Peracarid crustaceans contribute to the homogenization of macroinvertebrate communities as one of the most important group of aquatic invaders. This study investigated the relationship between alien peracarids and physical and chemical parameters indicative of nutrient and organic pollution, and their contribution to biocontamination of macroinvertebrate assemblages. The impact of alien macroinvertebrates, particularly alien peracarids, on selected biological metrics was examined. Sampling was conducted twice (2015 and 2016/2017) at 46 sites on four major rivers (Danube, Sava, Drava, Mura), accompanied with eight measurements of physical and chemical parameters. Invasive peracarids showed predominantly negative correlations with nutrient pollution, the strongest negative correlations with ammonia, nitrites and orthophosphates. Biocontamination of macroinvertebrate assemblages, calculated as family-level Site-specific Biocontamination Index, was mostly high and severe, whilst the abundance of alien Peracarida mainly determined the biocontamination class. Sites with higher densities of alien Peracarida had lower organic and nutrient pollution and higher biological metrics than sites with lower densities. Biological metrics showed a positive correlation with alien Peracarida densities, whilst their exclusion or exclusion of all alien macroinvertebrates species affected biological metric values. Invasive peracarids can be used as indicators of nutrient and organic pollution and should be included in the calculation of biological metrics for assessing ecological status.
The ENSO (El Niño-Southern Oscillation) phenomenon affects, through climate teleconnections, hydrometric variables of water bodies worldwide, influencing biota communities. The aim of this work is to analyze ENSO effects on water discharge, water level, cyanobacterial blooms and, consequently, on the reproduction of migratory fishes with high-frequency monitoring of ichthyoplankton data from Salto Grande, a large South American reservoir. Two highest peaks of ichthyoplankton density were observed; the first one (2015–2016) occurred during a very strong El Niño event, while the second one (2019–2020) was preceded by weak El Niño events that lasted 18 months. These results suggest that ichthyoplankton abundance may be affected by the intensity and temporal extent of the episodes. In contrast, mean fish larval and egg densities were reduced by 65% and 85%, respectively during La Niña periods. Cross-correlation function (CCF) analysis indicates that water discharge, water level, and ichthyoplankton abundance were positively related to the Oceanic Niño Index, while cyanobacteria showed an inverse relationship. Cyanobacterial density increased by 574% during La Niña compared with El Niño events. Based on an uninterrupted monitoring of ichthyoplankton over 11 years, it seems reasonable to consider ENSO as a predictive tool for the intensity of reproductive activity of migratory fishes.
Pseudunio auricularius (Spengler, 1793) is one of the most threatened unionid species worldwide. Translocation is considered one of the ultimate actions that can save this species from extinction in the Iberian Peninsula. Since 2013, massive mortalities have been recorded in the Canal Imperial de Aragón (CIA), an anthropogenic habitat where the highest density of P. auricularius had been recorded in Spain. An adequacy habitat index was calculated assigning scores to different environmental variables to select the most suitable river stretches receiving the translocated specimens. A total of 638 specimens have been translocated: 291 in 2017, 291 in 2018, and 56 in 2019. The first-year survival in the group of individuals translocated in 2017 was 41.6%. The next year, 95% of these specimens were found alive, suggesting a successful initial establishment. Specimens translocated in 2018 and 2019 showed a survival of c. 69% and 49%, respectively. In contrast, the control group left in CIA in 2017 showed a much lower survival rate of 19.7% after one year, which remained equally low during the next two years. Currently, the conditions in the Ebro River seem to allow a higher survival rate for P. auricularius than those in the CIA; nevertheless, future monitoring should confirm their long-term success.
Eutrophication is a common phenomenon in aquatic ecosystems caused by human disturbance and is regarded as one of the major threats to biodiversity in rivers throughout the world. However, no consistent pattern explains the relationship between eutrophication and biodiversity in rivers. In the present work, we explored fieldwork in connection to the influence of eutrophication on biodiversity in nine streams in a boreal river ecosystem in China. We aimed to test the intermediate disturbance hypothesis (IDH) in our model, which predicts that biodiversity reaches its maximum at intermediate disturbance. We used total phosphorus (TP) as a direct indicator of eutrophication and divided TP concentration into five levels of eutrophication, which represented anthropogenic disturbance of varied intensity. The results obtained from periphyton, macroinvertebrate, and fish assemblages showed that species richness was higher at intermediate eutrophication levels, and the pattern was not impacted by other factors. Our findings may provide important insights into the influence of anthropogenic disturbance on biodiversity in stream ecosystems.
Anthropogenic habitat alteration can rapidly disturb native fish species by hybridization with introduced species. In Korea, the construction of water conduits has unilaterally introduced the allopatrically separated fish species Cobitis tetralineata from the Seomjin River to the Dongjin River where its sister species C. nalbanti inhabits. To assess the impact of this secondary contact on the native species, we investigated the genetic and phenotypic characteristics of populations from the known hybrid zone and other river tributaries of the Dongjin River. Genetic studies of eight microsatellites, one mitochondrial gene, and five protein-coding nuclear genes showed a consistent admixture pattern. Multivariate morphological analysis with 29 meristic and morphometric characters exhibited hybrid populations’ morphological intermediacy to their two parental species. However, all the tributaries being confluent downstream of the Dongjin River were free from hybridization, protecting the native purebred species from the risk of genomic extinction. The present study calls attention to a genetic survey throughout the whole distributional range of native fish species to identify the location containing purebred natives and to evaluate the extent of hybridization, and helps set a conservation priority to prevent further expansion of the current genetic invasion.
We evaluated the biomass of the algae with luxury P uptake (LPU) and mixotrophy in the periphyton in a shallow reservoir mesotrophic. We analyzed the relationship between the two adaptive strategies and light and P availability in the environment and periphyton TP content. Water and periphyton on artificial and natural substrates were sampled in different macrophyte stands in dry and rainy periods. Algae with LPU and mixotrophy represented a large part of total biomass and density, respectively. P was a significant predictor of changes in biomass of the algae with LPU and mixotrophy on artificial substrate. For natural substrate, light was a significant predictor for algal biomass in the periphyton. We found a negative relationship between the biomass of algae with LPU and mixotrophy and TP concentration and light. Biomass of algae with both strategies tended to decrease with the increase in TP content in the periphyton. Algae with LPU and mixotrophy had growth success in periods of high shading and low P and both were associated with the P-limiting condition. In conclusion, algae with LPU and mixotrophy can contribute to the storage of the P in the periphyton. Changes in the proportion of autotrophic and mixotrophic algae in the periphyton can affect the potential for removal and retention of P of the community in lakes and shallow reservoirs.
