Ryszard Kornijów

Hydrophyte-macroinvertebrate interactions in Zwemlust, a lake undergoing biomanipulation

In two years after biomanipulation of Lake Zwemlust (The Netherlands), macrophytes (helophytes, elodeids) and filamentous algae developed luxuriantly in the lake. They influenced the structure of macroinvertebrate communities inhabiting them. Macrophytes and algae, by changing environmental and trophic conditions, also affected the composition of macrozoobenthos. Vascular plants served as an important source of food for zoobenthos and phytofauna, mainly after they were decomposed. Filamentous algae were consumed readily alive by many animals. Invertebrates appeared to be important as a potential nutrient source for hydrophytes.

The distribution of chydorids (Branchiopoda, Anomopoda) in European shallow lakes and its application to ecological quality monitoring

This study describes the chydorid (Branchiopoda, Anomopoda) assemblages from 66 European shallow lakes, and presents data relating the assemblages to lake type and ecological quality. Forty species, out of a total recorded European fauna of 60 species, were found in the study sites. No significant differences were found between chydorid assemblages associated with rock and plant substrata. Patterns of distribution were best explained primarily by latitude and pH. Chlorophyll-a, total phosphorus, water temperature and Secchi depth were also correlated with assemblage descriptors. Alonopsis elongata, Alona rectangula, Alonella excisa and Pleuroxus uncinatus were shown to have higher prevalence in certain lake types. The dominance of Chydorus sphaericus in a third of the study sites was linked to eutrophication and high levels of chlorophyll-a. The relationship between chydorids and lake ecological quality was more apparent at species rather than community level. This study identifies important typological factors affecting chydorid distribution, and confirms that patterns of chydorid distribution previously reported from regional studies hold true across Europe.

The impact of predation by perch on the size-structure of Chironomus larvae — the role of vertical distribution of the prey in the bottom sediments, and habitat complexity

The study was performed in June–August 1993, in eighteen enclosures (1 x 2 m) built in a fertile, small (area 2.5 ha) and shallow (max. depth 1.7 m) lake, Little Mere (north-western England). Three densities of Nuphar lutea leaves were manipulated in enclosures to 10%, 50% and 90% coverage of the water surface. Perch (total length ca. 15 cm) was stocked in half of the enclosures in a density 3 fish m–2. The vertical distribution of Chironomusf.1. plumosuslarvae (classified in the size classes: 0-5, 5–10, 10–15, 15–20 and >20 mm) in the bottom sediment showed a clear pattern, with bigger larvae burrowing to the greatest depth. Densities of all larval size classes except 0-5 mm were negatively affected both by plant density and by perch in three sediment layers considered (0–2, 2-5 and 5–10 cm). The larvae formerly at the surface did not move deeper in the sediments to avoid fish predation. The size distribution of the larvae, with the prevalence of the 15–20 and 10–15 mm larvae, found in the guts of perch was the most similar to that in the upper sediments at low and medium plant densities, and to that in the intermediate, 2-5 cm, sediment layer at high plant density. The effect of the interaction between plant density and fish was significant for all the larvae except those of 10–15 and 15–20 mm. Although the results of the experiment showed size-selective feeding by perch, the direct overall effect of the fish on the size-structure of the larvae was limited by vertical distribution of the prey in the bottom sediment. In addition, it was modified by nymphaeids, which, at high density, altered food conditions and acted as a refuge for Chironomuslarvae both directly (providing shelter) and indirectly (providing fish with the additional, epiphytic prey).

A simple apparatus for sampling epiphytic communities associated with emergent macrophytes

The apparatus allows the sampling of both algal and animal components of the epiphyton. It consists of a perspex tube, 100 cm long with an internal diameter of 4 cm, and of an epiphytic sieve. The latter is made of two 2.5 cm cross-sections of perspex tubing with a piece of circular mesh glued between them. While sampling, a randomly chosen shoot is isolated from the ambient water by means of the tube, cut at the bottom sediment and removed together with epiphyton. The water, taken together with the shoot is then removed using the epiphytic sieve, joined with the tube under the water surface. The detached organisms, associated with the stem and those scraped from the stem with a stiff brush afterwards, concentrate on the mesh.

Cumulative consumption of the lake macrophyte Elodea by abundant generalist invertebrate herbivores

Previous investigations have shown that macrophyte biomass can be substantially reduced by invertebrate herbivores but have not provided evidence for the links between the magnitude of the observed damage and the densities of herbivores. The results of this study support the hypothesis that the abundant occurrence of the epiphytic generalist herbivores may result in their cumulative consumption which, in turn, can be regarded as the mechanism responsible for often observed relatively high level of herbivory on freshwater macrophytes. The percentage of Elodea sp. biomass consumed by invertebrates was estimated for six European lakes, based on analysis of gut contents, daily rations and the density of epiphytic herbivores. Although the daily ration of these invertebrates when feeding upon Elodea averaged only 14.6% of their dry mass, their biomass was relatively high (from 0.163 to 1.161 g DW per 100 g DW plant). The estimated percentage of Elodea biomass consumed during one summer month by epiphytic invertebrates ranged from 0.5 to 5.9%. These values, after extrapolating to the whole growing season would mean that the biomass of Elodea lost to herbivory was between about 2 and 23%, an estimate which are within the range of consumption reported by other authors.

