Cleaning mutualisms: potential effects on fish community structure and herbivory rates

Abstract Herbivores play key roles on reefs by consuming algae that compete with corals. Cleaning mutualisms can alter the distribution and feeding behavior of herbivorous fishes and may indirectly affect benthic communities. These dynamics were examined on patch reefs with and naturally without the bluestreak cleaner wrasse, Labroides dimidiatus , in July 2021 in Moorea, French Polynesia (17°28’35.52"S, 149°48’58.35"W) using herbivory assays, fish and benthic community surveys, and behavioral observations of cleaners and the client Ctenochaetus striatus . Herbivory rates on two macroalgae ( Asparagopsis and Sargassum ) were similar between reefs with cleaners present versus absent. Benthic communities were also similar, although turf algae associated with Stegastes damselfish was more abundant on reefs with cleaners. Smaller reefs with cleaners had greater fish abundances than smaller reefs lacking cleaners, though fish community trophic composition was similar between the two reef types. Bite rates for Ctenochaetus striatus were unaffected by cleaner presence, suggesting no foraging tradeoffs associated with cleaning. Rates of different cleaner behaviors (cleaning, cheating, chasing) varied among client trophic groups, with most interactions involving herbivores/detritivores. Moreover, the relative positiveness of cleaner behaviors (i.e., ratio of cleaning to cheating and chasing) was correlated with the difference in the densities of client species between reefs with cleaners present versus absent: i.e., clients with more positive cleaning interactions were more abundant on reefs with cleaners. These results suggest that cleaners did not affect herbivory, and that the hypothesized indirect effects were weak, because cleaner-client interactions were dominated by negative cleaner behaviors, which impeded strong responses of clients.