You are probably aware of the symbiotic relationship between Acropora and coral gobies, with the coral providing shelter and the coral gobies in return fighting off predators and other threats to the health of the coral. Now however, researchers at the Georgia Institute of Technology have found that the relationship between the two might stretch farther than the previously perceived relationship.
It turns out some Acropora species actually chemically signal the gobies when threatened by toxic algae, a 911 call for help so to say. The gobies are able to sense the chemicals and were found to respond to the call within minutes. This relationship is the first record of a coral species chemically signalling a consumer species to remove competitors.
Acropora nasuta colonies hosting Gobidon histrio (green clown goby) and Paragobiodon enchinocephalus (on different corals) were used in the experiment. Chlorodesmis fastigiata, a toxic seaweed was placed in contact with the coral, and the reactions of the gobies were observed. Within five minutes all gobies headed over to the site, removing seaweed coming in contact with the coral. Over the course of three days 30 percent of the seaweed was removed, and the damage to the coral was decreased by 70 to 80 percent as to compared to corals not hosting coral gobies.
To confirm what was attracting the fish, further experimentation was conducted. Three different water samples were taken; near the seaweed, where seaweed was in contact with the coral, and near a coral where the seaweed was removed 20 minutes earlier. The samples were released near other corals hosting coral gobies, and the gobies were found to only respond to samples taken near the coral and not the seaweed itself. This suggests that the gobies react to the coral signals rather than the noxious seaweed, confirming the hypothesis. Further research regarding the diet of the coral gobies found that Gobidon histrio actually consumes the algae, while Paragobiodon enchinocephalus just merely rips off the algae not actually ingesting the seaweed.
Any implications regarding the hobby are very unlikely, but it furthers our understanding of the complicate relationships found even within our personal aquariums. Who knows, maybe this is one of many cases where chemical signalling occurs within symbiotic relationships. The Georgia Institute of Technology intents to do a lot more research regarding these complex relationships, so we may very well find out in the future.