Biomass and photosynthetic activity of phototrophic picoplankton in coral reef waters (Moorea Island, French Polynesia)

Abstract

In April 1984, chlorophyll a and photosynthetic activity of phytoplankton were measured above a coral reef and in the deep chlorophyll maximum (100m) of adjacent oligotrophic oceanic waters. Samples were frachonated into 3 sizes: 0.2-2. 2-5 and 2 5 km. Total chlorophyll a concentrahons were about 0.1 mg m-3, and phytoplankton > 5 pm never exceeded 104 cells I-'; picoplankton were not enumerated. Reef samples differed from oceanic waters by containing higher proportions of diatoms and lower proportions of coccolithophorids Chlorophyll biomass was dominated by the 20 mg C mg chl-' h-') occurred in the < 2 m subsequent grazing of small cells by corals and other constituents of the food web ('picoplankton loop'), may contribute to nutrient cycling within the reef ecosystem.