Phytoplankton biomass and production in two tuamotu atoll lagoons (French polynesia)

Abstract

Nutrient concentrations, phytoplankton biomass (chlorophyll a, chl a) and primary production (14C uptake) were measured over a 5 yr period (1990 to 1994) in the atoll lagoons of Takapoto (4 yr water residence time; with pearl oyster aquaculture) and Tikehau (0.5 yr residence time; without pearl oyster but with a fishery), French Polynesia. In both atolls, phosphate and silicate concentrations (0.1 μM PO4 and 0.8 μM SiO2) were tower inside the lagoon the n in surrounding oceanic surface waters Picoplankton <1 μm dominated phytoplankton biomass (61%) and productivity (55%) in both lagoons Average assimilation numbers were high (13 mg C mg-1 chl a h-1) and average chl a doubling rates of the <1 μm fraction were estimated to be 1.1 and 1.3 d-1 in Takapoto and Tikehau, respectively. Average daily primary production during the 1991 to 1994 period in Takapoto and Tikehau lagoons was estimated to be 0.8 and 0.7 g C m-2 d-1, respectively.