To understand the spatiotemporal overlap in the habitat use of sympatric predators, we studied longitudinal activity and reservoir section and depth use of pike (Esox lucius), pikeperch (Sander lucioperca) and catfish (Silurus glanis) in the Římov Reservoir, using an autonomous telemetry system for 11 months. We found significant differences among these species in studied parameters that varied considerably over tracked period. Pike consistently used the same sections of the reservoir, while pikeperch and catfish frequently visited a tributary during the warm season (late spring and early autumn), and moved closer to the dam during the cold season (late autumn to early spring). Pike longitudinal activity was highest in the cold season, pikeperch in the warm season, and catfish activity peaked in both seasons. Overlap in the depth use among species was higher in the warm season, when all species used the upper layer of the water column, and lower in the cold season, when pikeperch and catfish used deeper areas. These results demonstrated overlay and temporal variation of habitat use among these predators, as well as potential spatiotemporal space for their direct ecological interactions.
The characteristics of propagules markedly impact the germination and plant growth of submerged macrophytes. Vallisneria spinulosa S.Z. Yan is a common submerged macrophyte and has been widely used in lake restoration projects. The responses of tuber germination and plant growth to different tuber sizes and burial depths are not well known for this species and may vary with light intensity. In this study, the tuber germination and plant growth of V. spinulosa germinated from two levels of tuber sizes (large and small) and two different burial depths in the sediment (5 and 15 cm) were tested at two light intensities (high and low) by measuring morphological and physiological traits. Although light intensity, tuber size and burial depth did not affect the tuber germination, they significantly influenced the morphological and physiological traits of the plants. Light intensity had the greatest effect on plant growth, followed by tuber size, while burial depth had the least effect. High light, large tuber and shallow burial depth favoured the plant growth performance (plant biomass, ramet and leaf numbers). The growth performance of plants germinated from small tubers was more susceptible to changes in light intensity and burial depth. Soluble carbohydrate and free amino acid contents were negatively and starch content positively correlated with the morphological traits. The study highlights the importance of tuber size and burial depth for plant growth as well as their interactions with light, which should be considered when determining lake management and restoration strategies.
We conducted a monitoring study on the dynamics of the abundance, biomass, and vertical distribution of the cryptophyte population in meromictic saline Lake Shira (90.11 E, 54.30 N) in the periods of stable meromixis (2012–2014), meromixis breakdown and mixing of the entire water column (2015–2016), and the subsequent reestablishment of meromixis (2017–2021). When stable stratification was broken down, cryptophyte biomass increased sharply: from 0.1 to 6 g m⁻² on average in the water column (to 4500 cells ml⁻¹ in the vertical maximum). The shape of the vertical distribution of cryptophytes has also changed. Changes in the abundance of cryptophytes caused by the breakdown of meromixis have largely endured after it was reestablished. Such a considerable increase of cryptophyte biomass did not correlate with the corresponding parameters of other components of the Lake mixolimnion ecosystem, whose biomass changed by a factor of no more than two. The explosive growth of cryptophyte abundance can be explained by a decrease in the trophic pressure of zooplankton—copepods and rotifers.
The emergence of reproductive isolation is key in maintaining within- and between-species diversity and one of the initial steps of speciation. In the Iberian Peninsula, the diverging populations of the Brachionus plicatilis rotifer create an ideal system to shed light on the mechanisms that give rise to the emergence of reproductive isolation. Herein, we quantify the degree of behavioural reproductive isolation in two groups of B. plicatilis populations, namely, neighbouring populations diverging by adaptation to the local environment and populations diverging in the absence of gene flow due to geographic distance. We conduct behavioural no-choice assays to test mating reproductive isolation between these populations. The analysis shows signatures of ongoing behavioural reproductive isolation in most of the population crosses, which is more pronounced in populations with a higher level of adaptive divergence, presumably under high migration rates. Overall, this study suggests that local adaptation is associated with mating behaviour resulting in reproductive isolation.
Testing ghost crabs as indicator species usually fail to depict the mechanisms behind low burrow densities in urban coasts, neglecting individual traits as diagnostic variables. We conducted metaanalyses to compare the diameter of ghost crab burrow openings across gradients of human disturbances. Length–weight regressions were calculated, hypothesizing that crabs condition difer between beaches with high and low disturbance. The dataset regarding burrow opening diameter included 78 beaches (latitudes between 36° N and 30° S), and length–weight regressions were calculated based on 1,172 crabs data from 11 beaches (latitudes between 23° N and
30° S). Mean burrow diameter was smaller in high
disturbance beaches, but a linear relationship with
the level of human modifcation was not found in our
gradient analysis. The higher the number of stressors
acting locally, the greater the negative efects on burrow diameter. The body condition of ghost crabs was
lower in high disturbance beaches; this result challenges the hypothesis that ghost crabs are smaller
on disturbed beaches merely because individuals die
before reaching adult ages. Our results have implications within the scope of ghost crab ecology, particularly regarding the inclusion of trait variation in
investigations of mechanisms underlying spatial contrasts and in application of ecological-disturbance
The upside-down jellyfish Cassiopea has become a model organism for the study of symbiosis between dinoflagellates and cnidarian hosts. Most previous studies have indicated that the presence of symbiotic zooxanthellae is a key requirement for strobilation in Cassiopea. Indole compounds have been shown to induce strobilation in many scyphozoans, including symbiotic Cassiopea xamachana. To determine if indoles could induce aposymbiotic Cassiopea polyp strobilation, we acquired algal-free Cassiopea andromeda polyps and used three indoles (indomethacin, 2-methyl indole, and 5-methoxy-2-methyl indole) to induce metamorphosis by applying single doses within a range of 0.005–100 μM. Analysis showed that indoles successfully induced aposymbiotic polyp strobilation and that the induction effects were compound- and dose-dependent. 5-Methoxy-2-methyl indole and 2-methyl indole were significantly more effective than indomethacin (P < 0.001). Data showed that it took 3 to 9 days for 5-methoxy-2-methyl indole or 2-methyl indole to induce strobilation and that 25 μM of 2-methyl indole was the most effective inducer of strobilation in algae-free C. andromeda polyps. Indole-induced strobilation was associated with several developmental abnormalities, including failed or retarded regeneration of residual polyps after strobilation, a reduction in the size of ephyrae, and abnormal morphology of the ephyrae.
