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we could limit ocean acidification to
40 percent by 2100. But in a high-
emissions scenario, the ocean could
become 150 percent more acidic than
it was before we began burning fossil
fuels. In effect, we’re running a giant chemistry
experiment in the ocean, and nobody has a clear
understanding of how it will turn out.
The increasingly acidic waters in the Pacific
are already impacting the shells of Dungeness
crabs, jeopardizing the $200 million crabbing
industry on the West Coast. To prevent the
acidic waters from dissolving those shells, oyster
farmers in Oregon and Washington have to raise
baby oysters in incubators before planting them
on the beach to grow to adulthood.
In lab experiments, scientists have found
acidification can do strange things to a fish’s
mind. Clown fish, for example, normally stayclose to home in coral reefs. But as
the water becomes increasingly
acidic, they wander farther and far-
ther away, making them more likely
to be eaten. Greater acidity also “im-
pairs their ability to discriminate between the
smell of kin and not, and of predators and not,”
according to Philip Munday, a professor at the
Coral Reef Studies center at James Cook Univer-
sity in Australia.
Over time, the biggest threat from acidifica-
tion is the impact it could have on the food chain.
Pteropods, a.k.a. “the potato chips of the sea,”
are a food source for everything from seabirds
to whales. Their thin shells are extremely sen-
sitive to changes in ocean pH. A collapse of the
pteropod population would have a domino effect
on the entire ocean food chain, especially in the
Southern Ocean.On coral reefs, most of which are already
weakened by bleaching events, acidification at-
tacks the calcium skeletons that they build to
support themselves. “By midcentury, pretty
much every reef in the world will be eroding
away,” says Stanford’s Ken Caldeira. That’s aston-
ishing. Coral reefs have been around for about
250 million years, evolving into some of the most
complex, diverse, and beautiful living structures
on Earth. And yet if nothing changes, within
40 or 50 years, they will be crumbling ruins.
“I think if we stopped emitting C02 tomorrow,
some reefs would probably survive,” Caldeira
says. “But if we go on a few more decades, I
think the reefs are gone. Over geological time
scales, they will come back, depending how long
it takes the ocean chemistry to recover. But it’s
likely to be at least 10,000 years before anyone
sees a reef again.”Purple sea urchins —
the “cockroaches of
the sea” — thrive in
a hotter world, and
they devour giant
kelp forests.COURTESY OF KATIE SOWUL/CALIFORNIA DEPARTMENT OF FISH AND WILDLIFE/UC DAVIS