Topographic and climatic descriptors determining the distribution of temperate benthic invertebrates in a commercial fishery

Under climate change scenarios, rises in ocean temperature are likely to impact the range and spatial scale of species distributions. The rate of warming in south-east Australia is several times faster than global averages and... [ view full abstract ]

Under climate change scenarios, rises in ocean temperature are likely to impact the range and spatial scale of species distributions. The rate of warming in south-east Australia is several times faster than global averages and therefore, we are likely to see a tropicalisation of temperate ocean systems through range expansions. Abalone are high value fisheries species in south-east Australia and Australia’s commercial fishery contributes to over 50% of global abalone wild catch production. Abalone stocks are under threat through a range of factors including disease, changes in habitat and overexploitation that has resulted in some localized extinctions. In the state of Victoria, the stock is particularly under pressure following an outbreak of a herpes-like virus during 2006-2007 that resulted in mass mortality in the western zone of the fishery. Whilst in the east, strengthening of the Eastern Australian Current and southward extension and intensification of warmer ocean flows has resulted in a shift in the distribution of marine species such as the sea urchin Centrostephanus rodgersii competing with abalone especially for food. Overgrazing of macroalgae communities by sea urchins and subsequent formation of urchin barrens has implications for productivity of the abalone fishery. Knowledge of existing distributions and patterns in abundance relative to seafloor structure and oceanographic variables are critical to understanding how a species may respond to multiple stressors and give an indication to the resilience of a species to climate change. In this study we integrate diver survey records from 121 sites characterising the habitat and abundance of blacklip abalone Haliotis rubra and urchin species Centrostephanus rodgersii and Heliocidaris erythrogramma with bathymetric LiDAR-derived seafloor surrogates and satellite-derived oceanographic parameters (sea surface temperature [SST] and chlorophyll-a) to develop predictive models of species distribution and abundance over 4000 km2 in Victorian coastal waters, south-east Australia. Assessing the relative importance of the model predictors indicated the role of SST and seafloor complexity in the description of the species distribution patterns. We also explore predicted climate scenarios to assess the potential conflict between urchin range expansion and abalone fishing grounds and discuss implications for ecosystem based fisheries management.