Reservoirs in semi-arid regions are increasingly exposed to eutrophication driven by nutrient enrichment, hydrological alteration and climate variability. In Algeria, water-quality monitoring still relies mainly on physicochemical parameters, whereas biological indicators remain underused. This study evaluates the usefulness of plankton-based indices for assessing trophic state in two connected but also contrasting reservoirs in northwestern Algeria: Cheliff, a shallow diversion reservoir, and Kerrada, a deeper storage reservoir. Water samples were collected monthly from November 2020 to October 2022. The trophic state of reservoirs was compared with different phytoplankton and zooplankton-based metrics. Cheliff was classified as a reservoir with a higher trophy of water (eutrophic to hypereutrophic). In contrast, Kerrada reservoir, which receives water from Cheliff, was classified as a reservoir with lower trophy (mesotrophic). Multivariate analysis indicated that nutrient enrichment, turbidity and particulate matter structured Cheliff plankton communities, while depth and water transparency were the main drivers in Kerrada. Phytoplankton indices reflected the trophic contrast while zooplankton-based metrics showed variable performance due to regional environmental influences such as temperature and predation. Our findings demonstrate the potential of plankton-based metrics to provide complementary information on trophic conditions in contrasting reservoirs. However, differences in absolute trophic-state classification highlight the need for regional calibration of zooplankton-based indices before their application in routine monitoring of semi-arid reservoirs. Nevertheless, this study provides a baseline for Algerian reservoirs.
Microzooplankton (MZP; 20–200 µm), comprising predominantly heterotrophic and mixotrophic plankton, constitute a key component of the microbial food web, linking the microbial loop with the classical food chain. The present study investigated a comparative assessment of spatial variability in MZP abundance, composition and carbon biomass in the coastal waters off Port Blair (PB) and Neil Island (NI), separated by 34 km in the Andaman Sea, during the fall intermonsoon (October 2024). Marked spatial differences in hydrographic and hydrochemical conditions between the two study domains were reflected in their biological characteristics, particularly phytoplankton biomass (chlorophyll a) and MZP communities, specifically protozoans. The relatively mesotrophic waters off PB, characterized by higher nitrate concentrations (mean 0.87 ± 1.3 µM) and chlorophyll a (mean 1.17 ± 0.77 mg m−3), supported higher MZP abundance, biovolume, and carbon biomass than the oligotrophic waters surrounding NI. Protozoans dominated the MZP assemblages in both regions, although their community composition differed substantially. Dinoflagellates dominated the MZP community at PB (98.8
Inputs of metals and metalloids to freshwater ecosystems are highly variable, and their speciation can shift rapidly; therefore, snapshot water samples often fail to represent long-term exposure. Aquatic bryophytes can integrate metal(loid) exposure through surface binding, ion exchange, and tissue accumulation, generating time-integrated biological signals that support source apportionment, spatial comparisons, and monitoring-based assessment. Following the PRISMA framework, we combined a systematic review with bibliometric analysis to build an evidence base using the Web of Science Core Collection and citation chasing. We synthesized relevant studies from the past decade and assessed research output, thematic structure, and methodological characteristics. The literature is largely concentrated in Europe, with study settings dominated by running-water systems and controlled exposure designs. Both the bryophyte taxa used and the target elements are focused on a limited set of commonly adopted groups and frequently investigated elements. Monitoring signals are primarily reported as tissue concentrations and enrichment-related indices, while the proportion of studies addressing physiological and biochemical responses and removal-performance evaluation has increased in recent years. Cross-study comparability is mainly constrained by differences in pretreatment and particulate-matter control, sample preservation and exposure duration, and the completeness of background water-chemistry reporting. On this basis, we clarify the roles of aquatic bryophytes in freshwater metal(loid) monitoring and in verifying the effectiveness of mitigation or remediation actions, highlight that between-study heterogeneity is closely linked to inconsistent methodological reporting and contextual information, and provide a foundation for future evidence synthesis across broader habitats and within cross-compartment comparison frameworks.
