Mass mortality events — the rapid death of large numbers of a species — appear to be on the rise, according to a new study by researchers from the University of San Diego and two other universities.
“The increase in mass mortality events appears to be associated with a rise in starvation, disease, biotoxicity and events produced by multiple interacting stressors,” said Adam Siepielski, assistant professor of biology and the study’s co-lead author.
The study was jointly conducted by USD, Yale University and UC-Berkeley, and published this week in the Proceedings of the National Academy of Sciences.
The analysis of 727 published events from across the globe, affecting 2407 animal populations, found that the magnitude of such events since 1940 has been intensifying for birds, fishes and marine invertebrates, decreasing for reptiles and amphibians and staying the same for mammals. The most severe events were those with multiple causes, the paper shows.
Although mass mortality events are often a natural event “the most alarming and interesting result was the sheer magnitude of some of these mortality events,” Siepielski said. “Billions of individuals dying are just huge numbers to comprehend.
“The study provides yet another example of the challenges to life that organisms are confronted with on a planet increasingly dominated by the influence of humans in the environment.”
Siepielski’s interest in the subject began after hearing a report about a die-off on National Public Radio. Surprisingly, he found that little research has actually been done on the subject. As an aquatic ecologist, he had also observed such die-offs in his studies of lake and pond communities in California during the ongoing drought.
He and his colleagues from Yale and UC-Berkeley then found that the number of major events has been increasing by about one event per year over the 70 years the study covered.
Funding from the Environmental Protection Agency and the National Science Foundation helped support this research.
