Aquatic Sciences最新文献

Flood pulses in floodplain rivers affect fish food webs, with seasonal hydrological changes altering carbon and nitrogen sources and, consequently, species’ trophic attributes. In this study, we assessed the effect of the flood pulse on the trophic attributes and isotopic signatures (δ¹³C and δ¹⁵N) and assimilated resources of the cichlid Geophagus argyrostictus in the Xingu River (Amazon basin), a site impacted by dams. These features of G. argyrostictus were investigated by combining stomach content inspection and isotopic analysis over a hydrological cycle. Sampling was conducted monthly from 2020 to 2021, and digestive tract, muscle tissue and food resource samples were analyzed. Indices of diet (alimentary index and feeding intensity) and variation in isotopic signatures were evaluated and tested using permutational multivariate ANOVA and a generalized linear model. The contributions of food resources (Bayesian mixing models), trophic position and niche width were also analyzed. The main items in the stomach analysis were sediment (87%) and terrestrial plants (8.4%), with the composition varying mainly between high and low water periods; there was no variation in feeding intensity between these periods. The carbon isotopic signature varied according to flow rate, with aquatic molluscs and sediment being the most important assimilated resources across the periods. G. argyrostictus maintained a stable trophic position. In conclusion, hydrological variation influenced the composition of G. argyrostictus’ diet, with autochthonous resources being the main items structuring it. Our findings may reflect strategies used by this species in response to artificially regulated flow variation, and show that trophic studies are crucial for understanding ecological patterns in environments such as the Xingu River impacted by this type of change.

Graphical abstract

In the Patos Lagoon estuary (PLE) and the adjacent oceanic Cassino Beach surf zone (CBSZ), physical and chemical factors and the biovolume and composition of phytoplankton and protozooplankton were evaluated monthly over a 26-year period. Water temperature was similar in both environments, while salinity was lower and the concentration of dissolved inorganic nutrients was higher in the PLE; their similar seasonal cycle in both environments was associated with the main freshwater discharge, which was influenced by the El Niño–Southern Oscillation. The main driver of the plankton composition and biovolume was salinity, followed by nitrate and silicate; temperature was more significant in the PLE. Phytoplankton composition differed in both environments: In the PLE, freshwater and euryhaline species of diatoms and cyanobacteria were the main groups responsible for most of the variability, and the diatom Asterionellopsis in the CBSZ. The effects of global rising temperature and eutrophication on the plankton communities was evidenced by the increasing long-term trends of water temperature and inorganic nutrient concentrations, which coincided with the increasing trend of the photosynthetic species of diatoms, cyanobacteria, and green algae biovolume. The decreasing trend of Asterionellopsis in the CBSZ, likely influenced by mud deposition events on the beach, is a signal of environmental change potentially disrupting the food web. The decreasing trend of ciliates and the distinct trends of mixotrophic and heterotrophic dinoflagellates in both environments should be further investigated to understand the complex behavior of their feeding habits and contributions to top-down processes.

Intermittent and ephemeral streams are watercourses that cease to flow and/or dry up during part of the year. Their seasonal drying is sometimes preceded by a stream fragmentation phase with formation of isolated pools where the biogeochemistry differs from that of perennial reaches. Our objective was to analyse how hydrological fragmentation alters the spatial variability in dissolved nutrient and organic matter concentrations in a temperate-oceanic and agriculture-impacted headwater stream, where nutrient loadings are high. We conducted repeated synoptic sampling campaigns at high spatial resolution (150–200 m) along the stream network of the Naizin catchment (7 km²) during the spring–summer-fall of 2023. We sampled 38 sites and analysed dissolved organic carbon (DOC) concentrations and fluorescence properties, dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) concentrations, during four sampling campaigns: stream recession, early and late fragmentation and reconnection. Our results showed an increase in the spatial variability of concentrations, with monotonic longitudinal gradients along the stream disappearing during hydrological fragmentation. Both DOC and SRP concentrations were higher in isolated pools than in flowing reaches, while DIN concentration was lower. The chemical composition of DIN and DOC also changed with stream fragmentation, with increasing proportions of nitrite and ammonium in DIN and humic-like organic matter in DOC. These results suggest that the main controlling processes in the isolated pools were streambed mobilisation of SRP and DOC, along with denitrification under anoxic conditions. We expect the observed spatio-temporal patterns in nutrient and DOC concentrations to become more widespread in the future as intermittent streams will become more frequent owing to climate change.

