Warmer and More Acidic Oceans Spell Trouble for Jumbo Squid

Chalk up another potential victim of global warming. A new study warns that the jumbo squid (also known as the Humboldt squid) may not fare well in the coming decades, as the oceans get warmer and absorb carbon dioxide from the atmosphere, which makes the water more acidic. Jumbo squid blood carries very little oxygen – with each cycle through its body, the oxygen can be used up entirely. This means they must “recharge” constantly, and makes the animals very dependent on what oxygen is available in the water around them. Yet, the warmer water is, the smaller the amount of oxygen it can hold [New Scientist].

What’s more, the squid’s blood cells can carry less oxygen in acidic water. Their blood-oxygen delivery system is highly sensitive to pH, so “the organisms are thought to live chronically ‘on the edge of oxygen limitation,’” the authors wrote. During the day, the squid descend to lower depths in the ocean to rest, slowing down their metabolism to deal with the lower oxygen levels there. At night, they return to well-oxygenated waters nearer the surface to feed [LiveScience]. However, if surface waters are both warmer and more acidic, the squid trying to feed at the surface will get much less oxygen, which will slow down their metabolisms. And lethargic squid are easy targets for predators like sperm whales, researchers say.

In the study, published in the Proceedings of the National Academy of Sciences [subscription required], researchers placed the jumbo squid in tanks where the temperature and acidity of the water could be varied. When they subjected them to acidification levels corresponding to possible conditions in the year 2100, they found that the squid’s metabolisms slowed by about 30 percent, and the length of time the squid spent contracting their muscles dropped by almost half, making them move sluggishly in the water.

If the increasing acidification trend isn’t reversed with swift action to curb greenhouse gas emissions around the world, the jumbo squid may have trouble remaining in their ecological niche, researchers say. “In the future, the habitable window between low oxygen at depth and acidified and warmer waters at the surface will grow narrower,” warns [study coauthor Rui] 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” [BBC News].

Discover, 16 December 2008. Article.

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