Ponto-Caspian gobies have invaded many river systems in the northern hemisphere, but their colonization patterns often remain unrecognized at the early stages of invasion. Here, we analyzed the ...ongoing invasion of the round goby
Neogobius melanostomus
(Pallas, 1814) in the Elbe River (Germany) by combining literature research with electrofishing and environmental DNA (eDNA) sampling. Along the surveyed 517 km, abundances peaked in the upper and lower sections, while low or no goby abundances were detected in the middle section. Combining the results of the field survey and literature data, we inferred four dispersal modes, jointly appearing during the colonization. (1) Human mediated transport, which was responsible for the initial colonization of the tidal Elbe and for a jumpy expansion to the upstream sections. (2) Fast downstream colonization, which was particularly observed for juvenile individuals. (3) Slow upstream migration, which was also recorded for another goby species, the bighead goby
Ponticola kessleri
(Günther, 1861) and (4) Lateral invasion via a major shipping canal in the middle river section. The eDNA analyses generally supported these conclusions and showed a high sensitivity and thus increased detection strength at low goby densities. Our study showed that the location of the first occurrence, as well as the dispersal mode, strongly determines the invasion process of non-native gobies.
Dissolved organic matter (DOM) is an important resource for microbes, thus affecting whole-stream metabolism. However, the factors influencing its chemical composition and thereby also its ...bio-availability are complex and not thoroughly understood. It was hypothesized that whole-stream metabolism is linked to DOM composition and that the coupling of both is influenced by seasonality and different land-use types. We tested this hypothesis in a comparative study on two pristine forestry streams and two non-forestry streams. The investigated streams were located in the Harz Mountains (central Europe, Germany). The metabolic rate was measured with a classical two-station oxygen change technique and the variability of DOM with fluorescence spectroscopy. All streams were clearly net heterotrophic, whereby non-forestry streams showed a higher primary production, which was correlated to irradiance and phosphorus concentration. We detected three CDOM components (C1, C2, C3) using parallel factor (PARAFAC) analysis. We compared the excitation and emission maxima of these components with the literature and correlated the PARAFAC components with each other and with fluorescence indices. The correlations suggest that two PARAFAC components are derived from allochthonous sources (C1, C3) and one is derived autochthonously (C2). The chromophoric DOM matrix was dominated by signals of humic-like substances with a highly complex structure, followed by humic-like, fulfic acids, low-molecular-weight substances, and with minor amounts of amino acids and proteins. The ratios of these PARAFAC components (C1 : C2, C1 : C3, C3 : C2) differed with respect to stream types (forestry versus non-forestry). We demonstrated a significant correlation between gross primary production (GPP) and signals of autochthonously derived, low-molecular-weight humic-like substances. A positive correlation between P / R (i.e. GPP/daily community respiration) and the fluorescence index FI suggests that the amount of autochthonously produced DOM increased overall with increasing GPP. In accordance with the coupling between DOM and the metabolism, our data also indicate that the composition of DOM is subject to seasonal fluctuations. We concluded that temporal and spatial differences in DOM composition are driven by whole-stream metabolism, in addition to pronounced effects coming from allochthonous sources.
Whereas much is known about the biodiversity of prokaryotes and macroorganisms in the deep sea, knowledge on the biodiversity of protists remains very limited. Molecular studies have changed our view ...of marine environments and have revealed an astonishing number of previously unknown eukaryotic organisms. Morphological findings have shown that at least some widely distributed nanoflagellates can also be found in the deep sea. Whether these flagellates have contact with populations from other habitats is still uncertain. We performed a molecular comparison of strains isolated from deep-sea sediments (>5000 m depth) and surface waters on the basis of their small subunit ribosomal DNA (SSU rDNA). Sequences of Rhynchomonas nasuta, Amastigomonas debruynei, Ancyromonas sigmoides, Cafeteria roenbergensis and Caecitellus parvulus were analysed, and 2 contrasting results obtained. Firstly, we found nearly identical genotypes within 1 morphospecies (C. roenbergensis), and secondly, quite different genotypes within certain morphospecies (R. nasuta, A. sigmoides and C. parvulus). In addition, high genetic distances between the different strains of A. sigmoides and C. parvulus indicate that these morphospecies should be divided into different at least genetically distinguishable species. In contrast, some heterotrophic nanoflagellates must indeed be regarded as being cosmopolitan. According to the low genetic distances between isolates of R. nasuta, A. debruynei and C. roenbergensis as well as between our isolates of A. sigmoides from deep-sea and surface waters, exchanges between these habitats and also on a global scale might be possible. In summary, our results show that 3 morphospecies obviously contain several cryptic species, while some of the investigated genotypes occur in both deep-sea as well as in surface waters.
