One third of humankind’s current annual emissions of CO2 are absorbed by the oceans. However this vital service comes with the cost of ocean acidification. This could have serious impacts within the 21st Century for the sustainability and management of marine and coastal ecosystems and fisheries.
Photo: Antarctic coral recently discovered 800m below ocean surface (photo: courtesy Martin Riddle (AAD)
The Southern Ocean contains a disproportionate amount of the oceanic inventory of anthropogenic CO2, and acidification is strongest there. Examining ecosystem responses in the Southern Ocean thus offers a bellwether for impacts further afield.
View: Dr Donna Roberts talking about the impact of ocean acidification on marine organisms
View: Dr Donna Roberts discussing the importance of the Southern Ocean in studying ocean acidification
The ecological effects of ocean acidification are still largely unknown. Research so far has focussed on how acidification lowers pH and the level of carbonate ions available for calcifying organisms to form their shells. These organisms include plankton species that contribute to the foundation of the Southern Ocean food web. However acidification may impact on a broad range of other physiological and ecological processes, such as fish respiration, larval development and changes in the solubility of both nutrients and toxins.
ACE scientists are working on an initial assessment of the possible impacts of ocean acidification on microbial components of the marine ecosystem. Measurements of the ocean’s pH will be taken to map the progress of acidification. ACE scientists will also estimate the abundance of carbonate-forming organisms that may be affected.
Recent work by ACE scientists found a reduction in the shell-forming ability of small zooplankton in the Southern Ocean, including planktonic foraminifera and planktonic snails, known as pteropods. Pteropod shells are made of a more soluble form of calcium carbonate, which is likely to put them at greater risk of ocean acidification. Both foraminifera and pteropods are important food sources for marine predators in the Antarctic food web. Impacts on these calcifiers in this environment will serve as a harbinger for the impacts of acidification.
The Australasian sector of the Southern Ocean is relatively well studied in terms of ocean chemistry and oceanography and has several long-term sediment trap collection sites. It thus provides us with a unique laboratory in which to observe the effects of ocean acidification on marine calcifiers in situ.
Projects and project leaders
· Determining the Progress of Ocean Acidification: Professor Tom Trull
· Responses and Vulnerabilities of Planktonic Calcifiers in the Southern Ocean to Ocean Acidification: Professor Tom Trull, Dr Donna Roberts