Abstract. Experiments and models reveal that moderate dispersal rates between local communities can increase diversity by alleviating local competitive exclusion; in contrast, high dispersal rates can decrease diversity by amplifying regional competition. However, hitherto experimental tests on how dispersal affects diversity in the presence and absence of environmental heterogeneity are largely missing, although it is known that environmental heterogeneity influences diversity. For the first time we experimentally show that the interaction between dispersal rate and the presence of an environmental gradient with onaverage lower resource availability than the homogeneous control treatment affects diversity. In metacommunities of nine co-occurring species of marine benthic microalgae we factorially manipulated dispersal rate and the presence and absence of a light intensity gradient across local patches to test effects on local, regional, and beta diversity and to compare results to predictions from monoculture experiments. Although species in this experiment did not show resource partitioning along the light gradient as assumed by source-sink models, dispersal limitation maintained diversity in metacommunities with light gradients but not without. Local diversity and evenness were high under low light intensities when dispersal was limited and decreased with both increasing light intensities and dispersal rates. These diversity changes can be explained by the reduction of growth of the regional superior competitor at low light intensities alleviating its competitive strength. Increasing dispersal rate in turn compensated for the superior competitor's slow growth in those local patches with rather unfavorable light conditions and thus led to decreasing diversity and evenness. In contrast, diversity in the metacommunities without a light gradient was constantly low. Here, the superior competitor contributed 90% to total community biomass in all patches. High dominance, however, likely resulted from on-average higher resource availability (i.e., higher light intensities) compared to metacommunities with light gradient and not from patch homogeneity in itself.

Monitoring the quality of drinking water is an important issue for public health. Two of the main objectives of the European Project μAQUA were (i) the development of specific probes to detect and quantify pathogens in drinking water and (ii) the design of standardized sampling programs of water from different sources in Europe in order to obtain sufficient material for downstream analysis. Our phylochip contains barcodes that specifically identify freshwater pathogens for enabling the detection of organisms that can be risks for human health. Monitoring for organisms with molecular tools is rapid, more accurate and more reliable than traditional methods. Rapid detection means that mitigation strategies come into play faster with less harm to the community and to humans. Samples were collected from several waters in France, Germany, Ireland, Italy and Turkey over 2 years. We present microarray results for the presence of freshwater pathogens from brackish and freshwater sites in Northern Germany, and cyanobacterial cell numbers inferred from these sites. In a companion study from the same samples, cyanobacterial toxins were analyzed using two methods and those sites with highest toxin values also had highest cell numbers as inferred from this microarray study.

The coast of the Bulgarian Black Sea is a popular summer holiday destination. The Dam of Iskar is the largest artificial dam in Bulgaria, with a capacity of 675 million m3. It is the main source of tap water for the capital Sofia and for irrigating the surrounding valley. There is a close relationship between the quality of aquatic ecosystems and human health as many infections are waterborne. Rapid molecular methods for the analysis of highly pathogenic bacteria have been developed for monitoring quality. Mycobacterial species can be isolated from waste, surface, recreational, ground and tap waters and human pathogenicity of nontuberculose mycobacteria (NTM) is well recognized. The objective of our study was to perform molecular analysis for key-pathogens, with a focus on mycobacteria, in water samples collected from the Black Sea and the Dam of Iskar. In a two year period, 38 water samples were collected—24 from the Dam of Iskar and 14 from the Black Sea coastal zone. Fifty liter water samples were concentrated by ultrafiltration. Molecular analysis for 15 pathogens, including all species of genus Mycobacterium was performed. Our results showed presence of Vibrio spp. in the Black Sea. Rotavirus A was also identified in four samples from the Dam of Iskar. Toxigenic Escherichia coli was present in both locations, based on markers for stx1 and stx2 genes. No detectable amounts of Cryptosporidium were detected in either location using immunomagnetic separation and fluorescence microscopy. Furthermore, mass spectrometry analyses did not detect key cyanobacterial toxins. On the basis of the results obtained we can conclude that for the period 2012–2014 no Mycobacterium species were present in the water samples. During the study period no cases of waterborne infections were reported.

The original article was updated because some proofcorrections were not implemented. The legends to figures 4-6 were updated as follows: Fig. 4. Heat map of the relative abundance of (a) the bacterial hierarchical probes from family to kingdom and (b) from genus to species. The online version of the original article can be found at http://dx.doi.