In late 2023, the CSIRO and The Bureau of Meteorology predicted an imminent marine heatwave on the South-East Coast of Australia. Marine heatwaves are long periods of above average sea surface temperatures, which occur as a result of climate change.  These heatwaves are similar to the terrestrial equivalent where we see negative impacts on the environment. In the ocean, we also see significant repercussions on ecosystems such as kelp forests, seagrass meadows and we can even see tropical species moving down the coast into sub-tropical and temperate locations.  You can use this tool to view marine heatwaves in real time as they develop around the globe.

“In a way, marine heatwaves are like underwater bushfires, they can have truly devastating impacts for our marine ecosystems,” says Professor Adriana Verges from UNSW and SIMS. 

“For example, in western Australia an extreme marine heatwave in 2011 resulted in the loss of golden kelp across 96,000 hectares. Similarly, the same heatwave caused extensive die-off of seagrass meadows, which then led to declines of turtles and dugongs that depend on this habitat for food”, she explained.

SIMS flagship project, Project Restore is focused on kelp and seagrass restoration and to ensure robust monitoring and restoration can occur it is important to quantify the impacts of a marine heatwave. Over the 2023 summer,the Project Restore team deployed 42 temperature loggers across all Project Restore locations in Sydney Harbour. 3 loggers were installed  at each site, at 3 depths (shallow, mid and deep) and positioned within key habitats. The temperature probes are attached to bricks so that they stay in place, and the GPS location is recorded to ensure their retrieval at the end of the monitoring period. 

This will allow us to collect long-term water temperature data and determine the variation compared to mean annual temperatures, and potentially confirm the presence of a marine heatwave at our sites. This data will then be used to calculate the impact of marine heatwaves upon key habitat-forming species including local kelp, Ecklonia radiata, and seagrass, Posidonia australis

“It’s actually really hard to understand how heatwaves impact ecosystems underwater, as we often only see the  aftermath of the event. For example, we may see extensive kelp mortality, but we won’t know what exactly caused the kelp to die: was it the direct effects of warm water or was it perhaps a bacterial infection that got out of control because of the warmer temperatures?” asks Professor Vergés. 

“The benefits of forecasting marine heatwaves is that scientists can prepare for this and take measurements and monitor the ecosystems before, during and after the heatwave. In turn, this can then help us to understand the mechanisms of any negative impacts and may allow us to devise potential solutions or protection measures.”

SIMS and Project Restore will provide further updates as we determine the extent of the heatwave impacts at our sites within the harbour.