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Biological invasions may act as conduits for pathogen introduction. To determine which invasive non-native species pose the biggest threat, we must first determine the symbionts (pathogens, parasites, commensals, mutualists) they carry, via pathological surveys that can be conducted in multiple ways (i.e., molecular, pathological, and histological). Whole animal histopathology allows for the observation of pathogenic agents (virus to Metazoa), based on their pathological effect upon host tissue. Where the technique cannot accurately predict pathogen taxonomy, it does highlight pathogen groups of importance. This study provides a histopathological survey of Pontogammarus robustoides (invasive amphipod in Europe) as a baseline for symbiont groups that may translocate to other areas/hosts in future invasions.

Non-indigenous species (NIS) contribute to the decrease of native species’ diversity on a local and global scale. One of Europe's most significant donors of freshwater invasions is the Ponto-Caspian region. Following the construction of artificial canals connecting isolated water bodies and resulting heavy boat traffic, the Ponto-Caspian Amphipoda started to spread in Europe. Four species: Dikerogammarus haemobaphes, Dikerogammarus villosus, Pontogammarus robustoides and Chaetogammarus ischnus invaded Masurian Lakeland (North-Eastern Poland). Based on the literature and our data, we studied their distribution in 14 lakes in the region in the years 2001 - 2016. We analysed their distribution against several water quality parameters and levels of anthropogenic pressure. Our results are also the first records of two new invaders - D. villosus and C. ischnus in the studied area. We show that the relative abundance and frequency of these two species rapidly increase, and simultaneously the populations of the older invaders, D. haemobaphes and P. robustoides, decrease. The native species - Gammarus lacustris - seems to be negatively affected by NIS richness as well as by the proximity of cities. The NIS found in the lakes appear to be facilitated by boating and the lower complexity of the shoreline. Our study shows how anthropogenic pressure and tourism in the specific, may directly aid bioinvasion, mining the survival of native biodiversity without proper regulation.

Additional file 4: Maximum-Likelihood phylogenetic reconstruction based on small ribosomal subunit (SSU) rDNA for the microsporidian genus Dictyocoela (detailed version of Fig. 3). Maximum-Likelihood phylogenetic reconstruction based on small ribosomal subunit rDNA for the microsporidian genus Dictyocoela infecting amphipods. Four taxa including infections in G. balcanicus were ascribed a color i.e. D. duebenum (grey), D. muelleri (red), D. roeselum (green) and D. berillonum sl (blue). While the three later clades strictly reflect recent reassessment of the genus taxonomy by Bacela-Spychalska et al. (2018), the former one putatively extends this taxon i.e. D. duebenum sl (see text and Additional files 2, 5). Sequences used for species formal description by Bacela-Spychalska et al. [24] are indicated with a star (*). Haplogroups from the present study are in bold. Dictyocoela sequences from Genbank include the accession number and the host species abbreviated name(s) (see Additional file 2). Values at nodes are bootstrap values > 50%.

Additional file 7: Figure S1. Phylogenetic tree for infections by microsporidians of the genus Dictyocoela in European freshwater amphipods, including all haplogroups. Bayesian phylogenetic reconstruction based on small ribosomal subunit rDNA alignment of Dictyocoela spp. Dictyocoela cavimanum was used as outgroup. Divergent lineages were ascribed to the same color code as Fig. 5, and follow recent reassessment of the genus taxonomy by Bacela-Spychalska et al. [24]. Sequences from the present study are in bold and labels include haplogroup names, and the hosts found infected by the haplogroup. Sequences from GenBank are all other Dictyocoela haplogroups (Additional file 4: Table S3). Labels include, in this order, the accession number, the microsporidia species name given in the associated publication and the species abbreviated name(s). For abbreviations of host species names: see Additional file 4: Table S3. Numbers on the branches indicates Bayesian posterior probability.

Additional file 5: Data S2. Alignments based on SSU rDNA sequences, used for trees in Figs. 2, 3, 4, 5 and Additional file 1: Figure S1.

Additional file 3: Data S1. Alignments based on SSU rDNA sequences, used for Additional file 2: Table S2.

Additional file 6: Data S3. Sequences under 200 bp for which no GenBank number can be attributed.

13 pages; International audience; 1. The alien freshwater amphipod of Ponto-Caspian origin, Dikerogammarus villosus, also known as the killer shrimp, is recognized as being one of the worst invasive alien species in Europe, representing a major conservation problem. 2. Recently, the species has been reported to invade lakes in the Alps in putative association with overland transport linked with recreational activities. 3. This study provided a method to assess risk associated with this overland transport and an opportunity to set up a rationale for effective preventive conservation management. 4. A field survey of 60 lakes encompassing all the Alpine area has revealed the presence of killer shrimp in 12 lakes. Subsequent multivariate data analysis showed that the occurrence of the amphipod was associated predominantly with large lakes at low altitudes and high recreational boating activity, always inhabited by the invasive zebra mussel (Dreissena polymorpha). The distribution pattern of killer shrimp was not associated with water conductivity and pH. 5. Laboratory experiments demonstrated that, compared with two other amphipods Gammarus pulex and G. roeselii, killer shrimp seems to attach itself more effectively to ropes used by boaters, as well as diving wetsuits. They remained attached to the ropes even while being strongly shaken for 5 min (mimicking movements associated with overland transport). Moreover, the species is able to survive up to three and a half days out of water, between the layers of diving wetsuits. 6. These results show that even in isolated Alpine lakes there is a high risk of overland spread of killer shrimp by recreational boats and diving wetsuits. Thus, even simple measures such as mechanical cleaning and washing of water sports gear would greatly reduce such risk.