Procambarus clarkii is a prominent example of a successful invasive species, and its locomotion ability is known to be a key characteristic. As such, the goal of this study is to deepen the knowledge of P. clarkii locomotion capabilities. To achieve this, two laboratory experiments were conducted to address the crayfish’ locomotion, namely their speed, under controlled conditions. The first experiment tested the effect of the interaction of temperatures (16 °C and 22 °C), food (presence or absence) and photoperiod (light or dark). The second experiment tested the effects of pairing two individuals of the same or opposite sex and of different or similar sizes. Results show that when exposed to the higher temperature and in the absence of food, crayfish increased their speed. The smallest crayfish have the lowest mean velocity values, increasing up to individuals with cephalothorax lengths between 25 and 30 mm, after which speeds remained comparable with no significant differences. When paired, size differences between crayfish does not affect velocity. Sex also did not affect velocity, neither when alone nor when paired. These results suggest that P. clarkii rate of spread may be greater in areas at 22 °C. However, if provided with a reliable food source, crayfish may disperse less. Still, more research is needed to expand our understanding of which factors could contribute to P. clarkii dispersive capabilities, as this may prove important in formulating new plans and strategies to limit its impacts.
Parasitoid communities associated with summer dinoflagellate blooms in the north-western Mediterranean showed temporal partitioning, taxon-specific dynamics and contrasting associations with the water column and sediments. Several zoosporic parasitoid lineages co-occurred, including perkinsids, chytrids and Syndiniales such as Amoebophrya and Euduboscquella-like taxa. Members of the Amoebophrya complex (Dino-Group-II clades 2 and 4) had the highest relative sequence abundances in the water column, and their increases coincided with peaks or declines in dominant host populations, a pattern consistent with density-responsive infection dynamics. Perkinsids also exhibited patterns consistent with density-responsive dynamics, with peaks near declines in host abundance; they were detected in both the water column and sediments. Chytrids occurred sporadically, with low infection prevalence in the water column and only occasional detection in sediments. These contrasting patterns were consistent with temporal differentiation among host–parasitoid interactions associated with differences in host tracking, infection timing and habitat use. Overall, infection prevalence remained low and parasitoid peaks were not consistently associated with bloom termination, although persistent, low-intensity infections may have influenced competitive interactions among hosts and species coexistence. Differences in temporal occurrence and compartment associations may facilitate coexistence among parasitoid lineages. Sediments may act as reservoirs, particularly for perkinsids, suggesting that benthic–pelagic coupling contributes to the structure of marine parasitoid communities.
Freshwater microalgae are key components of aquatic ecosystems, but their dispersal mechanisms remain poorly understood. Animal-mediated dispersal of microalgae has been documented for birds, mammals, and invertebrates, yet the role of amphibians in microalgal transport under natural conditions remains largely unknown. We conducted a field survey in coastal wetlands of the southern Brazilian Coastal Plain to investigate potential epizoochorous transport by eight anuran species across grassland and dune habitats. A total of 320 individuals were sampled, and microalgae adhered to 12.81
It is expected that the spatial distribution of ichthyofauna in reservoirs within mining areas will be affected by environmental changes imposed by damming and the progressive deposition of tailings. In this context, we evaluated variations in the taxonomic and functional diversity of fish communities at five locations within the Gelado tailings dam, formed by a dammed stream in the Brazilian Amazon region. Among these locations, two are additionally affected by the continuous deposition of iron tailings. We sampled fish (collected using standardized gill nets) and environmental data in 2006, 2007, 2008, 2009, and 2021. We used linear mixed-effects models (GLMM) and permutational analysis of variance to assess differences in alpha and beta diversity among the different locations, respectively. We used the longitudinal gradient and expedition years to control for potential spatial and temporal autocorrelation effects during the analyses. Our results revealed that species composition varied significantly only between areas with and without tailings, while taxonomic structure, functional structure, and functional composition showed no variations among the different locations. The longitudinal gradient was significant only for functional evenness. Differences in species composition were due to variations in the abundance and capture frequency of Leporinus friderici, primarily in the area with tailing. Consequently, effects related to tailings deposition, along with the longitudinal gradient, exert a greater influence on the spatial structure of communities than local environmental variations, such as the presence of specific microhabitats. In conclusion, the fish community exhibited low species richness when compared to the regional species pool, an expected effect of the 45-year-old damming, and displayed an altered spatial structure in areas with continued deposition of iron tailings.
