GROWTH OF ATTACHED (ENCRUSTING) BENTHIC FORAMINIFERA IN THE FIRST YEAR OF SETTLEMENT, SAN SALVADOR, BAHAMAS

Actualistic studies of attached foraminifera can be used to improve interpretations of ancient depositional environments in carbonate regimes. Our previous research has shown a distinct zonation of foraminifera attached to the underside of cobbles at San Salvador, Bahamas, especially along an onshore-offshore transect in Fernandez Bay: Homotrema rubrum was very abundant and well preserved near the shore, Planorbulina dominated a diverse community at a mid-shelf site, and Gypsina plana covered much of the surface at the platform margin. In order to examine distribution and rates of growth in these zones, we attached travertine tiles to concrete blocks and deployed them in March 2011 in the three areas, at depths ranging from 1-2 m near shore to 31 m on the wall at Vicki's Reef. Blocks were recovered after 3 and 6 months. Previously deployed blocks provided one-year data from the near shore and platform margin, and from sites elsewhere on the island. Tiles were retrieved and analyzed for encrusting growth by foraminifera and non-foraminifera such as crustose coralline algae. All encrusters were counted and their areas determined by using ImageJ.

The settlement experiments described herein represent the first phase of our program: growth within the first year. Consistent with the existing literature, our findings show that early settlers were a low-diversity assemblage of opportunists: chiefly Planorbulina acervalis, Acervulina inhaerens, Cornuspiramia sp., and small Nubecularia. On the platform top, Planorbulina was the dominant species overall, occurring in the first 3 months along with Acervulina and Nubecularia. Homotrema rubrum was essentially absent within the first 6 months, but was fully developed by one year. In general, attached foraminifera in shallow water were conspicuously more abundant at one year, with assemblages dominated by Planorbulina, Homotrema, and patches of Nubecularia covering over 90% of surfaces in some quadrats. At the platform margin, encrusters were scarce and foraminifera were especially rare and small. Gypsina plana was found only here, where it was represented by two small (~4 mm) specimens. The settlement dynamics of the second half of year one, growth in subsequent years, and the contrast between platform top and platform edge sites will be the subjects of continued research.