Hydrobiologia

Published by Springer Nature
Online ISSN: 1573-5117
Learn more about this page
Recent publications
Sampling sites (46) along the four major large rivers in Croatia: the Danube-DA (4 sites), Sava-SA (21), Drava-DR (20) and Mura-MU (3) Rivers. Values of the site-specific biocontamination index (SBCI-Fam, family level) are presented in different colours (of two sampling times in 2015 and 2016 or 2017, the worse SBCI-Fam is shown). Main map shows enlarged part of the Drava between the Varaždin and Dubrava Reservoirs, whilst right inset map shows the position of study area in Croatia (rectangle indicates the Pannonian lowland ecoregion) and Europe, with country codes (HR: Croatia, AT: Austria, BA: Bosnia and Herzegovina, HU: Hungary, IT: Italy, ME: Montenegro, SI: Slovenia, RS: Serbia)
a PCA for 46 sites with 8 environmental parameters (average values for eight months) that indicate nutrient and organic pollution; b PCA with the same 8 environmental parameters for 31 sites (Sava-15 sites, Drava-16) where alien Peracarida had low (L) or high (H) densities (Sites abbreviations: DA Danube, SA Sava, DR Drava, MU Mura)
Medians and 95% confidence intervals corresponding to the difference between the medians of seven physical and chemical parameters for nutrient (NH4⁺, NO2⁻, NO3⁻, PO4⁻³) and organic (BOD, organic N, TOC) pollution (a–g), and for PCA Score 1 (h), for two groups of sites with lower (Low) and Higher (H) densities of alien peracarids in the Sava and Drava Rivers
Medians and 95% confidence intervals corresponding to the difference between the medians of biological metrics on sites with lower (Low) and higher (High) densities of alien peracarids in the Sava and Drava Rivers: a Croatian saprobic index (HR-SI), b No. Taxa, c No. Families, d EPT%, e EPT taxa, f BWPT, g IBE, h Saprobity module
Croatian saprobic index HR-SI (left row) and BMWP indices (middle row) calculated with all taxa, without all alien macroinvertebrate species and without alien Peracarida and PCA Score 1 (right row) (positively correlated with eight parameters indicating pollution as in Fig. 3, right row) in the a Sava River, b Drava River and c with all studied sites included
Article
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.
 
Article
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.
 
Ebro River and Canal Imperial sections where recipient and donor localities were selected, respectively (Aragón region, Spain)
Ebro River flow (m³/seg) during the study years (2016–2020) (blue arrows: translocation actions; red arrows: field survey of the previous year(s) translocation(s); stars: evaluation and selection of the plots)
Global survival, detection, and mortality results of P. auricularius translocation experiment for the control group and the groups of specimens translocated in 2017, 2018, and 2019 (*one locality could not be checked due to high river water level)
Photographs of a a group of dead P. auricularius specimens from CIA, b selected locality L1 with the transect marked, c selected locality L2, and d selected locality L3
Article
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.
 
Location of the study area and the sampling sites in the Taizi River Basin of China
Eutrophication levels based on the concentration of total phosphorus in Taizi River Basin. The solid circle with different colors represents different disturbance levels, and dark green is level 1 (oligo–mesotrophic), light green is level 2 (mesotrophic), yellow is level 3 (moderate eutrophic), orange is level 4 (eutrophic), and red is level 5 (hypereutrophic)
Species richness of three assemblages in five eutrophication levels. The solid circle represents mean values of each group and the abscissa represents the eutrophication levels. The upper whiskers represent the 97.5 and the lower whiskers the 2.5 percentile
The response curves of species richness of three aquatic assemblages to eutrophication levels. The gray area represents the 95% confidence intervals
Article
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.
 
A Map of sampling localities. Circles with numbers indicate sampling sites. The hatched rectangles represent two water conduits (A and B), transferring the waters of Lake Okjeong to the Dongjin River by the difference in altitude. The black trapezoid indicates the Seomjin River dam. The Dongjin River flows into the Yellow Sea, and Lake Okjeong is located upstream of the Seomjin River, which flows into the South Sea of Korea. The orange, green, and pink shadings denote the areas where Cobitis nalbanti, hybrids, and C. tetralineata were observed, respectively. B Population genetic structure obtained by STRUCTURE using the combined dataset of eight microsatellites and five nuclear gene loci. C Genetic assignment of two parental Cobitis fish species and their hybrid offspring by NewHybrids with the same combined genetic data. Each vertical row represents each fish and comprises each genetic portion of each group in proportion to the height and corresponding color. The total length of the bar represents a probability of 1.0, which is the estimated membership coefficient in Structure and maximum posterior probability in NewHybrids. (P0, Pure Cobitis nalbanti; P1, Pure C. tetralineata; F1, F1 hybrid of two different parental species; F2, post-F1 hybrid; B0, F1 backcrossed with P0; B1, F1 backcrossed with P1). Species identification by mitochondrial cytochrome b gene is marked on the bar plot of (B)
Graphical matrix of pairwise FST between populations, including two parental species and their hybrids. A Mitochondrial Cytb gene, B nuclear genes, and C microsatellite markers. Each sampling location of the 12 sites on the map shown in Fig. 1A was treated as a population
Haplotype networks of Cobitis nalbanti (red, sites 1 to 4), C. tetralineata (blue, sites 11 and 12), and their hybrids (from white to black, sites 5 to 10) based on SH3PX3, myh6, tbr1, ENC1, RAG1, and cytochrome b, with 30, 13, 4, 24, 7, and 23 haplotypes, respectively. The size of the circle was drawn proportionally to the number of individuals sharing identical haplotypes, and the ticks crossing the line connecting two circles represent mutational steps between them.
Linear discriminant analysis (LDA) of the morphological data of two sister species of C. nalbanti and C. tetralineata and their hybrid offspring based on 26 morphological characters. The irregular polygons represent six distinct groups based on the preliminary information about species identification and sexes of the samples. Pure parental species and hybrid offspring were labeled according to a working hypothesis, that is, sampling sites; the fish collected in the hybrid zone of the Dongjin River was regarded as putative hybrid offspring (green, Fig. 1, site 5), while the others were considered putative pure parental species (orange for C. nalbanti and pink for C. tetralineata) because they were collected out of the hybrid zone. Symbols in the graph are as follows: open squares, C. nalbanti females; open triangles, female hybrids; open circles, C. tetralineata females; filled squares, C. nalbanti males; filled triangles, male hybrids; filled circles, C. tetralineata males; and filled rhombuses in polygons, group centroids
Article
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.
 
