DISTRIBUTION OF ATTACHED (ENCRUSTING) FORAMINIFERA ACROSS A CARBONATE PLATFORM, SAN SALVADOR ISLAND, BAHAMAS: PRELIMINARY RESULTS

In general, benthic foraminifera cemented to hard substrates have not received as much research attention in actualistic distribution studies as have free specimens. However, these attached (encrusting) species are worthy of study for numerous reasons: (1) They occur in seafloor sediment samples where they are attached to sand- and pebble-sized grains and as partial tests broken from their substrates. (2) Because they are also cemented to larger clasts and to stationary objects such as coral heads, attached foraminifera are less likely to be transported and abraded than are free tests. (3) Some flourish within a narrow range of environmental conditions, such as the low-light levels found in cavities and crevices. (4) Consequently, studies of ancient limestones have shown the applicability of attached foraminifera in paleoenvironmental reconstructions. The purpose of this study is to investigate the distribution of attached foraminifera from shore to the shelf edge and along a range of environmental gradients on a small, isolated carbonate platform.

Field work took place at San Salvador Island, Bahamas, primarily in May 2008. Using SCUBA when necessary, clasts were collected along a shore-to-shelf-edge transect through Telephone Pole Reef in Fernandez Bay (lee side of island), through the channel at Cut Cay (North Point), in various coastal caves, and at numerous spot localities. Marble tiles attached to concrete blocks were deployed to study settlement. In the laboratory, attached specimens were counted in 10-cm² quadrats and their taphonomic conditions were recorded.

Zonation results primarily from differences in relative abundance of the same taxa/morphotypes in different zones and from differences in average taphonomic states. In Fernandez Bay, midshelf assemblages had the highest diversity and were typically dominated by Planorbulina, with minor amounts of Cornuspiramia and Homotrema and/or Miniacina. Major taxa at shelf-margin sites were Gypsina plana, Nubecularia(?), and Planorbulina. Many of these were relatively poorly preserved. Surprisingly, the shallow subtidal sites nearest to shore had assemblages with the highest abundance and best preservation. Homotrema/Miniacina was dominant here, with a wide range of morphotypes; Nubecularia(?) was also present along with minor Gypsina plana.