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Clam diggers and other harvesters are reporting huge shellfish die-offs in mudflats around town. Harpswell’s harbormaster and marine resources administrator, Darcie Couture, said it may be linked to a type of algae that’s not toxic to humans but is known to kill shellfish.
Couture said she started getting calls Tuesday afternoon from harvesters and others who were noticing dead and dying clams and the intense smell of rotting shellfish on exposed mud, especially in Middle Bay. She is asking for the public’s help to understand the extent of the bloom’s effects.
A public health alert sent by Maine’s Department of Marine Resources on Tuesday said the agency is monitoring an algal bloom of the plankton Karenia mikimotoi in Casco Bay. The plankton has been linked to fish and shellfish deaths in Maine and around the world in the past, although it is not dangerous to humans.
The department noted that blooms have also been reported to the south, in New Hampshire and Massachusetts. Couture said the plankton’s presence has not been confirmed in Harpswell’s waters yet, but she suspects the prevailing winds of the last few days have pushed the bloom toward town.
Some algae produce toxins that are poisonous to humans or marine life, but even blooms of nontoxic algae can kill. As the plankton multiply and grow, they use up oxygen, suffocating other species, said Mike Doan, a staff scientist at the organization Friends of Casco Bay. When the plankton die, they continue to take oxygen from the water and mud as they rot.
Clam digger David Wilson, who is the chair of Harpswell’s Marine Resources Committee, said he noticed “a wicked smell” as he approached the mudflats yesterday near Pennellville, on Middle Bay in Brunswick. He said at first he thought it might be a dead whale that had washed ashore, but as he and the diggers he was with got closer, they saw dead and dying clams spread across the mud.
He visited Long Cove, off Orr’s Island, on Wednesday. While the clams there were alive, he saw large numbers of young clams on the mud’s surface, a sign of stress, along with piles of dead worms.
Wilson filmed a video of the devastation that was shared on the harbormaster’s Facebook page.
Much is still unknown at this stage. Couture and Wilson said they have been fielding calls from harvesters in Harpswell, Brunswick, Wiscasset and elsewhere. Some have reported scenes similar to Wilson’s video. Murky, discolored brown water was visible near the Safe Harbor Great Island marina in a video that Couture showed the Anchor. But she said there are also areas of town that appear to be unaffected.
A digger who lives in Harpswell Center, Mike Bernier, said he has not noticed dead clams on the beaches and rocky shorelines where he harvests, but those higher areas tend to be less affected by blooms than mudflats.
He pointed out that algal blooms that kill fish and shellfish are often associated with very high temperatures or with heavy rainfall that washes nutrients into bays and spurs plankton growth. Harpswell has had neither recently, leaving Bernier and others wondering whether something like pollution from boats could be to blame.
Scott Moody, owner of Moody’s Seafood on Cundy’s Harbor Road, which buys clams up and down Maine’s coast, said he is still gathering information from diggers. He said he worries that many species could be affected, from soft-shell clams to wild and cultivated oysters. He is concerned that the episode may even impact quahogs, or hard clams, which have been more resilient to algal blooms in the past.
Couture said it appears the Department of Marine Resources knew about the bloom for days or a week before making an announcement about it. “I’m a little irritated,” she said.
A water quality-monitoring buoy in Middle Bay shows spikes in chlorophyll levels — a sign of an algal bloom — starting Sept. 3. If Couture had known about the plankton, she could have connected the dots and possibly helped some aquaculturists limit their losses, she said.
But it isn’t clear whether the earlier bloom is related to the current Karenia mikimotoi bloom. A spokesperson for the Department of Marine Resources said that it did find an algal bloom on the New Meadows River on Sept. 1, but it was made up mostly of another species, with only trace amounts of Karenia mikimotoi.
The spokesperson, Jeff Nichols, said the department learned about another bloom in central and southern Casco Bay on Monday and identified Karenia mikimotoi there on Tuesday, the same day it notified harvesters and the public.
As the bloom wipes out clam and worm populations, harvesters are watching the source of their income disappear.
“It could be pretty catastrophic for the southern part of the state,” Moody said.
Wilson estimated that he and his two partners could miss out on $40,000 over the next month if all the clams die in the flats they dig. He said all the clams he saw Tuesday were dead. It was only last year that the Middle Bay mudflats came back after a 2022 die-off, and Couture said a survey of the area in the first week of September found the clam population there was booming.
While Wilson has other jobs he can fall back on, like construction, he is worried about diggers who rely on shellfish for their entire income. For someone like Bernier, the effect might be more competition in the areas he digs from harvesters whose grounds have been wiped out.
It can take as long as seven years for shellfish populations to rebuild, Wilson said. The recovery from the 2022 die-off took three or four years. But he said if enough shellfish die, they will acidify the mud and make it impossible for new clams to survive until the chemistry returns to normal.
The Department of Marine Resources said the last Karenia mikimotoi bloom was in 2017, and saw plankton levels 20 times higher than what the agency reported from Portland on Tuesday.
At a Harpswell Fisheries Committee meeting on Wednesday night, Couture said she is collecting samples for scientists at the Bigelow Laboratory for Ocean Sciences in East Boothbay and the National Oceanic and Atmospheric Administration to test for Karenia mikimotoi. She also said she has spoken to NOAA scientists working to map the bloom from satellite images to try to locate its origin and where it might be spreading.
Couture hopes some kind of economic relief might emerge, although she doesn’t know where it would come from: the state, the federal government or somewhere else. She is trying to gather evidence of the bloom’s impact, and she wants people to email her about what they are seeing at harbormaster@town.harpswell.me.us.
“I can’t visit the whole coast,” she said. “I’m relying on citizens to help me so that we can find some way to help the clammers.”