Algal biomass and density of algae with luxury P uptake and mixotrophic in the periphyton on artificial substrate (n = 72), Nymphaea spp. (n = 48) and Utricularia foliosa (n = 45)
Biomass of mixotrophic algae in the periphyton on artificial substrate (n = 72), Nymphaea spp. (n = 48) and Utricularia foliosa (n = 45) in relation to light availability (%) and TP concentration. Note different scales for each substrate type
Biomass of algae with luxury P uptake (LPU) in the periphyton on artificial substrate (n = 72), Nymphaea spp. (n = 48) and Utricularia foliosa (n = 45) in relation to light availability (%) and TP concentration. Note different scales for each substrate type
Biomass of mixotrophic algae and with luxury P uptake (LPU) in the periphyton on artificial substrate (A, B; n = 72), Nymphaea spp. (C, D; n = 48) and Utricularia foliosa (E, F; n = 45) in relation to P content in the community. Note different scales for each substrate type
Boxplot of periphyton N:P and C:P molar ratios on artificial substrate (n = 72), Nymphaea spp. (n = 48) and Utricularia foliosa (n = 45). The black circle represents the average ratio
Article
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.
 
A Positions of the two telemetry arrays and dataloggers deployed in the Římov Reservoir. B Development of water column temperature and oxygen stratification at the dam and upper sections throughout the whole tracking period (note that, at the dam, where maximum depth is 42 m, the data loggers were deployed at 20 m depth). The thermocline is represented by a dashed line
A Density of locations of all tagged individuals as a function of distance from the dam and time. B Seasonal preference for different sections of the Římov reservoir by Northern pike, pikeperch, and wels catfish, estimated with the Ivlev’s electivity index as a function of the proportion of a section used (on the y-axis) and the relative availability of the section with respect to the total area of the reservoir. Relative use of a section was estimated from cumulative probabilities using a cumulative link mixed-effects model analysis (CLMMres), which sets the dam as the starting point of the measured longitudinal migration distance. Negative Ei values indicate that a reservoir section is avoided relative to its proportional availability, positive values indicate that this section is preferred, with 1 indicating overuse, and zero values indicate proportional use of the section relative to its area
A Effect of smooth time functions on longitudinal movement (km day⁻¹) of pike, pikeperch, and wels catfish in Římov Reservoir in different seasons. The fitted spline with 95% confidence interval (CI, shaded area) represents the average trend effect from April 2017 to April 2018 based on the additive mixed-effects models (Table 4). B Rate of change in longitudinal movements over time, determined from the estimated first derivative of the fitted trend spline function from each of the above GAMMs. The periods of statistically significant increasing (thick white) and decreasing (thick black) rates of change in the trend series are depicted. The shaded area is the 95% simultaneous confidence interval calculated using posterior Bayesian simulations for the data predicted from the models. C Estimation of smooth differences (95% CI, shaded area) in longitudinal movement trends among species using the GAMMsp_diffs model (Table 3). Periods where the value zero (horizontal line) is not included in the 95% CI indicate significant differences between two species (outlined by a red line)
A Mean daily depths of all tracked individuals (black dots) as a function of temperature (colours) and time. The thermocline is represented by a dashed line; B Cumulative probabilities of depth use in Římov Reservoir by Northern pike, pikeperch, and wels catfish at different times of the year from April 2017 to April 2018, estimated using a cumulative link mixed-effects model analysis (CLMMdepth). Depth was divided into seven levels corresponding to increasing depth in the water column, from 0–1 to > 10 m. The y-axis represents the probability of using the depth in each season (x-axis). Depth 0–1 m was set as the reference category in the analysis
Article
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.
 
Article
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.
 
Article
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.
 
Ranked coefficients associated with the interaction effect for the 45 population combinations in each study group: locally adapted (LA) and phylogeographically structured (PS) groups. The higher the value is, the higher the propensity for mating. Black bars: intrademic crosses; grey bars: interdemic crosses. The average values of intrademic and interdemic crosses are shown
Article
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.
 
Relationship between ghost crab burrow opening diameters and human disturbances on sandy beaches: a according to the categorical human impact level; and b according to a continuous metric of human modification (HMc); black dots are dissipative beaches, white dots are non-dissipative beaches, and squares are beaches with no information to determine morphodynamic stages. The categorization of beaches into “high disturbance” and “low disturbance” (a) was based on the mean HMc calculated for beaches that had originally been classified by authors regarding disturbances (see methods)
Response ratios (RR) of ghost crab (Crustacea: Ocypodidae) burrow opening diameters according to different types (a), combination (b), and amount (c) of human stressors on sandy beaches. Response ratios were calculated as RR = ln (meandisturbed/meancontrol) for each pair of beaches sampled in studies gathered from a literature review. Lines inside boxes are medians and boxes are interquartile ranges. Black dots inside boxes are mean values. V vehicle, T trampling, M mining, D dune suppression, C cleaning, and A armoring
Relationship between body weight and carapace length of ghost crabs (Ocypode spp.) from high (gray dots) and low (white dots) disturbance beaches in Brazil and Mexico. Data from Burrows and Hoyle (1973), Alberto and Fontoura, (1999), Yogamoorthi and Sankar (2010), Ocaña et al. (2016), and Oliveira et al. (2016) were included along with unpublished data from three beaches in Southeastern Brazil
Article
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 indicators.
 
