Articles | Volume 13, issue 15
Biogeosciences, 13, 4379–4388, 2016
Biogeosciences, 13, 4379–4388, 2016

Research article 08 Aug 2016

Research article | 08 Aug 2016

Assessing approaches to determine the effect of ocean acidification on bacterial processes

Timothy J. Burrell1,2,a, Elizabeth W. Maas1,b, Paul Teesdale-Spittle2, and Cliff S. Law1,3 Timothy J. Burrell et al.
  • 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.

Short summary
Bacterial extracellular enzymes play a significant role in the degradation of organic matter in the open ocean. Using artificial fluorogenic substrates, this research highlights potential artefacts in the response of bacterial glucosidase and aminopeptidase to ocean acidification, and the effects of three different acidification techniques. We conclude that fluorogenic substrate degradation is affected by, or alters pH, and bubbling CO2 may lead to the overestimation of carbohydrate degradation.
Final-revised paper