Hydrobiologia

The decline in fishery yields in Japan's enclosed coastal seas has been accompanied by a reduction in phytoplankton biomass, suggesting a widespread decrease in ecosystem productivity. Oligotrophication in Mikawa Bay has caused substantial declines in phytoplankton biomass and Manila clam (Ruditapes philippinarum) production. To assess whether external nutrient enhancement could stimulate phytoplankton growth, a controlled demonstration experiment using treated effluent from two sewage treatment plants (WWTPs) was conducted (spanning fiscal years 2022 to 2024) based on analysis using a three-dimensional non-hydrostatic model. Although effluent DIP and nitrogen concentrations were increased, model results showed that WWTP-derived nutrients represent only a minor portion of the total nutrient budget. Field observations revealed limited increases in surface water phosphorus, strong seasonal variability, and only temporary rises in chlorophyll-a and clam harvests. Monthly TP data demonstrated that seasonal DIP pulses, especially spring phosphorus bursts, dominate nutrient dynamics and overshadow external loading effects. Laboratory experiments further showed that phosphate is efficiently fixed by Fe(III) under oxidizing conditions and rapidly released during reductive dissolution of [FeOOH-HPO4]2- complexes, confirming iron as the principal regulator of internal P cycling. Because current numerical models omit iron-driven internal cycling, they cannot accurately predict bioavailable P or ecosystem responses. Overall, the study indicates that localized nutrient enhancement is insufficient to counter long-term oligotrophication, and effective management must integrate nitrogen limitation, internal Fe and P cycling, oceanic exchange, and seasonal variability in Ise and Mikawa Bays.

Boreal forested streams receive substantial inputs of terrestrial carbon (C) from riparian vegetation in the form of leaf litter, which is processed by litter-associated microorganisms. In addition to these leaf-litter C inputs, boreal streams also receive significant concentrations of dissolved organic carbon (DOC), which may represent an alternative major resource pool for litter-associated microorganisms. As leaf litter quality decreases over the process of decomposition, DOC may increasingly become a more suitable C source for the microbial communities. We investigated how DOC availability, litter type, and microbial succession influenced respiration and decomposition. Alder, birch, and spruce litter were incubated for 65 days in 12 outdoor experimental channels supplied with natural boreal stream water. Higher time-adjusted DOC concentrations were associated with higher respiration and lower relative mass remaining, whereas DOC flux received less support. Respiration and mass loss followed litter-specific trajectories, with birch showing a respiration peak that was not matched by proportional mass loss. Prokaryotic and eukaryotic communities differed among litter types and changed through time but explained process variation only for specific litter types and responses. Our results suggest that DOC can sustain litter-associated microbial activity and partly decouple respiration from litter decomposition, thereby affecting boreal stream C processing.

Introduction: Despite decades of investment, stream restoration often fails to recover diverse benthic macroinvertebrate communities, as restored reaches tend to remain dominated by pollution-tolerant taxa. This shortfall in recovery is commonly attributed to either poor habitat quality or dispersal limitation of aquatic macroinvertebrate taxa, yet these hypotheses are rarely tested directly. Objectives: We conducted a manipulative field experiment in the eastern Piedmont region (Maryland, USA) within the Chesapeake Bay Watershed to evaluate whether restored streams can support pollution-sensitive taxa when dispersal barriers are removed. Methods: We translocated whole macroinvertebrate communities from three nearby reference streams into three restored streams using standardized habitat substrates and quantified macroinvertebrate survival after 28 days. We also assessed how effective leaf vs rock substrates were for accumulating diverse and abundant macroinvertebrate communities for translocation. Results: Across all sites, 77% of translocated individuals and 16 of 22 taxa sensitive and moderately sensitive to pollution persisted under restored stream conditions, demonstrating that restored reaches can support short-term survival of pollution-sensitive taxa that typically fail to recover. Substrate comparisons revealed that leaf packs accumulated higher macroinvertebrate abundances, whereas both substrates accumulated macroinvertebrate communities with similar taxa richness, EPT richness, and Shannon Diversity. Conclusions: This work suggests that dispersal limitation, rather than unsuitable habitat, may be an underappreciated constraint limiting macroinvertebrate recovery in restored streams. These findings challenge the assumption that habitat restoration alone is sufficient for biological recovery and highlight the potential for whole-community translocations to accelerate recovery and ecological uplift as part of stream restoration practices. Implication for Practice: Our study highlights the need to consider habitat connectivity and dispersal pathways during stream restoration designs. Restoring streams to meet habitat requirements of pollution-sensitive macroinvertebrate taxa may not be sufficient for their populations to recover if these taxa are unable to reach the restored stream. In scenarios where restoring connectivity to source populations is infeasible, whole community translocations may offer a novel restoration tool to overcome dispersal barriers and accelerate biological recovery in restored streams.

