MEPS 580:83-100 (2017)  -  DOI: https://doi.org/10.3354/meps12310

ABSTRACT: Fast repetition rate fluorometry (FRRF) provides a means to examine primary productivity at high resolution across broad scales, but must be coupled with independent knowledge of the electron requirement for carbon uptake (K_C) to convert FRRF-measured electron transfer rate (ETR) to an inorganic carbon (C) uptake rate. Previous studies have demonstrated that variability of K_C can be explained by key environmental factors (e.g. light, nutrients, temperature). However, how such reconciliation of K_C reflects changes of phytoplankton physiological status versus that of community composition has not been well resolved. Therefore, using a dataset of coupled FRRF and C uptake measurements, we examined how the environmental dependency of K_C potentially varied with parallel changes in phytoplankton community structure. Data were combined from 14 campaigns conducted during the summer season throughout 2007 to 2014 in the East China Sea (ECS) and Tsushima Strait (TS). K_C varied considerably, but this variability was best explained by a linear relationship with light availability (R² = 0.66). Co-variability between K_C and light availability was slightly improved by considering data as 2 clusters of physico-chemical conditions (R² = 0.74), but was best improved as 2 taxonomic clusters: samples dominated by micro-phytoplankton (>20 µm) versus small phytoplankton (nano + pico, <20 µm; R² = 0.70-0.81). Interaction of phytoplankton community structure with light availability therefore explains the majority of variance of K_C. The algorithms generated through our analysis therefore provide a means to examine C uptake with high resolution from future FRRF observations from these waters.

KEY WORDS: Electron transfer rate · ETR · Primary productivity · Quantum requirement · Carbon fixation · Phytoplankton composition · Fast repetition rate fluorometry