Seasonal changes in habitat structure underpin shifts in macroalgae-associated tropical fish communities

Habitat shifts play an important role in structuring faunal assemblages; however, research has focused on the influence of random disturbance events and information on how regular seasonal changes to habitat affect marine fauna remains largely unexplored, especially in the tropics. We recorded seasonal changes in the structure of tropical macroalgae fields within the Ningaloo lagoon (Western Australia) and related this to the density, biomass and species richness of fishes that represent key processes: juveniles, predators of juveniles and herbivores. The extent and direction of seasonal changes in macroalgae were inconsistent among sites, creating a highly dynamic habitat matrix across time and space. Species richness and density of fishes were largely maintained where density of holdfasts from canopy-forming macroalgae and/or cover was high across seasons, but shifted markedly in areas of macroalgae habitat loss: suggesting stable habitat structure is critical for the persistence of macroalgae-associated fishes. Our results demonstrate that macroalgae fields that maintain high structural complexity across different seasons are more likely to preserve key ecological processes and therefore warrant greater conservation attention within a spatial management framework.