Today’s factismal: The same chemical that builds reefs can also destroy them.
Coral reefs are amazing things. They are a cross between the skeleton and the poop of dead critters, inhabited by live critters that are a cross between a jellyfish and a plant. They range in size from smaller than a pencil to larger than New Mexico. And, though they cover less than 0.1% of the total ocean area, they are home to more than 25% of the species in the ocean. But perhaps the most amazing thing about them is that the same chemical that the critters use to make the reef is one that can destroy them.
The critters that form most reefs is the eponymous coral polyp. These little critters look like an armored jellyfish mainly because they are armored jellyfish (or at least, close cousins to the jellyfish). Each polyp on a particular piece of coral is an identical clone of every other polyp on the coral as the critters mostly reproduce by budding. Though the corals have tentacles that they use to catch small fish and other foods, they mostly rely on energy that they get from symbiotic photosynthesizing algae that they keep in special internal sacs. (Well, mostly; there are some corals that do not have those algae. But most do.) The polyps absorb calcium and carbon dioxide from the water around them and excrete it as calcium carbonate , forming a thin layer of reef material.
But when calcium carbonate is added to water, it forms a weak acid known as carbonic acid. If the amount of CO2 in the water is high enough, then the carbonic acid can get strong enough to actually eat away at the coral. And if the coral is eaten away faster than the polyps can replace it, then they get washed away and the coral dies.
If you’d like to learn more fascinating facts about coral and maybe even help to monitor them, then head on over to Reef Check California, a citizen science group dedicated to monitoring the coral reefs off the California shore: