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Plastic contamination in aquatic ecosystems all around the world is on the rise. Microplastics (MPs) interfere with the ecological functions of different aquatic animals, including zooplankton. Other contaminants can also be transported by microplastics, resulting in higher toxicity. Here, we evaluated the effect of microplastics alone and in combination with cyanotoxins (CT) on the demographic and feeding responses of the freshwater rotifer Brachionus calyciflorus. The microplastics used were polystyrene spheres of 30 μm diameter. The cyanobacteria were obtained from a sample collected from the Valle de Bravo reservoir in Central Mexico, and the secondary metabolites were obtained after 5 cycles of freezing, thawing and sonication. We conducted acute (LC 50 , 24h bioassay) and chronic toxicity tests involving population growth, life table experiments, and feeding experiments. The LC 50 value using microplastics was 21.91 mg/L, and for the cyanobacterial crude extract it was 2.56 μg/L, but the combination of both resulted in a higher adverse effect (16.64 mg/L) due to the microplastics. Rotifer survival, reproduction, and feeding decreased in the presence of either MPs or CT but the adverse effect was more in the presence of both contaminants. We found that the adverse effects of MPs and CT on the test rotifer species were enhanced when exposed to both contaminants simultaneously., Competing Interests: Declaration of competing interest We have no conflicts of interest to declare., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Microplastics (MPs) are becoming increasingly common in freshwater ecosystems. Rotifers may involuntarily ingest MPs through non-selective filtration, thus causing non-real satiety, leading to adverse effects on their demography. Here, we evaluated the acute and chronic effects of MPs (30 µm) on two successive generations of Brachionus calyciflorus s.s. at 20 and 25 °C. Demographic variables and ingestion rates were compared in the absence and presence of microplastics (550 spheres mL -1 ). For the life table experiments, cohorts of twenty neonates were introduced into 20 mL medium with four replicates per treatment. Ingestion rates of the rotifer were tested at both test temperatures in the absence and presence of the microplastics in 20 mL containers with 1 ind. mL -1 per container. The rotifer population growth rates ranged from 0.55 to 1.05 d -1 depending on the treatment. MPs decreased the fecundity by 20-24 %. The average lifespan of rotifers exposed to MPs in the F 0 generation was lower than that in the F 1 generation at both temperatures, indicating that pre-exposure of mothers may offer some protection to the offspring. The population growth rate was higher at 25 °C. The ingestion rates were significantly lower in the presence of the microplastics. Our observations indicated that this strain of B. calyciflorus was better adapted to 20 °C; microplastics and higher test temperature resulted in a pronounced changes in the demographic variables of the rotifer., Competing Interests: Declaration of competing interest We have no Conflict of Interest to declare., (Copyright © 2024. Published by Elsevier B.V.)

Plastic debris is thought to be widespread in freshwater ecosystems globally 1 . However, a lack of comprehensive and comparable data makes rigorous assessment of its distribution challenging 2,3 . Here we present a standardized cross-national survey that assesses the abundance and type of plastic debris (>250 μm) in freshwater ecosystems. We sample surface waters of 38 lakes and reservoirs, distributed across gradients of geographical position and limnological attributes, with the aim to identify factors associated with an increased observation of plastics. We find plastic debris in all studied lakes and reservoirs, suggesting that these ecosystems play a key role in the plastic-pollution cycle. Our results indicate that two types of lakes are particularly vulnerable to plastic contamination: lakes and reservoirs in densely populated and urbanized areas and large lakes and reservoirs with elevated deposition areas, long water-retention times and high levels of anthropogenic influence. Plastic concentrations vary widely among lakes; in the most polluted, concentrations reach or even exceed those reported in the subtropical oceanic gyres, marine areas collecting large amounts of debris 4 . Our findings highlight the importance of including lakes and reservoirs when addressing plastic pollution, in the context of pollution management and for the continued provision of lake ecosystem services., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Many urban lakes in Mexico City such as Lake Chapultepec are infested with high densities of cyanobacteria, particularly Microcystis. We tested the effect of cyanotoxins from cyanobacterial crude extracts on the demographic variables of zooplankton. The rotifers Brachionus havanaensis and Brachionus calyciflorus, and the cladocerans Ceriodaphnia dubia and Moina macrocopa were used for the assays. Temperature effects on the response of B. calyciflorus and 2 clones of M. macrocopa were tested. We hypothesized that with an increase in cyanotoxin concentration and temperature there would be an increase in the adverse effect on the test species and that the clone of Moina previously exposed to cyanobacteria from Lake Chapultepec would be more resistant to the cyanotoxins. Demography experiments showed that B. havanaensis was more sensitive than C. dubia. The negative effect of the cyanobacterial crude extract on B. calyciflorus was greater at 30 °C than at 20 °C or 25 °C. The strain of M. macrocopa isolated from Lake Chapultepec was more resistant to the cyanotoxins than the strain that had not been previously exposed to the cyanobacteria. The present study indicated that cyanobacteria in Lake Chapultepec are highly toxic and, considering the recreational use of this lake, should be controlled. Environ Toxicol Chem 2020;39:2409-2419. © 2020 SETAC., (© 2020 SETAC.)

Cyanobacterial blooms have been recognized as a problem in fresh water for about 150 years. Over the past 50 years, experimental studies on the subject have gained importance considering the increasing need to control toxic cyanobacterial blooms. This article presents information on the different lines of research that have been undertaken on zooplankton-cyanobacteria interactions over the past 50 years. These include information on filtering/ingestion rates and phytoplankton preferences of small and large rotifers, cladocerans, and copepods; growth rates of zooplankton on cyanobacterial diets; feeding rates of other freshwater invertebrates on cyanobacteria; role of zooplankton in top-down biomanipulation efforts; effect of cyanotoxins on zooplankton; bioaccumulation of cyanotoxins; and physical and chemical control of cyanobacterial blooms. We also highlight measures that have led to successful lake management and improvement of water quality in selected waterbodies.

The emerging contaminant 4-nonylphenol is an active ingredient in many surfactants. Though 4-nonylphenol has been reported in Mexican waterbodies, no stringent law is available to establish its permissible limits. Most ecotoxicological assays using zooplankton species are based on previously unexposed populations, and multigenerational experiments are rare. Plationus patulus and Brachionus havanaensis are widely distributed species in Mexico and have been used in ecotoxicological assessments. In this work, the median lethal concentration of 4-nonylphenol (LC 50 , 24 h) for both rotifer species was derived. Based on our acute toxicity data (24 h LC 50 of 4-nonylphenol for P. patulus and B. havanaensis were 500 and 250 µg L -1 , respectively), three sublethal concentrations (µg L -1 ) (7.81, 15.82 and 31.25 for B. havanaensis and 15.62, 31.25 and 62.5 for P. patulus ) were used in the life table demography tests for two successive generations (F0 and F1) of either rotifer species. Regardless of the concentrations used, 4-nonylphenol had an adverse effect on both rotifer species over two successive generations. P. patulus was more sensitive than B. havanaensis in chronic toxicity tests. F1 generation of both rotifer species was far more adversely affected than the F0 in all toxicant treatments.

Diurnal temperature fluctuations affect ectothermic species more than endothermic taxa. We tested the effect of three fixed temperatures (20, 25 and 30 °C) and a 24 h variable (20-30 °C) on the population growth and fatty acid profiles of the common rotifer Brachionus calyciflorus. Depending on the temperature treatment, the peak population abundances of B. calyciflorus varied from 65 to 80 ind./ml, the lowest being on variable temperature range. The rate of population increase varied from 0.31 to 0.52 per day, highest being at 30 °C. There was a curvilinear relationship between the population density and the egg ratio (number of eggs/female) in all the tested temperature regimes. The egg ratio was higher (>0.6) for treatments involving fixed temperatures, but for variable temperature regime, the egg ratios were lower (<0.5). Temperature also induced changes in the fatty acid content of B. calyciflorus. While the total saturated fatty acids increased, both mono-unsaturated and poly-unsaturated fatty acids decreased with increasing temperature regime. These results have been interpreted in relation to the role of temperature (both intensity and mode of exposure) on the population growth characteristics of rotifers., (Copyright © 2020. Published by Elsevier Ltd.)

