Fish of the family gobiodon are known to have mutualistic relationships with other creatures in the sea. The pistol shrimp/goby relationship (There are approximately 130 species of goby that have relationships with 20 species of pistol shrimp) is probably one of the most common seen in the wild and in the aquarium trade. However, scientists have discovered a new relationship in the wild between the earspot coral goby (Gobiodon histrio) and Acropora nasuta coral that is mutually beneficial.
In a paper published in the journal Science, Georgia Tech researchers Danielle L. Dixson and Mark E. Hay studied that relationship. What they found was intriguing. According to a report in Scientific American, Dixson and Hay removed the resident gobies from a reef in Fiji and blanketed Acropora nasuta coral with fake seaweed designed to resemble Chlorodesmis fastigiata. They physically blanketed the coral with the fake seaweed, which did not have the toxic chemical present. This had no effect on the coral. When they covered the coral with the toxic seaweed, the coral was damaged. However, on coral reefs where the gobies were not removed, the seaweed in which they covered the coral was reduced by 30 percent by the fish, while the corals experienced just 20 percent damage, 30 percent the damage of the corals that had the fish removed from the area, according to the report.
Within minutes of the seaweed (or its chemical extract) making contact with Acropora nasuta, the coral releases an odor that recruits the earspot coral goby, also known as the green coral goby, to come to the rescue by eating the seaweed. When the goby eats this particular seaweed, the toxins in the seaweed causes the goby to become more toxic. This helps to ward off predation by other fishes. What the researchers also noticed was the gobies would come to the rescue of their host coral, and not to that of a related coral that also released chemicals when it came under attack of the toxic seaweed.
“I’m an ecologist that studies chemically-mediated interactions, but the wonderfully subtle, nuanced, and specific chemical dance being conducted here is still shocking to me,” said Hay. The report noted the importance of mutualistic relationships on the reef. “Competition among some seaweeds and corals has been important enough to drive the evolution of this wonderfully well-tuned signaling among a coral and its mutualistic fishes.”