FREEPORT, Maine — From the one-lane bridge over the Little River at low water, you can see men hunched over the mudflats, hundreds of yards from shore, flipping the sea bottom with their pitchfork-like hoes to reveal the clams hiding there.
The clams, the basis of livelihood for generations of diggers from Cape Porpoise to Lubec, are back, at least for now, their numbers slowly recovering from a climate-driven disaster that will almost certainly strike again.
Six years ago, after the Gulf of Maine warmed to unprecedented levels, green crabs flooded over these northern embayments of Casco Bay like a plague of locusts, tearing away seagrass meadows, pockmarking salt marshes with their burrows, and devouring most every mussel and soft-shell clam in their path.
Farther out to sea, puffin chicks starved and right whales abandoned their summer grounds for lack of food. Fishermen began hauling up southern creatures such as black sea bass and Maryland blue crabs. Lobsters shed so early they flooded the market, setting off a chain of events that resulted in angry Canadian lobstermen blockading New Brunswick processing plants to prevent the unloading of lobster trucks from Maine.
The Gulf of Maine is the second fastest-warming portion of the world’s oceans, a vast laboratory for ocean scientists studying how global warming affects the marine environment and for policymakers trying to figure out how to minimize the damage to fisheries, communities or, as in the case of the 2012 lobster glut, civic peace. Their discoveries underscore the seriousness of the changes and the complexity of the required policy responses.
“We’re trying to go from being reactive to being proactive, so we can get ahead of these events rather than sit back and wait for them to unfold,” says Andrew Pershing, chief scientific officer at the Gulf of Maine Research Institute in Portland, who has been at the forefront of tracking the rapid warming of the gulf.
Since the record-breaking heat wave of 2012-2013, the Gulf of Maine has continued to warm, seeing its second and third warmest sea surface temperature years on record in 2016 and 2018. Researchers have also learned that the whole while, even during cooler years at the surface, the depths of the gulf have been steadily warming – due, almost certainly, to the ongoing meltdown of Greenland and the Arctic, which is altering the interplay of the deep ocean currents that feed what has been one of the most productive marine environments on Earth.
“The surface waters tend to respond quickly to whatever is going on in the atmosphere and change from year to year, but the deep waters take far more energy and time to change, so they’re a really good indicator of what is going on,” says Nick Record, an oceanographer at the Bigelow Laboratory for Ocean Sciences in Boothbay. “If you see something getting a lot warmer down there, it’s a lot more likely to stay.”
To understand why the Gulf of Maine is so vulnerable to climate change, it’s important to know what it is and how it works. It’s nearly a sea of its own, extending from Cape Cod in Massachusetts to Cape Sable at the southern tip of Nova Scotia, including the Bay of Fundy, and the coast of Maine, its connections with the open Atlantic to the south nearly blocked by two shallow plateaus, Georges Bank and Browns Bank.
Two narrow channels provide the only deep-water connections into the gulf. The larger of these, the Northeast Channel, is only 22 miles wide, but through it often flows a cold, nutrient-rich current originating among the ice floes of northern Labrador. It courses around the end of Nova Scotia and spins around the gulf in a giant, life-sustaining gyre that — together with the gulf’s myriad rivers, staggering tides, and island- and peninsula-studded coastlines — mix the ocean, keeping life-giving nutrients near the surface where light sustains the microscopic plants at the base of its oversize food chain.
But the deep currents entering the Northeast Channel haven’t been as cold of late, as the melting Arctic and Greenland ice sheet have altered ocean currents and helped cause Atlantic Ocean circulation to slow by 15 percent since the mid-20th century. Recent oceanographic studies have found the Gulf Stream is shifting northward, carrying more warm water to the Gulf of Maine than climate models have generally predicted.
Warming on the scale of 5.4 to 7.2 degrees Fahrenheit over the next 80 years in the Gulf of Maine “will cause more extreme effects on the ecosystem” than previously anticipated, concluded an influential 2016 study led by Vincent Saba of the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory.
In April 2018, researchers working from the Canadian Coast Guard cutter Hudson recorded temperatures exceeding 57 degrees at depths of 150 to 450 feet – nearly 11 degrees above normal for that time of year and the highest seen in 15 years of surveys. In the two cruises since, the temperatures have been lower but still well above the averages of the 30-year period from 1981 to 2010, according to research scientist David Hebert of the Bedford Institute of Oceanography, a Canadian Department of Fisheries and Oceans facility in Dartmouth, Nova Scotia.
“It’s like there are these eddies of warm, Gulf Stream-influenced water coming in through the channel in pulses,” Hebert says, because the cold water currents that normally dominate the passage have weakened.
All that warm water flooding into the gulf’s deep basins is implicated in the catastrophic wave of deaths that have pushed the endangered North Atlantic right whale back to the brink of extinction. At least 25 of the whales have died over the past three years, reducing the worldwide population to just 411. Most appear to have been struck by ships or entangled in fishing gear after leaving their feeding grounds, where protection measures had been in place.
Why did they move? Record, of the Bigelow lab, found this year that the warmer water in the eastern gulf’s deep basins has sharply reduced their food supply: the tiny flealike copepod Calanus finmarchicus, which they scoop up by the millions with their sieve-like baleen. The warm water, he and his colleagues found, caused the copepods – which hibernate in the deep basins in winter – to decline by as much as 90 percent, leaving the whales’ summer feeding grounds off Lubec and Grand Manan Island effectively barren. (Disclosure: This reporter is a Bigelow trustee.)
