Pulley Ridge is new frontier

Coming Monday: Technical divers who are the first to explore Pulley Ridge are using cutting edge rebreather technology.

 

BY TIMOTHY O'HARA

Citizen Staff

 

PULLEY RIDGE — A small craft hovers over a slimy purplish red creature feeding on small organisms, as a diver combs the dark terrain, scooping up a spineless creature that looks so bizarre, it couldn't possibly be from Earth. The vessel and explorer drift off into the cobalt blue abyss in search of more species.

"We've got worms," a voice from the vessel radios to the mother ship, as the sub crosses a field of tubular white invertebrates.

A small red grouper swims by, reminding the diver that he's not on Mars or the moon, but exploring a coral reef hundreds of feet below the surface of the Gulf of Mexico. The reef offers as many questions for scientists as outer space, but it's a lot closer to home, and to some degree, a lot less explored.

Very few people have made the 250-foot descent down to Pulley Ridge. Fishermen knew it was a grouper and tilefish habitat and that there were sponges down there, but it was not until last month that it was really explored on foot — or , in this case, on fin.

A submersible vessel made the journey in the late 1990s and allowed scientists to see it. Last month, a few brave souls dove the reef and for the first time man was able to touch it. The trip also led to the most profound research of the area ever, scientists said.

A collection of the world's leading coral ecologists, scientists and divers embarked on a scientific armada to Pulley Ridge, 150 miles west of the Dry Tortugas, from June 22 to July 2. The goal was to search the sea floor in search of coral, fish and other unusual sea life that call the deepest coral reef in the continental United States home.

The research trip was reminiscent of early space exploration of the 1960s. Instead of a moon rover and space suits, they had a one-person submersible, a remote operating vessel and some of the most high tech diving gear the world has to offer.

The research project is a collaborative effort among the Harte Research Institute, Mote Marine Laboratory, Florida Keys National Marine Sanctuary, U.S. Geological Survey, the University of South Florida and the Florida Institute of Technology. The goal was to map, photograph and collect specimens.

Researchers with the organizations are still analyzing the treasure chest of samples brought back and are cataloging information. The Harte Institute and state Department of Environmental Protection provided $50,000 for the research trip and the sanctuary donated funding, equipment and manpower totaling another $50,0000, organizers said.

The research ships Tiburon and Sun Coaster served as floating laboratories and sample depositories and the Florida Keys marine sanctuary boat Irene C housed some of the scientists and researchers. The RV Bellows, using side-scan sonar, conducted days of mapping to give scientist a better picture of its size. Pulley Ridge encompasses 700 square miles, but the area's showpiece, the dense patch of colorful agaricia coral, is in a much smaller section of the southern tip of the ridge.

David Guggenheim, Sylvia Earle, G.P. Schmahl and other internationally renowned scientists took turns working the submersible and taking video images of the reef, as hardcore technical divers dove the dark depths to collect the samples. Crews worked through the night to process samples and made one of the expedition's most interesting findings with the help of the night skies: the discovery of a bioluminescent algae that could yield clues to the corals' health.

Earle, oceanographer and the National Geographic Society's explorer-in-residence, called the reef "enormously rich with life and diversity."

"It's like a beautiful garden," said Earle, who viewed the reef the first time via a submersible in the late 1990s on a National Geographic/NOAA Sustainable Seas Expedition.

The coral on the reef is exceptionally healthy compared with many shallow reefs in the Florida Keys and Caribbean. The reef may be isolated from the mainland but it is not immune from some of its problems. And the reef sits downstream from the notorious "dead zone" that forms each year in the Gulf at the mouth of the Mississippi River. However, strong currents, clear blue water and possible symbiotic relationships among organisms could allow it to thrive.

Scientists are puzzled about how the agaricia coral survive and thrive in deep water with such little light. Other coral reefs lie no deeper than 150 feet, but the Pulley Ridge reef sits below 250 to 275 feet of water, coral ecologist Wes Tunnell said. The 10-day research trip allowed some of the leading coral researchers to explore the relationships among coral, bioluminescent algae, red grouper and other creatures that call the reef home.

