Characterization of the microbial community of lotic organic aggregates ('river snow') in the Elbe River of Germany by cultivation and molecular methods

Aerobic and anaerobic cultivation techniques, 16S rDNA-based phylogeny, and fluorescent in situ hybridization were used to describe the phylogenetic diversity and physiological versatility of lotic microbial aggregates ('river snow') obtained from the river Elbe. In the course of the year the 'river snow' community changed. It was characterized by a great bacterial diversity in spring, the predominant occurrence of algae in summer and reduction of the total bacterial cell count in autumn and winter. In all 'river snow' samples, more than 70% of the bacteria counted with the general DNA stain DAPI also hybridized with the Bacteria-specific probe EUB338. In situ analysis of the bacterial 'river snow' community with a comprehensive suite of specific rRNA-targeted probes revealed population dynamics to be governed by seasonal factors. During all seasons, beta-Proteobacteria constituted the numerically most important bacterial group forming up to 54% of the total cell counts. In contrast to this, the relative abundance of other major bacterial lineages ranged from 2% for the order Planctomycetales to 36% for Cytophaga-Flavobacteria. Cultivation of 'river snow' under aerobic and anaerobic conditions with a variety of different media resulted in the isolation of 40 new bacterial strains. Phenotypic and phylogenetic analyses revealed these new strains to be mostly unknown organisms affiliated to different bacterial phyla. Application of newly developed specific oligonucleotide probes proved the cultivated bacteria, including clostridia and the numerically abundant beta-Proteobacteria, as relevant in situ members of the 'river snow' community.     

The future distribution of river fish: The complex interplay of climate and land use changes,species dispersal and movement barriers

The future distribution of river fishes will be jointly affected by climate and land use changes forcing species to move in space. However, little is known whether fish species will be able to keep pace with predicted climate and land use‐driven habitat shifts, in particular in fragmented river networks. In this study, we coupled species distribution models (stepwise boosted regression trees) of 17 fish species with species‐specific models of their dispersal (fish dispersal model FIDIMO) in the European River Elbe catchment. We quantified (i) the extent and direction (up‐ vs. downstream) of predicted habitat shifts under coupled “moderate” and “severe” climate and land use change scenarios for 2050, and (ii) the dispersal abilities of fishes to track predicted habitat shifts while explicitly considering movement barriers (e.g., weirs, dams). Our results revealed median net losses of suitable habitats of 24 and 94 river kilometers per species for the moderate and severe future scenarios, respectively. Predicted habitat gains and losses and the direction of habitat shifts were highly variable among species. Habitat gains were negatively related to fish body size, i.e., suitable habitats were projected to expand for smaller‐bodied fishes and to contract for larger‐bodied fishes. Moreover, habitats of lowland fish species were predicted to shift downstream, whereas those of headwater species showed upstream shifts. The dispersal model indicated that suitable habitats are likely to shift faster than species might disperse. In particular, smaller‐bodied fish (<200 mm) seem most vulnerable and least able to track future environmental change as their habitat shifted most and they are typically weaker dispersers. Furthermore, fishes and particularly larger‐bodied species might substantially be restricted by movement barriers to respond to predicted climate and land use changes, while smaller‐bodied species are rather restricted by their specific dispersal ability.     

Environmental factors as forces structuring the fish community of the Elbe Estuary

Smelt, flounder, eel, three-spined stickleback, twaite shad, ruffe and herring were the major species among 62 forming the fish community of the Elbe estuary. Species richness, species diversity, evenness and total fish biomass decreased in the upstream direction. Total abundance was greatest during summer. Salinity was the most significant physico-chemical factor affecting species richness and total fish biomass, whereas water temperature was the best predictor of total abundance. Marine fish species decreased with decreasing salinity, while the freshwater species roach and ide were absent at salinities > 15‰. Bream, blue bream, white bream, perch and pikeperch occurred more frequently in shallow marginal regions with lower current velocities, while herring and other marine species occurred closer to the deep central regions with high current velocities. Annual and seasonal variations of the community structure mainly reflected in population dynamics of smelt, flounder, twaite shad, three-spined stickleback and eel, especially those of 0-age smelt. Populations of smelt and ruffe and their importance in the fish community increased between 1989 and 1992, while those of twaite shad and eel decreased. At oxygen concentrations <3 mg I¹, smelt and flounder were rare, but eels were at their maximum at 3.5 mg I⁻¹. Changes of species composition and fish abundance were closely related to daytime and tidal cycle.     

