Ocean temps full of ‘surprises’ – and not the good kind

PORTLAND — Maine fishermen face plenty of challenges including proposed whale protection rules, depredation of the state’s softshell clam stock by invasive green crabs, restrictions on seaweed harvesting and rising operating expenses.

It isn’t only the cost of running a fishing operation that’s rising, though.

Two new, recently published studies report that marine ecosystems around the world are experiencing unusually high ocean temperatures more frequently than researchers previously expected. These warming events, including marine heat waves, are disrupting marine ecosystems and the people who depend on them.

Andrew Pershing, chief scientific officer at the Gulf of Maine Research Institute, led the study “Challenges to natural and human communities from surprising ocean temperatures,” published in early August. Working with him on the project were researchers from several Maine-based institutions as well as scientists from laboratories in California and Colorado.

Pershing previously identified the Gulf of Maine as one of the most rapidly warming ecosystems in the global ocean. This time around, Pershing and his colleagues examined 65 large marine ecosystems between 1854 and 2018 to identify the frequency of “surprising” ocean temperatures, which they defined as an annual mean temperature substantially above the mean for the previous three decades.

They identified “surprises” all over the world, including in the Arctic, North Atlantic, eastern Pacific and off of Australia and found that those warming events occurred at nearly double the expected rate.

“Across the 65 ecosystems we examined, we expected about six or seven of them would experience these ‘surprises’ each year,” Pershing said. “Instead, we’ve seen an average of 12 ecosystems experiencing these warming events each year over the past seven years, including a high of 23 ‘surprises’ in 2016.”

The impacts of these warming events on both natural and human communities have been substantial.

In affected coral reefs, for example, new species of fish, plankton and the like that prefer warmer conditions often replace cold-loving species that suffer when an ecosystem warms. The impact of those changes depends on how fast they occur.

According to the study, in gradually warming ecosystems the changeover of species should be able to keep pace. In ecosystems that experience faster change, though, the size and diversity of natural communities are likely to be reduced.

Fishermen in the Gulf of Maine have already seen evidence of these changes as the lobster population seems to be moving east toward the colder waters off Canada and species formerly found only in warmer waters, such as black sea bass, have become common, at least in southern Maine waters.

The researchers explored the challenge rapid ecosystem changes pose to people making decisions about ocean resources. As the planet continues to warm, ecosystems and human communities will have to adapt to the changing conditions. It is unclear, though, whether the adjustments will keep pace as the climate trends accelerate.

Fisheries decisions are generally based on either historic data or forward-looking assumptions. The researchers also found that, as ecosystems change, forward-looking decisions fare much better as the rate of warming increases.

“We are entering a world where history is an unreliable guide for decision making,” Pershing said. “In a rapidly changing world, betting that trends will continue is a much better strategy.”

The findings of the Pershing-led study published in August were reinforced just last week by an alarming report published by the UN Intergovernmental Panel on Climate Change (IPCC).

“The world’s ocean and cryosphere (frozen regions of the earth) have been ‘taking the heat’ from climate change for decades, and consequences for nature and humanity are sweeping and severe,” Ko Barrett, vice chair of the IPCC, said in a statement last Wednesday. “The rapid changes to the ocean and the frozen parts of our planet are forcing people from coastal cities to remote Arctic communities to fundamentally alter their ways of life.”

Stephen Rappaport

Stephen Rappaport

Waterfront Editor at The Ellsworth American
Stephen Rappaport has lived in Maine for nearly 30 years. A lifelong sailor, he spends as much time as possible messing about in boats. [email protected]

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