University of South Carolina study in Nature Geoscience: Neurotoxin has lengthy stay in ocean

COLUMBIA, SC – March 20, 2009 – A neurotoxin produced by marine algae is escaping from surface waters off California and invading the deep ocean, according to a study by researchers at the University of South Carolina.

Blooms of the diatom Pseudo-nitzschia in the upper ocean generate dangerously high levels of domoic acid. The neurotoxin is thought to be the cause for the 1961 case of wildly abnormal marine bird behavior in Capitola, Calif., which became the basis for the vicious attacks in Alfred Hitchcock’s chilling movie The Birds. In recent decades, domoic acid has been linked to the deaths of sea lions, whales and other marine mammals.

Shellfish contaminated with domoic acid also affect people, causing symptoms from mild gastrointestinal problems and headaches to memory loss, disorientation and seizures. In rare cases, it has caused deaths.

Dr. Claudia Benitez-Nelson of the University of South Carolina’s department of geological sciences said that large quantities of domoic acid are sinking to the ocean floor off the coast of California, where it invades the deep-sea food chain.

The study, reported this week in the online edition of Nature Geoscience, is the first to show that large amounts of domoic acid reach the sea floor where it potentially can linger long after a toxic bloom occurs.

“Previously, we believed that once the blooms went away that the neurotoxin was gone, too,” said Benitez-Nelson.

“However, by studying the remains of the algae in the ocean sediment, we found that the toxin sinks to the ocean floor where it remains and can enter the food chain,” she said. “In some cases, the sinking particles contain more than eight times the U.S. federal limit for domoic acid.”

Large Pseudo-nitzschia blooms also have caused beach closures and disruptions to the shellfish industry in the Western United States. Pseudo-nitzschia has been implicated in toxic blooms throughout the coastal waters of Europe and Asia and along the coasts of North America. Recently, National Oceanic and Atmospheric Administration (NOAA) researchers found Pseudo-nitzschia off South’s Carolina coast, but have yet to confirm if they contain domoic acid.

“It is important that we understand the environmental conditions that lead to the formation of Pseudo-nitzschia blooms, what’s triggering the production of domoic acid, and whether the neurotoxin stays in the surface water or sinks to the ocean floor,” said Emily Sekula-Wood, a University of South Carolina doctoral student and the study’s lead author.

“All of this has an impact on human and coastal health,” she said.

Harmful algal blooms, including Pseudo-nitzschia, are expected to increase in frequency and expand their geographical base as human activities in coastal areas affect nutrients entering nearby waters, said Sekula-Wood.

With the development of coastal areas and the potential for increased sewage and agricultural runoff, researchers believe that nutrients, such as nitrogen and phosphorous, will find their way into the ocean, thus increasing the proliferation of harmful algal blooms.

“Understanding the transport and fate of these toxin-loaded cells will help us to better address the human-health issues associated domoic acid,” Sekula-Wood said.

Other University of South Carolina researchers contributing to this work include Dr. Robert Thunell from the department of geological sciences and Dr. John Ferry and post-doctoral student Justina Burns from the department of chemistry and biochemistry.