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Paleoshorelines and Spawning Groupers—Deep Diving at the Shelf Edge, Northeastern Gulf of Mexico

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Technical diver Lance Horn poses during a decompression stop.
Above: Technical diver Lance Horn (NURC/UNCW) poses during a decompression stop. Support divers were standing by in a small boat whenever the technical divers were in the water. Additional safety for the divers was provided by a recompression chamber onboard the Liberty Star. Photograph by D. Kesling (NURC/UNCW). [larger version]

Chris Koenig, Kathy Scanlon, and Julia Knisel examine rock samples obtained by divers.
Above: Happy scientists Chris Koenig, Kathy Scanlon, and Julia Knisel (left to right) examine rock samples obtained by divers. At least two distinct rock types were recovered: a carbonate-cemented oolitic sandstone from the long ledges of the paleoshoreline outcrop and what appear to be concretions of shells and other carbonate material from shelf-edge pinnacles. Photograph by M. Tubridy (United Space Alliance). [larger version]

From March 21 to 28, 2005, Kathy Scanlon and Julia Knisel of the U.S. Geological Survey (USGS) Woods Hole Science Center were in the northeastern Gulf of Mexico collecting rocks near the West Florida shelf edge. The work was conducted from the National Aeronautics and Space Administration (NASA)'s 176-ft retrieval ship Liberty Star, one of two ships built to recover the Space Shuttle's solid rocket boosters and return them to Kennedy Space Center for refurbishment. Owned by NASA and operated by the United Space Alliance, the ships also support other missions, such as scientific investigations.

Collecting rocks at water depths of 75 m (nearly 250 ft) was not a trivial task—it required a remotely operated vehicle (ROV) equipped with video cameras, and a team of four divers qualified to do deep technical diving, breathing specially mixed gases instead of ordinary air. The divers could stay on the bottom for about 15 minutes and needed to spend 1 to 1.5 hours at shallower depths for decompression. Rock outcrops were first located using the ROV, and then the divers followed the ROV cable to the bottom and set to work quickly with chisels and sledges to collect fresh rock samples.

The cruise was part of a collaborative effort between USGS geologist Kathy Scanlon (Woods Hole, MA) and Florida State University (FSU) biologists Felicia Coleman and Chris Koenig (Tallahassee, FL). Coleman and Koenig are studying the effects of fishery-closed areas on spawning grouper populations. The ROV was used to assess the numbers and sizes of gag, scamp, red grouper, and other fish at numerous sites both inside and outside the protected areas, and to observe spawning behavior. Many of these fish spawn at rocky shelf-edge outcrops that are believed to have been formed along paleoshorelines during the Pleistocene, when sea level was considerably lower. Analyses of the rocks collected on this cruise will help determine their age and environment of formation, knowledge that may lead to refinement of paleo-sea-level curves. It will also allow us to model where similar paleoenvironments may occur, information that is very useful for fishery management. In addition, compositional analysis may help shed light on the mystery of why groupers spawn at some outcrops but not at others.

Funding for this work came from the National Oceanic and Atmospheric Administration (NOAA)'s National Undersea Research Program (NURP) through the National Undersea Research Center at the University of North Carolina, Wilmington (NURC/UNCW), which paid for the ship time and provided the technical divers, the ROV, and the ROV operators.

Julia Knisel stands by to assist technical diver Doug Kesling as he gets ready to enter the water. A curious red grouper watches as technical diver Jay Styron
Above Left: Julia Knisel (USGS, right) stands by to assist technical diver Doug Kesling (NURC/UNCW) as he gets ready to enter the water. Each diver carried about 200 lb of gear, including four tanks (two on his back and one under each arm) in order to have enough gas of various mixtures for the deep depths and for the decompression. Photograph by K. Scanlon (USGS). [larger version]

Above Right: A curious red grouper watches as technical diver Jay Styron (NURC/UNCW) prepares to break off a rock sample. Photograph taken by L. Horn (NURC/UNCW) using the ROV. [larger version]

Related Sound Waves Stories
Shelf-Edge Habitats in the Northeastern Gulf of Mexico—Multi-Agency, Interdisciplinary Field Work
June 2000

Related Web Sites
Woods Hole Science Center
U.S. Geological Survey (USGS), Woods Hole, MA
NOAA's Undersea Research Center at UNCW
University of North Carolina, Wilmington (UNCW), National Oceanic and Atmospheric Administration (NOAA)

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May Publications List

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