At a Glance
- Unprecedented ocean heat wave raised ocean temperatures to record highs.
- Dolphins in the vast Shark Bay conservation area had fewer calves and shorter lifespans afterward.
- Extreme climate events are challenging conservation efforts, researchers say.
An unprecedented marine heat wave in western Australia that raised ocean temperatures to record highs had a long-term impact on the lifespan and breeding habits of dolphins, highlighting the risks of warming oceans for the species, a new study shows.
The research, released this week in the journal Cell Press, found that dolphins’ survival rate in Shark Bay dropped by 12 percent after the 2011 heat wave and had not risen back to normal levels. It also found that female dolphins were having fewer calves.
“One of many challenges in the conservation of biodiversity is the recent trend in the frequency and intensity of extreme climatic events,” wrote Sonja Wild, a biologist at Leeds University and author of the study.
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The 2011 heat wave raised water temperatures to as high as 90 degrees Fahrenheit, or 37 degrees above normal, in the Indian Ocean along parts of Australia’s western coast, according to a previous study in the Journal of Marine Systems.
The near hot tub-like temperatures killed off vast beds of seagrass as well as fish and other sea life in Shark Bay, an 8,500-square-mile UNESCO World Heritage Site known for its rich marine ecosystem.
Wild and her colleagues have been following the dolphins in Shark Bay for years, and used data collected from 2010 to 2017 for their study.
"The extent of the negative influence of the heat wave surprised us," Wild told Science Daily, adding that the decline in reproduction is of particular concern.
They were also intrigued to find that some dolphins were affected more than others. A group of dolphins in the bay who use sponges as tools to forage for food seem to have fared the heat wave better, the study showed. The researchers speculated that those dolphins might have access to other food sources because they forage in deeper water.
The findings are just the latest in a long list of potentially dire consequences that climate change could have on oceans, the creatures that live in them and subsequently the entire planet.
Ocean heat waves have become longer and more frequent in the past 25 years, having a severe impact on marine life including depleted fish stocks, changing migration patterns and other stresses. The trend is expected to continue as sea surface temperature, ocean heat content, sea level rise, melting of glaciers and ice sheets, and carbon dioxide emissions all increase.
And scientists have called rising ocean temperatures "the greatest hidden challenge of our generation."
The researchers thought the study’s findings mirrored those observations, and could indicate that climate change has more dire effects on marine mammals than previously thought.
"Marine heat waves are likely to occur more frequently in the future due to climate change," Michael Krützen, a professor at the University of Zurich and also a researcher on the study, told Science Daily. "This is worrying not only for the long-term prospects of marine mammal populations, but also for the entire oceanic ecosystems."