Environmental DNA (eDNA) sampling is a promising approach for marine biodiversity monitoring, potentially offering a significant adjunct to traditional observational methods. This study evaluated eDNA as a marine biomonitoring tool for fish and marine mammal detection. Here we assess the overall utility of passive and active eDNA sampling methods, and the benefits and disadvantages of both techniques for marine mammals and fishes. Active sampling involved vacuum filtration of 2 L of water through a filter membrane, while passive sampling involved the immersion of filters for passive absorption at 1 m below the sea surface with deployment durations of 5–60 min. In total, 51 samples (23 active and 28 passive) were collected from two embayments in southeastern Australia, both with and without visual confirmation of marine mammals in the area at the time. Using a universal vertebrate primer targeting the mitochondrial 12S ribosomal RNA gene, fish DNA was detected in 28 samples, while marine mammal DNA was found in ten, despite visual confirmation of marine mammals on 30 occasions. Notably, one active sample detected marine mammal DNA without a corresponding sighting, illustrating an instance where eDNA sampling detected a marine mammal species that would have been overlooked by traditional monitoring. No single passive submersion time was optimal for detecting fishes or marine mammals. Although the passive method proved to be the more cost-effective approach, active sampling yielded more detections and was quicker to conduct in the field. This study extended the application of eDNA sampling for marine biomonitoring and identified areas for improvement.

Cellular demands for phosphorus (P) in ectotherms are hypothesised to increase at low temperatures to maintain the rate of protein synthesis. Additionally, consumers can exhibit luxury uptake, i.e. the storing of essential nutrients for use when they are scarce. However, studies on P content in cold-adapted invertebrates have been limited to marine and freshwater zooplankton, and data on P content in glacier and proglacial microinvertebrate consumers are scarce. We report the first comparison of mass-specific P content (% per dry weight) in tardigrades and rotifers, two common extremophilic microinvertebrate consumers, using a novel X-ray emission approach. Our scientific objectives were twofold: (1) to compare P content in glacier consumers with their counterparts from ponds in the glacier forefield, which represents a habitat with a higher average temperature, and (2) to determine the mass-specific P content of the common and well-identifiable glacier tardigrade Fontourion glaciale between glaciers with different P concentrations. We found that glacier tardigrades had a high P content comparable to that of P rich and fast-growing invertebrates. Overall, glacier consumers had higher P content than consumers from the forefield pond; however, only one forefield pond was investigated, and further analyses are needed to verify our assumptions. Analysis of the tardigrade species F. glaciale revealed a low mass-specific P content in cryoconite that has a high available P and the opposite at some glaciers. Since tardigrades and rotifers are abundant limno-terrestrial consumers in polar regions, are exposed to low temperatures and have a short active season, investigation of their elemental content and stoichiometry is greatly needed, not least to model the impact of glacier melt on nutrient cycling in downstream habitats.

Comparative influences of minnows (mainly fathead minnow Pimephales promelas), black bullhead Ameiurus melas, and common carp Cyprinus carpio on shallow lake ecosystems are poorly known, as are factors driving patterns of distribution of these species among lakes. We explored these relationships by studying 67 shallow lakes in three study regions in the southern half of Minnesota (USA) during 2010. We used ordinal regression to test for effects of lake size, watershed area, lake depth, and connection to another fish source on four types of fish communities: fishless (FISHLESS), minnows-dominant (MINNOWS), minnows + black bullhead (BULLHEADS), and minnows + black bullhead + common carp (CARP). We also used redundancy analysis to test whether the four types of fish communities differed in invertebrate community composition, water quality, and abundance of submerged plants. Results showed FISHLESS lakes were the least common and occurred in lakes with the smallest watersheds and no connection to a fish source. As watersheds became larger, fish communities became increasingly complex, starting with MINNOWS, then BULLHEADS, and finally CARP in the largest watersheds in lakes connected to a fish source. Ecosystem characteristics differed among the fish communities and reflected the same ordinal change in fish communities with increasing watershed area, as invertebrate and plant abundance was the highest, and phytoplankton and nutrient levels the lowest, in FISHLESS lakes. These variables changed in concert along the gradient to lakes with MINNOWS, then BULLHEADS, and ending with CARP having the lowest invertebrate and plant abundance and the highest phytoplankton and nutrient levels. Our results showed that lake connectivity and watershed area indirectly influence shallow lake characteristics by influencing fish community composition.

Non-perennial rivers (NPRs) are highly dynamic ecosystems that cease to flow or dry up partially or completely across time and space, representing over half of the global river network. These systems are expanding globally under climate change, yet their biodiversity patterns remain poorly understood in tropical semi-arid regions. We evaluated the effects of seasonal drying on the taxonomic (α and β) and functional diversity of fish and aquatic insects in the Cruxati NPR. Fish α-diversity remained stable between the two phases, likely reflecting physiological, trophic, and reproductive adaptations of dominant species. Insects exhibited higher α-diversity during the non-flowing phase, driven by lentic-adapted taxa. Fish β-diversity increased during the non-flowing phase because of environmental heterogeneity across isolated pools and founder effects, whereas insect β-diversity did not vary, possibly because of the limited spatial scale. Functional diversity remained unchanged between flowing and non-flowing phases in both fish and aquatic insect communities, likely because of historical periods of intense and frequent droughts. Our findings reveal that aquatic communities in semi-arid NPRs exhibit distinct results from those in temperate regions, showing seasonal persistence and highlighting the importance of historical and regional contexts in shaping biodiversity responses to hydrological fluctuations. Given the strong dependence of these communities on remnant isolated pools during the non-flowing phase, proper water resource management is crucial to ensure the ecological resilience of NPRs.

