Phytoplankton biomass and production in two Tuamotu atoll lagoons (French Polynesia)

Abstract

Nutnent concentrations, phytoplankton biornass (chlorophyll a, chl a ) and prlrnary productlon (I4C uptake) were measured over a 5 yr period (1990 to 1994) In the atoll lagoons of Takapoto (4 yr water resldence tlme with pearl oyster aquaculture) and Tlkehau (0 5 yr resldence hme, without pearl oyster but wlth a fishery) French Polynesia In both atolls phosphate and silicate concentrations (0 1 p M PO, and 0 8 pM S O z ) were lower Inside the lagoon than in surrounding oceanlc sulfdce waters Picoplankton < l pm dominated phytoplankton blomass (61 %) and productivity (55",)) In both lagoons Average assimilation numbers were hlgh (13 mg C mg ' chl a h ' j and average chl a doubllng rates of the < l pm fractlon were estimated to be 1 1 and 1 3 d ' in Takapoto and Tikehau respectively Average dally pnmary production dunng the 1991 to 1994 period in Takapoto and Tikehau lagoons was estimated to be 0 8 and 0 7 g C m d.', respectively