Reef "Cat Scans" Reveal Another Way Acidification Speeds Erosion

The stunning biodiversity of a "coral" reef. Photo by Laura D Rising carbon dioxide levels in our atmosphere are changing Earth's climate at an unprecedented rate. Not only is our planet getting warmer on average—in the oceans, a chemical reaction spurred by dissolved CO2 is altering water chemistry, causing a decrease in pH. This effect of climate change, called ocean acidification, can dissolve the calcium carbonate foundations of coral reefs and other calcifying organisms, making it impossible to build and maintain healthy reefs. Luckily, recent studies on how corals react to lower pHs has given scientists hope that they may be more resilient than previously thought. However, to truly understand how reefs will respond to climate change, we have to look at more than just corals. Reefs are complex ecosystems, the bases of which are comprised of so much more than corals. There are other species which act as calcifiers, adding to the carbonate foundation (such as crustose coralline algae). The contribution of these non-coral species to reef growth, called secondary accretion, helps shape the surface and guide the settlement of larval corals. There are also species that eat away at the reef, including many worms and sponges. These bioeroders can weaken reef structures until they crumble apart. Whether a reef grows or shrinks over time depends on the interplay between its corals, other reef-builders, and the burrowing organisms which eat their way through the reef's carbonate foundation. The corals have received a lot of scientific attention, with many laboratories around the world conducting field and lab experiments in an attempt to predict how these essential species will react to the higher temperatures and the altered seawater chemistry that will come with our changing climate. Relatively less attention has been paid to the other species that also determining the size and shape of the reef—in part because such studies are harder to design. After all, there could be hundreds of species on a reef contributing to secondary accretion or bioerosion. While it's somewhat simple to take a coral into a lab tank and monitor changes as you tinker with water parameters, it's impossible to do the same to a whole reef at once.