Maine DMR Public Health Bureau phytoplankton sampling volunteers Carol White and Julia Maine created this photo of Pseudo-nitzschia, the algae that can cause Amnesiac Shellfish Poisoning, under a microscope. PHOTO COURTESY OF MAINE DMR

Shellfish sampling ramps up

By Ari Leach, DMR Biotoxin Monitoring Specialist

BOOTHBAY HARBOR — Maine has a long history of monitoring harmful algae that impact the state’s shellfish industry. In 1996 the Marine Biotoxin Monitoring Program run by the Department of Marine Resources (DMR) began tracking the harmful algae Pseudo-nitzschia, a genus of pennate diatoms which range in size and toxicity responsible for the production of the biotoxin domoic acid, which can cause Amnesic Shellfish Poisoning (ASP) including such symptoms as memory loss, brain damage and in extreme cases, death in humans.

While Pseudo-nitzschia (PN) has been present in Maine’s waters since monitoring began, the first toxic shellfish scores occurred in 2016, with scores jumping from no toxicity in early September to over the regulatory quarantine limit in late September.

This prompted a shellfish harvesting closure of nearly all of eastern Maine and a recall of one week of blue mussel harvest, one lot of quahogs that had been contained in wet storage and three days of softshell clam harvest. In total, nearly 11,000 lbs. of shellfish were impacted, with 96 percent of product recovered and destroyed. There were no reported illnesses.

Since the high shellfish scores in late September of 2016, Maine has seen fluctuating shellfish scores and PN concentrations. In 2017, water samples from up and down the coast showed elevated numbers of PN, but no toxicity in shellfish throughout the summer.

However, in September there was a shift in the composition of the bloom from being dominated by small cell to large cell varieties, which resulted in shellfish scores over the quarantine limit. This caused a portion of eastern Maine to close for shellfish harvesting. DMR also recalled five days of blue mussel harvest totaling 58,480 lbs., 98 percent of which was successfully recovered and destroyed. Again, there were no reported illnesses.

The 2017 closure that resulted from high shellfish scores lasted from September until early October in the Frenchman Bay region, with smaller precautionary closures lasting into early December of 2017. However, Maine hadn’t seen the last of PN for the winter. A relatively large bloom of PN occurred in Casco Bay, comprised of mostly large cells, extending the shellfish harvesting closure through mid-January.

This extension of the harvesting closure led to DMR staff collaborating with local shellfish wardens to collect shellfish and water samples from an increased number of sites in and around Casco Bay. With the help of the wardens, DMR could carefully monitor the bloom and reopen harvest areas.

DMR collaborated with other laboratories to understand what caused the blooms of 2016 and 2017 to be so toxic and determined that a new species, Pseudo-nitschia australis, had entered the Gulf of Maine.

How it came to be in Maine waters is still a topic of debate. This species is large for its genus and can be toxic at low concentrations. DMR now watches for the shift in bloom composition from small to large cell as an additional early warning that a PN bloom may be becoming toxic.

Collaboration with other laboratories is ongoing in working to develop new technologies to more rapidly determine the species contained within a bloom.

In 2018, DMR held an ASP conference to provide information and improve understanding of the occurrence and management of ASP in Maine. The conference included presentations on direct toxin detection, reasons for ASP occurrences in Maine, challenges and successes in monitoring for ASP, the usage of short-term precautionary closures and continued research and management strategies for the future.

With the 2019 ASP season fast approaching, DMR and a network of volunteer partners are gearing up for increased phytoplankton and shellfish sampling, including the use of traps to hold shellfish for testing in areas of low resource.

These traps allow DMR field staff to quickly and efficiently collect shellfish resources in areas that have experienced resource decline, or that have historically low availability of shellfish. Inter-laboratory collaborations, innovative phytoplankton monitoring strategies, precautionary closures, shellfish traps, additional phytoplankton monitoring volunteers and shellfish warden participation are all being utilized to closely monitor PN and work to keep important shellfish harvesting areas open for business.


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