Corals under attack send out chemical ‘Goby Signal’ to summon helper fish

Scientists at the Georgia Institute of Technology (GA Tech) have discovered an interesting 'bodyguard' symbiotic relationship between corals and tiny fish known as gobies. The gobies use the corals for protection and food, and whenever the corals are threatened, they release a chemical into the water that acts as a 'Goby Signal', summoning the fish to deal with the threat.

In this particular case, Professor Mark Hay and post-doc fellow Danielle Dixson, both with GA Tech's School of Biology, have discovered evidence that specific corals that come under attack from toxic seaweed algae give off a chemical signal that attracts gobies, which consume the algae.

"This species of coral is recruiting inch-long bodyguards," said Hay, according to Science Daily. "There is a careful and nuanced dance of the odors that makes all this happen. The fish have evolved to cue on the odor released into the water by the coral, and they very quickly take care of the problem."

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Hay and Dixson isolated a specific type of coral, called Acropora nasuta or Small Staghorn Coral, in small cages. They then subjected the corals to an attack by a seaweed known as Chlorodesmis fastigiata or Turtleweed, which, according to Science News, Hay describes as "a really pretty and really nasty little plant."

When these seaweed begin to grow on the coral, the fronds excrete a chemical that is highly toxic to the corals, killing them within two days of contact. When under attack, other types of coral-dwelling fish — such as damselfish — were of no use to the corals, however two species of gobies responded to their plight, moving to lend their assistance.

"These little fish would come out and mow the seaweed off so it didn't touch the coral," said Hay. "This takes place very rapidly, which means it must be very important to both the coral and the fish. The coral releases a chemical and the fish respond right away."

Symbiotic relationships are quite common in nature, but most of these relationships are passive in nature, with each species in the relationship getting benefits simply by the presence of the other. In this case, though, there appears to be a more active relationship, with the fish fulfilling its part of the bargain by responding directly to a call for assistance.

"The fish are getting protection in a safe place to live and food from the coral," Hay added. "The coral gets a bodyguard in exchange for a small amount of food. It's kind of like paying taxes in exchange for police protection."

The research of Hay and Dixson is funded by the National Science Foundation, the National Institutes of Health and the Teasley Endowment at Georgia Tech. They are conducting a long-term study of the coral reefs around Fiji Island in order to study their response to pollution and climate change. They are also searching for potentially new pharmaceuticals, which — before anyone gets too upset at them — is proving to be an excellent way to get increased support from governments and corporations towards conservation efforts.

(Photo courtesy of Science Daily)

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