Several abiotic factors influence the ecological responses of aquatic invertebrates to metal toxicity. We examined the effect of salinity (10, 20, and 30 psu) and temperature (25 and 32 °C) on acute and chronic arsenic (As) toxicity to the euryhaline rotifers, Proales similis and Brachionus ibericus. In general, higher salinities and low temperature resulted in lower arsenic toxicity. The population growth studies indicated that P. similis was more sensitive than B. ibericus to As. Arsenic toxicity intensified the vulnerability of P. similis to B. ibericus competition. Life table parameters decreased with increasing As levels in the medium. Chronic toxicity bioassays were more sensitive than acute toxicity tests for determining the adverse effect of As to rotifers. Our findings provide useful insights on the effect of arsenic on rotifer populations exposed to different temperature and salinity scenarios. Proales similis could be an important complement to brachionid rotifers for marine toxicity bioassays., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

We quantified the effect of two cyclopoids, an invasive (Mesocyclops pehpeiensis) and a native (Mesocyclops longisetus curvatus) species on the population growth of the rotifers Brachionus havanaensis and Brachionus calyciflorus. We hypothesized that the invasive copepod would have a greater adverse effect on the test rotifers. The population growth of B. havanaensis was tested in the indirect presence of B. calyciflorus (used as prey for the predatory copepods), and the predatory copepods, M. pehpeiensis and M. longisetus curvatus. For B. calyciflorus the experimental design was as above except that we used B. havanaensis as prey. The test rotifers were separated from the competitors and predators by mesh cages placed in the experimental jars. Rotifer density and the egg ratios were quantified, followed by a daily medium change, until the population density declined. The population growth rate of B. havanaensis ranged between 0.26 and 0.30 day−1, while that of B. calyciflorus between 0.19 and 0.21 day−1. The presence of the invasive copepod had an adverse effect on the smaller (< 110 µm) B. havanaensis, but not on the larger (> 180 µm) B. calyciflorus. The results are discussed with emphasis on the differences in the indirect impact invasive and native predatory copepods. [ABSTRACT FROM AUTHOR]

Intensive interspecific competition for limited resource often can result in the exclusion of inferior competitors, decrease the species diversity and alter the structure of the zooplankton community. Competitive experiments between Brachionus calyciflorus and Brachionus angularis were conducted at three Scenedesmus densities (0.5 × 106, 1.0 × 106 and 2.0 × 106 cells ml−1) and four initial inoculation densities (numerically, 100% B. calyciflorus, 75% B. calyciflorus and 25% B. angularis, 50% each of the two species, 25% B. calyciflorus and 75% B. angularis, and 100% B. angularis). The results showed that at the low food level, B. angularis outcompeted B. calyciflorus and vice versa at the high food levels. At the intermediate food level, B. angularis was displaced by B. calyciflorus at nearly all the initial inoculation densities except for 75% B. angularis, at which both species coexisted until the termination of the experiment. When grown alone at 0.5 × 106, 1.0 × 106 and 2.0 × 106 cells ml−1 of Scenedesmus, B. calyciflorus reached the peak abundance values of 34 ± 4, 69 ± 5 and 101 ± 9 individuals ml−1 and had population growth rates of 0.608 ± 0.032, 0.654 ± 0.033 and 0.518 ± 0.039 d−1, respectively. The corresponding values for B. angularis were 265 ± 8, 330 ± 30 and 802 ± 87 individuals ml−1 and 0.623 ± 0.020, 0.770 ± 0.036 and 0.871 ± 0.013 d−1. The results suggest that the outcome of competition depends not only on the size of the competing species and food availability but also on their colonizing density. At the low food level, Brachionus angularis outcompeted B. calyciflorus and vice versa at the high food level. At the intermediate food level, B. angularis was displaced by B. calyciflorus at nearly all the initial inoculation densities except for 75% B. angularis at which both species coexisted. [ABSTRACT FROM AUTHOR]

Proliferating cyanobacterial blooms due eutrophication in reservoirs is a major global problem. The production of cyanotoxins often increases with grazing pressure and temperature while the sensitivity of zooplankton to cyanotoxins is directly related to temperature. Here we evaluate the effect of different concentrations of the crude extract of cyanobacteria from Valle de Bravo reservoir during dry (January) and rainy (September) seasons at 20 and 25 °C on the rotifer Brachionus calyciflorus based on acute and chronic toxicity tests. We filtered 20 or 150 l of lake water, depending on the intensity of the bloom, and estimated the density and diversity of the cyanobacteria. The crude extracts, after 5 cycles of freezing, thawing and sonication at 14 MHz, were filtered and the microcystin concentration quantified based on ELISA. The extracts were used to conduct the acute and chronic toxicity tests, all in quadruplicate. Acute toxicity tests were based on 24 h mortality. Chronic toxicity tests (population growth and life table experiments) were conducted at 5 and 10% of the median lethal concentration. The field samples were dominated by Microcystis sp. (January) or Woronichinia naegeliana (September). The microcystin concentration in lake water was 9.57 μg/l and 0.097 μg/l and the median lethal concentration was 5.34 μg microcystin/L and 0.35 μg microcystin/L in January and September, respectively. Survival and reproduction of B. calyciflorus were lower in the presence of the cyanobacteria crude extract, more so at 20° than at 25 °C. Our results highlight the urgency of regular monitoring based on zooplankton assays for reservoirs in tropical and temperate regions, subject to frequent and dominant cyanobacterial blooms, often as a result of climate change., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Cyanotoxins from toxic blooms in lakes or eutrophic reservoirs are harmful to several organisms including zooplankton, which often act as vectors of these secondary metabolites, because they consume cyanobacteria, bioaccumulate the cyanotoxins and pass them on along the food chain. Microcystins are among the most commonly found cyanotoxins and often cause zooplankton mortality. Although cyanobacterial blooms are common and persistent in Mexican water bodies, information on the bioaccumulation of cyanotoxins is scarce. In this study we present data on the bioaccumulation of cyanotoxins from Planktothrix agardhii, Microcystis sp., Cylindrospermopsis raciborskii and Dolichospermum planctonicum blooms in the seston (suspended particulate matter more than 1.2 μm) by zooplankton and fish (tilapia (Oreochromis niloticus) and mesa silverside (Chirostoma jordani) samples from Lake Zumpango (Mexico City). The cyanotoxins were extracted from the seston, zooplankton and fish tissue by disintegration using mechanical homogenization and 75% methanol. After extraction, microcystins were measured using an ELISA kit (Envirologix). Concentration of microcystins expressed as equivalents, reached a maximum value of 117 μg g -1 on sestonic samples; in zooplankton they were in the range of 0.0070-0.29 μg g -1 . The dominant zooplankton taxa included Acanthocyclops americanus copepodites, Daphnia laevis and Bosmina longirostris. Our results indicate twice the permissible limits of microcystins (0.04 μg kg -1 d -1 ) for consumption of cyanobacterial products in whole fish tissue of Chirostoma jordani. The data have been discussed with emphasis on the importance of regular monitoring of water bodies in Mexico to test the ecotoxicological impacts of cyanobacterial blooms and the risk that consumption of products with microcystins could promote., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Cladocerans are constantly exposed to humic substances in nature, yet the effects of these substances on their survival and reproduction are not well known. Here, the effects of humic substances (20 and 40 mg L -1 ) (HS) on the life history variables of three common cladocerans, Ceriodaphnia dubia , Moina macrocopa , and Daphnia pulex were evaluated. The results showed that the effect of humic substances on the tested cladocerans is species-specific, affecting either survival, reproduction or both. For M. macrocopa , exposed to HS at a concentration of 40 mg L -1 , the average lifespan and the life expectancy at birth were significantly reduced as compared to controls, but for C. dubia and D. pulex these parameters were increased. Gross reproductive rate was unaffected by the HS level for both D. pulex and M. macrocopa , but it was significantly higher for C. dubia . When compared to the corresponding controls, for HS-exposed cladocerans, the rate of population increase was significantly reduced in case of D. pulex while it was stimulated for both C. dubia and M. macrocopa . It appears that humic substances had a slightly stronger influence on survivorship than on reproduction of the tested cladocerans.

