Effect of high CO2 and low pH on benthic communities of the deep sea

The increase of carbon dioxide (CO2) concentration in the atmosphere will intensify climate change although the ocean moderates climate change due to its considerable capacity to store large amounts of CO2. As a consequence the pH in seawater decreases, a process known as ocean acidification. Current state of the art of science and technology proposes mitigation strategies such as Carbon Capture and Storage (CCS) to reduce the amount of CO2 reaching the atmosphere. Storage locations are geological formations of the deep sea, where liquefied CO2 is sequestered. Risks to the environment, caused by CO2 leakage are not satisfactorily studied so far, although commercial projects are already running since 1996. The deep sea is characterized a stable high pressure, low temperature regime and organisms have adapted to this extreme environment. Changes in environmental conditions as for leakage of CO2 will enhance mortality rates of organisms directly exposed to CO2. This may result in a shift in community structure and potentially the loss of functional groups that maintain ecosystem functioning. In this context, natural laboratories , such as the Yonaguni Knoll IV hydrothermal system located in the Okinawa trough characterized by high CO2 fluxes, are appropriate sites to study responses of the deep-sea benthic community to high CO2 concentrations and thus low pH in situ. In the present study, the influence of these factors on the distribution, abundance and diversity of the deep-sea benthos was investigated, including all size classes of the benthic community from a reference site to low and high CO2 seepage sites.