The loss of animal species in the planet's oceans is expected to "rapidly intensify" due to human-caused activities, but swift intervention could still prevent "disaster of the magnitude observed on land," according to a study published Friday in the journal Science.
Humans have "profoundly decreased" the number marine animals, large and small, though there have been few outright extinctions, the study notes. That’s because animal loss attributed to human activity "began in earnest tens of thousands of years later in the oceans that it did on land."
But there is growing concern that low extinction rates seen today “may be the prelude to a major extinction pulse, similar to that observed on land during the industrial revolution” — and that has wider implications for humans and marine life, such as "imperiling food sustainability" for humans and depleting "a wide range of ecologically important marine fauna."
“We may be sitting on a precipice of a major extinction event,” ecologist Douglas J. McCauley, of the University of California, Santa Barbara and a co-author of the study, told the New York Times, referring to marine life.
Unsustainable fishing is the principal threat to marine life today, according to the study, but the ocean life faces a number of dangers.
The study’s authors say the great whale species, while no longer being hunted on a wide scale, face hazards that include noise pollution and oil exploration. Bottom trawling, an industrial fishing method that can alter marine habitats, can also put species at risk.
The development of coastal cities and a practice known as "seasteading," or building artificial lands in the ocean — with one such example being the United Arab Emirates famous construction of artificial islands off the coast of Dubai — also present problems to marine habitats, along with seafloor mining and oil and gas extraction.
But there is still time to change course and avoid the damaging repercussions already seen in land animals, the study notes.
The authors say there is time to “avert the kinds of defaunation disasters observed on land" through "efforts to slow climate change" and rebuild animal populations, while ensuring marine mining and energy development "take important marine wildlife habitats into consideration."
The study cites The International Union for Conservation of Nature, or IUCN, which has recorded 15 global extinctions — none of which occurred in past five decades — of marine animal species over the past 500 years. That number pales in comparison to the over 500 extinctions of terrestrial animals over that same period of time.
Marine animal loss, however, remains significant, the study noted, with changes that affect the bottom of the food chain and travel upward.
"Depletions of fauna such as anchovies, sardines, and krill cause reductions in food for higher-trophic level (position on the food chain) animals such as seabirds and marine mammals, potentially resulting in losses in reproduction or reductions in their population size," the authors said.
And this has troubling implications for humans, by “imperiling food sustainability and increasing social conflict,” said the scientists, who point out that fish makes up a large part of global protein intake — especially true in poorer coastal countries. "Declines in this source of free-range marine food represent a major source of concern," said the report.
Also at risk is coastal protection like coral reefs, which "can dissipate up to 97 percent of the wave energy reaching them, thus protecting built structures and human lives."
Nevertheless, the report makes clear that "we are not necessarily doomed to helplessly recapitulate the defaunation processes observed on land in the oceans."
“We’re lucky in many ways,” Malin L. Pinsky, a marine biologist at Rutgers University and a co-author of the report, told the Times. “The impacts are accelerating, but they’re not so bad we can’t reverse them.”