Acidic Oceans Threaten Fish by Hannah Hoag

                                 Fish could be most susceptible to carbon dioxide when in the egg, or just hatched.

Stocks could suffer as seas soak up more carbon dioxide.

Ocean acidification — caused by climate change — looks likely to damage crucial fish stocks. Two studies published today in Nature Climate Change reveal that high carbon dioxide concentrations can cause death and organ damage in very young fish.

The work challenges the belief that fish, unlike organisms with shells or exoskeletons made of calcium carbonate, will be safe as marine CO₂ levels rise.

Oceans act like carbon sponges, drawing CO₂ from the atmosphere into the water. As the CO₂ mixes with the water, it forms carbonic acid, making the water more acidic. The drop in pH removes calcite and aragonite — carbonate minerals essential for skeleton and shell formation — from the marine environment.

This can mean that corals, algae, shellfish and molluscs have difficulty forming skeletons and shells or that their shells become pitted and dissolve.

Flawed belief?

At present, atmospheric CO₂ levels exceed 380 parts per million and are expected to climb throughout the century to approximately 800 p.p.m. if emissions are not kept in check. And the oceans are expected to continue to sop up the gas, dropping ocean pH by 0.4 units to about 7.7 by 2100

However, many scientists have suggested that acidification wouldn't be problematic for marine fish because they don’t have exoskeletons and because as adults they possess mechanisms that allow them to tolerate high concentrations of CO₂.

But a handful of studies have shown that increased CO₂ levels can wreck the sense of smell of orange clown fish larvae and increase the size of the otolith — a bony organ akin to the human inner ear — in white sea bass larvae.

Read more @ Nature.com