Green2009-herbivore monitoring

Monitoring Functional Groups of Herbivorous Reef Fishes
Grazers/detritivores
Grazers play an important role in coral reef resilience by intensely grazing epilithic algal turfs, which
can also limit the establishment and growth of macroalgae (Paddock et al 2006, Hughes et al 2007).
Unlike scrapers and excavators, they do not scrape or excavate the reef substratum as they feed.
Grazers include most rabbitfishes (except Siganus canaliculatus and S. lineatus), small angelfishes
(all Centropyge species), and many species of surgeonfish including all Zebrasoma and Acanthurus
species except those that feed on exclusively on plankton (see Key Families and their Feeding
Modes) or are grazers/detritivores (see below). Acanthurus lineatus is included in this group because
while they are predominately territorial (Polunin and Klumpp 1989, Craig 1996) they also move around
and consume algal turf outside their territories (Craig 1996).
Grazers: surgeonfish (left: Acanthurus triostegus) and angelfish (right: Centropyge loricula). Images by G. Allen.
Ringtail surgeonfishes of the genus Acanthurus (see Key Families and their Feeding Modes) are
grazers/detritivores that feed on a combination of epilithic algal turf, sediment and some animal
material (Choat 1991). Similarly, the rabbitfish S. lineatus appears to be a grazer/detritivore, feeding
primarily on off-reef detrital aggregates (Fox et al in press). Although only a small proportion of their
diet is algal turf, grazers/detritivores are combined with grazers because many are schooling species
that can be abundant and consume significant amounts of epilithic algal turf. They also play similar
roles in coral reef resilience by removing macroalgae before it becomes established (see above).
Grazers/detritivores: rabbitfish (left: Siganus lineatus) and ringtail surgeonfish (right: Acanthurus nigricauda).
Images by G. Allen.
30