Diverse life history strategies allow species to spread risk across a mosaic of habitat conditions. In Chinook Salmon (Oncorhynchus tshawytscha), particularly in the Central Valley of California, this is expressed through varied adult run timings and juvenile outmigration strategies. Anthropogenic impacts, particularly dams, disrupt these fundamental life stage transitions, often forcing managed populations to adapt to homogenized, less stochastic hydrologic regimes. This is exemplified in the Sacramento River, where the conservation of endangered Sacramento River winter run Chinook salmon requires balancing complex water operations with the ecological needs of a population confined to a short stretch of suitable habitat downstream of Shasta Reservoir. Using a 23 year dataset (2002 to 2024), we evaluated the combined effects of flow, temperature, and spawner abundance on juvenile production and life history expression in this habitat. We found that flow and spawner abundance best predicted juvenile abundance at Red Bluff Diversion Dam while temperature had considerably less support. The proportion of juveniles migrating as smolts exhibited significant density dependence that was negatively correlated to both female spawner abundance and peak flows. These results suggest focusing on temperature management alone may be insufficient. Effective management strategies should consider flow variability and habitat restoration to facilitate varying migration strategies and expand upstream rearing capacity. By addressing these physical and hydrologic constraints, managers can better support the full suite of life history strategies necessary for the resilience of winter run Chinook salmon.

Okanagan sockeye salmon have shown a strong recovery over the past three decades, but the contribution of environmental conditions and management actions to this recovery has not been determined. We developed a hierarchical Bayesian model linking spawner abundances to fry emergence observations to evaluate how flow and water temperature during adult upstream migration and incubation periods influence spawner-to-fry production. Production declined by 62% in years with earlier onset and longer duration of periods when warm river temperatures created barriers to adult migration, indicating that migration conditions can have carry-over effects on reproductive success even when spawners successfully reach the spawning grounds. Additionally, production was 46% lower when flows fell above or below the management target range designed to minimize scour and desiccation during egg incubation. In contrast, we found little support for effects of pre-spawning flows or incubation temperature on production. These findings provide quantitative evidence that current flow management is increasing freshwater spawner-to-fry production and has likely contributed to the Okanagan sockeye recovery. Effective flow management may therefore help offset climate-driven impacts that increasingly threaten this population.

Bottom trawling is the most widespread human disturbance on the seafloor, known to affect seabed structure and benthic biota. Yet, its impact on benthic communities remains documented mainly for taxa identifiable through morphology, leaving microscopic benthic communities largely overlooked. The Gulf of Lion continental shelf has been trawled for decades by French and Spanish fleets, to the point that encountering untrawled reference areas became elusive. Here, we examined prokaryote, protist and Animalia benthic communities at eight stations, using eDNA metabarcoding of core sediment samples, with five primer-pairs. Benthic communities were cross-referenced with contrasted trawling impacts, integrated across three periods: over one month, three years or ten years preceding the sampling. The community composition was primarily structured by ecological habitats, yet, trawling pressure showed association with prokaryotes and Animalia diversity. Diversity was higher at sites trawled more intensively in the preceding month, whereas long-term trawling was associated with a significant erosion of Animalia alpha diversity. Unexpectedly, communities did not display consistent vertical structure and the relative contributions of trawling and hydrodynamic reworking remain unresolved due to the absence of untrawled sites. Overall, our results show that trawling effects extend to prokaryotic compartments rarely considered in impact assessments, providing a proof of concept for eDNA-based assessment, and underline a pervasive long-term effect on Animalia communities. This study also highlights the importance of the timescale used to quantify fishing pressure and underscores the complexity of impact assessment when monitoring begins too late to establish a clear baseline, particularly when no reference site remains.

