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 lower inside the lagoon than 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.

KEY WORDS: Nutrients · Phytoplankton · Production · Pearl oyster · Atoll lagoon · French Polynesia

Published in MEPS Vol. 145 (1996) on December 31
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996