December 16, 2008

Jumbo Squid May Be Impaired By CO2 Levels In Ocean

Researchers say the elevated carbon dioxide levels expected to be found in the world's oceans by 2100 will likely lead to physiological impairments of jumbo (or Humboldt) squid.

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

Oceans are becoming more acidic as a result of absorbing the carbon dioxide released by human activities, according to climate models. Rises in acidity have already been shown to affect shellfish and corals.

Jumbo squid (Dosidicus gigans) are an important predator in the eastern Pacific Ocean, and they are a large component of the diet of marine mammals, seabirds and fish.

The squid have 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.

Lead author Rui Rosa, from the Department of Oceanography at Lisbon University, Portugal, said when the squid feed near the surface they have a very quick metabolism.

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

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

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

But 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, researchers said.

The research team 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.

Dr. Rosa explained that 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.

The squid are 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, she said.

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

"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.

Squid populations on the move 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.


Image Caption: Humboldt squid (Dosidicus gigas) swarm around Tiburon, possibly attracted to its lights. Several of the large (about 1- 2 meter, or 3-6 foot) animals clouded the water with greenish-gold ink. NOAA


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