New herbicides pose threat to corals

New herbicides used in agriculture and anti-fouling paints pose a new threat to corals by killing their symbiotic algae.

According to research by Ross Jones of the Centre for Marine Studies at the University of Queensland, which has just been announced in the journal Marine Pollution Bulletin, the recent discovery of new Photosystem II (PSII) herbicides in the marine environment has raised concerns about their effects on the symbiotic algae within corals.

Jones says that PSII herbicides appear to be able to penetrate coral tissues within minutes and cause the algal symbionts, called zooxanthellae, to become much less productive in terms of photochemical efficiency. This could have grave consequences for the corals they live within.

The zooxanthellae of corals appear to be as sensitive as any other phototrophs tested so far. It could take as little as nanograms of PSII per litre to harm them, says Jones.

In tests it has been shown that when the exposure to PSII has been short, and the concentration low, that corals should be able to recover quickly if they are returned to clean seawater, so the effects can be reversed.

However, higher concentrations of the pollutant, or more longterm exposure, can produce a sustained reduction in the photochemical efficiency of zooxanthellae, which is bad news for corals.

The chronic photoinhibition PSII is capable of causing could lead to bleaching, which may take many months to recover from.

For more details see the paper: Jones, R (2005) - The ecotoxicological effects of Photosystem II herbicides on corals. Marine Pollution Bulletin. 2005. July 26.