Algal bloom, closure affects aquaculture sites in West Passage

March 15, 2017, WAKEFIELD – The recent closure of areas of Rhode Island Sound, lower Narragansett Bay and lower Sakonnet River to shellfish harvesting has impacted a number of aquaculture sites, but shows the revised monitoring protocol is working, according to the R.I. Coastal Resources Management Council (CRMC).

R.I. Departments of Environmental Management (DEM) and Health (DOH) announced the closures in late February because of a confirmed harmful algal bloom caused by the phytoplankton Pseudonitzschia spp. Shellfish samples collected on February 26 and 27 from five lower Bay locations off Jamestown, Newport, and Little Compton showed levels of domoic acid in four locations ranging from 14-32 parts per million, prompting the mandatory closure. A similar bloom led to closures last fall.

CRMC’s Aquaculture Coordinator David Beutel said that it’s a signal that DEM’s revised monitoring protocol is working – if one were to look at the bright side of things.

“The surveillance program is working,” he said. “DEM never monitored during this time, but knowing [this algae] affects us in the fall, they changed the protocol. This is DEM and DOH keeping people safe, and we applaud them for that effort, which in this case has obviously paid off.”

Last fall, the closure was precautionary, Beutel said – initial tests showed no signs of domoic acid, but the algae levels were higher than had ever before been seen. Ten days later, testing showed domoic acid, prompting another closure.

“This is the third closure due to Pseudonitzschia in six months, when we’d never had one before,” Beutel said.

The quahog industry in the upper Bay has not been affected by this because there’s no significant harvest below the Newport Pell and Jamestown Verrazzano Bridges, but the closure impacts seven permitted oyster and mussel aquaculture sites.

“When the algae proliferate in the fall, the oysters are eating a lot, fattening up for the winter, and they eat the algae,” Beutel said. It’s only a problem, he added, if the domoic acid is present. And while oysters slow down their eating and filtering in the winter months (a metabolic depression), mussels do not. They accumulate the domoic acid faster than all the other shellfish present, and so their meat is tested for presence of the harmful acid.

The good news is that the acid will eventually flush from both the oysters and mussels, and it’s not a danger to humans because no one is harvesting right now. And as long as Rhode Island does not experience another similar closure, the product that is marketable size will go to market, Beutel said.

Relatedly, Beutel said that less (predominantly oyster) product sold in 2016 because of the summer closure, which was a different algae, Cochlodinium polykrikoides (red tide). While not toxic to humans, it is toxic to fish, and oysters do not like it, Beutel said. As a result, during the summer of 2016 and this particular algal bloom, the oyster stock stopped eating, and so less product was large enough at harvest to be sold at market. Mortality was also higher than usual as a result of the red tide.

For updates on this and other closures, contact the DEM 24-hour shellfishing hotline at (401) 222-2900 and/or sign up for the DEM Marine Fisheries email list at rimarinefisheries-subscribe@listserve.ri.gov. Follow the CRMC on Twitter, as well, for updates - @RI_CRMC, and check our home page for updates and news – www.crmc.ri.gov.