Article
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.
 
Article
  • Xue WangXue Wang
  • Yue LiYue Li
  • Lianxi ShengLianxi Sheng
  • [...]
  • Wenbo LuoWenbo Luo
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.
 
Models of succession in monsoonal and prairie pothole wetlands from Middleton (1999)
Idealized habitat cycle in a semi-permanent prairie pothole (van der Valk & Davis, 1978)
Water-level changes in a seasonal and a semi-permanent prairie pothole at the St. Denis National Wildlife Refuge, Saskatchewan, Canada. The gaps in the records indicate periods when these wetlands were frozen, and no data were collected. From van der Valk (2005).
Adapted from Van der Camp and Hayashi (1998)
Vegetation transect zones (dashed lines) in the aquatic blocks (B, D, E, F, G, K, L, and M) of the monsoonal wetland in the Keoladeo National Park, Bharatpur. From Davis & van der Valk (1988)
Time series of monsoonal rainfall (1871–2005) expressed as percentage departure from summer rainfall long-term normal (from Yadav, 2008)
Article
  • Arnold G. van der ValkArnold G. van der Valk
  • Beth MiddletonBeth Middleton
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.
 
Read abundance of the 40 most common bacterial genera in the dataset (> 1000 reads) in the different samples. Samples are grouped by rotifers from cultures, freshwater rotifers from the environment, and brackish rotifers from the environment. Colours of the bubbles denote the different rotifer species. Size of the bubbles is proportional to the number of reads
Non-metric multidimensional scaling (nMDS) plot of the differences in microbiome composition between samples, with shape according to their freshwater or brackish origin and colour (same as in Fig. 3) according to their lab or environmental origin
Tanglegram of host-microbiome relationships. The host phylogeny on the left is a Bayesian ultrametric tree with branch length and scale bar proportional to evolutionary rates in a combined COI + 18S alignment and with numbers on branches representing posterior probabilities. The cladogram on the right represents clustering of dissimilarities in microbiome composition between samples. Each sample, connected with a curved line to the host species (in grey for Bdelloidea and black for Monogononta) is marked with different colours depending on whether it is from freshwater or brackish water and from lab culture or from the environment
Article
  • Ester M. EckertEster M. Eckert
  • Tommaso CancellarioTommaso Cancellario
  • Paul L. E. BodelierPaul L. E. Bodelier
  • [...]
  • Diego FontanetoDiego Fontaneto
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.
 
Experimental design used to assess the effects of gradual eutrophication on phytoplankton communities. The procedure was initiated with the stabilization phase (when nutrients were added to reach the concentrations of the lake) followed by the enrichment phase (when nutrients were added to the eutrophic treatment in increasing concentrations with the time). Before the enrichment phase, the water was mixed among all tanks
Temporal variation in mean temperature (a), pH (b), dissolved oxygen (c), conductivity (d), and turbidity (e) for eutrophic treatment and control, considering the sampling events. Open and filled squares indicate data for control and eutrophic, respectively. Vertical bars represent 95% confidence intervals
Temporal variation in mean species richness (a), chlorophyll-a (b), total density (c), H’ species (d), H’ MBFG (e), J’ species (f), and J’ MBFG (g) for eutrophic treatment and control. The open and filled squares indicate data for the control and eutrophic, respectively. The vertical bars represent 95% confidence intervals. H’ = Shannon diversity; J’ = Pielou’s equitability. MBFG = Morphologically Based Functional Groups
Temporal variation in the first and second axes of Non-Metric Multidimensional Scaling Analyses (NMDS) for species composition and Morphologically Based Functional Groups (MBFG) for eutrophic treatment and control. Open and filled squares indicate mean values for the control and eutrophic, respectively. Vertical bars represent 95% confidence intervals
Article
  • Karine Borges MachadoKarine Borges Machado
  • Luis Mauricio BiniLuis Mauricio Bini
  • Adriano Sanches MeloAdriano Sanches Melo
  • [...]
  • João Carlos NaboutJoão Carlos Nabout
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.
 
Comparison of cichlid opsin expression through development in single cones (left column) and double cones (right column). a Tilapia have a normal progression from short to long wavelength sensitivity as fish develop from larvae through adults. We take this to represent the ancestral progression. By comparison b neotenic species, such as Metriaclima zebra, retains the ancestral larval-like genes and c direct developing cichlid species, such as Tramitichromis intermedius, turn on the ancestral adult-like genes. dA. burtoni goes through a developmental progression in the single cones but is direct-developing in the double cones
Developmental opsin expression for control A. burtoni as compared to thyroid hormone (TH) treatment. Fish were treated with TH from 9 to 24 dpf under fluorescent lighting. Sampling occurred after 3 h (9 dpf), 1 day (10 dpf), 5 days (14 dpf), 10 days (19 dpf), and 15 days (24 dpf) of TH exposure. Expression of each opsin is measured as a percent of the total expression of single cone (SC) or double cone (DC) opsins. Sample size is n = 6 (3 replicates of 2 fish) at each timepoint for both groups. Error bars show mean ± s.e.m. The inset in (d) shows higher resolution of the rh2b data. Significant differences between control and TH treatment at each age are shown with an asterisk (*). P-values are given in Table 1 and actual data is in Table S3
Opsin expression for adult A. burtoni treated with either thiourea or thyroxine to decrease or increase TH levels. Adult fish were treated for 14 days. Expression of each opsin is measured as a percent of the total expression of single cone (SC) or double cone (DC) opsins. Sample size is n = 5 for each treatment and individual points are shown. Box and whiskers represent median, quartiles, and range. Significant differences between controls and treatments are shown with an asterisk (*). P-values are given in Table 2 and actual data is in Table S4
Opsin expression for A. burtoni development under different environmental lighting. A. burtoni were raised either under fluorescent light (FLR) or under metal halide lamps (UV) which are more similar to solar illumination and contain ultraviolet light. Treatment began at 3 dpf with sampling at 12, 19, 33, 47, 61, and 75 dpf. Expression of each opsin is measured as a percent of the total expression of single cone (SC) or double cone (DC) opsins. Sample size is n = 6 for the first two ages and n = 3 for both treatments at other ages, except n = 2 at 75 dpf FLR. Error bars show mean ± s.e.m. The inset in (d) shows finer detail for the rh2b data. Significant comparisons between fluorescent and UV treatment at each age are shown with an asterisk (*). P-values are given in Table 3 and actual data is in Table S5
a Regulatory regions surrounding the rh2b coding sequence based on a Geneious alignment. The rh2b exons are shown as connected yellow arrows. Conserved elements of either the known rh2 locus control region (LCR) or conserved non-coding elements (CNE) are shown in blue. These were identified through Multipipmaker comparisons between the stickleback (Gasterosteus aculeatus), medaka (Oryzias latipes), and the cichlids Oreochromis niloticus and Metriaclima zebra. These were considered as key regulatory elements along with the rh2b promoter (green). These are placed on the Geneious alignments of sequences from Astatotilapia burtoni (Aburt), Metriaclima zebra (Mz), and the tilapia Oreochromis niloticus (Til). Potential models are shown for how b in most cichlids, an upstream transcription factor (TF) turns on rh2b expression versus c in A. burtoni, the transcription factor has either a coding sequence or regulatory mutation preventing its turning on rh2b expression
Article
  • Melissa M. SchreinerMelissa M. Schreiner
  • Miranda R. YourickMiranda R. Yourick
  • Scott A. JunttiScott A. Juntti
  • Karen L. CarletonKaren L. Carleton
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.
 
