Key species protect reefs

Written by DIVE Magazine Friday, 15 February 2013 16:40

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. Two species of unicornfish 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 were responsible for 97 percent of the bites taken from all the seaweed.

The study found that the removal of any of the four species could allow some seaweed – also known as macroalgae – to multiply. 

'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.'

Hay along with graduate student Douglas Rasher  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 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.