Page last updated at 01:55 GMT, Tuesday, 16 December 2008

Rise in CO2 'affects jumbo squid'

jumbo squid
Jumbo squid can weigh up to 50kg and grow to two metres in length

Jumbo squid, common to the eastern tropical Pacific, may become rarer if current climate change continues.

Writing in the journal PNAS, researchers say the squids' lifestyle could be strongly influenced by changes in ocean acidity.

Climate models suggest oceans are becoming more acidic as a result of absorbing the carbon dioxide released by human activities.

Rises in acidity have already been shown to affect shellfish and corals.

Metabolic change

An international team of researchers says the jumbo squid (Dosidicus gigans) has an unusual feature that makes it particularly susceptible to changes in ocean acidity; the squid has the ability to dramatically vary the pace at which its body systems function.

"When the squid feed near the surface they have a very quick metabolism," says lead author Rui Rosa, from the Department of Oceanography at Lisbon University, Portugal.

"But as they dive deeper they are able to slow their metabolism by as much as 80%," he adds.

During the night the squid feed rapidly near the ocean surface. Yet during the day, they seek out deeper waters that contain less oxygen, causing their metabolism to slow down.

According to the UN's Intergovernmental Panel on Climate Change (IPCC), CO2 released by human activities is continually dissolving in the world's oceans. As a result, oceans are becoming more acidic.

The researchers say increased acidification of the ocean will reduce the availability of oxygen near the surface and so depress the squids' metabolism in a similar manner to what happens when the creatures dive to greater depths.

The researchers caught squid at night and put them in chambers that mimicked the effects of climate change. They simulated the conditions they think the squid may have to endure in 2100.

Jumbo squid
The jumbo squid dives to deep water during the day

"Ocean acidification, at a level predicted for the end of the 21st Century, suppresses energy production by approximately 30%, making them more lethargic, especially at high temperatures," Dr Rosa explained.

The researchers say the squid is very vulnerable as a result of the combination of three factors: sea temperature rises; acidification; and the existing lack of oxygen in the deep ocean.

"In the future, the habitable window between low oxygen at depth and acidified and warmer waters at the surface will grow narrower," warns Dr Rosa.

"The net result will be that the squid may become more susceptible to predators, less able to capture prey, or may be forced to migrate elsewhere, altering the oceanic food web."

The squid may start to hunt different fish species, especially in shallower water where oxygen levels may be higher.

The movement of squid populations could also lead to a decrease in the availability of deep ocean squid for both commercial squid fisheries and whale populations that prey on squid.

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