Bacteria as a food source for microzooplankton in the Schlei Fjord and Baltic Sea with special references to ciliates

Abstract

In situ investigations revealed that number and biomass of microzooplankton increased with eutrophication along the length of the Schlei Fjord (FRG). The same observation was made for total bacterial numbers and biomass. Microzooplankton of the Schlei and total bacterial numbers showed a minimum in winter and major periods of development in late summer/autumn and spring. Usually the microzooplankton biomass in the Schlei was greater than the bacterial biomass. In contrast. the bacterial biomass for 5 of 6 stations in the Baltic Sea surpassed that of the microzooplankton during summer. Number and biornass of microzooplankton in both bodies of water can mostly be attributed to protozoans of the 3 to 30 pm fraction. Determined with the aid of radioactively labelled bacterial cultures, the filtration rate of 'natural' microzooplankton populations exhibited a distinct dependency on microzooplanktonic biomass and water temperature. In March 1982 microzooplankton populations in the eutrophic Schlei Fjord filtered 5 to 58 % of the water per day. In the central Baltic Sea in August 1982 the rate was 70 % d-' during the late stage of a decaying blue-green algae bloom. Laboratory experiments with Uronema marinurn clearly showed that bacteria concentrations exert a considerable influence on the development of ciliates. Only when a limiting concentration of about 1 X 106 bacteria ml-' is attained does a proliferation of ciliates commence. Hence, bacteria can represent an important food source for microzooplankton, especially in biotopes with a high bacterial number and biomass.

Ciliategrazing on picoplankton in a eutrophic reservoir during the summer phytoplankton maximum: A study at the species and community level

“…1) and almost no algal cells suggested that ciliates cannot survive exclusively on bacwithin the size range of 2-6 pm were available. Typical teria in pelagic systems because they require high bacterial raptorial feeders, such as prostomatids, had to be at least concentrations (Fenchel 1980;Gast 1985;Stoecker 1988) partly food limited because the phytoplankton compothat are usually found only in specific environments, such sition became dominated by large algae throughout the as the chemoclinc, oxycline, etc. (Fenchel et al 1990).…”

Vertical distribution of number, biomass and size-class spectrum of bacteria in relation to oxic/anoxic conditions in the Central Baltic Sea

“…One Nodularia agglomerate of l cm length and 0.5 cm diameter can be colonized by approximately 7.5 X 10* bacteria, as demonstrated by Hoppe (1981). Both very large numbers of attached bacteria and countless flagellates, clliates and rotatorians occur in these cyanobacterial agglomerates and contribute to the 02-consumption (Bursa 1968, Gast 1985.…”

Trophic interactions and carbon flow between picoplankton and protozoa in pelagic enclosures manipulated with nutrients and a top predator

“…Even if small ciliates can be effective grazers of bacterioplankton, especially the larger size-classes (Gast 1985, Rivier et al 1985, Albright et al 1987, Sherr & Sherr 1987, Sherr et al 1989, Epstein & Shiaris 1992, Simek & Straskrabova 1992, ciliate bacterivory never exceeded 40 % of the total bacterial loss. During Period IV ciliate grazing on bacteria approached zero.…”

“…In addition, grazing by mixotrophic algae (Bird & Kalff 1987, Sanders & Porter 1988, S~lndergaard et al 1988, Bennett et al 1990), heterotrophic ciliates (Gast 1985, Rivier et al 1985, Albright et al 1987, Sherr & Sherr 1987, Sherr et al 1989, and larger zooplankton -in fresh waters especially cladocerans (Geertz-Hansen et al 1987, Christoffersen et al 1990, Wylie & Currie 1991, Jeppesen et al 1992, Vague & Pace 1992) -has also been regarded as potential loss process for picoplankton.…”