Community stability and instability in ectoparasites of marine and freshwater fish

Abstract

Ectoparasite communities on the gills and skin of fish are non-saturated, with many vacant niches, which suggests that these fish ectoparasites live under non-equilibrium conditions. Such communities, often with several congeneric species, are not structured by interspecific competition, but show a high degree of aggregation. The structure of ectoparasite communities especially in freshwater fish is affected by temporal and spatial variability, which promotes the coexistence of potentially competitive species. Niche segregation in congeneric ectoparasites is linked to the morphology of their attachment apparatus. Congeners with morphologically similar attachment apparatus tend to occupy the same or adjacent niches within a host. Co-occurrence of congeners is facilitated by reinforcement of reproductive barriers due to morphological differences in copulatory organs. Ectoparasite communities of fish may show non-random structural patterns, the likely result of the demography of species living in these communities. Many congeneric ectoparasite species of fish are specialists, adapted to certain host species; host specificity therefore also represents an important factor involved in structuring communities. Using null model analysis, neither interspecific competition nor facilitation was found to affect the structure of ectoparasite communities of marine fish.