Population dynamics and trophic coupling in pelagic microorganisms in eutrophic coastal waters

Abstract

ABSTRACT: Pelagic bacteria, heterotrophic and autotrophic nanoflagellates, and ciliates were quan- tified in the marine shallow-water sound, Limfjorden, Denmark, from March to November 1983. During summer the populations showed pronounced oscillations with time scales of days or weeks. Concentra- tions of bacteria, heterotrophic nanoflagellates and ciliates ranged from 0.5 to 15.2 X 106 ml" (mean: 6.3), 0.2 to 15.2 X 103 ml-' (mean: 2.0), and 1.4 to 162.0 ml-' (mean: 17.1), respectively. Population sizes of bacteria and heterotrophic nanoflagellates were coupled, as were populations of total nano- plankton and ciliates; in contrast there was no direct coupling between bacteria and ciliates. It is estimated that heterotrophic nanoflagellates on average cleared 45 YO (range: 5 to 365 %) of the water- column for bactena per day during summer. Ciliates on average cleared 93 % (range: 4 to 352 %) of the water-column for nanoplankton per day. INTRODUCTION