Upstream movements of benthic macroinvertebrates in two different types of fishways in southwestern Germany

Upstream movements and migrations of benthic macroinvertebrates are an important component of running water dynamics. Many lotic organisms perform upstream movements at some stage in their life-cycle. We investigated whether a boulder ramp and a concrete bypass fishway on two streams in Baden-Württemberg, Germany, are successfully used by benthic invertebrates to reach upstream areas. We compared macroinvertebrate distribution at sites upstream and downstream of the fishways, rated the fishways according to their constructional features and conducted migration experiments with marked Gammaridae in the passages. The number of taxa and densities of macroinvertebrates did not significantly differ between upstream and downstream sites in both rivers. Constructional features and the results of the mark-recapture experiments indicated that the boulder ramp allows upstream migrations in principal, whereas the bypass is more difficult for macroinvertebrates to ascend. Both fishways immediately exit into an impoundment, which is a potential barrier for migrating invertebrates. High average current velocities, lack of lenitic banks and sheltered interstices, as well as problems caused by the operation of a power plant are factors explaining why the Enz River bypass is only marginally functional for invertebrates. The investigation concludes that in constructing fishways suitable for upstream movements of lotic invertebrates, more attention should be paid to their specific requirements.     

Treatment and utilization of wastewater in the Beijing Zoo by an aquatic macrophyte system

This paper deals with a nutrient cycling experiment in the Beijing Zoo that uses macrophytes as the added link to make a purification system. The whole system consisted of macrophyte cultivating area and no macrophyte area. By making up the different functional groups of aquatic plants, a multilevel cycling network is formed, which has a rather high purification capability. During the experimental period, the water quality of the Waterfowl Lake and the Peony Pavilion Lake improved significantly, with total nitrogen and total phosphorus reductions of up to 58 and 38%, respectively. Other parameters also confirmed the good purification effect of this system. The economic and social benefits met the requirement of the original design.     

The influence of aquatic surface respiration (ASR) on cardio-respiratory function of the serrasalmid fish Piaractus mesopotamicus

When exposed to severely hypoxic water, many teleosts skim the better oxygenated surface layer (aquatic surface respiration, ASR). Information is scarce concerning the thresholds triggering ASR and its cardio-respiratory consequences. To assess the ambient conditions leading to ASR and to evaluate its effects on cardio-respiratory function, we exposed specimens of Piaractus mesopotamicus to gradual hypoxia (water oxygen tension ranging from 120 to 10 torr) with or, alternatively, without access to the surface. Concurrently, ASR, cardiac and respiratory frequencies, O₂ uptake and gill ventilation were monitored. With surface access, ASR developed below the critical tension for O₂ uptake (34 torr) by normal gill ventilation. Moreover, the time spent in ASR increased with prolonged hypoxic exposure to a maximum of 95% of total time. Without surface access, the species exhibited hypoxic bradycardia, that had not occurred in the group with fully developed ASR. Even without ASR, P. mesopotamicus recovered readily from hypoxic exposure, showing that this species possesses a number of mechanisms to cope with environmental hypoxia.     

Water deprivation tolerance and humidity response in a larval dragonfly: a possible adaptation for survival in drying ponds

Abstract.  Water deprivation tolerance is investigated in the last larval stadium of Libellula depressa under various conditions of relative humidity (60–100% relative humidity; RH). Most of the larvae maintained at 100% RH emerge and, at lower RH levels show some resistance to dehydration because they die after a mean period ranging from 1.4 days at 60% RH up to 6.7 days at 90% RH. In dual-choice chambers with humidity gradients from 63–74% RH and from 68–84% RH, larvae spend most of the time in the moist side of the chamber. In a Y-tube olfactometer, the larvae reveal a positive hygrotaxis to two airstreams carrying different amounts of water vapour (98% vs. 50%) and spend most of their time in the 'humid' arm. The ecological significance of desiccation tolerance and hygropositive response in the last larval stadium of L. depressa is discussed in relation to the presence of hygroreceptors in dragonfly larvae.     

Colonisation of Heliconia caribaea by aquatic invertebrates: resource and microsite characteristics

Abstract.  1. Colonisation of ephemeral aquatic habitats via oviposition by invertebrates may be influenced by a variety of factors, such as the quality of aquatic habitat and the characteristics of the surrounding terrestrial environment. The water-holding bracts of Heliconia caribaea , a subtropical herb that produces ephemeral aquatic habitats, are colonised by a variety of aquatic invertebrates. To date, no experiments have been conducted to identify the cues that affect colonisation patterns via oviposition selection in Heliconia .
2. Artificial bracts were used to assess the influence of two types of resources found in bracts (plant produced carbohydrates and terrestrial snail faeces) on oviposition site-selection by invertebrate taxa via a replicated factorial design at four locations in the Luquillo Experimental Forest of Puerto Rico, U.S.A. Eleven microsite characteristics thought to affect oviposition were measured for each experimental container.
3. Most taxa responded in a minor way to microsite characteristics, whereas site selection by the most numerically dominant groups (e.g. Syrphidae) were influenced principally by resources within artificial bracts. Overall, the greatest response by particular taxa was to the presence of snail faeces. At the community level, total abundance, richness, and evenness of invertebrates increased with increasing biomass of faeces. Variation in sugar produced a more complex response.
4. In general, the terrestrial matrix surrounding these aquatic habitats was only a secondary determinant of population and community attributes; the principal factor affecting site selection was the quality of the aquatic habitat.     

