COMPARISONS OF PRIMARY PRODUCTION VALUES ESTIMATED FROM DIFFERENT INCUBATION TIMES IN A COASTAL SEA

In shallow coastal systems dominated by vertical mixing, phytoplankton cells experience light variations due to vertical excursions. Therefo re, it would be unusual for phytoplankton to experience constant irrad iance 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 sit u incubations (SIS). Values of primary production estimated from 4 and 24 h SIS incubations have been compared with estimates of primary pro duction based on photosynthetic parameters, which were determined on s hort incubation times (40 min). Sampling was conducted under different conditions of vertical mixing. It appears that daily primary producti on rates computed from 24 h incubation times are the lowest at each sa mpling station, whereas differences between daily production rates est imated from 4 h and 40 min incubation times depend on the sampling sta tions. Vertical mixing and available light intensity could control dif ferences between the computed daily production rates on 4 h and 40 min incubation times. In fact, under conditions of non-limiting light int ensity for photosynthesis, photoadaptation processes could occur in lo ng-term SIS incubations, which do not take into account vertical mixin g, and enhance primary production estimates.