Non-hydrophyte species experience the re-flooding hypoxic conditions in wetland; however, how they exist in wetland is still not well studied. A field experiment was developed in Jinchuan wetland with different water level conditions (high water level: 6–7 cm; low water level: 1.5–2.5 cm). The above-ground biomass, the heights and areas of tussocks, and the names and number of species on each tussock were measured, and the proportions of non-hydrophyte species (PNH) were calculated. In the high water level condition, tussocks accumulated more biomass, increased the heights and reduced the areas. Importantly, PNH were significantly higher in the high water level condition compared with low water level condition (51.22 ± 11.26% vs 45.95 ± 14.02%). Interestingly, the number of non-hydrophyte species and PNH decreased with the increasing of the heights of tussocks and the decreasing of the areas of tussocks. Overall, tussocks could grow well and provide living space for non-hydrophyte species in re-flooding condition; thus, tussocks could be regarded as nurse plants, which is a new mechanism of non-hydrophyte species to exist in wetland. Moreover, it is valuable to know non-hydrophyte species preferred to grow on lower and bigger tussocks for wetland management. Degradation in Jinchuan wetland can be retarded through controlling the morphological characteristics of tussocks.
As a result of a field trip in 1980 to the monsoonal wetland of the Keoladeo National Park, India, which was organized by Dr. Brij Gopal, a study of the vegetation dynamics of this wetland was initiated. The original hypothesis for this study was that the seasonal vegetation changes caused by the annual summer monsoon was a compressed habitat cycle. Habitat cycles are a characteristic of prairie potholes in North America. Habitat cycles are the result of wet–dry cycles that last from 5 to 25 years during which the vegetation of a pothole changes from dense emergent vegetation (dry years) to open water with only submerged vegetation (wet years). In retrospect, our field studies were not consistent with our hypothesis. The increase in water level caused by the monsoon was not large enough to kill the emergent vegetation, as happens during prolonged high-water years in prairie potholes. However, both wetland types have significant seed banks that allow their plant species to survive adverse conditions. We now believe that the vegetation dynamics of monsoonal wetlands are best described as seasonal shifts between a wet marsh phase when the wetland is flooded and a dry grassland phase when it is not.
The holobiont concept places emphasis on the strict relationship between a host and its associated microbiome, with several studies supporting a strong effect of the quality of the microbiome on the host fitness. The generalities of the holobiont have been questioned for several invertebrates, including zooplankton. Here we assess the role of host ecology, habitat, and evolutionary history to explain the differences in the microbiomes associated with rotifers, across a broad taxonomic spectrum and from different habitats. The analyses of 93 rotifer-associated microbiomes from 23 rotifer host species revealed that a combination of effects from the host ecology and its habitat seem to be stronger than host phylogenetic distances in explaining differences in microbial composition of the microbiomes. This pattern is in line with the idea of habitat filtering being a stronger explanation than co-evolution in shaping the relationship between a microbiome and its rotifer host.
Eutrophication is a key threat to aquatic biodiversity around the world, but especially in the Cerrado biome that has undergone intensive land use conversion and fertilizer use. In this study, we investigated how water conditions and different taxonomic and functional indicators of phytoplankton communities responded to eutrophication over time and also identified which of these variables can act as early indicators of eutrophication. We used a mesocosm experiment to simulate shallow lakes and added nutrients to produce eutrophic and oligo-mesotrophic environments. We found that conductivity and turbidity increased with the nutrient enrichment process. Eutrophication did not change species richness; however, it increased the total phytoplankton density and chlorophyll-a concentration and decreased the diversity indices (Shannon–Wiener diversity and Pielou’s equitability) over time, for both taxonomic and functional facets. Our results indicate that eutrophication may not have marked effects on the composition of the initially dominant organisms in the short term but does increase the density of certain organisms and exclude rare species and functional groups in eutrophic environments along the time. Furthermore, the diversity indices are more sensitive indicators of eutrophication compared to abiotic indicators and composition of species and functional groups. Therefore, they may be considered reliable early warnings of ecosystem changes.
Cichlid fishes show remarkable variation in visual sensitivities through differential expression of seven cone opsin genes. Many species undergo spectral sensitivity shifts from shorter to longer wavelengths as they develop from larvae to adults. However, while some species retain larval-like short wavelength sensitivities, others show adult-like longer wavelength sensitivities throughout life. The riverine cichlid, Astatotilapia burtoni, shows a single cone progression from ultraviolet to violet to blue sensitivity, while their long wavelength double cones maintain green and red sensitivities throughout life. To identify mechanisms that regulate these sensitivities, we asked whether thyroid hormone (TH) or light environment can drive shifts. We find that developmental treatment with TH can speed shifts to longer wavelength sensitivity, but only in single cones. TH inhibition can short wavelength shift adult opsin expression. Exposure to light regimes containing UV wavelengths induce short wavelength shifts in single cones early in development. None of the treatments produces double cone shifts or significant expression of the shortest wavelength double cone opsin, rh2b, although we detect no cis-regulatory variation. This suggests that while single cones show both TH and light plasticity, A. burtoni double cones have lost this plasticity, perhaps through changes in trans-acting opsin regulation.
Phenotypic plasticity allows organisms to rapidly adjust to environmental changes. Cichlid fish inhabit a wide range of light environments and show a large diversity in visual system properties, which makes them a good model system to address the role of phenotypic plasticity in visual adaptation. Cichlid retinal cone pigments consist of opsin proteins bound to Vitamin A1 or A2-derived chromophores. Plasticity in expression has been shown for cichlid opsin genes, but less is known about the contribution of cyp27c1, the enzyme that converts Vitamin A1 into A2,. Here, we studied both opsin and cyp27c1 expression patterns for three closely related cichlid species from different visual habitats in Lake Victoria, across different light treatments. We found differences in cyp27c1 as well as in opsin expression patterns between the three species. Experimental light treatments affected the developmental trajectory of cyp27c1 expression in one species and opsin expression in all three species. Within each species, we found large individual variation in cyp27c1 expression levels and no consistent association with opsin expression levels. These results indicate that visual system plasticity of even closely related species can be differentially mediated by opsin and cyp27c1 expression, possibly associated with species differences in visual niche.
Shelter availability is one of the key features governing crayfish habitat quality. It can directly influence crayfish’s individual survival of by lowering the risk of predation, but the ecosystem-wide impacts of sheltering on water quality are largely unknown. To test the effects of shelter availability for Procambarus clarkii in clear-water macrophyte-dominated lakes, we performed a 24-day mesocosm experiment in 20 tanks (4 with one crayfish with and without shelters, 4 with two crayfish with and without shelters and 4 controls). The bottom of each tank was almost completely covered by the eelgrass Vallisneria denseserrulata. Compared with the treatments with shelters, more broken leaves occurred in the treatments without shelters at both crayfish densities at equivalent crayfish numbers, and total phosphorus was higher in the treatments without shelters. Total suspended solids and total nitrogen concentrations were higher in the treatments with two crayfish without shelters than in those with shelters, whilst these variables did not differ between treatments in the mesocosms with one crayfish only. Our results suggest that shelter availability reduces the activity of crayfish (e.g. movement and burrowing) and agonistic behaviour, thereby decreasing the negative effect of the invasive P. clarkii on water quality in V. denseserrulata-dominated clear-water lakes.
