ZONATION OF ATTACHED (ENCRUSTING) FORAMINIFERA ACROSS A SMALL CARBONATE PLATFORM, BASED ON SPECIES ASSEMBLAGES AND AREA COVERED, SAN SALVADOR, BAHAMAS

Foraminifera attached to hard substrates have received little research attention in actualistic distribution studies relative to free specimens. However, these attached (encrusting) species are useful as paleoenvironmental indicators for numerous reasons: (1) Because they are cemented to clasts and to stationary objects such as coral heads, attached foraminifera are less likely to be transported and abraded than are free tests. (2) They also occur in seafloor sediment samples where they are attached to sand- and pebble-sized grains and as broken tests. (3) Some flourish within a narrow range of environmental conditions, such as the low-light levels found in cavities and crevices. The purpose of this study is to investigate the distribution of attached foraminifera from shore to the shelf edge on a small, isolated carbonate platform, using two different data gathering techniques.

Field work took place at San Salvador, Bahamas, primarily in June 2008, May 2009, and June 2010. SCUBA was used to collect clasts along shore-to-shelf-edge transects through Telephone Pole Reef in Fernandez Bay and at Rocky Point, and through the channel at Cut Cay (North Point). Numerous spot localities were also sampled, including two sites on the windward side of the island. Clasts were examined with light microscopy in 10-cm² quadrats: attached specimens were counted and their taphonomic conditions were recorded. Clasts were photographed and area covered by each taxon was determined with image analysis (ImageJ).

Zonation results primarily from differences in relative abundance and area covered of the same taxa in different zones, as well as overall taphonomic states. The near-shore and bank-barrier reef assemblages show the greatest amount of foraminifera per area and are dominated in area and in counts by Homotrema rubra. Bank-barrier reef assemblages differ from the near shore ones by a relatively high proportion of Gypsina plana. Patch reefs assemblages show variability, but have a larger amount of Planorbulina and lower area covered than the near-shore. Assemblages in areas of low coral growth are similar in assemblage to patch reefs but are notably more barren in area covered. The assemblages at the wall were very distinct in having the highest area covered due to dominance by the larger foraminifer Gypsina plana.