Our body is about ⅔ water. Earth’s surface is about ⅔ oceans. This is not a coincidence. All of our lives began in water. Every plant and animal living on dry land today can trace its family tree back to the sea. Each of us, in every salty cell of our bodies, are a bit of the ocean that grew legs, walked up on shore and learned to build sports cars, skyscrapers, and spaceships.
But in taking over the land, we’ve put a lot of extra carbon in the air, and that’s having serious effects on our climate. Much of that change isn’t happening in the atmosphere. It’s in the oceans, and for one colorful group of creatures that could spell disaster. Coral reefs. Can they survive climate change? Animal. Vegetable. And mineral. Coral reefs are a little hard to classify, because, they’re kind of all three. The animal bits come in the form of tiny invertebrates called polyps, that use tentacled arms to feed on plankton and other small sea creatures. But living inside each polyp are single-celled, plant-like algae.
These can make up as much as a third of the polyp’s body, and they’re what give coral reefs their colors. These organisms have a sort of cooperative living arrangement called symbiosis. During photosynthesis, the algae consumes the polyp’s waste CO2 and in return burps out oxygen and nutrients to feed its host. The coral says thanks by giving the algae a nice, safe place to live: inside its own body. Together, massive colonies of these symbionts secrete calcium carbonate exoskeletons, building up the multicolored megastructures that we call coral reefs. Marine biologist Sylvia Earle called coral reefs the “jeweled belt around the middle of the planet.” Because they rely on photosynthesis, we mostly find ‘em anchored between the tropics, where Earth receives the most sunlight.
Unfortunately, thanks to the extra carbon dioxide and other greenhouse gases we’ve pumped into the atmosphere, more and more of that sunlight’s heat is being trapped in Earth’s atmosphere. But most of it hasn’t stayed there. Since 1955, 90% of the atmosphere’s excess heat has been absorbed by the oceans. And in addition to all that energy, it’s estimated that oceans have soaked up half of all CO2 emissions since the industrial revolution. And that’s not like a bubbly soda, instead much of that CO2 gets chemically converted into acid.
If climate change is stressing you out, you’re not alone. These warm waters, acidic conditions and increased pollution are straining the delicate symbiotic relationships between algae and their coral hosts, and many coral are kicking their colorful roommates to the curb. Now, ejecting the algae leaves reefs looking rather blah and colorless, so the phenomenon is called coral bleaching. Bleaching leaves polyps without nutrients and susceptible to disease, and if it lasts long enough, the coral will die. Losing coral reefs would mean losing the most diverse ecosystems that our planet has to offer. Even though they cover just a tenth of a percent of the ocean floor, reefs provide a home to a quarter of all ocean species. In some tropical reefs, a thousand different species can live in a single square meter. In many places, this change already happening. Half of all tropical reefs have disappeared in the past 30 years, and if the ocean continues to get warmer like it is today, coral may die off completely by 2050. It’s reefer badness out there. “Carl, Carl, Carl, Coral? Carl, Coral…”
Right now, we’re changing the planet faster than coral can adapt, but there is hope. Some scientists from Australia and Hawaii have figured out how to breed coral in the lab, and similar to how farmers cross plants to select for bigger fruit or drought resistance, they think that they can accelerate the evolution of polyps and their algae accomplices to create stress-resistant super coral. We’ve changed a lot since our ancestors left the shore, but from the air we breathe to the water within us, each of our lives is still connected to the ocean. Helping coral will help us all.