Ultraviolet-B (UV-B) radiation, intensified by ozone depletion, is a major stressor for aquatic primary producers. Titanium dioxide nanoparticles (TiO2 NPs) are widely used in industrial and consumer products, leading to their increasing discharge into aquatic systems. These particles interact with cyanobacteria (e.g., Microcystis aeruginosa) and macrophytes (e.g. Lemna minor). This study examined the interactive effects of UV-B radiation (0.8 W/m2 and 2 W/m2) and TiO2 NPs (48 mg/L) on the physiological responses and allelopathic interactions between M. aeruginosa and L. minor. Our findings showed that low UV-B exposure significantly reduced chlorophyll a and total protein levels in M. aeruginosa, accompanied by increased microcystin, hydrogen peroxide (H2O2), and malondialdehyde (MDA) levels under UV-B exposure. High UV-B particularly upregulated peroxidase (POD) activity in M. aeruginosa. In L. minor, low UV-B enhanced chlorophyll a, whereas high and low UV-B and TiO2 exposure suppressed pigment and growth. Co-culturing M. aeruginosa with L. minor under low UV-B and TiO2 exposure further suppressed algal growth and reduced protein content. UV-B and TiO2 increased oxidative damage, reduced algal biomass and toxin production, and potentially disrupted allelopathic interactions. Exposure of L. minor to M. aeruginosa and high UV-B increased H2O2 levels and POD activity. Our results show that allelopathic interactions between L. minor and M. aeruginosa are highly sensitive to UV-B radiation and are further increased when TiO2 nanoparticles are present. Additionally, UV-B radiation and TiO2 nanoparticles exert synergistic physiological stress on M. aeruginosa and L. minor, potentially changing species interactions and reshaping community structure in freshwater ecosystems.
The alien species Chaetomorpha valida, first found in sea cucumber ponds in Liaoning and Shandong, has severely harmed China’s ecology, economy, and society. The periodic abundance of this alga greatly affects water quality and sometimes leads to the loss of aquaculture. Spore reproduction may be one of the main reasons for its rapid growth. Adaptability to the environment also determines its rapid adaptation and expansion of territory. However, the invasion potential remains poorly understood. We investigated reproductive characteristics in different lengths of fragments excised from C. valida, the detailed process and environmental adaptation conditions of spore reproduction and the variation of the enzyme activity of cells during sporangium formation. Results: shorter fragments boosted spore reproduction (more sporangia, spore release) but reduced vegetative reproduction; algal cell oxidation favored sporangium formation. Salinity 20–30 psu best promoted sporangium formation/release (salinity 40 psu inhibited both); high nitrogen enhanced sporangium production. Low water flow promoted spore release, high flow inhibited it and reduced spore attachment. Suitable fragment lengths and environments enabled massive spore production and new individual development, so spore-producing fragments drive C. valida’s biomass accumulation. Analyzing spore reproduction/germination helped predict its spread, aiding biological invasion control.
Anthropogenic microfibers are pervasive contaminants in aquatic ecosystems, yet their interactions with organisms are predominantly studied through ingestion. External adhesion represents a potentially important but overlooked pathway of anthropogenic microfiber transport. Here, we assessed the occurrence of putative anthropogenic microfibers adhering to the skin of adult anurans in coastal wetlands of southern Brazil, evaluating their potential role as external biological vectors. We sampled 165 individuals from nine species spanning aquatic, terrestrial, and arboreal ecological groups across four sites. Samples were processed using stereomicroscopy, and microfibers were identified based on morphological features and characterized by size and color. Differences in occurrence and load among ecological groups were evaluated using hurdle models. Microfibers were detected in 28.5
Tube-dwelling anemones of the subclass Ceriantharia are important components of benthic ecosystems, contributing to habitat complexity and supporting diverse biological interactions. Despite their ecological relevance, most species remain poorly studied due to sampling difficulties and the limited knowledge available regarding their ecology, biogeography, and dispersal. In this context, habitat suitability modeling provides a valuable framework for identifying environmentally suitable areas for understudied marine taxa. Here, we present the first broad-scale habitat suitability assessment for nine Atlantic Ceriantharia species using MaxEnt models. Model projections were interpreted as environmentally suitable areas sharing conditions with known occurrences rather than as estimates of realized or potential geographic distributions. All models showed satisfactory predictive performance (AUC ≥ 0.70; TSS ≥ 0.40). Bathymetry emerged as the dominant environmental predictor, followed by temperature and slope, indicating that broad-scale oceanographic gradients strongly influence habitat suitability. Three major centers of environmental suitability were consistently identified across the Atlantic basin, encompassing the western Atlantic, the eastern Atlantic, and high-latitude regions. Although several models recovered suitability patterns consistent with documented occurrences, others projected environmentally suitable areas beyond currently known records, highlighting the influence of limited knowledge regarding species dispersal, population connectivity, and historical biogeography. These results provide the first comprehensive overview of habitat suitability patterns for Atlantic Ceriantharia, identify priority regions for future sampling, and demonstrate the importance of integrating ecological, oceanographic, and life-history information to improve habitat suitability assessments for poorly known benthic marine invertebrates.
