In a 2-year field study, abundance, biomass and community structure of benthic macroinvertebrates and their seasonal dynamics were assessed along the depth gradient in the stony littoral zone of Lake Constance, Central Europe. The macroinvertebrate community patterns differed significantly between the depth zones, partly because of species turnover, but mostly as a result of different dominance structures. These distinct differences should be considered when designing surveys of benthic invertebrates also for applied purposes, since sources of variation should be kept small and particularly on hard substrates, extensive efforts are required to obtain sufficient data for a powerful statistical analysis. A large seasonal variability in the macroinvertebrate communities of the eulittoral zone indicates a strong influence of physical disturbances, particularly of water-level fluctuations. The community pattern of the drift line samples was influenced by the previous development of the water level. The cumulated water-level fluctuations and their net tendency accounted for three quarters of the variation in a PCA. Since Lake Constance is the only large pre-alpine lake whose water level is not extensively regulated, the uniqueness of the littoral community should have implications for nature conservation measures.

The Ponto-Caspian amphipod Dikerogammarus villosus (Sowinski) invaded Lake Constance, Central Europe (47°39'N, 9°18'E,) in 2002 and within four years had colonized the entire littoral zone of the upper lake basin, replacing the formerly dominant species Gammarus roeseli Gervais. Fifteen fish species were sampled from six littoral sites in the upper lake basin in 2005 and 2006, and their stomach contents were compared with samples taken prior to the replacement of G. roeseli by D. villosus. Three zoobenthivorous fish species (European eel Anguilla anguilla (L.), Eurasian perch Perca fluviatilis L., and burbot Lota lota (L.)), which had regularly consumed G. roeseli, included D. villosus immediately into their diet in similar proportions. Shifts in amphipod consumption have thus not been detected, whereas effects of the invasive amphipod on the macrozoobenthos community, which on their part might affect the food base of littoral fish, require detailed study.

We studied the effects of predation by juvenile burbot (Lota lota) on the macroinvertebrate community in mesocosm experiments in the stony littoral zone of Lake Constance, a large prealpine lake in Central Europe. Although the growth data of the burbot suggest that the benthivorous fish exerts strong predation pressure on the invertebrate community, the predicted level of consumption is only poorly reflected by changes in biomass and abundance of most invertebrate prey taxa. High exchange rates of the prey between the mesocosms and the ambient littoral environment apparently masked the true predation effects of fish. Also, life-history events such as hatching or synchronised emergence of larvae led to temporal effects that obscured the impact of predation. However, for the dominant prey organism, the freshwater amphipod Gammarus roeseli, direct lethal effects appeared when its migration was limited. When exchange with the ambient littoral zone was possible, abundance and biomass of G. roeseli were unexpectedly high in the mesocosms stocked with burbot, indicating behavioural responses to fish presence. During the experiment, the burbot gained ca. 15% in length and about 60% in body mass. According to stomach content analyses at the end of the experiment, the ingested prey consisted mainly of relatively large and abundant invertebrates. Our study indicates that predation by juvenile burbot should be an important factor in structuring the benthic invertebrate community in terms of qualitative and quantitative effects.

Food consumption by Eurasian perch (Perca fluviatilis L.) and ruffe (Gymnocephalus cernuus [L.]) was studied in single and mixed-species treatments in the laboratory, where alternative food resources, chironomids and zooplankton, were offered simultaneously. The effects of structural complexity, which was represented by substrate grain size, and of feeding level on food consumption were analysed. Across all experiments, the outcome of competition between perch and ruffe depended on food abundance and on the structural complexity of the environment. Perch and ruffe both changed their food consumption in the presence of a heterospecific competitor. With high food supply, perch consumed more benthic food than ruffe. With low food supply, the consumption of perch decreased strongly, while that of ruffe remained high on fine sediment. Under all conditions tested, the mechanism of competition appeared to be of interference rather than of exploitative nature. It is suggested that with decreasing lake productivity caused by re-oligotrophication, habitat shifts of both species will occur, which will alleviate interspecific competition. Ruffe will forage over fine sediment and perch over coarse sediment, whereby both species will achieve the highest foraging efficiency under conditions of low food supply.

The importance of sediment type and of kairomones released by juvenile burbot (Lota lota) on behavioral responses of the freshwater amphipod Gammarus roeseli was studied in laboratory experiments. In the absence of kairomones, G. roeseli preferred coarse substrates; the highest preference was shown for the most coarse sediment. In the presence of kairomones, the amphipods preferred the less-coarse substrate pebbles over gravel. This difference is an effective antipredator response; G. roeseli is able to hide efficiently in the interstices of the pebbles. Juvenile burbot have a low foraging efficiency on pebbles and preferentially forage in the interstices of coarser sediments. G. roeseli responded differently to kairmones in different sediment types. The amphipods decreased their activity only in pebbles. In gravel, the rate of exploration behavior increased, and on a bare surface, the area containing fish kairomones was avoided.

To date, no regressions for invertebrates from lentic environments are available to facilitate biomass estimation. Predictive length-dry mass regressions for 20 freshwater invertebrate taxa from a pre-alpine lake littoral in Central Europe are presented here. Regressions were calculated by fitting a power function to body-length parameters. For Gammarus roeseli, the head height, an easily measurable length parameter, was used. Differences between regressions of different taxa were confirmed by analyses of covariance. Equations for invertebrates grouped at a higher taxonomic level had lower coefficients of determination; therefore, the use of regression equations at the lowest possible taxonomic level is indicated. A comparison of regressions with those published for related taxa in streams revealed significant differences, supporting the opinion that equations should be applied carefully and their use restricted to waterbodies with similar abiotic conditions.

Predator avoidance via alternative microhabitat choice by the freshwater amphipod Gammarus roeseli was examined in laboratory y-maze experiments, where predator presence was simulated by fish-conditioned water. The amphipod responses to three benthivorous fish species, which differ in their mode of feeding, were examined. G. roeseli avoided habitats with water conditioned by juvenile burbots (Lota Iota) and crucian carp (Carassius carassius), but not by juvenile Eurasian perch (Perca fluviatilis). Responses to predator-conditioned water only took place at high fish densities. Thus the amphipods were capable of distinguishing between acute predation risk, represented by high infochemical concentrations, and the low background level of infochemicals. The results of the study imply that proper microhabitat choice is an alternative to decreased locomotory activity, for enhanced survival of amphipods in the presence of fish predators in both lentic and lotic environments. A preliminary characterisation of the infochemical suggested that it is different from that which causes responses in Daphnia, as it could not be extracted by lipophilic solid phase extraction.