Effects of water regime and habitat continuity on the plant species composition of floodplain forests

Questions: 1. How big is the difference in the herbaceous layer composition between flooded and unflooded stands? 2. Are there species or species groups which have an affinity to ancient vs. recent forests in stands with different water regimes? 3. Are patterns of life history traits different between flooded and unflooded stands as well as between ancient and recent forests in stands with a different water regime? Location: Floodplain forests in the Middle Elbe region and district of Leipzig, Central Germany. Location: The herbaceous layer was studied in randomly selected quadrats of 9 m² in 2000 and 2001. Six ancient (n_plot=59) and six adjacent recent forests (n_plot=108) were investigated in flooded stands as well as three ancient (n_plot=41) and three recent forests (n_plot=70) in stands that have not been flooded for 50 years. The association of single species, species groups and life history traits were statistically tested for flooded vs. unflooded stands and for ancient vs. recent forests. Results: Interruption of flooding caused a complete species turnover in the herbaceous layer composition. Whereas in the still flooded stands typical alluvial species prevail, species composition in stands without flooding for 50 years showed a closed relation to the Stellario‐Carpinetum. Six herbaceous species in the flooded and five in the unflooded stands showed a preference for ancient forests. Only one species in the flooded and six herbaceous species in the unflooded stands are significantly associated with recent forests. Life history traits differ between flooded and unflooded stands but are similar in ancient and recently flooded stands, while unflooded ancient forests have more geophytes and myrmecochorous species than recent forests. Conclusions: The specificity of species composition in floodplain forests can only be maintained by regular flooding. Interruption of inundations lead to differences in the patterns of species composition and life history traits between ancient and recent forests.     

Hydrological prerequisites for optimum habitats of riparian Salix communities – identifying suitable reforestation sites

Question: What are the hydrological requirements for the successful reforestation of riparian Salix communities? Do differences in site conditions between various life stages of woody vegetation types need to be considered? Do interactions between hydrological factors influence distribution patterns? Location: Mid‐reaches of the Elbe River, Germany. Methods: Young and old life stages of two different riparian Salix communities were surveyed in 1067 plots of 400 m² to determine hydrological growth conditions using habitat distribution models. Models were extrapolated in a Geographic Information System to quantify the extent of potential stands available for reforestation measures. Results: Average water level and water level fluctuations were related to different vegetation types as well as to the age classes of the vegetation types. Differences in hydrological niches of young and old vegetation of the two vegetation types (tree community versus shrub community) could be identified. Moreover, the shrub vegetation was influenced by the interaction of average water level and fluctuations. Comparison of the distribution of current vegetation and suitable habitat revealed that considerable areas of the floodplain were suitable for the reforestation of Salix woodland communities. Conclusions: Hydrological variables explain the distribution patterns of riparian Salix communities in the active floodplain when different life stages, vegetation types and interaction of variables are included in the analyses. This information can be used to recommend suitable sites for Salix plantings in riparian landscapes.     

Benthic macrofauna communities of the submersed Pleistocene Elbe valley in the southern North Sea

