Primary production was dominated by the picophytoplankton, but its biomass specific primary productivity was lower than in other atoll lagoons. They showed significant spatial (sites) and temporal (seasonal and day to day) effects on the measured processes for the two size fractions of phytoplankton. The variables size fraction of the phytoplankton, water temperature, season, the interaction
term station ∗ fraction and site, explained significantly the variance of the data set using redundancy ICG-001 analysis. However, no significant trends over depth were observed in the range of 0–20 m. A consistent clear spatial pattern was found with the south and north sites different from the two central stations for most of the measured variables. This pattern was explained by the different barotropic cells highlighted by Dumas et al. (2012) in their hydrodynamic study. Lefebvre et al. (2012) hypothesized the existence of a fast regeneration mechanism of nitrogen through pulses, a process that fuels the larger phytoplankton’s production better than the picophytoplankton one. Sediment interface
and cultured oysters were good candidates to explain, at least partly, the fast regeneration processes Selleck Autophagy inhibitor of nitrogen organic material. A precise spatial evaluation of the cultured pearl oyster stock remain necessary for future studies, as well as measurements of nutrient ambient conditions, preferentially with flux
methods using carbon and nitrogen tracers rather than measurement of nutrient stocks that are rapidly assimilated and transformed by autotrophs (Furnas et al., 2005). Charpy et al. (2012) suggests that relatively low particulate organic carbon content compared to other lagoons localized at the same latitude could reflect the impact of pearl oyster aquaculture. However, this impact does not appear on phytoplankton biomass. Indeed, as shown by Fournier et al. (2012b), oysters do not feed directly on phytoplankton, but rather graze heterotrophic plankton. Fournier et al. (2012b) refined the knowledge on P. margaritifera diet by demonstrating with the flow through chamber method that the main factor influencing clearance rates of pearl oysters was the biovolume of planktonic FER particles. Thus, the diet of P. margaritifera was mainly driven by fluctuation of the relative biomass of the nano- micro- planktonic communities. Both heterotrophic nano- and micro-plankton represented an important part of the diet of P. margaritifera depending on their relative biomass in the water column. The picoplankton communities displayed the lowest clearance rates but represented however a detectable contribution to the diet. Whether or not this selective grazing may induce a change in plankton assemblage in cultivated lagoons compared to uncultivated ones remain unknown.