Population of the freshwater amphipod Gammarus fossarum was investigated in a calcareous stream with almost constant temperature (7-8• C) in the Chočské Vrchy Mts (West Carpathians, Slovakia). Quantitative samples of G. fossarum taken during 2005 showed population densities varying from 100 m −2 in August to 585 m −2 in late November. The population was split into juveniles, mature males, mature females without eggs and females with eggs. The percentage of juveniles (40-64%) was always the highest of any of the categories. Ovigerous females occurred throughout the year. The mean sex ratio was 1 : 2.4 (male: female), although its values varied considerably with the time of year. Breeding was continuous, although juvenile recruitment peaked in early spring, summer and early winter. Three discrete cohorts were distinguished from the size frequency distributions. The life span was 6-7 months and the individuals matured approximately in the half of life cycle. The mean fecundity was 9.6 embryos per brood. Variation in fecundity was mostly explained by size of the incubating females. The absolute growth of this species was best described by the Gompertz growth function. Relative growth rates (% body DM day −1 ) fluctuated in a nonlinear manner with size and age. The highest values of daily growth (2-4% of dry mass per day) were noted approximately in the half of life cycle. Annual production, estimated by the size-frequency method, was 1618.9 g dry mass m −2 and P/B ratio was 5.15.
A method is presented for defining the five classes of ecological quality based on a multimetric index (MMI) of macroinvertebrates, as required for implementation of the Water Framework Directive for small (catchment area 10-100 km 2 ), medium (101-1000 km 2 ) and large (> 1000 km 2 ) streams. Our method (expert judgment) allows us to overcome an absence of reference sites for some stream types. The key was selection of suitable metrics for all stream types. The whole procedure was divided into two parts. 1. Small streams with reference sites: suitable metrics were selected according to their ability to distinguish reference and monitoring sites -SI, Oligo [%], BMWP, RhiTI, Rheoindex, IBCR, % Aka+Lit+Psa [%] and EPT. Here the high-good boundary value was set as the 25 th (for metrics decreasing with increasing pollution) or 75 th percentile (for metrics increasing with increasing pollution). 2. Medium and large streams which lack reference sites: here the idea was applied that some metrics, the values of which change along an altitudinal gradient, also react to anthropogenic stress -SI, Oligo [%], BMWP, [%] metarhithral, RhiTI, Aka+Lit+Psa [%] and EPT for both medium and large streams with, in addition, IBCR and NFam for medium streams. This assumption was supported by regression analysis of altitude and metrics from small streams. Not all the metrics were related to altitude but metrics with a good ability to separate reference and monitoring sites did show a significant relationship to altitude. The boundary between high and good class for medium and large streams was set as the 95 th or 5 th percentiles.Key words: ecological quality ratio; reference status; streams; benthic invertebrates; multimetric index; Slovakia
The nymphal biology (life cycle, secondary production and feeding) of a population of Protonemura intricata was studied in a calcareous stream with almost constant temperature (7-8 °C) through the year at Prosiek valley (Chočské Vrchy Mts., West Carpathians, Slovakia). The results were compared with those previously known for this species in other areas. According to our data, the species has a complicated life cycle consisting of two cohorts with different duration (probably a cohort splitting). This life cycle seems to be uncommon among the Plecoptera, which usually has simple univoltine or semivoltine life cycles, and could be probably attributed to the constant temperature regime similar to that of tropical environments. One factor, the photoperiod length, was positively correlated with monthly growth rates. The nymphal growth varied throughout the year, but the highest growth was in late spring and summer, and the lowest was in winter. The annual secondary production was very high (909.4 mg · m -2 ) despite not being the most frequent taxon in the stream. The highest monthly production values were observed in the autumnal-winter period (November-December) due to massive hatching of nymphs. The lowest production values were observed in late summer and early autumn. Analyses of gut contents showed that this species behaves mainly as gatherer-collector, but also as shredder and, occasionally, as scraper. Changes in the gut content composition were detected in relation to the size. Comparing our results with those of the literature, it can be inferred that different populations of P. intricata can show notable differences in their life history when inhabiting places with different thermal conditions. IntroductionOne of the most important aspects for understanding freshwater ecosystems is the biology of the species that live in them. In this context, the study of the life history of single species is essential in order to achieve a full knowledge of the ecosystem itself and the relations within it. Many studies have tried to reach this goal through generalizations taken from the study of a reduced number of species, assuming that the rest of the members of their genus or family behave in the same manner. As pointed out by several authors (ZWICK, 1981;STEWART and STARK, 1993), this is neither a good approximation nor an appropriate * Corresponding author 58 Z. KOZÁČEKOVÁ et al.
Abstract:The effects of land use on black fly assemblages were investigated in submontane rivers (the Ľubochnianka River, the Revúca River, upper Váh River catchment) in the Carpathians. We recorded 11 black fly species in the Ľubochnianka River and 10 species in the Revúca River. Land use differs between the catchments; the Ľubochnianka is a primarily forested catchment, and the Revúca is markedly deforested catchment. Fifteen environmental variables were analysed. Based on the results provided by CANOCO, phosphorus level and stream slope are the most important variables and have significant influences on the variability of black fly assemblages. In spring, Prosimulium rufipes occurred along the entire lengths of the streams. The black fly assemblage of the Revúca River differs from the assemblage of the Ľubochnianka River mainly by its higher abundances of Simulium variegatum and Simulium ornatum, by the presence of Simulium carthusiense, and by the absence of Prosimulium hirtipes.
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