Top predators still roamed the oceans 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, with a number of animals and even apex predators managing to survive the disaster.

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

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

Given that so many species went extinct, scientists have hypothesized that ecosystems became much simpler in the wake of the extinctions. A fully functioning ecosystem has a variety of species that depend on each other: plants that produce sugar using energy from sunlight, herbivores that eat the plants, predators that eat the herbivores, and possibly apex 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-Permian would remove trophic levels, leaving simpler ecosystems.

To find out if this really happened, Baran Karapunar of the University of Leeds in the UK and his colleagues studied the preserved remains of seven marine ecosystems from around the world, from just before and just after the extinction. Based on the species present, they suggested the structure of each ecosystem. Karapunar refused to be interviewed because the study has not yet been peer-reviewed.

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

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

Afterwards, the ecosystems recovered differently depending on how close they were to the equator. Tropical ecosystems were dominated by low-trophic animals such as herbivores, which often lived 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 hazards caused by human activities.

“I’m not aware of any other study that has pulled so many regions together,” says Peter Roopnarine of the California Academy of Sciences in San Francisco. He agrees with the finding that many ecosystems maintained their trophic levels despite the extinctions, something smaller studies had already suggested.

However, Roopnarine says that we cannot rely too much on the details of the researchers’ ecosystem models. For example, they had to lump all photosynthetic organisms together, because the fossil record doesn’t reveal which ones survived and which ones didn’t – so they couldn’t simulate the consequences of such organisms going extinct. “They are true of the fossil record, but the fossil record is incomplete,” he says.

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