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

Abstract

Pelagic bacteria, heterotrophic and autotrophic nanoflagellates, and ciliates were quantified 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. Concentrations 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 nanoplankton 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 watercolumn for bactena per day during summer. Ciliates on average cleared 93 % (range: 4 to 352 %) of the water-column for nanoplankton per day.