International Review of Hydrobiology最新文献

The Lake Victoria Basin (LVB) is a global hotspot of aquatic biodiversity, but aquatic ecosystems are under threat from multiple stressors. Most studies on fish have focused on Lake Victoria, while patterns of fish diversity, distribution, and assemblage structure in influent rivers remain poorly understood. To assess threats and conservation status of riverine fishes, we used sampling surveys and searches of published and gray literature to compile data on diversity, distribution, and abundance. In total, 72 fish species were found to inhabit Kenyan rivers and associated wetlands and lakes (excluding Lake Victoria). Low-order streams (first to third order) in headwaters of rivers are species-poor and dominated by small-bodied cyprinids (Enteromius spp.) and clariids (Clarias spp.). A small number of fishes are endemic to rivers, and species turnover across river basins is low. Species dominance is high, with 10 species accounting for >90% of all individuals and weights. Two cyprinid species (Labeobarbus altianalis and Labeo victorianus) account for >65% of all individuals and weights (biomass) per unit effort. Most species occur in small numbers and low biomass is insufficient to sustain a commercial riverine fishery. A review of the literature continues to indicate a reduction in migratory runs of potamodromous fishes from Lake Victoria into influent rivers, although some species, such as L. victorianus and L. altianalis, also maintain stenotopic populations in rivers. Most of the exotic fishes introduced in Lake Victoria, such as Oreochromis nilotics, Oreochromis, Coptodon zillii, Coptodon rendalli, and Gambusia affinis, have invaded and established themselves in rivers, thereby posing a threat to riverine populations. Although this study focuses on Kenyan rivers, the distribution patterns of fishes reflect other rivers of the LVB and have broad implications on threats to riverine biodiversity in other regions undergoing development around the world.

Invasion of non-native species in freshwater ecosystems often alters the indigenous macroinvertebrate community and food web structure by changing the resource availability. One of these species is the invasive amphipod Dikerogammarus villosus, whose impact by predation, especially on coexisting amphipods, is still under debate. In this study, we aim to apply compound-specific stable isotope analysis of amino acid δ¹⁵N, which is the state-of-the-art approach for marine systems to estimate trophic positions, (1) to calculate β values (i.e., the differences in δ¹⁵N values of trophic and source amino acids in primary producer) for freshwater systems, based on field samples of freshwater primary consumers (i.e., mussels) from the River Rhine, and (2) use these β values in a case study to calculate the trophic position of the invasive D. villosus in comparison with coexisting indigenous and non-native amphipod species from the river Alb sampled in 2013 and river Speyerbach sampled in 2014, two tributaries of the River Rhine, Central Europe. Our results show that our freshwater β values calculated for six combinations of trophic and source amino acids were lower by between approximately 0.85‰ and 5.67‰ than those found for marine animals in previous studies. This highlights that more attention is needed on the variability of the natural differences in β values between ecosystems. By using the freshwater β values, we showed that the trophic position of D. villosus is comparable to those of coexisting amphipod species. These findings confirm that D. villosus has a flexible and omnivorous feeding strategy like other amphipod species, and suggest that predation is not the main responsible factor for the impact of D. villosus on other species.

Our understanding of functional roles of aquatic invertebrate taxa is still limited even for common species, although being crucial for explanations of patterns observed in natural communities. As only recently shown, the common native European amphipod Gammarus fossarum, traditionally treated as a shredder of leaf litter, shows predatory behaviour which may influence the composition of invertebrate assemblages. However, the evidence for the predation effect of G. fossarum on natural assemblages at the within-site scale is still lacking. Therefore, we collected 50 quantitative samples of macroinvertebrates along with the important environmental variables within a heterogeneous calcareous spring fen. Using linear regression, we explored the relationships between the abundance of G. fossarum (separately adult and juvenile) and the abundance and number of taxa for two groups of invertebrates differing in their susceptibility to predation, (a) hard-bodied taxa with protective body structures, such as shells and calcified cuticles, and (b) soft-bodied taxa without those protections. We separated the effect of G. fossarum from that of environmental conditions using variation partitioning. Our results showed that only the abundance of soft-bodied invertebrates was negatively correlated with the abundance of adult G. fossarum. However, the proportion of variation explained purely by predation (5.5%) was much lower than the one explained by the environment (33.8%). Both G. fossarum and soft-bodied invertebrates were positively associated with organic matter. Although hard-bodied invertebrates consisted of only a few taxa, they were more numerous than soft-bodied invertebrates, and only environmental control was confirmed for them. Despite the limitations of the used correlative approach, we conclude that G. fossarum can significantly control the abundance of vulnerable taxa in natural assemblages. Its predatory effects, however, may be relatively low and easily confounded by the effect of environmental control.