Microplastics (MPs) contamination was assessed in the water and surface sediment in the upstream, dam, and downstream zones of the Tapacurá Reservoir, a tropical public water supply system in northeastern Brazil, over the course of four sampling campaigns. MPs were detected in all samples, with abundances ranging from 13,880 to 27,780 MPs m−3 in the water and 10,940 to 50,760 MPs kg−1 in the sediment. Higher concentrations in the water occurred in the dam area, while accumulation in the sediment was greater downstream, reflecting contrasting transport and deposition dynamics along the longitudinal gradient. The composition of MPs differed significantly between compartments (PERMANOVA, p = 0.001), with fibers predominating in the water (73
Nutrient supply is an important determinant of N fixation rates in pelagic cyanobacteria. In shallow aquatic ecosystems, benthic primary producers can affect nutrient release from the sediment to the pelagic zone, yet the relationship between benthic primary producers and pelagic N fixation is not well understood. Here, we explore the effect of benthic primary producers on benthic nutrient fluxes and pelagic N fixation rates in shallow, eutrophic Lake Mývatn, Iceland. In paired benthic nutrient flux and pelagic N fixation assays, we showed that sites with increased benthic phosphate release were associated with increased pelagic N fixation. In turn, during assays of flux rates, benthic phosphate release was negatively associated with dissolved oxygen concentrations at the sediment–water interface, which was positively associated with benthic primary producer abundances. Together, these relationships suggest that benthic primary producers influence variation in within-lake pelagic N fixation via their effects on benthic nutrient flux rates.
This study assessed freshwater ecosystem health by integrating chemical, biological, and microbial indicators. We conducted an exploratory comparison of Loskop Dam and Nwanedi-Luphephe Dam, South Africa, using water quality parameters, fish Health Assessment Index (HAI) scores, parasite assemblages, and 16S rRNA gut microbiota profiling. Sampling occurred between March and May 2025. Selected water parameters were measured in situ, with nutrient and metal analyses conducted from 1 L water samples. Nineteen fish (Oreochromis mossambicus, n = 10; Clarias gariepinus, n = 9) were examined for parasites, and gut microbial communities and the HAI scores calculated. The microbial functional prediction potential was inferred using PICRUSt2. Loskop Dam showed elevated total dissolved solids (272.75 mg/L vs. 40 mg/L), conductivity (41.07 vs. 6.0 mS/m), and pH (7.69 vs. 7.14) values compared with Nwanedi-Luphephe Dam. Fish from Loskop Dam exhibited a higher mean HAI score (45.0 ± 25.50) than Nwanedi-Luphephe Dam (34.4 ± 14.24) and greater endoparasite loads, particularly Contracaecum spp., whereas fish from Nwanedi-Luphephe Dam harboured more ectoparasitic monogeneans. Gut microbiota was dominated by the phyla Fusobacteriota, Bacillota, Pseudomonadota and Planctomycetota, while classified genera were primarily represented by Cetobacterium, Romboutsia, Clostridium, Bacteroides and Sediminibacterium. In the final multivariable model, fish weight was the only significant predictor of HAI score (p = 0.03), whereas dam and fish species were not significant. PICRUSt2 identified ten metabolic pathways differing between dams, with nine core pathways enriched in Nwanedi-Luphephe Dam; PWY01479, PWY042, PWY-5747, PWY-5856, PWY-5857, PWY-5855, PWY-6708, UBISYN-PWY, and PWY-5920, while the nucleotide salvage pathway (PWY-6609) was enriched in Loskop Dam. Results reveal that Loskop Dam exhibits moderate anthropogenic impact, whereas Nwanedi-Luphephe Dam represents a relatively undisturbed ecosystem. Integrating water chemistry, fish health, parasite assemblages, and gut microbiota may offer a sensitive framework for monitoring freshwater ecosystem integrity and detecting early ecological disturbance.
