Effects of the cleaner fish Labroides dimidiatus on grazing fishes and coral reef benthos

Territorial and roving grazing fishes farm, and feed on, algae, sediment, or detritus, thus exerting different influences on benthic community structure, and are common clients of cleaner fish. Whether cleaners affect grazing-fish diversity and abundance, and indirectly the benthos, was tested using reefs maintained free of the bluestreak cleaner wrasse Labroides dimidiatus for 8.5 yr (removals) compared with controls. We quantified fish abundance per grazing functional group, foraging rates of roving grazers, cleaning rates of roving grazers by L. dimidiatus, reef benthos composition, and fouling material on settlement tiles. Abundances of 'intensive' and 'extensive' territorial farmers, non-farmers, parrotfishes and Acanthurus spp. were lower on removal than control reefs, but this was not the case for 'indeterminate' farmers and Ctenochaetus siriatus. Foraging rates of Acanthurus spp. and C. striatus were unaffected by cleaner presence or cleaning duration. This suggests some robustness of the grazers' foraging behaviour to loss of cleaners. Acanthurus spp. foraged predominantly on sediment and detritus, whereas C. striatus and parrotfishes grazed over algal turfs. Nevertheless, benthic community structure and amount of organic and inorganic material that accumulated over 3.5 mo on tiles were not affected by cleaner presence. Thus, despite greater abundances of many roving grazers, and consequently higher grazing rates being linked to the presence of cleaners, the benthos was not detectably affected by cleaners. This reveals that the positive effect of cleaners on fish abundance is not associated with a subsequent change in the benthos as predicted. Rather, it suggests a resilience of benthic community structure to cleaner-fish loss, possibly related to multiple antagonistic effects of different grazer functional groups. However, losing cleaners remains a problem for reefs, as the lack of cleaning has adverse consequences for fish physiology and populations.