PROCHLOROCOCCUS CONTRIBUTION TO PHYTOPLANKTON BIOMASS AND PRODUCTION OF TAKAPOTO ATOLL (TUAMOTU ARCHIPELAGO)

Prochlorococcus was observed for the first time in an atoll lagoon. Ph ytoplankton distribution was heterogeneous in the water column. In the upper 10 m, total biomass was lower and dominated by picoeukaryotes. Below biomass was higher and dominated by Synechococcus. Biomass and p roduction maxima were always below 10 m. In average (0-25 m), the perc entage of Prochlorococcus coccus, Synechococcus and picoeukaryote abun dance were respectively 20%, 78%, 2% and percent of fluorescence was 2 %, 57% and 41%. Maximum abundances were respectively 1.1 x 10(4), 7.5 x 10(4) 0.3 x 10(4) cells per ml and respective contributions to phyto plankton production were 2%, 55% and 43%. In surrounding oceanic water s (0-150 m) percentage of Prochlorococcus, Synechococcus and picoeukar yote abundance was respectively 98%, 1%, 1% and percentage of fluoresc ence 42%, 6% and 52%. Maximum abundances (cells ml(-1)) were 160 x 10( 4) Prochlorococcus, 0.15 x 10(4) Synechococcus and 0.2 x 10(4) picoeuk aryotes. Lagoonal conditions seem to be preferred by Synechococcus and oceanic conditions by Prochlorococcus.