Rabbitfish keep reef algae down

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Australian scientists have found an unlikely saviour to help keep coral reefs from being overrun by algae: the rabbitfish.

In a study to be published in the journal Coral Reefs, Rebecca Fox and David Bellwood of James Cook University used a series of seagrass and macroalgal assays to test the intensity of herbivory across a reef gradient in a study site on the Great Barrier Reef in Australia.

They used remote underwater video cameras to film the removal of assay material in order to identify the fish species responsible for the herbivory being quantified by the assays.

The authors found that contrary to expectations, many of the grazing herbivores associated with coral reefs (e.g. parrotfishes) were ignoring the macroalgae.

They also found that the white spotted rabbitfish (Siganus canaliculatus), a species not previously recorded at the study site, was primarily responsible for the removal of macroalgae.

Nearly half (46%) of the bites taken from the macroalgal (Sargassum) assays across all reef zones were carried out by the white spotted rabbitfish.

Although the authors found the scribbled rabbitfish (Siganus doliatus) to be mostly responsible for the remaining 54% of bites taken from the assay material, statistical analysis revealed that only the bites of the white spotted rabbitfish were removing macroalgal biomass.

However, the rabbitfish appeared to be most effective on clearing algae from reef crests, and were significantly less effective in clearing the reef flats and slopes of macroalgal growth. The reasons for this preference remain unclear.

Coral reefs face fierce competition from macroalgae, which can move in and establish themselves in degraded reefs, preventing the coral from re-establishing in these areas (a phenomenon known as phase shifting in which coral-dominated habitats are replaced by algae-dominated habitats).

These findings have important ramifications for the rehabilitation of coral reef habitats.

For more information, see the paper: Fox RJ and DR Bellwood (2008) Remote video bioassays reveal the potential feeding impact of the rabbitfish Siganus canaliculatus (f: Siganidae) on an inner shelf reef of the Great Barrier Reef. Coral Reefs DOI 10.1007/s00338-008-0359-6