Northwest Fisheries Science Center

When algae turn toxic

Understanding the causes of harmful algal blooms can help us predict future events Contributed by Al Brown October 2016

In the spring and summer of 2015, the largest and longest-lasting harmful algal bloom (HAB) of this century hit the U.S. West Coast. Domoic acid (DA), a neurotoxin produced by the Pseudo-nitzschia algae, was found in dangerous levels in razor clams and crabs from Washington to southern California. Fisheries were closed, damaging coastal economies for months.

What caused it? And can we predict when this might happen again?

Fortunately, a group of scientists from Oregon State University, the Oregon Department of Fish and Wildlife, and the Northwest Fisheries Science Center began monitoring levels of DA, among other factors, along the central Oregon coast in January 2015—before the bloom began—and continued to do so throughout the entire event. The next link/button will exit from NWFSC web site Results of their analysis have just been published in the online research journal PLOS ONE.

Two factors seem to have been to blame for the historic scale of this HAB. The first was the equally historic warm-water event that has come to be known as “the Blob.” Beginning in the winter of 2013-14, a large patch of warm water formed off the coast of Alaska and settled in the northern Pacific, providing ideal conditions for the algae to grow.

The Blob had reached the Oregon coast by September 2014. The upper 150-250 feet of the ocean stayed abnormally warm throughout the following winter, causing what scientists call stratification—a layering of the ocean that can keep vital deep-water nutrients from reaching the surface in their usual amounts.

The second factor was a bloom of phytoplankton, mostly diatoms, in February and March 2015. For these microscopic marine plants to appear at this time wouldn’t be unusual by itself, but this was the largest such growth observed in 20 years. Pseudo-nitzschia, the algae responsible for the toxic bloom later that year, are a kind of diatom.

Under ideal conditions, Pseudo-nitzschia aren’t harmful. But when starved for nutrients, they undergo certain physiological changes, one of which is that they start to produce domoic acid. This then makes its way into organisms higher up the food chain—from clams and crabs to fish, birds, marine mammals, and even humans.

The scientists are optimistic that the data they collected throughout 2015 will help them learn enough to be able to pinpoint when conditions are aligning for another HAB event. We may not be able to prevent it, but at least we can get ready sooner.