Fisheries are ‘at the point of the sword’ of ocean acidification
Posted on November 3rd, 2008By Lauren Morello
Climatewire: KODIAK, Alaska — On a crisp evening in early October, fishermen are steering their boats home into St. Paul Harbor, past the row of salmon and crab canneries that lines the docks here.
Across the harbor, scientists with the National Oceanic and Atmospheric Administration are creating the future in a series of cold-water tanks, and it doesn’t look promising for Kodiak’s fish.
In the basement of the Alaska Fisheries Science Center, they’re readying another round of experiments to determine how blue king crabs will fare in a more acidic ocean.
It’s more than an idle concern. As humans have increasingly turned to fossil fuels to produce electricity and power their vehicles, oceans have helped absorb hundreds of millions of tons of those extra carbon dioxide emissions. That has shifted the chemistry of the seas, with consequences scientists are only now beginning to understand.
In roughly 200 years, ocean pH has dropped 0.1 units on the 14-point pH range. While that may not seem like a lot, it translates into waters 30 percent more acidic than they were at the beginning of the 19th century.
It also signals the end of what scientists believe was a 650,000-year period of stable ocean chemistry.
Models used by the Intergovernmental Panel on Climate Change predict that the problem will only intensify in coming decades, with oceans becoming up to 150 percent more acidic than pre-industrial levels by the end of this century.
“We’re really hammering the system a lot harder than we have in at least the last 8,000 years, and perhaps the last 20 million years,” said Scott Doney, a marine chemist at the Woods Hole Oceanographic Institution in Woods Hole, Mass.
That kind of rapid change could rearrange the priorities of shellfish, corals and plankton by lowering their reproduction and growth levels. In extreme cases, it could dissolve the shells off their backs.
That may explain why one scientist, attempting to explain ocean acidification to lawmakers during a congressional hearing this spring, referred to the phenomenon as “global warming’s ‘evil twin.’”
Hard times ahead for the ‘popcorn of the sea’?
The king crabs being tested in the Kodiak laboratory are one piece of the puzzle. Researchers are conducting a series of experiments to see how the crabs — a signature Alaskan shellfish — will fare in tanks of water set to mimic conditions in 50 or 100 years.
“If I’m a crab, maybe I can just ramp up my physiology, ramp up my metabolism, and just keep making my shell,” explains Bob Foy, director of NOAA’s Kodiak lab. “Maybe I’ll be okay.”
But initial results have been stark. Crabs exposed to a pH drop of 0.5 units reduced their growth by an average of 15 percent. The survival rate of young crabs dropped by two-thirds.
Experiments on the tiny swimming snails known as pteropods have produced similar results. The shells of pteropods exposed to pH levels predicted to occur in the North Pacific Ocean by the end of century dissolved in just 48 hours.
“It was one of the experiments that really opened eyes wide to the effect of ocean acidification,” said Jeff Short of NOAA’s Auke Bay laboratory near Juneau.
And it hints at a potential problem for pink salmon. Their young’s voracious appetite for pteropods — which Doney called “the popcorn of the sea” — accounts for 45 percent of their diet.
In the end, “it becomes kind of an issue of energy budget,” said Chris Sabine, a biological oceanographer at the Pacific Marine Environmental Laboratory in Seattle. “If animals are expending more energy to maintain their shells, that’s less energy they have to make babies or grow themselves.”
The local economy and a way of life at risk
In Alaska, part of the problem is also logistics. The state’s geography is working against it.
The worldwide swirl of ocean currents dumps waters naturally rich in carbon dioxide off the coast of Alaska at much shallower depths than in the more temperate seas off the continental United States.
In the Gulf of Alaska, for example, water that is corrosive to marine organisms’ chalky shells can be found just 100 meters, or about 300 feet, below the ocean surface, and it’s creeping upward at rate of 1 meter per year.
Eventually, those acidic waters will reach the ocean surface, a situation that could happen in Alaska within the next 50 to 100 years, Sabine said. “When that happens, the organisms will have to actively keep building their shells, because their shells will be dissolving.”
Temperature also comes into play, since cold waters like those off Alaska can absorb more CO2 than warmer waters.
“Alaska is going to be at the forefront of these impacts,” said Short. “It’s because we have all of the factors that make us vulnerable.”
It’s a situation that the state’s fishing industry is watching closely (see related story).
The economic stakes are high: Alaska’s catch totaled 5.7 billion pounds in 2005, or 59 percent of the total U.S. catch. Last year, four of the state’s fishing communities ranked among the country’s top 10 fishing ports by value of catch.
With huge amounts of money and a way of life at risk, “ocean acidification has hit the radar screen of fishermen and scientists and legislators and managers like a rock in the last couple of years,” said Foy.
Only now are scientists and the fishing industry beginning to realize how ocean acidification could disrupt ecosystems, he said.
Mark Vinsel, executive director of United Fishermen of Alaska, an umbrella group whose members include 37 smaller fishing organizations, called ocean acidification “troubling and perhaps ominous” for Alaska’s salmon, crab, herring and groundfish industries.
“This is the very point of the sword for global warming, to fishing fleets and ocean ecosystems,” he said. “The chemical composition of the water will affect the ocean from top to bottom.”
