Warming Oceans May Threaten Krill, a Cornerstone of the Antarctic Ecosystem

SYDNEY, Australia — Every day for a week, So Kawaguchi peered intently into the jars of cold water holding harvested krill eggs. None were hatching. In his laboratory in Hobart, Tasmania, on the edge of the Southern Ocean, he could see that the carbon dioxide he had pumped into the icy seawater had killed the eggs.

“We thought the krill might be more robust,” said Dr. Kawaguchi, a biologist who works for the Australian government’s Antarctic Division. “We were not expecting such a clear result.”

Those key moments in his laboratory more than seven years ago were pivotal in the career of Dr. Kawaguchi, who has been studying krill for 25 years. His recent research has led to dire predictions about how global carbon emissions will significantly reduce the hatch rates of Antarctic krill over the next 100 years.

Krill, typically about the size of a pinkie and similar in appearance to shrimp, are one of the most abundant animal species on earth, and a cornerstone of the Antarctic ecosystem. They form schools that can be miles long and miles deep, with thousands of crustaceans packed into each cubic foot.

Commercial trawlers revisit known breeding grounds, where they can vacuum up thousands of tons of krill over a fishing season. Most of the catch is used to feed farmed fish. But extraction of krill oil for human consumption is more profitable, Steve Nicol, an adjunct professor at the University of Tasmania, said.

In the Southern Ocean, most marine life is a direct predator of krill or just one step removed. Diminishing krill stocks can mean less food for squid, whales, seals, fish, penguins and sea birds.

“Higher levels of carbon dioxide in the water mean greater levels of ocean acidification,” said Dr. Kawaguchi, whose laboratory holds the only research tanks in the world used to breed and study krill. “This interrupts the physiology of krill. It stops the eggs hatching, or the larvae developing.”

Conservationists want tracts of Antarctic waters protected until scientists better understand the links between different species of marine life there.

“We are concerned with the concentrated fishing around the Antarctic Peninsula, which is also the fastest warming place on the planet,” said Andrea Kavanagh, the Washington-based director of the Pew Charitable Trusts’ global penguin conservation campaign.

In Hobart, Dr. Kawaguchi pumped carbon dioxide into his jars, acidifying the water to mimic conditions that might occur over the next three centuries.

“If we continue with business as usual, and we don’t act on reducing carbon emissions, in that case, there could be a 20 to 70 percent reduction in Antarctic krill by 2100,” Dr. Kawaguchi said. “By 2300, the Southern Ocean might not be suitable for krill reproduction.”

From the tip of Patagonia to the Antarctic landmass, Antarctica’s waters swirl west to east, but the current is also vertical. The deep water in the Southern Ocean continualy rises, coming into contact with the atmosphere, and sinks again.

“It is like a conveyor belt carrying heat and carbon dioxide into the ocean,” said Dr. Steve Rintoul, an oceanographer with Australia’s national science agency, the Commonwealth Scientific and Industrial Research Organization. “And this is one reason it can absorb so much heat. The key question is how the acidification caused by the uptake of carbon dioxide will affect ecosystems.”

Krill eggs sink from the water’s surface into deeper seas where they hatch. They then swim back to the surface to eat algae. They grow through around 12 larval stages before reaching adulthood and breeding in what Dr. Kawaguchi describes as a complicated life cycle.

“Carbon dioxide levels increase the deeper you go,” said Dr. Kawaguchi, whose lab work has focused only on krill eggs and larvae. “Krill eggs are inanimate. As they sink, they can’t avoid areas of greater acidity.”

And as the ocean takes up more carbon dioxide, it becomes more difficult for sea animals to build shells and exoskeletons.

A subgroup of the Commission for the Conservation of Antarctic Marine Living Resources, which was established in 1982 by international convention to conserve Antarctic marine life, said earlier this year that it hopes to better quantify the abundance of krill in the Southern Ocean using acoustic instruments.

The last surveys were completed in 2000, which means that the data used to determine catch limits are 15 years old. The Antarctic conservation commission said that around 300,000 tons of krill was caught in 2014, significantly lower than the peak of around 500,000 tons caught around 30 years ago when trawlers from the former Soviet Union were the biggest krill fishers.

In Sydney in February, krill scientists, conservationists and King Harald V of Norway established an Antarctic Wildlife Research fund with a $500,000 donation for krill research from a Norwegian fisheries company, Aker BioMarine — the world’s largest krill fisher. The Antarctic conversation commission said Norwegians caught 165,899 tons of krill in 2014, Korean fisheries took 55,414 tons and Chinese 54,303 tons.

Dr. Nicol said Aker BioMarine had technology that allowed a trawler to suck up krill from swarms, avoiding damage to the krill and other fish it pulls in. Trawlers can operate year round, but ice melt means peak fishing is now done in winter.

“Krill is a remarkably adaptable and abundant animal,” said Dr. Nicol, who is also a scientific adviser to Aker BioMarine. “Can krill adapt to changing conditions fast enough? I hope so. They are remarkably resilient.”

Dr. Kawaguchi said he worried that krill may not adapt. “We have a lot of things to think about,” he said. “These experiments take a long time and we have started with krill in the very early stages of development. We have yet to understand what happens from stage to stage.”

Bron: http://www.nytimes.com/2015/10/20/s...ctionfront&_r=0 19/10/15

Mening: Ik vind dit een duidelijk bijgevolg van de opwarming van de aarde. We zijn vaak, als het over "de opwarming van de aarde" gaat, aan het denken over hoe we ons hiertegen kunnen beschermen omdat het zeeniveau zal stijgen. Er staan maar weinigen stil bij de andere gevolgen van de temperatuurstijging van het water. Zoals in het artikel vermeldt beloven voorspellingen van het verdwijnen van de krillkreeftjes niet veel goeds. De kreeftjes spelen een belangrijke rol in de voedselkringloop. Binnen enkele honderden jaren zal een belangrijk element uit de kringloop verdwijnen wat nog extra gevolgen met zich mee zal brengen voor de visvangst.