Cyp27c1 expression. (a) Over development and (b) in adulthood (> 190 dpf). Cyp27c1 expression decreased with age in the Pundamilia species, but increased in Pa. sauvagei individuals reared in broad-spectrum light. Irrespective of the light conditions, cyp27c1 expression was higher in Pa. sauvagei than in the Pundamilia species. Each symbol represents an individual (for 10 dpf two individuals were pooled). The grey line indicates the transition from juvenile state to adulthood. Shaded areas indicate ± 95% confidence intervals. Boxes represent 25–75th percentiles intercepted by the median. Error bars indicate 95% confidence intervals. Colours indicate light treatments (blue = broad-spectrum light; yellow = red-shifted light)
Relationship between opsin gene and cyp27c1 expression. (a) Opsin expression in adult P. sp. “pundamilia-like”, P. sp. “nyererei-like” and Pa. sauvagei, (b–c) Relationship between opsin gene expression (SWS2a/SWS2b and LWS/RH2 ratio) and cyp27c1 expression across species. (d) Light-induced changes in opsin expression, (e–f) Relationship between light-induced changes in opsin and cyp27c1 expression across species. Boxes represent 25–75th percentiles, intercepted by the median and black symbols are outliers. Shapes in (e–f) indicate species (Pa. sauvagei (■), P. sp. ”nyererei-like”(▲) and P. sp. ”pundamilia-like”(●). Sample sizes are indicated above each boxplot and error bars represent ± 95% confidence interval. *** indicates P < 0.001, **P < 0.01 and *P < 0.05
Expression profiles of cyp27c1 and opsins (a) form two clusters: the cluster dominated by Pa. sauvagei (▲) was characterized by positive PC1 scores, indicating high expression levels of cyp27c1 and Rh2, but low expression levels of LWS. The cluster dominated by P. sp. ”pundamilia-like” was characterized by negative PC1 scores, indicating low expression levels of cyp27c1 and Rh2, but high expression levels of LWS, while the cluster dominated by P. sp. ”nyererei-like” overlaps with Pa. sauvagei and P. sp. ”pundamilia-like”. Each symbol represents an individual. (b) Plastic responses in cyp27c1 and opsin expression were more pronounced in the two species experiencing a broader visual niche (i.e. P. sp. ”nyererei-like” and Pa. sauvagei). Colours indicate species: P. sp. ”pundamilia-like”(blue) P. sp. ”nyererei-like” (red) and Pa. sauvagei (orange). Linetypes indicate light treatment: broad-spectrum light (solid) and red-shifted light (dashed)
Relationship between opsin gene and cyp27c1 expression at individual level. Symbols represent individual fish. Shaded areas indicate ± 95% confidence intervals. **P < 0.01 and•P < 0
Article
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.
 
Article
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.
 
Article
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.
 
Total phenols from different parts of Myriophyllum aquaticum in relation to different months. Shown are the mean ± SE based on 15 plants. For a given month, data carrying similar alphabet are not significantly different among the macrophyte parts
Population growth curves of Plationus patulus in controls (squares) and in treatments with total phenols from macrophyte-conditioned medium (open circles, concentrations shown in upward arrows) and aqueous extracts (triangles); tests conducted separately with phenols only (concentrations shown in arrow down wards) from the conditioned medium (closed circles). Shown are mean ± SE based on 4 replicates
Age-specific survivorship (proportion of survival, lx) curves of P. patulus in controls (squares) and in treatments with total phenols from macrophyte-conditioned medium (open circles) and aqueous extracts (triangles); tests conducted separately with phenols only from the conditioned medium (closed circles). Shown are mean ± SE based on 4 replicates
Age-specific reproduction (offspring female⁻¹ day⁻¹, lx) curves of P. patulus in controls (squares) and in treatments with total phenols from macrophyte-conditioned medium (open circles) and aqueous extracts (triangles); tests conducted separately with phenols only from the conditioned medium (closed circles). Shown are mean ± SE based on 4 replicates
Article
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.
 
