We conducted comprehensive field investigations to characterise the trophic status and food web structure of Großer Vätersee (GV) and Kleiner Vätersee (KV), two stratified lakes in the Baltic lake region of northeastern Germany. The lakes will be used as manipulation (GV) and reference (KV) ecosystems in food web studies. Both lakes are mesotrophic to slightly eutrophic with mean epilimnetic total phosphorus (P) concentrations of 24 and 21 μg L–1 in GV and KV, respectively. Mean phytoplankton biomass was 0.9 and 0.5 cm3 m–3 in GV and KV. During summer, the algal community of both lakes was dominated by cyanobacterial picoplankton and Ceratium spp. Filamentous cyanobacteria (mostly Planktothrix sp.) prevailed in a deep chlorophyll maximum found within the chemocline of both lakes. Bacterial biomass in the epilimnion of GV usually ranged between 1 and 3 cm3 m–3. Mean ciliate abundance was 13 ind. mL –1 in GV and 14 ind. mL–1 in KV. While Oligotricha dominated in GV, Scuticociliata were found most frequently in KV. Mean annual crustacean biomass was high in both lakes (GV 2.5 cm3 m–3, KV 1.2 cm3 m–3); Eudiaptomus gracilis, E. graciloides and Daphnia spp. were the most prominent species. Total fish biomass of both lakes was dominated by roach (GV 52%; KV 57%) and perch (GV 24%; KV 34%) Vaucheria dichotoma and Chara spp. dominated the macrophyte community in GV; Chara spp. dominated in KV. The slightly more eutrophic character of GV was most likely a result of greater P accumulation in the sediments due to external loading, which resulted in greater hypolimnetic P concentrations throughout the summer in GV. However, on an annual basis these differences were only occasionally reflected at higher trophic levels. The differences in fish biomass, however, might have been a consequence of higher structural diversity in GV provided by submersed macrophytes rather than its more eutrophic character. We conclude that the trophic characteristics and food web structure of Großer Vätersee and Kleiner Vätersee are similar enough to be suitable as manipulation and reference lakes in food web experiments.

High densities of Nannochloropsis, reaching up to 5.7 x 10(9) cells per litre, were observed in small inland water bodies in Germany. This is one of the few evidences of a Nannochloropsis species in a freshwater habitat. We describe a new species, N. limnetica Krienitz, Hepperle, Stich ge Weller sp. nov, for which the critical taxonomic characterization is based upon 18S rRNA sequence data. The ultrastructure of this species is characterized by the absence of a plastidial girdle lamella and pyrenoids. The plastid-bounding endoplasmic reticulum is continuous with the nuclear envelope, and the protoplasm contains numerous rodlike, doubly refringent lamellate vesicles. The pigment content of N. limnetica corresponds to that of other Nannochloropsis, but echinone was also found. The fatty acid composition of N. limnetica is similar to that of marine species; however, the total amount of fatty acids (351 mu g mg(-1) C-1) is higher than in marine species.

The myenteric plexus-longitudinal muscle preparation of the guinea-pig ileum was preincubated with [3H]choline, then superfused and stimulated electrically (1 Hz 120 pulses). Oxotremorine reduced the evoked outflow of [3H]acetylcholine in a concentration-dependent manner. Each of the six antagonists (scopolamine, methylatropine, trihexyphenidyl, 4-DAMP, clozapine, pirenzipine) produced parallel shifts of the concentration-response curves for the prejunctional effects of oxotremorine. Similarly, in contraction experiments, the antagonists competitively antagonized the postjunctional responses to oxotremorine. The pre- and postjunctional pA2 values did not differ significantly for any of the antagonists. It is concluded that pre- and postjunctional muscarinic receptors in the guinea-pig ileum are pharmacologically similar.