Paper No. 160-3
Presentation Time: 9:00 AM-6:30 PM
DID HURRICANE JOAQUIN ALTER THE ONSHORE-OFFSHORE ZONATION OF ENCRUSTING FORAMINIFERA AT SAN SALVADOR, BAHAMAS?
Benthic foraminifera that are firmly attached to hard substrates (encrusting foraminifera) have been studied as part of the reef ecosystem and in actualistic studies to aid in paleoenvironmental reconstructions of shallow-water carbonates. A common research technique is to investigate their distribution by collecting cobble-sized pieces of reef rubble and other clasts from a range of environments. One benefit of focusing on encrusting foraminifera is that they are less likely to be transported out of their habitats than are free foraminifera. However, even large clasts can be transported great distances during high-energy storm events, an issue that has caused some concern for researchers. The small Bahamian island of San Salvador provides a good test case as its encrusting foraminifera are well known, and the island was impacted directly by a major hurricane.
Hurricane Joaquin, a category 4 hurricane with sustained winds of 130 mph, which moved very slowly (5-6 mph), impacted San Salvador in early October 2015. With storm surge as high as 15 ft in some areas, it eroded cays and deposited sediment on the island itself. We visited the island March 13-18, 2016 (5.5 mo after the event). Cobbles were examined in situ, and 5 or more specimens were collected from the following, previously studied sites: Telephone Pole Reef, Dump Reef, and Salt Pond 1 (near-shore); Snapshot Reef and Salt Pond 2 (patch reefs); Gaulin's Reef (bank barrier reef); and Vicki's Reef (platform margin). The south end of the island at French Bay was the site of an extensive rubble field and sand dunes; samples were taken there as well.
Previous studies on San Salvador have shown that near-shore assemblages are dominated by well-preserved Homotrema rubrum; lagoonal patch reefs are varied but typically have prominent Planorbulina spp.; bank barrier reefs are dominated by Homotrema rubrum but with some Gypsina plana; and shelf-margin assemblages are dominated by large Gypsina plana.
At Dump Reef (north end of island) one cobble was clearly overturned, and the high proportion of Planorbulina on cobbles found there may indicate transport shoreward from the lagoon. Similarly, shoreward transport likely occurred at the near-shore site at French Bay. Other sites were not affected; overall, the pattern of distribution observed previously was still intact.