Using wave gliders to understand the oceanography and plankton ecology of the Bremer Bay Canyon, Western Australia

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Using wave gliders to understand the oceanography and plankton ecology of the Bremer Bay Canyon, Western Australia

Paul G. Thomson, Alessandra Mantovanelli and Charitha B. Pattiaratchi

Australian National Facility for Ocean Gliders, School of Civil, Environmental and Mining Engineering and The UWA Oceans Institute, The University of Western Australia, 35 Stirling Highway, Perth WA 6007, Australia

Australia’s South-West Marine Region can be classified as an oligotrophic environment because of the dominance of the warm, low nutrient and low salinity waters of the southward flowing Leeuwin current. The Leeuwin current’s presence also inhibits large-scale upwelling, common to other eastern ocean basins, despite the upwelling favourable prevailing winds. Despite the oligotrophic dominance, regions of high productivity occur as a result of localised upwelling triggered by surface and subsurface current systems, strong winds and topography (headlands, islands, submarine canyons, etc.). The Bremer Bay canyon on the south coast of Western Australia stands out for its apparent enhanced primary productivity during the summer months which attracts marine megafauna, reportedly including killer whales, sperm whales, long-finned pilot whales, great white sharks, blue sharks and giant squid. Through this aggregation of marine life, the region has become popular as a tourist destination and a stage for an internationally acclaimed television nature documentary. However, most environmental knowledge of this region is anecdotal, and very little is known of the oceanographic conditions and primary productivity required to attract and support such an abundance of megafauna.

Our proposal is to better understand the oceanographic conditions and primary productivity required to support the seasonal aggregation of the marine megafauna in the Bremer Bay canyon, providing scientific evidence for further initiatives of conservation in the region. Two Liquid Robotics wave gliders will be deployed in the region to make sustained oceanographic and plankton measurements over a 2 month period between February and March 2016, the optimal period for the megafauna aggregation. The wave gliders will perform predetermined transects across the region and on detecting an event, such as an upwelling or phytoplankton bloom, one glider will be reassigned to follow the event closely. The wave glider sensor payloads will be designed to measure seawater conductivity, temperature, depth (CTD), ocean currents (ADCP), and nutrient concentrations (Satlantic Suna V2). Phytoplankton biomass and concentrations of other particles and hydrocarbons will be measured by a fluorometer, while primary productivity will be measured directly using an in situ FIRe (Fluorescence Induction and Relaxation) System. Zooplankton will be identified to the highest possible taxonomic level and counted using a video plankton recorder under design by Fastwave Communications in Perth, Western Australia, our Wave Glider integration partner. A standard wave glider weather station will provide air temperature, wind speed and direction, and barometric pressure data. As upwelling events may not necessarily be expressed in surface waters, we will deploy a Sea Glider with standard oceanographic instruments to measure subsurface processes up to 1000 m depth to complement the wave glider measurements.

This project is important for several reasons. The Bremer Bay canyon is just one of 32 known canyons along the south west coast of Western Australia. Understanding oceanographic processes and primary productivity at the Bremer Bay canyon will help us understand primary and secondary production along larger sections of our coastline. Furthermore, Bremer Bay region has leases for oil and gas exploration and this study can contribute to understand this valuable marine ecosystem and assist policy makers in determining whether the region requires protection.


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