Lake Sevan, Armenia, is the largest freshwater body in the Caucasus region. Cyanobacteria have become increasingly dominant in summer in Lake Sevan, reflecting the eutrophication of the lake and formed a massive bloom event in 2018. These recent observations mark the transition of this previously oligotrophic high mountain lake into an eutrophic lake with scum-forming cyanobacterial blooms. A bloom of Dolichospermum in July caused a sudden increase in chlorophyll-a concentrations up to, on average, 20 µg/L and a strong decrease in water transparency. The cyanobacterial genera Dolichospermum, Aphanizomenon, Anabaena, Cyanobium, and Synechococcus were detected by metagenomic analysis of the lake bacterioplankton. A qualitative and quantitative assessment of peptide-based secondary metabolites revealed the first detection of cyanotoxins in Lake Sevan. Ten types of microcystin congeners were found in Lake Sevan. The total concentration of microcystins in the phytoplankton varied from 0.34 to 2.49 µg/L. This first record of cyanotoxins in the largest lake in the Caucasus region calls for an urgent need for sustainable nutrient management and a systematic assessment of the ultimate causes that lead to the reoccurrence of scum-forming Cyanobacteria in this large Alpine lake.

Gammarus aequicauda and Artemia spp. are abundant crustacean species in Crimean hypersaline lakes. G. aequicauda preys on Artemia but there was no quantitative data on this before the current study. Predation of G. aequicauda on adult Artemia was studied in experiments with two different approaches evaluating (a) the time balance of the feeding process and (b) the grazing intensity. The threshold prey concentration, when consumption began to increase with increasing concentration, was approximately 15 ind./L in 200-ml vessels and about 5 ind./L in 500-ml vessels. When the Artemia abundance reached 20–25 ind./L, there was no further influence on the gammarid consumption rate. There was a significant negative correlation between the consumption rate of gammarids and Artemia abundance. According to study results, an individual G. aequicauda may eat up to 20–24 Artemia/day. Our study suggests that (a) G. aequicauda is an omnivorous species and can significantly suppress populations of its prey. (b) The two experimental approaches used to study the feeding of gammarids on Artemia produced similar results, and both may be used to quantitatively assess relations in a “prey–predator” system. (c) The abundance of predators and prey, as well as the experimental vessel volume, may influence the feeding rate. (d) The presence of plant food resources such as the leaves of Ruppia does not influence on the predatory feeding rate of G. aequicauda. (e) The rate of prey consumption by G. aequicauda is not constant and depends nonlinearly on prey and predator abundance. (f) Cannibalism occurs in the presence of plant resources only, but not in the presence of Artemia. (g) Other gammarids react to the capture of Artemia by one of them. They swim up to the successful individual and try to take some part of the prey.

Pharmaceutically active compounds (PhACs) are emerging contaminants that have been widely detected in water bodies in the last decades, with ecological effects toward aquatic biota that have not been fully elucidated. Most studies concerning their toxicity to microalgae have only considered short-term individual PhAC exposure, rather than combined exposure to several compounds for longer time periods. In this study, we investigated the effects of albendazole (ABZ) (anthelmintic) and carbamazepine (antiepileptic), alone and in combination with caffeine, on the growth and production of chlorophyll-a of the microalgae Raphidocelis subcapitata, during 16 days of exposure. ABZ alone had a more significant effect than carbamazepine alone on the growth rate and maximum cell density of the microalgae (p < .05; analysis of variance). These results were probably related to the effect of ABZ in inhibiting enzyme complexes and cell membrane proteins related to adenosine triphosphate synthesis, which is important for cell growth. The presence of caffeine lowered the toxicities of ABZ and carbamazepine to the microalgae, probably due to its antioxidant properties, positively affecting chlorophyll-a production, growth rate, and maximum cell density. Thus, caffeine had an antagonistic interaction with the studied PhACs. The results reinforce the importance of ecotoxicological assays that compare individual and combined PhAC exposure conditions. Our findings highlighted that caffeine can be a relevant factor influencing such assays, considering its widespread occurrence in impacted water bodies.

