Optimising cool-water injections to reduce thermal stress on coral reefs of the Great Barrier Reef

Abstract

Coral bleaching driven by ocean warming is one of the most visible ecological impacts of climate change and perhaps the greatest threat to the persistence of reefs in the coming decades. In the absence of returning atmospheric greenhouse gas concentrations to those compatible with ocean temperatures below the mass coral bleaching temperature thresholds, the most straightforward means to reduce thermal-stress induced bleaching is to cool water at the seabed. The feasibility of reducing the seabed temperature through cool-water injections is considered first by analysing the feasibility of doing so on 19 reefs with differing physical environments using a simple residence time metric in 200 m resolution hydrodynamic model configurations. We then concentrate on the reefs around Lizard Island, the most promising candidate of the 19 locations, and develop a 40 m hydrodynamic model to investigate the effect of the injection of cool water at differing volumetric rates. Injecting 27˚C seawater at a rate of 5 m 3 s −1 at 4 sites in early 2017 cooled 97 ha of the reef by 0.15˚C or more. The power required to pump 5 m 3 s −1 through a set of pipes over a distance of 3 km from a nearby channel is *466 kW. This power applied at 4 sites for 3 months achieves a 2 Degree Heating Weeks (DHWs) reduction on 97 ha of reef. A more precise energy costing will require further expert engineering design of the pumping equipment and energy sources. Even for the most physically favourable reefs, cool-water transported through pipes and injected at a reef site is energy expensive and cannot be scaled up to any meaningful fraction of the 3,100 reefs of the GBR. Should priority be given to reducing thermal stress on one or a few high value reefs, this paper provides a framework to identify the most promising sites.

Wave and Tidally Driven Flow Dynamics Within a Coral Reef Atoll off Northwestern Australia

“…A coupled version of Delft3D FM suite flow and wave modules was used to simulate the hydrodynamics of Mermaid Reef for a period of 3 months (1 December 2017 and 1 March 2018), encompassing spring and neap tidal ranges and a range of wave conditions. The Delft3D FM suite has been successfully applied to simulate the hydrodynamics of reefs (e.g., Baird et al., 2020; Green et al., 2018) and other complex coastal systems including estuarine environments (Thanh et al., 2017).…”

Coral Reef Bleaching under Climate Change: Prediction Modeling and Machine Learning

“…Coral may bleach for other reasons, like extremely low tides, pollution, or too much sunlight. For this reason, many studies have addressed the factors effect to coral reef bleaching [4][5][6][7]20,21]. Melissa et al [20] and Steve et al [21] studied the temperature factor affecting coral bleaching.…”

“…The current global temperature has an increasing trend, with simultaneous slight warming of the ocean waters. Warmer water is a major contributor to coral bleaching [4][5][6][7]. The coral bleaching effect is caused by climate change and other processes, such as runoff and pollution (storm generated precipitations can rapidly dilute ocean water and runoff can carry pollutants that can bleach near-shore corals), overexposure to sunlight (when temperatures are high, high solar irradiance contributes to bleaching in shallow-water corals), and extreme low tides (exposure to the air during extreme low tides can cause bleaching in shallow corals).…”