A first attempt at a holistic analysis of various influencing factors on the fish fauna in the Eastern European Alps

Fish are some of the most threatened vertebrates in the world due to their often-sensitive response to environmental changes. Major land-use changes in the European Alps have direct and indirect impacts on fish communities, and these impacts are expected to increase in the future. Therefore, the identification of factors that are associated with the distribution of fish communities is of great importance to develop guidelines for management, precautions and sustainable use of running waters. In this study, the relationship of various factors - landscape structure and land use, topography, morphology, hydrology, physical and chemical water characteristics, hormonally active substances, pesticides, food availability, fisheries and piscivores birds - with fish assemblages are analysed. Field data from 81 stream sections from 2001 metres above sea level (m.a.s.l.) down to 219 m.a.s.l. are used in the study. The results reveal that the number of fish species has a strong association with topographic characteristics in the catchment area as well as with landscape configuration. Fish abundance and biomass are associated mostly with land-use type, hydrology, morphology as well as topography. In addition, there are indirect connections between fish abundance and biomass through land-use type, topography, water properties and hydromorphology. The results clearly indicate that not a single factor, but a multitude of factors are associated with the fish communities in the Eastern European Alps.

Response of ectomycorrhizal and other Pinus sylvestris root-associated fungi to the load of allochthonous material from a great cormorant colony

Colonies of piscivorous birds nesting in forests bring in loads of allochthonous material in amounts significantly exceeding atmospheric depositions, eventually causing major ecosystem changes. We studied the effect of increasing ornithogenic impact on ectomycorrhizal (EMF) and other root-associated fungi in a Scots pine forest affected by a colony of great cormorants. We evaluated quantitative data of ectomycorrhiza (numbers of root tips and morphotypes) and identified fungal species from pine root tips and from sporocarps collected in three designated study zones: D (zone of active nesting), E (colony margin), and G (pristine forest). Species-bearing sporocarps were absent in zone D, and their number steadily decreased in zone E and was significantly lower than in zone G. Species communities and occurrence frequencies of individual species differed significantly between the zones. Environmental factors, both directly (nutrient addition) and indirectly (changes in vegetation cover), associated with bird activity have significantly influenced fungal communities. We hypothesize that the first signs of increased avian impact on root-associated fungi are the reduced diversity of sporocarps and the low presence and diversity of boletoid fungi in root tips.

Effects of multiple stressors on the distribution of fish communities in 203 headwater streams of Rhine, Elbe and Danube

Fishes in European rivers are threatened by manifold stressors such as structural degradation, water pollution, overexploitation, land-use changes in the catchment, invasive species and global processes including climate change. Identifying main stressors in a stream/river system is of utterly importance for efficiently utilizing the scarce funds for conservation measures in order to achieve the best possible outcome. Within 203 headwater streams of Rhine, Elbe and Danube, we quantified the relative influence of different environmental stressors (water chemistry, food availability (macroinvertebrates), terrestrial predators) and anthropogenic stressors (land use, structural modification of streams) on fish assemblages at different spatial scales based on multivariate biota-environment models. In our analyses, the predictor variables percentage of impoundments, crop farming (especially erosion-prone crops such as maize) and ground sealing in the catchments, the number of wastewater treatment plants and biogas plants in the catchments as well as structural modifications of river banks were most often identified as stressors influencing fish community composition. However, the effects of the stressors varied between the investigated survey-area scales (two different catchments sizes and riparian strips) and regionally (entire study area, major drainage systems, river catchments, stream sizes, geographical subregions). In most cases, fish community composition was simultaneously affected by multiple stressors, underpinning the need for a more holistic and ecosystem-based approach in freshwater conservation and restoration.

Spatio-temporal variability of ichthyophagous bird assemblage around western Mediterranean open-sea cage fish farms

Ichthyophagous birds aggregate at cage fish farms attracted by caged and associated wild fish. Spatio-temporal variability of such birds was studied for a year through seasonal visual counts at eight farms in the western Mediterranean. Correlation with farm and location descriptors was assessed. Considerable spatio-temporal variability in fish-eating bird density and assemblage structure was observed among farms and seasons. Bird density increased from autumn to winter, with the great cormorant being the most abundant species, also accounting largely for differences among farms. Grey heron and little egret were also numerous at certain farms during the coldest seasons. Cattle egret was only observed at one farm. No shags were observed during winter. During spring and summer, bird density decreased markedly and only shags and little egrets were observed at only a few farms. Season and distance from farms to bird breeding/wintering grounds helped to explain some of the spatio-temporal variability.

Accumulation of Mercury in The Tissues of the Great Cormorant (Phalacrocorax carbo) From Common Carp

The aim of this work is to assess mercury content in the great cormorant in the Třeboň region pond systems (Czech Republic) in terms of its potential to accumulate mercury from common carp. Selected tissues samples were taken from 51 cormorants and 30 common carp. In the food chain the cormorant was found to have the potential to accumulate mercury, where the muscle total mercury was roughly 35 times higher compared to the total mercury content in the carp muscle as its food. A statistically significantly higher overall mercury content (p < 0.01) has been found in the kidney and liver (2.23 ± 0.30, 2.12 ± 0.22 mg/kg) compared to other tissues examined in cormorants. The proportion of muscle methylmercury in the total mercury content of the cormorant was within the range 64.3%-87.3%. The results can help us to gain a better understanding of how mercury is distributed and accumulated in the aquatic food chain.