Ecosystem Responses

Change in cover of major benthos; the kelp Ecklonia, red Foliose algae, hard corals between 2010 and 2013 showing timing of loss and recovery around the 2011 marine heatwave in WA
Change in cover of major benthos around the 2011 marine heatwave in WA

WA-IMOS addresses marine observing around over a third of Australia’s continental shelf and coastal oceans. Understanding how environmental factors contribute to the variation primary productivity, pelagic ecosystems and benthic habitats, particularly under climate change, requires long-term time series of environmental data with the lower west coast of Western Australia identified as a climate change hotspot in the Indian Ocean. This highlights the value of the monitoring projects such as those undertaken by IMOS and their use in oceanographic modelling.

The NWS from North West Cape to Broome is one of the most productive fishing areas in Australia, with extraordinarily high biodiversity, yet the source of nutrients remains poorly explained. Both the Gulf of Carpentaria and the Arafura Sea are highly productive regions which each support significant commercial fisheries, however, there is a paucity of detailed biological oceanographic observations in the region. The Western Australian coastline is also richly endowed with marine megafauna, these being the larger more obvious fauna such as great whales, various dolphin and toothed whale species, whale sharks, dugong or sea turtles. 

The marine heat wave event in the Gascoyne and mid-west region of WA during the summer of 2010/11 provides an example of an extreme event that has had significant implications in the management of a number of fisheries, with a number of fisheries requiring a re-assessment of the stocks and significant fisheries management interventions, including closures. It also impacted the length of the west coast of Western Australia for weeks during February and March 2011 causing bleaching of corals from Ningaloo to Rottnest, defoliation of large areas of seagrass in Shark Bay and Houtmans Abrolhos and the loss of large brown algae from Kalbarri to Jurien Bay.

From an oceanographic perspective the key question was whether the marine heat wave could be viewed as a rare event that was unlikely to reoccur in the near future or whether is it likely to become more common as the climate changes.

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

Productivity

  • What is the role of krill in the Perth Canyon where localised upwelling appears to be supporting a blue whale feeding ground?
  • How does the Leeuwin Current influence the pelagic ecosystem eg prey availability for pelagic seabirds, especially those that nest on the Abrolhos Islands?
  • What is the mechanistic influence of the Leeuwin Current on southward distribution of larvae and juvenile blue fin tuna from the north, as well as, on tailor and herring larvae from spawning areas near Perth?

Distribution and Abundance

  • What is the natural variability of water quality (particularly under water light, TSS, temperature, Chlorophyll, primary productivity) in the region?
  • What is the influence of water quality on ecosystems?
  • What are the dynamics of regional nutrient supply associated with production?
  • What are the drivers and natural variability of planktonic community structure and primary production?
  • What are the processes driving productivity in LC eddies?
  • What is the seasonal variability in carbonate system parameters (pH, pCO2, TA, DIC), hence ocean acidification buffering capacity, in coastal waters?
  • Are WA coastal waters sinks or sources of atmospheric CO2? 

Effects of tidal and wave dynamics on marine habitats

  • What is the role of tidal fronts in controlling the biological productivity?
  • What is the role of internal waves on biological productivity?
  • What is the influence of tidal and wave stress on bottom habitats?
  • How are benthic and pelagic systems coupled?

Water column processes

  • What are the mechanisms of alongshore and cross-shelf dispersals of fish larvae and other biota?
  • What is the nature and variability of planktonic ecosystems supported by cross-shelf exchange?

Natural variability of populations and pathways of large marine fauna

  • What are the migration pathways of mega-fauna in the region? 
  • Can seasonal patterns of use be determined, or precisely when are they present and what controls this?
  • How can we monitor over the long term, trends in mega-fauna populations and link these to physical factors?
  • How can we use marine vertebrates as platforms to collect oceanographic data and to inform us of where and when regions of high productivity occur?