Climate change
will dramatically alter life in the oceans, scientists say, but there’s
so much still to learn about marine ecosystems that it’s hard to know
exactly how.
On Thursday, researchers with the British Antarctic Survey offered a glimpse of that future with the results of an unusual study years in the making.
The
scientists heated a patch of the sea floor off the coast of Antarctica
and tracked the effects on a few local species. Some animals responded
by doubling their growth, stunning the researchers.
At
the same time, there was evidence that animals that thrive on warmth
might crowd out less resilient species. The study was published in the
journal Current Biology.
The
cold, dry ecosystems on Antarctica itself can’t support anything bigger
than an insect. But the Southern Ocean swirling around the continent
paradoxically teems with life.
A
rich supply of nutrients fosters a food web that includes single-celled
algae, bottom-dwelling worms and other animals. This ecosystem
ultimately supports such predators as fish, penguins and whales.
Climate
change is a big concern here, because heat-trapping gases like carbon
dioxide are having their biggest impacts near the poles. Computer models
predict that in 50 years the Southern Ocean will warm by about 1.8
degrees Fahrenheit, and by 3.6 degrees Fahrenheit within a century.
“We’re
going to start to see changes there first,” said Gail V. Ashton, a
co-author of the new study and a marine ecologist now at the Smithsonian
Environmental Research Center in Tiburon, Calif.
Trying
to predict those changes, scientists have been gathering various sorts
of clues. Some look at the natural ranges of Antarctic species,
observing the highest temperatures they tolerate. Others put animals
into laboratory tanks and manipulate the aquatic environment.
But
these experiments have shortcomings of their own. “Control is also a
weakness,” said Rebecca L. Kordas, a marine ecologist at Imperial
College London who was not involved in the new study. “Too much control
may yield unnatural responses.”
In
recent years, scientists like Dr. Kordas have attempted another kind of
experiment: heating the ocean itself. The research typically involves
putting heated panels underwater, close to shore, and then observing how
the temperature increases affect the growth of tiny animals on the
seafloor.
Scientists
previously used this method off the coasts of British Columbia and
Australia. In the new study, British Antarctic Survey researchers picked
a much tougher site: about 45 feet deep in the Southern Ocean, off the
coast of the Antarctic Peninsula.
The
study sheds new light on Antarctic ecosystems, said Julian Gutt of the
Helmholtz Centre for Polar and Marine Research in Germany: “To my
knowledge, it is unique.”
Dr.
Ashton traveled to Rothera Research Station on Adelaide Island to begin
the experiment. She and her colleagues sailed offshore and then dove
underwater to set the panels on concrete footings on the ocean floor.
To
power the panels, the scientists ran 600 feet of cable to a station
generator on shore. The experiment began in January 2014, but before
long the cables were severed.
“We’re not sure if it was an iceberg or a ship that dinged them,” Dr. Ashton said.
She
and her colleagues rigged up more protections and started again in June
2014. They managed to keep the project running till March 2015.
Each
panel warmed the water, but just a thin layer eight-hundredths of an
inch deep. One set of panels had enough power to increase the
temperature by 1.8 degrees Fahrenheit; another set heated the water by
3.6 degrees Fahrenheit. For control purposes, a third set of panels was
left unheated.
Dr.
Ashton donned scuba gear and dove periodically to track the progress of
the experiment. (In the winter, she and her colleagues needed to use a
chain saw to cut a hole in the ice.) Sinking to the sea floor, she took
pictures showing that animal larvae had settled on the panels and had
begun to grow.
At
the end of the experiment, Dr. Ashton and her team hoisted the panels
from the seafloor. Back at the station, she inspected the marine life
under a microscope.
When the experiment began, Dr. Ashton had been skeptical that she’d see much change. “I was quite naïve,” she said.
Some
of her more optimistic colleagues had pointed out that biochemical
reactions can occur faster at higher temperatures. They thought animals
on the warm panels might grow 10 percent faster.
But
it didn’t take many dives for Dr. Ashton to realize that the animals
were growing even more quickly. One species of worm grew 70 percent
faster on a panel heated by 1.8 degrees Fahrenheit, compared with its
growth on unheated panels.
Filter-feeding
animals called bryozoans doubled their growth on heated panels,
crowding out other species that seemed to fare well on unheated panels.
What
drives this growth? “We don’t really know,” Dr. Ashton said. She is now
investigating whether higher temperatures might switch on a special set
of genes that speeds up development in some species.
The
results on the panels heating water by 3.6 degrees Fahrenheit were even
more puzzling. On some, animals grew more; on others, less. Even within
each species, Dr. Ashton and her colleagues found that individuals
varied a lot in how well they fared.
Grace
Saba, a marine ecologist at Rutgers University, cautioned that some
animals might not be able to grow so fast in a warmer climate.
During
the experiment, an abundant supply of algae fueled the growth of the
bryozoans. But when the whole ocean gets warm, the algae may suffer,
too, leaving the bryozoans to starve.
“With those increases in growth rates comes higher demand for food,” she said.
Dr.
Kordas said that it’s hard to tackle these questions when so few
climate experiments have been carried out in the ocean, compared to the
many that have been done on land.
“The marine scientific community really needs to catch up to broaden our understanding,” she said.
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