Gardens of the Gulf
A mass coral spawning event is just one of many marvels at the Flower Garden Banks.
By Melissa Gaskill
The Jell-O blue waters of the Gulf of Mexico undulate like a shaken carpet, a few boats rising on swells that roll from one watery horizon to the other. From the surface, the Flower Garden Banks National Marine Sanctuary, roughly 110 miles from the Texas shore, looks no different than the miles of gulf surrounding it.
But on this August night, some 60 feet below, a frenzy of activity begins — a mass coral spawning, or simultaneous release of eggs and sperm into the water column by millions of coral organisms. First documented here in 1991, the phenomenon occurs annually between seven and 10 days after the full moon in August. Spawning times for individual species are extremely consistent, often predictable within a few minutes. With a single exception, each species has a unique window of time in which it and no other species spawns, the chain of reproductive events filling the water with clouds of particles from tiny round pearls to irregular blobs, rising above the reefs like slow-motion rain in reverse.
"The reef is typically very quiet at night, except on the night of the spawn," says Peter Vize, professor of biological sciences at University of Calgary in Canada, and lead author of a research paper on the event. "All of a sudden, a large percentage of one species starts blowing out these giant clouds. When that species is finished, they all shut down and there is a little gap, then the next species goes off. It is an incredible transition over hours of crazed activity, quiescence and back to crazed activity, until after midnight. It is so intense that the water gets murky, and in a good year, the entire surface of the ocean is covered by a slick."
Three factors trigger the activity: water temperature cycles, phases of the moon and time of sunset. While research suggests that water temperature sets the month, moon phase the day and sunset the hour, scientists don't know how coral can tell water temperature, phase of the moon or time of day, Vize says. There are good reasons, though, for them to do so.
"Eggs and sperm have a limited life span, so fertilization has to happen within a limited window," says Vize. "In the ocean you also have diluting effects, and currents and waves carry things off, so if a coral spawns more than half an hour off from its reef-mates, it won't have much chance of reproducing. "As different species of coral developed, the triggers for spawning couldn't change much if the species was to survive, ultimately producing this chain reaction — which also occurs on coral reefs throughout the Caribbean and on Australia's Great Barrier Reef. A number of other Flower Garden Banks residents, including fish, brittle stars, sponges and Christmas tree worms, join in the reproductive frenzy. One advantage to piggy-backing on the coral's show could be protection from predation. With such a lavish buffet served all at once, predators fill up and simply can't eat it all.
The Reef Ccosystem
The frequency and volume of the annual spawning event are important indicators of the robust health of this reef ecosystem, according to Emma Hickerson, research coordinator for the Flower Garden Banks National Marine Sanctuary. The sanctuary is actually three separate areas taking in the northernmost coral reefs in the continental United States. The 100-acre West Flower Garden Bank and 250-acre East Flower Garden Bank grow on the caps of salt domes rising from the gulf floor 450 feet below and include some 21 species of coral. Stetson Bank, 30 miles closer to shore, is a 1,500-foot-long ridge of pinnacles jutting from the sea bottom, populated by fire coral and sponges. The closest coral neighbors lie off Mexico's Yucatan Peninsula, 400 miles away and the likely source of polyps that initially populated the Flower Garden Banks, and the Florida Keys, 750 miles distant.
These sessile inhabitants of the Flower Garden Banks — corals, algae and sponges — provide habitat, protection and food for a vibrant community of mobile creatures, including worms, crabs, shellfish, sea urchins, at least 280 species of fish, 20 of sharks and rays, loggerhead and hawksbill sea turtles, marine mammals and birds. Large schools of jacks congregate here. Surveys also indicate that this is important habitat for spawning aggregations of grouper and for juvenile red snapper. And while many reefs in the world are more diverse, the Flower Garden Banks are a healthy, well-populated marine environment that plays a vital role in the larger ecosystem of the Gulf of Mexico.
Threats to the Flower Garden Banks
Data have been collected on the Flower Garden Banks since the 1970s. One of the most sensitive biological communities in the gulf, its exceptionally good condition is largely thanks to geography. A northern location in waters cooler than most reefs offers protection from common coral diseases, and its remoteness reduces some other threats. The sanctuary is not, however, completely immune to damage. It is near oil and gas operations and shipping lanes and is affected by outflow from the Mississippi River basin, which carries runoff from cities, industry and agricultural operations in roughly two-thirds of the United States. A major oil spill in the gulf could have drastic effects, as could discharge of pollutants from ships.
Coral reefs globally are in decline due to disease, pollution, increased extraction and increased use, Hickerson says. "In comparison, the coral reefs of the Flower Garden Banks are very healthy, evidenced by high coral cover of between 50 to 70 percent. However, warning signs of declining health have been observed."
