windward side, including a bank barrier reef and the eastern platform edge. Encrusting foraminifera found on the undersides of cobbles were quantified and identified by taxa, morphotype, and taphonomic grade. Significant differences were found in the distribution of encrusting foraminiferal species across the carbonate platform, based on both counts of individuals and area of substrate covered. The zonation was particularly evident between platform-top and platform-margin assemblages. Nearshore assemblages were dominated by well-preserved Homotrema rubrum. Patch reefs, especially those found further from shore, were characterized by a relatively diverse assemblage with prominent Planorbulina spp. whereas bank barrier reefs were dominated by H. rubrum, often with Gypsina plana. Platform-margin assemblages were the most distinct because they were dominated by large, sheet-like G. plana, with other taxa being small, sparse, and poorly preserved.