No abstract

Protists play a crucial role for ecosystem function(ing) and oxygen is one of the strongest barriers against their local dispersal. However, protistan diversity in freshwater habitats with oxygen gradients received very little attention. We applied high-throughput sequencing of the V9 region (18S rRNA gene) to provide a hitherto unique spatiotemporal analysis of protistan diversity along the oxygen gradient of a freshwater meromictic lake (Lake Alatsee, SW Germany). In the mixolimnion, the communities experienced most seasonal structural changes, with Stramenopiles dominating in autumn and Dinoflagellata in summer. The suboxic interface supported the highest diversity, but only 23 OTUs95% (mainly Euglenozoa, after quality check and removal of operational taxonomic units (OTUs) with less than three sequences) were exclusively associated with this habitat. Eukaryotic communities in the anoxic monimolimnion showed the most stable seasonal pattern, with Chrysophyta and Bicosoecida being the dominant taxa. Our data pinpoint to the ecological role of the interface as a short-term 'meeting point' for protists, contributing to the coupling of the mixolimnion and the monimolimnion. Our analyses of divergent genetic diversity suggest a high degree of previously undescribed OTUs. Future research will have to reveal if this result actually points to a high number of undescribed species in such freshwater habitats.

Lake Karla, Greece, was dried up in 1962 and its refilling started in 2009. We examined the Cyanobacteria and unicellular eukaryotes found during two fish kill incidents, in March and April 2010, in order to detect possible causative agents. Both microscopic and molecular (16S/18S rRNA gene diversity) identification were applied. Potentially toxic Cyanobacteria included representatives of thePlanktothrixandAnabaenagroups. Known toxic eukaryotes or parasites related to fish kill events werePrymnesium parvumandPfiesteriacf.piscicida, the latter being reported in an inland lake for the second time. Other potentially harmful microorganisms, for fish and other aquatic life, included representatives of Fungi, Mesomycetozoa, Alveolata, and Heterokontophyta (stramenopiles). In addition, Euglenophyta, Chlorophyta, and diatoms were represented by species indicative of hypertrophic conditions. The pioneers of L. Karla’s plankton during the first months of its water refilling process included species that could cause the two observed fish kill events.

Predation by grazing protists in aquatic habitats can influence prokaryotic community structure and provides a source of new, labile organic matter. Due to methodological difficulties associated with studies of deep-sea (below photic zone) microbiota, trophic interactions between eukaryotes and prokaryotes in mesopelagic and bathypelagic realms are largely obscured. Further complicating matters, examinations of trophic interactions using water samples that have been exposed to upwards of hundreds of atmospheres of pressure change prior to initiating experiments can potentially introduce significant artifacts. Here we present results of the first study of protistan grazing in water layers ranging from the euphotic zone to the bathypelagic, utilizing the Microbial Sampler-Submersible Incubation Device (MS-SID) * that makes possible in situ studies of microbial activities. Protistan grazing in the mesopelagic and bathypelagic realm of the East Mediterranean Sea was quantified using fluorescently labeled prokaryotes (FLP) prepared from the naturally-occurring prokaryotic assemblages. These studies reveal daily prokaryotic removal due to grazing ranging from 31.3±5.9% at 40 m depth to 0.5±0.3% at 950 m. At 3540m depth, where a chemocline habitat exists with abundant and active prokaryotes above Urania basin, the daily consumption of prokaryotes by protists was 19.9±6.6% of the in situ abundance.

