Recent evidence for the occurrence of coastal upwelling during summer-autumn in the Kangaroo Island-Eyre Peninsula region suggests that during this period, surface waters may be enriched with nutrients and may promote high levels of primary productivity. Preliminary work conducted on phytoplankton and zooplankton communities has shown that the coastal waters of the eastern Great Australian Bight have a potential productivity that rivals the most productive regions of the ocean. However, productivity levels vary considerably both spatially and temporally. Variations in primary productivity are implicitly related to variations in meteorology and oceanography in the region, which drive the supply of nutrients to phytoplankton. In this context it is also critical to understand the lag between an upwelling event and the biological response, as well as the qualitative and quantitative nature of the food webs initiated by the upwelling. There is still much to understand about the productivity of these communities, their potential link with the microbial food web, and the bentho-pelagic and the ocean-atmosphere couplings.
The eastern Great Australian Bight also supports the greatest density and biomass of apex predators to be found in Australian coastal waters. Seasonal upwelling boosts primary, secondary and fish production in the region, making it Australia’s richest pelagic ecosystem. This productivity “hot-spot” forms an area of ecological significance. Key apex predators include the Australian sea lion, New Zealand and Australian fur seal, pigmy blue whales, pelagic sharks (mako, great white and whaler sharks) and southern blue-fin tuna. The variable nature of upwelling and seasonal production in the region presents significant challenges for apex predators and there appears to be a range of foraging strategies that species adopt in response to the variable states of the ecosystem. A marked shift in foraging locations of apex predators is predicted to occur in response to prey availability, driven by oceanographic processes. Key knowledge gaps include an understanding of how physical changes in boundary currents and upwelling systems effect the distribution and abundance of production and productivity in benthic and pelagic ecosystems, and how such variation influences the distribution and abundance of higher trophic levels. The impact that climate change will have on these boundary currents and upwelling systems, and how these changes will impact higher trophic levels is unknown.
Key Science Questions
Ocean chemistry - nutrients
- How do variations in oceanic nutrient supply (such as through the upwelled Kangaroo Island cold pool) impact of phytoplankton communities? What roles do canyons and gulfs play as a source of nutrients?
- How are variations in primary productivity related to variations in oceanic nutrient supply and what are the lags of biological response?
- What is the temporal and spatial variability in phytoplankton communities on the coastal shelf? What is the impact of the Flinders Current/Leeuwin Current and coastal shelf boundary currents on these communities?
- What are the critical fluxes such as primary productivity and the related changes in phytoplankton communities, ocean-atmosphere fluxes and vertical fluxes?
Mid trophic levels
- What is the temporal and spatial variability in secondary producers (e.g. zooplankton) on the coastal shelf? How this variability impacts on fish communities?
Ocean chemistry – carbon and acidification
- What is the space-time dynamic of the trophic state of S.A. shelf waters, and do they act as a source or a sink of CO2?
- What are the key physical oceanographic features that underpin the distribution, key foraging locations, movements and migratory patterns of apex predators?
- How do foraging distributions and movements of different apex predator species respond to the spatial and temporal variability in boundary currents and upwelling intensity?
- What are the likely physical and biological implications of climate change on the spatial and temporal distribution of benthic and pelagic production, and how will this impact the foraging distributions and movements of apex predator populations?
- How does exploitation of the Bonney coast upwelling by great whales vary across years? How does visitation of the Bonney coast by pygmy blue whales fit with seasonal migrations along the eastern and western Australian coasts? Can the presence of whales or fish choruses known to occur along the shelf edge, be used as an indicator of productivity or vice/versa?
- How does the breeding success and trends in abundance of apex predator populations respond to the spatial and temporal variability in boundary currents and upwelling intensity?
- What are the likely implications of climate change on the status, distribution and abundance of apex predator populations?
- What are the impact or viral infection and the subsequent lysis of marine microbes and other organisms? How does this impact aquatic food web and predators on the coastal shelf?