Regional and local drivers of macroinvertebrate assemblages in boreal springs

Aim To identify the most important environmental drivers of benthic macroinvertebrate assemblages in boreal springs at different spatial scales, and to assess how well benthic assemblages correspond to terrestrially derived ecoregions. Location Finland. Methods Benthic invertebrates were sampled from 153 springs across four boreal ecoregions of Finland, and these data were used to analyse patterns in assemblage variation in relation to environmental factors. Species data were classified using hierarchical divisive clustering (twinspan ) and ordinated using non‐metric multidimensional scaling. The prediction success of the species and environmental data into a priori (ecoregions) and a posteriori (twinspan ) groups was compared using discriminant function analysis. Indicator species analysis was used to identify indicator taxa for both a priori and a posteriori assemblage types. Results The main patterns in assemblage clusters were related to large‐scale geographical variation in temperature. A secondary gradient in species data reflected variation in local habitat structure, particularly abundance of minerogenic spring brooks. Water chemistry variables were only weakly related to assemblage variation. Several indicator species representing southern faunistic elements in boreal springs were identified. Discriminant function analysis showed poorer success in classifying sites into ecoregions based on environmental than on species data. Similarly, when classifying springs into the twinspan groups, classification based on species data vastly outperformed that based on environmental data. Main conclusions A latitudinal zonation pattern of spring assemblages driven by regional thermal conditions is documented, closely paralleling corresponding latitudinal patterns in both terrestrial and freshwater assemblages in Fennoscandia. The importance of local‐scale environmental variables increased with decreasing spatial extent. Ecoregions provide an initial stratification scheme for the bioassessment of benthic macroinvertebrates of North European springs. Our results imply that climate warming, landscape disturbance and degradation of spring habitat pose serious threats to spring biodiversity in northern Europe, especially to its already threatened southern faunistic elements.     

Evaluating Wetland Restoration Success Using Aquatic Macroinvertebrate Assemblages in the Sacramento Valley,California

Currently, there is little professional consensus as to which ecological metrics should be used to measure restoration success in wetlands. Aquatic macroinvertebrate communities have many qualities to recommend them as useful metrics in this manner; yet, they have not been widely used to evaluate wetland restoration success. We examined the macroinvertebrate communities of four restored seasonal wetlands across a chronosequence of postrestoration age and compared them to a remnant natural wetland in the Central Valley of California. We examined two qualitatively different sets of aquatic macroinvertebrate metrics, general measures of community properties (abundance, richness, and diversity) and specific assemblage membership (nonmetric multidimensional scaling and permutational multivariate analysis of variance). Our results using these two different sets of metrics give us different answers. The general measures suggest that wetland macroinvertebrate communities converge on relatively stable values sometime after 10 years postrestoration. The specific assemblage results imply that the particular set of taxa found in restored wetlands is not predictable over the chronosequence we examined. Taken together, our results suggest that aquatic macroinvertebrate communities may be useful for measuring some aspects of restoration success but that there is unlikely to be a final aquatic community pattern indicating restoration success.     

Re‐Evaluation of the EUK516 Probe for the Domain Eukarya Results in a Suitable Probe for the Detection of Kinetoplastids,an Important Group of Parasitic and Free‐Living Flagellates

ABSTRACT. Two frequently used universal eukaryote probes, EUK1209 and EUK516, are not consistent with one branch of the eukaryotic phylogenetic tree, the Kinetoplastida, which has undergone rapid evolution of their small subunit rRNA gene. Kinetoplastids include medically important parasitic organisms (e.g. Trypanosoma, Leishmania) and free‐living flagellates that occur in all aquatic environments and in soils (e.g. Bodo, Neobodo, Rhynchomonas). A modified probe presented here as KIN516, now based on the kinetoplastid sequence, provides a strong signal with Neobodo designis, Leishmania donovani, and Trypanosoma cruzi using the catalyzed reporter deposition protocol. EUK516 and KIN516 function as competitor probes, thereby greatly increasing discriminatory power when used in combination. The probe pair was tested in field samples collected in a freshwater pond in Norfolk, the mesohaline Elizabeth River, Norfolk, Virginia, and a tropical lagoon in Belize. The combined probes bound to 58–84% of organisms identified as eukaryotic based on having large DAPI‐stained nuclei. The contribution of kinetoplastids to total eukaryotes (positive signal of EUK516+KIN516) was much higher in marine samples (ca. 17%) than in either the freshwater or brackish water sites (<0.2%).     

Development of a Real-Time PCR assay for quantitative assessment of uncultured freshwater zoosporic fungi

Recently, molecular environmental surveys of the eukaryotic microbial community in lakes have revealed a high diversity of sequences belonging to uncultured zoosporic fungi. Although they are known as saprobes and algal parasites in freshwater systems, zoosporic fungi have been neglected in microbial food web studies. Recently, it has been suggested that zoosporic fungi, via the consumption of their zoospores by zooplankters, could transfer energy from large inedible algae and particulate organic material to higher trophic levels. However, because of their small size and their lack of distinctive morphological features, traditional microscopy does not allow the detection of fungal zoospores in the field. Hence, quantitative data on fungal zoospores in natural environments is missing. We have developed a quantitative PCR (qPCR) assay for the quantification of fungal zoospores in lakes. Specific primers were designed and qPCR conditions were optimized using a range of target and non-target plasmids obtained from previous freshwater environmental 18S rDNA surveys. When optimal DNA extraction protocol and qPCR conditions were applied, the qPCR assay developed in this study demonstrated high specificity and sensitivity, with as low as 100 18S rDNA copies per reaction detected. Although the present work focuses on the design and optimization of a new qPCR assay, its application to natural samples indicated that qPCR offers a promising tool for quantitative assessment of fungal zoospores in natural environments. We conclude that this will contribute to a better understanding of the ecological significance of zoosporic fungi in microbial food webs of pelagic ecosystems.