Algae disappears

Shellfish can again be gathered from Port Underwood, after the disappearance of a toxic algal bloom, which closed the area for two weeks.

Nelson Marlborough Public Health Unit medical officer of health Ed Kiddle said concentrations of the algal toxin in shellfish had rapidly declined to a safe level.

This was normal for the diarrhetic shellfish poisoning type of algal toxin which was water soluble, said Dr Kiddle. Other types were slower to break down once taken into shellfish.

Port Underwood mussel farmer Ray Thomas said with the main harvest season about to start, if the bloom had lasted longer, it could have caused problems for the industry.

Once mussels started to spawn they could not be harvested until early next spring. Mussels were fat at this time of year, but a good southerly coming through could trigger them to spawn, which made them skinny and not good to eat, he said.

Mr Thomas, who farms 5.5 hectares of mussels, said in the last 23 years toxic blooms had closed Port Underwood for harvesting three or four times.

Mussel farmers could not distinguish between beneficial algal blooms, which provided nutritious food for mussels and toxic algae, he said. They relied on water-quality testing to identify toxic blooms.

Diarrhetic shellfish poisoning could cause diarrhoea-type illness, Dr Kiddle said. It was produced by particular phytoplanktons commonly found around New Zealand and the world.

- The Marlborough Express