Spatial and temporal dynamics of size-structured photosynthetic parameters (PAM) and primary production (13C) of pico- and nano-phytoplankton in an atoll lagoon

Sébastien Lefebvre (1) , Pascal Claquin , Francis Orvain (2) , Benoit Véron , Loïc Charpy

1 LOG - Laboratoire d’Océanologie et de Géosciences (LOG) - UMR 8187
2 CRESCO - Centre De Recherche et d'Enseignement sur les Systèmes Côtiers

Atoll lagoons display a high diversity of trophic states due mainly to their specific geomorphology, and probably to their level and mode of human exploitation. We investigated the functioning of the Ahe atoll lagoon, utilized for pearl oyster farming, through estimations of photosynthetic parameters (pulse amplitude modulation fluorometry) and primary production (13C incorporation) measurements of the size structured phytoplankton biomass (<2 μm and >2 μm). Spatial and temporal scales of variability were surveyed during four seasons, over 16 months, at four sites within the lagoon. While primary production (P) was dominated by the picophytoplankton, its biomass specific primary productivity (PB) was lower than in other atoll lagoons. 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 analysis. No significant trends over depth were observed in the range of 0-20 m. A clear spatial pattern was found which was persistent over the seasons: south and north sites were different from the two central stations for most of the measured variables. This pattern could possibly be explained by the existence of water cells showing different water residence time within the lagoon. Photoacclimation strategies of the two size fractions differed through their light saturation coefficient (higher for picophytoplankton), but not through their maximum photosynthetic capacity (ETRmax). Positive linear relationships between photosynthetic parameters indicated that their dynamic was independent of light availability in this ecosystem, but most probably dependent on nutrient availability and/or rapid changes in the community structure. Spatial and temporal patterns of the measured processes are then further discussed in the context of nutrient availability and the possible role of cultured oysters in nutrient recycling

Domaines: Océanographie

Sébastien Lefebvre, Pascal Claquin, Francis Orvain, Benoit Véron, Loïc Charpy. Spatial and temporal dynamics of size-structured photosynthetic parameters (PAM) and primary production (13C) of pico- and nano-phytoplankton in an atoll lagoon. Marine Pollution Bulletin, 2012, 65 (10-12), pp.478-489. ⟨10.1016/j.marpolbul.2012.04.011⟩. ⟨hal-00807541⟩