Additional file 5: Maximum-Likelihood phylogenetic reconstruction based on small ribosomal subunit rDNA, as well as ITS and LSU when available, for taxon sub-sampling of Additional file 4, aiming at providing evidence of support of some key clades. Four taxa including infections in Gammarus balcanicus were ascribed a color i.e. Dictyocoela duebenum (grey), D. muelleri (red), D. roeselum (green) and D. berillonum sl (blue). Values at nodes are bootstrap values. Specimens representative of diversity and divergence within each clade were used. Sequences used for species formal description by Bacela-Spychalska et al. [24] are indicated with a star (*).

Additional file 5: Maximum-Likelihood phylogenetic reconstruction based on small ribosomal subunit rDNA, as well as ITS and LSU when available, for taxon sub-sampling of Additional file 4, aiming at providing evidence of support of some key clades. Four taxa including infections in Gammarus balcanicus were ascribed a color i.e. Dictyocoela duebenum (grey), D. muelleri (red), D. roeselum (green) and D. berillonum sl (blue). Values at nodes are bootstrap values. Specimens representative of diversity and divergence within each clade were used. Sequences used for species formal description by Bacela-Spychalska et al. [24] are indicated with a star (*).

We carried out a macroinvertebrate recolonization study in historically dry channels in the Krka National Park. The drying occurred through plant overgrowth. Invasive plant species Ailanthus altissima took over a part of the area with several streams at a tufa barrier causing the flow to change. Some of the active tufa-depositing habitats disappeared leading to changes in ecological features of the area. The revitalization and recolonization occurred after removal of the invasive trees. Streams revitalization contributes to the restoration of the balance in aquatic community, food chains and improves the circulation of organic matter, making a positive influence on biodiversity. Our goal was to determine the rate of recolonization for the macroinvertebrate taxa in the rewetted habitat that were completely dry until recently. We sampled the four non-concurrently rewetted sites to 3 cm depth monthly during the inital recolonization period. Simultaneously, we measured the physico-chemical properties of the water at each site. The most dominant recolonization i.e. pioneering taxa were non-biting midges and blackflies. They were among the most abundant taxa in the control site but their abundance was significantly higher in the revitalized channels. Beetles were the second most abundant taxon at the control site but also the taxa that recolonized the least. Judging by the number of taxa, the least favorable for the recolonization were the habitats at the most recenly rewetted channel. In addition, this was the channel that suffered the most severe loss of structure. Finally, most of the taxa at the control site were present at the revitalized channel 4 months after rewetting.

Predation is a biotic interaction that links water mites to different taxonomic groups and life stages of benthic invertebrate communities. Diptera larvae (Chironomidae, Ceratopogonidae) and microcrustaceans (Cladocera, Copepoda, Ostracoda) are determined as most common water mite prey preferences. Although these predation interactions are known from observations and ex-situ investigations, the distribution patterns and co-occurrence of water mites and their prey in littoral lentic habitats are not well known. Our goal was to determine if predation was a significant driver in water mite assemblage composition and distribution. Samples were taken from at least two littoral sites of twenty-one man-made lakes in the Dinaric ecoregion of Croatia (larger lakes had up to 6 sites). At every site ten samples were collected with regard to microhabitat composition and shore slope (depth). In total 490 samples were taken. On a longitudinal benthic profile (shoreline to one meter depth) of the littoral zone water mites showed no specific tendencies of grouping according to neither depth (p>0.05), nor microhabitat composition (p>0.05) but rather to other invertebrate groups they are known to prey on. Water mite abundances were found to positively correlate with those of Cladocera, Copepoda, Ostracoda, Ceratopogonidae, Chironomidae (p

Considering macroinvertebrate's inevitable role in energy flow of ecosystem, they are regarded excellent indicator of total ecological condition. Perceiving and researching both the community structure and biology of specific taxa therein, is fundamental for understanding the complex interactions within ecosystem. Accordingly, the aim of our research was to define and compare macroinvertebrate communities at the spring and at the tufa barrier of Plitvice Lakes (Croatia). Both sites are part of the karst landscape: a cool and environmentally stable, rheocrene spring of Bijela rijeka and a dynamic limestone depositing site at the tufa barrier Labudovac. Secondly, we aimed to determine the size structure and the secondary production of the dominant taxa. Physicochemical parameters of water were stable at the spring site and expectedly fluctuated at the tufa barrier. The most abundant taxon at the tufa barrier were non biting midges whilst stoneflies were dominant at the spring site. Since non biting midges are currently identified to family level, further ecological analyses were not advisable so we focused on the stoneflies. Stoneflies from both sites predominantly belong to Protonemura genus. After measuring the width of head capsules, using Scott's formula we found that Protonemura develops over a 14 stage cycle and individual mass 83 times during the life cycle. Secondary production calculated using the Size-frequency method was approximately 5 g per m²/year.