The demographic response of the brackish-water rotifers Proales similis and Brachionus plicatilis to mercury (0.5, 2, 8 and 32 μg L -1 of HgCl 2 ) at different salinity levels (10 and 20‰) and two temperature (25 °C and 32 °C) regimes were evaluated. Median lethal concentration (LC 50 ) for P. similis and B. plicatilis was 10 and 16 μg L -1 , respectively, showing that Proales similis was more sensitive to mercury than B. plicatilis. The rate of population increase (r) for both species was greater at 10‰ salinity and 32 °C (ranged from 0.6 to 0.95 d -1 ). The r-value decreased as the concentration of mercury in the medium increased. Regardless of the temperature, at lower salinity and higher mercury concentration (32 μg L -1 ), P. similis died within six days. The survivorship of P. similis and B. plicatilis was higher at 25 °C than at 32 °C (ranged from 5 to 8 and 7-13 d, respectively). Fecundity was higher at 32 °C than at 25 °C for both rotifers species. There was a significant effect of the interaction among salinity, temperature, and mercury in both species on the reproductive variables such as net and gross reproductive rates, generation time and the rate of population increase. Considering the sensitivity of P. similis, we suggest that this species be included in the list of marine bioassay organisms., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

We tested the effect of different food (Chlorella vulgaris) concentrations on the population growth and demographic variables of Dipleuchlanis propatula. In addition, we also tested the effect of competition from two other zooplankton species (a rotifer Plationus patulus and a ciliate Paramecium sp.). The parthenogenetic eggs of D. propatula carry a gelatinous matrix with a thickness of about 20 µm. Population growth of D. propatula increased with increase in the algal density. Depending on the food availability, the peak abundances of D. propatula varied from 9 to 50 ind. ml−1. The rate of population increase, r, varied from 0.18 to 0.23 per day. Food density had a significant effect (p < 0.05, Tukey test) on this variable too. In spite of higher peak densities observed at high food levels, the r values were not very different; this was due to the long lag phase before the population increased. Dipleuchlanis propatula growth was lower due to competition from ciliates. Food density had no significant effect on the average life span, which varied from 5 to 7 days. However, both gross and net reproductive rates increased with increase in algal food. These results show that D. propatula had growth patterns similar to other members of the family Euchlanidae. [ABSTRACT FROM AUTHOR]

Triclosan is a personal care product widely used in North America, Europe and Asia as antimicrobial ingredient in many consumer chemical products. In Mexico concentrations of triclosan have been reported in aquatic systems. However, there is no law regulating the presence of chemicals such as triclosan, in aquatic systems. The scarce data about this chemical has increased concern among ecotoxicologists regarding possible effects on aquatic organisms. Moreover, multigenerational studies are rarely studied and the results vary depending on the contaminant. Rotifers, are a dominant group of zooplankton, and have been used in aquatic risk assessments of personal care products due to their sensitivity and high reproductive rates. Plationus patulus and Brachionus havanaensis are common rotifers distributed in aquatic ecosystems of Mexico and have been used in ecotoxicological bioassays. In this study, the median lethal concentration (LC50, 24h) of P. patulus and B. havanaensis exposed to triclosan was determined. Based on the LC50, we tested three sublethal concentrations of triclosan to quantify the demographic responses of both rotifers for two successive generations (F0, and F1). The 24h LC50 of triclosan for P. patulus and B. havanaensis were 300 and 500µgL -1 respectively. Despite the concentration, triclosan had an adverse effect on both Plationus patulus and Brachionus havanaensis in both generations exposed. Experiments show that P. patulus was more sensitive than B. havanaensis when exposed to triclosan. When exposed to triclosan the parental generation (F0) of P. patulus was far more affected than F1., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Unlike temperate regions, tropical ecosystems are characterized by high temperatures (>18 °C) all year, promoting blooms of cyanobacteria which often produce secondary metabolites toxic to zooplankton. Nabor Carillo and the Recreational Lake are part of the saline, Lake Texcoco, in Central Mexico which is filled nowadays with treated waste water. Both water bodies are dominated by Planktothrix, Anabaenopsis, Spirulina and Microcystis. In this study we present the concentration of microcystins in these waterbodies over an annual cycle. We also evaluated the chronic effects of cyanobacterial crude extracts from both lakes on two clones of the rotifer Brachionus calyciflorus, one from Nabor Carrillo Lake and the other from a canal in the shallow, Lake Xochimilco. The experiments on population growth were performed, beginning with 10 individuals per container for each of the following treatments: control (no crude extract), concentrated crude extract, and diluted crude extract (50:50) with moderately hard water and Chlorella vulgaris in a concentration of 0.5 × 10 6  cells ml -1 . The cyanotoxin levels were measured using an ELISA test and ranged between 0.20 and 2.4 μg L -1 in the lake water. The results showed that the Recreational Lake extracts were more toxic, killing the rotifers in less than five days. The r values ranged from -1.74 to 0.48 in the presence of the crude extracts and 0.16 and 0.24 in the controls. The results have been discussed with emphasis on the importance of conducting regular studies to test ecotoxicological impacts of cyanobacterial blooms in tropical waters., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

In this study, we quantified intergenerational, demographic variability of Moina macrocopa subjected to cadmium stress. Exposure of M macrocopa to cadmium (0.2, 0.3, and 0.4 mg/L as CdCl 2 ) through 4 consecutive generations revealed changes in demographic responses not only in survivorship variables but also in reproductive parameters. Long-term demographic responses varied differently, depending on the demographic trait and the concentration of heavy metal in the medium. With the exception of generation time, all life history traits were significantly and adversely influenced due to increase in Cd concentrations. The average life span of M macrocopa varied up to 40% depending on Cd level and the generation of exposure. The highest gross reproductive rates were recorded in controls, while the lowest (∼30% less) were recorded at the highest Cd level. Survival-weighted net reproductive rates were reduced by nearly 50% due to Cd toxicity. The rate of population increase per day of M macrocopa was also significantly affected (∼25%) by Cd as compared to controls. This cladoceran showed a dose-response to Cd toxicity with a significance in both magnitude and frequency of offspring production., Competing Interests: Declaration of Conflicting Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Current research on the effects of cladoceran allelochemicals on rotifers has been inconclusive and the allelopathic effects of rotifers on cladocerans are unknown. We sought to fill this knowledge gap with life table demography experiments assessing the interspecific effects of Moina macrocopa-conditioned mediums (MCM) and Brachionus calyciflorus-conditioned mediums (CCM) on the main life history variables under different temperatures and algal densities. Our results demonstrate that, when compared to the allelopathic effects of M. macrocopa on B. calyciflorus, M. macrocopa had higher sensitivity to the allelochemicals from B. calyciflorus. When compared to the controls, the chemically-mediated effects of M. macrocopa on the net reproductive rate (R0), intrinsic rate of population growth (rm) and total number of offspring (NO) of B. calyciflorus were non-significant in many cases while in a few the impacts were stimulatory or inhibitory under different concentrations of MCM, temperatures, and food densities. However, when compared to the controls, the allelopathic effects of B. calyciflorus on the R0, rm and NO of M. macrocopa were stimulatory in many cases; some impacts were inhibitory or non-significant under different concentrations of CCM, temperatures, and food densities. In addition, life expectancy at birth (e0), generation time (T), and average lifespan (LS) of B. calyciflorus and M. macrocopa cultured in the conditioned medium nearly did not differ significantly from the controls. Our results suggest that the interspecific allelopathic effects of B. calyciflorus and M. macrocopa are dependent on the origin and concentration of the allelochemical, life history variable, temperature, and food (algal) density. Additionally, the underlying mechanisms should be further investigated. Interspecific allelopathic effects of B. calyciflorus and M. macrocopa were dependent on the origin and concentration of allelochemical, life history variable, temperature and food density. M. macrocopa had higher sensitivity to the allelochemicals from B. calyciflorus. The underlying mechanisms should be further investigated. [ABSTRACT FROM AUTHOR]