The principal threats to the Flower Garden Banks are climate change, pollution and fishing, says Jack Sobel, Ocean Conservancy senior scientist. Any type of stress, even slight changes in water temperature, can cause coral polyps to bleach, or expel their symbiotic algae. Without the photosynthetic algae, taking in enough food is difficult for coral and they usually die. Hickerson reports that temporarily elevated temperatures were documented at the Flower Garden Banks in association with a bleaching event in 2005, with 45 percent of coral in the sanctuary affected. Once temperatures returned to normal, the majority of bleached coral recovered. But that year, Hurricane Rita caused serious mechanical damage to the reef, tumbling coral boulders, causing loss of large barrel sponges and flattening fields of delicate finger coral. For the past four years, Hickerson and her colleagues also have been studying a condition suspected to be coral disease.
An invasive coral native to the Indo-Pacific was documented at the East Bank in 2002. Likely brought in on a ship's hull or discharged in ballast water, the species is common on oil and gas platforms in the gulf, which played a role in its spread. Invasives can upset the balance of delicate ecosystems like coral reefs.
Recreational scuba divers are the largest user group in the sanctuary, with around 3,000 divers visiting each year. Potential negative impacts of this activity include sound from boat engines and generators, light from underwater photography and the introduction of pathogens from other dive sites carried on diving equipment such as wet suits. Coral reefs in other parts of the world have suffered ill effects from increased recreational use.
Helping the Reefs
The Flower Garden Banks NMS is one of 14 underwater areas protected by the National Oceanic and Atmospheric Administration's National Marine Sanctuary Act. Eight full-time employees, based in Galveston, monitor the health of the reef and manage activities that can affect it. Marine sanctuary designation provides certain protections, with regulations prohibiting taking or injuring coral or coral reef organisms, discharging pollutants or disturbing the sea floor in the sanctuary. Oil and gas exploration and development are prohibited in "no activity" zones, but these do not include all of the sanctuary. Anchoring is also prohibited; one boat anchor can destroy thousands of years of reef growth in minutes. Spearfishing and trawling are prohibited, but conventional hook-and-line fishing is still allowed.
A Texas Parks and Wildlife Department program has created 30 artificial reefs, mainly from obsolete oil and gas platforms, between Stetson and the East and West Banks. These provide additional habitat that may take some of the fishing pressure off the banks, says John Embesi, diving safety officer of the TPWD Artificial Reef Program.
Protection would be greatly enhanced by additional restrictions, Sobel says, including prohibiting the taking of anything from the area. But enforcement of even existing regulations is difficult in an area located between 70 and 110 miles from shore and with limited staff.
Activities outside the sanctuary boundaries affect the reefs as well. "Through satellite imagery, use of tracking devices and anecdotal observations of freshwater vegetation floating near the sanctuary, it is generally accepted that freshwater from shore reaches far offshore," Hickerson says. Analysis by Kenneth Dunton, professor at the University of Texas Marine Science Institute, confirms ties between estuarine sources and the Flower Garden and Stetson Banks, with Stetson showing a higher connection. After Hurricanes Katrina and Rita in 2005, satellite imagery clearly showed plumes of discolored water extending from the shoreline to the Flower Garden and beyond.
"Coral reefs are groups of organisms that live and work almost as a single system." Sobel says. "Having all the parts of that system in place and intact makes them much more resistant to pollution, climate change and other issues, and we have good science to back that up.
"We need to protect the area surrounding the sanctuary as well," he says, "including other reefs and hard bottom areas that attract the same life." Boundary expansion is, in fact, one of six priority issues identified by sanctuary staff and members of the sanctuary advisory council. Currently, staff is developing a list of nominated sites to be considered for inclusion. The other priority issues are law enforcement, education and outreach, and the impacts of fishing, pollutant discharge and visitor use.
"The banks are little storehouses of biodiversity, key areas that sustain and replenish the gulf as a whole, even though they take up a relatively small area," Sobel says. "They are truly the jewels of the gulf." Jewels that need protection, for the enjoyment of future generations and the overall health of the Gulf of Mexico.
Year of the Reef
The year 2008 is International Year of the Reef, a worldwide campaign by the International Coral Reef Initiative to raise awareness about the importance of coral reefs and the things that threaten them, and to motivate people to take action. Coral reefs, often called the rainforests of the sea, are some of the oldest and most diverse ecosystems on the planet. Reefs provide resources and services — from food to storm protection, medicine and recreational opportunities — worth an estimated $375 billion a year, even though they cover less than one percent of the earth's surface.
According to Status of the Coral Reefs of the World: 2004 (published by the Global Coral Reef Monitoring Network and the International Coral Reef Initiative), 70 percent of the world's reefs are threatened or destroyed, 20 percent of those damaged beyond repair. In the Caribbean alone, many reefs have lost 80 percent of their coral species. Individuals can help protect coral reefs without ever leaving land, though.
The National Oceanic and Atmospheric Administration's Coral Reef Conservation Program offers a number of ways, including ensuring that sewage from boats and homes is properly treated, avoiding use of pesticides and fertilizers (even if you live thousands of miles away), buying marine life for aquariums only from suppliers that collect in an ecologically sound manner, recycling and conserving water. Those who visit reefs can help by supporting reef-friendly businesses, hiring local guides and never touching coral or anchoring on a reef. Find more information at <iyor.org>.