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

Date:
September 16, 2020
Source:
University of Washington
Summary:
New research 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. The findings provide a warning about climate change: Since
warmer waters will harbor less oxygen, some stretches of ocean that
are breathable today for a given species may not be in the future.



FULL STORY ==========================================================================
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.

The findings, published Sept. 16 in Nature, also provide a warning
about climate change: Since warmer waters will harbor less oxygen,
some stretches of ocean that are breathable today for a given species
may not be in the future.

"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.



========================================================================== Deutsch and his co-authors -- Justin Penn, a UW doctoral student in oceanography, and Brad Seibel, a professor at the University of South
Florida - - wanted to understand if breathability was a limiting factor
in determining the ranges of marine animals today. They combined data
on temperature and oxygen content across the oceans with published
studies of the physiology, oxygen demand and metabolism of 72 species
from five different groups of marine animals: cold-blooded vertebrates,
like fish, and their relatives; crustaceans; mollusks; segmented worms;
and jellyfish and their relatives.

The team modeled which parts of the ocean are and aren't habitable for
each species. Researchers show that a species' current range generally overlapped with the parts of the oceans predicted to be habitable for
it. Their model predicts that the northern shrimp, a crustacean, should
be able to get enough oxygen in cool waters north of about 50 degrees
north latitude -- and that is generally the shrimp's range today. The small-spotted catshark can inhabit temperate and cool waters at a variety
of depths, but near the tropics only near-surface waters -- above about
300 feet -- are breathable, which is also reflected in its current range.

In many cases, species ranges are right up to the edge of breathability,
which indicates that for marine animals the ability to get enough oxygen
may be a major limiting factor in determining where they can live,
Deutsch added.

Outside of that range, organisms run the risk of hypoxia, or not getting
enough oxygen.

Temperature affects both how much oxygen that seawater can hold, and how
much oxygen an animal needs to maintain the same level of activity. The already- tight overlap the researchers saw between breathability and
current ranges indicate that long-term rises in temperature, as expected
under climate change, will likely restrict the ranges of many marine
animals.

This new study follows a 2015 study of four Atlantic Ocean species
by Deutsch's team, and builds on its findings by showing that diverse
species in all ocean basins are generally inhabiting the maximum range
they currently can.



==========================================================================
In the future, Deutsch wants to include additional species, and further
explore the relationships among temperature, oxygen and physiology.

The researchers would also like to find historical examples of marine
species shifting their range in response to water breathability, as the
team showed earlier this year with the northern anchovy.

"What we really want to find are more observations of marine species
moving around in accordance with what we'd expect with temperature
conditions and oxygen availability," said Deutsch. "That will give us
firm examples of what to expect as temperature and oxygen conditions
fluctuate, and shift permanently with climate change." The research was
funded by the Gordon and Betty Moore Foundation, the National Oceanic
and Atmospheric Administration and the National Science Foundation.

Grant numbers: GBMF#3775, OCE-1419323, OCE-1458967

========================================================================== Story Source: Materials provided by University_of_Washington. Original
written by James Urton. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Deutsch C, Penn JL and Seibel B. Metabolic trait diversity shapes
marine
biogeography. Nature, 2020 DOI: 10.1038/s41586-020-2721-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200916113536.htm

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