C. Ferrier-pages et P. Furla, Pico- and nanoplankton biomass and production in the two largest atoll lagoons of French Polynesia, MAR ECOL-PR, 211, 2001, pp. 63-76
Pico- and nanoplankton concentrations were measured in the lagoonal waters
of the 2 largest atolls of French Polynesia (Fakarava and Rangiroa). Growth
, production and grazing rates were estimated using diffusion chambers near
the reef flat spillways and near the main channels of the atolls. The over
all microbial biomass was dominated by picoplankton, with very high abundan
ces of bacteria and cyanobacteria, these 2 groups representing each 20 to 5
0% of the total carbon. Nanoplankton (auto- and heterotrophic flagellates)
constituted only 10 to 15% of the total biomass. Microbial concentrations w
ere 1.5 to 3-fold lower near the reef flat spillways than near the channels
. This suggests an important biomass production inside the lagoon. At Rangi
roa, growth rates varied from 0.02 to 0.06 h(-1) for bacteria and from 0.01
to 0.04 h(-1) for the other groups (cyanobacteria, auto- and heterotrophic
flagellates). At Fakarava, growth rates were in the same range except for
the heterotrophic flagellates (0.05 to 0.17 h(-1)). Growth rates were signi
ficantly higher near the reef flat spillways than near the channels. More t
han 50% of both bacterial and cyanobacterial production was grazed by the h
igher trophic levels in both atolls. Bacterial production was enhanced by a
nitrogen enrichment whereas production of cyanobacteria and flagellates wa
s enhanced by both a nitrogen and a phosphorus enrichment.