"The Blob" – a severe marine heatwave in the North Pacific, not a monster from a 1950s B-movie – might have killed over 1 million seabirds.
A new study, published in PLOS One this week, argues that around 1 million common murres and other seabirds died of starvation in North America as a result of the marine heatwave known as "The Blob."
"The common murre die-off in fall/winter of 2015-2016 was the largest magnitude seabird die-off ever observed in any of the world's oceans," lead study author John Piatt, a research biologist at the USGS's Alaska Science Center, told IFLScience.
"Just as extraordinary was the complete breeding failure of multiple murre colonies ranging from the Bering Sea to the Gulf of Alaska to the California Current System over multiple years; 22 complete failures in total," he added.
"The magnitude and scale of these failures has no precedent."
Between 2015 and 2016, an Alaska-sized “blob” of warm ocean water was detected in the Pacific Ocean just off the West Coast of the US and Canada. Severe marine heatwaves first began in 2013, but they became dramatically intensified during the summer of 2015 due to a powerful climate cycle called El Niño. During this period, satellite data and other observations showed that the near-surface water was experiencing spikes of warmth that could be 3 to 6°C higher than the expected average temperature. By no surprise, this had a harsh knock-on effect throughout the ecosystem.
The warmer temperatures increased the metabolism of cold-blooded organisms, from zooplankton and small forage fish to larger predatory fish, like salmon and pollock. Since predatory fish needed to eat more than usual, murres and other seabirds started to be outcompeted and found themselves in short supply of small fish to eat.
Murres are big energy-burners, which the researchers explain is “the ultimate ‘Achilles heel’ for murres.” They need to catch and eat about 60 to 120 forage fish every day to survive and will die if they can’t find any food for 3 to 5 days. This makes them especially vulnerable to any disruptions in the food chain.
Between May 2015 to April 2016, approximately 62,000 dead murres were found on beaches from central California up through Alaska. However, this new study argues that the real figure is likely to be a lot higher since previous research has suggested that only a fraction of birds that die will wash to shore. Others might have been scavenged or were simply not found by people. Based on this, they estimate the death could be between 530,000 and 1.2 million birds, marking the largest mass die-off of seabirds in recorded history.
While “The Blob” was an unusual anomaly, these kinds of mass die-offs are expected to become all the more frequent due to the effect of increased sea temperatures on the wider marine ecosystem and food chains.
"Heatwaves are predicted by oceanographers to become more frequent and stronger as global warming continues. Therefore, it seems likely that we will see more events like those we observed in the 2014-2016 heatwave," added Piatt.