Other Features
Secrets of
a Hidden Habitat:

The Quest to Understand and Rebuild the Oculina Banks

In this extreme close-up view, individual coral animals can be seen covering the branches of an Oculina thicket.
(photo: J. Reed)

Notes from HBOI Chief Scientist, John Reed --

No one knows for sure why there are extensive areas of dead coral on these reefs. Some may be due to irresponsible fishing, and some may be due to natural processes. Perhaps the coral has been infected with diseases like their shallow water counterparts. The reefs also saw activity in World War II when the Germans used the reef structures to hide their submarines and our Navy tried to bomb them. In very deep water (> 2000 feet) another coral called Lophelia also forms pinnacle-like reefs that are several hundred feet tall. These too have extensive areas of dead coral rubble and were never trawled or bombed.
Hundreds of feet beneath the rolling waves off Florida's Atlantic coast, a sub pilot flew his small craft low over a trackless plain of barren sand. Seated next to him, a marine biologist held her notepad ready...but the cold, dark scene yielded nothing worth noting. The spherical, transparent cockpit of the JOHNSON-SEA-LINK (JSL) sub afforded a panoramic view of an underwater desert passing through beams of artificial daylight shining from the sub's xenon arc lamps. A voice from the research vessel above crackled over a small speaker. "Don...we have you approaching it at heading 0-3-2, that's 0-3-2. You should be seeing it in about 10 seconds."

The pilot slowed the sub's thrusters...the biologist craned foward, squinting into the darkness. Indistinct forms moved in the shadows--large shapes darting, branches of coral slowly coming into sight. In seconds, the human visitors found themselves in the midst of a thriving oasis--all around them, huge thickets of delicate white coral teemed with fish life, from schools of tiny tropicals to large predatory grouper. They had arrived at the Oculina Banks -- a mysterious, hidden reef ecosystem unlike any other in North America.

Oculina varicosa--the Ivory Tree Coral--forms the backbone of this critical habitat. While some Oculina live in the shallows like most other corals, the deep-water Oculina are bizarre little animals, quite unlike those that decorate tropical vacation brochures. The most obvious difference is the environment in which they live; 150 - 300 feet beneath the surface in waters that are icy cold, midnight dark, and not in anyone's snorkeling guidebook. The darkness relates to another important difference between the deep-water Oculina and other corals--that being the Oculina's lack of zooxanthellae.

Zooxanthellae (zoo-zan-thelly) are a type of algae that live in a symbiotic relationship with corals. They take up residence inside living coral polyps, where they absorb light from above and convert it into energy. Zooxanthellae are responsible for giving coral polyps their color, and for providing a good bit of the food that their corals use to live and grow. Shallow water corals cannot survive long without their algal symbionts. Yet the colorless, thriving thickets deep off the Florida coast show that the Oculina have found a way.

Another odd characteristic of the Oculina reefs is that they do not build true hermatypic reefs. Most of the animals we think of as reef building corals build on top of the stony remains of previous generations. Generation after generation lives, dies, and leaves behind a stony foundation for future growth. The Oculina, on the other hand, doesn't form such solid underpinnings. As the colony grows, the new branches prevent water flow to the center of the colony, which subsequently dies. Burrowing animals invade the dead coral, hollowing out the center of the tree-like formations. This makes the Oculina exceedingly fragile, and eventually the colony collapses on itself, the new branches continue to grow and the process continues, creating large, unconsolidated thickets. Unlike hermatypic reefs which are solid, these thickets are very easily crushed and damaged, a tendency which has combined with human encroachment to disastrous effect.

From 1976 through 1985, Biologist John Reed of the Harbor Branch Oceanographic Institution (HBOI) worked to describe the distribution and structure of the Oculina Banks. Where nobody had expected to find corals at all, Reed found thriving coral thickets. The Oculina were used as spawning grounds for commercially important fish species such as gag and scamp grouper, as a mating habitat for squid, as nursery grounds for snowy grouper, and as feeding grounds for amberjack, porgy, and snapper. In a short time, Reed counted 350 species of invertebrates living among the Oculina branches, and discovered 10 previously unknown species of crustaceans. Although scientists had only just discovered this rich ecosystem, fishermen had been reaping a rich harvest over the reefs for several years.

In 1984, the South Atlantic Fishery Management Council designated 92 square miles of the Oculina Banks as a Habitat of Particular Concern, closing the area to mobile fishing gear. In 1994, the reserve was closed to all bottom fishing. Unfortunately, much of the northern extent of the deep Oculina thickets had been reduced to rubble. The specific cause of this damage is not known, but trawling nets with heavy rubber bumpers seem a reasonable guess.

A flurry of activity overtakes the aft deck of the Research Vessel SEWARD JOHNSON as biologists and technicians prepare the JSL sub for a dive.

