URI oceanographer explains mystery of Narragansett Bay toxic algae bloom

Posted on

NARRAGANSETT, R.I. – March 8, 2017 – The toxic algae bloom that has closed parts of Narragansett Bay to shellfishing is somewhat of a mystery. Although the algae species has not been identified and why it is 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, the longest of its kind in the world, 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 continuing toxic bloom.

Q: Describe the mechanics of an algae bloom. How does a bloom get started?

A: 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, like 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.

Q: Isn’t the timing of this bloom unusual, considering that it’s the middle of winter?

A: You don’t generally think of blooms happening in winter – there are no flowers out yet and no leaves on the trees. 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. The classic spring bloom happens many places around the world, and it’s really important for fisheries and to support the food web. That spring bloom is what kick-starts biological activity for the year. What makes this particular bloom interesting is that it includes an organism that is toxic.

Q: What do we know about this particular toxic organism, Pseudo-nitzschia?

A: Pseudo-nitzschia is a genus of diatoms that has formed harmful algal blooms on the West Coast for quite some time. A lot of research has been done to try to figure what‘s going on out there. 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. So that’s what makes it hard to predict and understand. There are clearly things going on that we don’t understand.

Q: How does it become toxic and what does it do to us?

A: The reason it’s toxic is because, as a member of the plankton, it gets eaten by things like clams and mussels and quahogs, which are filtering everything that’s in the water, and they’re filtering the Pseudo-nitzschia. The Pseudo-nitzschia is producing a toxin called domoic acid. The filter feeders bring that into their bodies, and those shellfish get harvested and eaten by people. That 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.

Q: Where did it come from? Has it always been here?

A: We don’t actually know where it came from. We know that Pseudo-nitzschia is present in the bay and has been for a long time. Maybe there’s a new species that we can’t identify yet. There are about 48 species in this genus, and many of them don’t look very different under the microscope; they’re hard to tell apart. We know that the genus is around, but we don’t know if there’s a new species that’s come in or a new strain that’s come in, or if the existing inhabitants of Narragansett Bay have now turned toxic.

Q: How long is it likely to be here?

A: There are probably two dozen species that produce domoic acid, and they may be here and just aren’t producing domoic acid. The one that’s producing domoic acid now might stick around and stop producing it. So we probably need to figure out what species it is and why it’s producing domoic acid. We can get a sense of that from the Narragansett Bay Long Term Plankton Time Series, which has been run out of the Graduate School of Oceanography since the mid-1950s. For most of that time it was run by Prof. Ted Smayda, and it continues today. It gives us context for interpreting the Pseudo-nitzschia dynamic that we’re seeing now. For the last 60 years, we’ve been taking weekly plankton samples from the bay, so we can now get a sense of whether the Pseudo-nitzschia is there at all, is it in normal numbers, is this more than normal. We don’t test for domoic acid, but we know what algae are there, and we can start to contextualize the dynamics and abundance of this organism in the water now. We’re in a unique situation because we have all this data, and now we can go and mine the data and say ‘what have we been seeing and is this year different from all the past years? What’s going on that’s generating these blooms?’ Most places that have these blooms don’t have a time series; they don’t have any way to contextualize what they’re seeing.

Q: Is there anything that can be done about this bloom? Or do we just sit here and wait for it to go away?

A: There are grazers out there that will eat these algae, and they’re probably eating them now. And the filter feeders are eating them. There’s also a pretty good flushing rate in Narragansett Bay, so maybe they’ll flush out into the ocean. And the algae community tends to change over time. So at this point, we can sit and wait and watch, and we can take samples during this event so we can figure out why it started. While we’re not sure why this particular bloom happened now, there are a lot of vectors in the marine environment that can bring new algae into a new location. Was it a bird that came from a harmful algal location and brought spores of this species; is it just regular circulation that caused it; were they here already and they’re just now responding to a particular environmental cue? All those things are unknown, so it would be unwise to do something about it since we don’t know at this point what led to the bloom and if it’s anything more than natural variation. Rhode Island DEM is really trying to stay on top of this. They’ve been taking samples, they shut the shellfishery down in certain parts of bay, so they’re concerned and are trying to do everything they can. While we keep an eye on it, they also want to keep everyone safe.