Zooplankton are essential components of the aquatic food chain. Their density and composition are influenced by abundant of particular nutrients which promotes planktonic bloom. Domestic sewage is mostly anoxic to hypoxia in nature that favours largely pollution resistant species of zooplankton. The present study deals with the density, biochemical composition and gut microbes of Cladoceran (Moina macrocopa) from domestic sewage water monthly and seasonally. Hydrological parameters and zooplankton density in sewage water showed much variation in different seasons. The monthly variations of M. macrocopa density showed minimum (766.67 ± 152 Ind./L) during December 2019 and maximum (11,600.00 ± 360 Ind./L) during March 2020. Further, seasonal mean density was minimum during monsoon (1444.44 ± 185 Ind./L) and maximum during post-monsoon (9744.44 ± 725 Ind./L) showed distinct seasonal variations. Untreated sewage water in canal boost up solitary zooplankton M. macrocopa abundantly even in anoxic condition with optimum nutrients during the post-monsoon season. Total proteins and carbohydrates of M. macrocopa were maximum during post-monsoon and minimum during monsoon whereas total lipids were maximum during pre-monsoon and minimum during monsoon season. Present finding reveal that, M. macrocopa was found in untreated domestic sewage waste water solitarily in high density in different seasons. Physico-chemical parameters and availability of rich nutrients were the key factors which favouring high density and biochemical profiles of M. macrocopa. Further, abundant anaerobic coli form bacterial strains viz. Klebsiella pneumonia, Exiguobacterium profundum, Escherichia coli JSG and Escherichia coli JSG2 in gut of M. macrocopa indicates its preferred food in anoxic condition and reflect well adaptation in polluted environment. [ABSTRACT FROM AUTHOR]

The toxicity of triclosan (TCS) on the freshwater cladoceran Moina macrocopa was investigated by acute and chronic toxicity assessments followed by genotoxicity and oxidative stress response analyses. The 48-h LC 50 of TCS for ≤24-h-old M. macrocopa was determined as 539 μg L -1 . Chronic exposure to TCS at concentrations ranging from 5 to 100 μg L -1 showed a stimulatory effect at low concentrations (≤10 μg L -1 ) and an inhibitory effect at high concentrations (≥50 μg L -1 ) on growth, reproduction, and population-growth-related parameters of M. macrocopa. The genotoxicity test results indicated that TCS concentrations ranging from 50 to 100 μg L -1 can alter individuals' DNA. Analysis of the antioxidant enzymes catalase (CAT) and glutathione s-transferase (GST) demonstrated increased levels of these enzymes at high TCS concentrations. Our results indicated that TCS concentrations found in the natural environment have minimal acute toxicity to M. macrocopa. However, TCS at even low concentrations can significantly affect its growth, reproduction, and population-growth-related characteristics. The observed responses suggest a hormetic dose-response pattern and imply a potential endocrine-disrupting effect of TCS. Our molecular and biochemical findings indicated that high concentrations of TCS have the potential to induce oxidative stress that may lead to DNA alterations in M. macrocopa., (© 2023 Wiley Periodicals LLC.)

To understand the population growth potential of different species of rotifers in nature, field collections through seasons are essential. We sampled zooplankton (and measured selected physicochemical variables) from the Madín reservoir, a high altitude eutrophic urban waterbody from Mexico, every month for a year. Qualitative analysis of zooplankton revealed 28 rotifer species and four cladoceran crustaceans plus one unidentified copepod. Cephalodella catellina (1400 ind L-1), Horaella thomassoni (550 ind L-1), Conochilus dossuarius (380 ind L-1) and Filinia longiseta (25 ind L-1) had higher peak density than other rotifers. Based on the concentrations of nitrates and phosphates, chlorophyll a levels or different diversity indices (e.g., Carlson, Shannon-Wiener, Pantle and Buck, Ejsmont-Karabin's TSIRot), the waterbody is eutrophic to hypertrophic, depending on the season. In this waterbody we observed high densities of Aphanothece sp. which is a toxic picocyanobacterium. During the blooms of Aphanothece, we also recorded higher densities of H. thomassoni and C. catellina. Based on the gut contents we found that both these rotifer species feed on Aphanothece in this waterbody. This study thus suggests the potential growth of Horaella, Cephalodella, Conochilus and Filinia in this eutrophic reservoir containing blooms of Aphanothece. [ABSTRACT FROM AUTHOR]

We hypothesized that cyclopoids, being predators, have a stronger allelopathic influence than calanoids on life-history variables of herbivorous rotifers. To test this hypothesis, we quantified the allelopathic effects of conditioned medium obtained separately from males and females of a calanoid (Arctodiaptomus dorsalis) and a cyclopoid (Mesocyclops longisetus) on the life table demography of the rotifer Brachionus havanaensis. The conditioned medium of the male and female A. dorsalis and male M. longisetus caused a significant reduction (14–18%) in the life expectancy at birth of B. havanaensis. Gross and net reproductive rates of rotifers reduced significantly on the conditioned medium of male or female A. dorsalis; however, the conditioned medium from either sex of M. longisetus had no significant effect on these variables. The population growth rate, r, varied from 0.53 to 0.64 d−1 depending on the treatment; the r was significantly lower when cultured on the conditioned medium from A. dorsalis (males or females) and female M. longisetus Contrary to our hypothesis, calanoid allelochemicals adversely affected the life history variables of rotifers more than those produced by the cyclopoids. [ABSTRACT FROM AUTHOR]

The mechanism of decline in continuous plantations is currently a popular research topic in forestry. Continuous cropping is a common obstacle in poplar production and management, and maintaining productivity is a technical challenge. Recent studies have shown that continuous cropping of poplars leads to a reduction in biomass, but there is a lack of information summarizing the effects of plant secondary compounds on belowground interactions. This paper explores the allelopathic phenomenon, which refers to the inhibitory or promoting effects of poplar tissue extracts on plants. The paper also considers the environmental behaviors of allelochemicals derived from poplars, including their secretion, degradation, adsorption, retention, and phytotoxicity. A conceptual model of the autotoxicity mechanism of continuous cropping poplar is proposed from three aspects: microorganisms, soil enzymes, and nutrient changes, with the goal of overcoming poplar autotoxicity. Finally, the research results and potential application prospects of biotechnological methods related to the allelopathic effects of poplar are presented. [ABSTRACT FROM AUTHOR]

