Investigating Fish-Habitat Associations on Mesophotic Reefs Using Stereo-BRUVS

Fish-habitat associations are fundamental ecological relationships characterising marine community assembly. The strength of fish-habitat associations can be indicative of ecosystem resilience, making them important benchmarks for ecological monitoring. These relationships are relatively unknown in mesophotic (30–150 m) marine systems due to the constraints of sampling in deeper waters. We aimed to assess fish-habitat associations in two unstudied no-take National Park Zones in the recently established Abrolhos Marine Park, Western Australia. We used the first baited remote underwater stereo-video systems (stereo-BRUVs) in this area to quantify demersal fish and benthic habitats between 33 and 154 m depth and modelled associations among fish species, traits and environmental covariates using Hierarchical Modelling of Species Communities (HMSC). Significant evidence of species-environment, trait-environment, and species-species associations was identified which may influence local community assembly. Benthic habitats explained 62.4% of the modelled variation in fish abundance, and 7 of the 21 modelled species showed strong statistical relationships with habitat, particularly macroalgae. The modelled species-environment relationships enabled us to infer the distribution of a subset of fish species across these understudied no-take zones. This study demonstrates the potential of discrete opportunistic studies using stereo-BRUVs for investigating the key drivers of community assembly in mesophotic marine environments. Our findings emphasise the importance of ongoing efforts to map and monitor benthic habitats and bathymetry as influential drivers of higher order species distribution beyond the coastal zone.