Effects of metal pollution across different levels of biological organisation in the River Rhine system with a special focus on Theodoxus fluviatilis as a potential indicator organism

Pollution through anthropogenic activities is a major threat for freshwater ecosystems. Metals are a relevant group of contaminants that affect aquatic organisms, communities, and ecosystems. This thesis aims at examining the effects of metal pollution across different levels of biological organisation in the anthropogenically degraded environment of the German River Rhine system and at discussing the role of the freshwater snail Theodoxus fluviatilis as an indicator organism. A field investigation to detect the effects of metal pollution at the macroinvertebrate community level in the River Rhine system shows that the measured metals are less relevant than geogenic originated factors at the sampling sites (paper 1). Additionally, the community structure is strongly characterised by a separation of non-native taxa in the River Rhine and native taxa in its tributaries. This indicates that the occurrence of invasive species could possibly be a factor structuring the macroinvertebrate community to such a high extent that the effects of other stressors are masked. Regarding the effects of metal pollution on the population, organism, and physiological level of the Danubian form of T. fluviatilis in the River Rhine, only the metal chromium affects the snail specimens negatively (paper 2). As the Danubian T. fluviatilis seems to be able to cope with the partly high concentrations of copper and zinc at the sampling sites, its suitability as an indicator for metal pollution is questionable. However, in the practice of Rhine monitoring, a distinction between the two occurring, phylogenetically different forms of T. fluviatilis is not made, though the original, native indicator has been replaced by the presumably more tolerant non-native Danubian form. An intraspecific variability in T. fluviatilis is assumed, for what first indications are found regarding differences in the infection of the two forms with parasitic trematodes (paper 3). The investigations about a possible intraspecific variability have to be complemented by comparative laboratory analyses, for which purpose an experiment with the two forms of T. fluviatilis is developed (paper 4). The results of this thesis show that investigations about the effects of pollutants in ecosystems should encompass a variety of responses across different levels of biological organisation, as well as the co-occurrence and interaction of various abiotic and biological stressors. Further, a possible intraspecific variability in the indicator organism T. fluviatilis has to be included in the monitoring strategies and ecological assessment of the anthropogenically degraded River Rhine system

The Danubian cryptic invader Theodoxus fluviatilis (Gastropoda: Neritidae) in the River Rhine: a potential indicator for metal pollution?

Metal pollution poses a major threat to aquatic systems especially in anthropogenic influenced areas, in as much as metals are persistent in the environment. The freshwater snail Theodoxus fluviatilis has often been used as an indicator species for the ecological status in river monitoring. In the River Rhine, the native Northern-European form of T. fluviatilis is nowadays extinct, whilst the Danubian form is spreading along the river. The aim of our study was to investigate if the cryptic invader is affected by metal exposure present in the River Rhine and to discuss its potential as an indicator for metal pollution. Several environmental abiotic (14 water environmental variables plus five common metal concentrations in water and biofilm) and biotic parameters (biofilm mass) were measured across 23 sites along the River Rhine. Five population and six histopathological parameters were evaluated on snails collected at all 23 sites. Aqueous chromium concentration was positively correlated to the damage of male reproductive organs of T. fluviatilis, and higher ammonium concentration was correlated to a decrease in snail size and an increase in the proportion of juveniles. None of the analysed snail parameters was negatively correlated to concentrations of other metals measured, like copper and zinc. Therefore, based on the parameters evaluated, our results indicate that the Danubian form of T. fluviatilis is only restrictedly suitable as an indicator for metal pollution in the River Rhine system. Further field and laboratory investigations including other stressors are necessary to evaluate the indicator potential of the cryptic invader holistically

The Danubian cryptic invader Theodoxus fluviatilis (Gastropoda: Neritidae) in the River Rhine: a potential indicator for metal pollution?

Metal pollution poses a major threat to aquatic systems especially in anthropogenic influenced areas, in as much as metals are persistent in the environment. The freshwater snail Theodoxus fluviatilis has often been used as an indicator species for the ecological status in river monitoring. In the River Rhine, the native Northern-European form of T. fluviatilis is nowadays extinct, whilst the Danubian form is spreading along the river. The aim of our study was to investigate if the cryptic invader is affected by metal exposure present in the River Rhine and to discuss its potential as an indicator for metal pollution. Several environmental abiotic (14 water environmental variables plus five common metal concentrations in water and biofilm) and biotic parameters (biofilm mass) were measured across 23 sites along the River Rhine. Five population and six histopathological parameters were evaluated on snails collected at all 23 sites. Aqueous chromium concentration was positively correlated to the damage of male reproductive organs of T. fluviatilis, and higher ammonium concentration was correlated to a decrease in snail size and an increase in the proportion of juveniles. None of the analysed snail parameters was negatively correlated to concentrations of other metals measured, like copper and zinc. Therefore, based on the parameters evaluated, our results indicate that the Danubian form of T. fluviatilis is only restrictedly suitable as an indicator for metal pollution in the River Rhine system. Further field and laboratory investigations including other stressors are necessary to evaluate the indicator potential of the cryptic invader holistically