Reservoirs are man-made water bodies that are usually created by using a dam or lock to store water that can be used for the production of electric energy, irrigation or flood control. The family Chironomidae is widely distributed and often among the most abundant taxa in benthic macroinvertebrate communities of reservoirs, and they are frequently used in the ecological quality assessment of these habitats. Littoral macroinvertebrate samples were collected from May to October 2016/2017 in 21 reservoirs of the Dinaric region in Croatia. With regard to the surface area of the reservoir, from 2 to 6 sampling locations were chosen in analysed man-made lakes. A sampling site covered the length of 25 m lakeshore and a distance of 10 m towards the open water – or alternatively, to the point at which the water depth exceeded 1 m. At each sampling site, a total of ten samples was collected using a benthos hand net (25 cm × 25 cm ; 500 μm). In the littoral microhabitat type, the strata are defined as a combination of a depth class and a substrate category proportionate to their coverage in the sampling site. Four waterdepth classes were defined: 0–0.25 m, 0.25–0.5 m, 0.5–0.75 m and 0.75–1 m. A total of 490 samples were analysed. Totally 112 358 chironomid larvae were found, belonging to 5 subfamilies and 61 taxa. Bray-Curtis based non-metric multidimensional scaling analysis based on chironomid assemblages clearly separated reservoirs with a very short water retention time. These reservoirs were characterised with the presence of lotic faunal elements, and species such as Paratendipes albimanus and Micropsectra contracta were present only in these reservoirs. In general, species richness was found to decrease with higher values of pH and water temperature (p

Reservoirs are heavily modified lentic waters, usually derived from lotic habitats. They are complex systems that represent a transitional ecosystem between lakes and rivers with substantial ecological impact on not only the remaining lotic habitat but also the surrounding terrestrial ecosystem. Specific macroinvertebrate communities, usually consisting of high ratios of resilient euryvalent taxa, inhabit these artificial lentic habitats. Our goal was to test how anthropogenic abiotic factors such as land cover, water fluctuations, and littoral zone depth (slope) influence benthic macroinvertebrate community composition. Macroinvertebrate communities were studied at 15 reservoirs located in the Pannonian ecoregion of Croatia. Prior to sampling at each reservoir, sites with both “more natural” and “less natural” shorelines were selected. The sampling site covered 25 m of lakeshore length up to a distance of 10 m towards the open water, or to a point where the depth of water surpasses 1 m, depending on the steepness of the shore. Four levels of depth were defined: 0 to 0.25 m, 0.25 m to 0.50 m, 0.50 m to 0.75 m and 0.75 m to 1.00 m and ten samples were collected using a 25 × 25 cm benthos hand net (500 μm mesh) at each site. Non-metric Multidimensional Scaling Analysis (nMDS) of littoral benthic macroinvertebrate community similarities between reservoirs showed clustering of locations with similar water level fluctuations. One group consisting of reservoirs with water fluctuation above, and the other one with water fluctuation less than one meter. Differences in community composition between these two groups of reservoirs are due to the macroinvertebrate community’s ability to adapt to rather harsh conditions of habitats that remain after the water is withdrawn or abruptly inundated. Land cover of the catchment area was examined in relation to the macroinvertebrate community species richness, abundance and alpha diversity. Increased ratios of intensive agricultural surfaces in the catchment area were positively correlated with species richness and alpha diversity (p

Supposedly, there is a process going on called climate change. The issue has been somewhat trumped recently though. Nevertheless, there are data and predictions that precipitation volume and its locations may be altering, and it seems we are witnessing these changes. Simultaneously, temperatures fluctuate and coincidentally or not at similar locations as for aforementioned water dynamics shifts. Water dynamics, consequently may differ from what biota is adapted to in a respective aquatic habitat. That is why many freshwater researchers are focusing their investigations towards this issue. We have done a study in which we mimicked water scarcity at an ecosystem level. At a tufa barrier where normally, aquatic and other vegetation limits the flow, creating lotic channels, we enabled broader flow area by removing the vegetation. With its removal, water level dropped and flow velocity decreased – hence mimicking water scarcity event. We focused research on moss mats at normally open canopy sites and away from removed vegetation to avoid including physical effects of vegetation removal other than the flow change. We sampled the moss mats half a year before the impact and half a year after it. In second study, we observed changes in macroinvertebrate communities in a mountain stream at an artificially broadened site that resulted in similar changes – flow inhibition and water level decrease. In both cases, inhibited flow caused a decrease in macroinvertebrate abundance and diversity. Rheophilic taxa were the most impacted. In addition, we noted an increase in detrital accumulation especially for the fine detritus.