Marine heatwaves are extreme events where ocean temperatures rise above the normal range for more than five days in a row. Like heatwaves on land, marine heatwaves can harm plants, animals and the environment. This can impact ocean-dependant industries and communities.
Marine Heatwaves in Tasmania
Tasmania is particularly vulnerable to marine heatwaves, as our marine ecosystems are used to cooler water temperatures. Many of these ecosystems are already facing pressure from long-term rising water temperatures (Oliver et al. 2018).
Marine heatwaves in Tasmania can impact our environment in many ways, including:
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shrinking or shifting kelp forests, seagrass beds and other marine habitats;
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important fisheries species, like abalone, are more likely to die from temperature related diseases; and
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warmer water species, like Yellowtail Kingfish or Longspined Sea Urchin, may become more common.
In the summer of 2024-25, marine heatwaves were observed around Australia. The reported impacts included fish kills, coral bleaching, algal blooms and declines in fish catch.
Impacts of the summer 2024-25 marine heatwave. Source: CSIRO
Tasmanian Marine Heatwave and Related Event Response Plan
The Tasmanian Marine Heatwave and Related Event Response Plan (the Plan) guides Tasmania’s decision making and coordination in response to marine heatwaves and related events.
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Frequently asked questions
What causes marine heatwaves?
Like heatwaves over land, heatwaves in the ocean occur due to a range of factors, including ocean currents and the warming of the ocean surface from the atmosphere due to climate change.
Climate drivers, like El Niño, are known to impact the frequency, intensity and duration of marine heatwaves.
Are marine heatwaves part of climate change?
Marine heatwaves compound the damage being caused by long-term warming of the ocean. Australia’s marine ecosystems are expected to have some of the largest climate-driven changes in the Southern Hemisphere.
Over 100 Australian marine species have started migrating south towards cooler waters, including to Tasmania. These changes in distribution, abundance and species composition in our ecosystems mean that Australian fisheries are already being affected by climate change.
For example, the Longspined Sea Urchin is migrating south, from its native habitat in NSW to the warming waters off the east coast of Tasmania. These urchins eat kelp forests, creating urchin barrens and damaging abalone and rock lobster habitats.
Can marine heatwaves cause disease in marine mammals and seabirds?
In other parts of the world, past marine heatwaves have seen unusual mortality events. These have included coral bleaching and mass die-off of marine mammals or fish. If there is an unusual mortality event in Tasmania, there are a variety of channels to make a report. Reporting helps us investigate and take any further action (such as issuing a public health alert). It may also help us understand why an event occurred.
A marine heatwave is when the ocean is unusually hot to a significant depth for a number of days, weeks, months or even years.