A marine heatwave killed approximately half of the population of common murres in Alaska, marking the highest mortality rate of a single species in modern history, according to a study.
The catastrophic loss points to broader changes in marine environments driven by warming ocean temperatures, rapidly restructuring ecosystems and hindering these animals’ ability to thrive.
The Blob: the culprit behind the highest species mortality
The Northeastern Pacific marine heatwave, known as “The Blob”, spanned the oceanic ecosystem from California to the Gulf of Alaska between late 2014 and 2016.
This event, considered the largest and longest-lasting marine heatwave known, saw temperatures rise between 7 and 12 degrees Celsius above normal levels.
Common Murres and their role in the ecosystem
Common murres, or Uria aalge, are known for their black and white feathers. These predators play a crucial role in regulating the flow of energy within the marine food web in the Northern Hemisphere.
While they have experienced small die-offs in the past, the magnitude and speed of the mortality during this heatwave were alarming.
Researchers monitored extreme population declines in 13 colonies in the Gulf of Alaska and the Bering Sea. By the end of the 2016 heatwave, they counted over 62,000 common murre carcasses, representing only a fraction of those lost.
The murre population in 13 colonies decreased between 52% and 78% between 2016 and 2022, with no signs of recovery.
Causes and challenges for murre recovery
The study revealed that as temperatures rose, the food supply for murres decreased. With the collapse of Pacific cod, around 4 million murres died in Alaska from 2014 to 2016. The lack of recovery could be due to fluctuations in the marine ecosystem, reproductive challenges, and relocation difficulties.
As temperatures continue to rise, tropical or subtropical waters are shifting, creating a new ecosystem. Murres, along with other species like the tufted puffin and king salmon, are struggling to adapt. However, some homeothermic animals have shown neutral or positive responses to abnormal heat exposure.
Additional mortality factors
In addition to rising temperatures, other factors such as microplastics, ocean acidification, sea level rise, and oil spills also contribute to massive mortality in marine environments.
Long-term studies on the climate effects on marine life are limited, so future impacts are still unknown.
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