Ecological aspects,explosive range extension and impact of a mass invader,Corophium curvispinum Sars, 1895 (Crustacea: Amphipoda), in the Lower Rhine (The Netherlands)

A few years after it invaded, the amphipod Corophium curvispinum Sars appeared to be the most numerous macroinvertebrate species in the River Rhine. From 1987 to 1991 the densities of this species on the stones of groins in the Lower Rhine at a depth of 0.5 m increased from 2 to 200000 specimens per m². In the Lower Rhine and its branches the densities of C. curvispinum increased with increasing current velocities and with increasing water depths. So far, a maximum population density of 750000 specimens per m² has been found in the Lower Rhine, which is many times the densities recorded elsewhere. Population parameters, densities and distribution of C. curvispinum were studied in the Lower Rhine and its branches, using artificial substrates and sampling stones from groins. The success of this immigrant is related to its competitive strategy, which shows several aspects of a r-strategy. In addition, the heavily eutrophicated Lower Rhine provides abundant food (phytoplankton, suspended organic matter) for this opportunistic filter-feeder. The increased salinity and water temperatures in the Lower Rhine resulting from industrial discharges have contributed to the current success of this southern species originating in brackish waters. The very high densities of C. curvispinum might have an enormous impact on the river ecosystem by changing food webs.     

Timing of downstream migration and food uptake of juvenile North Sea houting stocked in the Lower Rhine and the Lippe (Germany)

In 1992 a stocking programme was established to re‐introduce North Sea houting Coregonus oxyrinchus , which disappeared from the River Rhine in the 1940s, in the Lower Rhine. Juvenile North Sea houting have been stocked since 2001 in a gravel pit lake permanently connected to the Lower Rhine, and in the Lippe, a potamal tributary of the Rhine. Monitoring studies showed that the majority of the small North Sea houting left the gravel pit lake within 4 days after stocking. In the Lippe, some of the juveniles were found in the drift immediately after stocking, generally preferring the middle surface areas of the river. Other North Sea houting waited until dawn before they started their downstream migration. Juveniles immediately started to feed on the zooplankton resources in both waters. Pond studies revealed high growth rates of juvenile North Sea houting, ranging from 0·44 to 0·94 mm day⁻¹. This study suggests that the stocking strategies at both waters of the Lower Rhine comply with the requirements of the migration behaviour of juvenile North Sea houting.     

Biodiversity of floodplain forests in Europe and eastern North America: A comparative study of the Rhine and Mississippi Valleys

In this study, we investigate the mechanisms driving biodiversity in floodplain forests with a comparison of the composition and dynamics in the warm-temperate floodplain forests of the lower Mississippi Valley and the cool-temperate floodplain forests of the lower Wisconsin and Rhine River Valleys. We employ data from original research, as well as from the literature. We compare species, genus, and family diversity across regions with respect to species richness, numbers of species per family and genus, and a similarity index. We examine these results within a historical context, as well as with respect to river-floodplain dynamics. We also compare productivity data and successional stages for each region. We find a lower species, genus, and family richness in the cool-temperate forests of the Rhine compared to the cool-temperate forests of the Wisconsin, a probable result of the lack of available refugia for Rhine species in times of glacial expansion. We find the highest richness in the lower Mississippi Valley, likely a result of climatic factors and the availability of refugia in this region. In each of the regions, floodplain forests are more diverse than their upland counterparts, demonstrating the role of river-floodplain dynamics in maintaining species diversity. Each region maintains a high and relatively similar level of productivity in the floodplain forests. They also experience similar stages of succession, although succession becomes more complex in the warm-temperate forests of the Lower Mississippi.     

Extensions to the known range of the whitefin gudgeon to Europe and biogeographical implications

In 1998 and 1999, the whitefin gudgeon Gobio albipinnatus was common in the Rivers Rhine, Elbe and in the Lower Odra.     

A New Genus and Species of Scombrid Fish (Perciformes,Scombroidei, Scombridae) from the Lower Oligocene of the Caucasus

A new genus and species of scombrid fish Caucombrus histiopterygius gen. et sp. nov. is described from the Lower Oligocene (Lower Maikopian, Pshekha regional state) of the north-western Caucasus (Russia) and Abkhazia (rivers Belaya, Pshekha and Gumista). The new taxon differs from the other known Scombridae, both fossil and Recent, by the high and sail-like first dorsal fin. Osteological characters of Caucombrus gen. nov. indicate its relationship with the Spanish mackerels (subfamily Scomberomorinae). It is assumed that either C. histiopterygius gen. et sp. nov. or the related species of Caucombrus gen. nov. inhabited the Mid-Oligocene sea basin in the territory of the Rhine Graben (Germany).     

