Contrasting effects of habitat complexity and connectivity on biodiversity in seagrass meadows

Variability in habitat positioning within seascapes (over kilometres) influences fauna assemblage composition, but the characteristics of a habitat patch (10–100s of metres) influence how species use that patch and how variable assemblages are within habitats. Understanding the relative influence of these two contrasting scales is crucial to improving the management of marine habitats. We used baited remote underwater video systems (BRUVS) to quantify seagrass fish assemblages, and took seagrass cores to quantify seagrass metrics, at ten sites across three seasons in Moreton Bay, Australia to determine if fish are influenced more by seascape context or metrics of seagrass habitat complexity. We found that fish species richness and assemblage composition are most influenced by large-scale variability in seascape (e.g. proximity to ocean and mangroves). However, variability in habitat complexity (e.g. seagrass blade length and density) and proximity to mangrove forests had the greatest effect on assemblage beta diversity. Connectivity with other habitats plays a vital role in structuring the fish community, as it is crucial for daily feeding excursions (mangrove forests) and spawning/reproduction (proximity to ocean). Continuous, non-patchy seagrass beds are however vital to how individuals use a seagrass meadow, with beta diversity being higher in seagrass meadows that were less patchy. Identifying how habitat attributes and context influence fish assemblages is vital for optimizing conservation initiatives. Therefore, we suggest that monitoring populations with biodiversity metrics such as beta diversity can be effective in determining areas that are critical for conservation.