Marine animals live where ocean is most breathable, ranges may shrink with climate change

https://www.eurekalert.org/pub_releases/2020-09/uow-mal091420.php

News Release 16-Sep-2020
University of Washington

As oceans warm due to climate change, scientists are trying to predict how marine animals -- from backboned fish to spineless jellyfish -- will react. Laboratory experiments indicate that many could theoretically tolerate temperatures far higher than what they encounter today. But these studies don't mean that marine animals can maintain their current ranges in warmer oceans, according to Curtis Deutsch, an associate professor of oceanography at the University of Washington.

"Temperature alone does not explain where in the ocean an animal can live," said Deutsch. "You must consider oxygen: how much is present in the water, how well an organism can take up and utilize it, and how temperature affects these processes."

Species-specific characteristics, overall oxygen levels and water temperature combine to determine which parts of the ocean are "breathable" for different ocean-dwelling creatures. New research led by Deutsch shows that a wide variety of marine animals -- from vertebrates to crustaceans to mollusks -- already inhabit the maximum range of breathable ocean that their physiology will allow. 

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"Organisms today are basically living right up to the warmest temperatures possible that will supply them with adequate oxygen for their activity level -- so higher temperatures are going to immediately affect their ability to get enough oxygen," said Deutsch. "In response to warming, their activity level is going to be restricted or their habitat is going to start shrinking. It's not like they're going to be fine and just carry on."

Oxygen levels and temperatures vary throughout ocean waters. Generally, water near the equator is warmer and contains less oxygen than the cooler waters near the poles. But moving from the surface ocean to deeper waters, both oxygen and temperature decrease together. These principles create complex 3-D patterns of oxygen and temperature levels across depths and latitudes. An organism's anatomy, physiology and activity level determine its oxygen needs, how effectively it takes up and uses the available oxygen in its environment, and how temperature affects its oxygen demand.

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