A marine heat wave known as “the mass” is responsible for the largest die-off of a single species in modern history.
‘The mass’ is a large body of unusually warm water off the coast of North America in the Pacific Ocean, and scientists have blamed it for killing half the population of Alaska’s common guillemot, a small seabird that It resembles a flying penguin.
The birds are short and stocky, with tuxedo-style feathers, and nest in large colonies on islands or coastal cliffs, staying close to the ocean where they hunt for fish, squid, octopus and crustaceans.
The heat wave between 2014 and 2016 appears to have been the most intense marine heat wave in history, scientists say, raising ocean temperatures by up to seven degrees Fahrenheit.
This destabilized climate and coastal marine ecosystems of California to Alaska, decreasing the food supply for seabirds like the common guillemot and causing mass die-offs.
Their loss has a particular impact on Alaska Native communities, as murres have traditionally been an important source of meat and eggs. Population decline now threatens traditional gathering practices and cultural connections, experts say.
Before the heat wave, about 8 million common murres lived in Alaska, about a quarter of the world’s population of the animal.
But now, scientists estimate the population has dropped to about 4 million based on an analysis of survey data collected after the heat wave. What’s more, the murres show no signs of recovery.
A marine heat wave known as ‘the blob’ has killed half of Alaska’s common murre population, marking the largest known die-off of a single species in modern history.
In 2020, researchers studying common murre carcasses concluded that the most likely cause of death was starvation due to the impact of the marine heatwave.
In 2020, researchers studying common murre carcasses concluded that the most likely cause of death was starvation due to the impact of the marine heat wave. At the time, they estimated the death toll to be between 62,000 and 1 million.
A new study has revealed the full magnitude of this die-off, underscoring the catastrophic effect that ocean warming is having on animal populations.
Study co-author Julia Parrish, professor of biology and aquatic and fisheries sciences, said, “This study shows clear and surprisingly long-lasting impacts of a marine heat wave on a major marine predator species.”
He added: “Importantly, the heatwave effect was not due to heat stress on the birds, but rather to changes in the food web that left the guillemots suddenly and fatally without enough food.”
Parrish was part of a team of researchers led by the U.S. Fish and Wildlife Service that analyzed years of data from studies of common guillemot colonies to estimate total mortality from this extinction.
They analyzed 13 colonies surveyed between 2008 and 2022, and found that the size of colonies in the Gulf of Alaska decreased by about 50 percent after “the mass.”
Colonies along the eastern Bering Sea experienced an even steeper decline, of 75 percent.
Collectively, this represents the death of approximately 4 million common murres in Alaska due to this marine heat wave. Investigators said they have found “no evidence of recovery” since the death occurred.
A new study has revealed the full magnitude of this die-off, estimating that four million common murres (about half of Alaska’s population) died after the marine heat wave.
Investigators said they have found “no evidence of recovery” since the death occurred.
They published their findings earlier this month in the journal. Science.
Common guillemot populations have fluctuated before, experiencing smaller die-offs than they were eventually able to recover from, the study authors said.
But this unprecedented decline may be too severe for Alaska’s population to recover, they said. And as marine heat waves become more common due to climate change, this may not be the last time the species suffers such a blow.
A 2023 study led by many of the same authors showed that a sea surface temperature increase of 1.8 degrees Fahrenheit lasting more than six months causes multiple seabird deaths.
That study also suggested that it would take at least three years for seabird populations to recover from a marine heatwave.
“Whether the warming comes from a heat wave, El Niño, the loss of Arctic sea ice or other forces, the message is clear: warmer water means massive ecosystem changes and widespread impacts on seabirds. “Parrish said in a statement.
“The frequency and intensity of seabird mortality events are increasing at the same rate as ocean warming.”
It’s been seven years since ‘the mass’ decimated Alaska’s common murre population. According to Parrish, the fact that they have yet to show signs of recovery is concerning.
While it is difficult to identify the reasons why this population has not been able to recover, it is likely that the marine heatwave has altered the resources and dynamics that common guillemots depend on, ultimately destabilizing the entire ecosystem.
For example, the marine species that make up their food supply may also be struggling to recover from the heat wave. Or perhaps the loss of four million common murres affected their social interactions, which help them survive and thrive.
“We may now be at a tipping point in ecosystem rearrangement where it is not possible to regain pre-extinction abundance,” Parrish said.