‘Catch-22’ for toxicity of algae that produce ‘red tides’

Toxic algae in the Gulf of Mexico multiply because of excess phosphorus, but when supplies are limited, they become more toxic, according to a new study by scientists from North Carolina State University and the National Oceanic and Atmospheric Administration.

Writing in the online journal PLOS ONE, they say their study shows that harmful and ubiquitous Karenia brevis algae, which cause red tide blooms across the Gulf of Mexico, become two to seven times more toxic when levels of phosphorus are low.

Red tide blooms in the Gulf are linked to fish kills and other ecological and economic damage in the region, and are also linked to respiratory ailments in humans. These blooms occur annually in the Gulf, but it’s hard to predict where or when they’ll occur or how long they’ll last.

The irony of the inverse relationship between phosphorous and algal toxicity is not lost on the researchers, says a PLOS ONE release. In a modern-day ‘catch-22,’ excess nutrients like phosphorus and nitrogen play key roles in fuelling algal growth and harmful algal bloom development. As bloom density increases, cells use up the available nutrients such as phosphorous. This slows the growth of K. brevis cells causing them to become more toxic.

Previous research showed similar effects when nitrogen was the limiting nutrient.

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