The oceans are more acidic now than they’ve been at any time in the last 300 million years, conditions that marine scientists warn could lead to a mass extinction of key species.
Scientists from the International Programme on the State of the Ocean (IPSO) published their State of the Oceans report Thursday, a biennial study that surveys how oceans are responding to human impacts. The researchers found the current level of acifification is “unprecedented” and that the overall health of the ocean is declining at a much faster rate than previously thought.
“We are entering an unknown territory of marine ecosystem change, and exposing organisms to intolerable evolutionary pressure,” the report states. “The next mass extinction may have already begun.”
Acidification causes major harm to marine ecosystems, especially coral, which has a hard time building up its calcium carbonate skeleton in acidic water. Coral reefs serve as nurseries to many young fish, so they’re essential both to ecosystem health and the survival of the fishing industry. If temperatures rise by 2 degrees C, the study found, coral may stop growing altogether, and may start to dissolve at 3 degrees C. Similarily, acidic ocean waters can hamper shellfish larvae’s ability to grow shells. Acidification is already hurting the shellfish industry — in the U.S., northwestern and East Coast shellfish industries have struggled to adapt to increasingly acidic waters. And pteropods, tiny sea snails that are a keystone species in the Arctic and are an essential food source for many birds, fish and whales, are also threatened by acidity — they too require strong calcium carbonate shells to survive.
It’s not just acidification that’s threatening the oceans, either — the report found the oceans are facing a “deadly trio” of stressors, with warming waters and decreasing oxygen also majorly affecting marine ecosystem health. Warming waters coupled with ocean acidification are posing increasingly severe threats to Antarctic krill, which play a vital role in the Antarctic marine food chain, and are also helping lead to huge outbreaks of jellyfish. And as water temperatures rise, coral is increasingly vulnerable to bleaching.
Meanwhile, depletion of oxygen is caused by two things: climate change and nutrient runoff, mostly from agriculture, the report stated. Scientists have predicted ocean oxygen content could experience a decline of between 1 and 7 percent by 2100. The impacts of this decrease in oxygen and increase in “dead zones” or areas with no oxygen, are varied, but include a decrease in habitat for large ocean predators such as tuna and marlin that have high oxygen requirements. Dead zones, as their name suggests, are deadly to creatures on the ocean floor, who aren’t able to escape to more oxygen-rich waters. Since the 1960s, the number of dead zones have doubled every ten years, according to the report.
The report urged world governments to take fast action to ensure temperatures don’t rise past 2 degrees C. Current limits, it warned, weren’t enough to ensure the health of coral reefs, since there is will be a time lag of several decades between a decrease in levels of atmospheric CO2 and the levels of dissolved CO2 in the ocean. It also found overfishing is still causing major declines in key ocean species. At least 67 percent of fish stocks are being overfished, the report found, but stricter oversight and monitoring of commercial fishermen and giving more control of fisheries to local communities would help decrease overfishing. Indeed, some local governments have been successful in stopping depletion of fish in their waters. When one Mexican town banned fishing, it saw its marine biomass increase by 463 percent while fishing improved in regions just outside the preserve.
Yet even if governments take the suggested steps, the report notes, they must do more to save the oceans as we know them.
“Ultimately, however, [these measures] must be undertaken within a wider re-evaluation of the core values of human society and its relationship to the natural world on which we all rely,” it states. “The future of humanity and the future of the ocean are intertwined.”