Worldwide freshwater salinization may significantly alter ecosystem functioning and affect biodiversity. We studied the effect of salinity on hatching success of resting eggs of different ages and life history traits of post-diapause females of cladoceran Moina macrocopa. The hatching success of resting eggs was almost unaffected by the salinity we tested (up to 5.9 g L−1). We observed a distinct difference in the hatching success of resting eggs of different ages, which was lower by ca. 50% for 4-year-old resting eggs compared with 1-year-old resting eggs. We found a decrease in the values of the life-history traits of the females hatched from 4-year-old resting eggs compared with the females hatched from 1-year-old resting eggs exposed to salinity within the range of 0.08–3.5 g L−1: a shorter lifespan, a lower juvenile somatic growth rate, a delay in the day of the first reproduction, and a smaller number of parthenogenetic clutches produced. Analysis showed that at a salinity of 3.5 g L−1, females hatched from resting eggs are more vulnerable to the effect of salinity than directly developing females. The post-diapause females exposed to salinity showed a shorter lifespan and reduced reproduction parameters (produced fewer clutches and neonates) compared with the directly developing females. Thus, the hatching of resting eggs can be considered as a critical period of the development of a species with the diapause in its life cycle due to the vulnerability of post-diapause females to increased salinity, which can be crucially important for the ecological success of the population. [ABSTRACT FROM AUTHOR]

The Transbaikalia (Russia) hosts a number of shallow endorheic saline alkaline lakes. The outcome of our studies demonstrated changes in phytoplankton and zooplankton in selected lakes covering a wide salinity gradient (from 0.69 to 128.33 g/L) over a number of years. Our main goal is to assess the variability of structural and functional indicators of phytoplankton and zooplankton communities at the various salinity levels. The gradient of abiotic factors significantly determines the dynamics of planktonic community diversity, abundance, biomass, and production. High values of secondary production was ensured by nonpredators (bacteriovorous, herbivorous, and detrivorus). We found that species and functional diversity of phytoplankton and zooplankton decrease with increasing salinity, whereas their abundance, biomass, and daily secondary production did not. In phytoplankton, a shift occurred from the small-medium cell size unicellular and colonial non-flagellated forms to the large-extra large filamentous cyanobacteria and colonial algae. A shift from selective raptorial and microphagous carnivores to herbivorous copepods and cladocerans and further to more generalist filter-feeder of rotifers and anostracans was observed in zooplankton. These findings are important because they provide a meaningful view of phytoplankton-zooplankton trophic interactions and contribute to an improved understanding their functional effects on aquatic ecosystems. Our results also complement existing knowledge and provides new information about the diversity and functioning of planktonic communities in soda lakes. [ABSTRACT FROM AUTHOR]

Aluminum (Al) use has increased greatly during the last two decades, yet little information is available on its toxic effects in relation to pH particularly on zooplankton. In this work, we determined the acute toxicity (LC) and life table responses for Moina micrura exposed to 0.008, 0.016 and 0.08 mg of Al L at pH of 5, 6 and 7. The age-specific survivorship and reproduction showed a steep decline (80% mortality by the second day) at pH 5, independent of Al level. Both gross and net reproductive rates were significantly lower at pH 6 compared to pH 7, regardless of Al concentration. At pH 7 the rate of population increase of M. micrura was not significantly influenced by the Al level, while at pH 6 it was significantly lower ( p < 0.05), suggesting that M. micrura is sensitive to changes in Al under slightly acidic conditions. [ABSTRACT FROM AUTHOR]

We compared the demographic variables and bacterivory of two strains of Diaphanosoma mongolianum from two water bodies in Spain, one without Microcystis (Maidevera in Zaragoza) and the other with dense Microcystis (La Albufera of Valencia). We hypothesized that the strain rarely exposed to Microcystis would be unable to grow on this cyanobacterial diet. We fed both strains Monoraphidium caribeum and Microcystis aeruginosa, together and separately, and compared their demographic variables. Monoraphidium caribeum was cultured in the laboratory on a defined medium, while the cyanobacteria were collected from La Albufera and sonicated before feeding the cladocerans (at 0.5 × 106 cells ml−1). We also tested the growth of D. mongolianum on bacterial diets by using seston (0–15 µm), bacterioplankton (0–3 µm) and mixed fractions (3–15 µm), from sieving Lake Albufera. We conducted population growth and life table demography experiments at 25 °C, using the two strains of D. mongolianum. Both strains had r (population growth rate) ranging from 0.05 to 0.3 d−1, on all diets. The r was higher (0.18 d−1) on the 0–15 µm seston compared to the mixed fraction (0.12 d−1) although D. mongolianum also grew well on bacterioplankton (0.16 d−1) alone. The response of the strains collected from two different water bodies was different to the test diets. We found that both strains of D. mongolianum could effectively utilize Microcystis for survival and growth, regardless of previous exposure to the cyanobacteria. The tested cladocerans could also grow well on small sized food particles (0–3 µm and 0–15 µm). Our results explain why D. mongolianum is common in eutrophic water bodies [ABSTRACT FROM AUTHOR]

Aquatic organisms are constantly exposed to effluents which often contain microplastics. Microplastics adversely affect aquatic organisms as a result of mechanical damage during ingestion or intoxication by chemicals adsorbed on the microplastics. Sub-optimal temperatures may acerbate the adverse effects of microplastics on aquatic biota. Brachionid rotifers, such as Brachionus havanaensis and Brachionus calyciflorus, are common in tropical freshwaters. They are generalist filter feeders capable of consuming microplastic particles of a wide size range 0.05 to 40 µm, which can eventually affect growth and competitive interactions among species. Here, we evaluated the effect of 30 µm beads of polystyrene microplastics at 10 and 20 mg l−1 on the population growth and competition of B. havanaensis and B. calyciflorus at 20 and 25 °C using 0.5 × 106 cells ml−1Chlorella vulgaris as food. Population growth decreased in treatments with microplastics at both temperatures as compared to the controls. The population growth rates ranged between 0.21 and 0.38 d−1 for B. calyciflorus, and between 0.27 and 0.48 d−1 for B. havanaensis. The presence of the competing species significantly lowered the population growth rate for B. calyciflorus but not for B. havanaensis. On the other hand, while the presence of the microplastics had little impact on the population growth rate of B. calyciflorus in the presence of the competitor, the reverse was true for B. havanaensis, especially at 20 °C. Our results show that the presence of microplastics may affect rotifer community structure in natural water bodies. [ABSTRACT FROM AUTHOR]

To test the hypotheses that multigenerational predation risk favors clones with longer postero-lateral spines and a larger body, and that fitness consequences of selection depend on both tested fitness variables and selection intensity, we expose replicate Brachionus dorcas populations in low (LK) and high (HK) concentrations of Asplanchna kairomones. Over 60 days (23 asexual generations) of selection, LK-selected populations showed the highest equilibrium population densities, and median mictic ratios and postero-lateral spine lengths, and HK-selected populations showed the lowest equilibrium population densities, the highest mictic ratios, and the longest postero-lateral spines, among all the control and treatment populations. In the absence of Asplanchna kairomones, and compared with populations with the control selection history, populations with an LK selection history showed increased growth rates/intrinsic rates of population increase and net reproductive rates, but decreased mictic ratios, indicating three fitness gains and a fitness cost; and those with an HK selection history showed increased life expectancy at hatching and mictic ratios, but decreased growth rates, indicating two fitness gains and a fitness cost. Asplanchna kairomones might increase the heritability of higher equilibrium densities or mictic ratios, and longer postero-lateral spines, and thus enable the prey to survive predation. [ABSTRACT FROM AUTHOR]

Authors have attributed the statement "All science is either physics or stamp collecting" to the Physicist, Ernest Rutherford. Putting this sarcastic quip aside, we know that scientific disciplines come of age when they can generate testable, repeatable, and falsifiable hypotheses; yet disciplines begin, and continue, by simply collecting observational information. It is clear, even with a casual assessment of all 16 International Rotifer Symposia, as well as the extensive literature published since our first congress, that rotifer research has moved beyond describing species, making lists of their occurrences, and describing changes in their population dynamics. In spite of the excellent progress that has been made in rotiferology we believe more remains to be done. In this review we nominate 10 fields in rotifer research that we believe will advance understanding of rotiferan biology; these include the following topics: (1) neurobiological connectomes, (2) genomic architecture and control systems, (3) physiology, (4) life history, including sexuality, development, and aging, (5) ecological responses to stresses, (6) biogeography and distribution of cryptic species, (7) analysis of rotiferan morphospace, (8) rotifer evolution within Gnathifera including Acanthocephala, (9) educational opportunities for beginning students, and (10) fostering international collaboration. [ABSTRACT FROM AUTHOR]

