“The sea is everything,” wrote Jules Verne in his 1870 novel 20,000 Leagues Under the Sea. “It covers seven-tenths of the terrestrial globe. Its breath is pure and healthy.”

However, the findings of an eight-year scientific study to be published next month will show that the world’s oceans are now far unhealthier than they were in Verne’s time.

The BBC reported this month that the survey, to which more than 250 scientists contributed, will show the increasing acidity of the world’s oceans is likely to have a harmful effect on every living sea creature. Young marine life will be hit especially hard.

The findings of the study, by the Biological Impacts of Ocean Acidification, or Bioacid, Project will be presented at a climate change conference in Bonn in November. The BBC says some research for the report was done in the lab but other studies were conducted in the North Sea, the Baltic, the Arctic and Papua New Guinea.

Nina Hall, a marine biologist and head of editorial at Frontiers in Marine Science, said the study would be “the most complex report on the impacts of ocean acidification published so far”.

How do oceans become acidic?

Image: Climate Central

The US-based Smithsonian Institute says ocean acidification “is a significant and harmful consequence of excess carbon dioxide (CO2) in the atmosphere”.

It adds: “At least one-quarter of CO2 released by burning coal, oil and gas doesn't stay in the air, but instead dissolves into the ocean. Since the beginning of the industrial era, the ocean has absorbed some 525 billion tons of CO2 from the atmosphere, presently around 22 million tons per day.”

When carbon dioxide dissolves in seawater, the water becomes more acidic. “In the past 200 years alone,” the institute adds, “ocean water has become 30 percent more acidic - faster than any known change in ocean chemistry in the last 50 million years.”

For some time scientists speculated that increased CO2 might be good for the oceans and the sea creatures that inhabit them, but they have now changed their minds.

Hall says: “What is most alarming are the negative effects of acidification not just on corals but on the entire ocean foodweb, including all creatures from deep-sea microbes to starfish to whales, that co-exist in a delicate balance.”

The BBC said that the synthesis of more than 350 publications on the effects of ocean acidification showed almost half of the marine animal species tested reacted negatively to already moderate increases in seawater CO2 concentrations.

Atlantic cod, blue mussels, starfish, sea urchins and sea butterflies were particularly affected in the early stages of their development. However, some species such as barnacles were not affected by increased concentrations of acid, and some, such as algae, which photosynthesize using CO2, may benefit.

However, the report authors warn that even species that may not be directly harmed by acidification may still suffer if the food web is disrupted.

Hall noted: “Almost half of all marine animal species are expected to show a decline in numbers, including commercial fish species, such as cod. This will threaten the resources that millions of people rely for on for their livelihoods and that feed a large part of the world’s population.”