Great whites and whale sharks are among the species at risk of extinction over the next century, a new study has found. In analyzing the marine megafauna and their potential extinctions, researchers found sharks would be hit hardest, with greater losses in terms of "functional richness."
"Functional richness is the extent of ecological roles in a community—the many different ways species 'make a living' and in turn affect ecosystems," Catalina Pimiento and John Griffin, from the University of Swansea, U.K., told Newsweek in an email.
Pimiento is lead author of a study published in Science Advances that looks at how the extinction of large marine species would impact the ecological roles of ocean ecosystems. "The extinction crisis challenges scientists to better measure biodiversity: how will the total variety of life on Earth be affected as human activities lead to the losses of more-and-more species?" they said. In the oceans, the biggest animals are thought to play crucial ecological roles, and are also facing high levels of threat from human activities such as fisheries and climate change."
The team was looking to move beyond traditional species extinctions, to find out the functional diversity, the range of roles that species performs, and how biodiversity might respond under different extinction scenarios.
They ran two different extinction scenarios. In one, researchers looked at extinction probability based on their current IUCN (International Union for Conservation of Nature) status. In the second, they assumed all species listed as threatened, around 40 percent, had gone extinct.
Their findings showed that an estimated 18 percent of marine megafauna could go extinct in the next century and this would reduce the functional richness of global ecosystems by 11 percent. If all threatened species went extinct, functional richness fell by 48 percent globally.
Douglas McCauley, from the Marine Science Institute at the University of California Santa Barbara, who was not involved in the study, discussed the idea of functional richness: "Let's say a pandemic hit your country," he told Newsweek. "You will want to know the total number of deaths caused by the tragedy. That is species richness—it is the body count of extinction. But what if the pandemic particularly affected people in unique jobs, you would really want to know that as well as it would affect how society worked. If the pandemic disproportionately affected water utility workers, package delivery service employees, or doctors—unique and irreplaceable functions to the human ecosystem—we would want to have this insight early so we didn't find life grinding to a halt around us.
"It is the same deal in the sea. There are certain species that perform truly unique ecological jobs. And the analyses of these authors suggest that we are setting ourselves to see a lot of them go missing, if we don't take action."
With their new metric, Pimento and Griffin were able to identify species that contribute most to maintaining functional diversity by having the most distinct ecological roles.
Sharks were found to be one of the worst affected groups. "We already knew that sharks are one of the most threatened groups in the ocean," they said. "They are also very vulnerable due to their large size and low reproductive rate. Our results show that future extinctions would be selective against the most functionally unique and specialized shark species, resulting in greater projected losses."
In almost all their 1,000 simulations, whale sharks went extinct. Great whites disappeared in a handful of the first scenario, and were lost in the second. "The whale shark is a giant filter feeder which is also highly mobile. It therefore consumes large amounts of plankton and transports nutrients long distances. The great white is a large migratory apex predator that regulate their prey populations," Pimento and Griffin said.
They said the biggest threats to marine megafauna are fishing, either through accidentally getting caught up or directly targeted, and climate change. Mitigating these threats could be the best way to protect these species. Of the marine megafauna, 22 are listed as critically endangered. These include the Hawksbill sea turtle and the Largetooth sawfish. "Without urgent mitigation of threats these species are likely to go extinct, Pimento and Griffin said.
McCauley said sharks appear to be "particularly screwed," saying "they are already undergoing significant declines and local extinctions in many regions." Sharks, he notes, are long lived, have few offspring, are a delicacy in some parts of the world and come into competition with humans. These factors "make them especially susceptible to extinction. Many sharks play unique and irreplaceable roles in ecosystems so their elevated vulnerability matters."
He said the good news is that the study identifies key species that can be targeted and protected: "Sometimes ocean conservation can be a triage game. This science helps us know which species really need our help and which species we really cannot afford to lose."