Abstract: Biogeographic transition zones in marine temperate systems are often hotspots of biodiversity, with high levels of resilience to short-term climate shifts due to naturally occurring cyclic oscillations of oceanographic conditions. However, these environments are likely vulnerable to a steady global warming scenario in which these cyclical conditions could be disrupted. Here, we evaluate how changes in local oceanography affect the structure of rocky reef fish assemblages over a period of 50 yr in a biogeographic transition zone. Using a 12 yr time series of rocky reef fish assemblage structure, we identified the set of oceanographic variables that most influenced assemblage dynamics. Descriptive and predictive models (multivariate regression trees) were compared to observed data using the area under the curve. Winter northward wind stress and sea surface temperature (SST) were the most important drivers of change in assemblage structure. Only warmer years had indicator species with warm-temperate or tropical affinities. A fish assemblage ‘tropicalization’ index was developed in response to both local-spatial resolution and short-term environmental variation (1993−2011), and to regional spatial resolution and long-term SST (1960−2012). Predictive modelling for the last 50 yr revealed that species with tropical affinities have increased in frequency compared to cold-temperate species, coinciding with the trend of increasing mean winter SST. Since the mid-1980s, warm-temperate and tropical species have responded rapidly to more frequent warm winters, suggesting that species distributions are shifting polewards. Our results support a hypothesis that cold species retreat more slowly than the advance of warm species. We discuss the importance of transition zones as ‘barometers’ of climate change.
Biography: Emanuel Gonçalves is Associate Professor at ISPA – Instituto Universitário (Portugal) and is the President of the Board of ISPA,CRL, the cooperative that runs the Institute. Emanuel coordinates the Eco-Ethology Research Unit of ISPA, classified as Excellent in the last evaluation process of the Portuguese Science and Technology Foundation. Currently, this research Unit integrates a large center which includes 6 universities and 4 former research centers, MARE – Marine and Environmental Sciences Centre, where he is a Vice-President. His research interests are marine conservation (in particular the role of marine protected areas for ocean governance), marine ecology and connectivity in marine ecosystems, behaviour of marine animals, in particular fish, larval ecology and recruitment. He has been involved in the creation, monitoring and implementation of Marine Protected Areas in several regions, including discussions on the high seas and coordinates the studies which lead to the implementation and monitoring of MPAs in Portugal. He was deputy-head of the Portuguese Task Group for Maritime/Marine Affairs where he contributed to the approval and implementation of the National Ocean Strategy. He was coordinator of the European Union Group that led the negotiations on marine and coastal issues at the 9th Conference of the Parties of the Convention of Biological Diversity which approved the CDB Scientific Criteria for Identifying Ecologically or Biologically Significant Areas (EBSAs) in the marine realm (the Azores Criteria). He is a member of the National Council of Environment and Sustainable Development (Portugal).