Global warming may result in shift of marine habitats

Warmer temperatures will cause oxygen levels in the oceans to decline which may result in marine animals shifting away from the equator, a new study has found.
Just as the combination of physical exertion and lack of oxygen at high altitudes creates the need for mountaineers to carry tanks of oxygen while climbing mountains, warmer water temperatures will speed up the animals' metabolic need for oxygen, researchers said.
However, the warmer water will hold less of the oxygen needed to fuel the animals' bodies, similar to what happens to humans at high altitudes.
"If your metabolism goes up, you need more food and you need more oxygen," said lead author Curtis Deutsch, a University of Washington associate professor of oceanography.

"This means that aquatic animals could become oxygen-starved in the warmer future, even if oxygen doesn't change. We know that oxygen levels in the ocean are going down now and will decrease more with climate warming," he said.
The study focused on four Atlantic Ocean species whose temperature and oxygen requirements are well known.

These included Atlantic cod that live in the open ocean; Atlantic rock crab that live in coastal waters; sharp snout seabream that live in the subtropical Atlantic and Mediterranean; and common eelpout, a bottom-dwelling fish that lives in shallow waters in high northern latitudes.
Deutsch used climate models to see how the projected temperature and oxygen levels by 2100 due to climate change would affect these four species' ability to meet their future energy needs.

If current emissions continue, the near-surface ocean is projected to warm by several degrees Celsius by the end of this century. Seawater at that temperature would hold 5-10 per cent less oxygen than it does now, researchers said.
The study results showed that rock crab habitats would be restricted to shallower water, hugging the more oxygenated surface.
For all four species, the equator-ward part of the range would become uninhabitable because peak oxygen demand would become greater than the supply.
Viable habitats would shift away from the equator, displacing from 14 per cent to 26 per cent of the current ranges.

Climate models predict that the northern Pacific Ocean's relatively low oxygen levels will decline even further, making it the most vulnerable part of the ocean to habitat loss.
"The Atlantic Ocean is relatively well oxygenated. If there's oxygen restriction in the Atlantic Ocean marine habitat, then it should be everywhere," Deutsch said.
The study was published in the journal Science.