Abstract
Cleaning behaviour is deemed a mutualism, however the benefit of cleaning interactions to client individuals is unknown. Furthermore, mechanisms that may shift fish community structure in the presence of cleaning organisms are unclear. Here we show that on patch reefs (61–285 m2) which had all cleaner wrasse Labroides dimidiatus (Labridae) experimentally removed (1–5 adults reef−1) and which were then maintained cleaner-fish free over 8.5 years, individuals of two site-attached (resident) client damselfishes (Pomacentridae) were smaller compared to those on control reefs. Furthermore, resident fishes were 37% less abundant and 23% less species rich per reef, compared to control reefs. Such changes in site-attached fish may reflect lower fish growth rates and/or survivorship. Additionally, juveniles of visitors (fish likely to move between reefs) were 65% less abundant on removal reefs suggesting cleaners may also affect recruitment. This may, in part, explain the 23% lower abundance and 33% lower species richness of visitor fishes, and 66% lower abundance of visitor herbivores (Acanthuridae) on removal reefs that we also observed. This is the first study to demonstrate a benefit of cleaning behaviour to client individuals, in the form of increased size, and to elucidate potential mechanisms leading to community-wide effects on the fish population. Many of the fish groups affected may also indirectly affect other reef organisms, thus further impacting the reef community. The large-scale effect of the presence of the relatively small and uncommon fish, Labroides dimidiadus, on other fishes is unparalleled on coral reefs.
Highlights
On coral reefs, cleaning organisms - which include shrimps and fishes - perform the function of removing ectoparasites from ‘client’ organisms, usually reef fishes [1]
Size distribution and abundance of two resident damselfish species Size frequency distributions of P. moluccensis per reef differed with cleaner presence (VGLM, see methods for definitions of statistical terms: x2 = 35.4, df = 5, P,0.001), with the mean abundance per size class on reefs without cleaners skewed toward smaller individuals, compared with control reefs (Fig. 1a, c)
P. moluccensis abundance did not differ between removal (208.0629.4, least square mean 6 s.e. per reef, here and hereafter) and control reefs (265.3625.7) (F1,12 = 2.3464, P = 0.1515); abundance per reef was higher at Casuarina Beach (292.79634.0) compared with the Lagoon (180.5622.6) (P = 0.0185, Table S1b)
Summary
On coral reefs, cleaning organisms - which include shrimps and fishes - perform the function of removing ectoparasites from ‘client’ organisms, usually reef fishes [1]. On Atlantic and Indo-Pacific coral reefs, cleaner fishes interact with many client fish species [5,6,7]. The most common Indo-Pacific cleaner fish, Labroides dimidiatus [8], inspects an average 2297 clients day and consumes an average 1218 ectoparasites day21 [9]. Individual clients are often cleaned repeatedly, some up to 144 times day21 [10]. Cleaner fishes often reside in ‘cleaning stations’ [3]; this site fidelity makes them an ideal model system for the study of localised effects of cleaning interactions
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