We quantified the population growth of the predatory heliozoan Actinosphaerium eichhornii fed separately four rotifer prey (Anuraeopsis fissa, Brachionus calyciflorus, Brachionus havanaensis and Plationus patulus) at three densities (0.5, 1 and 2 ind. ml−1 per day). All the four prey rotifer species were consumed by A. eichhornii. Regardless of the prey species, increasing rotifer prey density resulted in an increased population growth of the heliozoans. Higher cyst production in A. eichhornii occurred at higher prey densities on all prey species. A. fissa offered at the lower densities of 0.5–1.0 ind. ml−1 day−1 did not lead to cyst production by A. eichhornii. The predator did not survive beyond 2 days on Chlorella vulgaris alone. When cultured together with heliozoans, A. fissa, B. calyciflorus and B. havanaensis were eliminated within 4 days. However, the prey rotifer Plationus patulus continued to survive for about 10 days with heliozoans. The highest rate of population increase of heliozoans (0.91 day−1) was recorded when fed B. calyciflorus at a density of 2 ind. ml−1 day−1, while of those of prey varied from 0.30 to 0.41 day−1 when fed Chlorella vulgaris at 1 × 106 cells ml−1 day−1. We have analyzed the impact of heliozoan predation on rotifers. [ABSTRACT FROM AUTHOR]

Predation is a well-known factor that structures rotifer communities. However, the role of protists as predators is relatively understudied. Here, we investigated predatory behavior of Actinosphaerium sp., a freshwater heliozoan, on seven rotifer species. Predators and prey were collected from a local playa; except for Brachionus calyciflorus that served as a naive prey control. Prey included large species (≥ 175 µm mean length: Asplanchna sieboldii, B. calyciflorus, Platyias quadricornis, and Lacinularia flosculosa) and small species (< 175 µm: Cephalodella gibba, Euchlanis dilatata, and Lepadella patella). Four experiments were conducted. (1) Single prey items of varying size and motility. Larger prey types were ~ 1.7 to 3.0 times more likely to be ingested than small prey. No L. flosculosa were ingested, contrary to field observations. No correlation was found between swimming speed and predation risk. (2) Preference tests. Asplanchna sieboldii and B. calyciflorus were favored prey. (3) Growth rate of Actinosphaerium on mixed diets, with and without Asplanchna. Highest population growth of Actinosphaerium was observed in presence of A. sieboldii. (4) Prey defenses. Susceptibility of spined versus unspined B. calyciflorus resulted in no significant difference in predation risk. Thus, size and being mobile (compared to sessility) are the primary risk factors influencing rotifer predation vulnerability. [ABSTRACT FROM AUTHOR]

Most species of Keratella possess dome-shaped, dorsal plates comprising a network of polyhedral units (facets), delineated by slightly raised ridges. The arrangement of facets define a species' facet pattern (FP), with the resulting structure resembling a geodesic dome. Researchers have sorted species into categories based on their FPs, but those have not been analyzed. Additionally, while a strong lorica has been suggested to protect Keratella from predatory attack or other actions causing blunt force trauma (BFT), we know little of how that occurs. Thus, in our study we tested two hypotheses. (1) There is support for categorizing Keratella species into unique groupings based on their FPs. (2) FPs provide resistance to physical stresses. To test that hypothesis we used the structural analysis software SkyCiv©. Our results indicate support for four FP categories. Additionally, the SkyCiv analysis provided preliminary 'proof-of-concept' that Keratella FPs have a functional significance: i.e., adding or subtracting facets in our model was followed by a change in predicted structural reliability. We posit that FPs are adaptations protecting Keratella from fractures to the lorica that may result from BFT incurred during predatory attack by copepods or while caught within the branchial chambers of daphnids. [ABSTRACT FROM AUTHOR]

Metal pollution of aquatic ecosystems continues to be a worldwide concern, and many studies have previously been conducted evaluating metal toxicity to aquatic organisms. However, these studies have mainly been focused on temperate species and only evaluated aqueous exposure, whereas aquatic organisms under real-world conditions are also exposed to metals through their diet. Toxicity tests were conducted evaluating the effects of Cr on cell density and biochemical composition of the microalga Chlorella vulgaris. Additionally, the toxic effects of Cr on the temperate Ceriodaphnia dubia and the tropical Ceriodaphnia silvestrii cladocerans were investigated through three contamination routes: contaminated medium (CM), contaminated food (CF; C. vulgaris), and the combination of both situations (CMF; contaminated medium and food). The toxicity tests with the cladocerans evaluated the metal effects on survival, number of newborns, and feeding activity. Exposure to 48 µg L−1 total dissolved Cr reduced cell density and increased protein, carbohydrate, and lipid content in C. vulgaris. The increase in the biochemical composition and hence food quality of the microalgae after Cr exposure have contributed to the absence of toxic effects to the cladocerans in the CF treatment. No toxic effects were observed to the temperate cladoceran at any treatment. The tropical cladoceran C. silvestrii showed reduced filtration, ingestion and reproduction rates in the CM and CMF treatments at a Cr concentration below national and international standards. Implications for considering different exposure pathways in ecotoxicological studies, (tropical) risk assessments and indications for future research are discussed. [ABSTRACT FROM AUTHOR]

We quantified the feeding behavior (encounter, attack, capture and ingestion) and demographic parameters (survival and reproduction) of the predatory rotifer Asplanchna sieboldii fed on the prey Plationus patulus previously exposed to microplastics (MPs), Cd or their combination. As compared to controls, capture and ingestion rates of P. patulus by A. sieboldii decreased by 71 and 61%, respectively, with prey previously exposed to mixed MPs and Cd treatment. Life table data showed that the predator died earlier in controls than when fed on prey exposed to both Cd and microplastics. Regardless of the prey treatment, the offspring production by A. sieboldii increased as the available prey numbers increased (from 1 to 4 ind. ml−1). Compared to controls, the fecundity rate of the predator decreased when contaminated prey was offered as food. [ABSTRACT FROM AUTHOR]

Endocrine disruptors can alter biological functions in aquatic organisms at low levels. Triclosan, a commonly used active ingredient in personal care products around the world, is frequently detected in the environment. Likewise, 4-nonylphenol is used in products such as plastics, personal care products, and cleaning agents. Zooplankton species such as cladocerans are used in acute and chronic ecotoxicological assays. Daphnia laevis is a commonly found cladoceran in Mexican water bodies and has been used in previous ecotoxicological experiments. In this work, median effective concentration of triclosan and 4-nonylphenol (EC50, 24 h) for immobilization for the cladoceran were derived. Based on the acute toxicity data (368.6 and 200 µg L−1, respectively), three sublethal concentrations of both compounds (30, 60, 120 and 10, 20, 40 µg L−1, respectively) were used to evaluate population responses. Population growth curves of D. laevis were affected significantly, indicating decreases in peak abundances in all treatments (0.5 for triclosan and 1 ind mL−1 for 4-nonylphenol) compared to controls (2 ind mL−1). The effect of the exposition of both endocrine disruptors was significant in the majority of the treatments; however, 4-nonylphenol was more toxic to D. laevis, than triclosan. This can be explained through the great number of interactions of binding sites on the amino acid, arginine kinase, contributing to the inhibition of the regulation of cellular energy used in survival and reproductive pathways of the cladoceran. [ABSTRACT FROM AUTHOR]

