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Tuesday September 24, 2013 MYT 12:00:00 AM
Tuesday September 24, 2013 MYT 7:37:32 AM
by craig welch
What’s in store: Ecologist Katharina Fabricius swimming through carbon dioxide bubbles off Papua New Guinea. The waters here offer a glimpse of how acidification is likely to transform the seas. – MCT photos
Ocean acidification threatens to scramble marine life on a scale almost too big to fathom.
KATHARINA Fabricius plunged from a dive boat into the Pacific Ocean of tomorrow. A bleak portrait emerged: instead of tiered jungles of branching, leafy corals, Fabricius saw mud, stubby spires and squat boulder corals. Snails and clams were mostly gone, as were worms, colourful sea squirts and ornate feather stars.
Instead of a brilliant coral reef like the one living a few hundred yards away, what the Australian Institute of Marine Sciences ecologist found resembled a slimy lake bottom. The cause: carbon dioxide (CO2). In this volcanic region off Normanby Island in Papua New Guinea, pure CO2 escapes naturally through cracks in the ocean floor, altering the water’s chemistry the same way rising CO2 from cars and power plants is changing the marine world. As a result, this isolated bay offers a chilling view of the future of the seas under ocean acidification.
As the burning of coal, oil and natural gas belches carbon dioxide into the air, a quarter of it gets absorbed by the seas, changing ocean chemistry faster than at any time in human history. Ocean acidification is helping push the seas toward a great unravelling that threatens to scramble marine life on a scale almost too big to fathom – and far faster than first expected.
Already, it has killed billions of oysters along the US Washington coast. It’s helped destroy mussels on some US Northwest shores.
It is a suspect in the softening of clam shells and in the death of some baby scallops. It already is dissolving tiny plankton, called pteropods, in Antarctica that are eaten by many ocean creatures – and that wasn’t expected for 25 years.
The problem: when CO2 mixes with water, it takes on a corrosive power that erodes some animals’ shells or skeletons. It also robs the water of ingredients animals use to grow shells in the first place. New science shows ocean acidification also can bedevil fish and the animals that eat them, from sharks to whales and seabirds.
Shifting sea chemistry can cripple the reefs where fish live, rewire fish brains and attack what fish eat. Those changes pose risks for food supplies, from the fillets used in McDonald’s fish sandwiches to the crab legs sold at seafood markets.
Sea-chemistry changes are coming as the oceans also warm, and that’s expected to frequently amplify the impacts. This transformation – once not expected until the end of the century – will be well underway before today’s pre-schoolers reach middle age.
“I used to think it was kind of hard to make things in the ocean go extinct,” said James Barry, of the Monterey Bay Aquarium Research Institute in California. “But this change we’re seeing is happening so fast it’s almost instantaneous.”
Globally, the world can arrest much of the damage by bringing down CO2 emissions soon. But the longer it takes, the more permanent these changes become.
“There’s a train wreck coming and we are in a position to slow that down and make it not so bad,” said Stephen Palumbi, a professor of evolutionary and marine biology at Stanford University.
“But if we don’t start now, the wreck will be enormous.”
Species’ reaction to high CO2 can vary dramatically. Acidification can kill baby abalone and some crabs, deform squid and weaken brittle stars while making it tough for corals to grow. It tends to increase sea grasses, which can be good, and boost the toxicity of red tides, which is not.
It makes many creatures less resilient to heavy metal pollution. Roughly a quarter of organisms studied by researchers in laboratories actually do better in high CO2. Another quarter seem unaffected. But entire marine systems are built around the remaining half of susceptible plants and animals.
“Yes, there will be winners and losers, but the winners will mostly be the weeds,” said Ken Caldeira, a climate expert at Stanford’s Carnegie Institution for Science, who helped popularise the term ocean acidification. Many species, from sea urchins to abalone, do show some capacity to adapt to high CO2. But they may not have time.
“We can see that the potential for rapid evolution is there,” said Gretchen Hofmann, a University of California Santa Barbara marine biologist.
“The question is, will the changes be so rapid and extreme that it will outstrip what they’re capable of?”
