Two Decades of Marine Protection: Assemblage-Wide and Species-Specific Responses of Fish in a No-Take MPA

Marine protected areas (MPAs) are critical tools for conserving biodiversity and managing fisheries, yet their effectiveness must be regularly evaluated to ensure they meet conservation goals. This study assessed the ecological effects of an MPA established in 2002 in Port Phillip Bay, Victoria, Australia. Baited remote underwater video stations (BRUVS) were deployed inside and outside the MPA over three time periods from 2018 to 2022. We aimed to evaluate the impact of long-term no-take protection on fish assemblages and key species, while examining the role of habitat associations. Significant differences were found in fish assemblage structure between MPA and non-MPA sites. While species richness, total abundance and evenness showed no significant differences, slight increases in total abundance within the MPA were detected via generalised additive models (GAMs). Bluethroat wrasse Notolabrus tetricus and six-spine leatherjackets Meuschenia freycineti exhibited significantly higher abundances within the MPA, whereas sand flathead Platycephalus bassensis and snapper Chrysophrys auratus, both subject to fishing pressure, showed no effects. Fiddler rays Trygonorrhina dumerilii demonstrated a limited response, with higher abundance outside the MPA indicated by GAM alone. We found reef-associated species were more likely to benefit from protection than those associated with soft sediment habitats. These findings highlight the variability in MPA effectiveness based on species-specific ecological characteristics and habitat use, underscoring the need for targeted conservation strategies.