Atlantic Blue Crabs are one of many species along the Eastern Seaboard expanding their northward travels. (U.S. National Archives)

Changing Currents Shake Up Species

Due to warming and acidification, ocean creatures are on the move

By Aaron Tremper

12/29/2021

When marine biologist Chris Paparo isn’t managing Stony Brook University’s Marine Sciences Center, he’s snapping photos or shooting video for Fish Guy Photos, his web site featuring shots of nesting ospreys, lunge-feeding humpback whales and pods of bottlenose dolphins in the ocean off Long Island. 

Paparo often sets up a 360-degree video camera on the ocean floor inside a metal cage baited with clam or fish chum to photograph the passing marine life. 

“It’s a surprise until I get home and watch the video,” says Paparo, who often passes the footage on to his colleagues at the Marine Sciences Center for research. “Some days nothing, others cool stuff.”

One of Paparo’s videos from August showed more than passive fish gliding by. A school of gray triggerfish attempted to devour the camera. The video shows mouths packed with formidable teeth. 

Grey triggerfish, whose chompers enable them to eat local lobsters, aren’t unheard of around New York during the summer and early fall, when they migrate north from the Gulf of Mexico. Yet thanks to ocean warming, this hungry predator joins several species grabbing the attention of anglers and researchers as it stays longer in the Northeast before heading south again.

Climate change isn’t just warming the air, it’s warming marine ecosystems as well. As aquatic creatures move in search of food and other necessities, they are exposed to other species in novel ways. Some are hardier and better equipped to thrive than others. Ocean warming is a sort of survivalist story, a deep-sea version of the “Hunger Games.” 

Underwater winners and losers

Increased ocean acidification caused by climate change thins the shells of mussels and clams. That benefits blue crabs which find it easier to break open the less sturdy shells, and the crabs are expanding their range as well. And the triggerfish have been munching on local lobster populations, which for many reasons, have been dwindling.

“We’re going to see more and more species that you would see between New Jersey and North Carolina,” says Todd Gardner, a fish researcher with Biota Aquariums, a U.S. company that sells sustainable saltwater aquariums stocked with fish bred in captivity.

 “We’re already seeing that.” 

Some fish populations, like Atlantic cod found in the Gulf of Maine, are seeing a population dive because of ocean warming, according to a 2018 National Climate Assessment. Others, including New England lobsters, are saving themselves by settling further north, including in Canadian waters. The lobsters aren’t actually migrating. Instead, more young lobsters are making it to adulthood in the Gulf of Maine, where the water is still cooler, than in the southern parts of New England. Both developing and adult lobsters are sensitive to overheating. Adult lobsters begin to face respiratory, parasitic and immune issues once the thermometer goes past 68 degrees Fahrenheit.

Maine’s warming waters may push lobster populations farther north (Jeremy Bezanger)

American lobsters are among the most commercially important species affected by this transition. A 2018 study found a 97.7% decrease in registered lobster catches in New York between 1996 and 2014. A local die-off event in September 1999 led to severe drops in annual catches in following years. Maine began reaping the benefits of this shift, with a more than 200% increase in catches between 1994 and 2014. 

The Maine lobster renaissance won’t last forever. The coastal water temperatures there are expected to see a 2 to 3 degree Celsius increase by 2100. A 2016 study that replicated those conditions found increased die-offs among developing lobsters.

The Gulf Stream shift

According to the Gulf of Maine Research Institute, sea-surface temperatures have increased 99% faster there than the rest of the world’s oceans over the past decade. The study authors say their models showed that a poleward shift in the warm oceanic current known as the Gulf Stream had the strongest impact on temperatures in the Gulf of Maine. 

The tropical waters of the Gulf Stream have a strong impact on the climate of the eastern North American seaboard before flowing across the Atlantic to Europe. Previous research has suggested that this shift in the Gulf Stream is linked to increased greenhouse gases and less cold water flowing southward. This warming isn’t yet intense enough to keep lobsters from thriving, but it is encouraging other warm-water species that prey on lobsters to trek north.

Gray triggerfish are among the most cunning of these hunters. Their knack for raiding lobster pots and bait lines have led to New England lobstermen hauling up traps with live triggerfish feeding on their catch. 

Gardner says that while gray triggerfish prefer warmer waters, they’re able to tolerate a greater range of temperatures than lobsters, so they are steadily extending their range northward during the summer months. The species is now being spotted more frequently in areas as far north as Nova Scotia and even across the Atlantic in Great Britain. He says they are a highly migratory species that, as temperatures warm, are gradually becoming semi-permanent residents off New York from June to December.  

Another predatory fish that’s moving north due to climate change is the black sea bass, a voracious predator that, like triggerfish, has an appetite for young lobsters. 

The black sea bass is itself a prized commodity for commercial and recreational anglers. They have become so abundant off Long Island that the New York Department of Environmental Conservation won an appeal this spring to expand federal fishing quota allocations. 

The dangers expand

For now, the blue crab also appears to be a winner in the ocean-warming sweepstakes.

Like the American lobster, blue crabs are a fishing staple in their most popular range, the Chesapeake Bay. Unlike lobsters, the crabs seem able to prefer the heat.  

A 2019 study predicted that Chesepeake blue crabs will fare well as oceans continue to warm. And while the crabs hibernate when ocean temperatures fall below 50 degrees Fahrenheit, warmer waters may mean that blue crabs may remain active year-round by the end of the century.

Blue crabs are also extending their range. Still thriving in Chesapeake Bay, more crabs have been found in the Northeast over the past 35 years and now can be found as far north as Nova Scotia. Young blue crabs often fall prey to the likes of red drum and cobia, predatory fish species that Paparo and Gardner say are also expanding their range. 

In these scenarios, it might seem that the shifts due to ocean warming are benefiting humans as well. Gray triggerfish and black sea bass are palatable to people. Paparo and others caution against such reductive thinking: Species that are bountiful now may move or die out as warming continues. Changing marine ecosystems are rooted in complex relationships that defy simple explanations. 

“Some people may think ‘Oh, that’s great, I can start catching tarpon here,’ or things that they might have to go to say, Florida, the Carolinas for,” says Paparo. “But those places are going to start to become deserts.“

That’s what has happened off Florida, where coral die-offs have been caused by climate change and excess nitrogen run-off. In its 2014 Assessment, the Intergovernmental Panel on Climate Change lists coral reefs as one of the most vulnerable marine ecosystems, with little room for adapting to all the ways humans threaten the seas. Dredging, overfishing and trash are only a few of the threats.  

“It’s not just climate change, it’s us,” says Paparo. “We’ve had such a negative impact on this planet as far as temperatures rising, ocean acidification and adding too many nutrients to waterways. It’s a bigger problem than just climate change.”