VERTICAL DISTRIBUTION OF IN-BENTHOS IN RELATION TO FISH AND FLOATING-LEAVED MACROPHYTE POPULATIONS

Several papers have described the vertical distribution of in-benthos in fresh waters (e.g., Kajak and Dusoge, 1971; Becket et al., 1992; van de Bund and Groenendijk, 1994), but the reasons for such distributions of invertebrates as midge larvae or tubificid worms in deep bottom sediments are often obscure. One reason may be reduced abundance in the surface sediment due to fish predation (Hershey, 1985; Lammens et al., 1987; Kornijow, 1997). However, a behavioral response by the in-benthic invertebrates to avoid fish (i.e., migration to deeper sediments) may play an important role as well but has not been tested.

Are the larvae of Propsilocerus lacustris Kieffer 1923 (Diptera: Chironomidae) favoured by nutrient-rich lakes?

Abstract The larvae of Propsilocerus lacustris were found at densities ranging from 30 to 150 ind. m−2 in the hypertrophic Lake Syczyńskie, eastern Poland. They burrowed in the top 5 cm of soft sediment at a water depth of ca. 1 m along the reed belt. The sediment was well decomposed, with fair contribution of organic matter (16.5 – 31.6%) and of neutral pH (6.5 – 7.7). Concentrations of total phosphorus in the sediments ranged from 1.64 to 5.04 mg g DW−1. The sediment pore water contained cyanobacterial microcystins (1 – 2 μg MC-LR eq. l−1). The analysis of subfossil remains indicates that the larvae appeared in the lake in the middle 1960s, i.e. a few years before the system switched from eutrophy to hypertrophy. Densities increased parallel to the increase in the lake trophic status, estimated as concentrations of organic matter and total chlorophyll in the sediment. The results suggest that P. lacustris, as its close relative P. akamusi, favours nutrient-rich lakes.

Trophic cascade structuring a plankton community in a strongly vegetated lake littoral

Vegetated lirroral habirars eonsrirure a mosaie o f horizontal and verrieal mierohabirars provided by emergent and submerged maerophyres, togerher with rheir epiphyrie eommuniries, and open parehes wirh higher potential produerion for planktonie algae. Predaror-prey interaerions may rhus beeome very eomplex in rhe lirroral environment, and rhe rrophie easeade beeomes diffieulr ro view due ro rhe sparial and remporal heterogeneiry of rhe environment, as well as to rhe diffieulries in rhe sampling. Consequenrly, evidenee for fish-mediated rrophie easeade among maerophyre vegetation is seanry and has been based primarily on experiments in field o r laboratory enclosures (ef. }EPPESEN er al. 1998). In rhis srudy, the impaets of fish predarion on mid-summer plankton development, and on a potential rrophie easeade, were invesrigared wirhin a dense maerophyre bed. Changes of planktonie eommuniries were eompared wirhin rhe lirroral areas whieh were eirher open, or closed wirh mesh, for rhe entry and foraging of natural fish popularions.

Investigation on competitors and predators of herbivorous aquatic Lepidoptera (Acentria ephemerella) on submersed macrophytes in a large prealpine lake

Submersed macrophytes offer a large colonization area for many macroinvertebrates. Numerous studies investigated the interaction between plant species, growth and leaf form and the abundance and species composition of invertebrates (e.g. SOSZKA 1975, KORNIJOW & KAIRESALO 1992). Grazers and detrivores assist the plants by removing epiphyton and allowing more light to reach the photosynthetic tissue. Only recently has the paradigm that aquatic angiosperms are not subjected to a high degree of herbivory been challenged (LODGE 1991, NEWMAN 1991, KORNIJOW 1996, LODGE et al. 1998). A detailed study of the literature reveals that aquatic insects were frequently observed feeding on submersed macrophytes. For example, Acentria ephemerella, a true shredder–herbivore, was found associated with pondweeds and other macrophytes in several studies (BERG 1942, MULLER-LIEBENAU 1956, SOSZKA 1975). Acentria seems to prefer large lakes to small ponds as habitat (JOHNSON et al. 1998). Data on its abundance in different lakes range from a few dozen to many hundred species per square meter (SOSZKA 1975, HEDAL & SCHMIDT 1992, BANZIGER 2000, JOHNSON et al. 2001, GROSS et al. in prep.).

Crustacean communities as food resources for fish in shallow Polesie lakes with contrasting development of submerged macrophytes

The aim of the research was to evaluate crustacean forage resources for fish in five shallow lakes varied in respect to species richness and coverage of submerged macrophytes, and thus representing different alternative stable states. The results revealed that lakes with a high or moderate abundance of macrophytes and moderate visibility (macrophyte-dominated Lake Rotcze, phytoplankton-macrophyte dominated lakes Sumin and Głębokie) displayed reach crustacean forage base for fish. Poor feeding conditions were found in two extremely different lakes: turbid phytoplankton-dominated Lake Syczyńskie devoid of macrophytes, and heavily vegetated, clear-water macrophyte-dominated Lake Kleszczów. Possible reasons for these differences are discussed.