Mutualistic Cleaner Fish Initiate Trait-mediated Indirect Interactions by Influencing the Behaviour of Coral Predators

1. Indirect interactions resulting from changes in organismal traits such as behaviour [i.e. trait-mediated indirect interactions (TMIIs)] are widespread in biological communities, yet few studies have explored the potential for mutualisms to initiate TMIIs. 2. This study used a combination of behavioural observations and manipulative field experiments to investigate potential TMIIs resulting from a mutualism between specialized cleaner fish and the 'clients' that visit cleaners for the removal of ectoparasites. 3. Behavioural observations indicate that the bluestreak cleaner wrasse, Labroides dimidiatus, increases local predation pressure on corals at cleaner stations by attracting corallivorous butterflyfish to their territories. 4. Observations of the ornate butterflyfish, Chaetodon ornatissimus, suggest a trade-off between seeking cleaning and foraging; individuals decreased their foraging rate at cleaner stations and shifted their diet to include a greater proportion of less preferred prey items. Nonetheless, predation pressure on corals was higher at cleaner stations because the spatial response of butterflyfish to cleaners more than compensated for their lower foraging rates. 5. The results of a field experiment suggest that the greater predation pressure observed at cleaner stations may be sufficient to reduce the growth rate of the unpreferred coral Porites rus. 6. Together, these results emphasize the need to consider mutualists as potential initiators of TMIIs and highlight the importance of integrating individual movement into conceptual analyses of TMIIs.