We analyzed periphyton structure, elemental composition: carbon (C), nitrogen (N) and phosphorus (P), and algal composition along an urban gradient in three water courses of Ushuaia City. We hypothesize that periphyton stoichiometric ratios (C:N, C:P and N:P) decrease with the increase of urban land use. Also, community structure is affected by urban land use; sites with major surrounding urban and higher nutrient load host larger biomass and different algae composition compared to more pristine sites. P content and mass fractions of periphyton increased along the urban gradient as well as dissolved P in the water. Periphyton molar ratios N:P and C:P showed a negative lineal relationship with the gradient of urban land use. In general, periphyton was dominated by diatoms although Chlorophyta biovolume, mainly composed of filamentous algae, increased significantly in sites with 70% of urban land use. Our data suggest that there is no homeostatic balance in the periphyton community in Sub-Antarctic streams; we detected more P in periphyton in urban sites and the community became thus less heterotrophic. This study helps to better understand the dynamics of nutrients and its influence over a sessile community in sub-Antarctic lotic ecosystems impacted by urbanization.
We studied temporal variations in phenolic compounds from the hydrophyte Myriophyllum aquaticum collected from a shallow lake. The effects of macrophyte-conditioned medium containing phenols with other compounds and phenols only as well as plant tissue extracts were tested on the survival and reproduction of the rotifer Plationus patulus. Apical tissue of the hydrophyte had the highest levels of total phenols. Rotifers in controls, and those exposed to phenols from the macrophyte-conditioned medium grew rapidly within two weeks, but cultures exposed to phenols extracted from the apical region took longer. Age-specific survival of P. patulus showed a rapid decline within one week when exposed to plant extracts compared to conditioned medium. The average lifespan of P. patulus was longer in the macrophyte-conditioned medium as compared to the controls, but shorter in the aqueous plant extract. Gross and net reproductive rates showed similar trends, wherein the controls had significantly higher values than those exposed to plant extracts, but increased with the conditioned medium only at the two lower concentrations tested. The demographic response of rotifers exposed to phenols only from the macrophyte-conditioned medium differed from those of the macrophyte-conditioned medium containing both phenolic and non-phenolic compounds. Macrophyte phenolic compounds influenced the survival and reproduction of P. patulus but depended on the other chemicals released into the medium.
Variation in jaw protrusion is critical to cichlid fish trophic diversification. For instance, jaw protrusion distance can influence suction, attack speed, as well as bite force, and jaw protrusion angle is associated with exploiting prey from different substrates. Interestingly, premaxillary ascending process length has been shown to influence the maximum distance some cichlid fishes protrude their oral jaws, but its relationship to jaw protrusion angle is unclear. Using phylogenetic comparative methods, morphometrics, and field measurements in Malawi cichlid species, we tested the relationship between the length of the premaxillary ascending process and two components of jaw protrusion. In Malawi, the premaxilla's ascending process length ranged from 6.9 to 15.2% with respect to standard length. Maximum jaw protrusion ranged from 1.4 to 9.1% of standard length and jaw protrusion angle varied from 17° to 76°. Although jaw protrusion angle was not associated with premaxillary ascending process length, phylogenetically adjusted correlations between the ascending process and maximum jaw protrusion distance were highly significant. Evolutionary change in the premaxilla is likely critical for determining the maximum distance, but not the angle, of Malawi cichlid jaw protrusion. Examinations of this type of potential phenotypic multi-functionality will continue to illuminate the mechanisms contributing to cichlid fish diversity.
Species are often exposed to novel thermal regimes as a result of anthropogenic activities. Understanding the extent to which populations are locally adapted to the thermal regime may allow us to better predict the response of organisms to novel thermal conditions. We collected virile crayfish, Faxonius virilis, from eight populations along a latitudinal gradient and measured their routine metabolic rates (RMR) and thermal tolerance. Countergradient variation suggests that organisms from northern latitudes may spend more energy foraging as an adaptation to the shorter growing season. Thus, we hypothesized that crayfish RMR would be positively related to latitude. We also expected high latitude populations to have a greater sensitivity to acute temperature change and a lower thermal tolerance. In support of our hypothesis, there was a significant positive relationship between latitude and crayfish RMR at night when crayfish are most active, and crayfish from high latitude populations were more thermally sensitive. Thus, changes in the thermal regime are likely to alter the activity level of this species, which could alter its ecological impacts. In addition, virile crayfish across the latitudinal gradient had a high thermal tolerance, which may contribute to the success of this species in novel environments.
The present work comprehensively investigated the responses of submerged Ceratophyllum demersum to exudates and extracts of toxic Microcystis aeruginosa at the exponential (EU, ET) or declining phase (DU, DT). The highest amount of MC-LR was detected in medium with DT, the value of which reached 6.36 μg/l, and C. demersum exhibited the highest absorption of MC-LR with a value of 1.73 ng/g FW upon exposure to DU. Significant negative effects on C. demersum was detected under the treatment with EU of toxic M. aeruginosa, expressed with the reduction of freshweight, Chla/Chlb, and the Superoxide Dismutase (SOD) activity. Meanwhile, increased carotenoid/total chlorophyll ratio might be employed by submerged C. demersum as the defense strategy to EU of toxic M. aeruginosa. In addition, under EU treatment, the microorganisms Flavobacterium Bergey, and Chryseobacterium Vandamme, which exert negative effects on aquatic organisms, increased, whereas the Rhizobacter Goto & Kuwata, Limnothrix Meffert, and Pseudanabaena Lauterborn, which are beneficial to the growth of the plants, were lower. The research highlighted the significance of toxic cyanobacterial bloom development and different growth phases on submerged macrophytes, providing more insights for the allelopathic interaction between submerged macrophytes and toxic cyanobacteria in natural freshwater ecosystems.
