Grazing and assimilation rates of natural populations of planktonic cladocerans in a eutrophic lake

The filtering rates of ¹⁴ carbon-labelled Chlamydomonas sp. by 4 dominant species of Cladocera were studied in eutrophic Lake Aydat. The mean individual filtering rates were 364, 399, 403 and 408 µl ind^–1 h^–1 for Bosmina longirostris, Daphnia longispina, Chydorus sphaericus and Ceriodaphnia quadrangula, respectively. Their maximum assimilation efficiencies attained ± 50%. These populations collectively could consume the available food in less than 4 days during August (maximum daily grazing rate = 29%).In eutrophic conditions lake Aydat D. longispina appears to be more efficient in energy utilization than other cladocerans. Some individuals of Daphnia and Chydorus continued to filter in the zone of low oxygen where an important bacterial biomass had developed. Our results support the importance of the cladocerans in the regulation of phytoplankton production.     

Abundance,succession and morphological variation of planktonic rotifers during autumnal circulation in a hypertrophic lake (Heiligensee,Berlin)

Quantitative samples were taken in the pelagial zone of hypertrophic Heiligensee (Berlin, Germany) in the late summer and autumn of 1990. Abundances of 26 species occurring in the plankton, as well as physical and chemical parameters (water temperature, O₂, total phosphorus, SRP, NO₃ ^–, NO₂ ^– NH₄ ⁺ , chlorophyll a) were determined at different depths. Erosion of the hypolimnion due to autumnal storms and decrease in temperature was interrupted by fine weather periods with the occurrence of re-stratification, thus allowing mass production of algae and rotifers (Synchaeta oblonga, S. tremula, Keratella cochlearis) through exploitation of newly available nutrients. Warm stenothermal summer species (e.g. Pompholyx sulcata, Trichocerca pusilla, Liliferotrocha subtilis) became less abundant as a consequence of the progressive mixing process, whereas the appearance of new species was a rare event. The late summer occurrence of Liliferotrocha subtilis in the fraction < 30 µm (up to 3500 ind. l^–1) is remarkable. Keratella cochlearis showed morphological variation from spineless summer forms to spine-bearing autumnal forms, the latter particularly dominating the deeper water layers. The prevailing phenomenon was the dramatic decrease of the total number of individuals and of species towards completion of autumnal turnover. The impact of falling temperature, increasing mixing depth and mass production of phytoplankton on the rotifer plankton community is discussed.     

The temporal and spatial distribution of planktonic and benthic protozoan communities in a small productive lake

An investigation into the spatial and temporal distribution of protozoa in Esthwaite Water, a small eutrophic lake in the English Lake District, was carried out from mid-June until late September, 1977, during the period of summer stratification. Quantitative analyses of planktonic protozoan populations were performed on water samples collected at 1 m intervals throughout the water column and individual depth-time distribution profiles were constructed for the major ciliate species. Population density and species succession of the benthic protozoa was also studied.     

The temporal and spatial patterns of protozooplankton abundance in a eutrophic temperate lake

The temporal and spatial distribution of planktonic protozoa of Esthwaite, a eutrophic lake, was investigated at 7–10 day intervals between February to October 1988. Sarcodine protozoa were of little significance, the plankton was dominated by ciliates and flagellates. Ciliate density peaked in late May to early June with densities reaching 9.2 × 10³ 1^-1. There was considerable variation in spatial distribution and greatest species diversity occurred in March/April. After the establishment of summer stratification the planktonic ciliates were confined to water of >25% oxygen saturation in the water column. Oligotrichs, particularly the genus Strombidium and tintinnids, and peritrichs dominated the ciliate assemblages. There was no correlation between chlorophyll a concentrations and ciliate numbers, but a correlation was apparent between ciliate numbers and flagellate density. There were significant differences between the protozooplankton communities at the different sampling sites in the lake.