Non-native fish significantly contribute to biodiversity loss, with severe ecological and economic repercussions, particularly when they occupy apex consumer roles. This study examines the trophic ecology and niche overlap of native and non-native apex consumers within a floodplain subjected to varying degrees of human disturbance, using stable isotope analysis. Our results reveal that native apex consumers generally utilize a broader resource base than non-native species. However, the degree of trophic niche overlap between native and non-native apex consumers varies with the level of human disturbance: in highly disturbed environments, non-native species exhibit expanded trophic niches and reduced overlap with natives, likely reflecting their generalist feeding strategies and adaptation to altered habitats. Despite these differences, native and non-native consumers occupy comparable trophic positions and rely on similar basal energy sources, though some non-native species depend more on resources linked to anthropogenic disturbance, such as grass-derived carbon. These findings suggest that human disturbance modulates the trophic interactions and ecological success of non-native apex fish, highlighting the importance of considering disturbance gradients when assessing their impacts. Overall, the reduced trophic differentiation in less disturbed environments underscores the strong potential for competition and ecological consequences in these systems.

Human activities have pervaded aquatic ecosystems worldwide. As a result, riparian zones (the areas adjacent to rivers and streams) display high proportions of non-native vegetation, which is often considered symbolic of degradation and poor river health. Research suggests that riparian vegetation is essential for maintaining river health. However, whether this is due to the relative effect of vegetation species composition (including non-native vegetation) or vegetation structure (attributes such as canopy cover and linear continuity) is unclear. We used a comprehensive, regional ecosystem-health monitoring dataset to determine the effects of riparian vegetation across several spatial scales on river health and macroinvertebrate community composition. Constrained ordination methods revealed that riparian vegetation structure at the site scale influenced macroinvertebrate assemblages. However, when explicitly assessing the effect of non-native vegetation at the site scale, the proportion of non-native vegetation in the canopy did not influence macroinvertebrate assemblages. Notably, when species composition including both native and non-native species was assessed across all strata (canopy, shrub, and ground), it was found to significantly influence macroinvertebrate assemblages. This is likely driven by the different structural attributes of the various riparian vegetation communities found throughout the region. Therefore, the dominant effect of riparian vegetation structure may reflect the impact of different land uses within the area, rather than a strong influence of vegetation species identity on instream condition. These findings have important implications for riparian restoration. Our results suggest that the common restoration practice of focusing on non-native riparian vegetation removal combined with small-scale native replanting may not improve water quality and macroinvertebrate diversity, particularly where vegetation structure is modified in the process.

Interactions between organisms of different trophic levels are not only involved in the functioning of aquatic systems such as rivers but also crucial to maintaining taxonomic and functional diversity. This study aimed to evaluate the diversity of benthic cyanobacteria and their role as facilitating species for the colonization of benthic macroinvertebrates (MIB) in tropical mountain rivers with varying ecological conservation statuses. We sampled ten river segments in central Mexico, assessing physical and chemical parameters and collecting macroscopic cyanobacterial growths. A taxonomic and morphofunctional characterization was conducted for both biological groups, while a land-use change index (CDI) was calculated to assess the ecological quality of the sites. The analysis of similarities (ANOSIM) showed that cyanobacterial taxa are the factor that determines significant differences in the composition of MIB assemblages, with Cricotopus, Tanytarsini, Simulium, and Baetis being the most representative taxa according to the similarity percentage analysis (SIMPER). We also constructed an interactions network comprising eight cyanobacterial and 32 MIB taxa. The dominance of dipterans reflects substrate specialization, while the prevalence of collector morphologies suggests indirect food acquisition. While MIB were observed in unilateral associations with filamentous cyanobacteria, they formed multilateral associations with colonial species. Cricotopus showed a preference for both Nostoc tlalocii and Cyanoplacoma aff. regulare, revealing nonexclusive mutualistic relationships. This study demonstrated that cyanobacteria are important substrates for MIB to complete their life cycle, including the use of different species that are similar in their level of organization and therefore thallus morphology. This interaction network demonstrates adaptability, with some interactions being nonexclusive. Substrate turnover and voltinism in MIB may be linked to resiliency in the face of habitat changes caused by anthropogenic activities in the studied river basins.