Ecosystem Responses

The waters of southern Australia, and the eastern Great Australian Bight (GAB) in particular, were traditionally perceived as having limited biological activity due to low nutrient availability. However, evidence of the occurrence of coastal upwelling in summer-autumn characterised by low surface water temperatures and elevated concentrations of chlorophyll a, suggest that during this period surface waters may be enriched with nutrients and promote high levels of primary productivity.

More recent observations have shown the significance of the upwelled water mass for generating double-diffusive instabilities, which drive enhanced vertical nutrient fluxes during summer, and have highlighted their significance for supporting the enhanced productivity of the upwelled water mass.

Southern Australia’s coastline varies from cliffs, rocky shores, and sandy beaches in the South-East and West Coast, to mud flats and mangrove habitats in the upper Gulf St Vincent and Spencer Gulf. Over 100 estuaries, which are significant breeding and nursery habitats for a broad range of species, are also found across the region.

The region’s waters support more than 6,000 invertebrate species, 1,200 algal species, 350 fish species, 16 breeding seabird species, 33 mammal species and 12 seagrass species (Edyvane 1999a, b). In addition, the level of endemism found in Southern Australian waters is high, accounting for 75% of red algae, 85% of fish and 95% of seagrass species. Additionally, the southern shelves also host the largest temperate “carbonate factory” in the world, and the shelf waters of the eastern GAB support significant commercial fisheries, and the most diverse marine ecosystems with the greatest density of apex predators in Australia. 

The following high-level science questions will guide the SA-IMOS observing strategy in this area:

Productivity

a) How do variations in oceanographic processes, nutrient dynamics (speciation, supply ratios), and connectivity between oceanographic sub-regions influence ecosystem productivity, carbonate sediment production, and shifts in food web structure between the microbial and classic upwelling food webs?

b) What is the extent of spatial and temporal variation in primary and secondary productivity in southern Australian waters, how is this influenced by variation in oceanographic processes and connectivity between oceanographic sub-regions, and what are the resultant seafloor sediment facies?

c) What is the lag between an upwelling event and increased primary and secondary productivity?

d) What role does upwelling driven primary and secondary productivity play in explaining the spatial dynamics and temporal windows that constitute ‘hot spots’ (Areas of Ecological Significance) for apex predators and high carbonate sediment?

e) What combination of physical and biological oceanographic factors and conditions define the ‘marine deserts’ that comprise the migration and movement pathways of predators between ‘hot spots’?

Distribution and abundance

a) How do variations in oceanographic processes, nutrient dynamics (speciation, supply ratios), and connectivity between oceanographic sub-regions influence the distribution, abundance, and size structure of microbial (i.e., viruses and bacteria, nano- and pico-phytoplankton), and planktonic (i.e., phytoplankton, micro-, meso-, and macro-zooplankton) communities and thus calcareous sediment distribution and apex predators?

b) What roles do short- and long-term variations in upwelling cycles play in the success of larval dispersion, recruitment, growth and population dynamics of key species in the SA-IMOS Node region?

c) What are the key physical and biological oceanographic features that underpin the distribution, key foraging locations, movements and migratory patterns of apex predators? How are predator distributions and abundance impacted by dynamic changes in physical and biological oceanography at seasonal, annual and longer-term time scales?

d) What have been the changes in past carbonate sediment patterns driven by oceanographic change and thus what are the likely implications of climate change and extreme climate events on the status, distribution and abundance of microbial, planktonic and apex predator populations?

e) What are the present relationships between climate change and ocean acidification as reflected in biogenic and sediment mineral specific dissolution?