Invasive Algae Smothering Florida Coral Reefs

By Cat Lazaroff

PALM BEACH, Florida, January 24, 2003 (ENS) - An invasive, coral smothering seaweed has spread like a green tide across the reefs along the south Florida coast. Recent reports from divers and fishers show that the seaweed has become so thick on reefs in Florida's Palm Beach County, about an hour north of Miami, that it is forcing lobsters and fish away.

The species, a type of macroalgae, has also now been spotted as far north as Ft. Pierce, Florida, about 60 miles away.

Caulerpa brachypus is a nonnative macroalgae that has invaded Florida's coral reefs. (All photos courtesy Harbor Branch Oceanographic Institution, Inc.)

Lapointe said the threat posed by the seaweed, called Caulerpa brachypus, 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 may have been released from a saltwater aquarium or from a ship's ballast water.

Because it is not native to Florida waters, Caulerpa brachypus has no natural predators, a problem compounded by the fact that the species is very hardy, and can spread rapidly if the nutrients it needs are available.

"It can really undergo explosive growth," Lapointe said.

Based on past research, Lapointe believes 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 treated sewage pumped offshore each day.

Caulerpa brachypus's explosive growth devastates coral reefs. Besides smothering and killing the coral itself, it blankets the food on which many fish rely, forcing them and their predators away from a reef. The weed can also fill in the ledges and crannies that attract lobster.

Despite this destructive capacity and the potential for serious economic impact, there is no scientific information available about how fast the species is spreading or even how much area it already covers in Florida.

A research diver examines an infestation of Caulerpa brachypus.

Florida's 2002 budget, as approved by the state legislature, had included about half a million dollars for Lapointe's team to study the macroalgae problem, but this funding was later eliminated by a line item veto. So Caulerpa brachypus's spread has not yet been studied in any detail.

But Lapointe has now received a grant through the U.S. Environmental Protection Agency's national Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) initiative that will allow his studies to move forward.

Over the next two years, Lapointe and his colleagues plan to complete a comprehensive study of the factors controlling the spread of Caulerpa brachypus and two other problematic seaweed, or macroalgae, species. The work will help predict the amount of damage Florida should expect from macroalgae in coming years, and may provide information about how best to control or prevent its spread.

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 team will conduct quarterly surveys of the sites known to be colonized by the seaweed, along with laboratory experiments aimed at determining how seasonal changes in light, temperature, and nutrient availability control the growth and spread of harmful macroalgae. The researchers will study whether algae 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 also compare how well each species grows when nitrogen from 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.

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.

The seaweed is so pervasive in some areas that it has been called a green tide.

"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," said Lapointe.

He added that it is critical that leaders take the threat from the Caulerpa brachypus seriously, citing other regions that have faced similar problems. In the Mediterranean, for instance, government officials failed to act when Caulerpa brachypus's cousin, Caulerpa taxifolia, was first found there.

Thousands upon thousands of acres of reef have now been destroyed and billions of dollars worth of damage done.

Caulerpa taxifolia was also discovered off the coast of California in 2000, and the state has launched a massive effort to prevent the spread of the toxic algae.