Hydrodynamic conditions and habitat configuration structure juvenile fish assemblages across a tropical seascape

Abstract

Context: Landscape structure and environmental conditions influence the distribution and abundance of adult fish, with significant implications for ecosystem functioning. However, our understanding of seascape effects on juvenile fish remains comparatively limited. Objectives: We examined how habitat composition, seascape configuration, and environmental context shape juvenile fish assemblages across a tropical seascape. Methods: We surveyed juvenile fish in multiple habitats over three consecutive years in the Dampier Archipelago, Western Australia. We employed a combination of modelling approaches to assess the relative importance of habitat, seascape, and environmental variables for explaining variation in juvenile fish abundance and diversity, and the distribution of common taxa. Results: Abundance and genus richness of juvenile fish were consistently higher in macroalgal habitats, yet assemblages in coral, macroalgae, and mangrove habitats were taxonomically distinct (~ 57% of species only observed in a single habitat). Hydrodynamic conditions emerged as a significant factor influencing juvenile community structure, seemingly acting as environmental filter for taxa with lower swimming capability. Conditions that maximised total abundance differed from those that optimised taxonomic distinctness. Similarly, predictor variables that best explained patterns in abundance varied both among individual species, and for the same species across different habitats. Conclusions: These findings highlight the central role that local hydrodynamics play in shaping the distributions of juvenile fish, while emphasising the diverse taxa-specific responses to habitat composition and environmental conditions. Accordingly, effective conservation and restoration strategies for tropical seascapes should incorporate the full range of habitat types and consider both hydrodynamic and seascape context to maintain high abundance and diversity of juvenile fishes.