Human-induced water level fluctuations (WLFs) are among the major pressures threatening lake ecosystems. Their effect on meiobenthic species of the littoral zone has been poorly investigated. In this study, we aimed at assessing the effects of human-induced WLFs on the composition and functionality of the benthic copepod assemblages of the littoral zone of Lake Maggiore, Italy and Switzerland. From 1942 to present, the water level of Lake Maggiore has been regulated through the Miorina Dam. We monitored copepod assemblages during different water levels defined within the period of regulation by the dam, using taxonomy- and trait-based metrics. We observed variation in the overall abundance and biomass of copepods, as well as in the number of individuals belonging to some trait classes such as ovigerous females, opportunists, omnivores and deposit feeders. None of the investigated trait class was completely lost. The results of our study suggest that ecosystem services supplied by the littoral zone of Lake Maggiore are likely altered by human-induced WLFs. Our findings provide a first picture of WLF impacts on benthic copepod assemblages, which can be useful for future research expanding on other functional traits.
Beta diversity is the variability in species composition among sampling units for a given area and can be influenced by several environmental drivers, including environmental heterogeneity. Here, we considered the contribution of seven tributaries flowing into the Upper Paraná River channel as the mains drivers of environmental heterogeneity and zooplankton beta diversity. We used Mantel test to examine the relationships between zooplankton functional beta diversity components (total, turnover, and nestedness) and environmental and geographical distance. Generalized dissimilarity modeling (GDM) was run to test which environmental variables were the best predictors of beta diversity components. Mantel’s test results revealed that total beta diversity was positively related with environmental heterogeneity in almost all periods. GDM analysis results showed that total beta and turnover were related to temperature, organic suspended matter, dissolved oxygen, NH4, and pH, while nestedness was influenced by depth and geographic distances. Our results support the idea that smaller rivers are a main source of diversity for large rivers, especially the ones with cascading reservoirs. Overall, our study shoes that variation in limnological variables results in higher dissimilarity in zooplankton communities and that environmental change filters and sorts species according to their functional traits.
Small streams in the temperate continental region of central Europe have been recently exposed to frequent drying. We investigated the effects of drying on clitellate communities in 25 small streams evenly distributed along the gradient of flow intermittence. We observed that the community exposed to both irregular and periodic drying could maintain local species diversity. However, significant differences in clitellate species composition were observed between perennial, irregularly drying, and intermittent streams. The effect of drying was even stronger in intermittent streams, where significantly lower beta diversity was observed compared to perennial streams. The most important changes in clitellate composition were controlled by water temperature and geographical variables in perennial streams, while streams affected by drying were controlled by climate, with high mean July air temperature and low annual precipitation sums amplifying the effect. The abundance of semiaquatic species was also affected by the periodicity of the dry phase, with their proportion predicted in the regression tree analysis to be 11% in perennial and irregularly drying streams, and 40% in periodically drying streams. The observed changes in clitellate community structure suggest a gradual adaptation to increasing drying severity, in which sensitive species (e.g., rheobionts) may be replaced by desiccation-tolerant and semiaquatic species.
Freshwater mussels are important functional components of aquatic ecosystems. Westralunio carteri is a threatened freshwater mussel species, endemic to south-western Australia, which has suffered a recent, dramatic decline in range. The density, size structure and distribution of adult mussels of this species within river reaches were investigated using quadrat searches and modelled against a range of microhabitat factors. Mussels were found from 26 sites in 14 different rivers at a mean density of 28.4 ± 2.3 individuals m ⁻² . The distribution of W. carteri was highly aggregated within river reaches. The most important factors explaining mussel distribution were substrate grain size, substrate debris and distance from the riverbank, with finer substrate, the presence of woody debris and proximity to the riverbank associated with greater abundance of mussels. In all rivers where mussels were found, most populations appeared to be actively recruiting. However, no mussels were found in six sites, despite them having been recorded as present within the last 20 years, which suggests that the range of the species is still in decline. The identification of microhabitat requirements for W. carteri will assist in identifying suitable release sites for translocation and/or captive propagation, which may be required to prevent extinction of the species.
Our study incorporates high-resolution, multivariate ecological niche modeling (ENM) to test whether two putative state-threatened mussel species in East Texas (Fusconaia askewi and F. lananensis) are ecologically differentiated. We forecasted suitable habitat to identify any differences in the taxa’s habitat associations, using a total of 60 environmental layers comprising climate, soil, and hydrology in a multivariate framework. We found the two species were not ecologically different, consistent with other work (e.g., morphology and genetics) suggesting that they are synonymous. We synonymized the two to make an ENM that was then ground truthed by sampling 25 novel sites throughout East Texas. Our ENM significantly distinguished suitable from unsuitable habitat for these sites, identifying five new records. We compared model evaluation metrics using the original data versus the ground-truthed data, and we found that some metrics were more reliable than others. The verified ecological niche modeling approach that we present here can be applied in other studies in riverine environments and has particular relevance to conservation science.
In the present study, we aimed to demonstrate that allelopathic compounds from the cyanobacterium Phormidium sp. can induce the collapse of large populations of the cyanobacteria Microcystis aeruginosa Kützing Kützing. We employed several strains of this toxic cyanobacteria, from six different locations, in order to test for adaptive variation in resistance to allelochemicals. As a preliminary test to detect allelopathic effect, we performed bioassays with Phormidium allelochemicals against the different strains of M. aeruginosa at low population abundances. Then, we combined long-term competition experiments and mechanistic modelling with two purposes: (a) demonstrate that the inhibitory effect of Phormidium sp. against M. aeruginosa was due to allelopathy and not resource competition; (b) test the effectiveness of these allelochemicals at inducing the collapse of large populations of M. aeruginosa. Our results showed a strong allelopathic effect of Phormidium, which induced the collapse of large populations of M. aeruginosa, without evidence of differences in sensitivity between strains. We demonstrated that allelopathy (interference competition) can reverse the outcome predicted by resource competition (exploitation competition). These results are encouraging in order to take further steps in the development of a bioremediation method, based in Phormidium allelopathy, against blooms of toxic cyanobacteria.
Plant invasions often lead to homogenization of plant communities, but the potential for homogenization of other trophic levels is understudied in many systems. Biotic communities in coastal wetlands are closely tied to daily and yearly water-level fluctuations. We compared the bird community in invasive Phragmites australis (European common reed) habitat and remnant, uninvaded marsh in a year with average water depths and a year with above-average water depths in Long Point (Ontario, Canada), a World Biosphere Reserve. Our results demonstrate the spatial and temporal homogenization of the wetland bird community following P. australis invasion. The bird community present in P. australis was a nested subset of the species present in remnant marsh, and total beta diversity in P. australis habitat decreased when water depths were above average. In contrast, total beta diversity was high in remnant marsh vegetation. The distinctively structured vegetation zones in remnant marsh yield structural complexity and habitat heterogeneity that support greater taxonomic turnover in the bird community. These results provide evidence that invasion by a plant has resulted in the biological homogenization of the wetland bird community and illustrate that habitat use will change with prevailing environmental conditions, such as high- and low-water levels.
