A neurotoxin produced by marine algae is escaping from surface waters off California and invading the deep ocean, according to a study online in Nature Geoscience.

Blooms of the algae Pseudo-nitzschia in the upper ocean generate dangerously high levels of the neurotoxin domoic acid that threaten coastal ecosystems worldwide. Claudia Benitez-Nelson and colleagues show that large quantities of this toxin are sinking to depth off the coast of California, where it can invade deep-sea food webs too. In some cases, concentrations of domoic acid exceeded the United States federal limit by over five times.

Domoic acid causes amnesiac shellfish poisoning in humans, and is linked to mass mortality of marine mammals, including the deaths of over 400 California sea lions in 1998. Large Pseudo-nitzschia blooms have also caused beach closures and disruptions to the shell-fish industry in the western United States.