GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 273-10
Presentation Time: 3:45 PM


LEWIS, Ronald D.1, TICHENOR, Hal Ray2, SMITH, Christopher Wayne3, EUBANKS, Eric M.4, GILLEY, Sara Elizabeth5, ASHER, Sarah1 and SUNDBECK, Sally6, (1)Department of Geosciences, Auburn University, Auburn, AL 36849-5305, (2)Tetra Tech, Orlando, FL 32801, (3)Department of Geosciences, University of Georgia, Athens, GA 30602-3636, (4)Wood PLC, Blue Bell, PA 19422, (5)Anchor, QEA, LLC, Birmingham, AL 35243, (6)Department of Geosciences, Middle Tennessee State University, Murfreesboro, TN 37132

Benthic foraminifera that are cemented by calcium carbonate or are otherwise firmly fixed to hard surfaces are known as encrusting or attached foraminifera. This report summarizes actualistic research on distribution done by the team at Auburn University from 2008 to present at three of the outer islands of the Bahamian archipelago: San Salvador, Cat Island, and Mayaguana. Our primary approach has been to collect reef-rubble cobbles with additional data from deployed travertine tiles. In the laboratory, the underside of cobbles were washed, photographed, and examined with binocular microscopes in 10 cm2 quadrats. Taphonomic grades were assessed, and the area of each test was measured using ImageJ.

Early on we recognized a pattern in Fernandez Bay, San Salvador: Homotrema rubrum dominated nearshore assemblages; lagoonal assemblages were diverse although characterized primarily by Planorbulina; and platform-margin reef had numerous very large tests of Gypsina plana. In addition, Nubecularia was commonly found nearshore, and Haddonia was restricted to the platform margin (neither had been reported from the Bahamas previously). Samples studied in 2008-2015 were used to assess the effects of Hurricane Joaquin, a category 4 hurricane with sustained winds of 130 mph, which hit the island in October 2015. Although some cobble transport apparently took place near shore, the overall onshore-offshore zonation observed previously was not disturbed.

The same onshore-offshore zonation was found at nearby Cat Island. Importantly the average size of Planorbulina and H. rubrum and the overall density was seen to decrease with distance from shore. The same pattern of assemblages, size, and density was seen on Mayaguana. Here water and sediment samples were recovered from underneath the collected cobbles in order to assess the potential food items. The amount of meiofauna in the sediment correlated with the size trends observed; less food appears to have resulted in fewer and smaller foraminifera. Furthermore, some foraminiferal taxa appeared to be linked with categories of meiofauna; e.g., H. rubrum and crustaceans.

Research opportunities abound. Very little is known of the systematics, significance of morphotypes, modes of feeding, the presence of photosymbionts, and life histories in general for most encrusting species.