By Keerthi Chandrashekar ( | First Posted: Nov 08, 2012 11:17 PM EST

If you're a seaweed looking to take over some coral, watch out for these guys (Photo : Wikimedia Commons)

Coral reefs may seem like an underwater sunny paradise for fish and other exotic creatures, but don't be fooled by the colorful exterior. A sinister war is taking place for sunlight, one of the most important resources in the ocean. Seaweeds attempt to take over coral reefs' prime real estate, but it turns out that coral reefs have learned to recruit some friends to help them out - little fish called gobies.

Scientists studied the interaction between coral and a toxic seaweed known as Chlorodesmis fastigiata. This particular type of seaweed emits lipid toxins that can severely damage coral. 

When the coral was aware of the presence of Chlorodesmis fastigiata, it emitted a chemical which attracted the gobies, which began gnawing away the seaweed. The response was so timely, that it bears a similar response to a 911 emergency call. 

"This species of coral is recruiting inch-long bodyguards," said study co-author Mark 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." 

The interesting thing is that the gobies only respond to these emergency calls from their native coral, and not from others.

Don't think the gobies are being completely selfless, they stand to gain from this relationship as well. When the gobies eat the seaweed, they also munch on the coral's mucus, taking a small payment for their services. In addition, one species of the fish was found to gain a special toxin from eating the toxic seaweed, helping it ward off predators. 

"One of the gobies was known to produce a toxic skin secretion," explained Hay. "This goby consumed the toxic seaweed and became more toxic."

Coral reefs are incredibly important to our ecosystems, and widely considered 'underwater rainforests' due to their biodiversity and importance in our planet's oceans. While they have been recently devastated, this study does show the complexity and endurance of the coral reef. 

"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. 

"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."  

The study is published in the journal Science.

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