Invasive species exploit a warming Gulf of Maine, sometimes with destructive results
BRUNSWICKS tory by Colin Woodard/ Staff WriterPhotos by Gregory Rec/ Staff Photographer
Compare intertidal flats in Brunswick’s Maquoit Bay in June 2001 (left) and in August 2013 (right).Photos courtesy of Hilary A. Neckles, United States Geological Survey
Until two years ago, if you had walked down to the shore of Maquoit Bay at low tide, you would have seen a meadow of eelgrass stretching nearly as far as the eye could see across the exposed seafloor. Here near the head of the bay, the sea grass stretched for two miles to the opposite shore, creating a vast nursery for the shellfish and forage species of Casco Bay, of which Maquoit is a part.
Now there’s only mud.
Green crabs took over the bay in the late fall of 2012 and the spring and summer of 2013, tearing up the eelgrass in their pursuit of prey and devouring almost every clam and mussel from here to Yarmouth. Fueled by record high water temperatures in 2012 and a mild winter in 2013, the green crab population grew so huge that the mudflats of Casco Bay became cratered with their burrowing, and much of the Maquoit and adjacent Middle Bay bottom turned into a lunar landscape.
Eelgrass coverage in Maquoit Bay fell by 83 percent. With nothing rooted to the bottom, the seawater turned far muddier, making life hard on any plants or baby clams that tried to recolonize the bay.
“We were astounded,” says Hilary Neckles of the U.S. Geological Survey’s Patuxent Wildlife Research Center, who linked the destruction to the green crabs. “The ecological ramifications really reverberate throughout the ecosystem, because sea grass is the preferred habitat of so many fish and shellfish species.”
Over the past decade, the Gulf of Maine has been one of the fastest-warming parts of the world’s oceans, allowing warm-water intruders to gain a toehold and earlier invaders such as the green crab to take over. Coupled with declines of the cold-loving species that have dominated the gulf for thousands of years, the ecological effects of even more gradual long-term warming are expected to be serious, even as precise forecasting remains beyond the state of scientific knowledge.
Scientists say the 2012 “ocean heat wave” was an unusual event, and that the 10-year accelerated warming trend is likely part of an oceanographic cycle and unlikely to continue. But the gulf has been consistently warming for more than 30 years, and long-term forecasts project average sea surface temperatures in our region could reach 2012-like levels by mid-century. The events of 2012 and the nearly as warm year that followed likely provide a preview of things to come, of a gulf radically transformed, with major implications for life on the Maine coast.
Genevieve MacDonald, who fishes for lobster out of Stonington, was standing on the dock at Isle au Haut one morning that summer, looked in the water, and couldn’t believe her eyes. There, swimming around the harbor like mackerel, were dozens and dozens of longfin squid, temperate creatures rarely seen in the chill waters of eastern Maine. “If you had a cast net you could have brought in a whole basket full of squid,” she recalls.
Genevieive McDonald replaces a bait bag in a lobster trap while fishing off the coast of Stonington. In 2012, McDonald saw dozens of longfin squid near Isle au Haut. The squid like warmer water and are rarely seen in the Gulf of Maine but there were numerous sightings of the squid during the “ocean heat wave” of 2012. Photo by Gregory Rec/Staff Photographer
Since then, people from Brunswick to Bristol have been encountering gigantic beds of gelatinous, finger-shaped pods in shallow water at low tide, some measuring four feet across. Researchers from the University of Maine’s Darling Marine Center ran across one in the Damariscotta River in August 2014 and, perplexed as to what they were, brought them back to the lab. A colleague recognized it at once: a longfin squid egg mass containing thousands of squirming embryos.
The squid, apparently, are intending to stick around, and MacDonald hopes they do, since they’re the stuff of calamari. “Climate change is real, but it might also provide some new opportunities if we’re careful,” she says. “Lobstering is really lucrative, and I hope it stays that way, but if something happens it would be nice to have a backup plan.
”Marissa McMahan spent that notoriously warm summer of 2012 lobstering with her father out of Georgetown and encountered a different visitor, a large, stout gray-and-black fish she’d never seen before. The fish, which began turning up in lobster traps up and down the coast, was the black sea bass, a succulent mid-Atlantic species normally unable to tolerate