The benthic protozoans were investigated along a transect in the eastern Mediterranean Sea from the Ionian to the Levantine Sea. Sediment samples were taken during
Meteor cruise 25/1 in May and June ...1993 at water depths of between 156 and 4617
m with a box corer and a multiple corer. A semi-quantitative cultivation technique was applied by placing sediment in petri dishes and diluting with sterile biotope water. Microscopic analyses of the protozoan taxa were conducted immediately after sampling, and then daily after enrichment with organic substrate. A total of 134 protozoan morphospecies were recorded, including 87 flagellates, 12 naked amoebae and 35 ciliates. 58% of the species could be attributed to genera known from shallow waters, demonstrating the wide distribution of these taxa. The number of recorded species per location ranged from 0 to 35 and decreased with increasing water depth. At stations deeper 1300
m very low species numbers as well as low potential abundances were recorded. Qualitative changes in the taxonomic composition with increasing depth were recorded as a decrease in the proportion of amoebae and euglenid flagellates and as an increase in the proportion of dinoflagellates. Ciliates were found down to a depth of 4260
m. The number of species was also dependent on the chloroplastic pigment equivalent (CPE), indicating a dependency on sedimented phytodetritus. The observed species included picophagous species, which feed mostly on bacteria, as well as nano- and microphagous species, which generally feed on protists, suggesting the existence of several trophic levels within the deep sea microbial food web.
Heterotrophic nanoflagellates (HNF) make up a large fraction of the zooplankton biomass of rivers. Their abundance can be strongly affected by water discharge, but the consequences of this highly ...dynamic factor for their main prey, the bacteria, is still unknown. The focus of this study was on bacterial-HNF interactions in the Lower River Rhine (Germany) with respect to the discharge-dependent dynamics. The bacterial and HNF abundances and biomasses were determined over the course of 17 months. The potential consumption of bacteria by HNF was calculated based on the biomass data and on data on the HNF production. The mean bacterial abundance in the Rhine at Cologne ranged from 0.3× 106to 3.5× 106cells mL-1, with lowest abundances in winter and highest in late spring. No significant changes in abundance during the downstream passage were found. Neither could a significant correlation be found between bacterial and HNF abundance. The ratio of bacterial to HNF abundance showed high variations which lay between 166 and 19,055 and was negatively dependent on water discharge. Monthly routine calculations on the potential bacterial consumption by HNF revealed a clearance of between 2 and 66% of the bacterial standing stock d-1. The values increased greatly with water discharge and could exceed 100% d-1at times of high water flow. The presented data suggests a change in the top-down control of the planktonic bacteria due to the water discharge: The importance of benthic predation at low water flow (high contact probability to benthic predators) gives way to an increased importance in predation by planktonic HNF at high water flow.
