Red tide toxins ride in on wave of salt

TEXAS A&M (US) — Changes in salinity may explain why red tide algae in the Gulf of Mexico becomes toxic as it moves onshore, killing marine life and posing health hazards to humans.

Red tide refers to the periodic blooms of microscopic algae that usually crop up in late summer or early fall throughout the Gulf Coast states.

A study published online in the journal the Proceedings of the National Academy of Sciences finds that as red tides move onshore and mix with fresher water  Karenia brevis cells must adjust rapidly to the change in salinity.

As they adjust, brevetoxins—a collection of potent neurotoxins that cause gastrointenstinal and neurological problems in other organisms—within the cell increase to allow them to keep their water and salt content in balance more efficiently.

Until now, a functional role for the diverse collection of toxins produced by dinoflagellates was a mystery, with possible theories focusing on aiding prey capture, deterring grazers, or inhibiting growth of neighboring algae.

“The connection between salinity conditions and an increase in toxin production in K. brevis cells provides the simplest explanation,” says Reagan Errera, a graduate student working with Lisa Campbell, professor of oceanography at Texas A&M University.

In the new study, Errera and Campbell demonstrate that brevetoxin production increases dramatically when cells are shifted from higher concentrations of salt typical of the open ocean to lower salinity typical of coastal waters. In fact, the transition to a lower salinity environment triggered a 14-fold increase in brevetoxin, they say. In addition, the findings indicate a significant increase in an additional compound called brevenal, already being studied to treat cystic fibrosis.

Red tides, or harmful algal blooms as they are more correctly known, have far-reaching ramifications on human and ecosystem health, as well as a significant influence on the local economies of bloom prone areas.

Karenia brevis blooms directly affect human health. Eating shellfish contaminated by accumulated brevetoxins causes neurotoxic shellfish poisoning, and aerosolized brevetoxins in sea spray can cause reduced respiratory function, they explain

“Now that we have a plausible explanation for why Karenia brevis produces toxins, it will help coastal managers, public health officials and others prepare for and respond to the impacts,” says Quay Dortch, program manager for the National Oceanographic and Atmospheric Administration that funded the research.

“We now understand that maximum toxicity will occur in the zone near the coast where shellfish are harvested and where people are exposed to toxic aerosols, especially when near-shore salinities are low.”

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