Researchers say that changes they've detected in water in the Gulf of Maine -- which includes water around Acadia National Park, pictured -- could affect the types of life there, and the lucrative fish stocks the gulf has long been known for. Photo courtesy National Parks Service
BANGOR, Maine, July 8 (UPI) -- Scientists have known the Gulf of Maine is warming rapidly, but new research suggests it's also getting saltier, more acidic and increasingly stratified -- raising concerns for its fish stocks.
The dramatic shifts in the gulf's biochemistry are raising questions about the future of a region that has historically produced some of the world's richest fish stocks -- from cod to lobsters -- and has built billion-dollar industries around them.
"We found that primary productivity, the rate at which the phytoplankton is fixing carbon in the ocean, has dropped to about a third of what it was in the early 2000s," Barney Balch, a biological oceanographer and senior researcher at the Bigelow Laboratory for Ocean Sciences, told UPI. "That really raised alarm bells with us."
According to Balch, decreases in primary productivity -- the carbon fixing -- may affect life in the gulf from phytoplankton all the way up the food chain, including fish that humans eat.
Boats of opportunity
For more than 20 years, Balch and his research partners have been helping NASA calibrate and validate ocean surface temperature data collected by the agency's polar-orbit satellites.
"They need someone down on the water making measurements precisely as the satellites go over," Balch said.
Because measurements can only be collected during fair weather -- and because the research team is mostly reliant on "boats of opportunity" -- whenever a high-pressure system approaches, the crew hops in their truck-turned-mobile research lab and drives it onto a ferry bound for Nova Scotia.
"We're basically turning these ferries into ocean research vessels," Balch said.
The monitoring effort remains ongoing, but this summer, Balch and his co-authors compiled 20 years of data into a single paper, highlighting dramatic shifts in water temperature, salinity, acidity and biological production within the Gulf of Maine.
Many researchers have pointed to the Gulf of Maine as one of the world's most rapidly warming bodies of water, but Balch's paper, published this month in the Journal of Geophysical Research: Biogeosciences, is one of first to showcase the full scope of the gulf's regime change.
Balch said an intrusion of warm water came up through the Northeast Channel between 2008 and 2010, with researchers seeing water 3 degrees Celsius warmer between 300 and 400 feet deep.
At the same depths, data also revealed an increase in salinity.
"That's a fingerprint of North Atlantic Slope Water, water just north of the Gulf Stream that is warmer and saltier," Balch said.
Historically, the gulf has been influenced by warm water flowing north from the North Atlantic and cool, nutrient-dense water flowing south from the Arctic through the Labrador Channel.
The data now suggests the influence of the North Atlantic has become dominant, causing a phase change within the Gulf of Maine. It isn't simply heating up because the atmosphere is getting warmer, the body's plumbing has fundamentally changed.
"With changes in both ocean circulation and atmospheric circulation, we've seen more warm water entering into the gulf in recent decades," Sean Bickel, a Maine state climatologist, told UPI.
"It's important to think about these climate effects on the gulf as going beyond just temperature effects and the direct effect on species ranges," Richard Wahle, marine ecologist and professor at the University of Maine, told UPI.
"We also have these really interesting changes in the oceanography as result of circulation changes in the North Atlantic," Wahle said.
While it's not yet clear how these changes will impact the region's ecosystems, data collected by Balch's team suggest the base of the marine food web in the gulf is in the midst of a transformation.
Phytoplankton aren't just less efficient and abundant, their diversity has shifted. Just as changes in diet and environment can alter the microbial community inside a person's gut, sea surface changes can reshape phytoplankton demographics.
The tropical water arriving via the Northeast Passage hosts fewer diatoms, a class of phytoplankton rich in silica and a vital source of sustenance for zooplankton, crustaceans and other members of the second rung of the food ladder -- all the species that eat primary producers.
There is a phrase among oceanographers and marine biologists: All fish are diatoms. The phrase -- which Balch credits to renowned oceanographer Henry Bryant Bigelow, founding director of the Woods Hole Oceanographic Institution -- is a twist on a Bible verse: All flesh is grass.
"What Bigelow was saying was that the biomass of fish is reliant on this one class of phytoplankton," Balch said. "And he understood this back in the early 1900s."
Lobsters aren't fish, they're shellfish, and technically speaking, they're crustaceans. But they, too, indirectly rely on diatoms.
While adult lobster feed on an array of small species, from fish to clams, lobster larvae rely on zooplankton -- specifically, a copepod species called Calanus finmarchicus.
Calanus finmarchicus really likes to eat diatoms.
Over the last 30 years, warming has mostly proven a boon to lobsters in the Gulf of Maine, especially in places, like the Penobscot Bay and the Bay of Fundy, that were historically on the chillier side of a lobster's comfort zone.
Beginning in the 1990s, more comfortable conditions and dramatic declines in the number of lobster-eating ground fish, such as cod, monkfish, haddock and halibut, led to year after year of record lobster landings.
But while there are more fertile female lobsters roaming the gulf than ever, Wahle, a lobster expert, said juvenile settlements are stagnating.
"The larval settlement index has been falling off in the Gulf of Maine right at a time when we would expect to see it trending up," Wahle said.
Early stage larvae numbers look as expected, given that females are laying plenty of eggs, but late-stage larvae numbers are down.
"The one correlation that really stands out is the correlation with late-stage larvae and the abundance of this one species of copepod," said Wahle, who is researching the phenomenon. "It's also the same species that herring depend on and that right whales depend on. It took us by surprise because no one really knew what lobster larvae were eating."
It's no surprise a lot of species like munching on Calanus finmarchicus.
"They're so lipid-rich, they're like little tiny butterballs -- about 60% of their body weight is fat," Wahle said.
Wahle can't say for certain that a decline in copepod numbers is responsible for diminished late-stage lobster larvae totals, but early results from his experiments suggest the butterball is an important part of larval lobsters' diets, especially late-stage larvae.
And though Balch isn't privy to the data being collected by Wahle and his research partners, he says it's not a stretch to hypothesize that declines in diatoms, a primary source of nutrients for copepods, are likely to have ripple effects up the food chain -- ripple effects that will ultimately impact the lobsters and some number of other fisheries.