Benthic Ecology Program
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| Jim K. Culter Senior Scientist, Program Manager |
| The Benthic Ecology Program focuses on the science and ecology of bottom-dwelling organisms and how these organisms respond to environmental disturbance. The Program, created in 1979, has conducted hundreds of research projects and monitoring studies in partnership with federal, state and local agencies as well as partners in business and industry. The Program’s projects include shellfish restoration and monitoring in places like Pine Island Sound and Boca Ciega Bay and the investigation of “blue holes,” which are former springs and sinkholes that formed on the west Florida continental shelf during a period of lower sea level. The program also investigates coastal springs. The Benthic Ecology Program has also coordinated large multidisciplinary projects such as environmental assessments in conjunction with other Mote research programs focused on manatees, sea turtle, fisheries, ecotoxicology, phytoplankton ecology, sharks and coral reefs. |
| Oil Spill Response Following the explosion of the Deepwater Horizon Oil Rig in the Gulf of Mexico in 2010, Mote scientists gathered baseline samples of water, sediment, total organic carbon and bottom-dwelling organisms like oysters, clams and seagrasses from sites in Sarasota Bay, barrier island beaches and Charlotte Harbor, Fla. Scientists also assisted the National Oceanic and Atmospheric Administration’s Mussel Watch program in collecting oyster samples from Apalachee Bay, Fla., to the Florida Keys. |
| Depth Charge: Exploring Blue Holes in the Gulf of Mexico Reprinted from Mote Magazine |
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| The journey might not take them to the center of the Earth, but when the four divers gear up to explore a blue hole in the Gulf of Mexico, it looks as if they could be headed there. First, there are the tanks: Lots of them. Each diver needs a minimum of four per dive; one for the trip down, two large tanks for the deepest part of the dive and another tank of pure oxygen for the final 20 feet of ascent. There are gauges to measure gas supply (at these depths, divers don’t breathe just air, which would become toxic; instead they use mixes of helium, oxygen, nitrogen), a dive computer and a back-up computer to measure depth and time. Then there are dive lights — because it’s dark 200 to 400 feet below the surface of the Gulf of Mexico — and dive reels — because once you go into a hole, you need to find your way back out again. The divers also have various water and biological sampling devices and video and still cameras to record what they see. And, of course, there are the more standard diving accoutrements: mask, fins, wetsuit, dive boots, dive knife, buoyancy compensation device, or BCD. All told, when they’re finally geared up, the divers are lugging at least 200 extra pounds from one side of a rocking boat to the other before they finally slip into the water with about as much grace as a car shoved off the roof of a building. So what drives this group to such extreme dives? “These are habitats that have never been scientifically explored before,” says Jim Culter, Mote senior biologist who since 2005 has been leading a team of technical divers in the first-of-its-kind scientific exploration of the Gulf’s blue holes. “Very little is known about them. Do fish aggregate here for reproductive reasons? How important are they as habitat? Are they connected to our freshwater aquifers?” Other questions include whether they are a source of nutrients and whether they are a source for freshwater to discharge into the Gulf of Mexico. BLUE HOLE BASICS To understand Florida’s blue holes, you first have to understand that most of Florida is built on porous limestone. For millions of years, acidic rain and groundwater flowed through the limestone, in some cases dissolving it into crags and crannies that eventually became underground caverns and conduits. Some of these caverns collapsed, forming sinkholes. Generically, much of Florida’s underlying geologic structure is known as “karst terrain,” defined by caves, springs, underground drainage systems and sinkholes, which are still swallowing homes today. One of the most well known sites inland is Weeki Wachi Springs in Central Florida, which is at least 400 feet deep and is only now being explored by divers. Others include Warm Mineral Springs and Little Salt Spring in Sarasota County. Given that Florida’s west coast once extended at least 100 miles west before the last rise in sea level, it’s no surprise that similar karst features can be found today in the Gulf of Mexico, Culter says. “It’s sort of like a honeycomb,” he says. “There’s no reason to think that offshore would be much different than what we find inland. Probably these features existed closer to shore as well, but they’ve been filled in by sand and shell.” Much of Culter’s exploration has been based on information he and his group have gleaned from fishermen or the small group of advanced divers