Shallow-water benthic macroinvertebrate community of the limnic part of a lowland Polish dam reservoir

AbstractBiodiversity, abundance and taxonomic composition of shallow-water zoobenthos were studied in the Włocławek Dam Reservoir (the lower Vistula River, central Poland). The following habitats located near the shore were studied: (1) sandy bottom in the flooded part of the reservoir; (2) sandy bottom close to the main riverine flow in the reservoir and (3) organic-rich bottom covered by a thick layer of plant remnants in a shallow, isolated cove. In each habitat we investigated two sites (ca. 0.5 and 1m depth). Also examined was the bottom of a phytolittoral site (sandy bottom, with elodeids and nympheids, 1m depth), located in the flooded zone. In general, the bottom fauna was highly diverse and abundant in these habitats. The highest biodiversity (38 taxa, Shannon–Wiener index=4.3) was found on the bottom rich in organic matter. However, the zoobenthos abundance in this habitat was comparatively low, probably due to periodical oxygen deficiencies. The highest density of bottom fauna (>30,000 individuals per m2), accompanied by its high biodiversity, occurred at the phytolittoral site. The benthic community of the organic-rich sediments was the most distinct, with many taxa occurring exclusively in this area. The composition of the bottom fauna, from the two sandy habitats and phytolittoral, also differed from one another. The differences in taxonomic composition between the shallower and deeper sites were less pronounced. Lower densities at the shallower sandy sites and a very high variability of taxonomic composition among particular samples from these sites indicated lower stability of their environmental conditions. These were certainly due to water level fluctuations and/or destructive wave action. On the other hand, no such differences were found between the sites of various depths from the organic-rich sediments, showing that this substratum provided better protection against adverse hydrodynamical factors

The impact of zebra mussel (Dreissena polymorpha) periostracum and biofilm cues on habitat selection by a Ponto-Caspian amphipod Dikerogammarus haemobaphes

Dikerogammarus haemobaphes is one of several Ponto-Caspian gammarids invading Europe in recent decades. Previously, it exhibited active preferences for habitats associated with another Ponto-Caspian alien, zebra mussel. Now we tested gammarid preferences for living mussels and their empty shells with biofilm and/or periostracum present or absent, to find the exact cues driving gammarid responses. We observed a strong preference of gammarids for biofilmed shells, even if the biofilm was relatively young (2-day old). However, the biofilm quality, related to the substratum on which it had developed (shells with or without the periostracum, or coated with nail varnish) did not affect their behaviour. In the absence of biofilm, gammarids positively responded to the shell periostracum. Furthermore, they clearly preferred living zebra mussels over old empty shells, independent of the presence or absence of biofilm, confirming the importance of a periostracum-associated cue in their substratum recognition. On the other hand, shells obtained shortly after mussels’ death were preferred over living bivalves. Thus, the attractant is associated with fresh mussel shells, rather than with living mussels themselves. The ability of alien gammarids to locate sites inhabited by zebra mussels may contribute to their invasion success in novel areas inhabited by this habitat-forming bivalve

Contribution of invasive bivalves (Dreissena spp.) to element distribution: phase interaction, regional and seasonal comparison in a large shallow lake

After introduction, the invasive bivalve dreissenids became key species in the biota of Lake Balaton, the largest shallow lake in Central Europe. The contribution of dreissenid soft tissue and shell, as biotic phases, in element distribution and its interaction with the water and upper sediment phases were examined in two basins with different trophic conditions in spring and autumn. Six metals (Ba, Cu, Fe, Mn, Pb, Zn) were detected in all investigated phases. In general, metals were abundant in the water and soft tissue in the eastern basin in spring, and in the sediment and shells in the western basin in autumn. This might be associated with the more urbanized surroundings in the eastern, and the enhanced organic matter production in the western basin. High relative shares of Ba, Cu, Mn, and Pb were associated with the water and shell samples, whereas high shares of Fe and Zn were noted in the soft mussel tissue and sediments. Results suggest that dynamics of metal uptake by dreissenids depend on the seasonal change in metabolic activity. Shell metal content is less changeable; shells might absorb metals from both the soft tissue and water phases. Metallothionein peptides, the scavengers of intracellular metals, were determined to be biomarkers of the bulk contaminants rather than only metals. The present study shows that invasive bivalves, with high abundance, filtering activity, and storing capacity can significantly contribute to element distribution in the shoreline of a shallow lake ecosystem

