2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 12
Presentation Time: 1:30 PM-5:30 PM


HALLEY, Robert B.1, HINE, Albert C.2, JARRETT, Bret D.2, TWICHELL, David C., Jr3, NAAR, David F.2 and DENNIS, George D.4, (1)USGS, 600 4th St. S, St. Petersburg, FL 33701, (2)College of Marine Science, Univeristy of South Florida, 740 7th Ave. S, St. Petersburg, FL 337091, (3)USGS Coastal and Marine Geology Team, 384 Woods Hole Rd, Woods Hole, MA 02543-1598, (4)U. S. Fish and Wildlife Service, 1339 20th St, Vero Beach, FL 32962, rhalley@usgs.gov

Pulley Ridge is a 100+ km-long series of N-S trending, drowned, barrier islands on the southwest Florida Self approximately 250 km west of Cape Sable, Florida. The ridge has been mapped using multibeam bathymetry, submarines and remotely operated vehicles, and a variety of geophysical tools. The shallowest parts of the ridge are about 60 m deep. Surprisingly at this depth, the southern portion of the ridge hosts an unusual variety of zooxanthellate scleractinian corals, green, red and brown macro algae, and typically shallow-water tropical fishes.

The corals Agaricia sp. and Leptoceris cucullata are most abundant, and are deeply pigmented. These corals form plates up to 50 cm in diameter and account for up to 30% live coral cover at some localities. Less common species include Montastrea cavernosa, Madracis formosa, M. decactis, Porities divaricata, and Oculina tellena. Sponges, calcareous and fleshy algae, octocorals, and sediment occupy surfaces between the corals. Coralline algae appear to be producing as much or more sediment than corals, and coralline algal nodule and cobble zones surround much of the ridge in deeper water (greater than 80 m).

More than 60 fish species share this unusual habitat. Commercial species include Epinephelus morio (red grouper) and Mycteroperca phenax (scamp). Typical shallow-water tropical species co-occur with deeper water fish along the ridge. Malacanthus plumieri (sand tilefish) and red grouper construct large burrows and mounds that serve as refuge for multiple species. Mounds and pits larger than 1m2 are apparent on side-scan sonar images and have been counted in excess of 200/km2 for parts of the ridge. Several factors help to account for the existence of this community. First, the underlying drowned barrier islands provided both elevated topography and lithified substrate for the hard bottom community that now occupies the southern ridge. Second, the region is dominated by the western edge of the Loop Current that brings relatively clear and warm water to the southern ridge. Third, the ridge is within the thermocline, a water mass that is known to provide nutrients during upwelling to shallow reefs in Florida.