U.S. Geological Survey

Oculina Bank - Geology of a Deep-Water Coral Reef Habitat off Florida

Figure 1

Figure 1. The Experimental Oculina Research Reserve off Florida's east coast was established in 1994 to protect gag grouper spawning areas from overfishing.

Shelf-edge prominences, or limestone "pinnacles," lie near the 80-meter depth contour off east-central Florida (fig. 1) and extend tens of meters above the surrounding sea floor. Because mounds of the deep-water coral Oculina varicosa grow on the pinnacles, the area has come to be called Oculina Bank. Oculina Bank provides habitats for many species of reef-dwelling fish. One species that is particularly important to commercial and recreational fishermen is gag grouper. These fish aggregate at the pinnacles each year to spawn; this behavior makes them particularly vulnerable to overfishing.

In 1984, the South Atlantic Fishery Management Council (SAFMC) recognized the special significance of the habitat and designated Oculina Bank as a Habitat Area of Particular Concern. This action closed a 92-square-kilometer area to trawling, dredging, longlining, and trapping. In 1994, the SAFMC created the Experimental Oculina Research Reserve (EORR), which closed the same area to all bottom fishing for 10 years. The area was closed in order to allow the National Marine Fisheries Service (NMFS) to evaluate the effectiveness of the reserve for the management and conservation of reef fish. The U.S. Geological Survey (USGS) and NMFS, in cooperation with Florida State University, collaborated in 1995 to collect continuous-coverage sidescan-sonar data (fig. 2) and sediment samples in the EORR and a nearby control area. Concurrently, scientists from the two organizations made submersible and video photography observations to estimate the distribution and abundance of fish and to describe the surficial geology of the sea floor.

Figure 2 Figure 2. This small piece of the sidescan-sonar mosaic of the Experimental Oculina Research Reserve (EORR) and the corresponding depth profile show several reef pinnacles. The brightest areas in the mosaic are created by the hard rock and coral of the pinnacles. Other bright areas are covered by coarse-grained sediments (sands and gravels); the darker areas are covered by finer sands and silts. The north-northwest streaks suggest current scour by the strong Gulf Stream currents that flow through the EORR. Arrows in the depth profile indicate four reef pinnacles.

The initial research revealed that much of the habitat designated for protection by the EORR had already been destroyed or damaged (figs. 3 and 4). Oculina varicosa is a fragile, branching coral and grows only on the limestone pinnacles. Three decades of dredging and trawling in the area had crushed many of the delicate corals. The scientists concluded that recovery of the overfished grouper population would not be possible without the restoration of the Oculina Bank habitat. USGS scientists, by interpreting the sidescan-sonar mosaics (fig. 2) and sedimentological data, identified areas of former and current Oculina growth. NMFS scientists used this geologic information to choose sites for live coral transplant experiments. In 1996, the first live Oculina colonies were collected by a remotely operated vehicle (ROV), attached to concrete-block modules (fig. 5), and carefully lowered to the sea floor. By 1998, 56 of these experimental coral transplant modules had been deployed with the hope that they will provide information necessary for restoring the Oculina Bank habitat.

Figure 3

Figure 3. This photograph of Jeff's Reef in the Experimental Oculina Research Reserve was taken in 1980, before the area was heavily fished. Notice the numerous fish and the heads of living Oculina varicosa in growth position. (Photograph by R. Grant Gilmore, Harbor Branch Oceanographic Institution.)

Figure 4

Figure 4. The area shown in this photograph (taken in 1995) typifies the Oculina Bank habitat after many years of damage from trawling and dredging. The broken coral rubble comprises dead specimens of Oculina varicosa. (Photograph by Christopher Koenig, Florida State University.)

Figure 5 Figure 5. This chunk of living Oculina varicosa, a fragile, branching, deep-water coral, has been secured to a transplant module made of concrete blocks. The module will be lowered to the sea floor, where it is hoped that the coral will grow and eventually help restore the shelf-edge reef habitat that is used by spawning grouper and other fish. (Photograph by Christopher Koenig, Florida State University.)

Coral transplantation appears to be a viable restoration strategy. Video data collected in 1997, 1998, and 1999 by an ROV confirmed that the transplants are alive and growing. It is estimated that a 6-centimeter-wide transplant colony will grow, at a rate of 1.6 centimeters per year, to a 0.5-meter-diameter coral head in 15 years. The video images also showed new settlement and recruitment of other species to the modules.

For more information, please contact:
Kathryn M. Scanlon
U.S. Geological Survey
384 Woods Hole Road
Woods Hole, MA 02543-1598
Telephone: (508) 457-2323
E-mail: kscanlon@usgs.gov

Christopher C. Koenig or Felicia C. Coleman
Institute for Fishery Resource Ecology
Department of Biological Science
Florida State University
Tallahassee, FL 32106-1100
Telephone: (850) 644-4509
E-mail: koenig@bio.fsu.edu

      Christopher T. Gledhill or Mark Grace
National Marine Fisheries Service
3209 Frederic Street
Pascagoula, MS 39568-1207
Telephone: (228) 762-4591, ext. 284
E-mail: cgledhil@triton.pas.nmfs.gov

Also see U.S. Geological Survey Open-File Report 99-0010 at

U.S. Department of the Interior
U.S. Geological Survey
                                                  USGS Fact Sheet 108-99
October 1999

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