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Scientists Share New Metrics, Findings for Largest Marine Species at Risk of Extinction, Signaling Risks for Ocean Ecosystem Decline

Sharks, other animals play larger-than-realized ecological roles, study of species traits shows

Los Angeles, CA (April 17, 2020)—Published today in Science Advances, a new study sheds light on the largest marine species at risk of extinction, or megafauna, and the key roles they play. Conducted by an international team of scientists, the new research, which examines species traits, is the latest to cast light on profound changes impacting ecosystems and Earth’s overall environment. 

Great white shark, Carcharodon carcharias. October 18, 2014. Photograph by Mike Krampf. © Mike Krampf.  (CC-BY-NC)

The study is the first of its kind to calculate marine megafauna functional diversity— the measure of each animal’s role in an ecosystem. Marine megafauna are the largest animals in the oceans. Species include: sharks, rays, whales, seals, sea cows, polar bears, sea turtles, emperor penguins, and mollusks; including clams, squids and octopuses. Each type of animal performs a role in ecosystem functioning. Animals do different jobs, like eating plankton, transporting nutrients by excretion, connecting oceans through migration, or altering habitats by what they eat, how they move and where they die. When one species declines or disappears, an entire ecosystem could be at risk of profound transformation or collapse. Just as these changes pose risks to ocean habitats, they are also problematic for people. Human communities, economies and culture–our way of life–are inherently dependent on natural resources. 

Sharks, the most threatened marine vertebrate group, are projected to undergo the biggest losses of functional diversity. They fill vital ecological roles in many marine ecosystems. 

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Dr. Matt Davis, vertebrate paleontologist and exhibition developer at the Natural History Museum of Los Angeles County, was part of the research team. "This is the first study to look at the interconnected roles of all large ocean animals from walruses and giant clams to sharks and dolphins. We can now pinpoint weak links in the ecosystem like endangered species that are doing a job no other animal can replace." Davis added. “These results mirror what we have already found for large animals on land: we are losing some of the most important species. Important not just for their habitats in the ocean but important for us here on land as well. Even if you don’t live near the beach, your life depends on the sea."

The lead scientist on the study, Dr. Catalina Pimiento of Swansea University, described the importance of these findings and continued studies. “Our previous work showed that marine megafauna had suffered an unusually intense period of extinction as sea levels oscillated several million years ago. Our new work shows that, today, their unique and varied ecological roles are facing an even larger threat from human pressures.”

Scientists employed a new metric called FUSE to measure each animal’s importance to an ecosystem and the level of risk it faces. FUSE—or “functionally unique, specialized and endangered”—offers a measurement system that may be used in future studies as conservation biologists and resource stewards study and identify at-risk species in need of immediate protection and long-term preservation. 

Dr. John Griffin, Pimiento’s collaborator at Swansea University and a co-author on the study, adds: “Facing escalating extinction crises, scientists are seeking answers to questions: does nature offer back-up systems? When one vital species becomes extinct, can other animals within a given ecosystem fill in its role?” After calculating the functional diversity of marine mammals, the study simulated two extinction scenarios to predict how functional richness (the number of different jobs animals do) would change in the future.

To understand species’ risk of extinction, the researchers used the International Union for Conservation of Nature’s Red List of Threatened Species Criteria. The first scenario (IUCN 100) predicted what would happen in the next 100 years if current conservation trends continue and found that functional richness declined 11 percent. The second scenario predicted what would happen if all threatened species (as measured by IUCN) went extinct and functional richness declined 48 percent. 

Sharks face the biggest change in functional diversity. In the second scenario, 62 percent of all shark species could go extinct, removing most (87 percent) of their roles from the environment. For example, the great white shark is an apex predator and migrates, controlling populations across a large area. And the whale shark is a giant filter feeder, essential to a balanced marine ecosystem. 

"Sharks have been in our oceans for hundreds of millions of years and have become an extremely important part of the ecosystem,” said Dr. Bill Ludt, assistant curator of Ichthyology at the Natural History Museum of Los Angeles County, who was not involved with the study. “This study does an exemplary job of not only highlighting sharks’ importance, but also showing what may happen if we don't take the necessary actions now to preserve their biodiversity."

Human impacts are driving the rapid decline of key species and ecosystems though overfishing, pollution, plastic wastes, and climate change. 

“We hope these findings inspire greater public awareness, ocean appreciation, and more effective conservation,” Davis said. “Science can point the way but everyone will have to pitch in if we want to reach a more sustainable future."

Paper: “Functional diversity of marine megafauna in the Anthropocene”
Authors: C. Pimiento, F. Leprieur, D. Silvestro, J. S. Lefcheck, C. Albouy, D. B. Rasher, M. Davis, J.-C. Svenning, J. N. Griffin
(Catalina Pimiento of Swansea University) 
(Matt Davis of Natural History Museum of Los Angeles County)

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