Extremitätenreste einer Mönchsrobbe (Phocidae,Carnivora, Mammalia) aus dem Miozän von Bocholt (Niederrhein)

From the Reinbekian deposits of Bocholt (Lower Rhine) a left femur and the distal fragment of a left tibia are described. A comparison with known fossil specimens results no direct conformity. The morphological relationship of the limb bones is nearest to the Monachinae. They are introduced with the termMonotherium sp. Due to their stratigraphical age, in comparison to younger relations, they own some primitive features.     

Reconstruction of the colonization route from glacial refugium to the northern distribution range of the European butterfly Polyommatus coridon (Lepidoptera: Lycaenidae)

Genetic analyses are useful tools for reconstructing glacial distribution patterns and postglacial expansion corridors. However, little information is available about the latter. We reconstruct the expansion corridors of the butterfly Polyommatus coridon from its glacial refugium to the northern edge of its current distribution by comparing populations from southern Lower Saxony (central Germany) to other existing genetic data sets. The populations from Lower Saxony clearly belonged to a western lineage that expanded postglacially from the Adriatic‐Mediterranean region. They form part of a southern German group passing through the Burgundian Gap. In the southern German group, populations belong to a western subgroup. Therefore, expansion followed the Rhine valley and through Hesse, finally reaching southern Lower Saxony and western Thuringia in central Germany. Thus, we present a complete colonization route from the glacial refugium to the northern distribution range of P. coridon. Such data are useful for understanding the biogeographic structure and migration corridors for other mobile Mediterranean species.     

Diversity,occurrence and feeding traits of caddisfly larvae as indicators for ecological integrity of river-floodplain habitats along a connectivity gradient

In order to assess ecological values of Lower Rhine and Meuse floodplain habitats we studied the spatial and seasonal variation in diversity, species assemblages and feeding traits of caddisfly larvae in water bodies over the lateral connectivity gradient: eupotamon: main and secondary channels; parapotamon: channels connected permanently with the main channel only at their downstream ends; plesiopotamon: disconnected channels close to the main channel; paleopotamon: abandoned meanders at a greater distance from the main channel.Spatial variety was studied by analyzing the summer species composition in 70 Lower Rhine and Meuse water bodies which were categorized in connectivity habitats, whereas seasonal variety was studied in Lower Rhine water bodies along a connectivity gradient by monthly sampling over a whole year. Physico-chemical data and environmental parameters were recorded for each water body during sampling. Diversity and species assemblages of caddisfly larvae varied in relation to connectivity, macrophyte diversity and abundance and stream velocity. A comparison with historical records and species lists from less disturbed rivers showed that diversity in the main channel was very low.Caddisfly larvae species assemblages varied over the connectivity gradient. Lotic habitats (eupotamon) were separated from the lentic ones, and the well vegetated paleopotamon from the sparsely vegetated parapotamon and pleisopotamon habitats, indicating the overall importance of vegetation and current velocity for the species assemblages. Hydropsychidae have been found in the eupotamon exclusively, whereas Limnephilidae, Hydroptilidae and Polycentropodidae have been found predominantly in the paleopotamon water bodies. Leptoceridae were found in all floodplain water body categories. A similar pattern of distribution of families along the lateral connectivity gradient was found in more natural rivers.Caddisfly larvae species feeding traits showed a clear differentiation over the lateral connectivity gradient with filter-feeders and scrapers most important in the eupotamon and parapotamon, and shredders, piercers and predators most dominant in the paleopotamon habitats, indicating the importance of nutritional resources in relation to hydrological connectivity for the structure and functioning of caddisfly larvae species assemblages. The analysis of the species feeding traits allows generalizations towards the entire aquatic community and general prognoses for other floodplain ecosystems.     

