The macroecology of marine cleaning mutualisms.

1. Marine cleaning mutualisms generally involve small fish or shrimps removing ectoparasites and other material from cooperating 'client' fish. We evaluate the role of fish abundance, body size and behaviour as determinants of interactions with cleaning mutualists. 2. Data come from eight reef locations in Brazil, the Caribbean, the Mediterranean and Australia. 3. We conducted a meta-analysis of client-cleaner interactions involving 11 cleaner and 221 client species. 4. There was a strong, positive effect of client abundance on cleaning frequency, but only a weak, negative effect of client body size. These effects were modulated by client trophic group and social behaviour. 5. This study adds to a growing body of evidence suggesting a central role of species abundance in structuring species interactions.