The Braveheart amphipod: a review of responses of invasive Dikerogammarus villosus to predation signals

Predator pressure is a fundamental force driving changes at all levels of the community structure. It may protect native ecosystems from alien species. Therefore, resistance to diverse predators resulting from a universal anti-predator strategy seems crucial for invasion success. We present a comprehensive review of the responses of an invasive amphipod Dikerogammarus villosus to sympatric and allopatric predator signals. We summarize diverse aspects of the gammarid anti-predator strategy, including predator identification, morphological and behavioural adaptations, effectiveness of shelter use and resistance to indirect predator effects. The response of D. villosus is independent of predator species (including totally allopatric taxa), which assures the high flexibility of its predator recognition system. It has a harder exoskeleton and better capability of utilizing shelters compared to other gammarids, resulting in relatively high resistance to predators. Therefore, it can use predator kairomones as indirect food signals (sharing the diet with the predator) and follow the predator scent. This resistance may allow D. villosus to reduce the costs of its physiological responses to predators and sustain growth in their presence. This might facilitate invasion success by increasing its competitive advantage

Keep calm and don't stop growing: Non-consumptive effects of a sympatric predator on two invasive Ponto-Caspian gammarids Dikerogammarus villosus and Pontogammarus robustoides.

Predators shape prey populations by elimination of individuals (consumptive effects) and by inducing modifications in prey behaviour, physiology or morphology (NCE-non-consumptive effects). Due to the resource allocation to defence, decreased feeding and higher stress, the costs of predator NCEs can be considerable. Therefore, the resistance to NCEs may be crucial for population growth and interspecific competition. We tested the resistance of Ponto-Caspian gammarids Dikerogammarus villosus and Pontogammarus robustoides to NCEs imposed by their predator, the racer goby Babka gymnotrachelus. As D. villosus is often avoided by predators in the presence of alternative food, we hypothesised that it would bear lower behavioural and physiological costs of anti-predator responses. We tested gammarid feeding in short-time experiments (2-4 h) with food (chironomid larvae) located at various distances from the stony shelter (to enforce food searching, Experiment I) or in the direct gammarid proximity (no searching needed, Experiment II). Moreover, we checked the predator effect on gammarid growth in a 2-week Experiment III. Both gammarids exposed to predators reduced feeding efficiency outside the shelter (Experiment I). Contrary to our expectations, the response of D. villosus was stronger. When food was provided in their direct proximity (Experiment II), the feeding of both species was unaffected by predators, indicating that a shelter supplied with food can reduce predator NCEs. The growth of P. robustoides was reduced in the presence of predators (Experiment III), whereas that of D. villosus was unaffected. Although D. villosus has a more effective defence strategy than P. robustoides, it bears similar or even higher behavioural costs of NCEs. However, it exhibits the higher resistance to the long-term predator presence, sustaining its growth rate under such conditions. This may be one of the factors contributing to the great invasion success of D. villosus, currently taking place in European fresh waters

Shelter competition between the invasive western tubenose goby and the native stone loach is mediated by sex

Shelter, regarded as a protection against predators and/or nesting site, constitutes one of the basic resources for which organisms compete in the wild. Ponto-Caspian gobies are a good example of a territorial species, which can have negative impact on native species with similar biology due to competitive interactions. Thus, the aim of the present study was to investigate the potential impact of the invasive Ponto-Caspian western tubenose goby Proterorhinus semilunaris on the native stone loach Barbatula barbatula through shelter competition. We used male and female gobies in their reproductive season to test whether they would be more aggressive towards native stone loach, accounting for different light conditions in a limited shelter competition scenario. The results of our study showed that both tested species occupied the shelter mostly during the daylight. Only male goby reduced the shelter occupancy of stone loach despite the fact that interspecific aggressive acts were very rare. It was associated with the nest guarding by male gobies, considering that the study was conducted during their reproductive season. Based on our results, it is possible that, under natural conditions, male tubenose goby would force stone loach to stay away from the shelter, especially in late spring and early summer, when gobies are in reproductive state. This might affect stone loach populations by devoiding them of optimum sites and increasing their exposure to predators. </p

Experimental setup for Experiment I to test the effect of the predator presence and food proximity on the consumption of chironomids by gammarids.

<p>Experimental setup for Experiment I to test the effect of the predator presence and food proximity on the consumption of chironomids by gammarids.</p