Impact of hydrology on the chemistry and phytoplankton development in floodplain lakes along the Lower Rhine and Meuse

The impact of hydrology (floods, seepage) on the chemistry of water and sediment in floodplain lakes was studied by a multivariate analysis (PCA) of physico-chemical parameters in 100 lakes within the floodplains in the lower reaches of the rivers Rhine and Meuse. In addition, seasonal fluctuations in water chemistry and chlorophyll-a development in the main channel of the Lower Rhine and five floodplain lakes along a flooding gradient were monitored. The species composition of the summer phytoplankton in these lakes was studied as well.At present very high levels of chloride, sodium, sulphate, phosphate and nitrate are found in the main channels of the rivers Rhine and Meuse, resulting from industrial, agricultural and domestic sewage. Together with the actual concentrations of major ions and nutrients in the main channel, the annual flood duration determines the physico-chemistry of the floodplain lakes. The river water influences the water chemistry of these lakes not only via inundations, but also via seepage. A comparison of recent and historical chemical data shows an increase over the years in the levels of chloride both in the main channel of the Lower Rhine and in seepage lakes along this river. Levels of alkalinity in floodplain lakes showed an inverse relationship with annual flood duration, because sulphur retention and alkalinization occurred in seepage waters and rarely-flooded lakes. The input of large quantities of nutrients (N, P) from the main channel has resulted, especially in frequently flooded lakes, in an increase in algal biomass and a shift in phytoplankton composition from a diatom dominated community towards a community dominated by chlorophytes and cyanobacteria.     

Siebengebirge – im Saum der Großlandschaften. Die Exkursion

The Siebengebirge Mountains, facing Bonn and situated between the Lower Rhine Bight and the well known Middle Rhine valley, cover an area of only some 4800 ha, but represent a fairly unusual complex with respect to landscape and nature. Already some famous exploring travellors of the 18th century such as Georg Forster, Johann Wolfgang von Goethe, and Alexander von Humboldt consistently emphasized the striking diversity and natural beauty of this area. No other part of Germany has hitherto been dealt with by a comparable array of special (geologically as well as biologically centered) investigations and compiling contributions. An excursion proposal recommends a closer inspection of that fascinating landscape.     

Route choices, migration speeds and daily migration activity of European silver eels Anguilla anguilla in the River Rhine, north-west Europe

Downstream migration of Anguilla anguilla silver eels was studied in the Lower Rhine, Germany, and the Rhine Delta, The Netherlands, in 2004–2006. Fish ( n = 457) released near Cologne with implanted transponders were tracked by remote telemetry at 12 fixed detection locations distributed along the different possible migration routes to the North Sea. Relatively more A. anguilla migrated via the Waal than the Nederrijn, as would be expected from the ratio of river discharges at the bifurcation point at Pannerden. Downstream migration from the release site to Rhine-Xanten, close to the German–Dutch border, generally occurred in the autumn of the year of release but migration speeds tended to be low and variable and unaffected by maturation status or river discharge rates. Detection frequencies were not significantly related to discharge peaks or lunar cycles, but there was a minor detection peak 1–6 h after sunset. Between 2004 and 2009, 43% of the 457 A. anguilla released were never detected and of the 260 detected entering the Netherlands, 83 (32%) were detected escaping to the sea, 78 (94%) via the Nieuwe Waterweg and three (4%) and two (2%) via the sluices in the Haringvlietdam and Afsluitdijk, respectively. Possible causes of non-detections are discussed and it is suggested that many A. anguilla temporarily ceased migration, but that fishing mortality could have been important during passage through the Dutch parts of the Rhine. Practical implications of the results for predicting emigration routes, timings and magnitudes and use in management initiatives to promote escapement of A. anguilla silver eels to the sea are critically discussed.     

Strong genetic exchange among populations of a specialist bee, <Emphasis Type="Italic">Andrena vaga</Emphasis> (Hymenoptera: Andrenidae)

Habitat fragmentation is believed to be a key threat to biodiversity, with habitat specialists being stronger affected than generalists. However, pioneer species might be less affected by fragmentation, as their high colonization potential should increase gene flow. Here, we present an analysis of the genetic structure of populations of the solitary bee Andrena vaga, which naturally occurs in sandy habitats and is specialized on willow (Salix) pollen as larval food and sandy soils as nesting sites. While the species is widespread in the young sandy landscapes of our main study area (Emsland, northwestern Germany), it occurs less frequently in the Lower Rhine valley. Our analyses of six polymorphic microsatellites show that the populations are only slightly differentiated, suggesting a relatively strong gene flow. No genetic structure corresponding to the geographic origin was found as the variability within populations accounted for the major proportion of variation. F_ST values were higher and allelic richness was lower in the Lower Rhine valley, supporting the hypothesis that habitat availability affects the degree of genetic exchange between populations. Inbreeding coefficients were generally high and nearly all populations had a heterozygote deficiency, which could be explained by the breeding strategy of A. vaga, which nests in aggregations.     

