Predicting the response of reef communities to climate change: lessons from Pleistocene coralline algal communities

There is now little debate that anthropogenic climatic warming is occurring. Strong evidence exists from both terrestrial and marine realms of shifts in species distributions and abundances in response to this warming. Understanding patterns of population movement in response to different climatic periods provides valuable information for understanding how species are distributed and on population responses to future climatic changes. There are, however, few long-term ecological datasets that enable realistic predictions of how species are likely to respond to future change. Using a comparative paleoecological and ecological approach we have investigated the regional effects of climatic warming on the community composition and biogeographic range of crustose coralline algae along a 12 degree latitudinal gradient of Western Australia's coral reefs. Our study compares Late Pleistocene (118-135,000 years ago) coralline algal community composition adjacent modern (living) communities. Sea-surface temperatures during the Pleistocene were 2°-3°C warmer than today and similar to temperatures predicted for Western Australia by 2100. Although our results are still being analysed it is anticipated that there will be a latitudinal gradient in coralline algal diversity in both the Pleistocene and modern communities. In addition it is anticipated that coralline algal species with warm/tropical centres of biogeographic distribution will be found further south along the latitudinal gradient in the Pleistocene compared to their modern counterparts. This is the first study to quantitatively investigate the magnitude and direction of latitudinal range shifts in reef assemblages caused by Pleistocene climate change. Such studies can provide valuable information on the likely responses of modern communities to future anthropogenic climate change.