Distribution models of temperate habitat-forming species on the continental shelf in eastern Australia: setting the baseline and predicting future changes

Habitat-formers (e.g. kelp beds, corals, sessile invertebrate assemblages) are key to the structure and functioning of reef ecosystems worldwide. In southeast Australia, a region identified as a global hotspot for climate-driven ocean warming, the structure and distribution of deep (> 30 m) benthic sessile communities are poorly known given these habitats are hard to quantitatively survey. Using high-­‐resolution imagery of the seafloor from a recent national-scale AUV‐based survey program, we establish a critical baseline about the latitudinal gradient in benthic community composition from 27°S to 43°S on the eastern seaboard of Australia. Large-scale latitudinal variability between three major community types (sub-tropical, warm temperate and cool temperate) mostly correlates with primary productivity and temperature climatology, while local scale variability relates well with depth. Using environmental variables that capture recent and future climatology both in terms of means and extremes (frequency and magnitude), we develop alternative distribution models for several habitat-­‐forming species. Our models characterise the optimal environmental window of individual morphospecies, discriminate between different types of latitudinal distribution (e.g. truncated or continuous), and identify potential indicator morphospecies more likely to respond to climate-driven changes in ocean conditions. Model predictions under projected climate change provide some insights on the potential effects of ongoing and future ocean changes on these deep reef communities. Our study provides an important benchmark to detect and predict future climate-driven changes in southeastern Australia, and our methodology has general applicability for monitoring of deep reef environments.