An asteroid strike 66 million years ago triggered a mass extinction that wiped out countless species — including a vast number of molluscs. Today, scientists are turning to this ancient catastrophe for clues to help protect mussels, scallops and their bivalve relatives from modern threats pushing them towards extinction.
Bivalves, a group which includes clams, oysters and mussels, are among the most diverse marine animals on Earth. Found across the globe, they play a vital ecological role by filtering water and supporting marine biodiversity. They also serve as a key food source for millions of people.
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Yet despite their ecological importance and resilience, bivalves are under increasing pressure from human activity. Habitat destruction, overharvesting and the effects of climate change are all contributing to a rise in extinction risk. Many researchers now consider this part of what is being dubbed a modern mass extinction. To better understand how bivalves might fare in the future, scientists are looking to their past. A new study published in Science Advances has explored how mass extinctions alter the ecological roles played by bivalves.
Dr Katie Collins, a curator of benthic molluscs at the Natural History Museum and one of the study’s co-authors, explained that although bivalves have survived previous extinction events, it is unclear which species will endure in the future.
“After the Cretaceous mass extinction, there was a total shuffle in which bivalves were doing what,” said Dr Collins. “Most of the same taxonomic families survived, but their abundance and ecological roles changed.”
“As a result, we can’t predict which species will survive if we continue to change our planet. While we can be relatively sure that bivalves as a whole will continue, there’s no way to know if commonly eaten species will win the survival lottery.”
The extinction event at the end of the Cretaceous Period is one of the most well-known in Earth’s history. Some 66 million years ago, a 15-kilometre-wide asteroid struck the region now known as Mexico, instantly devastating the surrounding area and causing global environmental upheaval.
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Debris from the impact blocked sunlight, interrupting photosynthesis and collapsing food chains. As a result, an estimated 78% of all life was wiped out. While dinosaurs often dominate the narrative, marine life suffered greatly too — with bivalves among the hardest hit.
“We know the asteroid caused major changes in the oceans,” said Dr Collins. “Temperatures fluctuated dramatically, and marine ecosystems were affected by the debris, though there’s no single explanation for the high extinction rate. What we do know is that more than 60% of bivalve genera were lost.”
To understand what happened next, the research team examined nearly 2,000 genera of bivalves from before and after the extinction event — and compared them with those living today. Analysing shell shapes allowed scientists to infer how ancient bivalves lived.
“The shell is the tool bivalves use to interact with the world,” Dr Collins explained. “Its shape determines what they can and can’t do. Just like birds need certain shapes to fly, bivalves need specific forms to swim. If they’re not the right shape, they simply can’t manage it.”
Rather than a straightforward recovery, researchers discovered what they call a “chaotic rebuilding”. Although few ecological roles were lost overall, most families were reduced to just one or two surviving lineages. These went on to diversify, but the families that came to dominate particular roles had changed dramatically.
This finding has significant implications for conservation today. Since it’s nearly impossible to predict which species will survive future environmental change, the researchers argue that conservation efforts should prioritise preserving the ecological functions bivalves perform.
“If we have to prioritise conservation at a species level, then we want to pick groups that are likely to evolve new functions relatively easily,” said Dr Collins. “True mussels, for example, are fantastic at adapting.”
“We also need to protect groups with unique traits unlikely to evolve again. Take the glass scallops — they swim and are carnivorous, a highly unusual combination. If they disappear, we may never see anything like them again. We must do all we can to ensure their survival.” In learning from the deep past, scientists hope to chart a more resilient future — not only for bivalves, but for the marine ecosystems they help sustain.