The goal was not only to explore and sample, but possibly to lay the groundwork for better management of this very special, but fragile area.

 

The creatures

The iridescent multi-color coral called agaricia served as the main lure to Pulley Ridge. Scientists collected samples of the red, purple and blue lettuce-like coral and its neighboring green, leafy algae called anadyomene.

Corals are some of the only animals that need sunlight to flourish. They have a relationship with zooxanthellae, single-celled dinoflagellates living in the surface tissues of stony corals. During photosynthesis, zooxanthellae draw in large amounts of carbon, some of which they pass on to their host polyp.

The vertical distribution of living coral reefs is usually restricted to the depth of light penetration, which is why most coral reefs are in shallow waters. At Pulley Ridge, the clear cobalt blue water and strong currents definitely lift some obstacles blocking the sun, but scientists wonder if it is enough.

The answer to Pulley Ridge's coral health could be tied to another symbiotic relationship, between the coral and a bioluminescent bacteria. Scientists discovered bacterial strains that glow in the dark and range in intensity and color from a neon green to greenish blue, said Kim Ritchie, manager of microbiology research at Mote Marine Laboratory in Sarasota, who likens the bacteria's properties to "superpowers."

Corals have never been shown to harbor bioluminescent bacterial symbionts. The glowing bacteria may help the coral access additional light. Ritchie speculates that the Pulley Ridge corals could also use the bioluminescence in the bacteria to attract zooplankton, a coral food source, she said.

"How come these corals have adapted to a lot less light? These are the same species of coral that are found in shallow reefs off the Florida Keys," Ritchie said. "The exact significance in coral ecology is not known. It's not even clear if there are enough of these symbionts to play a significant role in the deep-sea corals biology."

Some deepwater fish species, such as the flashlight fish and anglerfish, use bioluminescent bacteria for survival. The anglerfish, which lives hundreds of feet below the surface, has strategically placed bioluminescent bacteria in a pouch that hangs from its head and looks and acts like a fishing rod. Other fish are attracted to this lure and get eaten.

Researchers stumbled across the bacteria while going through samples at night aboard one of the research vessels. They were going through specimens with a flashlight and noticed a strange light coming out of the water. The scientists have taken the samples to Mote's lab in Sarasota and are in the process of identifying the bacteria. They also don't know if the bacteria lives in the polyp or in the slimy surface mucus that covers the coral.

"They're incredibly spectacular," Ritchie said. "I and others at Mote have had the most fun watching them since we returned from the cruise. They light up the corner of my lab, when the lights are out .... It's eerie."

Another interesting find that perplexed scientists and required extra research was the discovery of a field of wispy, fragile calcium carbonate tubes created by segmented worms. The worms build the tubes as a source of shelter. The tubes line the sea floor 250 feet under the surface. The tubes are so delicate that propulsion from the submersible thrusters uprooted some branches and blew them about the sea bottom.

The tubes are created by small animals scientists speculate are polychaetes, a small invertebrate that creates the hollow calcium-carbonate as a form of protection. The creature has small, feather-like tentacles that grab passing plankton and other small animals as meals.

"They may be a new species. I have never heard of this type of worm being discovered in the Gulf regions. This is all new," Guggenheim said.

Explorers also brought back an 8-inch-wide nudibranch, a type of sea slug resembling a snail without a shell. The creature normally breathes through long, feathery projections on its back called cerata. Nudibranchs use these projections both for breathing and for defense against predators.

"It's huge," said Guggenheim, a member of the Harte advisory board and conservation policy expert. "I haven't seen anything like this anywhere around here or anywhere in Caribbean and Atlantic. This is very unusual."

For those not stuck to the bottom, the red grouper is the main ecosystem engineer of the reef, Earle said. The grouper burrow holes and pile up debris to create habitat. The grouper use the burrows to attract prey. Scientists at Woods Hole Institute analyzed a video from the area and found 250 burrows per square kilometer, each hole about 10 to 20 feet across and 1 to 2 meters deep.

Their importance can't be overlooked, Earle said. She worries about fishermen overfishing the grouper population there and upsetting the delicate balance of the deep-water ecosystem.

 

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