The most severe known mass extinction event eradicated over 80 percent of marine species. However, surprisingly, many ecosystems did not collapse. A diverse array of animals, including top predators, managed to survive this cataclysm.
These findings suggest that the survival or demise of individual ecosystems was influenced, at least partly, by their unique species compositions. This observation may hold relevance for modern marine ecosystems, which currently face considerable threats from climate change.
The end-Permian extinction occurred approximately 252 million years ago. It is believed to have been triggered by extensive volcanic activity in the region now known as Siberia. This event led to severe global warming, depleted oxygen levels in the oceans, and a cascade of other environmental pressures. Certain animal groups, such as trilobites and eurypterids (often referred to as sea scorpions), vanished entirely. Other groups experienced significant losses. In the period following the extinction, numerous new animal groups emerged, including dinosaurs and ichthyosaurs.
Given the substantial loss of species, researchers had previously assumed that ecosystems became considerably simplified in the aftermath of these extinction events. A fully functional ecosystem typically comprises interconnected species: primary producers like plants that convert sunlight into sugar, herbivores that consume plants, carnivores that prey on herbivores, and often apex predators that hunt smaller carnivores. However, animals occupying higher trophic levels, such as apex predators, could be more susceptible to extinction because their survival depends on a consistent prey supply. Consequently, a mass extinction event like the end-Permian could dismantle these trophic levels, resulting in simpler ecological structures.
To investigate this theory, Baran Karapunar from the University of Leeds in the UK, along with his colleagues, examined fossilized remains from seven marine ecosystems globally. These samples spanned the periods immediately before and after the extinction event. By analyzing the species present in these ancient environments, the researchers inferred the structure of each ecosystem.
Despite species loss rates reaching as high as 96 percent, five of the seven studied ecosystems managed to retain at least four trophic levels throughout the post-extinction period.
In most regions, particularly those closer to the poles, the most severe losses were observed among herbivorous species. These animals were often slow-moving and inhabited the seabed. In contrast, organisms capable of free swimming in open water, such as fish, appeared to be less affected by the extinction.
In the wake of the event, ecosystem recovery varied significantly based on their proximity to the equator. Tropical ecosystems were largely dominated by lower-trophic-level organisms, primarily herbivores, many of which lived on the seafloor. Conversely, ecosystems situated closer to the poles adapted by incorporating additional trophic levels, as predatory fish species migrated away from the equator to escape the most extreme heat.
These findings suggest that contemporary marine ecosystems are also likely to exhibit diverse responses to climate change and other human-induced environmental stressors.
Peter Roopnarine, a researcher at the California Academy of Sciences in San Francisco, commented that he is unaware of other studies that have integrated data from such a broad range of regions. He concurs with the conclusion that many ecosystems maintained their trophic structures despite significant species loss, a pattern previously indicated by smaller-scale research.
However, Roopnarine cautioned against placing excessive reliance on the precise details of the researchers’ ecosystem models. For example, the study had to group all photosynthetic organisms together because the fossil record does not clearly distinguish which species survived and which did not. This limitation meant the model could not simulate the specific consequences of extinctions among these primary producers. He noted that while the models are informed by the fossil record, that record itself is inherently incomplete.