International Review of Hydrobiology最新文献

Freshwater ostracods are commonly found in temporary ponds and lakes, surviving drought periods by producing resting eggs. We investigated the hatching phenology of ostracod resting eggs from the sediments of temporary floodplain lakes, considering both the taxonomic distance between species and their functional traits, such as carapace size (length and height) and shape, valve ornamentation, and reproductive mode. In addition, we tested the hypotheses: (1) that the hatching time is more similar between congeneric ostracod species than between noncongeneric species; (2) that differences in hatching time between congeneric species are often related to differences in functional traits; (3) that both species composition and functional traits composition of hatchlings change over the incubation time, but with a reduction in the variability over time. The experiment was conducted for 98 days in the laboratory, and the microcosms were monitored weekly. The first hatching of an ostracod was recorded during the second week of incubation after hydration of the sediments. A total of 12 ostracod species hatched, belonging to the families Cyprididae and Candonidae. The above three hypotheses were corroborated. The time between inundation and first hatching was mostly similar for congeneric species in the genus Chlamydotheca, but was different between some species of Strandesia, which might be owing to differences in functional traits. The species composition and functional trait composition of the hatched ostracods were significantly different over the 14 weeks of incubation due to the different hatching phenology of different species. Furthermore, our results show that both taxonomic distance and functional traits can influence the hatching time of ostracod resting eggs from temporary floodplain lakes. Thus, future studies addressing the hatching phenology of ostracod resting eggs (and resting stages from other invertebrates) should also emphasize the use of functional traits.

We studied seed transport in the Upper Eider River (Northern Germany). Our main questions were: Diaspores of what species are transported in the river and which of them remain viable after the drift? Could functional species traits be used as predictors for the survival of plant propagules in course of water transport? The water body of the Upper Eider River was sampled for plant diaspores at two bridges with each four traps changed weekly during the whole year. Samples were separated into two equal groups. Each two samples per bridge and week were dried and seeds were counted manually. The other two samples were spread on sterilised soil for germination. Species composition and community weighted trait means were compared for dried samples (total transport) and seedlings (germinated after drift). About half of the species and 1/10 of the seeds were able to survive hydrochorous transport. Species traits (community weighted means) were not reliable predictors for survival of species during the hydrochorous transport, but the majority of traits reflect the differences between the transport pools of seeds and seedlings. Small seed size, ruderal life strategy, and high light preference correlate positively with germinability after the drift, while large-seeded species adapted to endozoochory tend to lose viability during hydrochory. Dispersal of terrestrial plants with running water in the studied small river system is a highly stochastic event. We did not find evidence that specific adaptations to hydrochory significantly contribute to its success. Nevertheless, a few functional traits can increase the probability for the species to pass through the ecological filter “hydrochory.” Among those traits are (i) small seed size (less vulnerability for mechanical stress), (ii) generalist dispersal mode, less dependent on other particular vectors, and (iii) ruderal life strategy.

Studies of metacommunities are of great importance for ecological knowledge because they assess how the processes related to the species' niche and the dispersion processes structure the communities. In this context, the objective of the present study was to investigate the main assembly mechanisms responsible for the structuring of the zooplankton community in a complex of neotropical palm swamps (“veredas”), consisting of sets of small common ponds in the Brazilian savannah, similar to swamps. Zooplankton were sampled in the pelagic region of 15 veredas in April 2018. The zooplankton total community showed a distribution related to spatial and environmental factors. For Rotifera the relative importance of environmental factors was greater, while Cladocera and Copepoda were more structured by space. The community was still structured according to the Gleasonian model of distribution, where Rotifera presented a Gleasonian structure, Cladocera quasi-Gleasonian, and Copepoda quasi-nested random. The influence of environmental and spatial factors and the resulting structure of the zooplankton metacommunity seem to be directly related to the dispersal capacity in each group. Differences in relative importance of the factors that shaped the community highlight the idiosyncratic characteristics of zooplankton species. Thus, we emphasize the importance of using the two approaches of metacommunity studies to help to elucidate the processes that govern the structuring of metacommunities.

Floodplain forests have become rare in Europe due to anthropogenic changes. A critical aspect of their restoration is reintroducing flooding via dike relocation, as implemented at the Elbe River near Lenzen/Germany. How forest development is influenced by dike relocation is still unclear and difficult to predict. Inside the dike relocation area at the Elbe River, most trees were planted. Due to high tree mortality, we asked if the relative elevation of the planted trees and thus the number of flooding days inside the relocation area was comparable to the prevailing flooding regime in the surrounding active floodplain. Therefore, the positions of Ulmus laevis, Quercus robur, and Crataegus monogyna individuals were recorded using a DGPS and merged with a digital terrain model. Subsequently, relative elevations and numbers of flooding days per year and growing season (averages for 2011–2017) were calculated. The most flooding tolerant species, U. laevis, occurred at the lowest sites and tolerated the highest number of flooding days, followed by Q. robur, and finally by the least flooding tolerant species C. monogyna. All three species occurred at lower sites inside the dike relocation area and were exposed to longer flooding durations compared to sites outside the area. This was due to the complex morphology of this area and its special flooding and flow dynamics, which differed from the conditions in the surrounding active floodplain. Although the mean flooding duration was within the growth range of hardwood floodplain forests (Ficario-Ulmetum), most individuals may not have established at the planted sites under natural conditions. Therefore, we recommend not relying only on plantings but also allowing natural succession. Then, species that can cope with the hydrological site characteristics may also establish in the long term.

