Major MHWs have had significant impacts on a wide range of species, from plankton to fish to sea birds, by affecting biological processes such as growth, reproduction and survival (Smale et al. 2019). For example, the ‘Blob’ – a massive long-lasting MHW that developed in the northeast Pacific in 2014 – disrupted the entire foodweb and led to mass die offs of sea birds and mammals (Smith et al. 2021). Rogue animals can also find their way well outside their normal range, following the warm waters of a MHW, such as this tropical fish found off Tasmania during the 2015/16 event. 

MHWs can affect ecosystem structure, by favouring certain species and suppressing others. For example, after the 2011 marine heatwave in Western Australia the fish communities had a much more “tropical” nature than previously (Wernberg et al. 2013) and switched from kelp forests to seaweed turfs (Wernberg et al. 2016).

MHWs can cause major economic losses through impacts on fisheries and aquaculture, and changes to carbon and nutrient cycles (Smith et al, 2021). In 2011 in Western Australia, a MHW led to the closure of an abalone fishery and in 2015/16 a MHW off southeastern Australia led to high levels of abalone mortality in Tasmania. Another MHW in the Pacific Ocean caused mass mortality of farmed salmon in Chile due to harmful algal blooms, with an estimated export loss of US $800 million. Some MHWs have had positive as well as negative impacts, such as an event in the Canadian Arctic which led to increased cod reproduction in 2009.

Marine life can be drastically affected by MHWs if temperatures become stressful. In 2016, MHWs across northern Australia led to severe bleaching of the Great Barrier Reef. Multiple MHWs in the Mediterranean Sea have been linked with mass mortalities of soft corals

How do we raise awareness of Marine heatwaves?

Due to human-induced climate change, MHWs are likely to become more severe in coming decades, as the oceans contain more heat. MHWs clearly have the potential to devastate ecosystems and cause economic losses in fisheries, aquaculture, and ecotourism industries. They can also disrupt carbon and nutrient cycles, which has major implications for ocean systems. However, MHW impacts are often hidden from view under the waves until it is too late. By raising general awareness of these phenomena, and by improving our scientific understanding of their physical properties and ecological impacts, we can better predict future conditions and protect vulnerable marine habitats and resources.
 
Work by our group and others aims to develop forecasts that can predict when and where MHWs will occur, and how they might impact marine life. Such tools will be vital to adapt to a warmer future with more frequent and stronger MHWs. For example, if salmon or oyster farmers have enough warning of an emerging MHW, they can plan ahead and take proactive measures to reduce the impacts, such as moving animals to cooler waters or harvesting early. Such approaches will become more and more important in a warmer world.