In order to analyse the relationship between oceanographic factors and the distribution of marine phytoplankton in oligotrophic conditions, an oceanographic cruise was carried out in the waters surrounding Cozumel Island, Mexico. Due to the contrasting bathymetric characteristics around Cozumel, and the possible influence of such feature on the stratification and phytoplankton ecology, physico-chemical and biological variables were measured on both sides of the island in the surface, fluorescence maximum and the halocline. Our results show that there is a strong stratification in the water column at the east side of the island, unlike the Cozumel Channel on the west, where stratification is milder and there is an uplift of the picnocline associated with the powerful Yucatan current and the reduced bathymetry of the channel. The phytoplankton community, mainly composed of diatoms, dinoflagellates and the dominant cyanobacteria Trichodesmium, showed high dissimilarity between sides of Cozumel and presented low richness, diversity and cell density. The difference between the density and species composition of the surface phytoplankton (related with high temperature), compared to the halocline layer (related with high nutrient concentrations), suggests that the effect of dynamic uplifting on stratification is a key factor that controls the phytoplankton community structure in oligotrophic waters.
Herbivorous macroinvertebrates make up a large fraction of secondary production in wetlands, but little is known about how water flow affects herbivorous macroinvertebrate production. Reintroducing measurable water flow (1–5 cm/s) to the oligotrophic (phosphorus-limited) Everglades has the potential to improve herbivorous macroinvertebrate production by providing a constant low supply of phosphorus (P) to periphyton and improving food quality. This study investigated potential effects of flow-mediated nutrient loading on growth rates of herbivorous grazers, juvenile apple snails (Pomacea maculata). Periphyton was grown on standard substrates, within a landscape-scale flow addition experiment, in two sloughs that received elevated velocities (3–5 cm/s) and two control sloughs. The flowing sloughs produced periphyton with greater biomass, higher concentrations of nutrients, and lower C:P ratios. Snails, in a laboratory setting, gained more than 3.7-fold greater total mass when fed periphyton from flowing sloughs than snails fed periphyton from control sloughs. Water column nutrients were slightly elevated in flowing sloughs, but the amount could not fully explain differences in periphyton nutrients or snail growth. Increasing flow above background conditions improved food quality, which subsequently increased growth rates. Restoring flow has the potential to increase nutrient accessibility that could enhance food webs, but additional study will be needed to determine whether increased growth rates translate into increased standing stocks.
To clarify the effect of paternal life-history form and egg size on offspring life-history traits (e.g., growth and maturation) in masu salmon (Oncorhynchus masou), we studied an artificially fertilized population for 3 years using mark-recapture methods. The body size of offspring in early life was associated with egg size, but not paternal life-history form. By contrast, the growth rate of individuals during summer and winter seasons was not influenced by egg size or paternal life-history form. Movement within the tributary differed between males and females, with more females moving downstream during early life stages compared to males. However, the effects of egg size and paternal life-history form on the movement of offspring were not detected. Out of 192 males that remained in the tributary, 77 had relatively large body sizes and reached sexual maturity at one year old. The probability of maturation was associated with the body size in September, but not with paternal life-history form and egg size. We concluded that offspring life-history traits are profoundly influenced by environmental conditions, whereas they are slightly influenced by parental genetic effects.
The small-scale whelk (Rapana venosa) and Asian paddle crab (Charybdis japonica) pot fishery are of great socio-economic importance to coastal communities of the Yellow Sea, China. However, the conventional pot with a regulated mesh size of 25 mm is unfavorable to the sustainability of these two species due to its poor selectivity. In this study, we intend to improve the size selectivity of pots by configuring escape vents. Three different escape vent sizes (diameter of 45 mm, 50 mm, and 55 mm) were tested using a catch comparison method. Our results demonstrated that escape vents significantly improved the size selectivity of pots for whelk and crab. The escape vent with a diameter of 55 mm released the maximum number of undersized whelk and meanwhile maintained the catch efficiency of individuals above the Market Reference Size (MRS; 45 mm) compared with the conventional (control) pots. The escape vent with a diameter of 50 mm significantly reduced the retention of undersized crab to 21% and increased the catch rates of individuals above the Minimum Landing Size (MLS; 50 mm) to 112%. Although hard to achieve “perfect selectivity” for morphologically different species in mixed fisheries, we recommend a compromise escape vent size of 52 mm in comprehensive consideration of resources’ sustainability and fishermen’s profits. The promising results of this study can provide feasibility and insight to develop management strategies for small-scale pot fishery.
The population genetic structure and female philopatry to nursery grounds of the scalloped hammerhead shark (Sphyrna lewini) were studied in different mangrove estuaries along the Mexican Pacific coast containing putative nurseries. These nurseries were grouped into northern (Sinaloa-Nayarit), central (Jalisco), and southern (Oaxaca-Chiapas) regions. Neonates and young of the year were collected near estuaries or river inlets, and their genetic variation was compared based on mitochondrial DNA (mtDNA) genome sequences and 11 nuclear microsatellite loci. The mtDNA analysis showed significant differences between the abovementioned regions, accompanied by genetic homogeneity of microsatellites. Based on the genetic divergence of mtDNA and the lack of differences in nuclear markers, our results are congruent with female philopatry to nursery areas, as observed in other shark species. The parentage analysis applied to the microsatellite data showed moderate levels of relatedness among individuals within nurseries, suggesting philopatry as a cause of the observed results. The pattern of nursery grounds of the scalloped hammerhead shark in the Mexican Pacific seems to be regional, as no differences were observed between neighboring estuaries within each studied region. These findings are relevant for delineating conservation plans to preserve key populations and minimize the effects of commercial fisheries.
We used experimental chambers to evaluate the effect of the temperature increasing and microbial conditioning degree on the survival and leaf consumption of two plant species [Protium spruceanum (Burseraceae) and Goupia glabra (Celastraceae)] by larvae of the shredder Phylloicus elektoros. We also evaluated the sporulation rate of the conditioned leaf debris. The leaf discs were incubated for 0, 7, and 15 days in a stream. Posteriorly, the treatments were inserted in chambers with temperatures of 23.2 °C and 27.5 °C. The higher sporulation rate was found in leaves of G. glabra, with no difference in sporulation among the microbial conditioning treatments. The larval survival was lower in treatments with leaves of P. spruceanum, and in the warming temperature. The microbial conditioning time did not influence larval survival. The effect of the conditioning time and temperature on the leaf consumption depended on the plant species. The foreseen temperature increases and reduction of the palatability of the leaves due to the climate change may result in negative effects on the leaf consumption and survival of larvae of P. elektoros.
