Copper decimates coral reef spawning

Copper decimates coral reef spawning

18 November 03

Emma Young, NewScientist.com news service

The successful mass spawning of coral reefs can be decimated by even low levels of copper pollution in seawater, according to new research in Australia.

Claire Bennett, a PhD student at Melbourne University, studied samples of coral from the Great Barrier Reef. Over a few days every November, corals spawn all over the reef, releasing larvae into the water. These swim free for a week or two before attaching to the reef and developing into juvenile coral polyps - a process that is crucial for the renewal of the reef.

But Bennett's unpublished lab work showed that even low levels of copper contamination - below that recorded around inshore reefs off Queensland - reduces the number of larvae that survive to the juvenile polyp stage by at least one third.

Copper is well known to be toxic to marine organisms at high levels. The new work should help coral reef managers predict the impact of even low levels of pollution, as well as revealing how the metal affects a key stage in the coral life cycle.

Andrew Negri, at the Australian Institute of Marine Science in Townsville, Queensland, is collaborating with Bennett on her work and says: "Not enough is understood about how pollutants like copper affect tropical marine species - particularly at different stages of their life history."

Arrested development

On 7 November, Bennett collected samples of two species of hard coral from part of the Great Barrier Reef near Magnetic Island, off Townsville. She placed some samples in "clean" seawater containing 2 to 3 parts per billion (ppb) of copper, some in seawater containing 5 ppb, and others in seawater containing 30 ppb. Then she waited for the coral to spawn.

The level of copper had no impact on the total number of larvae produced, Bennett told New Scientist. But at 5 ppb, 30 per cent fewer larvae developed into juveniles, compared with larvae in clean seawater. At 30 ppb, the number was reduced by 70 per cent.

Furthermore, larvae that did successfully mature took much longer to do so in the copper-laced waters than in clean water. Bennett will continue to coral samples for any long-term effects. She also plans lab work to investigate how copper interferes with larval development.

Copper is a common seawater contaminant. It is increasingly used in anti-fouling paints and is often present in urban and industrial run-off. Copper sampling surveys on the reef off Townsville are few and far between. But the most recent in 2000 found levels of 8 ppb in open water. Wet season storms can increase this markedly by stirring up copper-laden sediments.