Acid ocean, biodiversity decline

The ecological effects of ocean acidification have been largely unstudied until now and the results aren’t looking good. Research from the Australian Institute of Marine Science (AIMS) shows that rising carbon dioxide (CO₂) levels are having a detrimental effect on reef invertebrate populations including octopi, clams and crabs.

“We have shown how detrimental high CO₂ can be for corals. When CO₂ from the atmosphere mixes with water, it causes ocean acidification, lowering the pH of the water and changing its carbonate chemistry. This in turn makes it harder for a range of marine animals to form their shells and skeletons,” said AIMS coral reefs research scientist Dr Katharina Fabricius.

Ocean acidification slowly causes a decline in structurally complex branching and foliose (leaf-like) corals, which are the home of many species like crabs, shrimps and sea stars.

This has a domino effect: as the habitat structure decreases, the animals that live and hide in their nooks and crannies find it far harder to survive, simply because they cannot hide from predators.

Fabricius’ team has been investigating the consequences of long-term exposure to high CO₂ on coral reef communities around three, shallow volcanic CO₂ seeps (or vents) in eastern Papua New Guinea (PNG) in Milne Bay province over the past few years. This location is one of the few known CO₂ seep sites in tropical waters within coral reef ecosystems.

“The decline of the structurally complex corals means the reef will be much less rich and complex, and there will be less habitat for the hundreds of thousands of species we associate with today’s coral reefs,” she added.

The research provides the researchers with valuable insights into what tropical coral reefs could look like if human-induced atmospheric CO₂ concentrations continue to rise at the present rate.

The paper was published in Proceedings of the Royal Society B.