Comparisons of primary production values estimated from different incubation times in a coastal sea

Abstract

In shallow coastal systems dominated by vertical mixing, phytoplankton cells experience light variations due to vertical excursions. Therefore, it would be unusual for phytoplankton to experience constant irradiance during 4 or 24 h, the standard incubation times used to estimate daily primary production rates. The aim of this work was to determine conditions under which bias could occur in long-term simulated in situ incubations (SIS). Values of primary production estimated from 4 and 24 h SIS incubations have been compared with estimates of primary production based on photosynthetic parameters, which were determined on short incubation times (40 min). Sampling was conducted under different conditions of vertical mixing. It appears that daily primary production rates computed from 24 h incubation times are the lowest at each sampling station, whereas differences between daily production rates estimated from 4 h and 40 min incubation times depend on the sampling stations. Vertical mixing and available light intensity could control differences between the computed daily production rates on 4 h and 40 min incubation times. In fact, under conditions of non-limiting light intensity for photosynthesis, photoadaptation processes could occur in long-term SIS incubations, which do not take into account vertical mixing, and enhance primary production estimates.