The length of the ascending process a of the premaxilla bone (shaded gray) was measured in 37 Lake Malawi cichlid species. Two functional aspects of jaw protrusion b maximum protrusion distance and jaw protrusion angle were measured on cichlids in the field using calipers and a protractor. The congeneric species Nimbochromis polystigma (Regan, 1922) and N. linni (Burgess & Axelrod, 1975) highlight the rapid evolution of variation in these jaw protrusion traits in the Malawi cichlids
The relationships for the Lake Malawi cichlids used as a framework for comparative analyses (supplementary information 1) and pruned down to the study species from a phylogeny presented in Masonick et al. (2022). For the comparative analyses, this maximum likelihood phylogeny based on whole-genome resequencing was rendered ultrametric using penalized likelihood (Sanderson, 2002) and its branch lengths and topology permuted to simulate uncertainty in the phylogeny. In the upper left corner, Tyrannochromis nigriventer represents one of the species with the highest and Petrotilapia sp. represents a species with the lowest amount of jaw protrusion distance in the Malawi cichlids examined. At the phylogeny's tips separated by "/" and preceding the Latin name for each cichlid, we give the maximum jaw protrusion distance, jaw protrusion angle, and diet categories for each species (Table 2). To illustrate the general patterns of this trait evolution in the Malawi cichlids, ancestral states for maximum jaw protrusion distance (above each ancestral node) and jaw protrusion angle (below each ancestral node) were also reconstructed using maximum likelihood. The time axis in millions of years at the bottom of the phylogeny provides a rough temporal context for this diversification. This temporal scale was inferred simply from the smoothed branch lengths and the timeframe of ~ two million years over which the Malawi radiation is believed to have diversified (Danley & Kocher, 2001)
A representative sample of the relationships between phylogenetic independent contrasts of premaxillary ascending process length as a percent of standard length (%SL) and size-standardized maximum jaw protrusion distance (a) as well as jaw protrusion angle (b). While the premaxillary ascending process length was not evolutionarily correlated with jaw protrusion angle across a range of permuted phylogenetic relationships (mean picr = 0.02 ± 0.27 S.E.; mean P = 0.43 ± 0.31 S.E.), phylogenetically corrected analyses found the length of the ascending process had a substantial correlation with maximum jaw protrusion distance (mean picr = 0.74 ± 0.10 S.E.; mean P = 0.006 ± 0.06 S.E.)
Article
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.
 
Article
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.
 
Article
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.
 
Map of sampling stations located in three protected areas and distributed according to the north–south direction of the lake: Bolle di Magadino (BM; yellow triangles) in the northern part, Fondo Toce (FT; green triangles) in the central part and Angera-Sesto Calende (A; red triangles) in the southern part. Monitoring was conducted at each sampling station, in two sites, of which one was permanently wet (W) and the other subjected to drought (D). The border between Italy and Switzerland is marked by the yellow line; that between the Piedmont and Lombardia regions is indicated in white
Plots of the principal components analysis showing the separation of the samples according to: a sampling stations (ST), and b water level (WL). For the ST factor in a: Bolle di Magadino (light blue circles), Fondo Toce (green triangles), Angera-Sesto Calende (white squares). For the WL factor in b: medium water level (grey triangles), low water level (red circles) and high water level (green squares). Variables abbreviation as in Table 1
Article
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.
 
Map of the study area delimiting the ten sampling points in the Paraná River
Beta diversity indexes per month
Predictors variables
Article
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.
 
Map of the Czech Republic showing the sampling sites
Variation of total clitellate diversity (a), and variation in proportion of semiaquatic species (b) among the three types of streams based on drying periodicity. The central line of each box refers to the median value, box height indicates the first and third quartiles, whiskers refer to the non-outlier range. Statistically significant differences between the stream types are marked by asterisks (ANOVA and Tukey post hoc test, significance: ***P < 0.001; **P < 0.01)
Regression tree explaining variation in the proportion of semiaquatic clitellate individuals within the whole clitellate community. Numbers at each node indicate mean percentage of semiaquatic clitellates, its mean standard error, and number of samples assigned to that node (n). The primary splitter variable and surrogate splitter are given at each node
MDS ordination plot for clitellate communities with nine environmental variables with significant fit on 1st and 3rd axes (a). Classification of sites based on level of drying: black points for perennial streams, grey points for irregularly drying streams, and empty circles for intermittent streams. MDS ordination plot on 1st and 3rd axes showing species with frequency > 5 and significant fit (b). Abbreviations of taxa—NaiAlp, Nais alpina; ProVol, Propappus volki; StyBra, Stylodrilus brachystylus; NaiVar, Nais variabilis Piguet, 1906; LumVar, Lumbriculus variegatus (Müller, 1774); AulJap, Aulodrilus japonicus Yamaguchi, 1953; CogSph, Cognettia sphagnetorum; CogGla, Cognettia glandulosa; PsaBar, Psammoryctides barbatus; StyHer, Stylodrilus heringianus; EisTet, Eiseniella tetraedra; EpiPyg, Epirodrilus pygmaeus
Article
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.
 
Sampling sites for Westralunio carteri in south-western Australia, showing presence/absence of mussels. Numbers refer to rivers in which samples were taken. 1 Gingin Brook; 2 Yalyal Brook; 3 Brockman River; 4 Ellen Brook; 5 Bennett Brook; 6 Helena River; 7 Canning River; 8 Serpentine River; 9 North Dandalup River; 10 Harvey River; 11 Brunswick River; 12 Collie River; 13 Preston River; 14 Ludlow River; 15 Abba River; 16 Vasse River; 17 Carbunup River
Distribution of mussel shell length in mm over all sampled river populations of Westralunio carteri with sample sizes of 20 or more individuals
Distribution of mussel ages estimated from shell lengths (solid line—high estimate; dotted line—low estimate; see text for explanation) over all sampled river populations of Westralunio carteri with sample sizes of 20 or more individuals
Relationship between mussel abundance (number per quadrat) and environmental predictors: A substrate grain size (size index—see “Methods” section), B presence of debris (N = No; Y = Yes), and C distance to riverbank (m)
Article
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.
 
