Algae In The Gulf Of Mexico Purposefully Become Toxic When Food Is Scarce

The very-common “red tide” algae Karenia brevis is regularly responsible for a very large number of fish deaths through large-scale fish kills. And now new research has revealed that these large fish kills are partially a result of the algae purposefully becoming more poisonous as a result of limited nutrients, as a survival mechanism. When they don’t get enough nutrients, they use their remaining energy to become more poisonous, helping to ensure their survival.


The new research from North Carolina State University and the National Oceanic and Atmospheric Administration, states that the red tide blooms across the Gulf of Mexico, “become two to seven times more toxic when levels of phosphorus, a major algal nutrient found in fertilizers and human waste, are low. Like wearing a suit of armor, producing highly toxic cells allows the algae to defend themselves against opportunistic waterborne grazers like zooplankton.”

Red tide blooms in the Gulf result in significant economic losses to the surrounding states as a result of damage to the fishing and aquaculture industries and damage to tourism. The blooms also cause respiratory problems in some people. Though they are a very regular occurrence, it’s difficult to predict when exactly they will happen. This new research may help in the development of more accurate predictive systems.

“Public-health managers can test phosphorus levels in waters across various Gulf locations,” Drs. Rance Hardison, co-author on the paper, said, “and know that low levels could indicate highly toxic red tide blooms. Then they can close nearby shellfish beds or take other measures to keep sea life — and humans — safe.”

“The researchers tested five different K. brevis species from varied geographic locations and limited some samples’ growth by withholding phosphorus while allowing others to enjoy a full diet of phosphorus. Depending on the species, algal cells with limited access to phosphorus had 2.3 to 7.3 times more toxin than algal cells that were filled up with phosphorus.”

“At the end of a red tide bloom, when the nutrients are used up, K. brevis cells produce a burst of toxicity. Now we understand the biological mechanism behind some of the varied toxic levels seen in Gulf algal cells,” Damian Shea, an NC State professor of biology and environmental toxicology, said.

There’s some irony to this. Excess levels of phosphorus in the water, as a result of agricultural runoff, are largely responsible for the notable uptick in the number and extent of algal blooms in recent years. And yet its the depletion of phosphorus levels that triggers the production of the toxic compounds in algae.

Previous research from these same scientists has shown that nitrogen acts on K. Brevis in a similar way. Triggering the blooms to begin with, because of excess levels, and then once the nitrogen is depleted, triggering the toxicity.

“We believe the findings will be useful to help model future toxic algal blooms and how harmful they’ll be,” Hardison said.

The new research is being published online in the journal PLOS ONE.

Image Credit: Red Tide via Wikimedia Commons

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