Dr Brigitte Sommer1,2, Dr Maria Beger3, Prof John M Pandolfi2,4
1School of Life and Environmental Sciences, The University of Sydney, Camperdown, Australia, 2School of Biological Sciences, The University of Queensland, St Lucia, Australia, 3University of Leeds, Leeds, United Kingdom, 4ARC Centre of Excellence for Coral Reef Studies, The University of Queensland, St Lucia, Australia
Biogeographic transition zones, where tropical, subtropical and temperate species overlap, are being transformed by changes in species distributions and interactions and provide a unique ‘window’ into how climate change might influence complex biological systems. Here, we examine these dynamics in the tropical-to-temperate transition zone in eastern Australia, where corals occur at their high-latitude range limits and overlap with cold-water species such as kelp seaweeds. We combine fine scale field data for multiple taxa with species trait and environmental data to investigate the mechanisms that shape ecological dynamics in this region. For corals, results are consistent with the hierarchical filtering model of community assembly, whereby species pass through a regional climatic filter based on their tolerances for marginal conditions and subsequently segregate into local assemblages according to the relative strength of habitat filtering and species interactions. Moreover, patterns of algae, sea urchins and fish abundance point to the important role of these taxa on high-latitude reefs. For example, coral cover is negatively associated with algae cover, and sea urchins are more abundant at higher latitudes, where they likely release corals from competition with macroalgae. Understanding the links between community composition, species interactions and environmental conditions for multiple taxa leads to an ecosystem understanding of biogeographic transition zones and of how complex marine ecosystems may respond to climate change.
Brigitte Sommer is a Postdoctoral Research Fellow at The University of Sydney. Her research combines field ecology and statistical modelling to understand the processes that control the distribution and abundance of marine organisms and how they will be affected by climate change. She has a particular interest in ecosystems at the transition of biogeographical zones, where tropical and temperate species overlap at the limits of their geographical distributions and environmental tolerances.