The Paraná River Delta is one of the most biodiverse and largest mosaic of wetland ecosystems in South America. Yet its natural hydrological patterns are being strongly distorted by sustained land use intensification and extraordinary severe droughts. Understanding whether the aforementioned processes negatively affect wetland biodiversity is urgently needed to delineate accurate conservation actions. In this study we analyzed zooplankton diversity patterns at the local and regional scales, as well as compared species composition between natural (freshwater marshes) and artificial water bodies (ditches), all of them affected by livestock activities. Our study involved two hydro-meteorologically contrasting conditions within two consecutive years of sustained drought: a high water stage (HW) and a low water stage (LW). Adverse environmental conditions in the LW period enhanced local zooplankton abundance and taxonomic richness, but decreased beta diversity and individual biomass, leading to a simplification of functional diversity. Species composition differed between freshwater marshes and ditches; however, they equally contributed to the zooplankton diversity metrics, suggesting that both kinds of freshwaters acted as complementary contributors to regional zooplankton diversity. Considering the regional drought patterns occurring in this landscape, we expect a generalized biotic and functional homogenization of zooplankton wetland diversity in the very next few years.
Glass microscope slides were submerged for two to six week periods at selected sites in a small, spring-fed stream near Lennoxville, Quebec. Slides were oriented parallel and perpendicular to the current. Qualitative and quantitative data from transects across slides show that diatoms are randomly distributed on slides perpendicular to the current but not on slides oriented parallel to the current. In the later case, most individuals first settled near the upstream or downstream edge of the slide. Non-random distribution is most pronounced on slides containing Cocconeisplacentula. This species and two others, Achnanthes Iinearis and A. minutissima, are abundant and determine most distribution patterns found on slides. Preference of diatoms for the edges of slides appears to be affected by current. We propose a model, based upon water flow, to explain the preferential distribution of diatoms on slides oriented parallel to the current. Light appears not to affect settling patterns to a great extent in this study.
Homing is an essential aspect of the evolutionary ecology of salmon, and the final stages are guided by odors learned prior to migration from natal sites. Amino acids (AAs) have been hypothesized to provide olfactory information sufficient for homing. We sampled water from five tributaries to Lake Aleknagik, Alaska prior to and after the arrival of adult sockeye salmon to determine whether the AA composition or concentration differed among streams, or changed after adult salmon entered the streams and began spawning. The dominant AAs were generally similar before and after salmon entered, although some shifts in relative contribution were noted. However, there were dramatic increases in concentration of all AAs after the arrival of salmon. Analysis of AA concentrations and relative proportions indicated that clustering of samples in multivariate trait space depended on timing (pre- or post-arrival of salmon) but not among streams. The shift in AA composition in post-arrival samples was consistent with odors from the salmon (e.g., eggs). Collectively, these data are inconsistent with the idea that AAs alone differ sufficiently among streams throughout the migration period to guide homing, though they may contribute to more complex combinations of odorants.
Little is known on the dynamics of under-ice phytoplankton communities. We investigated phytoplankton communities in the upper (0–20 m) and lower (30–35 m) layer of oligotrophic Lake Tovel, Brenta Dolomites (Italy) over 6 years during summer and under ice. Winter conditions were different from one year to another with respect to ice thickness and snow cover. Proxies for light transmission (Secchi disc transparency, light attenuation) were similar between seasons, even though the incident solar radiation was lower in winter. Algal richness and chlorophyll-a were not different between seasons while biomass was higher during summer. In four of the 6 years, Bacillariophyta dominated during summer and Miozoa (class Dinophyceae) under ice while in 2 years Bacillariophyta also dominated under ice. Generally, a shift to larger size classes from summer to under ice was observed for Bacillariophyta, Chlorophyta, and Ochrophyta (class Chrysophyceae) while Dinophyceae showed the opposite pattern. No strong links between phytoplankton community composition and abiotic factors (under-ice convective mixing, snow on ice, under-ice light) were found. We suggest that inter-species relationships and more precise indicators of under-ice light should be considered to better understand under-ice processes.
Relating biological patterns to the physical environment is increasingly explored in current period of global biodiversity crisis and attempts to identify ecological status. Free-living marine nematodes (FMN) were proposed as ecological indicators, although often under approaches based on developing synthetic indexes of environmental quality, contextually neglecting the crucial issue of their spatial and temporal variability in abundance and diversity, and its relationship with environmental drivers. This study, carried out on the north-eastern coast of India as a region subject to various anthropogenic activities, assessed the patterns of FMN structure, richness, equitability, trophic guilds, life strategy and morphological traits at three sites, three times over 1 year, two beach levels and three sediment layers upto 15 cm deep. Nematode patterns were then related to the amount of sand, silt and clay, organic carbon, and salinity. Each FMN characteristic was largely variable in time and space, being organic carbon and salinity the environmental variables most correlated to such patterns. Monitoring designs suited to capture such variability are recommended to improve the use of FMN as bioindicators. Just relying on unidirectional data to define environmental status is questioned, while it is proposed to consider the Effect of Positional Constraints when assessing ecosystem health.
Stream restoration is meant to mitigate increasing anthropogenic pressure and re-establish ecosystem functioning and biodiversity. Extensive research has identified constraints hampering biotic recovery, but successful projects are still scarce. This study documents short-term macroinvertebrate colonisation in a near-natural environment with plentiful potential colonists, which has rarely been studied. Three streams contiguous with near-natural aquatic habitats were monitored over sixteen months after restoration. Sampling sections were categorised and compared to reference sections. Species richness and composition, abundance, functional parameters and similarity to reference were evaluated. Restored streams were colonised rapidly and, in multiple respects, reached reference levels within the study period. Distance from upstream colonisation source and restoration method (newly built and rebuilt channels) had little effect on recovery. However, species composition of upper and lower sections diversified, as they receive colonists from various sources. Repeated sampling revealed dynamic assemblage development with Chironomidae, Baetidae and Nemouridae being among the pioneer colonists. A common successional pattern was observed; gatherers/collectors and small, plurivoltine larvae decreased, whereas predators, grazers/scrapers and medium-sized, univoltine larvae increased. This study demonstrates that restoration of previously channelised streams in near-natural environment is followed by rapid macroinvertebrate colonisation, successfully promoting biodiversity.
