Marine heatwaves are causing massive seabird mortality events

Because they spend a substantial part of their lives soaring above remote oceans, seabirds have been under the radar of scientists for many years. Now, a study from the University of Washington has revealed a shocking revelation about seabird mortality. 

Based on data collected by coastal inhabitants, the research sheds light on the grim impact that marine heatwaves have on seabird populations. The new study, published in the journal Marine Ecology Progress Series, reveals how marine heat waves have led to an alarming number of seabird fatalities.

As a sentinel of the nearshore marine environment, seabirds play a critical role in the marine ecosystem. Study co-author Julia Parrish, a renowned professor of Aquatic and Fishery Sciences, highlighted the global scope of this research.

“This is truly a global data set that asked a global-sized question: Does a warming world significantly impact marine birds, among the top predators in the nearshore marine environment?” The answer, as the study indicates, is a resounding yes.

Shocking discovery 

The most startling discovery made by the researchers is the lag effect that the marine heatwaves have on seabird mortality. Parrish explained that “a warmer ocean, and certainly a suddenly warmer ocean as happens during an El Niño or a marine heat wave, will result in the death of hundreds of thousands to millions of marine birds within one to six months of the temperature increase.” 

Marine heat waves, such as the notorious “blob” which was observed off the Pacific Northwest between 2014 and 2016, along with prolonged El Niño events and warmer Alaskan waters owing to retreating sea ice, have only recently become a topic of concern among scientists and environmentalists.

This extensive study analyzed data spanning from 1993 to 2021, collected through beach surveys that traced the incidence of dead seabirds washed ashore from central California to Alaska. The research aimed to gauge the severity of these mortality events irrespective of species. 

“Rather than track the specific numbers of any one species, this study measures the magnitude of mortality events, regardless of seabird species, above long-term normal,” said Parrish. 

Catastrophic mortality events

The study showed that catastrophic mortality events, where the death toll crossed a staggering quarter-million birds, occurred approximately once every decade. However, this pattern changed dramatically between 2014 and 2019, during which five such events were recorded.

“This is unprecedented. This type of massive die-off can be compared to a catastrophic storm that we would usually expect once per decade; they happen, causing massive damage, but usually, there is enough time for areas to recover,” said study lead author Timothy Jones, a research scientist at the University of Washington.

From 2014 to 2019, the die-offs were not only some of the largest ever documented, but they kept happening year after year — like a catastrophic storm hitting without fail every year.”

Warming waters 

Statistical analysis presented a glaring link between these mass die-offs and the warmer marine conditions in the Northeast Pacific preceding them. Some seabirds, including murres, puffins, auklets, and shearwaters, were the most severely impacted species. 

The data encompassed more than 90,000 surveys of 106 seabird species across more than 1,000 beaches. The data was collected from citizen science projects, including COASST, BeachCOMBERS, Beach Watch, and the British Columbia Beached Bird Survey. These programs, through meticulous training, equipped participants to scout local beaches for avian casualties and report their findings.

Furthermore, data from the remote beaches of northwest Alaska were garnered through community members who reported to the U.S. Fish and Wildlife Service and Alaska Sea Grant. The study unveiled a trend wherein seabird carcasses started appearing ashore a few months after the marine warming initiated and persisted in a roughly three-year cycle. 

While the cause behind each seabird mortality event varied, warmer waters emerged as the common thread linking them. Warmer oceans foster harmful algal blooms and heighten the risk of disease outbreaks, which were both implicated in seabird deaths during the study period. 

In addition, the prolonged ocean warming altered the diversity, availability, and nutritional content of the prey that seabirds rely on, culminating in widespread starvation.

Implications of the study

The implications of this study are enormous, as it indicates an irreversible shift in marine ecosystems due to climate change. 

“With this intensity of warming, like the looming El Niño in the Pacific or the current marine heatwave in the North Atlantic, we are facing a new ocean. One with fewer birds,” said Parrish.

The research is not only a wake-up call for conservationists but also a call to action for humanity to address the escalating challenge of climate change and its far-reaching consequences on our planet’s invaluable biodiversity.

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