Fish can smell a bad coral reef

Young coral and fish know a crummy neighborhood when they see it, or when they smell it, rather. According to new research, damaged reefs give off distinct smells -- smells that say to a fish, don't set up shop here.
Damaged reefs generally begin with overfishing. When too many fish are removed from a local, seaweed (food for many small fish species) can grow on reefs unchecked. When seaweed takes over it begins to choke out coral. It also gives of a smell that warns fresh coral not to take root there. A damaged reef also colors the surrounding water with a smell that warns fish to keep on swimming. And as a new study by researchers at Georgia Tech suggests, it all combines to create a downward ecological spiral that even strong regulations can't counteract.
"If you're setting up a marine protected area to seed recruitment into a degraded habitat, that recruitment may not happen if young fish and coral are not recognizing the degraded area as habitat," explained study author Danielle Dixson, an assistant professor at Georgia Tech's School of Biology.
Previous studies have found similar results when looking at the way fish make reef preferences, but this the first to show coral larvae make similar distinctions between good and bad reefs based on smell.
"Not only are coral smelling good areas versus bad areas, but they're nuanced about it," said Mark Hay, biologist and the study's senior author. "They're making careful decisions and can say, 'settle or don't settle.'"
Har and Dixson say further research is need to see how removing certain quantities of seaweed might help jumpstart a damaged reef towards recovery. Their work is detailed in the latest edition of the journal Science.