Ocean acidification and marine ecosystems

Ocean acidification (OA) is one of the key challenges facing our society and often described as the “other CO2 problem.” The oceans are currently absorbing a third of the CO2 released by anthropogenic fossil fuel, biomass burning and cement manufacture. This has resulted in a change in ocean chemistry; a process called ocean acidification. There has been an average drop in pH of 0.1 since the beginning of industrialisation in the late 19th century and at the current rate of CO2 uptake the average surface ocean pH will be lower than that experienced by marine organisms at any time over the last several million years.

In the 2007 IPCC Fourth Assessment Report on Climate Change ocean acidification was listed as having a negative impact on marine organisms, which make their shell or skeleton from calcium carbonate. No ocean acidification event in the last 65 million years has occurred as quickly as current acidification, posing a risk to adaptation potentially leading to extinction in the ocean ecosystem in the future.

The Southern Ocean
The Southern Ocean has naturally low saturation levels of carbonate ion (because cold water stores large amounts of dissolved CO2 thereby decreasing carbonate ion concentrations). Therefore organisms in the Southern Ocean are particularly vulnerable and the impact of ocean acidification over the last 100 years is most likely to be felt in this region. Understanding whether ocean acidification has already impacted organisms in the Antarctic is important to recognise future effects and to provide information for policy decisions on future carbon emissions.

Historical collections
Our comprehension of biotic reactions to ocean acidification is strongly based on lab experiments. While these are invaluable to understanding physiological reactions they are relatively short and thus do not allow us to recognise how organisms may adapt or modify their behaviour to such perturbations over generations or within their lifetimes if they are long-lived.

We have chosen a different approach by comparing specimens which lived prior to changes in ocean chemistry with those living today. This approach is firmly based on the immensely valuable collections at The Natural History Museum arising from a series of groundbreaking expeditions to Antarctic waters in the late 19th and through the 20th century. We will compare specimens collected on the Challenger (1872-1876) and Discovery (1901-1904) expeditions to recently-collected specimens to examine whether benthic species from the Southern Ocean show evidence of acclimatising or adapting to the rapid change in ocean chemistry.

This project focuses on two important calcifying organisms: bryozoans and benthic foraminifers. The latter are single-celled organisms which live several years, whereas the former are colonial invertebrates living up to decades. Our results may demonstrate that the pH decrease since the late 19th century has already had an impact on organisms and that this should be taken into account in predictions of future vulnerabilities. Alternatively, if we find no effects of ocean acidification, we demonstrate that these species were able to acclimatise to the OA over the last 100 years.

Dr Daniela Schmidt and Dr Laura Foster
University of Bristol

Daniela was awarded a Research Project Grant in June 2011; providing £161,717 over 36 months.

Dr Daniela Schmidt & Dr Laura Foster, The Leverhulme Trust, Article.

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