The assessment of the exposure of aquatic wildlife to complex environmental mixtures of chemicals originating from both point and diffuse sources and evaluating the potential impact thereof ...constitutes a significant step towards mitigating toxic pressure and the improvement of ecological status. In the current proof-of-concept study, we demonstrate the potential of a novel Aggregated Biomarker Response (ABR) approach involving a comprehensive set of biomarkers to identify complex exposure and impacts on wild brown trout (Salmo trutta fario). Our scenario used a small lowland river in Germany (Holtemme river in the Elbe river catchment) impacted by two wastewater treatment plants (WWTP) and diffuse agricultural runoff as a case study. The trout were collected along a pollution gradient (characterised in a parallel study) in the river. Compared to fish from the reference site upstream of the first WWTP, the trout collected downstream of the WWTPs showed a significant increase in micronucleus formation, phase I and II enzyme activities, and oxidative stress parameters in agreement with increasing exposure to various chemicals. By integrating single biomarker responses into an aggregated biomarker response, the two WWTPs' contribution to the observed toxicity could be clearly differentiated. The ABR results were supported by chemical analyses and whole transcriptome data, which revealed alterations of steroid biosynthesis and associated pathways, including an anti-androgenic effect, as some of the key drivers of the observed toxicity. Overall, this combined approach of in situ biomarker responses complemented with molecular pathway analysis allowed for a comprehensive ecotoxicological assessment of fish along the river. This study provides evidence for specific hazard potentials caused by mixtures of agricultural and WWTP derived chemicals at sublethal concentrations. Using aggregated biomarker responses combined with chemical analyses enabled an evidence-based ranking of sites with different degrees of pollution according to toxic stress and observed effects.
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•Three lines of evidence characterised a longitudinal contamination profile.•Aggregated Biomarker Response (ABR) enabled identification of toxic hot spots.•Transcriptome analyses identified mechanistic drivers of biological effects in fish.•Combined approach enabled comprehensive characterisation of toxic stress in fish.•Integration with chemical data allowed site-specific ranking of contamination.
Biofilms, the complex microbial communities associated with surfaces, can play an important role in the flux of matter in running waters. In addition to bacteria and algae, heterotrophic protists and ...small metazoans can also occur in high abundances in biofilms. By grazing on planktonic prey, biofilm- dwelling grazers can act as a trophic link between planktonic and benthic food webs, parallel to filter-feeding benthic macroinvertebrates. Here we introduce a flow cell method for the quantification of grazing rates of semi- natural biofilms on suspended bacteria, parallel to microscopic biofilm community analysis. This technique was used to measure the temperature response of the grazing rates of complex biofilm communities (established in a bypass system to the River Rhine, Germany) on planktonic bacteria. Results showed that 14 d old biofilms (dominated by ciliates) clear planktonic bacteria at rates between 29 (in winter) and 99 l m super(-2) biofilm d super(-1) (in summer) at ambient temperature. These rates increased with test temperature, even at temperatures (>30C) at which the grazing rates of filter-feeding macrofauna in moderate climates are negatively influenced. The acclimation temperatures under which the biofilm developed can have a significant effect on community clearance rates, largely due to a temperature effect on the abundance and structure of the grazer community, whereas no indication of an acclimation effect on individual grazing rates could be found. In the function of bentho-pelagic couplers, biofilm-dwelling consumer communities can react to temperature changes substantially faster than macrofaunal filter feeders.
Summary
In a previous study we identified microcolony formation and inhibitor production as the major protective mechanisms of Pseudomonas aeruginosa biofilms against flagellate grazing Matz, C., ...Bergfeld, T., Rice, S.A., and Kjelleberg, S. (2004) Microcolonies, quorum sensing and cytotoxicity determine the survival of Pseudomonas aeruginosa biofilms exposed the protozoan grazing. Environ Microbiol 6: 218–226. Here we compared the efficacy of these two key protective mechanisms by exposing biofilms of the non‐toxic alginate overproducing strain PDO300 and the wild‐type toxic strain PAO1 to a range of feeding types commonly found in the succession of protozoans associated with natural biofilms. Alginate‐mediated microcolony formation conferred effective protection for strain PDO300 against the suspension feeding flagellate Bodo saltans and, as reported earlier, the surface feeding flagellate Rhynchomonas nasuta, both of which are considered as early biofilm colonizers. However, microcolonies of mature PDO300 biofilms were highly susceptible to late biofilm colonizers, the surface‐feeding amoeba Acanthamoeba polyphaga and the planktonic ciliate Tetrahymena sp., resulting in a significant reduction of biofilm biomass. Mature biofilms of strain PAO1 inhibited growth of flagellates and A. polyphaga while the grazing activity of Tetrahymena sp. remained unaffected. Our findings suggest that inhibitor production of mature P. aeruginosa biofilms is effective against a wider range of biofilm‐feeding predators while microcolony‐mediated protection is only beneficial in the early stages of biofilm formation.
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