Robert Stryjecki

Water mites (Acari, Hydrachnidia) of water bodies of the Krąpiel River valley: interactions in the spatial arrangement of a river valley

The present study is a discussion of the interactions between different types of water bodies in the spatial arrangement of a river valley, taking into account landscape data. The Hydrachnidia assemblages in particular types of valley water bodies (oxbows, riparian pools, permanent ponds, flooded alder carrs, sedge marshes, and springs) are strongly influenced by the spatial arrangement of the water bodies in the landscape. Moreover, the formation of a fauna in a particular type of valley water body is also influenced by its origin. For example, the faunas of the oxbow lakes and riparian pools would have many characteristics in common, as these two types of water body can be characterized as originating in the river. As many as 61 species common to the valley water bodies and the Krąpiel River were noted. In the interactions between the valley water bodies and the river, the direction of migration from the former to the latter was clearly predominant. Migration in the reverse direction, from the river to the valley water bodies, took place to a far lesser degree. CCA analysis of landscape variables showed the influences of certain landscape parameters on water mites. These should be regarded as indirect influences, but as a consequence of their effects, they influence the formation of specific types of Hydrachnidia assemblages.

Early post-dredging recolonization of caddisflies (Insecta: Trichoptera) in a small lowland river (NW Poland)

An analysis was made of the effect of dredging on the caddisfly fauna (Trichoptera) of the river Krąpiel (north-western Poland) a short time after the intervention. Pronounced changes were observed in the qualitative and quantitative structure and the biodiversity of Trichoptera. These changes should not, however, be characterized as unfavourable from an ecological perspective if we consider only the one group of insects analysed. Some species — Brachycentrus subnubilus and Lepidostoma hirtum — disappeared from the dredged parts of the river, but significantly more appeared, and these were typical river species. This replacement of species can be linked to habitat changes and the uncovering of larger patches of sandy bottom. The recolonizing species included accidental (eurytopic) species, which is typical in ecological succession for periods immediately following disturbances. On balance, despite the replacement of species, there was no decrease in species diversity, and typical river species appeared in larger numbers. In Trichoptera, recolonization following dredging first takes place as a result of drift of larvae, and then via dispersion of adults.

A thermocline as an obstacle to the spread of water mites (Acari: Hydrachnidia) across the lake profile

The aim of the study was to determine whether a thermocline may constitute a barrier discouraging vertical migration of water mites. The research was carried out in May, June, July, and August 1999 in Lake Lubie, and a total of 3252 water mites (1880 females and 1178 males) belonging to 29 species were collected. A strong negative correlation was observed between the drop in temperature in the thermocline and the abundance and number of water mite species living beneath the thermocline. The negative correlation resulted from a considerable limitation of vertical migration of water mites by factors such as: low temperature below the thermocline, large difference between temperatures above and below the thermocline, and considerable thickness of the thermocline. During summer season, lower layers of the lake were increasingly penetrated by water mites as the temperatures above and below the thermocline were becoming more uniform. Lake species displayed the greatest ability to penetrate lower water layers and were present below the thermocline during the whole study period; moreover, their numbers were quite steady. On the contrary, the species, which are characteristic for small water bodies, crossed the thermocline in comparatively large numbers in June when the thermocline was of the lowest thickness.

New host-parasite associations of Hydrachnidia (Acari) on Chironomidae (Diptera) from Poland

Abstract We present the first data from Poland concerning parasitism of Hydrachnidia on Chironomidae. Larvae of Hygrobates sp., H. setosus, Unionicola aculeata and Piona stjoerdalensis were found attached to adult Chironomidae (Cricotopus triannulatus, Tanytarsus sp., Paratanytarsus sp., Critocopus sp. and Orthocladius sp.). Intensity of infestation ranged between 1 to 2 larvae. All of the parasites were attached to abdomens of the hosts. The determination of parasitism of U. aculeata on Paratanytarsus and Tanytarsus genera extends the list of the hosts of this water mite species to the mentioned genera of Chironomidae. In case of H. setosus, the parasitism of this water mite on currently known hosts from the family Chironomidae has been confirmed.

The influence of environmental factors on water mite assemblages (Acari, Hydrachnidia) in a small lowland river: an analysis at different levels of organization of the environment

Research on the ecology of water mites in flowing water has focused mainly on analysis of factors directly affecting these organisms in the aquatic environment. The hypothesis of this study was that apart from factors acting within the aquatic environment, the formation of Hydrachnidia communities in lotic ecosystems may also be affected by factors acting in the terrestrial environment. The analysis was made at three different levels of organization of the environment: (1) landscape level (sub-catchments, terrestrial environment), (2) macrohabitat level (sampling sites, aquatic environment) and (3) mesohabitat level (sampling sub-sites, aquatic environment). Some correlation was noted between certain species and some sub-catchment parameters. This may indicate a link between some landscape features (terrestrial environment) and the formation of water mite assemblages in the river. The low percentage for physicochemical parameters together in explaining the variance in occurrence of species, very low correlations between species and physicochemical parameters and the discrepancy in the grouping of sites in the case of faunal data and data on the physicochemical indicates that physicochemical factors had little influence on water mites. Taking into account all three levels of organization of the environment analyzed, we can say that at the landscape level we can find only indirect relationships between environmental factors and the fauna inhabiting the aquatic environment; at the macrohabitat level the description of Hydrachnidia is more precise but still of a general nature. Only analysis at the mesohabitat level fully explains the specific character of Hydrachnidia assemblages.

