Research from the Bermuda Biological Station has shown that a herbicide commonly used in new boat anti-fouling paints is in fact highly toxic to the algae which gives corals their colour.

Use of such dangerous herbicides is set to increase after January, 2003, when a separate compound which was formerly used in anti-fouling paint will be completely banned as it also is extremely dangerous to marine life.

In an article published this week in `Marine Pollution Bulletin', an international scientific journal, Dr. Richard Owen, Assistant Research Scientist at the BBSR, describes in detail the toxic effect of the slime resistant herbicide, Irgarol 1051.

Dr. Owen and his research group at BBSR have conducted experimental research into the effects of Irgarol 1051, and discovered that even very low levels of the herbicide in the ocean acutely inhibit photosynthesis of the microscopic plants (zooxanthellae), which are essential to the health, growth and reproduction of corals, as well as giving them their colour.

Dr. Owen's group also reported that Irgarol 1051 is a common pollutant in the inshore waters of Bermuda.

"It is clear that Irgarol 1051 is a potent inhibitor of coral photosynthesis at environmentally relevant concentrations," said Dr. Owen in his article.

In more heavily contaminated areas such as Singapore, he added, "there was no net photosynthesis, suggesting a complete shutdown of the photosynthetic apparatus" - meaning that the zooxanthellae were unable to work at all, thus threatening the life of the coral.

"Any contaminant that inhibits their photosynthesis could undermine the cornerstone of these biologically and economically important marine habitats," said Dr. Owen in his article.

The group headed by Dr. Owen found, to their surprise, that the photosynthesis of isolated zooxanthellae was substantially reduced after only six to eight hours when at herbicide concentrations within the range reported for the coastal waters.

The herbicide Irgarol 1051, and another herbicide named diuron which is also common in boat paints, work by leaching slowly from the paint to prevent the build-up of biofilms on boat hulls.

They were first introduced in the early 1990's, when the compound which was previously used as an anti-fouling agent in boat paints, tributyl tin (TbT), was widely banned on small boats such as yachts because of the danger it presents to marine life.

The answer to TbT seems to travel in a circle back to the problem, however, as the herbicides Irgarol 1051 and diuron, both of which are moderately soluble and environmentally persistent, also contaminate coastal waters. Both are toxic to the photosynthesis of zooxanthellae.

"There are several alternatives to Irgarol 1051 and the Bermuda Government is continuing to provide funding to evaluate the toxicity of these compounds to coral photosynthesis," stated Dr. Owen.

"Although global usage patterns of these compounds are hard to evaluate, a recent survey in the UK found that 80 percent of anti-fouling paints contained either Irgarol 1051 or diuron. Diuron has also been found as a contaminant in the Great Barrier Reef region (in Australia)."