Great white sharks, whale sharks, sea turtles, and a number of the ocean’s most characteristic giants are facing serious trouble, and this could have a huge knock-on effect throughout the marine environment.
Researchers from Swansea University in the UK have recently investigated which traits could put marine megafauna – defined as sea-dwelling creatures with a body mass over 45 kilograms (~100 pounds) – at risk of extinction within the next 100 years. Reporting in the journal Science Advances, they estimate that up to 18 percent of these megafauna species could be lost if current trends continue. Under a worst-case scenario, whereby all threatened species currently listed on the IUCN Red List go extinct, they expect to see up to 40 percent of species disappear.
“This is a warning that we need to act now to reduce growing human pressures on marine megafauna, including climate change, while nurturing population recoveries,” Dr John Griffin, a co-author and associate professor of biosciences at Swansea University, said in a statement.
The megafauna at particular risk includes many species of sharks, rays, whales, seals, sea cows, polar bears, sea turtles, emperor penguins, giant clams, squids, and octopuses.
Some traits of these animals leave them especially exposed to the risk of extinction. For example, the study notes that great white sharks and whale sharks are extremely vulnerable because they are highly migratory species and known to cruise large swathes of the ocean, thereby increasing their risk.
Not only are these giant creatures some of the most beloved and recognizable characters from the sea, but they also play a hugely important role in the marine ecosystem by consuming gargantuan amounts of biomass, transporting nutrients across habitats, connecting ocean ecosystems, and physically modifying habitats through their behavior.
As one example, the researchers showed how declines of sea otter (Enhydra lutris) in Southwest Alaska triggered a massive shake-up of the kelp forest system in the Aleutian Archipelago, effecting everything from sea urchins to macroalgae.
So, if we lose these giants, the wider ecosystem will feel the tremors. The research also estimates that an 18 percent decline of marine megafauna species would also translate to an 11 percent loss of the extent of ecological functions. Under the 40 percent of species loss scenario, the extent of ecological functions could be reduced by almost half.
"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," lead study author Dr Catalina Pimiento, paleobiologist and macroecologist at Swansea University, said.