Péter Sály

Quantifying temporal variability in the metacommunity structure of stream fishes: the influence of non-native species and environmental drivers

Most studies characterize metacommunities based on a single snapshot of the spatial structure, which may be inadequate for taxa with high migratory behavior (e.g., fish). Here, we applied elements of metacommunity structure to examine variations in the spatial distributions of stream fishes over time and to explore possible structuring mechanisms. Although the major environmental gradients influencing species distributions remained largely the same in time, the best-fit pattern of metacommunity structure varied according to sampling occasion and whether or not we included non-native species in the analyses. Quasi-Clementsian and Clementsian structures were the predominant best-fit structures, indicating the importance of species turnover among sites and the existence of more or less discrete community boundaries. The environmental gradient most correlated with metacommunity structure was defined by altitude, area of artificial ponds in the catchment, and dissolved oxygen content. Our results suggest that the best-fit metacommunity structure of the native species can change in time in this catchment due to seasonal changes in distribution patterns. However, the distribution of non-native species throughout the landscape homogenizes the temporal variability in metacommunity structure of native species. Further studies are necessary from other regions to examine best-fit metacommunity structures of stream fishes within relatively short environmental gradients.

Ontogenetic variation in the body stoichiometry of two fish species

One of the central questions of ecological stoichiometry theory is to what extent animal species maintain constant elemental composition in their bodies. Although several recent studies demonstrate intraspecific variation in animal elemental composition, relatively little is known about ontogenetic changes in vertebrates, especially during early life stages. We studied the intraspecific and interspecific ontogenetic variation in the body stoichiometry of two fish species in two different orders; fathead minnow (Pimephales promelas) and sheepshead minnow (Cyprinodon variegatus), reared under controlled laboratory conditions. During ontogeny, we measured the chemical composition of fish bodies, including carbon (C), nitrogen (N), phosphorus (P), calcium (Ca), and ribonucleic acid (RNA) contents. We found that N and RNA contents were relatively high in early life stages and declined substantially during development. In contrast, body C and C:N ratios were relatively low in embryos, post-embryos and larvae, and increased remarkably thereafter. Concentrations and ratios of some elements (e.g., Ca, P, Ca:P) did not exhibit consistent ontogenetic trends, but fluctuated dynamically between consecutive developmental stages in both species. Specific growth rates correlated significantly with RNA contents in both species. Analyses of the relative importance of different P pools at each developmental stage revealed that RNA was a considerable P pool in post-embryos, while bone-associated P was the dominant body P pool in later stages. Our results suggest that the elemental composition of fish bodies changes considerably during ontogeny. Each ontogenetic stage has its own stoichiometric signature, but the timing, magnitude and direction of ontogenetic changes can vary substantially between taxa.

Non-native fish species in Hungarian waters: historical overview, potential sources and recent trends in their distribution

Due to its central position in the Danube basin and its considerable fishery sector, Hungary plays a key role in the spread of non-native fish species in Europe. Nevertheless, the status of non-native fish has not yet been reviewed for Hungary. Therefore, our aims were (1) to give a comprehensive historical overview regarding the occurrence of non-native fish species of Hungary, (2) to show their recent distribution patterns using GIS, and (3) to evaluate the importance of the possible drivers in their spread. Literature data show 59 non-native fish species from Hungary. The appearance of new species—mostly due to aquarium fish releases—shows an accelerating trend nowadays. Although non-native fish have appeared at 78.7% of the studied 767 sites during our recent countrywide survey, their distribution was uneven. Lowland streams, lowland rivers, and the River Danube were the most affected by non-native fish, particularly the gibel carp, topmouth gudgeon and pumpkinseed escaped from fish/angling ponds, and the recent invasion of Ponto-Caspian gobies. Our results indicated that in order to reduce the effects and intensity of further invasions, more rigorous control of aquarium trade, angling pond stockings, and inter-watershed fish transports are necessary.

The scales of variability of stream fish assemblages at tributary confluences

Tributary confluences play an important role in the dispersal of organisms, and consequently, in shaping regional scale diversity in stream networks. Despite their importance in dispersal processes, little is known about how ecological assemblages are organized in these habitats. We studied the scales of variability of stream fish assemblages over three seasons using a hierarchical sampling design, which incorporated three tributaries, three sites at the mouth of each tributary and using four sampling units at each site. We found strong scale dependent variability in species richness, composition and relative abundance. Most of the variation was accounted for by the interactive effect of season, between stream and between site effects, while habitat structure of the sampling units had a relatively minor role. Species richness showed a continuous decrease from the mainstem river in most cases, while species composition and relative abundance changed less consistently along the longitudinal profile. Consequently, we found that not only the junctions presented a strong filter on the species pool, but some species were filtered out if they passed this critical habitat bottleneck. In addition, spatial position of the tributaries along the river also contributed to assemblage variability in the confluences. Overall, our results suggest high variability in fish assemblages across multiple scales at tributary confluences. Environmental management should take a more critical care on the filtering role of tributary confluences in species dispersal, for better understanding patterns and processes in the branches of dendritic stream networks.

