Coral reefs can't seem to catch a break. Not only is ocean acidification -- the "other" CO2 problem -- threatening huge chunks of the world's coral, but overfishing may also destroy reefs.
A new study published in the journal Coral Reefs describes the connection between healthy fish populations and health reefs off the coast of Kenya. According to the research, overfishing near coral reefs doesn’t just keep fish populations low. It stunts coral growth, too.
When numbers of predatory fish -- which are often larger and more prized by fishers -- drop, the sea urchin populations explode. These spiny sea creatures graze heavily on coral, damaging their structure and consuming a type of algae that helps reefs develop. Crustose coralline algae contains calcium carbonate in its cell walls and hardens onto corals, helping solidify and stabilize the reef. Too much fishing, too many urchins, too little algae ... so long, reef.
The study, led by Jennifer O'Leary of the Institute of Marine Sciences at U.C. Santa Cruz, found that reefs in Kenya where fishing was permitted had only half the algae concentrations of reefs where fishing was banned. The density of the coral themselves was also substantially different based on the presence or absence of fishing on a given reef.
"Outside the protected areas, we're seeing the ecosystem collapse," O'Leary said in a press release. "When you look at the effects of fishing, you can't just think about the species that are being removed. You have to look at how the effects are carried down through the ecosystem."
Changing fishing practices, however, is hard enough when the targeted fish themselves are at stake. As we noted here, fishermen in Kenya and other East African countries are unlikely to change their profession, even when their bounties are half the size of what they once were. Changes in coral density won’t be nearly as obvious a consequence.
Meanwhile, ecosystems off the northeastern coast of the United States are having the opposite problem: too few sea urchins. There the fishing industry is targeting sea urchins because they are a sushi delicacy, and their populations have plummeted to the point of collapse. Fisheries management, whether off Kenya or Kennebunkport, is a complicated art, but at its heart, it is a balancing act.
Image: Charles Chan/Flickr