Climate change is already significantly impacting the Great Southern Reef (GSR) through various mechanisms. One of the primary effects is ocean warming, which has been particularly pronounced along the western and southeastern parts of the GSR, with warming accelerating 2–4 times faster here than the global average.
Along with ocean warming , a strengthening of poleward ocean currents and marine heatwaves have led to ecological changes in many parts of the GSR. Warming waters have facilitated the southward expansion of tropical and subtropical species into the GSR, a phenomenon known as 'tropicalisation.' This has led to increased competition for native species and altered community structures.
Specific examples of climate change induced shifts in the Great Southern Reef include:
The southward expansion of some species have caused pronounced impacts, notably the southward expansion of the long-spined sea urchin (Centrostephanus rodgersii) from the NSW and VIC coast into Tasmania, and an increase in tropical grazing fish that graze on kelp. This has led to overgrazing of kelp forests, causing significant habitat loss and altering the ecological balance of the reef system.
Once dense forests of Giant kelp (Macrocystis pyrifera) have declined by 95% on Tasmania’s East Coast and have been listed as an endangered marine community.
In Western Australia a significant marine heatwave in 2011 caused the loss of kelp from more than 960,000 hectares of the north-western GSR, along with many reef associated species including valuable abalone and lobster stocks.