Benthic Foraminifera at Platform-Margin Reefs, San Salvador Island, Bahamas
Wave and tidal action focused at the shelf edge preclude the establishment of seagrass-macroalgal communities in the unstable sandy seafloor. Halimeda and non-calcareous algae typically grow only on hard substrates, such as coral heads and rubble. Epiphytal foraminifera found on Halimeda are rare and are dominated by Cornuspiramia, Acervulina, and Planorbulina. Those found on soft algae resemble platform-top assemblages except for high proportions of the rotaliids Amphistegina gibbosa and Asterigerina carinata compared to the miliolids Archaias angulatus and Cyclorbiculina compressa.
Large tests found in the sediment on slopes at the platform margin are dominated by platform-top taxa (chiefly Archaias and Cyclorbiculina), which are commonly highly altered taphonomically. Ledge assemblages, in contrast, contain a suite of free-living agglutinates that are not found in shallow-water habitats. Also present are a significant number of attached species, some cemented on loose grains and others that have been broken free of their attachment sites on the wall above. Indigenous assemblages (found live) can be recovered from protected areas such as reentrants in the wall, where introduction of transported tests is minimized. These include Nubecularia(?), Haddonia(?), and Sporadotrema. Thus, platform-margin foraminiferal faunas are distinctive and may reveal the nature of the platform-edge bathymetric profile.