Dynamics of microbial plankton communities: experiments in Kaneohe Bay, Hawaii

Abstract

The dynamics of the microbial plankton community of Kaneohe Bay, Hawaii were investigated in September 1982 using in situ diffusion chambers and dilution manipulations. Total community carbon at the time of the experiments was estimated at 86 pg C 1-' of which Chlorella sp. accounted for 47 %, autotrophic microflagellates 14 %, chroococcoid cyanobacteria 11 %, and heterotrophic microflagellates and bacteria each 9 %. Instantaneous growth rates ranged from 1.2 to 1.9 d-' and 1.4 to 2.0 d-l, and mortality rates varied from 0.5 to 1.1 d-' and 0.1 to 0.4 d-' for heterotrophic bacteria and cyanobacteria, respectively, yielding net population growth rates of 1.0 to 1.3 and 1.5 to 2.7 doublings d-' for the 2 populations. Chlorella sp., on the other hand, experienced only slight net growth (0.1 to 0.3 doublings d-l) despite a growth coefficient of about 0.9 d-'. Phagotrophic microflagellates, presumed to be the dominant microbial grazers, consumed about 4.7 times their body carbon d-' and grew at net populationrates of 1.4 to 1.9 doublings d-l. However, microflagellates were food limited and did not control bacterial populations. From these data it appears that recent arguments for rapid material cycling within microbial communities of oligotrophic oceans may be overstated.