Top predators still roamed the seas after the greatest mass extinction

The worst known mass extinction wiped out over 80 percent of marine species. But despite these huge losses, many ecosystems did not collapse, and a variety of animals and even top predators managed to survive the cataclysm.

The findings suggest that the fate of each ecosystem was determined in part by its own unique mix of species. The same may be true of modern marine ecosystems, which also face major threats from climate change.

The end-Permian extinction occurred about 252 million years ago. It appears to have been caused by massive volcanic eruptions in what is now Siberia, leading to drastic global warming, low oxygen levels in the oceans, and a host of other threats. Some groups of animals such as trilobites and eurypterids (sea scorpions) were completely wiped out; others suffered huge losses. As a result, many new groups arose, including dinosaurs and ichthyosaurs.

Because so many species became extinct, scientists hypothesize that ecosystems became much simpler as a result of extinction. A fully functioning ecosystem has a number of species that depend on each other: plants that produce sugar using energy from sunlight, herbivores that eat plants, predators that eat herbivores, and possibly top predators that eat smaller predators. However, animals at higher “trophic levels”, such as apex predators, may be more vulnerable to extinction because they cannot survive without prey to eat. So a mass extinction such as the end of the Permian would eliminate trophic levels and leave simpler ecosystems.

To find out if this actually happened, Aries Karapunar at the University of Leeds in the United Kingdom and his colleagues studied the preserved remains of seven marine ecosystems from around the world, from just before and just after extinction. Based on the species that were present, they deduced the structure of each ecosystem. Karapunar declined to be interviewed because the study is not yet peer-reviewed.

Despite a species loss of up to 96 percent, five of the seven ecosystems retained at least four trophic levels.

In most regions, and especially toward the poles, the worst losses were among herbivores, which often moved slowly and lived on the sea floor. In contrast, organisms that could swim freely in open water, such as fish, were less affected.

As a result, ecosystems recovered differently depending on how close they were to the equator. Tropical ecosystems were dominated by low-trophy animals such as herbivores, often living on the sea floor. In contrast, ecosystems closer to the poles gained additional trophic levels as predators such as fish moved away from the equator to escape the worst of the heat.

The findings suggest that today’s marine ecosystems will also respond in different ways to climate change and other human-induced hazards.

“I don’t know of any other study that brings together so many regions,” he says Peter Roopnarine at the California Academy of Sciences in San Francisco. It agrees with the finding that many ecosystems have maintained their trophic level despite extinction, as already indicated by smaller-scale studies.

But Roopnarine says we can’t put too much faith in the specifics of researchers’ ecosystem models. For example, they had to lump together all photosynthetic organisms because the fossil record did not reveal which ones survived and which did not—so they could not simulate the consequences of the extinction of such organisms. “The fossil record is true, but the fossil record is incomplete,” he says.

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