James Sherwood, Conservation Campaigner, National Parks Association of NSW
Reports of 28-degree water temperature inside Pittwater Heads over autumn has made diving off Sydney coast more appealing than ever before. The sad reality, however, is the ecological cost of this year’s marine heatwave may cause irreversible changes to our marine environment along the NSW coast.
At world heritage-listed Lord Howe Island, scientists have confirmed the island is experiencing a severe bleaching event with all susceptible corals bleaching across the bay. This is a major concern as Lord Howe Island is NSW’s marine treasure, home to the world’s most southern coral reef and is a hotspot for endemic species. Even before the bleaching even, late last year, the NSW Fisheries Scientific Committee proposed listing the McCulloch’s Anemonefish as Critically Endangered due to its dependent relationship with the Bubbletip Anemone which has seen significant declines due to episodes of elevated sea temperatures. The lagoon at Lord Howe Island was the last remaining stronghold for the species and this current bleaching event has the potential to push the species towards extinction.
The marine heatwave is pushing south with the kelp forests of the NSW south coast next in the firing line. In 2015/16, a heatwave decimated Tasmanian’s giant kelp forests and created ideal conditions for migration of the invasive Long-spined Sea Urchin that have created urchin barrens spreading from southern NSW all the way to Tasmania. But it’s not just the benthic species that can suffer from marine heatwaves. A recent study by CSIRO shows that marine heatwaves are altering microorganism communities that form the base of food chains. Researchers found that following the Tasmanian marine heatwave, the microbial community changed to resembled that of an area over 1,000km to the north. This has led to the occurrence of unusual species with the potential to cause cascading effects across the ecosystem.
At Montague Island, on NSW’s far south coast, waters are warming at more than three times the rate of the global average. The island is home to the largest breeding colony of little penguins in NSW, but researchers have found that warming ocean currents are having a serious impact on the hunting success of the little penguins that ultimately results in a decrease in penguin breeding. The optimal offshore temperature range for the penguins to feed is 19 to 21 degrees. Lately, sea temperature has been at the upper threshold and could climb further with the heatwave tracking south.
So how do we best manage our coasts to ensure that they are resilient as possible to marine heatwaves?
There is not a lot we can do now to prevent marine heatwaves from occurring. The science has been clear for decades that countries globally needed to work together to phase out fossil fuel use and transition to renewable forms of energy. However, action has been too slow and now we must ensure that our natural ecosystems are best placed to cope under the changing climate. Resilience is key. This means ensuring our marine environment has enough protection to ensure that ecosystems can still function in a changing world.
Research from the Great Barrier Reef has demonstrated that no-take marine reserves have been shown to increase the resilience of coral communities to coral bleaching events and enhance recovery times. There is also evidence from California that marine protected areas can contribute to the long-term resilience of nearshore fish communities following marine heatwaves.
Armed with this knowledge, the NSW government must act fast to deliver a spatially connected comprehensive, adequate and representative sanctuary zone network across all NSW bioregions. It must be one that ensures connected refugia for species longitudinally and latitudinally but also at depth so species can move deeper to escape the warmer sea surface temperatures if needed. Healthy fish populations can help to reverse some of the impacts of coral bleaching events. For example, grazing fish remove the algae that build up on coral reefs following bleaching events, preventing permanent phase shifts where coral communities transition into algal dominated communities.
There is much uncertainty around the future of our oceans. Therefore, it is essential the government adopts a precautionary approach to the marine environment by establishing a robust network of marine sanctuaries across the entire coast of NSW. This can ensure the NSW marine environment is as resilient as possible, in the best possible position to adapt to the ever increasing impacts of climate change.
References and further information
Coral Bleaching Lord Howe Island
Loss of Southern Kelp Forests – Bull kelp / Heat Wave / Heat Wave
Heat waves and micro organisms
