Alistair J. Hobday, Jason Hartog, John F. Middleton, Carlos E. Teixeira, John Luick, Richard Matear, Scott Condie
global climate change, biophysical change, southeast Australia, marine fisheries, acidification
The waters of eastern and south eastern Australian have been identified as being the most vulnerable marine area to both climate change impacts and overall exposure in Australia. This vulnerability particularly relates to changes in the East Australian Current, which has strengthened by 20% in the last 50 years. As a result, water temperatures in the south-eastern region have risen and continue to rise more rapidly than elsewhere in Australia. This warm East Australian Current and other oceanic currents such as the warm Leeuwin Current (which is understood to suppress oceanic upwelling such as the Bonney Upwelling), the cool Flinders Current, and the cool Tasman Outflow converge in this region and together with local ocean processes such as coastal upwelling, are important factors in structuring the composition of marine species, functional groups and communities.
The changing climate in the south-east is already affecting many marine fishes and other organisms. These impacts will have flow-on implications for businesses, communities and economies that are dependent on the marine environment and its resources, such as the fisheries and aquaculture sector. Climate models predict that these physical trends in ocean conditions will continue into the future. Given projected changes, and their possible effect on the fisheries, the south-east Australia program (SEAP) was developed to harness the research capability in a coordinated way, and to link the research to the management needs of the region. This project set out to improve the understanding of change in the physical environment and determine if further oceanographic model development was required to support biological, social and economic aspects of the SEAP.
The objectives of this project were met. Oceanographic data for the entire south-east region were extracted and archived from the Bluelink ocean model hindcasts for comparison with observations (Objective 1) and can be used to examine historical patterns of change. These variables included sea surface temperature, temperature at depth (200 m), surface salinity, and currents. The Bluelink model variables were compared with observations at a range of distances from the coast (i.e. “do they sufficiently represent reality”) (Objective 2), which showed that SST was the best performing variable, and the currents were the poorest at the spatial and temporal scales considered. Development of the South Australian Regional Ocean Model (SAROM) model, which covers a smaller region in South Australia, was completed and comparison with in situ IMOS data showed the performance was very good in the regions considered (Objective 3). Qualitative comparison of the regional models was completed (Objective 4) and we recommend that both models will be useful for a range of biological uses. Projections of future acidification levels were completed (Objective 5). There are few studies on the impact of ocean acidification for the south-east region to date. Implications for commercial fishes and invertebrates (e.g. rock lobster and abalone) in the south-east region are unknown, and there is a need for more experiments and field studies before impacts can be more specifically determined. We have provided some future estimates of pH levels, such that critical experiments using realistic values can proceed. Finally, methods to determine marine connectivity in the south-east for the recent past were detailed and patterns of change reported (Objective 7). These analyses showed a recent trend towards increasing southward transport off eastern Tasmania, consistent with the documented increase in the strength of the East Australian Current and the associated warming of waters off eastern Tasmania that is predicted to continue over the next half century. We conclude and advise that
- Data can be extracted from the existing set of physical ocean models that is suitable for retrospective analysis of biological patterns.
- There is no single best ocean model for all purposes; careful selection and validation should be part of each use of model-based environmental variables. Each model does have strengths and will be appropriate for different uses. We suggest that case studies of fishery species in the south-east discuss their modeling needs with physical oceanographers.
- Development and improvement of the existing models is not a roadblock to further fishery adaptation planning in the south-east.
- The suite of available physical data is sufficient to support the next phase of biological case studies as part of SEAP.