A juvenile Gobidon (goby) fish is shown on an Acropora coral. These fish spend their entire lives with the same coral, protecting it from encroaching seaweed. (Photo: Georgia Tech/Joao Paulo Krajewski)

Coral reefs provide one of the world’s most vital ecosystems and some of these reefs are in danger of being destroyed.

While people are to blame for much of the destruction, nature also plays a role. Encroaching species of seaweed with poisonous compounds on their surfaces are one of nature’s threats.

The toxic seaweed begins its lethal damage upon contact with the coral, killing its tissue within two to three days of contact.

But now scientists at the Georgia Institute of Technology have found that one species of coral near the Fiji Islands  doesn’t sit around waiting to  destroyed; it actually sends out a call for help when it’s threatened by poisonous seaweed.

Small fish, known as gobies, which are about two centimeters long and spend their entire lives in the crevices of the coral, respond to the coral’s alarm within minutes.

The gobies go after the seaweed, chewing and mowing it away from the coral. Not only do the little fish protect their homes, but some species also use the toxic substances from the seaweed to build up their own protective arsenal.

Mark Hay, a biology professor at Georgia Tech and colleague Danielle Dixson conducted the research and published their findings in Science.

Hay said two species of goby serve as coral bodyguards.  One species simply chews away at the harmful seaweed and then spits it out, but the other type of fish actually ingests the poisonous substance. This enhances the fish’s already toxic characteristics, increasing its ability to protect itself from predators.

Coral protector Gobidon histrio (goby) in its living space on the coral Acropora nasuta. The coral is in contact with the toxic green alga Chlorodesmis fastigiata. (Photo: Georgia Tech/Danielle Dixson)

Researchers were unable to determine whether the fish were saving up the lethal seaweed compounds to use on enemies, or if they were already making their own poisons, and using the noxious material to build up their resistance to the poisons.

Not all fish possess the gobies’ protective instincts. Scientists also studied two other species of small fish that live in the coral.

According to Hay, these damsel fish simply swim away, moving on to other coral, when their homes are threatened.

“They just abandon it, say ‘It’s going to die, we’re out of here,’” Hay says.

Interestingly enough, the gobies are only protective when their particular species of coral is under attack.  The scientists placed the gobies within another closely-related species of coral and found that the little bodyguards did not respond or protect their new home when it was under a similar threat.

Hay hopes to study other species of coral in the future to see if they too are also aided by rapid responding protective fish.

Mark Hay joins us this weekend on the radio edition of Science World.  Tune in (see right column for scheduled times) or check out the interview below.

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Black coral and barrel sponge on coral reef in Saint Lucia (Photo: Chuck Savall/Marine Photobank)

More than 2,600 scientists are calling on governments worldwide to take steps to protect valuable coral reef ecosystems.

They’ve endorsed a statement  written by scientists brought together by the Center for Ocean Solutions at California’s Stanford University.

The statement was released this week to kick off the 12th International Coral Reef Symposium  being held in Cairns, Australia.

“Rising sea levels, more intense storms, changes in ocean chemistry due to air and water pollution – all these stress coral reefs,” said Steve Palumbi, an expert on corals with the Center for Ocean Solutions and the chief organizer in developing the consensus statement. “At least 25 percent of the world’s coral reefs have been degraded.  Because of the global origin of climate change, the only way to tackle this is through a worldwide effort.”

The  statement calls on governments to take action through global initiatives to reduce emissions of carbon dioxide and other greenhouse gases, and to increase local protection of coral reefs throughout the world.

A rare moment during the process of coral bleaching.  When corals are stressed by various changes in their conditions they blow out the symbiotic algae that live in their tissues, causing them to turn completely white(Photo: Ryan Goehrung/Marine Photobank)

The scientists referred to the world’s coral reefs as important ecosystems which, despite being ecologically, economically and culturally valuable, are in decline everywhere due to human-based factors such as pollution, sedimentation, overfishing and climate change, all of which, they say, are expected to rise in severity.

The statement lists changes  scientists have already been observed over the last century:

• Approximately 25-30% of the world’s coral reefs are already severely degraded by local impacts from land and by over-harvesting.
• The surface of the world’s tropical oceans has warmed by 0.8°C, resulting in unprecedented coral bleaching and mortality events.
• The acidity of the ocean’s surface has increased due to increased atmospheric CO2.
• Sea-level has risen on average by 18cm.

Unless action is taken now,  future impacts on coral reefs could include:

• Most corals will face water temperatures above their current tolerance.
• Most reefs will experience higher acidification, impairing calcification of corals and reef growth.
• Rising sea levels will be accompanied by disruption of human communities, increased sedimentation impacts and increased levels of wave damage.
• Together, this combination of climate-related stressors represents an unprecedented challenge for the future of coral reefs and to the services they provide to people.

The International Coral Reef Symposium, which runs through July 13, is held once every four years. Organizers say  this year’s symposium will draw more than 2,000 scientists from 80 countries. They’re expected to present cutting-edge science and to share the latest advances in coral reef conservation.