The relative importance of environmental selection, dispersal, and demographic stochasticity in structuring aquatic communities remains poorly resolved, especially in human-impacted Neotropical regions. Using diatoms, we assessed how local environmental conditions, catchment land use, and spatial factors shape community richness and composition in subtropical streams, and whether responses differ among common, rare, and very rare species. Diatoms were sampled in 50 streams of the Ibicuí river basin (Pampa biome, Brazil). Species were identified and categorized as common, rare, or very rare based on abundance quartiles. We measured local variables, land use, and spatial predictors (PCNM). Richness was modeled by multiple linear regression, while composition was analyzed via pRDA and variation partitioning. Local environmental variables were primary predictors of species richness across all groups, with canopy openness as a key filter. Conversely, community composition showed a strong spatial signature for the total assemblage and common species, where PCNM accounted for most variation; land use effects were minimal. The composition of rare species was explained only by water velocity, while very rare species were structured exclusively by fine-scale spatial predictors. These results indicate that metacommunity structuring mechanisms for benthic diatoms in the studied streams depend on the evaluated attribute and species rarity. Environmental gradients govern richness in all groups, but spatial processes dominate compositional changes, especially for common and very rare taxa. Rare species are filtered by hydrodynamic conditions, whereas very rare species reflect spatial configuration more than the measured environmental gradients. This study integrates multi-scale predictors and explicitly separates species by rarity, clarifying metacommunity organization in subtropical grassland streams. Ultimately, our findings suggest that diatom species rarity should be considered for effective biomonitoring and biodiversity conservation strategies in subtropical grassland streams.
Zoosporic parasites represent a pervasive and structurally embedded biosecurity challenge in large-scale microalgae cultivation systems. These fungal and fungal-like organisms, characterised by motile zoospores, combine active host localisation, rapid intracellular development, and long-term persistence through resistant resting stages. Under the high-density, monoculture conditions typical of industrial production, such life-history traits facilitate rapid transmission, nonlinear outbreak dynamics, and recurrent culture collapse. Despite their demonstrated impact on productivity, economic performance, and operational continuity, zoosporic parasites remain insufficiently integrated into routine monitoring frameworks and risk management strategies, with control practices still largely reactive. This review synthesises current knowledge on the diversity, infection strategies, and life-cycle dynamics of zoosporic parasites affecting microalgae, and links these biological mechanisms to environmental and operational drivers, including irradiance, temperature, nutrient stoichiometry, and pH regulation. A central conclusion emerging from this synthesis is that infection controllability is fundamentally time-dependent. Preventive and containment measures are most effective during early infection stages, when parasite prevalence is low and before intracellular amplification and resting-stage formation dominate system dynamics. Once critical prevalence thresholds are exceeded, management options narrow substantially, shifting from containment to damage limitation through salvage harvesting, system shutdown, and restart. To address this constraint, we propose a layered, stage-aware diagnostic framework that aligns monitoring tools with their functional role in outbreak detection and response. System-level early-warning indicators provide continuous surveillance but limited specificity; microscopy enables rapid confirmation; flow cytometry supports quantitative assessment of infection prevalence; and molecular tools, including metabarcoding and digital PCR, offer high-resolution taxonomic identification. Emerging digital diagnostics and AI-assisted analytics further enable integration of multi-parametric sensor data and anomaly detection, creating opportunities for anticipatory, data-driven decision support. Evidence from the ParAqua Survey indicates that late detection and recurrent outbreaks remain common across research and industrial facilities, underscoring a persistent gap between mechanistic understanding and operational implementation. We argue that effective management of zoosporic infections requires an integrated framework combining biosecurity-oriented system design, early-warning diagnostics, quantitative modelling of host–parasite dynamics, and predefined response strategies. Shifting from reactive contamination control toward resilience-oriented, model-informed management is essential for achieving stable, scalable, and economically viable microalgae production under sustained biological pressure.
