Standard Talk (15 mins) Australian Society for Fish Biology Conference 2022

Fine-scale bathymetry data explains variability in fish assemblages on mesophotic reefs in the Hunter Marine Park (#69)

Joel Williams 1 , Tim Ingleton 2 , David Harasti 3 , Alan Jordan 1 , Neville Barrett 1
  1. University of Tasmania, Hobart
  2. New South Wales Department of Planning and Environment, Lidcombe, NSW, Australia
  3. NSW Department of Fisheries, Nelson Bay, NSW, Australia

Temperate mesophotic reefs are located at depths of 30-150m and are a transition zone from algal dominated reefs to sessile invertebrate dominated reefs. It is expected that the structure of the fish assemblage would also change with depth. There’s a large knowledge gap of inter and intra reef variability in fish assemblage structure, including seasonal patterns of abundance of fish at mesophotic depths. Several of the newly established Australian Marine Parks recognised these mesophotic reefs as key ecological features. Through the support of the NESP Marine Biodiversity Hub we collected baseline mapping, habitat and fish abundance data for the Hunter Marine Park on the mid-north coast of NSW. Using joint species distribution models, we were able to investigate assemblage level seasonal variability, environmental drivers, species-species interactions, and trait-based patterns of fish distribution at mesophotic depths.  We found minimal seasonal variability in the fish composition of rocky reefs in the Hunter Marine Park. Species composition was primary associated with reef structure, with upper mesophotic high relief reefs being biodiversity hotspots. These results highlight the need for monitoring programs to stratify sampling across depths and habitats if trends in biodiversity through time are the core metrics of interest to marine park managers.