Salinization is a great threat to wetlands and freshwater ecosystems. Increased salinity can disturb native aquatic vegetation and provide an empty niche for invasion of non-native species. To understand the fate of aquatic flora under increased salinity levels, 14 dominant wetland species with different growth forms (submersed, amphibious, floating-leaved, emergent and woody/tree) were exposed to increased salinity conditions. The objective was to assess the salt tolerance threshold for each species and model their performance in response to a salinity gradient ranging from 0.2 to 20 parts per thousand (ppt). Plant growth and survival rate were analyzed using a nonlinear regression model to project sublethal salinity concentrations that would reduce biomass and visual quality of each species by 50% (LC50). Results showed that a few non-native species (alligatorweed: Alternanthera philoxeroides (Mart.) Griseb., torpedograss: Panicum repens L., and Brazilian peppertree: Schinus terebinthifolius Raddi) survived 20 ppt salinity, whereas all other native and non-native species perished at salinity below 10 ppt. Increased salinity can suppress salt-sensitive native plants and increase the opportunity of invasion for salt-tolerant non-native species. This suggests that alligatorweed, torpedograss and Brazilian peppertree pose a more significant threat to the ecosystem if salinity levels continue to increase in freshwater ecosystems and exacerbate the encroachment of non-native species into native plant communities.
Multicellular organisms and their microbiomes can have a restricted and enduring relationship, sometimes reflected in their phylogenies, called phylosymbiosis. However, in some organisms, such as freshwater zooplankton, these relationships appear to be more flexible and more easily influenced by the environment. Here, we analysed the microbiome of a freshwater flatworm, Stenostomum leucops and sequenced the 16S RNA gene of the microbiota of a strain that was maintained in the laboratory for 12 years. This strain underwent four different cultivation conditions over the past 6 years, and the microbiome was characterised for each of these conditions. In addition, the microbiome of a wild S. leucops population was analysed. The microbiomes were highly variable between populations (Shannon index ranging from 0.26 to 2.06). It was not possible to determine a core microbiome, although Bacillus, Pseudomonas and Ralstonia were the predominant bacteria in populations under stable conditions. Under culture conditions where the water was contaminated with iron, Rhodoferax ferrireducens, a bacterium involved in iron reduction, was the predominant species. Our results are consistent with other studies on freshwater zooplankton. The microbiomes were very flexible and were influenced by the environment.
This editorial is aimed at explaining why the editors of Hydrobiologia are so concerned with biological nomenclature and why we ask our authors the utmost precision when referring to species in their papers...
In these lines, we want to show that this is not just an old fashion formalism, but a necessity to correctly and univocally identify the biological subjects that are the basis of the research published in ecology-related journals.
The full editorial is freely available at https://rdcu.be/cRqBX
Striving for an integrated semi-natural stream-floodplain system as restoration target would optimally serve biodiversity and the provisioning of ecosystem services. This pursuit is currently limited by multiple pressures and constraints that come with, amongst others, a high human population density and intensive land-use. To be able to weigh the ecological and societal needs in lowland-stream watersheds, we analysed the developments in lowland-stream restoration in relation to the actual and potential state of ecosystems services these systems provide. To reach an ecological-societal balance in stream restoration, we pose five steps: (i) Choose a clear and realistic restoration target, (ii) Map and quantify environmental stressors at local to watershed scale, (iii) Map and quantify biological indicators at local to regional scale, (iv) List potential restoration measures to remove or mitigate stressors, and (v) Build scenarios, composed of combinations of measures fitting the societal context of the watershed. The most promising scenarios make use of watershed processes and involve establishing a transverse landscape zonation, from the streams’ riparian zone to the uplands. Such landscape transition poses a challenge for policy makers and implies a strong societal change. Therefore, a framework is provided with building blocks that help to find a suitable balance in practice.
Arcellinida (testate lobose amoebae) were examined in surface-sediment samples collected in 2015 from throughout Harvey Lake, New Brunswick, Canada to assess whether the passage of Post-Tropical Storm Arthur in 2014 impacted the distribution of taxa and assemblages. Cluster analysis and non-metric multidimensional scaling (NMDS) revealed four distinct arcellinidan assemblages: (1) Deep Water Reworking Assemblage (DWR; approximately unbiased, AU P-value = 89%); (2) Arsenic Impact Assemblage (AI; AU P-value = 92%); (3) Northern Shallow Water Assemblage A (NSWA; AU P-value = 66%); and (4) Northern Shallow Water Assemblage B (NSWB; AU P-value = 0%). Redundancy analysis (RDA) and partial-RDA results were used to identify four variables that significantly influenced the assemblage composition and explained 20.2% of the arcellinidan distributional variability: [arsenic (As), wind mixing probability (WMP), water depth and sedimentary grain size represented by the very coarse silt end member 2 (EM2) which was 40 μm]. Arsenic concentration in the sediments of Harvey Lake is an important control over the distribution of Arcellinida assemblages. Levels of sedimentary As in samples from the southern part of Harvey Lake, near As-bearing volcanic bedrock in the catchment, exceeded the Probable Effect Level (17 ppm) and Interim Sediment Quality Guideline (5.9 ppm) for this element. Shallower water (less than median water depth of 3.56 m) and highly diverse assemblages NSWA and NSWB (median SDI = 2.6) significantly correlated with wind mixing probability, while deeper water (greater than median = 6.2 m) and moderately to highly diverse assemblages DWR and AI (SDI range 2.4–2.7) associated strongly with EM2. EM2 was derived from the suspension of and redeposition of sediments when the storm water wave base was deepened during the passage of Arthur. Arcellinidans were carried into suspension along with very coarse silt grain particles during the passage of the storm and redeposited at all water depths when wave energy decreased. Water depth of sampling stations should be taken into consideration in lakes that may be periodically impacted by large storms.
Detritivores are pivotal in forest streams as they process detritus and promote secondary production. Many studies have addressed the preference of freshwater detritivores towards materials of differing quality. Nevertheless, few studies compare the resource preferences in the laboratory with the availability in the field. In the present study, feeding preferences of two stream detritivores (the caddisfly Sericostoma pyrenaicum and the amphipod Echinogammarus tarragonensis), over three native leaf species (alder, chestnut and oak) and an exotic species (eucalypt) were quantified in the laboratory. Preference for eucalypt leaves conditioned for 1, 2 and 3 weeks was also described. We then contrasted the preference patterns in the laboratory feeding experiments with a 15-month-long benthic standing stock time series of a stream below a native deciduous forest and another below a eucalypt plantation. Both detritivores preferred consuming alder leaves and more conditioned eucalypt leaves, although the amphipod was more selective than the caddisfly. The consumption preference in the laboratory was unmatched by the availability in the field, especially under eucalypt plantations and for the amphipod. Our results show that the strength of the preference for high-quality resources can differ among different taxa, which can modulate their response to land use changes.