Biologist Sandra Brooke affixes Oculina samples to small concrete blocks. The JSL pilot will grab the attached rope with the sub's robot arm and carefully place these samples in marked locations on Jeff's Reef.
One small, undamaged section of deep Oculina remains, in an area off Fort Pierce known as Jeff's Reef. A couple of weeks ago, I joined biologist Sandra Brooke on board the Research Vessel SEWARD JOHNSON (RVSJ) as she prepared for a sub dive on the reef. Brooke and biologist Chris Koenig from Florida State University are carrying out ongoing research on the Oculina ecosystem. While Brooke works to understand the Oculina itself, Koenig works to understand the fish populations that call the Oculina home.

As the RVSJ steamed seaward through calmly rolling water, I watched the green Florida coastline recede in the distance and enjoyed the brilliant, sunny day. Meanwhile, Sandra Brooke and company worked feverishly to prepare experiments for a sub ride. Sandra kneeled in front of the sub by a large cooler. This biological treasure chest held a dozen small coral branches, carefully labelled and zip-tied to small plexiglass plates. To Brooke's left lay a pile of small concrete blocks. Wrench in hand, the scientist set about gently attaching each coral branch to its own block. "These are samples of both shallow and deep-water Oculina," Brooke explained as her hands kept busy tightening bolts. "We're going to be setting these down among the deep water thickets to compare how they grow down there. If this works out O.K., pending a million additional things we have to learn, we may be able to use a similar technique to help restore damaged sections of the deep reef."

"If all goes well," I asked her, "how long will it take to restore the habitat this way?" I wasn't expecting the answer I got.

"A few hundred years." she said plainly,"but we have a lot yet to learn before we start being that optimistic. To help an animal live you have to understand how it lives, and we are just getting to know the Oculina."

If it takes centuries to restore the Oculina Banks to their former glory, it won't be for lack of effort. Brooke works long hours and weekends in her lab at HBOI, observing the Oculina lifestyle from just about every angle. She used genetic testing to determine that the shallow-water and deep-water Oculina are, indeed, the same species living in very different ways. She is growing shallow-water animals without the zooxanthellae they usually posess. She will attempt to grow deep-water animals with the zooxanthellae they wouldn't normally have. Growth rates are being measured for Oculina at various combinations of depth and temperature, with and without algal symbionts. And then there's the question of sex.

"My lab animals are spawning like mad," says Brooke with a chuckle. "It seems to be quite a wild party for them, so I can only assume they are happy." All of this mating activity has allowed Brooke to determine that the Oculina are 'broadcast spawners'--they mate by releasing large quantities of eggs and sperm into the surrounding water, and allow fertilization to happen according to the whims of the currents. Knowing this, scientists may be able to analyze currents in damaged sections of the Oculina Banks, and seed the 'downstream' sections of the reef with lots of nice places for baby Oculina to settle and grow.
These contrarian corals have been full of surprizes. Aboard the SEWARD JOHNSON, I stood on the aft deck as the JSL sub was hoisted aboard after a dive. Sandra had told me to be ready to work when she returned to the surface...new samples from the sub's collection buckets need to be carried very quickly into a refrigerated compartment on board the ship. When the sub settled on the deck, Brooke emerged from the hatch all smiles. Within seconds, she was handing me buckets of small coral samples and dashing off toward the cold room. In the rush, she exclaimed, "We found an AMAZING sample down there!"

Recently returned from the deep, Brooke holds a section of Oculina that has defied scientists' expectations.

The door to the cold room closed behind us, and Sandra excitedly drew my attention to the specimen in question. "This is a section of shallow-water Oculina that was placed on the deep banks by John Reed in the 80's. Look at how much it has grown! And it still seems to have it's zooxanthellae! That should not be possible, you know. Shallow water algal symbionts should never be able to survive in an environment that is that cold and dark. This is completely unexpected."

Later analysis in the lab confirmed that the zooxanthellae were alive and capable of photosynthesis after a decade in the depths. The phenomenon has scientists confounded...it is one of those results that opens up new, fundamental questions about the way that Oculina and algae interact. This one, smallish sample creates a lot more work for researchers who need to understand the Oculina before they help it thrive. I asked Brooke if "back-to-the-drawing-board" moments like this are discouraging.

"Not at all," she replied. "I'm going to be long dead before our work actually pays off with a restored reef. My contribution is just to lay the groundwork--to help understand what we need to know to start the restoration process. Unexpected results only take you farther from what you thought you knew. They get you closer to actually understanding."

"Do you plan on spending the rest of your life doing this work on the Oculina?" I asked.

Brooke thought for a moment, then replied. "Deeper water corals such as Oculina will be part of my long-term career, I think. But coral systems all over the world are threatened by damage, or have already been largely destroyed. I'd like to spend my life researching and teaching people what they need to know to stop the damage, and to repair it. Coral ecosystems are important to humanity because they provide spawning grounds for commercially important fish, and reefs are promising places to find potent new medicines. They are important to me because I've seen how beautiful they are--I've been enchanted by them. Healthy reefs are unique...irreplacable. Apart from any commercial considerations, I feel like something this complex and beautiful ought to be given a chance to...well, just to keep being."

Keep tuning in to @Sea, and we'll keep you updated on the progress of this long-term research project. If we're still online in a few hundred years, we'll be the first website to bring you live images of a fully restored deep-water Oculina reef!
© 1999, Harbor Branch Oceanographic Institution, Inc.