who focus on extreme diving. Better-known sites were first described by adventure divers 10 to 20 years ago, but ignored by science. Because fish such as amberjack, hogfish and various species of grouper tend to congregate at the mouths of blue holes, it’s mainly fishermen who have found the locations first. Getting them to divulge a spot, though, isn’t easy: Every angler has a secret fishing hole, and most hold the information the way diplomats hold state secrets — passing them around is akin to high treason in some circles. “The funny thing about it, though, is that just about every time we’ve been out to dive a blue hole, a fishing boat has shown up,” Culter says. “So I don’t know how secret these spots really are. Plus, lots of these places have multiple names, and there’s quite a bit of fishing debris down there.” THE DRAMATIC DEEP The deepest site is known as the “Green Banana,” a blue hole about 425 feet deep located 50 miles off Sarasota. The group has also discovered what may be the largest offshore Florida cave: Megadome, about 40 miles off Sarasota. “Megadome has to be the most dramatic blue hole we’ve explored,” Culter says. “There’s this tiny opening that ends in this huge cavern.” When Culter says “tiny” he’s not kidding. The only known opening to Megadome begins at 140 feet deep and is about 30 inches across. “We leave our tanks on,” Culter says. “The opening is just big enough to get through with a bit of bumping and wiggling.” Extra tanks for traveling to the site and back up to the boat, though, are left outside the cave near the anchor line. “The end of the line on a cave reel is attached to the tanks to make sure we can find them on our way back, especially if visibility deteriorates,” Culter says. The divers also attach additional emergency tanks at key points on the anchor line as back up. Preliminary mapping by Culter and crew indicates that Megadome is 210 feet from its roof to the floor, which seems to be about 365 feet deep, and 75 feet across at the top and 250 feet across at its bottom. Another surprise at Megadome is the fact that there is a marine fouling community inside — sponges, sea squirts and tube worms — 250 feet down. A resident goliath grouper and an occasional nurse shark also use the entrance to the tunnel into the cave but tend to stay near its ceiling. “The most productive areas of blue holes are at the rim and 10 to 15 feet out from the rim,” Culter says. “Fish don’t usually go deeper than 10 to 30 feet inside the rim of the blue holes. The bottom of most of these holes is below the anoxic layer, which contains hydrogen sulfide, and the bottom is anaerobic, meaning there’s no oxygen that deep, so nothing lives there except bacteria. Once it gets darker and colder, the diversity drops off really fast.” Culter has left thermographs — devices that measure temperature over time — in many of the holes and then later retrieved them. The one from Megadome was the first to show sharp temperature changes over 16 days in July, indicating tidal pumping. “That’s the biggest surprise,” Culter says. “We thought temperature would be static below a certain point. The main thing it shows is that there is water movement. That leads to questions: Where is it going? Is there a saltwater aquifer there? We also saw a hurricane effect with storms pushing warm surface water deep into the holes.” The blue hole called Diamond Rock Cave west of Sarasota also has a fouling community and indications of tidal pumping. “Such fluctuations are known to occur in terrestrial sinkholes near Florida’s west coast,” Culter says. “The implication here is that marine sinks or springs may serve as a direct conduit to the Florida freshwater aquifer.” With the research coming to a close, Culter is happy with the initial findings, but he hopes to find new funding to continue exploring Florida’s unique offshore features. “These dives are so deep that we can only spend a short period of time — minutes really — actually exploring inside the blue holes,” he says. “We spend a lot of our time coming back up to the boat during decompression stops that sometimes take an hour or more. “There isn’t any scientific data published about these habitats, so everything we learn is new. There’s so much we don’t know about these blue holes that it’s exciting to be studying this piece of Florida’s natural history.” —This study was supported in part by the National Oceanic and Atmospheric Administration Ocean Exploration Program. Support has also been provided by volunteer divers: Al Barefoot, Eric Reintsema, Bruce Robertson, Eric Osking and others. Curt Bowen, publisher of Advanced Diver magazine provided additonal information about dive locations and historic mapping efforts. |
About Us
Mote Marine Laboratory has been a leader in marine research since it was founded in 1955. Today, we incorporate public outreach as a key part of our mission. Mote is an independent nonprofit organization and has seven centers for marine research, the public Mote Aquarium and an Education Division specializing in public programs for all ages.
