The increase in frequency and intensity of ocean heatwaves over the past 30 years has had profound impacts on certain marine ecosystems and significantly impacted the industries that depend on them.
According to new research published today in Nature Climate Change, marine heatwaves are now a clear and present threat to global biodiversity. These concerns are heightened given that marine heatwaves are projected to increase further over the coming decades.
“We were particularly struck by the impact on globally significant foundational species of marine ecosystems, such as kelp, seaweed and coral,” said one of the authors from the ARC Centre of Excellence for Climate Extremes (CLEX), Associate Professor Alex Sen Gupta.
“We saw an ecological step-change with Australia’s Ningaloo-Nino marine heatwave in 2010/11 that saw hundreds of kilometres of kelp destroyed, that has still not recovered.”
“This example and the others we have found tells us that today marine management and conservation approaches must consider marine heatwaves if we are to maintain highly valuable marine ecosystems over the coming decades. We ignore their impacts at our peril.”
The researchers examined multiple marine heatwaves ranging from 10-day long events to 380-day events. They found most components of the associated marine ecosystems were negatively affected, with impacts that often persisted.
Even where positive effects were found (in the case of some fish species), this was the result of invasion by foreign species and not benefits to resident species.
The increase in marine heatwaves over the past century was stark, with 50% more marine heatwave days per year in the period 1987-2016 compared to 1925-1954.
To get their results the researchers overlaid global patterns of marine biological richness with trends in marine heatwave days. They then took into account other stressors on the marine environment, such as overfishing and pollution, which had the potential to further add to marine heatwave impacts.
Even accounting for other marine stressors, it was clear marine heatwaves contributed significantly to ecological impacts.
“To this point, ecological research as it relates to climate change has mainly focused on trends and average warming,” said co-author Associate Prof Lisa Alexander from CLEX’s University of New South Wales hub.
“However, we have found that individual extreme marine warming events are emerging as having a far more profound role in reshaping ecosystems.”
Past extremes have led to local extinctions in the Mediterranean Sea, coral bleaching across most tropical regions, mass dieback of mangroves across northern Australia and more. Recent observations have shown that equatorial ranges of plant and animal species have moved 100km towards the poles following some extreme marine heatwave events.
“The loss of key foundational species like kelp, coral and sea grass have a ripple effect, which also puts the species that rely on that habitat at risk,” said CSIRO co-author Dr Alistair Hobday from CLEX’s Tasmanian Hub.
For CLEX co-author Prof Neil Holbrook from the University of Tasmania, the marine findings mirrored the speed of change we have already seen over land.
“Our research highlights that, just as we see on land, the adverse impacts of marine heatwaves caused by human actions are causing changes to our environment on a global scale unlike anything we have witnessed before.”
- Paper: Smale, Dan A., Wernberg, Thomas., Oliver, Eric C. J., Thomsen, Mads., Harvey, Ben P., Straub, Sandra C., Burrows, Michael T., Alexander, Lisa V., Benthuysen, Jessica A., Donat, Markus G., Feng, Ming., Hobday, Alistair J., Holbrook, Neil J., Perkins-Kirkpatrick, Sarah E., Scannell, Hillary A., Sen Gupta, Alex., Payne, Ben L., Moore, Pippa J. Marine heatwaves threaten global biodiversity and the provision of ecosystem services. Nature Climate Change (2019). Doi: https://doi.org/10.1038/s41558-019-0412-1