Rising acidity erodes Alaska's fisheries
Alaska's marine waters - source of 60 percent of the United States' seafood harvest - show surprising impact as greenhouse emissions undermine the base of the food web.
A fisherman reaches for a crab pot in Alaska's Bering Sea. New research suggests ocean acidification stemming from climate change will be particularly problematic for the Arctic. Photo by Corey Arnold/flickr.
20 August 2009
By Douglas Fischer
Daily Climate Editor
The Arctic's increased vulnerability to climate change is not limited to higher temperatures and melting permafrost.
New research from the University of Alaska Fairbanks suggests Arctic oceans are particularly susceptible to acidification, with potentially dire consequences to Alaska's rich crab and salmon fisheries.
"Everything is acting in unison on the environment – it's not just the ice loss or the warming or the acidification," said UAF chemical oceanographer Jeremy Mathis. "The Arctic is taking a multilateral hit."
Mathis' newest data from the Gulf of Alaska show that acidity levels far higher than expected might already be impacting the food web. In several sites the increasing acidity has changed ocean chemistry so significantly that organisms are unable to pull crucial minerals out of the water to build shells, he said.
Ocean acidification, often called the sister problem to climate change, refers to the rising acidity of the world's seas as seawater absorbs carbon dioxide from the atmosphere.
By some accounts the oceans have absorbed 30 percent of the carbon dioxide humans have pumped into the atmosphere since the dawn of the industrial age, buffering the atmosphere from the harm posed by that greenhouse gas.
That storage comes with a price. The ocean's pH has dropped nearly 30 percent over the past 250 years to levels not seen in 800,000 years; if emissions continue unchecked, in 40 years the oceans could be more acidic than anything experienced in the past 12 million years, according to climate models. Scientists increasingly consider this change in ocean chemistry to be as consequential and potentially catastrophic for the globe as any temperature rise associated with climate disruption.
"When people talk about ocean acidification, it's a whole suite of changes in the chemical system," said Joanie Kleypas, an oceanographer with the National Center for Atmospheric Research in Boulder, Colo. "There's all sorts of stuff going on, and it's hard to piece it all together."
Arguably the most important impact is hampered shell formation: As ocean pH drops (and acidity rises), organisms such as corals, oysters, clams and crabs have trouble pulling from seawater the minerals to create protective shells.
It's too soon to say whether an acidifying Arctic means curtains for Alaska's lucrative king crab fishery, Mathis said.
But the impact is already being felt by a tiny creature at the base of the food web supporting the state's legendary salmon runs – the pteropod, or swimming sea snail. Accounting for up to half the diet of pink salmon, pteropods build shells from a form of calcium, aragonite, most vulnerable to acidification. Mathis' sampling of the Gulf of Alaska found several spots so undersaturated with aragonite that pteropods would find it impossible to create a shell.
Scientists estimate a 10 percent drop in the pteropod populations could drop the body weight of salmon by 20 percent; Mathis, talking with commercial salmon fishers in Alaska's Kenai Peninsula earlier this year, said many have reported smaller than normal fish.
That cannot be blamed on climate change, Mathis cautioned. But the conditions climate change will create in the oceans will set the stage for such changes. And that could leave a big hole in America's diet: Alaska in 2007 accounted 62 percent of the the country's commercial seafood catch, according to the Marine Conservation Alliance.
"The increasing acidification of Alaska waters could have a destructive effect on all of our commercial fisheries," Mathis said. "This is a problem that we have to think about in terms of the next decade instead of the next century."
Others are more cautious about stating that Arctic ecosystems are any more at risk by acidification than tropical ones.
Cold water holds more gas than warmer water – the reason why a refrigerated can of cola fizzes less aggressively when opened than a warm one. While this means frigid waters off Alaska's coasts can absorb more carbon dioxide from burning fossil fuels, it also means the waters were naturally more acidic and that species in those waters are adapted to lower pH levels.
"It won't necessarily have a more severe impact," said Oceana marine scientist Ellycia Harrould-Kolieb. "It's having an earlier impact."
"As more and more carbon dioxide is absorbed by the oceans, it's going to spread from the poles to the tropics."
There's also a question whether Arctic organisms are more vulnerable than their tropical counterparts, Kleypas said.
Northern critters might be able to adapt more successfully to changing ocean chemistry than tropical coral reefs, which Kleypas compared to "spoiled brats" that have existed for eons in comfortably stable, higher pH waters.
Indeed, the situation in the Arctic could be akin to adding a few degrees to the summertime highs in Phoenix, she said: the typical resident, well-adapted to the heat, wouldn't have to do much to adjust.
But force that same increase upon someone living in Hawaii, where temperatures stay comfortably constant, and the change is unbearable.
"If they're already used to (stress), they've figured out a way to deal with it," she said.
"Not that people are wrong," she added. But "we're assuming things we shouldn't assume yet."
Still, both Kleypas and Harrould-Kolieb cautioned that acidification's consequences are profound and need to be taken seriously, whether in the tropics or at the poles.
Mathis agrees. While the full range of acidification's effects remains uncertain, it's clear at this point that the changing oceans pose a threat to Alaska's commercial fisheries and subsistence communities, he said.
"Ecosystems in Alaska are going to take a hit from ocean acidification. Right now, we don't know how they are going to respond."
Photos of the F/V Rollo and the F/V Two Bears, both skippered by Eric Nyhammer, courtesy of Corey Arnold/flickr. Photo of Jeremy Mathis courtesy University of Alaska Fairbanks. Photo of pteropod courtesy Russ Hopcroft, UAF School of Fisheries and Ocean Sciences.
Contact Daily Climate editor Douglas Fischer at email@example.com
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