This little goby fish saves its host coral by keeping toxic algae at bay.
When coral are threatened by encroaching toxic algae, they do not have the luxury of running from their enemy. That is not to say these stationary creatures are defenseless, though. Acropora coral has evolved to emit a chemical call for help, and within minutes, a goby fish will show up on the scene, ready to nibble off the algae. Researchers recently discovered
this underwater partnership in the waters near Fiji. They say this symbiotic relationship is the first known example of a species chemically signaling another in order to remove a competitor species. The fish's response time is short because the goby fish are never far away from the coral. Nestled in the crevices of the reef, protected from predators, goby fish feast on a smörgåsbord of local fares: coral mucus, algae and zooplankton. In return, the goby is available for minor coral maintenance issues like mowing the toxic algae lawn. This task is pretty simple for the fish---one species of goby observed in this study ate the stuff and another just trimmed it off---and important for the coral. For a tenant-landlord-style relationship, this one's pretty amicable. Image credit: Danielle Dixson, Georgia Institute of Technology