Bottom fauna and littoral vegetation fauna in Lake Maarsseveen

Summary The littoral vegetation starts its development only in June and reaches its highest expansion in autumn. By that time the organic debris from these plants starts to play an important role for detritivorous organisms. The quantitative development of the fauna in the littoral is highest in autumn and early winter. The bottom fauna in the hypolimnetic parts of the lake is less dependent of the season. The experiments with artificial plants have shown that most species are present when the littoral vegetation is absent. Owing to the absence of substrate in the form of vegetation with epiphyton as a major food resource the numbers in spring and early summer are low. The most productive invertebrate isDreissena polymorpha.     

A characterization and description of the Maarsseveen Lake system

The Maarsseveen Lakes system, located near the City of Utrecht, The Netherlands, consists of two major bodies of water, a larger lake (Maarsseveen I) and a smaller lake (Maarsseveen II), interconnected by a maze of channels known as a ‘petgaten’ area. The hydrodynamics of the lake region coupled with this ‘petgaten’ area are responsible for the maintenance of the relatively oligomesotrophic character of Lake Maarsseveen I, as compared with the more eutrophic lake maarsseveen II. Both lakes are plagued by problems of summer anoxia, although this phenomenon is far more pronounced in the more eutrophic small lake. Atmospheric deposition is responsible for contributions of significant quantities of trace metals to both lakes, and the River Vecht acts as an additional source for Lake Maarsseveen II.     

Temporal and spatial patterns of water mites in Lake Maarsseveen I

The paper analyses the distribution and seasonal changes in numbers of the water mite fauna of Lake Maarsseveen I. Water mites were collected from 1977 until 1986 by dipnet, underwater light trap, hydraulic lift sampler and by frame net. Fifty-two species belonging to the Hydrachnellae and one to the Halacaridae were sampled. The faunal picture obtained is characteristic of mesotrophic to eutrophic lakes.Arrenurus nobilis. Piona paucipora andP. imminuta can be characterised as lake species. The dominant species in the littoral sand flat areHygrobates nigromaculatus andH. trigonicus, at a depth of 0.5–1 m, andMideopsis orbicularis at depths of 2–7 m.Limnesia maculata is also very common on depths between 2 and 7 m. In early summer, however, they prefer shallow water up to 1 m depth. Some species likeHygrobates nigromaculatus andH. trigonicus were not captured by the underwater light trap. The hydraulic lift sampler gave underestimations of the densisty of certain speciese.g. Hygrobates spp. andLimnesia maculata. Unionicola spp. even can avoid this sampler. Sampling by frame net gave the most realistic data. The highest number of water mites was observed in the littoral sand flat, generally up to 1000 ind. m⁻². The genusHygrobates was represented with an average of 800 adult ind. m⁻² throughout the year, and appeared to be the main invertebrate predator in this habitat.     

Habitat differentiation and feeding strategies in water mites in Lake Maarsseveen I

Summary The habitat preference as regards depth and vegetation areas is discussed for a number ofPiona species.P. conglobata mainly walks over the water plants and undertakes swimming excursions of short duration from there.Arrenurus crassicaudatus is a bottom dweller.This behaviour is related to the searching activities for preys. The main food ofA. crassicaudatus consists of ostracods.P. conglobata prefersDaphnia aboveCyclops, while forUnionicola crassipes the reverse holds true.P. conglobata andU. crassipes do not recognize ostracods as possible preys. The relative prey size greatly influences the rate of catching success.The feeding strategies (catching behaviour, prey preferences and handling time) of these three species are discussed. Differences in these strategies are also considered in view of species diversity.     

A diel study in a water column of Lake Maarsseveen I

Summary A study was made of vertical distribution of phytoplankton and zooplankton, primary production and grazing in a stratified lake, over a period of 24 hours. Photoresponse curves, made at sunrise and noon, showed great differences. Phytoplankton sampled from 0–5 m and from 5–10 m reacted more or less in the same way, but phytoplankton sampled from the meta- and hypolimnion between 10–18 m showed a low photosynthetic activity. The daily production could for 95% be ascribed to algae smaller than 30 m. Grazing byDaphnia longispina, Bosmina spec. andEudiaptomus gracilis, The dominant grazers, was concentrated on this small size fraction phytoplankton, especiallyCryptomonas species. At sunrise and at sunrise the next day, phytoplankton species abundancies were determined. A particular great increase was found forCryptomonas cf. erosa. Since other species had been at approximately constant population densities for days before as well as after the particular date, or were rapidly disappearing from the plankton, primary production was supposed to be due largely toC. erosa. A carbon balance over 24 h was made, comparing primary gross production, respiration and grazing with changes in carbon content based on algal cell counts.     

Algae of periphyton of Lake Teletskoye

The generalized data are given on the composition and structure of phytoperiphyton of Lake Teletskoye on different substrates (rocks, macrophytes and their residues). It is noted that in spite of the differences in the taxonomic structure and level of development the algocenoses of periphyton of various substrates have similar ecological range. This gives a possibility of using the algocenoses of periphyton on different substrates for assessing the quality of the lake water.     

The cladocerans of the littoral zone of Lake Maarsseveen I

The littoral cladocerans of aPhragmites australis vegetation, and incidentally, the benthic chydorids on a sandy flat were studied from March through September in Lake Maarsseveen I (The Netherlands). A total of 31 species was found. Comparing the species list with data of Lake Constance before and after eutrophication, it can be concluded that Lake Maarsseveen I is still in an oligo-mesotrophic state. The littoral cladocerans peaked in the beginning of June and on the end of July. The species involved differed between the leeward SW and the windward NE sides. A larger number of chydorid species were found on the leeward shore. In the reed vegetation, the benthic chydorid densities showed a high degree of heterogeneity. A range of 23,000–406,000 specimens per m² was observed. The pattern sampler described by WHITESIDE and WILLIAMS (1975) gave no reliable results for the truly benthic chydorids. They will not swim up into the tubed bottles of this apparatus.     

