PARTICULATE ORGANIC-MATTER IN 16 TUAMOTU ATOLL LAGOONS (FRENCH-POLYNESIA)

The standing stock and chemical composition of suspended particles wer e monitored in 16 Tuamotu atoll lagoons and surrounding oceanic water between 1983 and 1996. Temporal and spatial variability was estimated from 18 surveys performed in Takapoto. Atoll lagoon particulate organi c matter (POM) concentrations were compared using data taken during th e same months (March and November) and at the same time (morning). It appears that the lagoonal particulate organic carbon concentration dep ends on the latitude of each lagoon. We interpret this result as an in fluence of the waters deriving from the Peruvian and equatorial upwell ings. Phytoplankton biomass (chlorophyll) concentration was inversely related to the water exchange between lagoon and ocean. Therefore, the best atolls for pearl oyster farming seem to be those located north o f the Tuamotu Archipelago and with small exchange with the ocean. POM concentration was 2 to 5 times higher in the atoll lagqons than in the surrounding oceanic water, with a higher C:N ratio and a lower N:P ra tio. The small size of organic particles (70% < 3 mu m) and the low co ntribution of phytoplankton to particulate organic carbon (POC) (5 to 19 %) in the lagoons must be taken into account when calculating the p otential of pearl oysters, which cannot exceed the nutritional potenti al of Tuamotu atoll lagoons.