Picky Eaters Keep Endangered Coral Reefs Clean
February 14, 2013

Underwater Cameras Track Fish Cleaning Up Coral Reefs

[ Watch the Video: Picky Eater Fish Endanger Coral Reefs ]

Peter Suciu for redOrbit.com — Your Universe Online

Few pet owners would expect their dog or cat to clean up the house, and anyone who has ever camped in places such as Yellowstone Park knows that bears can visit and will leave a campsite in worse shape than they found it. Fish on the other hand could actually be doing some good in cleaning up coral reefs.

A recent study conducted in the Fiji Islands found that four species of herbivorous fish were primarily responsible for removing common and even potentially harmful seaweeds on reefs. This research has been published online ahead of the print journal Ecology, and was supported by the National Science Foundation (NSF), the National Institutes of Health (NIH) and the Teasley Endowment to Georgia Tech.

The study found that the removal of any of the four species could allow some seaweed — also known as macroalgae - to multiply. This poses a major threat to endangered coral reefs, as some seaweed emit chemicals that are toxic to the corals, while others smother or grind down the coral.

Seaweed growth thus needs to be kept in check, and it appears that herbivorous fish are the primary caretakers.

More surprisingly still was that different types of seaweed appear to be eaten by a different fish species, and the research demonstrates that particular species, and a mix of those species, are potentially critical to the health of a reef system.

The research also suggested that small marine protected areas, including those where fishing would be forbidden or otherwise prohibited, could actually encourage reef recovery.

“Of the nearly 30 species of bigger herbivores on the reef, there were four that were doing almost all of the feeding on the seven species of seaweeds that we studied,” said Mark Hay, a professor in the School of Biology at the Georgia Institute of Technology. “We did not see much overlap in the types of seaweed that each herbivore ate. Therefore, if any one of these four species was removed, that would potentially allow some macroalgae to proliferate.”

The researchers are now looking to determine which fish are most important in doing the caretaking of the coral, and since the fish can´t exactly be asked what their preferences in seaweed may be, the team at Georgia Tech turned to video capture methods.

Hay along with graduate student Douglas Rasher reportedly moved seven species of seaweed into healthy reef systems with large populations of fish, and set up three video cameras to determine what was on the preferred menu.

“The patterns were remarkably consistent among the reefs in terms of which fish were responsible for removing the seaweed,” said Rasher. “Because different seaweeds use different defense strategies to deter herbivores from eating them, a particular mix of fish — each adapted to a particular type of seaweed — is needed to keep seaweeds off the reef.”

The study found that among the most important were two species of unicornfish, which tended to dine on various brown algae; while a species of parrotfish had a taste for the red seaweeds; and rabbitfish opted for green seaweed. These four species reportedly are responsible for 97 percent of the bites taken from all the seaweed.

The researchers further looked to compare quality of coral reefs in marine protected area and the results were dramatic. The protected reefs supported as much as 11 times more live coral cover, thus suggesting that the fish can do a good job cleaning up coral.

However, another study from two years ago shows that fish probably can´t — or at least shouldn´t — be expected to clean up other ocean problems. A study from the Scripps Institution of Oceanography and University of California, San Diego, found that nine percent of fish from one of the most polluted patches of sea on the planet have plastic in their stomachs from the so-called Great Pacific Garbage Patch.

This suggests that fish will ingest a lot but, everything they eat isn´t good for them.