Chytrids (phylum Chytridiomycota) are zoosporic fungi that play key roles as parasites of aquatic microorganisms, yet they are understudied and genomic resources for algal-infecting chytrids remain scarce. Here, we present the first comparative genomic analysis of multiple isolates of a single chytrid species (order Rhizophydiales) infecting the cyanobacterium Planktothrix agardhii. Isolates were collected from Sandusky Bay, Lake Erie, across two bloom years (2018 and 2019). Using single cell sequencing and metagenomic assembly, we generated individual genomes averaging 15.36 ± 0.12 Mbp in size with 75
This study describes the community associated with the exogenous material covering the column of the sea anemone Aulactinia marplatensis, analyzes its composition and diversity, and compares it between two intertidal zones-Las Delicias and Punta Cantera- along the coast of Mar del Plata, Argentina. Over a two-year period, ten individuals of A. marplatensis were seasonally collected at each site; the seasons considered were summer, autumn, winter and spring. The exogenous covering was removed and the associated organisms were identified under a stereoscopic microscope. MDS, PERMANOVA and SIMPER analyses were used to assess differences in community composition, and a two-way ANOVA was applied to compare Simpson’s diversity index between sites and seasons. A total of 22 species were recorded, with syllid polychaetes, mytilids, amphipods and nemerteans as dominant groups. While overall diversity did not differ significantly between sites or seasons, species composition varied both spatially and seasonally. Spatial differences may be due to the higher organic enrichment and contamination exhibited by Las Delicias. Seasonal variations are consistent with previous studies conducted in the study sites and could respond to the reproductive cycles of the species. Our findings support the hypothesis that A. marplatensis functions as an autogenic ecosystem engineer by providing habitat and shelter for a diverse array of associated fauna, including juvenile stages, and highlight its potential role in facilitating habitat complexity within the intertidal zone.
The subclass Ceriantharia comprises tube-dwelling anemones that play important roles in energy flow and the structural organization of marine benthic ecosystems. Although ceriantharians function as habitat-forming organisms and support diverse associated fauna, current knowledge of the group remains fragmented and uneven. We conducted a mixed-methods literature review integrating bibliometric and systematic approaches to synthesize research trends, thematic focus, and knowledge gaps across 89 peer-reviewed studies on Ceriantharia retrieved from the Web of Science Core Collection and Scopus, spanning publications from 1900 to 2024. Our principal research questions were: (1) how has research output on Ceriantharia changed over time; (2) what thematic, geographic, taxonomic, and methodological biases characterize the existing literature; and (3) what environmental information is currently available to characterize the environmental niche of Ceriantharia. Our results reveal pronounced temporal, geographic, taxonomic, and methodological biases. Early research was largely descriptive and taxonomically oriented, whereas recent decades have been characterized by a marked expansion of molecular and phylogenetic studies. Research effort is concentrated in a limited number of ocean basins and taxa, particularly within the family Cerianthidae, while several marine regions and lineages remain poorly investigated. We also identified substantial Wallacean and Grinnellian shortfalls: only 18
Dissolved organic matter (DOM) comprises one of the most abundant forms of carbon in aquatic environments and plays a central role in the global carbon cycle. Phytoplankton is an important DOM source-however, a comprehensive understanding of how global warming impacts the quality, production and accumulation of phytoplankton-derived DOM (DOMp) is still a challenge. Here we subjected axenic cultures of the bloom-forming cyanobacterium Microcystis aeruginosa and the diatom Cyclotella sp. to warming assays (+ 4 °C), with and without acclimation. Samples at different growth stages were analyzed for dissolved organic carbon (DOC) concentration, cell counts by flow cytometry and DOM characterization by fluorescence spectroscopy. Short-term (non-acclimated) warming almost doubled DOC release rates in both species, but returned to baseline levels in M. aeruginosa cultures with long-term (acclimated) warming, while for Cyclotella sp. acclimated cultures these rates varied from baseline to increased values, probably reflecting the known negative effects of sustained temperature increase on many diatom species. Bioavailability proxies consistently increased with warming in M. aeruginosa exudates. In contrast, Cyclotella sp. showed a decline in bioavailability proxies with rising temperature. Coefficients of variation for fluorescent DOM in response to temperature and growth stage are similar, revealing that both factors may contribute equally for the observed shifts in DOMp. These findings indicate that warming can alter the quantity and composition of DOMp, a key resource with potential consequences for community structure and functioning under changing climate scenarios.
