Assessing approaches to determine the effect of ocean acidification on bacterial processes
- 1National Institute of Water and Atmospheric Research, Greta Point, Wellington, New Zealand
- 2Victoria University of Wellington, School of Biological Sciences, Wellington, New Zealand
- 3Department of Chemistry, University of Otago, Dunedin, New Zealand
- anow at: C-MORE, University of Hawaii at Mānoa, Honolulu 96822, Hawaii, USA
- bnow at: Verification Services Department, Ministry for Primary Industry, P.O. Box 12034, Ahuriri, Napier, New Zealand
Abstract. Bacterial extracellular enzymes play a significant role in the degradation of labile organic matter and nutrient availability in the open ocean. Although bacterial production and extracellular enzymes may be affected by ocean acidification, few studies to date have considered the methodology used to measure enzyme activity and bacterial processes. This study investigated the potential artefacts in determining the response of bacterial growth and extracellular glucosidase and aminopeptidase activity to ocean acidification as well as the relative effects of three different acidification techniques. Tests confirmed that the observed effect of pH on fluorescence of artificial fluorophores, and the influence of the MCA fluorescent substrate on seawater sample pH, were both overcome by the use of Tris buffer. In experiments testing different acidification methods, bubbling with CO2 gas mixtures resulted in higher β-glucosidase activity and 15–40 % higher bacterial abundance, relative to acidification via gas-permeable silicon tubing and acid addition (HCl). Bubbling may stimulate carbohydrate degradation and bacterial growth, leading to the incorrect interpretation of the impacts of ocean acidification on organic matter cycling.