Ocean acidification a lethal threat to krill

The Australian Antarctic Division has conducted study on ocean acidification and found that increased levels of carbon dioxide kill krill embryos.

Krill is one of the main types of plankton, itself the basic food source of nearly all animals in the ocean.

Krill were exposed to different levels of carbon dioxide to determine the potential effect of acidification on the early development of the species. Krill biologist Dr So Kawaguchi informed that, when exposed to higher levels of carbon dioxide, most of the embryos did not develop and none of them hatched properly.

“We used the Antarctic Division’s krill aquarium to set up three sea water tanks bubbled with the current (380 parts per million (ppm)), medium (1000ppm) and high (2000ppm) levels of carbon dioxide,” Kawaguchi said.

“There was no change detected in the development of the krill embryos in the tanks with the current and medium levels, but in the tank with higher levels, none of the embryos survived to hatch,” she explained.

It has been determined that ocean acidification is not uniform in the water column: the greater the depth, the higher the levels of carbon dioxide.

The carbon dioxide levels deep in the Southern Ocean could grow as high as 1400 ppm by 2100, a time when atmospheric carbon dioxide is anticipated to more than double to 788 ppm.

“If carbon dioxide increases to these levels and the ocean becomes more acidified, it could have a huge impact on krill populations and therefore the entire Southern Ocean ecosystem. Krill spawn eggs at the surface which then sink to between 700 and 1000 m before the larvae hatch and swim back to the surface,” Kawaguchi told.

“Hence, vertically migrating animals like krill will experience one of the most drastic changes in the ocean and potentially face greater mortality,” she concluded.

Because cold water absorbs carbon dioxide more quickly, it is expected that the Southern Ocean will be affected most brutally by ocean acidification.

Additional studies will be conducted to spot the exact carbon dioxide concentration “tipping point” and thereby the possible response of krill on the later stages of its life cycle to ocean acidification.

Further, a 20-year study found that krill in the Southern Ocean is declining at an alarming rate. Dr Graham Hosie, the scientist leading the project, is unable to explain the dive, ABC reports.

“Plankton are extremely sensitive to their environment. We’ve found that even subtle changes in pattern across the ocean with the oceanography, natural patterns, the plankton can respond very abruptly in composition,” he said.

“So they’re very good at telling us what’s happening in their environment,” he continued.

Hosie hopes to get some answers from the latest scientific expedition to Antarctica aboard the research ship Aurora Australis, which will carry a device that will collect plankton and help scientists identify the cause of the decline.

Meanwhile, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) will meet from 25 October–5 November in Tasmania to discuss various measures to protect krill.

Related articles:

Scientists survey krill fishery
The krill paradox

Natalia Real, http://www.fis.com, 22 October 2010. Article.

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