URI Oceanographer Dissects Bay's Toxic Algae Bloom

By ecoRI News staff

The toxic algae bloom that has closed parts of Narragansett Bay to shellfishing is somewhat of a mystery. Although the algae species hasn’t been identified and why it’s producing the toxin now, the nuts and bolts of how it happened and what will happen next are well studied, thanks to the Narragansett Bay Long-Term Plankton Time Series. The nearly 60-year research project at the University of Rhode Island’s Graduate School of Oceanography is designed to understand the changing patterns of plankton in the bay.

Managed by plankton expert Tatiana Rynearson, URI professor of oceanography, the time series involves the weekly collection and analysis of plankton from several depths in the bay. Based on her extensive knowledge of the algae in Narragansett Bay and how algae blooms form and dissipate, Rynearson provides answers to some of the pressing questions about the latest toxic bloom.

How does a bloom get started? She said an algae bloom is the result of the perfect set of conditions for that particular algae. Algae are like plants; they photosynthesize, so they need light and they need nutrients, such as nitrogen and phosphorous. They also need to have a situation where predators aren’t there to eat all the algae. The amount of algae growth is a combination of how well they’re growing, plus who’s there to eat them and how much they’re eating.

Isn’t the timing of this most recent bloom unusual? “You don’t generally think of blooms happening in winter — there are no flowers out yet and no leaves on the trees,” Rynearson said. “But in Narragansett Bay, we have a winter/spring algae bloom that often occurs exactly at this time of year and often even earlier. We have a lot of light now, it’s been pretty sunny, we have a lot of nutrients in the bay, and some of the grazers that are so important are not around.”

She noted that this particular bloom is interesting in that it includes an organism that is toxic.

What do we know about Pseudo-nitzschia? Rynearson said it’s a genus of diatoms that has formed harmful algal blooms on the West Coast for quite some time. Pseudo-nitzschia is comprised of a number of species, some of which produce the toxin and some that don’t, and the species that produce the toxin don’t always produce the same amount or any toxin at all — that’s what makes it hard to predict and understand.

How does it become toxic and what does it do to us? She said Pseudo-nitzschia produces a toxin called domoic acid. Filter feeders, such as clams, mussels and quahogs, bring that into their bodies, and those shellfish get harvested and eaten by people. Domoic acid causes an illness called amnesic shellfish poisoning — “you might vomit, get a headache, and you could also get a coma from it, short-term memory loss and even death. It’s quite a potent toxin.”

Is there anything that can be done about this bloom? Rynearson said there are grazers out there that will eat the algae. There’s also a pretty good flushing rate in Narragansett Bay. She noted that the algae community tends to change over time. “We can sit and wait and watch, and we can take samples during this event so we can figure out why it started.”