Aquatic Sciences最新文献

Habitat segregation is a common phenomenon among anguillids in rivers where multiple species coexist. However, despite the growing need to conserve their river habitats, the mechanisms underlying such segregation remain unknown. Here, we conducted tank experiments to investigate the competitive superiority for habitats between the temperate Japanese eel Anguilla japonica and the tropical Indo-Pacific eel Anguilla marmorata, which co-occur in East Asian subtropical rivers. Using eight interspecific pairs of these two species of comparable total length, we compared the use of a single pipe shelter, recorded over a 24-h experimental period, between solitary and paired conditions. The changes in shelter use patterns between conditions indicated that in the paired condition, the shelter was occupied by A. marmorata in five pairs (62.5%) by the end of the experiment while A. japonica appeared to occupy the shelter in only one pair (12.5%). Furthermore, agonistic behaviors, which occurred mainly at night, such as biting and head-butting, were observed much more frequently for A. marmorata toward A. japonica (mean ± standard deviation: 23.2 ± 36.6 times per individual) than for A. japonica toward A. marmorata (0.4 ± 0.5 times per individual), indicating an asymmetry in aggressiveness. These results suggest that A. marmorata can negatively affect the diurnal habitat use and nocturnal activities of sympatric A. japonica. These findings, combined with those from previous field studies, suggest that A. marmorata may competitively exclude A. japonica from stream habitats with large substrate sizes. This asymmetric competition can contribute to shaping their riverine distribution and composition within rivers where they co-occur.

(1) We investigated how local abiotic and biotic variables versus regional spatial and dispersal variables influenced the structure of a stream macroinvertebrate metacommunity (multiple assemblages linked by dispersal), and whether this varied by dispersal mode. (2) We collected 143 benthic macroinvertebrate samples and associated abiotic and biotic data related to local habitat and species interactions across three river basins on the Olympic Peninsula (Washington, USA). We assessed macroinvertebrate assemblage composition in relation to environmental and spatial variables using mixed effects linear regression and partial redundancy analysis. (3) We found that water temperature, substrate grain size, bankfull width, and salmonid density were the local factors significantly associated with macroinvertebrate assemblage composition. Local variables explained 19.7% of the variation in taxonomic composition, while overland spatial distance explained 7.4% (p = 0.014). Local variables were more important for aerially dispersing taxa than for aquatically dispersing taxa. (4) Our results indicated that local abiotic and biotic variables acted together with dispersal and overland distance to shape the macroinvertebrate metacommunity composition across river basins. The relative importance of local habitat variables and spatial processes depended on the dispersal mode, with evidence of dispersal limitation for aquatic dispersers. (5) Our study underscores the role of dispersal in influencing the effect of the local habitat on metacommunity organization, even at small spatial scales. We emphasize the need to apply metacommunity theory to stream management, such as incorporating distance between reaches and organismal dispersal traits in bioassessment models.

Ecological interactions, such as food webs, are fundamental for predicting ecosystem responses to environmental changes and anthropogenic disturbances. With wetland ecosystems facing escalating threats from intensified land use, our study aimed to assess the effect of land use on macroinvertebrate food webs across four riverine wetlands situated in lowland streams of the Pampean ecoregion in Argentina. Two wetlands were situated in peri-urban agriculture areas, whereas the other two were located in rural areas with extensive livestock. Through macroinvertebrate sampling and gut content analysis, we present a general description of the diet and a classification of species on the basis of the proportion of different food items in their gut contents. Food webs were constructed for each wetland using the gut content data and structural attributes, such as food web size, number, complexity, and density of trophic links among others, were estimated. Our findings reveal that detritus is the primary resource in macroinvertebrate diets across all wetlands, followed by animal and plant remains. Peri-urban agricultural riverine wetlands exhibited simpler food webs compared to the rural ones, with smaller food web size and lower number, density, and complexity of trophic links. Rural wetlands were characterized by a higher degree of omnivory and proportion of top nodes, whereas peri-urban agricultural wetlands presented a higher number of basal nodes and resource: consumer index. These results suggest that land use may affect the structure of macroinvertebrate food webs in riverine wetlands, contributing to a better understanding of the functioning of these valuable ecosystems.

The study explores phytoplankton diversity and community structure as indicators of Karanja Estuary health. Surface water samples were collected between January 2022 and March 2023, revealing 139 phytoplankton species across three stations and seasons. Cluster and multidimensional scaling analysis delineated three distinct spatiotemporal clusters within the estuary. Peak phytoplankton abundance and diversity during the post-monsoon period contributed to increased salinity, pH and optimal nutrients. The monsoon season witnessed the lowest phytoplankton abundance due to decreased water transparency and light penetration. Biota-environment (BIO-ENV) analysis highlighted water temperature, biochemical oxygen demand, ammonia, silicate and chlorophyll-a (ρ = 0.9084) as significant factors influencing phytoplankton distribution. Canonical correspondence analysis unveiled significant correlations between Skeletonema costatum, Skeletonema sp., Thalassionema frauenfeldii and Thalassionema nitzschioides with nitrate, ammonia, biochemical oxygen demand (BOD) and dissolved oxygen. Diatom species Asterionellopsis glacialis, Chaetoceros sp., Ditylum brightwellii, Ditylum sol and Pseudo-nitzschia pungens were associated with total phosphorus, chlorophyll-a and silicate. High BOD values suggest a significant presence of organic matter, potentially depleting oxygen through decomposition. A high Shannon–Weiner diversity index implies a diverse phytoplankton community with multiple species, indicating ecosystem resilience and stability. This situation may arise when a stressed ecosystem maintains diversity with pollution-tolerant species, which may be temporary and lead to detrimental long-term consequences. The ecological quality status (EcoQS) using six phytoplankton community indices concluded that all the stations ranged from ‘high’ to ‘bad’ condition, with disagreement among the six indices. This study employs a holistic approach, integrating physical, chemical and biological parameters with multivariate analysis techniques to acknowledge the complexity of ecosystem health.

This comprehensive review provides a thorough exploration of a mounting environmental issue: heavy metal contamination in aquatic ecosystems and its far-reaching impacts on fish populations and human health. Starting with the generalized sources of different heavy metals that lead to their entry into the aquatic environment, this review then considers each of the major heavy metals (copper, cadmium, chromium, arsenic, nickel, lead, zinc, and mercury) and ventures deep into the intricate mechanisms governing the uptake, bioaccumulation, and toxicity of heavy metals in fish, shedding light on the profound consequences these processes have for fish health and behavior. A critical aspect emphasized in this article is the activation of antioxidant defense mechanisms and involvement of metallothionein in fish as an adaptive response aimed at mitigating the pervasive oxidative stress triggered by heavy metal exposure. Of utmost concern is the trophic transfer of heavy metals from contaminated fish to humans through consumption, which poses a direct threat to human health regarding various physiological functions. The article underscores the urgency of addressing this issue comprehensively. Given the concerning discoveries at hand, this review fervently supports the enactment of rigorous regulations, the embracing of sustainable management techniques, and the stringent enforcement of pollution containment strategies.

We assessed the trophic roles of 13 medium-sized elasmobranchs in Central Patagonia (41°–47° S) by identifying their interspecific relationships and trophic overlap using stomach contents and δ¹⁵N and δ¹³C values. Specimens were collected from the bycatch of the Patagonian red shrimp Pleoticus muelleri trawling fishery and from the sport coastal fishing in areas without trawling. Results showed spatial differences in the diet composition of species between capture sites and from those previous diets reported for Argentina. Trophic positions assessment showed a group of top predators (TP ~ 4) and mesopredators (TP ~ 3.5). Three trophic guilds were identified for the chondrichthyan species recorded in the coastal and deep zones. We also found a dietary overlap among almost all elasmobranch species mainly related to the consumption of the shrimp P. muelleri. Despite not being reported previously in the diet of studied species, we consider the high consumption of this shrimp as an expected result for demersal mesopredators captured in shrimp fishing grounds. These findings underscore the importance of continually updating trophic information in a global change scenario to contribute scientific evidence to the development of adaptative management.

Maintaining hydrological connectivity is important for sustaining freshwater fish populations as the high habitat connectivity supports large-scale fish movements, enabling individuals to express their natural behaviours and spatial ecology. Northern pike Esox lucius is a freshwater apex predator that requires access to a wide range of functional habitats across its lifecycle, including spatially discrete foraging and spawning areas. Here, pike movement ecology was assessed using acoustic telemetry and stable isotope analysis in the River Bure wetland system, eastern England, comprising of the Bure mainstem, the River Ant and Thurne tributaries, plus laterally connected lentic habitats, and a system of dykes and ditches. Of 44 tagged pike, 30 were tracked for over 100 days, with the majority of detections being in the laterally connected lentic habitats and dykes and ditches, but with similar numbers of pike detected across all macrohabitats. The movement metrics of these pike indicated high individual variability, with total ranges to over 26 km, total movements to over 1182 km and mean daily movements to over 2.9 km. Pike in the Thurne tributary were more vagile than those in the Ant and Bure, and with larger Thurne pike also having relatively high proportions of large-bodied and highly vagile common bream Abramis brama in their diet, suggesting the pike movements were potentially related to bream movements. These results indicate the high individual variability in pike movements, which was facilitated here by their access to a wide range of connected macrohabitats due to high hydrological connectivity.

Urban waterbodies provide important services to humans and play a considerable role in biodiversity conservation. Yet, we still know very little about how urban pond ecosystems may respond to ongoing and future stresses operating at multiple spatial scales. Here we examined the littoral macroinvertebrates in 20 urban waterbodies as an indicator community to assess how local waterbody condition and urban land use affected their taxonomic and functional feeding group composition. Although macroinvertebrates were diverse (total richness of 60 family taxa ranging from 10 to 41), they were dominated by two major taxonomic groups, the Diptera Chironomidae (36%) and Annelida Oligochaeta (22%), which largely represent the dominant functional feeding group of the collector-gatherers (63%). Fuzzy clustering identified four different types of communities based on taxonomic and functional feeding groups. These reflected inversed gradients in the dominance of collector-gatherers versus ponds with higher abundances of herbivores (Gastropoda Pulmonata, Hemiptera, Trichoptera), collectors-filterers (Gastropoda Prosobranchia, Crustacea Ostracoda), predators (Odonata), and parasites (Nematoda, Hydracarina). Distance-based redundancy analysis identified macrophyte cover and green landscape (parks and buildings with green yards) within a 100-m radius as the best drivers to differentiate among the different waterbody clusters. Specifically, waterbodies characterized by high macrophyte cover and the presence of buildings with green yards within 100 m had the highest abundances and diversity. Our results illustrate the benefit of green spaces, beyond parks, up to 2000 m but especially within 100 m from ponds.

Trophic interactions are a critical component of ecosystem stability, governing prey-predator relationships. Crayfish are involved in numerous interactions within freshwater communities and, when non-native, they can negatively impact the structure and dynamics of ecosystems. During biotic interactions or unsuccessful molts, they are able to autotomize one or more claws, which can lead to changes in ecological performance among individuals. Because crayfish claws play an important role in feeding behavior, this creates an overlooked biotic context that could influence trophic interactions and impact on prey communities. It has been shown previously that crayfish claws have a minor role in predation of slow, soft prey, but their function concerning fast hard-bodied prey remains poorly studied. Here, we investigate whether the number of claws on marbled crayfish Procambarus virginalis modulates its ecological impact (focusing on predation rate) using functional response analyses against more mobile hard-bodied prey. We showed that the number of claws in P. virginalis significantly influenced the rate of predation on the prey Gammarus fossarum, with crayfish with two claws exhibiting a higher attack rate and lower handling time than clawless individuals. In addition, we found that non-trophic interactions increased with prey density, with generally antagonistic interactions between crayfish that reduced prey risk irrespective of claw presence. The influence of biotic contexts such as claw presence, prey density and prey type, as well as consumer density, should be considered in inferences of trophic and non-trophic interactions, as well as ecological impacts of invasive species.

Studies on the zooplankton community are essential for diagnosing the health of aquatic ecosystems, as these systems respond quickly to environmental changes. Using the multimetric TRIX index for the assessment of trophic status, we assessed the trophic state and its association with zooplankton composition, distribution, and environmental variables in a tropical estuary on the Brazilian equatorial margin. The results showed that significant seasonal and sectoral environmental differences contributed to biological heterogeneity, with the second spatial sector (SII) exhibiting the greatest impact, leading to decreased alpha diversity compared to that of the first spatial sector (SI). Salinity, pH, SiO₂³, and NO₂⁻ exhibited significant seasonal and sectoral variations (p < 0.05). The community consisted of 65 taxa, with copepods (81.5%), mainly from the Oithonidae and Paracalanidae families, dominating species number. Overall, the community exhibited medium diversity, low richness, and heterogeneity. Beta diversity, calculated using PERMDISP, reflected environmental heterogeneity with significant seasonal differences and biological variability between rainy and dry periods. Indicator species analysis identified 15 taxa, including copepods such as Euterpina acutifrons and Clytemnestra scutellata. Of these, nine taxa (60%) were indicators for the SI, and six (40%) were indicators for the SII. This study underscores the importance of identifying environmental filters and indicator species to understand estuarine dynamics and assess ecosystem trophic states.