Ecology of Heterotrophic Microflagellates. IV Quantitative Occurrence and Importance as Bacterial Consumers

Abstract

Heterotrophic nannoplankton flagellates and bacteria were quantified at regular intervals for a month in Limfjorden, Denmark. The number of flagellates averaged about 103 ml-1 and ranged from < 2 .times. 102 to .apprx. 3 .times. 103 ml-1. The composition of this fauna was dominated by choanoflagellates, non-pigmented chrysomonads and bicoecids; other forms are rarer. A substantial part of this fauna is associated with suspended particulate matter. Bacteria occurred in concentrations ranging from 1.5-3 .times. 106 ml-1. Flagellate numbers followed bacterial numbers and the bacteria-flagellate system showed a cyclical behavior with a frequency of about 16 days during the study period. Calculations based on laboratory data on the clearance of flagellates show that such organisms on the average filter 20% of the Limfjord water day-1 (range 12-67% day-1). This is consistent with previously published estimates of bacterial division rates in sea water provided that microflagellates are the main consumers of pelagic bacteria.