Macrozoobenthic community structure was studied in two surveys along a transect of 13 stations following the submersed Pleistocene Elbe valley in the south-eastern North Sea during May to June 2000 and March 2001. Two replicates of bottom samples were taken with a van Veen grab of 0.1 m² sampling size. In order to analyse the benthic macrofauna communities, the animals obtained were identified and counted, and MDS and cluster analysis were performed. Out of 200 taxa identified, 84 were polychaetes, 46 molluscs, 40 crustaceans, 15 echinoderms, and 15 belonged to other groups. Mean abundance was 4,860 individuals per m², mean biomass 32.9 g ash free dry mass per m². Mean diversity was 1.76 and mean evenness 0.54. The macrofauna of the Pleistocene Elbe valley is composed of three associations according to the cluster analysis. Each association is described by a combination of characterizing and discriminating species. An Amphiura-brachiata―Tellimya-ferruginosa-association was found in the south-eastern part of the depression, whereas a transitional association with elements of both assemblages lead to an Amphiura-filiformis―Galathowenia-oculata―Nuculoma-tenuis-association in the north-western part of the valley. In the context of the entire southern North Sea, both associations are small-scale substructures, and as such are contained in the Nucula-nitidosa-community and the Amphiura-filiformis-community, respectively. A north-westward shift of the community of the southern Elbe valley was found and discussed as a possible consequence of warm winters of the last decades.     

Carabid Beetles (Coleoptera,Carabidae) as Indicatorsof Hydrological Site Conditions in Floodplain Grasslands

The relationship of carabid beetle species occurrence patterns and environmental variables characterising the hydrological regime has been studied at the River Elbe in Central Germany. Both flood duration and groundwater depth had major influence on species assemblages as the ordination of study plots mainly followed a gradient along these two variables. The simultaneous ordination of the plots according to species occurrence and environmental parameters showed a highly significant joint structure with the first two axes of a co‐inertia analysis, explaining >98% of the variance. A total of 27 species out of 129 caught fulfilled criteria of fidelity and specificity to the plots of the five clusters revealed by their abiotic conditions and were sufficiently abundant to be suitable indicators for one or a combination of clusters of plots. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Four arguments why so many alien species settle into estuaries, with special reference to the German river Elbe

In one of the largest European rivers, the Elbe, from its source in the Czech Republic to the German North Sea, 31 alien macrozoobenthic species have been recorded in total. Most of these species have been introduced by shipping activities. With a total number of 21 species, many of the established aliens occur—partly exclusively—in the brackish area of the Elbe estuary. In order to explain this observed settlement characteristic, four main arguments come into consideration: (1) estuaries with intensive international shipping have a higher potential infection rate than other aquatic zones; (2) brackish water species have, due to specific physiological characteristics, a better chance of being transported alive than euhaline or freshwater species and they also probably have a higher perennation and establishment potential after release; (3) brackish waters have the greatest natural ‘indigenous species minimum’, so that more alien species can potentially establish; and (4) salt-tolerant limnetic alien species introduced into inland water reached the coast at first in the estuaries. It seems that the combination of brackish water with its unsaturated ecological niches and intensive international ship traffic has the highest potential infection rate for aquatic systems with alien macrozoobenthic species. And, estuaries are subjected to a two-sided invasion pressure by alien species, via the ocean (mainly shipping) and via inland waters (mainly shipping canal construction). The identification of such patterns is an important prerequisite for the development of a forward-looking alien monitoring and management strategy.     

Notes On The Occurrence Of Clathrus Cancellatus,Tournf., In Argyllshire

Background: Estuaries are characterised by salinity gradients and regular flooding events. These environmental factors form stress gradients, along which species composition changes.

Aims: Analyse and compare patterns of plant species diversity along the estuarine salinity and flooding gradients of the Elbe and Connecticut Rivers.

Methods: Vegetation was sampled at three elevations (low, mid, high) in five sites of each marsh type (fresh, brackish, salt) in both estuaries. Patterns of species density (SD) and evenness (E) along the gradients were analysed and compared between the two estuaries with three-factor ANOVAs.

Results: The regional species pool was 33% higher for the Connecticut than for the Elbe. SD of fresh marshes (19 ± 2.2) was more than twice in the Connecticut than in the Elbe. We found an overall increase in SD from low to high elevation and from salt to freshwater marshes in both estuaries. However, SD and E were strongly depressed at intermediate elevations in the Elbe fresh and brackish marshes.

Conclusions: Although diversity patterns in the two estuaries show overall similarities, patterns of SD and E differ, when particular elevational zones and marsh types are compared. We hypothesise this to be due to evolutionary and historical influences on the regional species pools, shaping the impact of local biotic and abiotic processes.