The spatial extent of the study (shaded in gray, bottom) shown within a broader spatial extent for context (top). Major rivers are traced in blue. The red-filled circles are the F. askewi occurrence locations and the yellow-filled circles are the F. lananensis occurrence locations that were used to train the ecological niche models
a Habitat suitabilities from Maxent modeling of F. askewi combined with its junior synonym F. lananensis (F. askewi sensu lato). Every parcel of the 100-m × 100-m loctic areas is assigned a suitability score ranging from 0 to 1, with 0 being the least suitable and 1 being the most suitable. The map is color coded where blues represent the lowest suitabilities (below 60th percentile; labeled as “lowest” suitability), greens to yellows represent higher suitabilities (between 60 and 95th percentile; labeled as “medium” suitability), and the oranges to reds represent the highest suitabilities (95th–100th percentile; labeled as “highest” suitability). b The same results presented as binary absence (black) versus presence (red), with a threshold chosen that maximizes the test sensitivity and specificity (see text for details). (c) Ground-truth locations based on the species distribution model. The red-filled circles are where we did not find new F. askewi populations and the white-filled circles are where we found new populations. Major rivers and their reservoirs are highlighted in bold
Box plots of habitat suitability (y-axis) for F. askewi sensu lato based on the ground-truthed locations where F. askewi were not found (“Absent”) versus where they were found (“Present”). The shaded circles are the habitat suitabilities of the individual ground-truthed sites. The box plots show the mean, inter-quartile range, and range. The sample sizes (n) and means (x) for each group are presented, as well as the t-value and P-value from the Welch’s t test comparing the mean of the sites where F. askewi were absent to the sites where F. askewi were present
Habitat suitability for F. askewi sensu lato (y-axes) as a function of different composite variables (x-axes): a PC1, b PC3, c PC5, and d PC6. The individual variables that are substantially loading on the composite variables are indicated beneath the x-axes, and the arrows indicate the directions of the eigenvectors, with left-to-right arrows indicating increasing values of those variables with increasing values of the composite variable and right-to-left arrows indicating decreasing values of those variables with increasing values of the composite variable
Article
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.
 
Scatterplot of bioassay data with fitted linear regressions for each of the M. aeruginosa strains
Barplots of bioassays’ data for each of the M. aeruginosa strains. Each bar represents the average growth rate ± standard deviation (n = 4). Letters indicate significant differences according to multiple comparisons with Mann–Whitney test
Results of long-term competition experiments between Phormidium and M. aeruginosa strain LEGE 91096. Blue line represents best model fit to Phormidium abundances and green line to M. aeruginosa. Numbers on upper left corner indicate the initial ratio (average of first 3 days) Phormidium: M. aeruginosa. (Color figure online)
Results of long-term competition experiments between Phormidium (blue) and all M. aeruginosa strains except LEGE 91096 (green). Numbers on upper right corner indicate the initial ratio (average of first three days) Phormidium: M. aeruginosa. (Color figure online)
Final abundances of M. aeruginosa in competition with Phormidium obtained from model simulations
Article
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.
 
Bird survey point counts that were established in 2014 and re-visited in 2015 in the western portion of Long Point peninsula, ON, Canada (A). Surveys were placed in areas invaded by Phragmites australis (n = 6) (B) and in remnant, uninvaded vegetation consisting of emergent marsh (n = 8) (C) and meadow marsh (n = 6) (D). Figure made with QGIS, base map from Esri Satellite (ArcGIS/World_Imagery)
Total bird abundance (A), species richness (B), Shannon-Weiner index (C), and Pielou’s evenness (D) values for remnant marsh and P. australis-invaded marsh sites sampled in 2014 and 2015. High Lake Erie water levels in 2015 resulted in deeper standing water in all vegetation communities. High abundances in 2015 are a result of remnant meadow marsh vegetation. Error bars represent standard error
The 3D NMDS ordination solution of Bray–Curtis dissimilarity matrix calculated using bird species abundances (stress = 15.56). The joint plots depict site ordination scores with arrows indicating movement from 2014 to 2015, overlaid with species scores (see Table S3 for American Ornithologist Union code definitions). Points are surrounded by convex hulls for each vegetation type
Beta diversity (A), and its turnover (B) and nestedness (C) components, calculated using pair-wise Sørensen dissimilarity for remnant marsh vegetation and P. australis-invaded marsh. Error bars represent the 95% CI of the null models for vegetation type
The relative contribution of each site to total beta diversity in 2014 (A) and 2015 (B), where an asterisk (*) indicates sites that contribute more than average. Changes in community composition between years (temporal beta diversity [TBI]) decomposed into species losses (C) and species gains (D) for each site. Figure made with QGIS and base map made with Boundary Files, 2016 Census, Statistics Canada Catalogue no. 92–160-X
Article
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.
 
Article
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.
 
A Location of sampling areas within the Water Conservation Area 3 of the central Florida Everglades (25° 51′ 46.6″; − 80° 39′ 12.6″). Stars are locations of sloughs receiving flow (RS1 and E250). Squares are the locations of the non-flowing control sloughs (C1-B and C1-C), and the circle is the third non-flowing slough (C1) where only water quality data were taken. Water flow radiates from the structure when opened (indicated by the white arrows) but flows in two predominate directions, south and east. B Racks and plates deployed at RS1. The racks were oriented perpendicular to flow so that the hanging plates would be parallel to flow. C Snail growth containers were evenly interspersed in four rows in the incubator to ensure there were no location effects caused by the incubator. D Plates with periphyton in whirl packs prior to being fed to snails. From left to right are plates from C1-C, C1-B, E250, and RS1
Logit-transformed proportion of edible periphyton (diatoms and green algae) from acrylic plates incubated in flowing and non-flowing sloughs in the Everglades plotted against velocity
Mean mass gained (final mg dry mass − initial mg dry mass) by juvenile apple snails (Pomacea maculata) fed periphyton grown in flowing and non-flowing sloughs in the Everglades from September to December 2019 (n = 8 snails tested per slough). Error bars represent 1 standard deviation from the mean. Different letters above the bars indicate significant between-group differences (P < 0.05). Mass was log transformed for data analysis
Article
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.
 
