Temporal and spatial changes in fish assemblages associated with the placement of a rock armoured pipeline complex in...

Despite growing knowledge of the effects of subsea pipelines for fishes, the influences of their associated protective structures, such as rock armour used for stabilisation, on fish assemblages remain understudied. We used baited remote underwater stereo-video systems (stereo-BRUVs) to assess how fish assemblage composition, biomass, and the number of species and individuals changed in response to the placement of a rock armoured pipeline complex within soft sediment habitat in northwestern Australia. We compared fish assemblage metrics before placement to those observed one, two, and eleven years after, and how responses varied with distance from the rock armour habitat. A total of 239 unique identifiable taxa were observed across all samples, 40 of which were unique to samples within or close to the rock armour habitat. Fish assemblages exhibited a strong but spatially limited response to the presence of the rock armour habitat, with a distinct assemblage composition characterised by reef-associated species and increases in fish abundance, biomass and the number of species observed within 30 m of the rock armouring following its placement. We demonstrate the potential ecological role of rock armouring as an artificial reef habitat for fishes and highlight the importance of having longer-term studies when assessing the impacts of artificial structures.