Estimation of zooplankton populations in Lake Maarsseveen I: Problems,procedures and results

During three successive years the zooplankton community of a small fresh water lake was sampled and counted weekly. A critical survey is given about the statistical methods employed in plankton research; much depends on sampling and subsampling strategies. It is shown that log-transformation is often unnecessary and that low densities can be estimated accurately with the aid of Poisson tables. For the analysis of time series, no straightforward mathematical instruments are available; spectral analysis has only limited value, so graphical methods are recommended. The results of the plankton counts are briefly discussed in relation to each other, temperature and phytoplankton biomass.     

Algological and bacteriological investigations on reed periphyton in Lake Velencei,Hungary

Hydrobiologia - In the shallow Lake Velencei (surface area 24.5 km2) reed communities (Scirpo-Phragmitetum) are of great significance due to extensive metabolic activity of algal-bacterial...     

Density and depth variations of Daphnia multilocus genotypes during a summer period in Lake Maarsseveen

The genotype composition of a Daphnia population complex during a summer period in Lake Maarsseveen (The Netherlands) was determined by allozyme analysis. The depth distribution, diel vertical migration and several parameters of the total population were measured. Young-of-the-year (0⁺) perch (Perca fluviatilis) were caught and species and allozyme types of Daphnia in the perch gut were also analysed. During May 1997, the densities of D. hyalina, D. galeata, the back-cross D. g x h – hyalina and the multilocus allozyme genotypes of the hybrid D. g x h decreased, except one multilocus genotype (MMMF). Total population size decreased and the ratio of females with eggs to those without eggs decreased as well. Food limitation during this clear-water phase in the lake is considered responsible. All genotypes, except MMMF, gradually descended in the water column. This drift is thought to be a reaction to the abundantly present 0⁺ perch or to the kairomones of this fish, although predation on the daphnids was still absent. In June, diel vertical migration started, except again part of the MMMF subpopulation. The other part migrated over a short distance compared with the other taxa and allozyme types. Within two weeks, the upper 5 m of the epilimnion was devoid of Daphnia, and guts of perch were predominantly filled with MMMF. The daphnids in the gut and the lake did not differ in allozyme type composition. By the end of July, population density had increased again. The size and composition of the Daphnia population complex continuously changed during the study period, as did the depth distribution of the components. Different genotypes within the population complex seem to have developed different strategies to cope with starvation and predation and the state at a particular moment can be understood only if past and present factors are considered.     

A study of phosphate limitation in Lake Maarsseveen: phosphate uptake kinetics versus bioassays

In order to assess possible phosphate limitation for the phytoplankton community of Lake Maarsseveen, two techniques (phosphate uptake experiments and bioassays) were employed simultaneously in February–March 1982. In that period the ambient phosphate concentration of the lake water was less than 0.03 µM P and the diatom Asterionella formosa constituted more than 90% of the phytoplankton population. The phosphate uptake experiments showed relatively high uptake capacities and low cell phosphorus contents for the natural phytoplankton community. This suggested phosphate limitation throughout the test period. The growth stimulation of the phytoplankton after enrichment with phosphate, however, only revealed phosphate limitation from the beginning of March and bioassays may therefore be regarded as a less sensitive method.     

The anthropogenically stressed periphyton of Lake Orta,Italy

A long history of discharge of industrial wastes has left Lake Orta contaminated with high concentrations of acid, ammonia and copper. To study the effect of this chronic pollution on periphyton, I sampled epilithic algae and associated invertebrates at several sites from 1987 to 1988. Although biomass varied both spatially and seasonally, the taxonomic composition of these communities remained relatively stable. The dominant algae were chlorophytes and the dominant invertebrates were trichopterans. Comparisons with nearby unpolluted Lake Mergozzo, and with general equations developed for neutral lakes in North America indicate that these anthropogenic stresses are more clearly reflected by changes in the taxonomic composition and size distribution of the community than by changes in its biomass.Contribution No 375 from the Groupe de recherches en Ecologie des Eaux douces, Université de Montréal.Contribution No 375 from the Groupe de recherches en Ecologie des Eaux douces, Université de Montréal.     

Population dynamic aspects of chironomid larvae of the littoral zone of Lake Maarsseveen I

Population dynamics of chironomid larvae in the littoral zone of Lake Maarsseveen I were investigated to a depth of 6 m. No essential differences in the composition and density between various sampling stations in the shallow sand flats were found. Two species,Cladotanytarsus mancus andStictochironomus sticticus, were found to be the main components of the chironomid population to a depth of 4 m. The density ofCladotanytarsus, which occurred predominantly to a depth of 1 m, increased from June to a maximum in December. In May and June, the entireCladotanytarsus population emerged.Stictochironomus had its peak of abundance in June. From this cohort, a part, differing in size for each of the various years, emerged in August. The remainder of this population, together with the offspring of the August adults, emerged in May. The size of the August midges, and the number of its eggs was smaller than that of the May midges. At depths greater than 4 m,Tanytarsus bathophillus was found to be the dominant chironomid.In summer the abundance of the small (second and third instars)Stictochironomus was primarily affected by water mite predation. In autumn and winter,Cladotanytarsus was the main food source for water mites. In autumn, whenStictochironomus larvae have molted into the fourth instar, predation by bream decreased the density of these larvae. In winter, the impact of this fish is negligible.