The carbonate banks, terraces and pinnacles of the study area experience frequent disturbance from tropical cyclones and tidal currents driven by some of Australia’s largest tidal fluctuations. Mud sediments are readily mobilised leading to high levels of turbidity in the water column. While the shelf is dominated by soft sediments, the terraces, banks and pinnacles provide hard substrates for filter feeding invertebrates (sponges, whips, fans, bryozoans, soft and hard corals) to attach and take advantage of local concentrations of flow.
Key Ecological Features (KEFs) are part of the marine environment considered regionally important for biodiversity or ecosystem function and integrity and are represented in the Commonwealth Marine Reserve Network. Qualitative modelling can be used to represent relationships between the physical and biological components of KEFs, and to assess potential threats.
New information gained from this Oceanic Shoals voyage made it possible for the first time to construct such models for its resident KEFs. The qualitative modelling was used to characterise ecosystem dynamics for the carbonate banks, terraces and pinnacles, and to predict future threats. It revealed no fundamental differences between terrace, bank and pinnacle communities, but the location of these features varied with respect to physical factors such as turbidity, water depth or shear stress associated with cyclones.
Attached invertebrate communities support fishes and mobile reef invertebrates through trophic interactions and habitat-effects, including refuge from strong currents and protection from predators. Invertebrate and plankton eating fishes are consumed by both benthic and pelagic predatory fish species. This latter predator-prey relationship links the benthic and pelagic ecosystems.
Based on the ecosystem structure, five key threats were considered plausible within a 50-year time frame. They included oil and gas spills, (affecting algae and planktivorous fishes), illegal fishing, (affecting benthic and pelagic piscivores), ocean acidification, (affecting tall algae), increased water column shear stress through increased storm intensity, and increased turbidity through increased agricultural run-off. The model, and the associated direct and indirect effects of the above five threats, will be used to identify ecological indicators of use to monitoring and management.
Related
Exploring the Oceanic Shoals Commonwealth Marine Reserve Brochure – Fact sheet