A handful of sea stars at Acadia National Park in Maine in July, 2021. Two species of sea stars are vigorously crossbreeding in a hybrid zone from Nova Scotia to Cape Cod, recent science published in Molecular Ecology has confirmed.Eliot Dudik/Supplied
It was somewhere off the East Coast, likely on the underside of a rock, that one sea star made the first move. She released several million eggs into the tidal waters as female sea stars are wont to do. Somewhere nearby, another sea star ejected his sperm into the salty sea.
You could say they were like an underwater Romeo and Juliet, from two different clans that just couldn’t be kept apart. Except it wasn’t lust that drew these sea star crossed lovers together. It was a hybrid zone – a swath of rapidly warming sea from Nova Scotia to Cape Cod where two species of sea stars are vigorously crossbreeding in the wild, recent science published in Molecular Ecology has confirmed.
As long suspected, the research confirmed that the common starfish, Asterias rubens, with its gently tapered arms and warm-water disposition, has been producing galaxies of hybrids with the plumper, sometimes purply, Forbes sea star, or Asterias forbesi, which prefers cooler ocean temperatures, said the study’s author, Melina Giakoumis, associate director of the Institute for Comparative Genomics at the American Museum of Natural History.
While there is no new species of sea star and it’s unclear whether one species will take over the other, the study’s results imply that the genetic makeup of North Atlantic sea stars is influenced by the environment.
“As a keystone species, sea stars are a crucial piece of this ecosystem and we need to know how they are adapting to their environment in order to understand the larger changes in this highly susceptible region,” she said.
Melina Giakoumis at Acadia National Park, Maine, in July, 2021. Giakoumis is the associate director of the Institute for Comparative Genomics at the American Museum of Natural History.Eliot Dudik/Supplied
The heart of the hybrid zone is the Gulf of Maine. Known as a sea within a sea, it’s a semi-enclosed part of the North Atlantic bordered by Nova Scotia, New Brunswick, Massachusetts, New Hampshire and Maine, and warming faster than 95 per cent of the world’s oceans.
With temperatures increasing three times faster than anywhere else in the world, the Gulf of Maine is a harbinger for climate change – and a sea change is already under way among teeming flora and fauna in its biologically productive marine ecosystem.
As the oceans warm, many sea creatures in the northeastern United States have been moving farther and farther north. Lobster, which are sensitive to changes to ocean temperature, have already begun to shift northward, according to science published in the Journal of Geophysical Research: Oceans in 2017.
This brave new world of a warmer Gulf of Maine has led to changes for individual species and for entire food webs, said Dalhousie University biologist Boris Worm. It’s being studied and closely watched by scientists all over the world to learn how ecosystems change as oceans warm.
“It’s a bit like a bathtub, as opposed to more open areas like the Scotian Shelf off Halifax,” said Dr. Worm.
The Gulf of Maine is also influenced by two currents – a cold-water tap coming down from the Labrador Current that has been weakening in part because of climate change, and the Gulf Stream which sends warm water up from the south.
The Gulf of Maine Research Institute has been tracking ocean temperatures for more than 40 years. The year 2021 was the warmest on record and the first time the gulf experienced a marine heat wave lasting the whole year, said the institute’s climate centre director, Dave Reidmiller, in a video on the organization’s website.
It’s also making the gulf inhospitable to some species while becoming a Goldilocks environment for others, he added.
A rapidly warming Gulf of Maine has already led to a decline in lobster catch in southern New England. And there’s no doubt the $2-billion Canadian lobster industry is already seeing bigger landings in the more northern range of the fishery and less in the south, said Lobster Council of Canada executive director Geoff Irvine.
“That’s something that we’re watching closely,” he said. “The trend is we’re catching more lobster in Newfoundland, Quebec and Cape Breton than we ever have and less in the Bay of Fundy and the Gulf of Maine than we ever have.”
A warming Gulf of Maine is also why more subtropical creatures are turning up in Nova Scotia waters, including the butterfly fish, triggerfish, seahorses and, at Lawrencetown Beach last month, a Portuguese man-of-war.
The changes have already affected food chains including plankton, which, like the sea stars, are a keystone species vital to the ecosystem. Copepods, a planktonic crustacean, is the main sustenance of right whales, which in recent years have moved from the Bay of Fundy in the Gulf of Maine to the more northern Gulf of St. Lawrence, in search of what scientists believe is a richer supply of copepods. Their shift has put the endangered species at increased risk of ship strikes and fishing gear entanglements.
Kelp forests, a major habitat for underwater creatures, particularly important for young fish to hide in, may also be at risk.
The sea is changing, said Dr. Worm, and some species may not be viable anymore, but the changes in the Gulf of Maine are not catastrophic. In other words, there is no Shakespearean tragedy – not yet anyway.
He said the hybridization or evolutionary changes seen in the sea stars may point to their ability to be resilient in the face of climate change.
“Part of that resilience of nature that we have seen is species can move,” said Dr. Worm. “They can evolve. They can form new relationships with other species. That’s part of how nature is rolling the dice over and over again, hoping to get a good outcome.”
With a report from The Canadian Press