Already, the oceans have grown 30% more acidic since the dawn of the industrial revolution – 15% since the 1990s. By the end of this century, scientists predict, seas may be 150% more acidic than they were in the 18th century. In fact, the current shift has come so quickly that scientists five years ago saw chemical changes off the US West Coast that hadn’t been expected for half a century.
Meanwhile, the Arctic and Antarctic are shifting even more rapidly because deep, cold seas absorb more CO2. The US West Coast has seen consequences sooner because strong winds draw its CO2-rich water to the surface where vulnerable shellfish live. Sea chemistry in the US Northwest already is so bad during some windy periods that it kills young oysters in Washington’s Willapa Bay. In less than 40 years, scientists predict, half the West Coast’s surface waters will be that corrosive every day.
These chemical changes threaten to reduce the variety of life in the sea. In six trips to Papua New Guinea, Fabricius was surprised to see sea cucumbers and urchins living near the CO2 vents, but shrimp and crab were almost non-existent. She saw fewer hard corals than on healthy reefs nearby, and only 8% as many soft corals.
Reefs were less intricate, offering fewer places for animals to hide. Sea grasses flourished but were less diverse. There was twice as much fleshy algae. Corals, she said “are suffering, and they are incredibly important”.
And study after study shows the same thing – the more reefs collapse and fleshy algae spreads, the more fish simply disappear. That loss comes at a price. One-sixth of animal protein consumed by humans comes from marine fish – in some cultures nearly all of it.
Yet reefs are just one way shifting ocean chemistry can harm fish. Biologist Danielle Dixson and James Cook University professor Philip Munday found that clownfish, when exposed to high CO2, lose their ability to distinguish among odours.
Since clownfish use smell to stay safe, the scientists then exposed baby fish in high-CO2 water to bigger fish that eat young clownfish. Normal clownfish always avoided the danger. The exposed fish lost all fear. They swam straight at predators.
Over the next few years, scientists learned CO2 changed many reef fishes’ senses and behaviours: their sight, hearing, the propensity to turn left or right. Most important, that caused them to die two to five times more often.
Last year, researchers figured out why. Elevated CO2 disrupts brain signalling in a manner common among many fish. Scientists have also been testing the most important fish in the United States: pollock. Fishermen in Alaska catch roughly 1.36 billion kg of pollock a year. It gets carved into fish sticks, sold overseas as imitation crab or packed in blocks.
Government scientists in Oregon exposed young pollock to high CO2 and introduced the scent of what they eat. The fish struggled to recognise their food.
It’s too soon to say how that might affect pollock fishing. Some tropical fish raised in high-CO2 water gave birth to young that adjusted to their new environment. Pollock might respond the same way. But the fish also might not.
“If the fish is less able to recognise the scent of its prey and then therefore locate food when it’s foraging out in the wild, obviously that’s going to have negative impacts for growth and then survival in the long run,” said NOAA biologist Thomas Hurst.
Food web disruption
And brain damage is not even the biggest threat to commercial fish. All over the ocean, usually too small to see, flutter beautiful, nearly see-through creatures called pteropods, also known as sea butterflies. Scientists have known for years that plummeting ocean pH later this century would begin to burn through their shells.
But they were alarmed late in 2012 when researchers announced that pteropods in Antarctica were dissolving already in waters less corrosive than those often found off Washington and Oregon.
That matters because birds, fish and mammals, from pollock to whales, feast on this abundant ocean snack. Pteropods make up half the diet of baby pink salmon and get eaten by other fish, such as herring, that then get swallowed by larger animals. And so little ocean monitoring is done of creatures at the bottom of the marine food chain, there’s no telling yet if other plankton species are experiencing changes, too.
So, to understand the future of the marine food web, government computer modellers have been studying how sea-chemistry changes could reverberate through the ocean. Their initial results, looking at just the US West Coast, are disturbing.
NOAA researcher Isaac Kaplan’s early work projects potentially significant declines in sharks, skates and rays, some types of flounder, rockfish and sole, and hake.
“Some species will go up, some species will go down,” said Phil Levin of NOAA’s Northwest Fisheries Science Centre. “On balance, it looks to us like most of the commercially caught fish species will go down.” – The Seattle Times/McClatchy Tribune Information Services
Stunted growth of Alaskan crabs
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Environment, Environment, ecowatch, climate change, ocean acidification, Papua New Guinea
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