Tropical reservoir ecosystems cover more than 3.51 million ha in India which are the major sources of fish production from inland open waters and supports rich diversity of fish. The present study quantifies fisheries enhancement and evaluates the impact of stocking of Indian major carp fingerlings in six large reservoir ecosystems of India. Analysis of time series data revealed a significant increase (p < 0.05) in fish yield from 12.3 kg ha⁻¹ year⁻¹ in 2004–2005 to 52.4 kg ha⁻¹ year⁻¹ in 2016–2017 due to stocking. The average fish yield of these six reservoirs was estimated to be higher than the national average of 33 kg ha⁻¹ year⁻¹ recorded for large Indian reservoirs. Fingerling stocking had a significant positive impact on fish yield (r = 0.238, p = 0.035). The reservoir water storage level was positively correlated (r = 0.621, p < 0.05) to fish production. The study also shows that the reservoir habitat support 99 finfish species in the central Indian reservoirs of which two species belong to endangered category warranting conservation efforts. This study is the first of its kind on assessing the impact of stocking in large number of tropical reservoirs including the largest reservoir in the country revealing positive effect on fish yield. The fish yield of 85.8 kg ha⁻¹ year⁻¹ obtained in Gandhisagar reservoir (72,300 ha), India revealed that fisheries enhancement is effective and remunerative. The study also highlights the global status of stocking impact in large reservoirs and deliberates issues and suggests management strategies for sustainable fisheries enhancement in large tropical reservoirs.

Bivalves can consume detritus, bacteria, phytoplankton, and zooplankton by filtering the water column. Ecological attributes like filtration rate (FR) and excretion rate (ER) are particularly important to better understand the role of bivalves in ecosystem. Here, we aimed to elucidate the FR/ER of Diplodon parallelopipedon in a five-times replicated laboratory experiment under five levels of temperature (10°C, 15°C, 20°C, 25°C, and 30°C) and three levels of phytoplankton biomass (low, middle, and high). Temperature was the main factor regulating FR and ER in our experimental conditions, as we hypothesized the experimental results showed a nonlinear relationship between FR and water temperature. D. parallelopipedon exerted top-down control over phytoplankton biomass throughout the temperature gradient tested. Contrarily to our expectation, FR and ER did not vary within the phytoplankton biomass range offered. The experimental evidence suggests D. parallelopipedon might control phytoplankton biomass in different temperature scenarios. Moreover, the excretion of nutrients by D. parallelopipedon, together with a capacity to avoid grazing shown by several phytoplankton species (i.e., buoyance regulation) reveal relevant challenges to our understanding of bivalve-phytoplankton dynamics, and consequently to the whole ecosystem response, particularly in the presence of more diverse natural phytoplankton communities.

Bank habitats provide important functions for riverine fish. Yet, they have been heavily modified by land use, technical flood protection measures, and hydropower installations. Fish species requiring specific habitats to complete their life cycle have strongly declined and therefore become target species of river restoration measures. This study compared abiotic conditions and fish community composition of three bank habitat types in a large alpine river, comprising different degrees of alteration compared to the natural state (concrete profile, bank riprap, and naturally restored riverbank). Significant differences in abiotic habitat characteristics such as bed material, water depth, turbidity, submerged vegetation, and temperature were detected between the three bank habitat types and sampling seasons. These water level-dependent structural changes had the strongest effect on fish community composition as detected by distance-based linear modeling. Small specimens between 3 and 13 cm TL and juveniles were most abundant in the restored areas, except for Lota lota, which was most abundant in the man-made bank riprap. Target species of conservation were mostly detected in restored areas, particularly the critical young life stages of Chondrostoma nasus, Barbus barbus, and Thymallus thymallus. Water level strongly determined accessibility and suitability of bank habitats, with shallow, gravel-dominated habitats comprising flat bank angles being most beneficial for these species. The findings of this study provide evidence for the success of bank habitat restoration in structurally impacted alpine rivers on target species of conservation. Fluctuating water levels and discharges typical for alpine rivers should be better considered in restoration planning, particularly in light of climate change, affecting the timing and amplitude of discharge in these systems.

Understanding seasonal patterns of assembly mechanisms are key to comprehending the metacommunity dynamics of organisms inhabiting temporary habitats such as wetland macroinvertebrates. However, tests of the seasonal variation in assembly mechanisms of macroinvertebrates in wetlands with differing hydroperiods are rare, especially in the Neotropical region. We tested for seasonal patterns in the metacommunity assembly mechanisms of macroinvertebrates in small subtropical highland wetlands of southern Brazil with different hydroperiods. We also tested whether patterns varied between macroinvertebrate taxa with different dispersal modes. Macroinvertebrates were sampled in 12 wetlands classified into “short,” “medium,” and “long” hydroperiods (N = 4 in each category) in three seasons (fall, winter, and spring) over two full hydrological cycles (from 2012 to 2014). We assessed the role of spatial and environmental variables to metacommunity structure using distance-based redundancy analysis and variation partitioning. Environmental and spatial variables explained macroinvertebrate metacommunity structure, although their relative influence markedly changed among seasons and hydroperiods. Environmental variables were important in fall and winter, whereas spatial variables predominated in spring. Different environmental variables influenced the metacommunity structure in each hydroperiod. Environmental variables influenced active-dispersing macroinvertebrates, whereas the influence of environmental and spatial variables on passive-dispersing taxa changed among seasons. We showed that the assembly mechanisms of macroinvertebrate metacommunities show a distinct temporal dynamic among wetlands with different hydroperiods. Our findings contribute to a more complete understanding of the metacommunity structure in temporary ecosystems.