BENTHIC FORAMINIFERAL ASSEMBALGES AT CUT CAY: A MICROCOSM STUDY OF THE EFFECTS OF WATER ENERGY AND SUBSTRATE PREFERENCE, SAN SALVADOR ISLAND, BAHAMAS

As one of the outermost islands in the Bahamas, San Salvador is not frequented by tourists, and it has no large population centers; it is a good natural laboratory for studies of benthic foraminifera. On the northeast end of the island, a narrow N-S eolianite peninsula (North Point) separates the open Atlantic Ocean on the east from the semi-protected, shallow waters of Grahams Harbour. A wave-cut channel at Cut Cay connects the two realms. The high-energy channel and the lagoon's seagrass beds with scattered sand flats allow the effects of water energy and substrate type to be studied in a small area.

Field work was conducted in early May 2007 immediately after a storm front had impacted the area from the northwest. Localities were sampled in the channel (lagoon end), in the low-energy seagrass beds of the lagoon next to the ridge both north and south of the channel, in a sand bed on the western side of the area, and in the grass bed adjacent to the sand. The most common seagrass and algal species at each site were bagged separately. Seafloor samples were taken at 2 sites per locality within a grid 10 cm on a side. Foraminifers on the 2 most common species of plants and algae per site were recorded, totaling ~300 per vegetation species. Seafloor sediment was screened with a 3-phi sieve, live and dead individuals were counted, and taphonomic condition was noted.

The mostly live foraminifers found on vegetation displayed a substrate preference, which appears to have been strongly affected by the shape and relative size of the substrate. The flat, relatively wide blades of the common seagrass Thalassia testudinum had a low-diversity fauna dominated by the relatively large tests of Planorbulina spp. Assemblages on the small, branching fibers of Penicillus sp.capitulae were dominated by Rosalina; Planorbulina was essentially absent. Halimeda incrassata hosted a more diverse fauna including mainly the genera Rosalina, Discorbis, and Planorbulina. Seafloor assemblages were largely dead tests, but live/dead ratios and taphonomic states varied with water energy and vegetation density. The highest live/dead ratios and the best test preservation were found at the protected sites on either side of the cut. The most taphonomically altered tests were found in the lagoon's sand bed, which is subject to an active infauna in fair weather as well as storm waves.