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Reefs and Wrecks
September 12-14, 2000
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We awoke before dawn to the sound of thunder that seemed to reverberate through the hull of the Gordon Gunter. Slipping across my stateroom in the dark, I peered from the porthole at a dramatic view. Great forks of lightning lunged from dark clouds, illuminating white-capped seas. Violent rains pelted my window, and I had a hard time imagining we would have any luck getting the sub in the water that day.
But by 7:00 a.m. as we mustered to the fantail to begin predive checks on the subs, the storm had passed us by, leaving in its wake a breathtaking sunrise and a vibrant double rainbow. Laura Francis was first to dive, this time exploring the slope just off the southern edge of Riley’s Hump (due north of Miller’s Mountain). In the afternoon, at a site nearby, coral researcher Erich Mueller continued exploration of this slope.
Riley’s Hump is an ecologically important seamount south of Loggerhead Key. It is densely covered with hard corals and richly populated with the diverse fish, invertebrates, and algae that make up a shallow coral reef system. While the top of the hump has been explored to some extent both by scuba divers and, during last year’s SSE mission, DeepWorker pilots, little is known about the surrounding areas. Where, exactly, does the hump drop off into deeper waters? How steep is that drop? What is the substrate like on the slope? What fish live there? How deep do hard corals continue to thrive there? What is the overall health of hard corals found in this area? Our hope was to find answers to some of these questions.
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Two fishing boats were almost on top of our planned dive site, a strong sign that this is a productive spot, but one that could be at risk for overexploitation. During her 3-1/2 hour dive, Laura saw no less than ten abandoned lobster traps, another sign that this spot, while unexplored by scientists, is well known to some of those who make their living by catching the local wildlife.
Starting at about 70 feet [21 meters], Laura began exploring the slope. In these shallower depths, she observed good coral cover, and numerous sponges, and completed two fish count transects. Moving down slope to 150 feet [46 meters], hard corals disappeared, unable to thrive at those depths. On sandy bottom with scattered rocky rubble, she completed another fish count, then headed back to shallower waters for one last fish survey before low voltage forced her to surface.
Erich Mueller, a scientist from Mote Marine Laboratory and a specialist in coral diseases, had several goals for his dive. He hoped to gather data on the maximum depth at which hard corals could be found at this site, assess the health of the corals in the area, and establish protocols for coral assessment transects with DeepWorker.
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He landed on sandy bottom on the shallow side of the slope, and found patches of hard coral interspersed with sandy bottom. Following the contour southwest, he observed fish and lobster traps, as so many of us have during our dives. Moving down slope, he found sparse corals down to 95 feet [29 meters], but none deeper, and returned to shallower waters. Coral health at this site compared favorably with that of corals closer to inhabited islands further up the Keys, but some signs of coral disease were, unfortunately, apparent. And it became clear that it is difficult to adhere to a formally structured set of transect lines, as he ended up following the natural contours of the bottom rather than maintaining the planned north-south headings.
That night, we had one of the most difficult planning meetings of the mission, trying to decide how best to spend the last day of the Dry Tortugas leg of our mission. Numerous options were considered, and by the time the meeting ended, it was still not entirely clear what the plan would be. But for starters, we had decided to have the ship gather more bathymetric data during the night, working one of the sites near Sherwood Forest that was of interest to Erich Mueller.
Emerging the next morning, I learned that we were at the site prosaically referred to as the “ballast pile.” The name of the site belies the potentially exciting nature of the site, as sanctuary staffer John Hollis explained. During the 1600s, a fleet of Spanish ships had been lost in the channel between the Florida Keys and Cuba. The so-called “ballast pile” was believed to be the wreck of one of those ships, discovered by fishermen who noticed anomalies on their depth finders, and by a trawler who brought up several clay pots in his nets.
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But whatever is left of this ship has been on bottom a long time. The ship’s structure itself has likely disintegrated and been torn apart by centuries of storms and decades of trawling. While we could identify the general vicinity of the remaining wreckage, it would be difficult to find it, buried under silt and sand, and scattered over a wide area. Kip Evans, freshly returned from a trip to his home in California, piloted the sub to around 200 feet [61 meters] in search of evidence of the wreck. Searching the area for three hours, he did indeed find some objects that might have been part of the wreck, but it will be up to future explorers to more thoroughly document this important cultural resource.
Our final dive of the day, and of the Dry Tortugas portion of the mission, was back at the area near Loggerhead Key. Erich Mueller continued efforts to document the corals in the area, and to test his transect methods. As before, he found that the corals were limited to the shallowest areas, generally less than 80 feet [24 meters]. This finding serves to emphasize the importance of protecting those few and relatively small areas in which coral reef communities are able to survive and thrive.
Tonight, we head back to Key West, where we will prepare for an open house on board the ship, in conjunction with education programs and a visit from the Secretary of Commerce and other dignitaries, including a delegation from Indonesia. The end of the field season is almost upon us. While we are feeling a great sense of accomplishment for everything we’ve achieved during the 2000 field season, I, for one, am sad that the end of the mission is so near. There is so much more exploring left to be done!
—Gale Mead
Sustainable Seas Expeditions
[Note: nationalgeographic.com does not research or copyedit dispatches.]