Body size distribution of masu salmon in the Naehata tributary during each investigation period. Black and striped bars indicate the matured or smolt males and females, respectively. Gray and white bars indicate the immature or non-smolt males and females, respectively
Growth rate (cm/day) of each female (open circle) and male (solid circle) during the summer season (June 2010 to September 2010) and winter season (September 2010 to May 2011). Initial body size for each season was correlated with growth rate during the summer season, but not during the winter season (see Table 3)
Body size and movement pattern of recaptured males during 2010–2012 spawning seasons. Open and solid circles indicate immature and mature males, respectively. Dotted lines indicate the movement patterns of males recaptured at 1 year old and 3 years old
Article
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.
 
Map of the study area where all hauls were conducted
Diagram of gear modification and operational mode. a Conventional pot (control pot). b Modified pot with different escape vent sizes (test pot). c A string of pots
Mean size selectivity curves estimated for R. venosa and C. japonica in the pots with different escape vent sizes (control, cir45, cir50, and cir55). Thick-solid lines represent the mean size selectivity curves. The dashed curves represent 95% confidence intervals for the selectivity curves. The vertical-dashed lines indicate the market reference size (MRS) and minimum landing size (MLS) of R. venosa and C. japonica, respectively. The gray lines represent the size population of shellfish entering the pots
Thick-solid curves denote the estimated size selectivity curves indicating the proportion of individuals caught in the four types of pots to the total catch. The dashed curves indicate the 95% confidence intervals for the fitted size selectivity curves. The hollow dots represent the experimental data. The horizontal gray baseline at 0.25 indicates equal catch efficiency, and the vertical-dashed line indicates the market reference size (MRS) and minimum landing size (MLS) of R. venosa and C. japonica, respectively
Difference in retention rates for pots between the control and cir45 (Delta 1), cir45 and cir50 (Delta 2), and cir50 and cir55 (Delta 3). Thick-solid curves and dotted curves indicate the mean and 95% confidence intervals for the differences of fitted size selectivity curves, respectively. The vertical-dashed line indicates the market reference size (MRS) and minimum landing size (MLS) of R. venosa and C. japonica, respectively
Article
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.
 
Sampling locations for scalloped hammerhead collection. Northern region: La Reforma (RE), Chametla (CH), Teacapan (TEC), and Boca de Camichín (NAY). Central region: Bahía de Navidad (BN) and El Rebalsito (REB). Southern region: Salina Cruz (SC) and Puerto Madero (PM). The ecoregions according to Wilkinson et al. (2009) are the Gulf of California (GC), Mexican Pacific Transition (MPT), and Middle American Pacific (MAP)
Minimum spanning network showing the relationships between haplotypes in terms of the numbers of differences and their proportions in each region. Each analyzed region is shown in a different color (box on the right), and the numbers inside the circles represent the frequency of haplotypes
A Discriminant spatial analysis of principal components (DAPC) for individuals of the scalloped hammerhead shark, S. lewini, from the Mexican Pacific using 11 microsatellite loci. B Posterior assignment probabilities to K = 5 clusters in the scalloped hammerhead shark, S. lewini
Article
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.
 
Sample design of the experiment evaluating consumption by Phylloicus elektoros (Trichoptera: Calamoceratidae) using leaf disks of Goupia glabra and Protium spruceanum under two simulated climatic conditions (Control = 23.2 °C; Warming = 27.5 °C) and microbial conditioning (0, 7, and 15 days)
Spore richness and sporulation rate in Goupia glabra and Protium spruceanum leaves after 0, 7, and 15 days of microbial conditioning. Gray rectangle average values
Leaf consumption rate by Phylloicus elektoros in Goupia glabra and Protium spruceanum leaves under simulated temperature (Control = 23.2 °C; Warming = 27.5 °C) and microbial conditioning (0, 7, and 15 days). Gray rectangle average values
Article
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.
 
Article
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.
 
Diversity of upstream edge, downstream edge. and middle of two and four week old slides throughout the sampling season at Station 2. The Shannon and Weaver formula was used for diversity calculations. The mean number of species for each section of the slide appears in parentheses.
Article
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.
 
Map of Lake Aleknagik, Alaska, showing the locations of the five tributaries sampled for AAs. The lake’s outlet, the Wood River, is at the lower right (southeast) side, draining into Bristol Bay via the Nushagak River
Relative proportions (left panel) and total concentrations (nM—right panel) of 17 AA, detected in five different streams (Bear, Eagle, Happy, Whitefish, and Yako creeks) before and after arrival of spawning salmon (designated “Pre/Post”)
Non-metric multi-dimensional scaling (NMDS) plots showing the ordination of each sample (point) in multivariate (AA) trait space. (1) all samples (pre- and post-salmon) from each stream (Eagle, Yako, Happy, Whitefish, and Bear creeks: panels a, c; and (2) all samples from all streams pooled into either pre- or post-salmon arrival collections: panels b, d). For each comparison, panels a and b display the absolute concentrations, and panels a and d display the relative concentrations
Comparison of loadings relative concentrations for 17 different AAs (arrows) on the first and second NMDS dimension, relative to the ordination of samples (points) collected from (i) each stream (Eagle, Yako, Happy, Whitefish, and Bear creeks, combining both pre- and post-arrival salmon collections) and (ii) samples from all streams pooled into either pre- or post-salmon arrival groups. Each panel also displays AA composition of water in which sockeye salmon eggs had been soaked (“eggs,” data from Dittman and Quinn 2000). Panels a and c color points for individual samples based on origin (i.e., stream or egg), while panels b and d color points based on treatment (pre-arrival, post-arrival, egg). NMDS loadings (blue arrows) have been overlaid on panels c and d
Pearson correlation coefficients of percent AA composition data between all pairs of streams before (solid squares) and after (open triangles) salmon arrival
Article
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.
 
Article
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.
 
Article
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.
 
