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Coral Coring in Flower Garden Banks National Marine Sanctuary—a Collaborative Effort
U.S. Geological Survey (USGS) scientists participated in a multiagency cruise during the week of May 23 to collect coral cores for paleoclimate studies in the Gulf of Mexico. The cruise was a milestone for managers at the National Oceanic and Atmospheric Administration (NOAA) Flower Garden Banks National Marine Sanctuary and researchers from Texas A&M University, who had postponed the cruise six times because of dive-boat engine failures or bad weather. This time it went off without a hitch—no mechanical glitches with the dive boat (merchant vessel Fling), the best weather the boat operators had seen in a long time, and a drilling team composed of some seasoned veterans from both NOAA and the USGS. In addition, Emma Hickerson, research coordinator for Flower Garden Banks National Marine Sanctuary, was able to gather a group of coral-disease researchers from Mote Marine Laboratory, George Mason University, and NOAA to look into a recent occurrence of white-plague disease in the sanctuary. The plague is the first-recorded coral disease for the area and has sanctuary management concerned about the future health of the pristine coral-reef system. Flower Garden Banks National Marine Sanctuary is composed of three banks (East Flower Garden Bank, West Flower Garden Bank, and Stetson Bank) and encompasses an area of approximately 40 mi2. The coral reefs cap the tops of salt domes that are believed to have formed approximately 10,000 years ago. East and West Flower Garden Banks are home to an almost-unheard-of 80-percent live-coral cover; Stetson Bank contains few corals as a result of its close proximity to the coast. For additional details on the Flower Garden Banks, visit the Flower Garden Banks National Marine Sanctuary Web site. The primary focus of the cruise was to collect coral cores from two species: Montastraea faveolata and Siderastrea radians. Three cores of M. faveolata were recovered from East Flower Garden Bank, and two from West Flower Garden Bank; the longest core measured 2.1 m. The estimated growth rate of this species is approximately 10 mm/yr; thus, the long core will provide a record going back about 210 yr. At West Flower Garden Bank, two S. radians heads were cored, and a 2.2-m-long core was recovered. On the basis of S. radians' typical growth rate of about 4 to 6 mm/yr, that core will give researchers an unprecedented record back some 500 years for the Flower Garden Banks area. This cruise is the first on which such long coral cores have been collected within the marine sanctuary boundaries. The cores will be analyzed for δ18O value, which will be used as a proxy indicator of paleoclimate sea-surface salinity and temperature for the Flower Garden Banks area of the Gulf of Mexico. Amy Bratcher (Ph.D. candidate at Texas A&M University and one of the drillers during the cruise) will slab the cores, sample the core slices, and run the samples on an inductively coupled plasma mass spectrometer (ICP/MS). In addition, Chuck Holmes (USGS, St. Petersburg, FL) will use laser-ablation ICP/MS techniques on the core slabs to observe variations in trace-metal contents. Variations in trace-metal contents within the coral skeletons may lead to a better understanding of Mississippi River discharge in the Gulf of Mexico, as well as fluctuations in the Gulf of Mexico Loop Current. These results, the first obtained for the Flower Garden Banks area, will provide new insights into coral growth and other physical-oceanographic processes. None of this work would have been possible were it not for the well-rounded cast of drillers and support divers assembled by Emma Hickerson. The corals were drilled by three teams, each consisting of three divers. This arrangement worked well because diving in water depths of 65 to 80 ft required divers to spend 2.5 hours at the surface between dives to avoid physiological problems. Continually rotating the three teams allowed each team to conduct three to four dives each day. All participants brought a wealth of knowledge about the Flower Garden Banks and shared their previous experiences in coral coring.
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in this issue:
Summer Internship at the USGS National Wetlands Research Center New Web Site About Indian Ocean Tsunami Public Forum About Coral Degradation Hurricanes: Predicting Their Path of Destruction
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U. S. Department of the Interior | U.S. Geological Survey
cover story:
