Hydrobiologia最新文献

Diatoms have been extensively used as paleolimnological indicators because they acutely respond to changes in their environment. Diatom assemblages recovered from sediment cores are a mixture of benthic and planktic assemblages that may have been transported away from their source environment or deposited near their habitat. Thus, there is an inherent variability in the diatom deposition across the sediments of a lake. With the aim of characterizing this variability and identifying how it may affect palaeoecological reconstructions, we identified diatom communities and assemblages from a series of sediment cores, surface sediment samples, and samples from different lake microenvironments (submerged macrophytes, sediments, marsh, meadow and attached algae). Comparing the sediment cores, we found differences in the timing of diatom assemblage shifts, which we attribute to differences in the diatom distribution in the sediments. Additionally, we identified gradients of diatom deposition where benthic and tychoplanktic diatoms dominate assemblages near shorelines and planktic assemblages dominate toward the lake center. We attribute benthic and tychoplanktic distribution to distance to the source and recognize that diatoms associated with modern microenvironments are underrepresented in the sediments because of their attachment to a substrate.

Functional traits are promising features for biomonitoring in freshwater ecosystems. Here, we focused on 23 floodplain lakes to evaluate the responses of taxonomic and functional traits of freshwater mollusks to the loss of lateral hydrological connectivity (LHC). Our results revealed that the disconnected lakes (DLs) had significantly lower species richness of most functional trait categories of mollusks compared to the connected lakes (CLs). For percentages of species richness, only percentages of burrowers and thick-shelled species were significantly lower in DLs than CLs, while percentages of thin-shelled and small-sized species were higher in DLs. Therefore, there has been a shift toward assemblages with thin-shelled and small mollusks following LHC loss. We also found that key environmental variables affecting taxonomic and functional composition were connectivity, lake area, aquatic vegetable coverage, and water quality. Moreover, the functional composition of all Mollusca, Gastropoda, and Bivalvia were all better explained (explained variation ranged from 0.462 to 0.684) by environmental factors compacted with taxonomic composition (0.213–0.401). Connectivity was the most important factor affecting functional trait composition, whereas area was the most important variable for taxonomic composition. Thus, the trait-based approach based on mollusks was more sensitive in assessing the impacts of disconnection than the taxonomy-based approach.

Understanding the trophic interactions and coexistence processes among waterbirds in floodplain ecosystems is of fundamental ecological importance. In the upper Paraná River floodplain, we assessed the diet of five sympatric waterbird species (Ardea alba, Ardea cocoi, Egretta thula, Nannopterum brasilianum, and Nycticorax nycticorax) and tested their differences in the diet, in addition to food overlap, differences in trophic niche breadths and stratum in the water column where they forage. The waterbirds’ stomachs were collected quarterly on the upper Paraná River floodplain, analyzed under a stereomicroscope, and the food items were identified. Only Egretta thula was classified as omnivorous, consuming various food resources, including insects, decapods, and fish. The other species were piscivorous, but differed in the types of prey. Food overlap was higher in the piscivorous species, but they exhibited high trophic niche breadth. The piscivorous waterbirds employ different strategies for exploiting food resources that allow species coexistence in the floodplain, avoiding direct competition. Our results highlight the importance of waterbirds as connectors across diverse environments, especially aquatic-terrestrial ecosystems. Since these waterbirds’ diet relies on fish, effective conservation and management strategies targeting fish communities are fundamental to maintaining biodiversity and functionality within the upper Paraná River floodplain.

This study determined the relative influence of nutrients and stream habitat on three biological assemblages in five regions of the USA. Nutrient samples were collected over a four-week period, followed by habitat assessment and the collection of biological samples. Biological sampling included diatoms, invertebrates and fish, with three assemblage metrics used for each taxonomic group. We developed boosted regression tree (BRT) models for each biological assemblage metric within each region. Diatom BRT models indicated that nutrients, primarily orthophosphate or total phosphorus, played a larger role than habitat. Nutrients and habitat were approximately equal for invertebrate models with ammonia nitrogen and total organic nitrogen dominant. For fish, habitat had greater importance than nutrients, with total organic nitrogen and total phosphorus the dominant nutrients. Invertebrates had the highest model performance with average CV (cross-validation) R² at 0.47, with diatoms at 0.31 and fish at 0.26. Strongest individual metrics included low phosphorus diatom taxa, tolerant invertebrate abundance and fish multimetric (fish MMI). These findings suggest that the influence of nutrient species varies regionally and by metric, with the relative importance of nutrients and habitat changing as one moves up the trophic level.

The different characteristics of phytoplankton species, such as morphology and the mechanism of resistance to sedimentation, can impact the effectiveness of the Floc & Sink (F&S) technique. In this study, we aimed to analyze the effects of the F&S on biomass and phytoplankton composition, in eutrophic waters from Brazilian semiarid. We applied a chemical coagulant (polyaluminum chloride—PAC), isolated and in combination with natural ballasts (planosol, beige lime and white lime). To assess adaptive strategies, such as positive buoyancy, we applied the morphology-based functional groups (MBFG) approach. The technique effects on the phytoplankton biomass and composition varied according to the sedimentation resistance mechanism. Group IV, lacking specialized characteristics, sedimented in all treatments. The presence of a mucilage sheath and aerotopes prevented its sedimentation in all treatments, and when Microcystis aeruginosa was not present, Group VII sedimented after all treatments. Neither Group V (flagellates) and VI (small diatoms) exhibited sedimentation. Also, filamentous cyanobacteria (Group VIII) demonstrated enhanced resistance to sedimentation and only sedimented when there was a combination of PAC + natural ballasts. Furthermore, employing natural ballast materials provides a cost-effective alternative for removing algal biomass, being observed a drop of 70–80%. Thus, the combination of PAC + natural ballasts was more suitable to remove biomass than PAC alone.

Submerged macrophytes have complex effects on spatiotemporal characteristics of river ecosystems, including trout habitat. We investigated the impact of submerged macrophyte coverage on trout habitat in the Henrys Fork of the Snake River, Idaho, USA. We hypothesized that higher submerged macrophyte coverage would create new habitat types beneficial for trout growth. We assessed river physical and biotic attributes, trout habitat preferences, and estimated trout growth potential with bioenergetics models across a gradient of submerged macrophyte coverage (32–94%). We identified four distinct habitat types within the riverscape shaped by submerged macrophyte coverage. Increased submerged macrophyte coverage increased the frequency of habitat types with higher trout growth potential but reduced the occurrence of preferred habitat types. We observed no relationship between reach-scale trout growth potential and submerged macrophyte coverage. However, an outlier of very high trout growth potential at 94% submerged macrophyte coverage suggests a potential threshold effect. More study is required but our observations suggest macrophyte growth homogenized physical habitat characteristics, reduced flow velocities, and increased invertebrate drift, thereby enhancing trout growth potential. Our findings underscore the complex interplay between submerged macrophytes and trout habitat dynamics across scales, emphasizing the importance of considering both physical and biological effects on trout habitat.

Modern biological invasions represent a major facet of the Anthropocene, yet the invasive potential of species remains poorly understood. In this context, this study compared ecological traits of native and non-native populations of Cichla kelberi, a powerful invader, to investigate the hypothesis that this fish exhibits phenotypic and behavioral variations, which may confer adaptability to different conditions. Data on population structure, trophic ecology, and reproduction were collected from populations in different Neotropical impoundments. We found differences in population structure, with larger mean sizes and a lower proportion of juveniles in the native population. All populations exhibited piscivore behavior, but a higher incidence of empty stomachs and a less diverse diet characterized some non-native populations, with the consumption of non-fish resources and cannibalism. Non-native populations also showed prolonged reproduction and early maturity. In general, differences were not restricted to the contrast native vs. non-native, as introduced populations showed considerable divergence among themselves. Results confirmed the existence of phenotypic and behavioral variation in C. kelberi, which must affect its invasive potential by conferring adaptability to novel conditions in specific localities and contexts. These aspects make C. kelberi an almost certain invader of artificial impoundments located in tropical ecosystems of the world.

Seasonal changes in biotic communities and basal food web resources, including algae and organic matter, have been well studied in temperate environments but less so in subtropical streams. We assessed spatiotemporal variation in algal biomass, measured as ash-free dry mass (AFDM) and chlorophyll-a, coarse (CPOM) and fine (FPOM) particulate organic matter, macroinvertebrate communities, and diatom communities in a subtropical stream in south-central Texas over three years at multiple habitat types. Linear mixed models revealed seasonality significantly influenced AFDM, chlorophyll-a, CPOM, and FPOM. Canonical correspondence analysis revealed strong seasonal changes in diatom but not macroinvertebrate communities. Seasonal patterns generally matched those of temperate latitudes but with altered timing, including algal biomass peaks in winter as opposed to spring and CPOM peaks in spring as opposed to fall. Leaf loss and regrowth and seasonal hydrologic variability likely caused seasonal patterns, similar to mechanisms in temperate streams. Within seasons, physical habitat influenced patch-scale biomass of algae and organic matter, and macroinvertebrate communities showed stronger responses to physical habitat than seasonality. Although seasonal changes of basal food web resources were similar to patterns in temperate streams, differences in timing and across biotic communities may influence food web structure and function in subtropical streams.

Global biodiversity faces imminent threats from climate change, altering species distribution. This study forecasts climate change's impact on diaptomid copepods richness in the La Plata Basin, identifying crucial refuge areas. We hypothesized that rising temperatures will exert in a negative impact on copepod diversity. We utilized climatic and environmental variables to model the geographic distribution diaptomid copepod species. The model forecasts unveiled a contraction in copepod distribution under future climate scenarios. The outcomes from our species richness analysis suggest a potential loss of diaptomid copepod species in the end of the century. Interestingly, certain tributaries of the Paraná River, integral components of the La Plata basin, emerge as prospective climate refuges for these species by 2080. Given the susceptibility of many rivers in the basin to damming and the anticipated severe impacts of climate change on these environments, the findings hold practical implications for strategic conservation planning, emphasizing the importance of maintaining rivers free from dams and promoting the restoration of degraded areas within identified climate refuges. By elucidating the potential consequences of climate change on diaptomid copepod populations, our research contributes valuable knowledge to the broader scientific understanding of the intricate interplay between climate change and freshwater biodiversity.

Surrogate groups are used to find indicator groups and are a fast and effective way to assess biodiversity. For a surrogate group to be efficient, it needs to have strong congruence between different or similar groups. Understanding the surrogate groups in this area with high deforestation rates is extremely important to avoid or minimize the loss of biodiversity, which is severely threatened. The objective was to evaluate the congruence between fish assemblages, Heteroptera, and Odonata in streams in the Amazon–Cerrado transition area. The results showed weak congruence between Odonata and Heteroptera for both data sets. Discordant Odonata and fish showed weak but significant congruence with the abundance data, and with the incidence data the congruence was not significant. A similar result was obtained in the analysis of fish and Heteroptera, which were not congruent with any of the data sets used. The variance partition test, with abundance data, showed that both environmental and spatial variations are responsible for structuring the Heteroptera community, diverging from fish and Odonata did not respond to any of the variations verified, with incidence and abundance data, showing no relationship with environmental and spatial variations. Suggesting Odonata as a surrogate group for this region.