Chloroquine (CQ) has been widely used for many years against malaria and various viral diseases. Its important use and high potential to being persistent make it of particular concern for ecotoxicological studies. Here, we evaluated the toxicity of CQ alone and in combination with copper (Cu) to the euryhaline rotifer Proales similis. All experiments were carried out using chronic toxicity reproductive five-day tests and an application factor (AF) of 0.05, 0.1, 0.3, and 0.5 by multiplying the 24-h LC 50 values of CQ (4250 µg/L) and Cu (68 µg/L), which were administered in solution. The rate of population increase (r, d -1 ) ranged from 0.50 to 52 (controls); 0.20 to 0.40 (CQ); 0.09 to 0.43 (Cu); and -0.03 to 0.30 (CQ-Cu) and showed significant decrease as the concentration of both chemicals in the medium increased. Almost all tested mixtures induced synergistic effects, mainly as the AF increased. We found that the presence of Cu intensifies the vulnerability of organisms to CQ and vice versa. These results stress the potential hazard that these combined chemicals may have on the aquatic systems. This research suggests that P. similis is sensitive to CQ as other standardized zooplankton species and may serve as a potential test species in the risk assessment of emerging pollutants in marine environments., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

In recent years, the frequent occurrence of algal blooms has posed continuous threats to aquatic ecosystems and social safety. Environmentally friendly algae-inhibiting methods utilizing allelopathic substances offer advantages such as convenient application and low costs, presenting a bright application prospect in the fields of water and ecological restoration. This study aimed to investigate the procedure for extracting total flavonoids from Zanthoxylum bungeanum leaves and assess allelopathic mechanism of Z. bungeanum leaf extracts on Microcystis aeruginosa. The optimal extraction conditions were determined as follows: solvent-to-material ratio = 10 mL/g; extraction time = 55 min; ethanol volume fraction = 80%; and ultrasonic temperature = 80 °C. Antioxidant activity tests revealed that Z. bungeanum leaf extracts exhibit superior capacity compared to Butylated hydroxytoluene (BHT) but inferior to Vitamin C (VC). Moreover, high-concentration Z. bungeanum leaf extracts can disrupt the structures of oxygen-evolving complexes at the donor sides of photosystem II (PSII) reaction center and influence energy distribution at PSII reaction centers, thereby inhibiting electron transmission activities at both donor and receptor sides of the PSII reaction center. The elucidated allelopathic mechanism of Z. bungeanum leaf extracts provides theoretical evidence for the algal-bloom control and the development of allelopathic algae-inhibiting agents, offering a reference for the further comprehensive development and utilization of Z. bungeanum., Competing Interests: Declarations. Conflict of interests: The authors affirm the absence of any conflict of interest. This study is exempt from conflicts, informed consent, and human or animal rights considerations., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

In recent decades the Amazonian ecosystem has received large amounts of domestic and industrial effluents, as well as mining-related waste contributing significant quantities of metal to water bodies. Thus, the main objective of the study was to verify the sensitivity of a native Amazonian ostracod (Strandesia rondoniensis) species to isolated and mixed metal salts (CuSO 4 ; ZnCl 2 ; CdCl 2 and HgCl 2 ). The sensitivity will be compared to other species using species sensitivity distributions (SSDs) for an ecological risk assessment (ERA). The experiment consisted of simultaneously exposing each metal alone and in mixture, through a factorial design for toxicity with 25 different combinations for 48 h. For the ERA, metal concentrations measured in the water of various aquatic environments in the Amazon basin were considered based on the risk quotient values. The results showed that the metal toxicity gradient was Cd>Hg>Cu>Zn, respectively. The toxicity in the mixture showed that the combination of Cu-Cd and Cu-Zn better fit the model (CA), indicating mainly synergism when copper predominated in the mixture. Meanwhile, the Cu-Hg interaction fit the model better (IA), again indicating synergism when copper was at a higher concentration. The ERA showed a high risk (RQ > 1) for the Cd, Cu, and Hg metals., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

This Assessment Update by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) considers the interactive effects of solar UV radiation, global warming, and other weathering factors on plastics. The Assessment illustrates the significance of solar UV radiation in decreasing the durability of plastic materials, degradation of plastic debris, formation of micro- and nanoplastic particles and accompanying leaching of potential toxic compounds. Micro- and nanoplastics have been found in all ecosystems, the atmosphere, and in humans. While the potential biological risks are not yet well-established, the widespread and increasing occurrence of plastic pollution is reason for continuing research and monitoring. Plastic debris persists after its intended life in soils, water bodies and the atmosphere as well as in living organisms. To counteract accumulation of plastics in the environment, the lifetime of novel plastics or plastic alternatives should better match the functional life of products, with eventual breakdown releasing harmless substances to the environment. [ABSTRACT FROM AUTHOR]

The River Nile is the artery of Egypt, as it presents more than 96% of the municipal, industrial, and irrigation necessities of Egypt. This study was dedicated to providing data about the effect of pollution at six stations on the River Nile at the Rosetta branch during the period from August 2019 to April 2020, using heavy metals analysis and zooplankton as biological indicators. It was found that the average of heavy metals concentration follows the descending order Al > Fe > Mn > Zn > Ni > Co. Most of the heavy metals recorded its highest values at El-Rahawy station. Zooplankton community was represented by 32 species in addition to 4 Meroplanktons. Five groups of zooplankton were recorded, viz. Rotifera (1717 org./L), Protozoa (552 org./L), Cladocera (54 org./L), Nematoda (46 org./L), and other Meroplankton (44 org./L), dominated by Rotifera followed by Protozoa, Cladocera, Nematoda, and other Meroplanktons contributing 71%, 23%, 2%, 2%, and 2%, respectively. The highest average density of total zooplankton was recorded during spring while the lowest was recorded during summer. The highest similarity of (79.12%) was observed between (Site 1) and (Site 5). Almost all diversity indices were conducted and showed its highest values in site 6. The principal component analysis conducted between heavy metals, and zooplankton showed a significant negative correlation was shown for the dominant zooplankton with the heavy metals except with cobalt. Nematoda and the rotifer Brachionus angularis recorded a positive correlation with heavy metals except cobalt. [ABSTRACT FROM AUTHOR]

Context: Climate change and global warming has led to changes in water-quality parameters, which in turn have negative consequences for zooplankton. Aims: To investigate the effects of various environmental stressors (pH, temperature, photoperiod, and food concentration) on the tropical freshwater microcrustacean Moina micrura. Methods: The study examined the effects of these stressors on survival (lifespan), reproduction (days to first brood, number of broods, and total offspring), growth (individual size and total moulting), physiology (heart rate), and sex-switching effects (total male offspring). Key results: Significant (P < 0.05) reductions in the total offspring, individual size, and heart rate of M. micrura were observed when exposed to acidic (pH 5) and alkaline (pH 9) conditions. Conversely, higher water temperatures (31°C) and longer light exposure (20 h) were found to increase total offspring and heart rate in M. micrura. Furthermore, male offspring were produced only under conditions of food scarcity (no food supply and 1 × 102 cells mL−1). Conclusions: Climate change has a significant effect on the life-history traits of M. micrura , a tropical cladoceran species. Implications: Vital insights that can guide policymakers and practitioners in developing more effective strategies to safeguard and preserve tropical freshwater aquatic habitats, especially those of zooplankton species. To explore climate effects on tiny aquatic life, we delved into how changes in water conditions affect Moina micrura , a small freshwater creature. Results showed that extreme pH harms the offspring and slows the heartbeat of this species, but warmth and longer daylight boost the numbers. Interestingly, M. micrura produces more males when food is scarce. This research informs strategies to protect these creatures in our tropical waters. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms are increasingly common in aquatic environments worldwide. These microorganisms cause concern due to their ability to produce cyanotoxins. Aquatic organisms, especially zooplankton, are exposed to cyanobacterial toxins by different routes, depending on the bloom phase. During cyanobacterial dominance, zooplankton is exposed to cyanotoxins through the ingestion of cyanobacterial cells, while at the bloom senescence, dissolved toxins are the most representative route. In this study, we assessed the effects of a microcystin-producing strain of Microcystis aeruginosa (NPLJ-4) on clones of the tropical small cladocerans Macrothrix spinosa (two clones) and Ceriodaphnia cornuta (one clone) exposed to intact cells and aqueous cell crude extracts. Short-term toxicity assays and life-table experiments were performed to assess the effects of the toxic M. aeruginosa on the survival and life history of the cladocerans. In the short-term toxicity assay, we found that cladocerans were more affected by intact cells. Both clones of M. spinosa were more affected when exposed to intact cells, while C. cornuta displayed about 5-fold more resistance. On the other hand, crude extracts had a low impact on cladocerans' survival. Also, we observed a significant decrease in survival, fecundity, and growth of animals exposed to sublethal and environmentally relevant concentrations of M. aeruginosa cellular biomass. However, even at high concentrations of dissolved microcystins, the crude extract did not have significant effects on the life history parameters of the cladocerans. Although they can be found during cyanobacterial bloom events, small-bodied cladocerans are still affected by toxic Cyanobacteria depending on the exposure route., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