Population Genetic Patterns of Threatened European Mudminnow (Umbra krameri Walbaum, 1792) in a Fragmented Landscape: Implications for Conservation Management.

The European mudminnow (Umbra krameri) is a Middle Danubian endemic fish species, which is characterised by isolated populations living mainly in artificial habitats in the centre of its range, in the Carpathian Basin. For their long term preservation, reliable information is needed about the structure of stocks and the level of isolation. The recent distribution pattern, and the population genetic structure within and among regions were investigated to designate the Evolutionary Significant, Conservation and Management Units (ESUs, CUs, MUs) and to explore the conservation biological value of the shrinking populations. In total, eight microsatellite loci were studied in 404 specimens originating from eight regions. The results revealed a pronounced population structure, where strictly limited gene flow was detected among regions, as well as various strengths of connections within regions. Following the results of hierarchical structure analyses, two ESUs were supposed in the Carpathian Basin, corresponding to the Danube and Tisza catchments. Our results recommend designating the borders of CUs in an 80–90km range and 16 clusters should be set up as MUs for the 33 investigated populations. How these genetic findings can be used to better allocate conservation resources for the long term maintenance of the metapopulation structure of this threathened endemic fish is discussed.

Fishes of the Drava River

The chapter presents the fish fauna of the Croatian-Hungarian section of the river by overview the fish faunistic literature of studies conducted between 1992 and 2016, provides an example for littoral fish assemblages, and evaluates the ecological status of a river reach on this basis. It seems that 66 fishes, most of them belong to the family Cyprinidae and one cyclostomata species occur in the studied river section. However, the number of species regularly inhabiting the Croatian-Hungarian section could be about 51, because some species require different habitat type than the main channel of the studied section, or they are not able to reach the studied section due to migration barriers. There are also some taxa with unclear taxonomic status. Twenty-two species are listed in one of the annexes of the European Union Habitats Directive. The ratio of native to non-native species is 52:15. Monkey goby (Neogobius fluviatilis) and western tubenose goby (Proterorhinus semilunaris), two non-native Ponto-Caspian gobies, appear to be among the most abundant fishes in the littoral zone. Recently, other goby species (Ponticola kessleri, and N. melanostomus) formerly not known from the Drava have been found at the lower end of the studied river section and results anticipate their potential future spreading upstream. Fish assemblages tend to mirror an overall good ecological status and the rich fish fauna is of considerable nature conservation value due to the minimum alteration of habitats and the relative geographical proximity of the Danube. Therefore, for an effective conservation of the fish fauna the actual seminatural status of the Drava riverscape is to be maintained.

Do diel variations in stream fish assemblages depend on spatial positioning of the sampling sites and seasons

The effect of diel period (i.e. day vs night) and its dependence on the spatial position of the sampling site were evaluated on the assessment of fish assemblage attributes in a wadeable lowland stream (Hajagos stream, Hungary). Species richness, composition and abundance data of two 150 m long reaches, one situated directly at the tributary mouth and one 6 km upstream were compared using three pass removal by electrofishing in three seasons (summer, autumn and spring) to test the effect of spatial position on day and night patterns. No differences in any assemblage level variables were found between day and night. Although fish assemblages showed large temporal variations, spatial position of the sampling site had the most influential effect on fish assemblage attributes compared with seasonal and/ or day night patterns. Consequently, the diel period had rather negligible effect in the studied stream. Daytime electrofishing data seems to be highly representative for the accurate assessment of fish assemblages in relatively small (less than 5 m wide) wadeable streams and maybe used reliably for any model of community organization (e.g. food web studies).

SOME MORPHOLOGICAL CHARACTERISTICS OF THE WATER SCORPION NEPA CINEREA (HETEROPTERA: NEPOMORPHA) ARE ASSOCIATED WITH HABITAT TYPE*

Morphological variation can enable species to successfully survive and reproduce in distinct habitats. Water scorpion (Nepa cinerea Linnaeus, 1758) occurs in different aquatic habitats from lentic to lotic conditions. We examined the morphology of N. cinerea collected from a diverse array of habitat types (creeks, canals, ponds) in order to explore possible morphological adaptations to the habitat. We addressed the following specific questions: (i) is there any morphological differences between specimens collected from distinct habitats, and if so, (ii) is it possible to relate differences in morphology of the N. cinerea to characteristics of the habitat structure? Altogether 121 individuals (69 males and 52 females) were sampled from 17 sampling sites in the catchment area of Lake Balaton (Hungary). 54 body parameters were determined on all individuals. According to five habitat parameters (bottom quality, current velocity of the water, water depth, submerse plant density, shading) sampling sites were clustered into two distinct groups. Submerse plant density proved to be the most important discriminating factor between the two groups. The morphology of the N. cinerea (both males and females) sampled from the two contrasting habitat types were different. No relationship was found between geographical position of the habitat type and body morphology of N. cinerea. Leg morphology, especially claws on the third leg and some body shape parameters showed relationships with habitat characteristics. These morphological variations, which may be the result of phenotypic plasticity, could contribute to an opportunistic habitat choice of the species.