Are beetles good indicators of insect diversity in freshwater lakes

Abstract The study verifies the usefulness of aquatic beetles as an indicator of biodiversity of a simple ecological system. Detailed analyses were carried out at the elementary level for the purpose of determining the significance of correlations between the biodiversity of Coleoptera and other groups of aquatic insects in single samples. The relation of selected taxa to selected habitats of the lake Wukśniki (north-eastern Poland) was also investigated. Moreover, the possibility of application of biodiversity surrogates, i.e. higher taxonomic units (genera and orders), in the determination of biodiversity was examined. A significant high correlation was determined between Coleoptera and the total remaining taxa (RR - Remaining Richness) in samples collected in the entire lake. The correlation has the highest value at the species level. The complementarity analysis reveals that the percentage contribution of Coleoptera in the overall biodiversity of the lake is similarly high at the species and genus level, and substantially lower at the family level. In accordance with the hypothesis, aquatic beetles can be used as indicators of the overall biodiversity of insects in the ecosystem of a mesotrophic lake. Biodiversity surrogates, i.e. higher taxonomic units (genera and families), can be applied instead of the species level.

The influence of the landscape structure within buffer zones, catchment land use and instream environmental variables on mollusc communities in a medium-sized lowland river

The world’s freshwater molluscan fauna is facing unprecedented threats from habitat loss and degradation. Declines in native populations are mostly attributed to the human impact, which results in reduced water quality. The objectives of our survey were to analyse the structure of the mollusc communities in a medium-sized lowland river and to determine the most important environmental variables at different spatial scales, including landscape structure, catchment land use and instream environmental factors that influence their structure. Our survey showed that a medium-sized river, that flows through areas included in the European Ecological Natura 2000 Network Programme of protected sites, provides diverse instream habitats and niches that support 47 mollusc species including Unio crassus, a bivalve of Community interest, whose conservation requires the designation of a special conservation area under the Habitats Directive Natura 2000. This survey showed that mollusc communities are impacted by several environmental variables that act together at multiple scales. The landscape structure within buffer zones, catchment land use and instream environmental variables were all important and influenced the structure of mollusc communities. Therefore, they should all be taken into consideration in the future restoration of the river, future management projects and programmes for the conservation of biodiversity in running waters. The results of this study may be directly applicable for the rehabilitation of river ecosystems and are recommended to stakeholders in their future decision concerning landscape planning, monitoring species and their habitats, conservation plans and management in accordance with the requirements of sustainable development.

Leeches (Clitellata: Hirudinida) of an upland stream : taxonomic composition in relation to habitat conditions

Abstract Hirudinida comprise a constant component of benthofauna in running waters and their taxonomic composition is often analyzed to evaluate the environmental quality. However, the indicatory role of particular species is still arguable. Thus, it is very important to provide more detailed information on the impact of environmental parameters on the species structure within this group of invertebrates. Representatives of nine species were found in the investigated upland stream including mainly Erpobdella vilnensis and E. octoculata. The research has demonstrated that the hydromorphological conditions and feeding behavior are the main factors determining the taxonomic composition of leeches in particular sections of a watercourse.

A very rare case of intersexuality in water mites of the genus Arrenurus Dugès, 1834 (Acari, Hydrachnidia)

In recent years, many authors have drawn attention to the fact that substances of anthropogenic origin introduced to the environment can disrupt the normal functioning of the endocrine system in animals, a phenomenon known as endocrine disruption. These substances are called endocrine-disrupting chemicals. It has been suggested that many cases of adverse changes in health (including the phenomenon of intersexuality) in a range of wildlife species are owing to exposure to endocrine disrupters. The main objective of this study was to report intersexuality in water mites of the genus Arrenurus. The intersex specimens of Arrenurus crassicaudatus Kramer, 1875 were more similar in their overall appearance to males than to females, but their external genital organ was more like the genital organ of a female than that of a male. Based on their morphological features and body measurements, intersex A. crassicaudatus individuals should be described as feminized males. The causes of intersexuality in aquatic invertebrates are still unclear and several mechanisms may be involved: parasitism, pollution affecting parasite function, and pollution directly causing the intersexuality seem to be the main factors increasing the frequency of the phenomenon.

Water mites (Acari, Hydrachnidia) of riparian springs in a small lowland river valley: what are the key factors for species distribution?

This paper examines the impact of disturbance factors—flooding and intermittency—on the distribution of water mites in the riparian springs situated in the valley of a small lowland river, the Krąpiel. The landscape factors and physicochemical parameters of the water were analysed in order to gain an understanding of the pattern of water mite assemblages in the riparian springs. Three limnological types of springs were examined (helocrenes, limnocrenes and rheocrenes) along the whole course of the river and a total of 35 water mite species were found. Our study shows that flooding influences spring assemblages, causing a decrease in crenobiontic water mites in flooded springs. The impact of intermittency resulted in a high percentage of species typical of temporary water bodies. Surprisingly, the study revealed the positive impact of the anthropogenic transformation of the river valley: preventing the riparian springs from flooding enhances the diversity of crenobiontic species in non-flooded springs. In the conclusion, our study revealed that further conservation strategies for the protection of the riparian springs along large rivers would take into account ongoing climatic changes and possible the positive impact of the anthropogenic transformation of river valleys.