A moderately intense red tide may contaminate the shellfish of New England this spring and summer. No need to cancel the clam bake though, a warning system will shut down the harvest if red tide concentrations reach dangerous levels.

In New England, red tides are caused by population spikes of the alga Alexandrium fundyense. The algae produce a toxin that builds up in the filter-feeding shellfish. That toxin, known as saxitoxin, attacks the human nervous system and causes potentially fatal paralytic shellfish poisoning.

“Red tide is a chronic problem throughout the Gulf of Maine, affecting commercial and recreational harvesting interests,” said Chris Nash, shellfish program manager for the New Hampshire Department of Environmental Services, in a press release.

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In 2005, a red tide led to closure of hundreds of miles of beaches and an economic loss of $50 million for Massachusetts and $23 million for Maine, reported the Bangor Daily News.

Since 2005 there have been advances in the forecasting and monitoring systems that do red tide reconnaissance. These advances result in only the dangerously affected regions being shut down. Now, fisherman can continue harvesting on beaches where the red tide hasn’t reached threatening levels.

Woods Hole Oceanographic Institution biologists measure the concentrations of A. fundyense cysts in marine sediments. Cysts are like the seeds of the alga, so abundant cysts can mean a dangerous red tide.

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Ocean conditions influence the severity of the red tide as well. Biologists use cyst abundance data and ocean conditions to program a computer simulation that forecasts the year’s red tide.

“Ultimately our goals are to protect public health and give consumers confidence in the quality of the seafood products they purchase from markets and restaurants, and these forecasts are useful in realizing those goals,” said Nash.

IMAGE: Shellfish, Alexander Baxevanis