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Climate Change Shifts Range and Behavior of Ocean Species

Despite slower temperature shifts in ocean waters, ocean life from plankton to fish have begun moving in response to global warming
Lobster Fishing Boat Victoria



Flickr/Rob Kleine

Although this year hasn't been too unusual, Maine lobsterman Steve Train has noticed several new species appearing in his nets over the past few years. Red hake is more common than it used to be in Casco Bay, he said, as well as sea bass and squid. Lobster is also showing up earlier than Independence Day, when he used to begin his yearly catch.

"If you wait for the Fourth of July to get them now, you're going to miss them," Train said.

What Train is seeing in Casco Bay could be a small example of a global trend. Despite the fact that continents are warming about three times faster than the world's oceans, marine species are nonetheless reacting to climate change as much as -- or more than -- land-based species, a new study shows.

Twelve times more, in some cases. Bony fish and the tiny phytoplankton that form the base of the ocean food web shifted their range an average of 72 kilometers (45 miles) per decade in response to climate change, the study's authors found, while species on land shifted by an average of only 6 kilometers per decade.

The paper, published yesterday in the scientific journal Nature Climate Change, compiled more than 1,700 long-term observations on a wide range of ocean species, from algae to polar bears, finding that about 80 percent of these data reflected shifts in range, population and behavior consistent with what scientists expect with a changing climate.

"We are seeing, across the globe, species responding to recent climate warming by shifting their ranges, generally pole-ward, and seeing advances in their phenology," said co-author Pippa Moore, a professor of aquatic biology at the Institute of Biological, Environmental and Rural Sciences at Aberystwyth University in the United Kingdom.

Great expectations matched by data
"What this data shows is that marine ecosystems are responding to environmental change, and they're responding at a faster rate than just simple metrics like mean global temperature rise would perhaps indicate," said Moore.

This meta-analysis will be included in the upcoming Intergovernmental Panel on Climate Change Fifth Assessment Report, and is the first comprehensive assessment of the impacts of climate change on the global marine system.

The authors focused on multi-species studies to avoid bias -- less than 11 percent of the observations used were based on single-species studies -- because journal editors are more likely to publish papers that exhibit larger, more dramatic results. They also chose studies that provided data for a span of at least 19 years and safely excluded impacts from other stressors like pollution and overfishing.

That 80 percent of the data are consistent with expectations under climate change is remarkable, said co-author William Sydeman, senior scientist with the Farallon Institute for Advanced Ecosystem Research in Petaluma, Calif. "The statistical significance of that is off the charts," he said.

Of the wide range of species studied, plankton showed some of the largest changes in distribution, said Sydeman, probably because these tiny animals and plants "go with the flow."

"Plankton, by definition, are organisms that go where the ocean takes them," Sydeman said. "Therefore, the movements or the changes of the distribution of planktonic organisms are really driving a lot of the differences that we saw between terrestrial organisms and marine organisms."

'Moving the dinner plate'
The major shifts seen in the ocean's plankton communities are "a really big deal," said co-author Benjamin Halpern, a research biologist with the National Center for Ecological Analysis and Synthesis at the University of California, Santa Barbara, because these tiny organisms are "what everything else ultimately feeds on."

"That's like moving the dinner plate to a totally different place in the ocean," Halpern said.

The authors also saw substantial shifts in marine species' phenology, or the seasonal timing of life cycle events like breeding or migration. Spring phenological change in the ocean has advanced by more than four days per decade, the paper states, while the shift for land-based species is estimated to be between 2.3 and 2.8 days per decade.

Like on land, behavioral timing shifts do not happen equally for all species, making it possible for "mismatches" to occur.

"There actually are differences in the rate of response between different taxonomies," Moore said.

"You're seeing quite large changes or advances in the phenology of zooplankton and fish, for instance, but seeing much-reduced changes in phenology for seabirds," she said. "If you think that seabirds perhaps eat the plankton and eat the fish, the differences in response can lead to what's called a trophic mismatch, which means that perhaps when the seabirds arrive on their colony to nest, their food supply is not there anymore."

An 'unpredictable' reorganization
The reason behind ocean species' swift adjustment to climate change is not explained in the paper. However, said Moore, it could be because parts of the ocean containing water of the same temperature, called isotherms, are changing location faster than land temperatures. Ocean isotherms span hundreds of miles, so marine creatures have to shift their ranges at a faster rate to stay comfortable.

Another unknown is exactly what the impact of these major shifts might be, but a major reorganization of underwater ecosystems seems likely.

"The structure and the functions of these ecosystems, and the services that they provide to society, are going to be more and more unpredictable," said Sydeman.

Halpern said that the impact of climate change on people like Train, whose livelihood depends on the distribution of different ocean species, is also worrisome: "It's not easy to move an entire community 200 miles up the coast when the fish move," he said.

"There's almost certainly going to be unexpected consequences from reshuffling species," he added. "Yes, nature and people can adapt, but I think at a pace slower than what we're seeing happening in response to what climate change suggests will be possible."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

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