Phagotrophic protists are an important mortality factor of prokaryotes in most aquatic habitats. However, no study has assessed protistan grazing as loss factor of bacterial biomass across the stratification gradient of a temperate freshwater meromictic lake. Protistan grazing effect was quantified in the mixolimnion, the transition zone, and the sulfidic anoxic monimolimnion of Lake Alatsee (Germany). Grazing experiments were performed using prey analogues from the natural prokaryotic assemblage. Daily grazing effect declined from the mixolimnion to the monimolimnion. Heterotrophic flagellates were phagotrophically active in all three water horizons and the main grazers in the monimolimnion. Pigmented flagellates accounted for 70% of total grazing in the mixolimnion and ciliates only for a small fraction of grazing in each depth. Prokaryotic biomass removal peaked in the interface, but protistan impact on the respective prokaryotic abundance was low. Grazing in the anoxic monimolimnion was negligible, with prokaryotic turnover rate being only 0.4% of standing stock. Our results support the assumption that protistan predation in anoxic waters is lower than in oxygenated ones and identify the interface as a microhabitat that supports high grazer biomass, pinpointing the importance of purple sulfur bacteria as carbon source for the upper mixolimnion and the bottom monimolimnion.

Delineating biogeographical regions is one of the primary steps when analysing biogeographical patterns. In their proposed quantitative framework, Kreft & Jetz (2010, Journal of Biogeography, 37, 2029–2053) recommended the use of the βsim index to delineate biogeographical regions because this turnover measure is weakly affected by differences in species richness between localities. A recent study by Carvalho et al. (2012, Global Ecology and Biogeography, 21, 760–771) critiziced the use of βsim in ecological and biogeographical studies, and proposed the β‐3 index. Here we used simple numerical examples and an empirical case study (European freshwater fishes) to highlight potential pitfalls associated with the use of β‐3 for bioregionalization. We show that β‐3 is not a richness‐independent measure of species turnover. We also show that this index violates the ‘complementarity’ property, namely that localities without species in common have the largest dissimilarity, which is an essential prerequisite for beta diversity studies.

Global environmental goals mandate the expansion of the protected area network to halt biodiversity loss. The European Union’s Natura 2000 network covers 27.3% of the terrestrial area of Greece, one of the highest percentages in Europe. However, the extent to which this network protects Europe’s biodiversity, especially in a biodiverse country like Greece, is unknown. Here, we overlap the country’s Natura 2000 network with the ranges of the 424 species assessed as threatened on the IUCN Red List and present in Greece. Natura 2000 overlaps on average 47.6% of the mapped range of threatened species; this overlap far exceeds that expected by random networks (21.4%). Special Protection Areas and Special Areas of Conservation (non-exclusive subsets of Natura 2000 sites) overlap 33.4% and 38.1% respectively. Crete and Peloponnese are the two regions with the highest percentage of threatened species, with Natura 2000 sites overlapping on average 62.3% with the threatened species’ ranges for the former, but only 30.6% for the latter. The Greek ranges of all 62 threatened species listed in Annexes 1 and II to the Birds and Habitats Directives are at least partially overlapped by the network (52.0%), and 18.0% of these are fully overlapped. However, the ranges of 27 threatened species, all of which are endemic to Greece, are not overlapped at all. These results can inform national policies for the protection of biodiversity beyond current Natura 2000 sites.

The rapid decline of the Greek native Valencia letourneuxi, and its recently described sister species Valencia robertae, has been often attributed to habitat degradation, as well as aggression from or resource competition with the alien mosquitofish Gambusia holbrooki. The mosquitofish is extremely wide-spread in Mediterranean freshwater ecosystems, however, documentation on its presumed negative impacts on native freshwater fishes is limited. In this study, we compared abundance, condition and gonad weight of Valencia spp. in no co-occurrence versus co-occurrence to the mosquitofish, using data collected from eight aquatic systems of Greece, over a five year period (2005 to 2009). Our results show that Valencia abundance is significantly lower in co-occurrence to the Eastern mosquitofish. Furthermore, female Valencia spp. individuals in co-occurrence to the mosquitofish were smaller in length and had poorer somatic condition compared to females in habitats not invaded by the mosquitofish. The mechanisms responsible for these effects of the alien mosquitofish as well as the conservation implications for native Valencia populations are discussed.