More worrisome, Calanus isn’t just important to whales; it’s a keystone species for the entire gulf ecosystem, providing food for herring, mackerel, the larval stages of cod and redfish, and, in turn, everything that eats any of those creatures.
“If the Gulf of Maine loses Calanus or it declines significantly, that’s when we really lose the sub-polar ecosystem that has characterized the gulf for centuries,” Pershing says. “An ecosystem that has Calanus in it is likely to have cod and herring and whales and all the other things that make a rich ecosystem.”
Fortunately, the Calanus declines are thus far limited to the eastern gulf. In Cape Cod Bay and the western part of the gulf – where right whales still come in large numbers in the spring – copepod numbers have remained strong, because the populations there are not as dependent on seasonal hibernation.
Meanwhile, at the surface, the gulf has continued to see lots of distressingly hot years, many of them the result of changes in the jet stream, the shifting front between cold arctic and temperate continental air masses that determines much about New England’s weather.
“As the Arctic’s atmosphere is heating up it is reducing the gradient, and that slows down the jet stream,” says Glen Gawarkiewicz, an oceanographer at the Woods Hole Oceanographic Institution who helped track the phenomenon. “It’s been having these big meanders and sometimes just gets stuck in one position for weeks at a time.”
That can give northern New England weeks of unusually warm or cold weather, depending on where the jet stream has decided to plant itself. This, Gawarkiewicz says, drove the unusually warm winter of 2011-2012, when people in Quebec City walked around in T-shirts in January. It also set the stage for the “ocean heat wave” of 2012, because the upper layers of the Gulf never properly cooled down, and came out of the winter about 4 degrees warmer than usual.
A similar stall, he notes, could set the stage for another year like 2012.
When surface waters get too warm, puffins are among the first to suffer. Like so many of the gulf’s creatures, the birds are at the southern end of their range, and warmer water drives their cold-loving prey deeper than they can dive. Adults can move but not during breeding season, when they protect their nests and feed hatchlings at places like Eastern Egg Rock, east of Pemaquid, or Machias Seal Island, off Jonesport. If the food fails, the chicks starve.
The seabird scientists who study and help protect the puffin colonies have recorded a clear pattern: In years when the sea surface temperatures are cool — like this year — the chicks do well. When they’re warm, they’re devastated, as in 2016, when only 12 percent of chicks survived at the gulf’s largest colony, Machias Seal Island, compared to 68 percent in 2017, a more moderate temperature year.
Warm surface waters also threaten the North Atlantic’s largest kelp forest, which covers the summit and ridges of a submerged mountain 80 miles southeast of Portland called Cashes Ledge, and shelters fish at a density 50 times that of typical coastal sites. When water gets into the high 60s, the kelp fronds and leaves start falling apart, Brown University biologist Jon Witman told the Press Herald in December.
Climate change has aquaculture firms on edge as well, as it has brought more frequent rainfall, which sets off chains of events that make bays and estuaries more acidic – which can damage developing shells and fish gills – and appears to trigger algae blooms with unexpected properties.
“We’ve heard more from our members in the last five years about changing environmental conditions and climate change than we have ever heard in the history of our organization,” says Sebastian Belle, executive director of the Maine Aquaculture Association.
Bill Mook, owner of Mook Sea Farm, an oyster hatchery in South Bristol, was so concerned about the rise in algal blooms that he’s invested nearly $3 million in a new, land-based facility where he can hold live oysters and protect them from pathogens and the increasingly frequent harvesting closures. He thinks the problem will become so acute for the industry that his firm is also now growing commercial quantities of the microscopic algae oyster larvae eat, which he expects to sell to other hatcheries.
“We’ve made a bet that as climate and environmental change continue on the predicted path, there will be a greater demand for the technologies we’ve had to develop,” Mook says. “The trends are increasing.”
But few people are more vulnerable than wild clam harvesters, who have seen their harvests battered when conditions warm and green crabs, milky ribbon worms and other invertebrate predators thrive.
Maine’s overall soft-shell clam harvest has fallen from nearly 34 million pounds in 1950 to just 7 million in 2018. In Freeport, at the epicenter of the 2013 green crab explosion, the harvest fell from 939,695 pounds to 289,775 from 2012 and 2015 but crept back up to 522,961 last year.
Marine ecologist Brian Beal of the Downeast Institute and University of Maine at Machias is now certain that warmth-loving predators are the central challenge. He’s discovered that if you protect a section of mudflats from predators – for instance, covering it with a fine mesh that lets planktonic clam larvae settle on the mud but prevents baby crabs and worms from getting in – it grows staggering quantities of clams, even in areas diggers have written off for decades as “dead mud.”
“This has drawn back the curtain for us in terms of understanding what is happening in this ecosystem,” Beal explains, noting that baby clams are eaten up by baby crabs just a few millimeters wide, and have gone unnoticed. Bottom line: “These flats could produce lots of clams if we had fewer green crabs.”
For now, clams around Freeport and Brunswick have been recovering from the 2013 adult green crab invasion, and the area’s seagrass meadows have regrown in many locations. “Because the water quality is so good in these areas, Casco Bay’s seagrasses have proven to be really resilient,” says Hilary Neckles of the U.S. Geological Survey, who documented the collapse.
“The clams are definitely on the mend,” says Daniel Devereaux, who was Brunswick’s marine resource patrol officer for 22 years until becoming the town’s coastal resource manager in June, “as long as we can keep the green crabs at bay.”