Outmigration pathways of stocked juvenile European sturgeon (Acipenser sturio L., 1758) in the Lower Rhine River,as revealed by telemetry

Working towards a future Rhine Sturgeon Action Plan the outmigration pathways of stocked juvenile European sturgeon (Acipenser sturio L., 1758) were studied in the River Rhine in 2012 and 2015 using the NEDAP Trail system. A total of 87 sturgeon of 3 to 5 years old (n = 43 in 2012, n = 44 in 2015) were implanted with transponders and released in May and June in the river Rhine at the Dutch‐German border, approximately 160 km from the sea. In total three sturgeons (3%) were found dead on river banks within seven days after the release. Based upon their wounds these sturgeons were likely hit by ship‐propellers. Tracking results were obtained from 57 (66%) of the sturgeons, of which 39 (45%) indicated movement into the Port of Rotterdam. Here the sturgeons remained for an average of two weeks, which suggests they spent time to acclimatize to higher salinities before entering the North Sea. Of the 45 (52%) sturgeons that were confirmed to have entered the North Sea, ten (22%) were recaptured (mainly by shrimpers and gill‐nets) close to the Dutch coastline; nine were alive and were released. From the results we obtained the preferred outmigration pathways, movement speeds and an indication of impacting factors (i.e. ship propellers and bycatch). Bycatches provided also localisations information in the coastal area. A next step to complete this work would be to assess habitat selection in freshwater and downstream migration of young of the year (YOY sturgeons) in the Lower Rhine.     

Impact of hydrology on phyto- and zooplankton community composition in floodplain lakes along the Lower Rhine and Meuse

Floodplain lakes along the rivers Lower Rhine and Meuse in TheNetherlands can be categorized according to their hydrologyand geomorphology. The impact of hydrology on the summer planktoncommunity composition in 100 floodplain lakes was studied bymultivariate analyses (TWINSPAN, FLEXCLUS, DCA) of relativeabundance data of plankton. The phyto- and zooplankton communitycomposition in floodplain lakes is clearly related to hydrology,relevant nutritional resources and habitat characteristics,mainly via input of N and P from the eutrophic main channelsduring floods. The plankton species richness was related tothe complexity of habitats formed by the presence of aquaticvegetation. There was a good agreement between the ecologicaland the environmental characterization of site groups. Cyanobacteria,Chlorophyta and filter-feeding zooplankton taxa associated withopen water are characteristic for floodplain lakes with a longannual flood duration, low Si/N and Si/P ratios, and a poorlydeveloped aquatic vegetation. Bacillariophyceae and scrapingzooplankton taxa associated with aquatic macrophytes are characteristicfor floodplain lakes with a short annual flood duration, highSi/N and Si/P ratios, and a well-developed aquatic vegetation.It is concluded that the restoration of connections betweenrarely flooded lakes and the highly eutrophic main channelsof the Lower Rhine and Meuse will result in hypertrophic conditionsand a reduced plankton diversity in these lakes.     

Distribution and ecology of anthozoa in the estuarine region of the rivers Rhine,Meuse and Scheldt

Data on the ecology and distribution in the estuarine region of the rivers Rhine, Meuse and Scheldt are given for ten species of Anthozoa. These data have been correlated with several environmental variables, but especially salinity. Communication nr. 142 of the Delta Institute for Hydrobiological Research.     

Gas permeable deep reaching fracture zones encourage site selection of ants

Difficulties with geological mapping of fault patterns occur frequently due to missing outcrops and typically fault mineralization (e.g. crystalline quartz and ore mineralization). Alternatively, in addition to other analyses, soil gas measurements (e.g. helium) can be carried out. Due to fault zone complexity, geologists must often rely on other, in some cases, easier indications of their existence. Geological studies in several areas of central Europe especially in the Middle Rhine Region (Rhenish Massif) indicate that active gas permeable fracture zones are linked to linear distributions of nests of hill-building forest ants. Therefore, the possibility of using formicines as indicators of gas permeable fault patterns was investigated. These preliminary data indicated the possible interaction of site selection and active gas permeable fracture zones. Consequently, regions in the Alps, the Black Forest, the Lower Rhine Embayment, Bavaria, Hesse and South Sweden were chosen, ant nests were mapped, and their sites subsequently compared to geological structures. Most of the investigated ant nests were located on or near active gas permeable faults. Additionally, in the Middle Rhine Region variations in population size of formicines on fault zones and inter fault zones have been observed. These primary data suggest formicines can be applied successfully as an aid to fault pattern location.     

