Monday, August 26, 2002

WILMINGTON, NC – Decades of research into how corals reproduce, learning to grow larvae in the lab, and re-seeding dead reefs are part of a pioneering effort in Florida to save declining elkhorn and mountainous star coral from extinction. In the midst of the annual coral spawning cycle, the two scientists leading the effort are once more diving into slick, fishy-smelling waters off Key Largo to gather batches of spawn.

In the late, dark hours of the night, just before the moon rise, reef-building corals throughout South Florida and the Caribbean repeat an ancient ritual: Each coral polyp releases a small bundle of gametes that represents the coral’s yearly attempt to reproduce and maintain its species. Scientists call this event a “mass spawning.”

The release is highly synchronized among colonies so that a virtual soup of gametes from hundreds, even thousands, of colonies forms a slick on the ocean surface. In this way the corals improve the chance of gametes from adjacent colonies fertilizing each other’s eggs, to produce a large number of coral larvae, or planulae. The tiny planulae (less than 1 mm long) live in the water column, at the mercy of currents, tides and predators, for several days until they are ready to descend and attach to the bottom, and with a lot of luck, grow into a new coral colony.

The exact timing of spawning is synchronized by some aspect of the lunar cycle that scientists still do not understand. But researchers have learned from experience what the timing is, and so can be there during the mass spawning to help the corals improve their chances of reproductive success. Drs. Alina Szmant from University of North Carolina at Wilmington’s Center for Marine Science, and Margaret Miller from NOAA Fisheries Southeast Science Center, co-leaders of a team that also includes researchers from the University of Miami, have been working for years to develop methods to capture large batches of the spawn as they are released by the corals, fertilize and culture them in various field and laboratory enclosures, and then help the planulae settle onto coral reef surfaces that have lost their live corals.

“With live coral cover declining at an alarming rate throughout the region because of temperature stress and disease, there are fewer adult corals left to reproduce, and thus fewer planulae being produced. Even under the best of circumstances few planulae survive to settle, and many are transported by currents away from reef areas during the water-borne period. In the end, there really aren’t enough larvae coming back to the reefs these days to do an adequate job of re-seeding them,” said Szmant.

Miller and Szmant are working with two of the most important reef-building species, the elkhorn coral Acropora palmata (which is being considered for Endangered Species status) and various species of mountainous star corals, Montastraea spp. Elkhorn coral generally spawns from two to four nights after the full moon of August, usually one-and-a-half to two hours after sunset, but has been known to skip years for unknown reasons. The star corals reliably spawn six to eight nights after the full moon, two to three hours after sunset.

Spawning, once it begins, only lasts 30 minutes, so the scientists need to be ready to work fast. Before dusk they place special collecting nets over the corals, and then mount a vigil to watch for “bundle setting,” when the pink bundles become visible though the polyps’ translucent tissues.

“When the corals mass spawn, divers feel like they are in the middle of a snow globe,” said Szmant. As soon as the corals finish spawning the collectors are brought back to the research vessel (the NOAA Florida Keys National Marine Sanctuary has been supporting their work with the 67-ft. R/V Odyssey) where the spawn from a large number of colonies are carefully mixed to obtain the highest rates of fertilization. In the ocean, if weather conditions are poor, the gamete soup may be too dilute and most of the eggs can go unfertilized and wasted. Then comes a week of intense effort to tend to the health of the developing “coral babies” before the larvae are encouraged to settle within experimental reef sites.

Over the years, the researchers have learned to laboratory culture the larvae in small batches of thousands, and are now developing methods to scale up to millions of larvae in field chambers. “Approaches to restore coral reefs lag way behind those we use to restore terrestrial ecosystems,” stated Dr. Miller. “After ship groundings, we have developed effective engineering approaches such as cementing boulders to restore lost reef complexity. But decades later we find that the reef-building corals themselves, the most critical component for the reef habitat to sustain itself, have not returned. The approach our team is pioneering in Florida is aiming to ‘replant’ these structure-building corals.”

Miller is particularly interested in the elkhorn re-seeding efforts since NOAA-Fisheries is considering listing this coral as an Endangered or Threatened species. “If you slice through any major spur and groove formation on Florida and Caribbean reefs, you find that they were built by elkhorn corals. Today we can barely find a few patches of live elkhorn on Florida reefs, and many of these remnants are infested by snail predators and disease,” Miller added.

This conservation-oriented work is the culmination of decades of work by Szmant and her coi-workers to describe basic aspects of the reproductive biology of reef corals. She began this research with National Science Foundation funding back in 1983, but her recent work has been funded by National Sea Grant’s Fisheries Habitat Program and the NOAA-Fisheries Coral Reef Initiative.

“It has taken a long time to tease these secrets from the corals. With the whole event done and over with in less than one hour (out of over 8,700 hours per year), you just have to be lucky to be out there the first time at the right time. And that right time is late at night, offshore, in the dark. We’ve been chased away many times by squalls and thunderstorms just at the crucial moment. It’s been difficult to assemble all of the personnel and equipment to get as far as we have. Only now, when coral reefs world-wide are in serious trouble, is there funding and interest in coral reef restoration,” said Szmant. “It would have been much easier to learn how to do all this when corals were healthier and more abundant.”

While the scientists recognize that it will take a long time for their efforts to pay off, or even to know whether their methods have been successful (corals started last year are now only 1 cm in diameter; it takes decades for a star coral colony to grow one foot high), they are determined to keep on trying. They are encouraged onwards each year by the magnificent experience of the spawning event itself. “It is such an amazing sight, we need to make sure it’s there for future generations to enjoy,” said Szmant.

For more information contact:

Dr. Alina Szmant (305)453-4792 or (910)262-2144

Dr. Margaret Miller (305)479-3386