The response of marine assemblages to ocean acidification

Abstract

Global industrialisation has led to the anthropogenic raising of global CO2 concentration from 280 pp to over 380 ppm in the last 200 years causing oceanic pH to drop by 0.1 unit as a result of a processes called ocean acidification. It is expected to further drop by between 0.3 and 0.4 units over the next 100 years. Quantifying the impact of such a pH shift has, to date, largely relied on laboratory studies of model organisms or simple assemblages in mesocosms. Conversely, this work undertook a series of field experiments to examine the effect of predicted pH environmental conditions on a robust marina fouling assemblage and microorganisms through the manipulation of local CO2 concentration. CO2 was delivered and controlled above replicated settlement panels that were freely accessible to normal propagule supply. Over 5 months, recruitment and development of macroorganisms and diversity of microorganisms in biofilms was shown to be largely unaffected by low pH. Results of this investigation were contrasted against microbial diversity in biofilms from a low pH volcanic vent site. Molecular analysis of biofilms failed to detect an influence of pH on diversity. The development of an alternative method of CO2 delivery using silicone membranes is described, which proved to have both antifouling and ocean acidification experimental applications. In conclusion, the marine organisms examined in this study showed little response to pH change of the order that is expected with the progression of ocean acidification. Significant methodological advances to in situ pH experimentation have been made, however, which should assist further investigations.