Even before he touched the shells, Steve Vachon knew something was wrong.

The stench of rot had led him to the little Maquoit Bay cove behind his home on Mere Point Road. He walked along the mudflats, noting the presence a strange white foam, until he reached clamshells.

When he turned the clams over to find their bellies oozing out, his fears were confirmed — the shellfish were all dead.

In late July and early August, a confluence of factors, including extreme heat, heavy rainfall and the possible presence of lawn fertilizers and pesticides, contributed to the death of 4 acres of softshell clams in Brunswick, according to Dan Devereaux, the town’s coastal resource manager.

Freeport and Harpswell saw similar clam deaths over the summer.

Devereaux, who presented the issue to the Brunswick Town Council Monday evening, said that samples from the affected areas in Maquoit, Middle, Mere Point and Tomas bays tested negative for diseases that could have led to further shellfish deaths. Yet he warned that the factors that likely caused this summer’s mortality event will only worsen over time.

“This is all part of the changing system in the changing climate and the warming oceans,” he said. “We suspect that will happen more and more, particularly with softshell clam species.”

A perfect storm

The clam deaths, Brunswick’s first significant shellfish mortality event since 2017, were the result of several elements working in concert, according to Devereaux.

“There’s so many different metrics that could have contributed to this,” he said. “You’ve got a perfect storm in certain spots.”

He said the first factor behind the clam death was extreme heat, which can be particularly damaging to softshell clams. This summer, high temperatures coincided with extreme low tides that left mudflaps baking, unprotected from the sun.

A report from Kennebec River Biosciences, a Richmond lab that analyzed tissue samples from the affected area, agreed high heat could be partly responsible for the mortality event.

The report also noted the presence of an unknown organism, likely an alga, and suggested the infection could have contributed to the clams’ death.

Algae can be good for marine life, when large, established shellfish populations operate as a filtration system that keeps water clear. Yet wild softshell clam populations in Maine have been declining for decades, as water temperature and acidity levels have risen, according to data from the Friends of Casco Bay.

Without a properly functioning natural filtration system, Brunswick’s waters are more susceptible to algae blooms, which occur when excess nutrients, including nitrogen and phosphorus, result in an explosion of algae growth. When the algae die and decompose, oxygen levels can drop dramatically, choking out other marine life — including both fish and the shellfish seedlings that could otherwise have helped to prevent future blooms.

Brunswick can do little to prevent rising ocean temperatures. In order to limit future algae blooms, Devereaux said, the town will need to focus on the problem it can control: the use of nitrogen-rich fertilizers and pesticides, which rains can carry from lawns into the ocean.

Something needs to be done

Cody Gillis Jr., chairperson of the Brunswick Marine Resources Committee, has a personal stake in preserving the town’s shellfish population: As a full-time clammer and fisherman, his livelihood depends on it.

Gillis is one of the more than 200 Brunswick residents involved in the local shellfish industry, which has an estimated value of $13 million, according to Devereaux.

While the 4 acres affected by the casualty event make up only about half of 1% of Brunswick’s approximately 750 productive acres of mudflats, Gillis was concerned about what it might mean for rest of the shellfish, fish and waterfowl that inhabit Brunswick’s waters.

“The clam flats are really the lifeblood filtration system of this bay,” he said. “If we lose it, everything is going to take a hit. It all goes downhill from there.”

Earlier this summer, Gillis wrote a letter to Brunswick Environmental Planner Bina Skordas requesting the town consider zoning ordinances changes that would tighten restrictions on pesticides and fertilizers in the shoreline zone.

While he’s happy with the commitment of Brunswick’s leadership, he said he’s concerned that homeowners will prioritize their well-manicured yards over an industry that supports hundreds of residents.

“It’s alarming,” he said. “People should really pay attention to what’s downstream from their beautiful green lawns.”

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