Der Einfluß des Bibers (Castor fiber albicus) auf die Fauna (Odonata, Mollusca, Trichoptera, Ephemeroptera, Diptera) von Mittelgebirgsbächen in Hessen (Deutschland)

Due to the return of the beaver an increasing number of brooks become restored to a natural condition. It is characterized by an alternation of flowing and standing sectors. In the summer of 1995, different groups of organisms (Odonata, Mollusca, Trichoptera, Ephemeroptera, Diptera) of two brooks in the Spessart mountains (Hesse, Germany) were studied to compare the composition of invertebrates in beaver homeranges and in the non-influenced sectors above. The new living conditions resulted in the disappearance of some species (Drusus anulatus, Trich., Sericostoma personatum, Trich., Radix peregra, Gastr.). Nevertheless the beaver homeranges accommodate a significant higher number of species of dragon flies and damsel flies, molluscs and caddis flies than the brooks above the homeranges. The heterogeneity of natural river systems make a coexistence of running water and silent water organisms possible. The examinations result in a significant higher group dominance of ephemeras (i.p. Cloeon dipterum) in a beaver pond than in lenitic sectors conditioned by the gradient without beaver influence. Here the dominance of chironomids was much higher. High current sectors with their characteristic organisms are also present in the beaver homeranges. The higher number of insects is the basis of nourishment for predatory insects and fishes. The potential effects of beaver ponds on fishes are discussed.     

Population dynamics of mayflies in a constant temperature spring stream in West Carpathians

We examined the life history and secondary production of four Ephemeroptera species (Baetis alpinus Pictet, 1843–1845, Baetis rhodani Pictet, 1843–1845, Rhithrogena carpatoalpina Klonowska, Olechowska, Sartoriet & Weichselbaumer, 1987 and Habroleptoides confusa Sartori & Jacob, 1986) in a temperature stable cold spring stream at Prosiek valley (Cho?ské vrchy Mts., West Carpathians, Slovakia). We have found asynchronous bivoltine life cycle for the most abundant species B. alpinus with growth rate positively correlated to photoperiod length. R. carpatoalpina have shown unusual asynchronous univoltine life cycle and B. rhodani have shown uncommonly low abundance in mayfly community. Total secondary production of mayfly community was very low, reaching 1654.8 mg DW m^?2 y^?1. We suggest that the observed asynchrony in growth could be related to the lack of temperature control.     

Plankton of lake Ototoa,a sand‐dune lake in Northern New Zealand

The seasonal cycles of abundance of the phytoplankton and zooplankton in Lake Ototoa, Northland, at 36° 31 S, 174° 14 E, are described. Concentrations of chlorophyll a were low (range 0.04–4.61 mg.m^‐3; mean 0.97 mg.m^‐3), and highest values were in winter. Phytoplankton densities were also low; an oligo‐trophic diatom‐desmid assemblage associated with Botryococcus, Dinobryon, and Svhaerocyslis was found.

The zooplankton was dominated by the calanoid copepod Calamoecia lucasi whose numbers remained fairly constant throughout the year, and the only other copepod found was the cyclopoid Mesocyclops leuckarti which was present in very low numbers. Bosmina meridionalis was the only limnetic cladoceran and was most abundant during autumn and spring. A number of rotifer species were also common.     

Mass stranding of molluscs at Te Waewae bay,southland, New Zealand (note)

A stranding of shellfish on the beach at Te Waewae Bay, Southland, occurred during a period of very cold, stormy weather in September 1970. More than 20 million shellfish were stranded, the majority being Mactra discors Gray. It is suggested that the cause was a combination of Strong inshore winds and low air temperatures, coupled with an increased flow of fresh, cold water across the beach.     

DIVERSITY OF EPHEMEROPTERA, PLECOPTERA AND TRICHOPTERA IN VARIOUS TRIBUTARIES OF TEMENGGOR CATCHMENT, PERAK, MALAYSIA

Ephemeroptera(mayfly),Plecoptera(stonefly)and Trichoptera(caddisfly)(EPT,3 kinds of insectorders)reach their maximum development in streamsand contain families that are entirely or almost con-fined to running water.Ross(1963)suggested thatthe early evolut…     

Macroinvertebrate assemblages in conditions of low-discharge streams of the Cerová vrchovina highland in Slovakia

Macroinvertebrate communities at 16 sites in Cerová vrchovina highland were sampled in 2000–2001 to analyze the influence of environmental factors on community structure with emphasis on Ephemeroptera, Plecoptera and Trichoptera (EPT). The extreme hydrological conditions of this area determine the macroinvertebrate community structure. Totally, 16 Ephemeroptera, 8 Plecoptera and 36 Trichoptera taxa were found. Predators of the families Perlidae, Perlodidae and Chloroperlidae (Plecoptera) were absent. The record of Protonemura aestiva is the second one in Slovakia. Ephemeroptera were represented mainly by rheophilous taxa. A rare lowland species Baetis tracheatus was found, known previously just from West Slovakia. Trichoptera were mainly represented by submontane rheophilous taxa. Species preferring low currents or backwaters from the family Limnephilidae were also recorded. Altitude and dissolved oxygen content were found to be the most important environmental variables determining the EPT community structure. Six types of streams were distinguished by the results of multivariate analysis, taxonomic composition and metric values. They belong to two main types: (1) EPT communities of the natural streams and (2) EPT communities of disturbed streams, where two types of stressor were identified–organic pollution and low discharge. A similarity between EPT communities of organically polluted streams and streams with very low flow was discovered. Values of biotic indices decreased in summer. The most diversified communities were found in the spring during higher water levels and better oxygen conditions.