Map of study area with channelised (blue lines) and restored stream (red lines) courses. Sampling sections are displayed as black points, see Table 1 for their description
Accumulation curves of species richness of all macroinvertebrates excluding Chironomidae (a) and of Chironomidae (b) over sixteen months after restoration. Line type and colour define three categories of sampling sections: newly built (solid black), rebuilt (dashed black) and reference (dotted grey). NBC newly built channel, RC rebuilt channel, REF reference
Relationships of macroinvertebrate-based indices and time since restoration. Species richness (a), abundance (d), functional richness (c) and functional redundancy (f) are shown for macroinvertebrates excluding Chironomidae, and species richness (b) and abundance (e) are shown separately for Chironomidae. Significant relationships (linear mixed effect model analysis, P < 0.05) are shown by solid line, insignificant by dashed line. Restored sections are in black and reference sections are in grey colour
Relationships of pair-wise Bray–Curtis similarities of macroinvertebrate assemblages excluding Chironomidae in restored sections to respective reference sections and time since restoration. Species composition (i.e., taxonomic) similarity of upper and lower restored sections to upstream (a) and downstream (b) reference sections, and functional composition similarity of upper and lower restored sections to upstream (c) and downstream (d) reference sections are shown. All relationships shown are significant (linear mixed effect model analysis, P < 0.05). Line type and symbol differentiate between upper (dot dash, circle) and lower (solid, triangle) restored sections. REST_UP upper restored sections, REST_LOW lower restored sections, REF_UP upstream reference section, REF_DOWN downstream reference section
Overview of changes in abundance (colour) and frequency (circle size) of macroinvertebrate families and chironomid tribes over time in restored and reference sections. Only families with more than 30 individuals in restored sections are shown. Caenidae, Calopterygidae, Perlidae, Hydroptilidae, and Athericidae, that were found only in reference sections are not included. Note that maximum frequencies in reference and restored sections differ. Numbers in brackets refer to the number of sampling sections in the upper row, and to the number of taxa in macroinvertebrate families and chironomid tribes in the remaining rows
Article
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.
 
Shoot and root growth rates under salinity treatments. Each point and error bar represent the mean and standard error for four observations. Species marked with the (*) are non-native in Florida, USA
Determined salinity thresholds for each aquatic plant species. The intermediate level shows the estimated LC50 value calculated based on visual quality data. Lower limit signifies the lowest salinity level that affected plant growth and visual quality, and upper limit denotes the highest salinity level that plant could survive for six or 9 weeks exposure before mortality. Species marked with the (*) are non-native in Florida, USA
Guideline for assigning visual quality scores to plants (1–10)
Article
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.
 
A A laboratory Stenostomum leucops isoline and its maintenance phases: 2009–2017, with distilled water under selection, in which only the worms were transferred for new cultures for a cleaner culture of other zooplankton (SLO-sm01); in 2017, a bottleneck occurred and "new" bacterial sources were added to save the vitality of the culture (SLO-sm02); in 2018, iron contamination was detected in the water and the culture became to be maintained with deionized water (SLO-sm03). In 2020, a subpopulation was maintained at home with tap water (SLO-hc). Microbiomes were sequenced in 2015 (SLO-sm01), 2017 (SLO-sm02) and 2021 (SLO-sm03 and SLO-home cultivation). B A wild population was collected in September 2021 in a pond at the Federal University of Santa Maria, Santa Maria, Brazil (53° 17′ W; 29° 28′ S). These specimens were identified according to Noreña et al. (2005) and by DNA barcoding according to Rosa et al. (2015). Fresh animals were used for DNA isolation and used for barcoding and sequencing of the microbiome (2021)
Venn diagram comparing bacteria in worm populations. A number of bacterial amplicon sequence variants (ASVs) in the laboratory population (SL0_sm03) and its environmental microbial community (background); B bacteria in home cultivation and background; C bacteria in the wild and background; D number of bacterial OTUs in the laboratory populations (SL0_sm01, SL0_sm02, and SL0_sm03); E number of bacterial OTUs in extant populations (SL0_sm03, SL0_wp, and SL0_hc)
Bacterial abundance in each population studied and in the environmental microbial community (background). The colours represent the different bacterial OTUs, and the height on the y-axis represents the respective abundance. Laboratory populations = SL0_sm01, SL0_sm02, and SL0_sm03; home cultivation = SL0_hc; wild population = SL0_wp. Background = sm03 back, SL0_hc back, SL0_wp back
Predominant microbiome found in different Stenostomum leucops populations
Article
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.
 
Article
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
 
Ecosystem services in a lowland stream watershed
The zonation of a lowland stream floodplain: 1 zone of human use, 2 extensive grassland, 3 wet shrub, 4 wet forest zone, and 5 the stream channel (A). The ecosystem services-biodiversity puzzle in lowland stream valleys (B)
Article
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.
 
Article
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.
 
Consumption rates of S. pyrenaicum and E. tarragonensis in the food preference experiments (mean ± SE)
a Benthic alder and leaf standing stock (AFDM), and b chi-square goodness of fit between the relative alder offer in the field and the food preferences shown by S. pyrenaicum and E. tarragonensis in the ‘leaves’ experiment (surplus of alder is denoted by positive values and shortage by negative ones) (mean ± SE)
Alder mass and leaf quantity index (see “Methods”) relationship for the stream under deciduous forest (D) and eucalypt plantation (E). The quantity indexes have been computed using laboratory leaf preferences of the two detritivores. Leaf quality index was Box–Cox transformed for the analysis, but untransformed values are shown in the plot together with the backtransformed regression lines obtained in the linear model
Article
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.
 
Top-cited authors
Erik Jeppesen
  • Aarhus University
Martin Søndergaard
  • Aarhus University
Luis Mauricio Bini
  • Universidade Federal de Goiás
Hendrik H. Segers
  • Royal Belgian Institute of Natural Sciences
Sidinei Magela Thomaz
  • Universidade Estadual de Maringá