RESTORING THE OCULINA BANK CONTINUES... MARCH 24, 2001
Sandra Brooke - Principal Biologist
Larval Ecology Department Division of Marine Science
Harbor Branch Oceanographic
It's a clear calm Saturday morning in March, the R/V EDWIN LINK (formally the R/V SEA DIVER) leaves the dock at Harbor Branch Oceanographic Institution for a one-day cruise to the Oculina Banks, about 16 miles offshore. The Oculina Bank supports a highly diverse deepwater ecosystem that is comparable to tropical reefs and is found only off a small portion of the Florida coast. We are here to help save this vital reef. By the early 1990s, heavy commercial fishing had directly contributed to the extensive coral destruction and greatly reduced the populations of grouper and snapper which feed and spawn off these reefs. Bottom trawling, dredging, bottom long lines and anchoring that destroys this delicate coral have decimated large portions of the Oculina Bank.
UNIQUE NATURAL TREASURE THREATENED
Most of the corals that we are familiar with live in the warm "gin-clear" waters of Earth's tropical oceans. The Ivory Tree coral, Oculina varicosa, however thrives in the often murky and chilly waters of Florida's Atlantic coast. In the shallows it forms stout wave resistant colonies that are colored golden brown by the tiny algal symbionts that live in their tissues. Progressing deeper along the shelf, these branching colonies become more fragile and pale as their symbionts are starved for light. At 100m on the shelf edge, the corals blossom into giant thickets of delicate white branches. These tangled reefs are home to hundreds of different kinds of invertebrates and provide essential habitat for many commercial fisheries species. The deep Oculina reef habitat exists nowhere in the world except the short tract of shelf edge between Fort Pierce and Canaveral. A small area of the reef system has been under protected status since 1984 when it was designated a Habitat of Particular Concern; but most of the reefs have been subject to destructive forces, which have reduced these ancient systems to rubble. With the loss of their food and shelter, the inhabitants of the reefs have either died or moved away, leaving behind a barren wasteland. In 1996 a restoration effort was initiated to try and bring back some of this important habitat, but without information on how and when the corals reproduce, or how far the larvae can travel, we are merely guessing at the best way to regenerate the reef.
Since 1998, we have been conducting research into the reproductive ecology of both the deep and shallow forms of the coral. The reproductive period of O. varicosa begins in late spring when the eggs and sperm begin to form in the mesenteries of the coral polyps. These gametes continue to develop until the late summer when the corals begin to spawn. O. varicosa is a broadcast spawning species that releases eggs and sperm into the water column. Unlike many tropical reef corals, Oculina does not spawn in a single synchronized event, instead, colonies continue to release gametes over a period of about one month. The eggs and sperm combine and develop into planktonic larvae called planulae. These tiny creatures are carried by the water currents until they find somewhere to settle and begin to form a new colony. A single large Oculina colony can produce many thousands of eggs or millions of sperm, so although larval mortality rates are high, there are many larvae in the plankton with the potential to re-colonize damaged areas of the reef tract. Despite protection and high recruitment potential, the damaged reef shows little signs of recovery.
HELPING MOTHER NATURE
One of the reasons may be lack of suitable substrate to settle on, since some of the reef has been reduced to fine rubble. Between 1996 and 1999, 56 large concrete structures were placed in various parts of the reef to assess coral recruitment rates. In 1998, a small colony of new coral growth was observed on one of the blocks at Jeffs Reef, using the JOHNSON SEA LINK submersible. In September 2000 the R/V Ferrel carried Chief Scientist Chris Koenig and collegues out to a damaged area of the Oculina banks to deploy 105 large reefballs and 450 smaller recruitment discs. Some of these reefballs and discs had small pieces of coral transplants attached in the hopes of initiating coral overgrowth. These artificial substrates will be visited in coming years to assess colonization and transplant survival. We will also be studying the genetic variability of the reef using small DNA sequences called microsatellites. This will give us some insight into the genetic exchange (i.e. larval transport) between reef tracts. We are beginning to understand enough about the biology of the coral to make an intelligent attempt at restoration, but we are still on the steep part of the learning curve with a long way to go.
