Why and where do oligochaetes hide their cocoons?

In Mondsee, a prealpine lake of Austria, abundance and vertical distribution of oligochaetes were investigated at four different depths (5, 10, 20 and 40 m). Adult oligochaetes and cocoons were found to be almost always absent in the uppermost centimeters of sediment. A hypothesis was developed that predation by fish is one factor, among others, inducing the observed vertical distribution patterns. In the laboratory the predation efficiency of the fish Abramis brama decreased with increasing sediment cover over the cocoons. Tolerance limits of embryonic worms to anaerobic conditions (LC 50 values) were found to differ for different developmental stages, ranging from 28 hrs for eggs to 43 hrs for fully developed embryos. Oxygen uptake rates of oligochaete embryos increased with their stages of development, eggs using 1.51 and fully developed embryos 3.32 nl O₂/ind./h (10°C).     

Vertical distribution and abundance of benthic invertebrates in profundal sediments of Mondsee,with special reference to oligochaetes

Two profundal sediment sites at the same depth (MO₁ and MO₇) in Lake Mondsee differed considerably in their trophic conditions. Based on organic carbon (weight loss on ignition) and redox values, MO₁ sediments could be classified as eutrophic, MO₇ sediment as oligo- to mesotrophic. Investigations on abundance, diversity and vertical distribution of meio- and macrofauna exhibited distinct differences between the two sampling sites. MO₇ showed a much higher diversity than MO₁. Seven species of ostracods and oligochaetes respectively, were found at MO₇, but only two species of oligocheates at MO₁. The vertical distribution of meiofauna at MO₇ corresponded to redox values. Chironomids were found in the uppermost 4 cm of sediments. Oligochaetes penetrated 15 to 20 cm into the sediment. Nearly 100% of the adult oligochaetes and cocoons occurred only below the first three centimeters of sediment. Their distribution patterns are discussed.     

Respiration of Cytherissa lacustris (Ostracoda) at different temperatures and its tolerance towards temperature and oxygen concentration

Summary The ostracod species Cytherissa lacustris was investigated with respect to its temperature and oxygen tolerance limits. In laboratory experiments the tolerance limits were found to be much wider than expected from field data. Hatching of first instars was observed in cultures up to 20° C. The tolerance limit for oxygen concentrations was less than 1 mg O₂·l^-1 at 10° C and 20 h exposure. The distribution pattern of C. lacustris along a depth profile in lake Attersee showed a maximum density between 10 and 20 m depth coinciding with temperatures between 4 and 15°C throughout the year. The size dependence of respiration rates of well adapted C. lacustris is within the normal range of small metazoans. Its weight specific rates of oxygen uptake indicate an adaptation plateau in the range between 10 and 15°C. Possible reasons and advantages of such an adaptation for C. lacustris are discussed.     

Annual cycles of benthic community oxygen uptake in a deep oligotrophic lake (Attersee,Austria)

Benthic community oxygen uptake of Lake Attersee sediments was measured between 1976 and 1979, along two profiles at 25, 50 and 100 m depth. Profile I was situated in the bay of Unterach into which the main tributary, Mondsee-Ache, discharges a high load of organic matter. Profile II was chosen at Weyregg to avoid the eutrophying effect of Mondsee-Ache. Oxygen uptake rates of Unterach sediments at 25 and 50 m depth were found to be higher when compared to the other sites (mean rates: Unterach 25 m = 15.56, 50 m = 11.05 mg O₂ · m⁻² · h⁻¹; Weyregg 25 m = 6.43, 50 m = 5.14 mg O₂ · m⁻² · h⁻¹). Organic content of the uppermost sediment layer was also higher in the bay of Unterach than at Weyregg. Oxygen uptake rates of undisturbed sediment cores vary considerably throughout the year, but no simple correlation existed with variations in organic content of the sediments. Peaks of organic matter were found to concur with following peaks of oxygen uptake rates, which implies that a certain time span is necessary for transforming freshly sedimented organic matter into a state digestable for the benthic community. The retardation between increasing organic matter of the sediment and the corresponding increase of benthic oxygen uptake was different at Unterach and Weyregg respectively, which is explained by the different quality of sedimenting material.     

Benthic community metabolism of three Austrian pre-alpine lakes of different trophic conditions and its oxygen dependency

Benthic community respiration rates of profundal sediments of Fuschlsee (37.6 mg · O₂ · m^–2 · h^–1 — eutrophic), Mondsee (40.19 mg · O₂ · m^–2 · h^–1 — eutrophic) and Attersee (11.5 mg · O₂ · m^–2 · h^–1 — oligo-mesotrophic) were measuredin situ, and in cores. By exposing the sediments to different oxygen levels in the laboratory it was found that benthic community metabolism reduced with decreasing oxygen concentrations. The slope of the regression lines, relating oxygen uptake rates to oxygen concentrations, differed significantly for the different sites investigated. These results were closely related to the trophic conditions of the lakes.     

The influence of ionic concentration on population parameters,development time,activity, and respiration rate of Arctodiaptomus spinosus (Daday) (Calanoida,Copepoda)

Summary For A. spinosus, significant correlations were found between population parameters and the ecological parameters of alkalinity and temperature. For the birth rate, 43.33% of variance is explained by alkalinity and 56.33% by alkalinity and temperature. Alkalinity, and alkalinity and temperature combined account for 48.22% and 70.23% respectively of the observed variances in nauplii hatching. It was demonstrated that, provided sufficient time for adaptation is allowed, the activity of individuals is not affected by differences in the alkalinity of the medium within the normal range of concentration. Embryonic development does not appear to be influenced by the ionic concentration, but significant increases in time of development of the nauplii (at alkalinity 100 meq/l: 8.8 days/20°C) and of the copepodites (at alkalinity 100 meq/l: 12.6 days/20°C) were recorded at both low and high ionic concentrations. The lowest respiration rates (3.7 nl O₂·h^-1·g dw^-1/20°C) occurred at an alkalinity of 100 meq/l. Rates increased at lower (10 meq/l: 5.7 nl) and at higher (400 meq/l: 11.9 nl) alkalinities.