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Systematic Mapping of Bedrock and Habitats along the Florida Reef Tract—Central Key Largo to Halfmoon Shoal (Gulf of Mexico)

USGS Professional Paper 1751

by Barbara H. Lidz, Christopher D. Reich, and Eugene A. Shinn

Introduction: Table of Contents Project Overview Project Objective Geologic Setting Primary Datasets Primary Products - Overview Maps & Evolution Overview: Introduction Depth to Pleistocene Bedrock Surface Reef & Sediment Thickness Benthic Ecosystems & Environments Sedimentary Grains in 1989 Summary Illustration Index Map Evolution Overview Tile-by-Tile Analysis Organization of Report Tiles: 1, 2, 3, 4, 5, 6, 7/8, 9/10, 11 Summary Acknowledg- ments References Disclaimer Related Publications

Tile 1 Geography Sector-Specific Studies Geologic Highlights Rodriguez Key Sinkhole Captain Roy's Reef Grecian Rocks Key Largo Dry Rocks Mosquito Bank, White Bank, Coral-Rock Ridges, and French Reef Carysfort Reef The Elbow Molasses Reef and Little Molasses Island Pickles Reef Molasses Reef and Little Molasses Island: Molasses Reef is a major reef that juts out from the margin in the Tile 1 sector (Fig. 33A, 33B). When the Gulf Stream meanders close to the shelf edge, Molasses Reef becomes vulnerable to ship groundings. One of the most damaging and best-documented groundings in the Florida Keys occurred at Molasses Reef in August 1984, when the M/V Wellwood ran hard aground and caused extensive damage. The ship pulverized ~5,000 m2 of reef (e.g., Hudson and Diaz, 1988). The Marine Sanctuary received $6.5 million in compensation in 2002. One year after hollow cement modules were placed on the site as "artificial reefs," they were encrusted with corals and sea whips and populated with fish and crustaceans. It has taken 19 years to achieve mitigation through renewed growth of the benthic community, but it has been suggested that the site is not likely to return to its pre-collision state within the next 100 years (J.H. Hudson, personal communication, 2003). Little Molasses Island is no longer an island but the name remains. The reef is adjacent to and just north of Molasses Reef (Fig. 33A). Perkins (1977) recovered ~32.7 m of coralline limestone belonging to the Q4 and Q5 Units in a 45-m-long core drilled from a truck-mounted drill rig at Little Molasses Reef. The bottom of the Q4 Unit was not penetrated. The site represents the thickest Q4-Q5 section cored in south Florida. continue to: Pickles Reef

Coastal & Marine Geology Program > Center for Coastal & Watershed Studies > Professional Paper 1751