Agnieszka Szlauer-Łukaszewska

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.

The Effect of Dredging of a Small Lowland River on Aquatic Heteroptera

Rehabilitation of river beds is sometimes necessary, particularly when a substantial amount of bottom sediment causes unnaturally slow water flow. However, it is difficult to predict whether such procedures will negatively affect biodiversity and species composition of organisms inhabiting these sites. The effects of such procedures were analysed in the Krąpiel river in northwestern Poland. It was postulated that dredging would not reduce Heteroptera diversity, but would alter the habitat significantly and create lotic habitats for rheophilous species. It was also postulated that conditions would become less favourable for taxa preferring a bottom with accumulated mud and abundant vegetation. According to our results, dredging did not significantly affect species diversity of Heteroptera, but did cause an increase in abundances of several species. Dredging increased the number of available habitats, which were mainly inhabited by abundant pioneer species. Aquarius najas, Aphelocheirus aestivalis, Plea minutissima, Sigara falleni, Notonecta glauca, Iliocoris cimicoides and Gerridae were most successful in recolonizing the sites after dredging. CCA showed that detritus and the effects of dredging were crucial to the distribution patterns of heteropteran species in this river.

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.

Groynes: a factor modifying the occurrence of dragonfly larvae (Odonata) on a large lowland river

The regulation of rivers and their valleys has had a strong, negative influence on the maintenance of their original biota. Nevertheless, some hydro-engineering works conducted along already regulated rivers may be beneficial, creating habitats for endangered species and assemblages. Such works include the construction of groynes. We analysed this effect on the occurrence of dragonfly larvae along middle and lower stretches of the Oder, where groynes were built over a distance of 306km, creating an area of uniform habitat. We demonstrated that the presence of groynes increased not only the abundance of dragonfly larvae, but also the species richness and diversity of these insects. Habitats were recreated for assemblages typical of a river with highly diverse habitat conditions, from typically riverine assemblages to those occurring in oxbow lakes, also endangered by regulations. The fauna along the stretches with groynes was richer and more valuable than that along the stretches without groynes, achieving values approaching those obtained from modelled unregulated rivers. This can be put down to greater habitat heterogeneity and groyne-reduced levels of waves produced by ships. The presence of groynes provides the key to the restoration or stabilisation of the populations of certain species and to renaturalisation processes.

Aulodrilus pigueti Kowalewski, 1914 (Annelida: Clitellata) – a new record for the Polish fauna from the Oder River and remarks on other oligochaetes rarely noticed in Poland

Abstract The cosmopolitan freshwater oligochaete Aulodrilus pigueti Kowalewski, 1914 (Naididae: Tubificinae) was recorded for the first time in Poland. The species was found at a few groyne field sites and in the main flow of the middle and lower course of the Oder River. Forty two other species of oligochaetes were found in the analyzed material, including rarely found in Poland Aulodrilus japonicus and Bothrioneurum vejdovskyanum, as well as alien species: Branchiura sowerbyi and Quistadrilus multisetosus.

First record of parasitism of water mite larva (Acari: Hydrachnidia) on the pupa of Trichoptera

During the studies on ecology of Trichoptera of anthropogenic water bodies we have unexpectedly discovered the parasitic larvae of water mites of the species Tiphys torris on the pupa of Triaenodes bicolor. This is the first documented case of the parasitism of water mites on the caddisfly pupa as well as the first ever record of the species which is regarded as a dipteran parasite on caddisflies. The situation is very untypical for preimaginal stages of caddisflies are used by phoretic and not parasitic water mite larvae. Parasitism has been confirmed in this case by the formation of stylostomes and enlarged sizes of the bodies of the larvae. This is probably the case of facultative parasitism in which the pupa has served as a substitute of the adult form of a caddisfly.

Environmental factors determining the distribution pattern of leeches (Clitellata: Hirudinida) in large river systems: A case study of the Oder River system

Abstract The largest rivers in Europe are under strong human pressure, resulting in habitat changes and consequently in structural changes in the quantitative and qualitative composition of fauna assemblages. The aim of this study was to identify the taxonomic structure of leech assemblages and the main environmental factors influencing their distribution pattern on a 306 km stretch of the Oder River encompassing different habitat types. Representatives of 28 leech taxa were recorded in 527 samples of bottom macrofauna. The most abundant and most frequently recorded species was the eurytopic Erpobdella octoculata, occurring in all examined habitat types. Although a significant influence of habitat type on the species composition of leech assemblages was noted, a significant positive correlation with habitat type was found only in the case of Piscicola pojmanskae and P. geometra. Our results show that abundance of food resources was the most important factor influencing the distribution of leeches.

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.

First record of Jaera istri Veuille, 1979 (Isopoda, Janiridae) in Poland: eastward invasion from the Mittelland Canal.

During a survey of zoobenthos along the middle and lower Oder River in October 2011, the Ponto-Caspian isopod, Jaera istri Veuille, 1979, was collected for the first time in Poland, ca. 160 km east from its earlier known localities in the river Elbe. The species was found in several locations in the lower part of the river: mostly downstream from the mouth of the artificial canal joining the river Havel in Germany to the Oder. As the species was not recorded in the Oder during extensive sampling in 2009 and in 2010, we can assume that it arrived in the Oder recently through the Havel-Oder Canal. No individuals of the species were found in the Oder more than 30 km upstream of the canal mouth so far.

Co-occurrence of Sinanodonta woodiana with native Unionidae in the lower Oder

Abstract The Asiatic bivalve Sinanodonta woodiana (Lea, 1834), which is more and more widespread in all parts of Europe, in Poland has been mostly reported from lentic waters, especially fish ponds. In contrast to some other European countries, no data have been published on its presence in rivers of Poland. In 2015, monitoring was carried out in the lower Oder River and in the mouth of the Warta River, as a result of which S. woodiana was recorded there for the first time. This was possible due to prolonged drought, which led to extremely low water levels in most of the inland water bodies and watercourses, so that other research methods could be used. The presented results confirm that the species spreads easily by colonizing waters of various types, which in the future may lead to the formation of large populations.