Physiological features of species can determine the resilience and adaptation of organisms to the environment. Swimming capacity and metabolic traits are key factors for fish survival, mating and predator–prey interactions. Individuals of the same species can display high phenotypic variation often in response to varying environmental conditions. We investigated the effects of captive breeding conditions on swimming capacity, metabolic traits and morphology by comparing a captive population with a wild population of the endangered Spanish toothcarp (Aphanius iberus). We measured swimming capabilities and oxygen-uptake rates simultaneously, the latter as a proxy for metabolic rate, using a swim tunnel respirometer. Results showed significant differences in standard metabolic rate (SMR), maximum metabolic rate (MMR) and absolute aerobic scope (AAS) between populations, as well as differences in morphological features between populations and sexes. In contrast, we did not find significant differences in critical swimming speed between populations or sexes. Differences in SMR between sexes were found in the captive population, and males showed nearly a twofold increase in SMR when compared with females. SMR, MMR and AAS were, on average, twofold lower for the captive population in comparison with the wild population. These differences in metabolic traits likely reflected captivity conditions, which were low food availability and the absence of predators, which in turn, may have influenced morphological traits, such as body and caudal peduncle shape and head size. At the same time, morphological traits also influenced metabolic traits of the populations. The lower SMR and MMR of captive individuals may be related to their deeper body shapes. Taken together, our results suggested that captive breeding conditions caused significant physiological and morphological changes in the endangered Spanish toothcarp. Reduced metabolic traits and changes in morphology may affect fitness-related traits of the captive populations once reintroduced into the wild, thereby compromising conservation efforts. We therefore recommend to experimentally testing for the effects and consequences of captive breeding conditions before fish are released into the wild for successful conservation of them and other endangered species.

Anthropogenic flow intermittency is considered a severe disturbance for benthic macroinvertebrates with largely unknown impacts on the organization of benthic communities and their food webs. We analysed the community composition (as taxonomic composition and relative abundance of taxa) and food webs of the macroinvertebrates inhabiting the pools and riffles of two Mediterranean streams with contrasting perennial and anthropogenic intermittent flow regimes. Our analyses comprised monthly measurements in two pools and two riffles of the community composition, food-web topology (the pattern in which specific links are arranged within the network) and food-web complexity indexes (the number of nodes and links regardless of their identity or arrangement) over 1 year. The food webs revealed a significant annual variation in size, complexity, and diversity within pools and under perennial flow (e.g., number of nodes, number of links, link density). Multivariate analysis showed strong differences in the composition and relative abundance of taxa and food-web topology of assemblages inhabiting pools and riffles. However, differences between communities inhabiting pools and riffles varied during the year; periods of great similarity were followed by periods in which communities were very different. This annual sequence of differences between pools and riffles was compressed under the anthropogenic flow intermittency regime. The anthropogenic intermittent flow studied here might represent a moderate stressor for Mediterranean communities well-adapted to dry conditions. Still, the reported deviation of the community composition and food-web topology from the reference status reflect the detrimental effect of this stressor on the benthic community.

Ultraviolet radiation (UVR) exposure has potentially hazardous effects on aquatic life, even more in the southern hemisphere, which is close to ozone layer depletion. Aquatic animals living in shallow water cannot escape from UVR effects swimming down, so they have to generate other traits to confront it (i.e., enzymes or pigments). Daphnia is a worldwide freshwater genus that inhabits ponds and lakes. Daphnia dadayana inhabits shallow lakes in Patagonia presenting a yellowish carapace and a horn-like structure in juveniles assumed for avoiding invertebrate predator attacks. We aimed to determine the effect of UVR exposure on the accumulation of melanin and if the development of the antipredatory defense affects the antioxidant response (glutathione S-transferase [GST] activity) to UVR. We carried out laboratory experiments with treatments with and without UVR exposure measuring melanin accumulation by photographic analyses. Also, we performed an experiment to generate the antipredatory structure exposing D. dadayana indirectly to the predaceous copepod Parabroteas sarsi. Our results showed that UVR increased melanin accumulation in D. dadayana and that the morphological structure against predators did not decrease the antioxidant enzymatic defenses (GST). Our concluding remarks are that D. dadayana is a successful organism that can use its phenotypic plasticity to cope with environmental stressors such as invertebrate predators and UVR exposure with no trade-off between these two stressors.