The primary objective of this cruise was to recover an acoustic doppler current meter that was deployed on the western side of the reef by HBOI's "Rescue" ROV during a cruise on the R/V SEWARD JOHNSON II (formally the R/V EDWIN LINK) in April 2000. The meter measures current speed and direction, and water temperature. This information, combined with data on the reproductive biology of the coral, will provide some insight into where the coral larvae might be carried, and how much potential exchange there might be between different areas of the reef. This information is important to a restoration effort; if there is a good supply of larvae into damaged areas, the potential for re-colonization is higher than if larval supply is low. Preliminary measurements of fecundity (egg production) of female coral polyps show that a single polyp can produce over 1000 eggs. If we multiply polyp production by the number of female polyps in an entire reef, the numbers of eggs produced in a single spawning season rise into the millions. Despite massive productivity, the numbers of larvae that survive to produce adult colonies are relatively few. Another of the cruise objectives was to survey the large concrete blocks that were deployed by Dr Koenig of FSU/NMFS between 1996 and 2000, and count the number of new coral colonies that had established on the structures.
If the colonization rates are low, we may need to transplant healthy corals into damaged areas to "kick start" the recovery process. The problem with transplantation, apart from expense and logistics, is the possibility of transplant mortality. In 1999, eighteen small concrete blocks with pieces of coral attached to them were deployed using the JOHNSON SEA LINK submersible and the R/V SEWARD JOHNSON. A third cruise objective was to survey these small blocks and assess transplant survival. We also wanted to collect some pieces of live coral for some genetic work and growth rate studies, and some dead Oculina rubble to look for signs of new coral colonies that had established on the dead rubble substrate.
ALWAYS AN ADVENTURE
We arrived on station, after a smooth transit, at 9.15am and launched the submersile CLELIA on the first dive at 9.45am. Dr Young and myself were in the sub along with pilot Ben Chiong. The visibility on the surface was great, over 50ft, but as often happens, once we reached the bottom at 80m, the visibility was reduced to approximately 5m. Back on the ship, John Reed (Senior Scientist in HBOI's Division of Biomedical Marine Research) and the sub techs helped Ben navigate around the complex reef system. After about 30 minutes, we found the current meter marker buoy, but during the recovery process, the sub blew a fuse and lost the vertical thrusters. We had to back away from the reef and set the sub down, while Ben wriggled into the confined rear section and replaced the fuse. This left me nominally "in charge" of the sub with instructions to 'hold her still'. Since we could barely see the substrate, the instructions were rather moot, but after 10 minutes Ben wriggled back into the pilots seat and we resumed our aborted hunt for the elusive current meter. With a lot of luck and some great navigation, we found the meter again and Ben adroitly recovered it safely. At this point we terminated the first dive.
On the surface the current meter looked quite unlike the shiny instrument that we deployed one year previously. Apart from the hundreds of barnacles that had encrusted the entire outer case, a small octopus had taken up residence in the PVC handle. He was quite upset at the rude invasion of his privacy and inked profusely until relocated in his PVC refuge into a clean bucket of water. The octopus will be donated to the new Smithsonian exhibit in Fort Pierce.
After a break for the submersible battery to re-charge and lunch of giant burgers, cooked on the grill, we once again descended to the reef to try and fulfill our other objectives. This time Maria Baker, a PhD candidate from Southampton Oceanographic Center in England, was the other observer and Tim Askew Jr. was the pilot. We hoped the visibility might improve with time, but despite a current change the conditions were still quite poor. We collected some rubble and 12 small samples from live colonies around the southern edge of the reef, but even finding the recruitment blocks and transplants was out of the question. We did find however, that trash, especially monofilament fishing line, had become an integral part of the reef. Many of the small colonies along the reef edge were so entangled with fishing line, rope or other garbage that we could not collect the sample. Several of those that we did manage to collect we also entangled with line. During the second dive, the topside science crew (Dr Cathy Allen, John Reed, Bill Hoffman and Eric Edsinger-Gonzalez) were busy filling coolers with clean seawater to accommodate the live specimens. Once the sub was back on the ship after the second dive, there was the usual flurry of activity to get animals in clean water and samples in fixatives.
Once all was safely stowed, we headed back to port with a great dinner, beautiful sunset and calm seas. We did not achieve all our objectives; frustration unfortunately is part of the scientific process. The reef will keep some of its secrets for another day, but thanks to the combined efforts of the submersible techs, the ships crew and the science party, the cruise was an overall success.