Population ecology, vertical migration and feeding of the Ponto-Caspian invader Hemimysis anomala in a gravel-pit lake connected to the River Rhine

1. The Ponto‐Caspian invader, Hemimysis anomala, was recently found in large numbers in a gravel‐pit lake connected to the Lower Rhine. Mysids were sampled with Perspex traps between September 2002 and April 2003 to study the population dynamics, vertical migration and feeding. 2. The abundance (as catch per unit effort, CPUE) of H. anomala declined from 270 individuals (ind.) trap^?1 (4 h)^?1 in December to below 4 ind. trap^?1 (4 h)^?1 in April. Average lengths ranged from 4.9 mm in autumn to 9.9 mm in March. The length–weight relationship of virgin females changed throughout the sampling period, from a size‐corrected wet weight of 5.1 mg in September to 16.6 mg in April for a female of 7.8 mm. 3. Successive monthly samples taken over 24 h revealed that H. anomala preferred the surface at twilight and night. During dawn the mysids migrated to the middle and bottom layers and were hardly found during day. Diel vertical migration clearly depends on the proximate factor light. 4. Stomach analyses revealed that larger H. anomala preferred zooplankton, whereas small individuals fed more on phytoplankton. The seasonal comparison showed an increasing percentage of zooplankton with increasing length. The proportion of zooplankton in the stomachs of large H. anomala individuals was highest during night and lowest during day. 5. The results suggest that H. anomala may become an important link between primary/secondary production and higher trophic levels in the food web of its new environments at the Lower Rhine.     

Genetic diversity, origin, and geographic distribution tendencies of biotypes of polyploid spined loaches (Cypriniformes, Cobitidae, Cobitis) in Ukraine

Sixteen of 28 possible biotypes of C. elongatoides-taenia s.lato (C. taenia, C. tanaitica, C. species-1) have been found in Ukrainian waters. Presumably, the biotypes of C. aff. melanoleuca-tanaitica has also been identified. The share of polyploids among Cobitis on average was 65%, where males made up less than 1% with the same ratio among tri- and tetra-polyploids. The absence of amphydiploidy and presence of individuals with recombinant genotype and abnormal electrophoretic specters, whose frequency sometimes is considerable, are attracting increasing interest. There are two centers of polyploid biotypes creation: southern (the Lower Danube) and northern (the Upper Danube, Oder, and Rhine). The C. taenia and C. species-1 type, which is typical for the northwestern basins of Ukraine, participates in the formation of polyploids in the Rhine alongside with C. elongatoides and C. tanaitica. It is determined that biotypes (C. 2(3) elongatoidestanaitica, C. elongatoides-2(3) tanaitica) in comparison with biotypes whose genome includes the chromosome set of C. taenia are limited in distribution towards the East. This is due to the hybridization of females from these biotypes with males of C. taenia afflicted by genetic instability and reduced viability of posterity.     

The Mayfly,Ephoron Virgo (Olivier), back in the Dutch parts of the rivers Rhine and Meuse

Due to severe water pollution, the mayflyEphoron virgo (Olivier) disappeared from the Dutch parts of the rivers Rhine and Meuse in the first half of this century. In August 1991, however, larvae were found in the littoral zone of the Rhine near the Dutch-German border. Later, other stages were found along the Rhine branches and a small section of the Meuse. The occurrence in The Netherlands is the result of further expansion from the upstream regions of the Rhine.     

Drei Höhe(n)punkte am Mittelrhein. Die Exkursion

Three highlights on the Middle Rhine The Upper Middle Rhine valley, part of the UNESCO World Heritage since 2002, has long been known as a classical travel region due to the impressive beauty of its landscape. The steep und narrow canyon comprises a complex series of remarkable geo‐ along with biotopes. These are characterized by their unique tectonics as well as by their floristic and faunistic elements. This excursion proposal highlights three selected destinations on the borderline of the valley which particularly appear equally promising and recommendable.