Northwest Scientists Study Toxins In Puget Sound's Algal Blooms

By Rita Sodt

Some algae produce harmful toxins and can form toxic blooms, called "green tides" and "red tides," whose names refer to the color of the massive carpets of algae that cover the water during the bloom.

In summer 2006, there was a bloom in Puget Sound of a large sea lettuce known as ulvoid alga that damaged eelgrass and released hydrogen sulfide and a strong rotten egg smell when it started to decompose. Eelgrass is a critical plant as habitat and food source in the marine ecosystem.

At that same time, a bloom of Heterosigma akashiwo, a microalga smaller than the width of a human hair, released toxins that killed thousands of fish in the Strait of Juan de Fuca and in Puget Sound. An aerial photo shows the bloom as a large dark "tongue" of water near Anacortes. In July 2006, the "bloom exploded within 24 hours," with no early indication, according to Kevin Bright of American Gold Seafoods, Anacortes, Wash., whose company suffered a considerable loss from the event.

Scientists at Seattle Pacific University (SPU) and Western Washington University (WWU) Shannon Point Marine Center in Anacortes are conducting lab and field work at six sites in Puget Sound to study the direct and indirect effects of toxins produced by algae on the environment and on marine food webs. They also study the effects of light, nutrient availability, and herbivores on the growth and physiology of macro- and micro-algal blooms.

Support for this area of research is provided by two grants from the National Oceanic and Atmospheric Administration (NOAA) and one from the National Science Foundation, totalling more than $1.1 million, which were awarded to Kathy Van Alstyne and Suzanne Strom from WWU and to Tim Nelson from SPU. Van Alstyne and Nelson primarily study ulvoid macroalgae and Strom primarily studies Heterosigma akashiwo microalgae. These studies provide a baseline for ongoing work on algal blooms and could ultimately help predict them.

Research focusing on these algae is relatively new in the Pacific Northwest, partly because the toxins they produce are harmless to humans. In the case of ulvoid algae, it was previously unknown that it had any toxic products. The harmful effects of ulvoid algae on the environment were thought to be caused only by their ability to cover the surface of the water, thus smothering plants and depleting the water of oxygen.

However, new studies show that when stressed by heat or immersed in nutrient-rich water, ulvoid algae can release toxins that harm marine life. It is less clear what causes the production of toxins by Heterosigma akashiwo, which are harmless in small numbers but lethal to fish during heavy summertime blooms.

Strom is searching for an explanation of the evolution of toxin-producing algae by studying the role that toxins play in marine food webs. Preliminary findings show that algae release toxic compounds that function as signals that say to zooplankton "don't eat me." It is a strategy that confers a huge selective advantage and could be one of the causes of large blooms. While most research looks at bottom-up factors such as light and nutrients, Strom's research explores whether or not those cells are going to be eaten by predators as they grow. Strom compared the growth of an algal bloom to a "net income," where the total amount of algae at the end of the day is the amount of growth minus the amount that was eaten by predators. Other factors Strom looks at are the role of salinity, light, nutrients and herbivores on the growth of blooms.

Additionally, Nelson is undertaking a large-scale video analysis of eelgrass surveys from the Washington Department of Natural Resources that he uses to track the occurrence of ulvoid blooms. The videos show year-to-year variation of bloom magnitude and indicate that ulvoid algae are "most abundant in central Puget Sound," he says.

Studying the causes of blooms and the conditions in which they occur helps identify sites to monitor for signs or early warnings of a bloom. Also, a new device allows scientists to monitor toxin levels and collect algae remotely. Scientists at NOAA and at the Monterey Bay Aquarium Research Institute in Monterey Bay have developed a remote detection device to assess algae and bloom toxin levels. This device "shows great promise for giving early warning of toxic blooms," says Vera Trainer, program manager of the marine biotoxins group at the Northwest Fisheries Science Center, "but it is critical to know the key locations, or hot spots, for bloom origination to know where to place the monitoring device."

Rita Sodt is an undergraduate in computer science at University of Washington.

Image: Heterosigma algae bloom in 2006 near Anacortes, Wash. Bloom is the dark "tongue" of water. Photo: Kerri Fredrickson