Measurement of benthic photosynthesis and calcification in flowing-through seawater with stable carbonate chemistry

Kunshan Gao, Juntian Xu, Yangqiao Zheng, Caihuan Ke

Limnol. Oceanogr. Methods 10:555-559 (2012) | DOI: 10.4319/lom.2012.10.555

ABSTRACT: Estimation of photosynthetic or calcification rates of benthic organisms under stable seawater chemistry is important to fathom their capacity of CO2 fixation under constant or controlled levels of pCO2 and acidity of seawater. The flowing-through system, introduced here, can hold large individuals or colonies and maintain the carbonate chemical parameters stable while photosynthetic or calcification rate is measured based on the assimilation pipe inlet and outlet differences in dissolved O2 concentrations or total alkalinity. The data obtained with this system for macroalgae showed constancy over time under controlled conditions, resulting in higher photosynthetic rates compared with those measured in a closed mode, which caused significant changes in the carbonate system (decreased pCO2 and DIC and increased pH). When the method was applied to measurements of calcification based on the changes in total alkalinity, reliable data were obtained for both coralline algae and oysters. In addition, it can also be applied to measure respiration of both macrophyte and animals and to test the effects of increased pCO2 and current speeds when these factors are controlled under either laboratory or field conditions while exposed to natural solar radiation.