Coral Smothering 'Green Tide' Seaweed Spreading On Florida Reefs

"It can smother just about everything down there," says Dr. Brian Lapointe, a marine ecologist at HARBOR BRANCH, of Caulerpa brachypus. He says the threat it poses is even more alarming than that of other troublesome species he has studied in the area because it is an invasive normally found in the Pacific, but, until a year ago, nowhere in Florida. The species was probably inadvertently released from a saltwater aquarium or from a ship's ballast water. Because it is not native to Florida waters, it has no natural predators, a problem compounded by the fact that the species is especially rugged and able to spread quickly if the nutrients it needs are available. "It can really undergo explosive growth," says Lapointe.

Lapointe believes based on past research that the spread of this and other macroalgae species, in Florida and at many troubled reefs around the globe, is driven by nutrients from land-based pollution. In South Florida, one of several key sources of such pollution is hundreds of millions of gallons of nutrient-rich, secondarily-treated sewage regularly pumped offshore each day.

Caulerpa brachypus's explosive growth devastates reefs. Besides smothering and killing the coral itself, it covers over the food on which many fish rely, forcing them and their predators away from a reef, and, among other problems, it can fill in the ledges and crannies that attract lobster. Despite this destructive capacity and the potential for serious economic impact, there is currently no scientific information available about how fast the species is spreading or even how much area it currently covers in Florida. Lapointe and his colleagues discovered C. brachypus for the first time in Florida waters about a year ago. At that time they found it had already covered acres of reef. Florida's 2002 budget, as approved by the state legislature, had included roughly half a million dollars for Lapointe's team to study the macroalgae problem, but this funding was later eliminated by a line-item veto. Consequently, C. brachypus's spread has so far not been studied in any way.

But Lapointe has now received a grant through the Environmental Protection Agency's national Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) initiative that will allow such work to move forward. A media press conference and dive event on Jan. 23 coincides with the first day of surveys on local reefs for this new project.

Over the next two years, Lapointe and his colleagues will complete a comprehensive study of the factors controlling the spread of Caulerpa brachypus and two other problematic seaweed, or macroalgae, species. Lapointe predicts that the spread of macroalgae on Florida reefs, sometimes referred to as a "green tide," will have devastating ecological and economic impacts unless controlled. His work should lead to forecasts for the amount of damage to expect from macroalgae in coming years as well as provide information about how best to control or prevent its spread.

Lapointe and his team will conduct quarterly surveys of these sites as well as laboratory experiments to determine how seasonal changes in light, temperature, and nutrient availability control the growth and spread of harmful macroalgae, and whether growth is seasonal or year-round, a key factor in determining how fast it spreads.

To test his hypothesis that nutrients from pollution are fueling macroalgae blooms in the area, Lapointe and his colleagues will be comparing how well each species grows when nitrogen in the form found in sewage is available versus how it responds to nitrogen as it occurs naturally in seawater. They will also analyze the chemical signature of macroalgae samples for evidence of which type of nitrogen is driving growth.

In addition, the team will measure the way the macroalgae species reflect light to establish a method for measuring the extent of macroalgae spread in Florida and around the globe using remote sensing from satellites or airplanes.

Lapointe believes that harmful macroalgae blooms are going to continue to spread north and south from Palm Beach County, devastating South Florida reefs, unless the flow of hundreds of millions of gallons of insufficiently treated sewage from offshore outfalls, septic seepage and deep injection wells is stemmed. "At some point the state is going to have to sit back and look at this situation and make some tough choices about how to safely discharge sewage around its coral reefs," says Lapointe.

Lapointe says it is critical that leaders take the threat from the Caulerpa brachypus seriously, and points to other regions that have faced similar problems as examples of why. In the Mediterranean, for instance, government officials essentially ignored the problem when Caulerpa brachypus's cousin, Caulerpa taxifolia, was first found there until it was too late to control. Thousands upon thousands of acres of reef have now been destroyed and billions of dollars worth of damage done.

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HARBOR BRANCH Oceanographic Institution, Inc., is one of the world's leading nonprofit oceanographic research organizations dedicated to exploration of the earth's oceans, estuaries and coastal regions for the benefit of humankind.