In hypertrophic waterbodies, seston may be an important food for planktonic rotifers. Therefore, we hypothesized that seston in the hypertrophic waterbody (Lake Xochimilco, State of Mexico) supports high diversity and density of rotifers. To test this, we conducted growth experiments using six rotifer species (Brachionus bidentatus, Brachionus budapestinensis, Brachionus calyciflorus, Brachionus caudatus, Brachionus havanaensis and Plationus patulus) cultured on three seston size fractions (< 3, 3–15 and < 15 µm) for 15 days. The three fractions of seston contained 3.15, 6.30, and 9.45 μg C ml−1, respectively. The physical and chemical variables of the waterbody were fairly stable during the study period. Brachionus budapestinensis, B. calyciflorus and B. caudatus showed negative growth rates when cultured on seston size of 3–15 or < 15 µm, while B. bidentatus had negative r on < 3 µm particle size. Brachionus havanaensis and P. patulus were well adapted to feed on different sizes of seston, while B. budapestinensis and B. caudatus had higher growth on < 3 µm particle size. These results explain the high diversity and density of brachionid rotifers in this waterbody where they coexist by partitioning the available seston. [ABSTRACT FROM AUTHOR]

Rotifers and cladocerans compete for resources in freshwater ecosystems. Cladocerans, due to their large size, are competitively superior to rotifers. Cladocerans also release secondary metabolites into the medium which may be allelopathic to rotifers. However, in many eutrophic water bodies, rotifers are competitively dominant to cladocerans. We therefore hypothesize that allelochemicals released by competing species of Cladocera have weak or no adverse effects on rotifers. To test this, we conducted cohort life table demography experiments of the three rotifers Brachionus calyciflorus, Brachionus havanaensis, and Plationus patulus with cladoceran-conditioned medium (CM) derived from Moina macrocopa, Ceriodaphnia dubia, and Daphnia pulex. All six zooplankton species were isolated at the same time from a shallow eutrophic water body in Central Mexico. We found that the following demographic variables of B. calyciflorus cultured in CM did not differ from controls: life expectancy at birth, gross and net reproductive rates, generation time and the rate of population increase. We further showed that B. havanaensis was most sensitive to the cladoceran-mediated chemicals and that M. macrocopa-CM caused varied demographic responses in rotifers. We conclude that cladoceran-conditioned medium had weak allelopathic effects on rotifers unlike the negative experience from direct physical contact with Cladocera. [ABSTRACT FROM AUTHOR]

In this study, high-throughput sequencing of 16S rRNA amplicons and predictive PICRUSt functional profiles were used to perform a comprehensive analysis of the temporal bacterial distribution and metabolic functions of 19 bimonthly samples collected from July 2019 to January 2020 in the surface water of Billings Reservoir, São Paulo. The results revealed that most of the bacterial 16S rRNA gene sequences belonged to Cyanobacteria and Proteobacteria, which accounted for more than 58% of the total bacterial abundance. Species richness and evenness indices were highest in surface water from summer samples (January 2020), followed by winter (July 2019) and spring samples (September and November 2019). Results also showed that the highest concentrations of sulfate (SO4–2), phosphate (P), ammonia (NH3), and nitrate (NO3-) were detected in November 2019 and January 2020 compared with samples collected in July and September 2019 (P < 0.05). Principal component analysis suggests that physicochemical factors such as pH, DO, temperature, and NH3 are the most important environmental factors influencing spatial and temporal variations in the community structure of bacterioplankton. At the genus level, 18.3% and 9.9% of OTUs in the July and September 2019 samples, respectively, were assigned to Planktothrix, while 14.4% and 20% of OTUs in the November 2019 and January 2020 samples, respectively, were assigned to Microcystis. In addition, PICRUSt metabolic analysis revealed increasing enrichment of genes in surface water associated with multiple metabolic processes rather than a single regulatory mechanism. This is the first study to examine the temporal dynamics of bacterioplankton and its function in Billings Reservoir during the winter, spring, and summer seasons. The study provides comprehensive reference information on the effects of an artificial habitat on the bacterioplankton community that can be used to interpret the results of studies to evaluate and set appropriate treatment targets. [ABSTRACT FROM AUTHOR]

Insecticides are widely used for pest control and frequently reach aquatic systems, imposing a risk to the biota. In this work, the effect of environmental concentrations of bifenthrin on the grazing capacity of Simocephalus vetulus (Cladocera) and Argyrodiaptomus falcifer (Copepoda) on phytoplankton was evaluated. Fifteen microcrustacean individuals and a natural phytoplankton assemblage dominated by Cyanobacteria were exposed during 46 h to three concentrations of bifenthrin (C0 0 μg L−1, C1 0.02 μg L−1, and C2 0.05 μg L−1). A significant decrease in both microcrustaceans grazing rates on total phytoplankton was observed in C2 compared to C0 and C1. The filtration rate (ml ind−1 h−1) of S. vetulus decreased significantly for the cyanobacteria Anabaenopsis arnoldii, Dolichospermum circinale, and Glaucospira sp. in C2 compared to C0 and C1. The ingestion rate (org ind−1 h−1) of A. falcifer decreased significantly in C1 and C2 compared to C0 only for A. arnoldii. Regarding phytoplankton morphological groups, the filtration rate of S. vetulus decreased in C1 and C2 compared to C0 for Colonies and Coenobiums in C2 concerning C0 and C1 for Filaments and in C2 compared to C0 for Silicified. For A. falcifer, the ingestion rate was reduced in C2 compared to C0 for Silicified, Flagellated, and Sessile. The results showed that bifenthrin affected both microcrustaceans grazing capacity on phytoplankton, especially at the highest insecticide concentration. [ABSTRACT FROM AUTHOR]

Daphnia (Ctenodaphnia) magna, a species widely used for ecotoxicological tests, was recorded for the first time in waterbodies of the Mexican protected area and RAMSAR site Ciénegas del Lerma. The identity of the species was confirmed using morphological traits and cytochrome oxidase I as a molecular marker. Haplotypes were 100% identical to cultures used in laboratory bioassays in México and Canada. Individuals analyzed are related to strains from Europe, and their sequences differed from natural populations reported from the United States of America and Canada. This Mexican wetland supports a rich community of migratory waterfowl; therefore, D. magna could quickly spread to other waterbodies and cause potential adverse effects on local Daphnia species. The utilization of non-native species in ecotoxicological tests must be undertaken with great care, to ensure escape to natural waters is prevented. [ABSTRACT FROM AUTHOR]