Heavy metal contamination of aquatic environments poses persistent risks to ecosystems and human health. Aquatic macrophytes such as Pistia stratiotes are increasingly used for phytoremediation due to their capacity to accumulate contaminants without displaying symptoms of abiotic stress. However, the molecular mechanisms underlying their metal tolerance remain poorly understood. Metallothioneins (MTs) are cysteine-rich proteins involved in metal binding and detoxification in plants. In this study, genome-wide analysis was performed to identify and characterise candidate MT genes in P. stratiotes and to assess their transcriptional response to copper exposure. Six novel MT genes (PsMT2f, PsMT3a-d, and PsMT4) were identified and classified into MT2, MT3, and MT4 subfamilies based on conserved cysteine motifs and domain architecture. Quantitative real-time PCR showed differential and tissue-specific expression of MT genes in roots and leaves following exposure to copper for up to 4 h. These findings provide the first comprehensive characterisation of the MT gene family in P. stratiotes and demonstrate their potential role in copper tolerance, supporting the application of this species in the phytoremediation of metal-contaminated aquatic systems.

This paper presents a comparative analysis of the floristic composition and site characteristics of four peat bogs in Bucovina, Romania: Poiana Stampei, Romanesti, Saru Dornei, and Gaina-Lucina. The research was based on phytosociological releves on 25 msq plots and direct field phenological observations, on six field visits from May to August 2026. Vegetation was characterised using the Braun Blanquet method, and floristic similarity between sites was assessed with the Sorensen and Bray Curtis indices. All four plots shared a common core of taxa characteristic of peatland vegetation: Sphagnum spp., Carex rostrata, Drosera rotundifolia, Eriophorum vaginatum, and Vaccinium species. Species richness was 13 taxa at Poiana Stampei, Romanesti, and Saru Dornei, and 12 at Gaina-Lucina. Romanesti and Saru Dornei showed the highest floristic similarity (descriptive values, not statistically tested, given a single releve per site), while Gaina-Lucina differed most markedly, not through species richness, which was similar across sites, but through species identity and through the presence of Betula nana, a glacial relict absent from the other sites. The results provide a descriptive basis for future research on the floristic composition and conservation of these habitats.

Hydropower development has emerged as a major driver of global environmental change, causing significant ecological damage to freshwater ecosystems and threatening aquatic biodiversity. However, the impact of cascade dams on fish communities in large river systems remains poorly understood, particularly in biodiversity hotspots such as China. Here, we used environmental DNA (eDNA) metabarcoding to assess the spatiotemporal patterns of fish diversity and community structure in the Ganjiang River, the largest tributary of the Yangtze River, in relation to cascade hydropower development. We collected water samples from 19 sites along the main stem and major tributaries in both wet and dry seasons, and analyzed the eDNA data using high-throughput sequencing and advanced bioinformatics pipelines. Our results revealed significant seasonal and spatial variations in fish diversity and community composition, with lower species richness and distinct assemblages in the impounded sections upstream of the dams compared to the downstream reaches. The fish communities were strongly influenced by environmental factors such as water temperature, pH, dissolved oxygen, and nutrients, which exhibited complex interactions with dam operation and land use practices. Spatial scale analyses further indicated that the impact of dams on fish diversity was most pronounced at the local scale, but also detectable at the regional scale. Our findings provide novel insights into the ecological consequences of cascade hydro-power development on fish communities and highlight the importance of considering spatial scales and environmental heterogeneity in assessing the impacts of human activities on freshwater biodiversity. Our study demonstrates the power of eDNA metabarcoding as a cost-effective and non-invasive tool for biodiversity assessment and conservation planning in large river systems facing multiple stressors and knowledge gaps.

The identification and use of stress-tolerant coral in outplanting efforts has been proposed as a method of restoring and bolstering reef health under increasing environmental change. Prior research has focused on understanding survival in cross-reef transplantation, but evidence of long term resiliency of outplanted corals remains limited. Here, we report data at a five-year timepoint of a reciprocal transplant study of the stress-tolerant Caribbean corals Pseudodiploria strigosa and Siderastrea siderea between a nearshore and offshore site in Belize. Extreme marine heat wave conditions in August of 2024 revealed species and site-specific bleaching patterns. Through assessments of mortality, energy reserves, and chlorophyll concentrations, P. strigosa appear to be more limited in long-term acclimatization potential to the nearshore environment while S. siderea maintain acclimatization capacity displayed 17 months post transplant to nearshore. This work conveys information relevant to managers in selecting species for restoration efforts based on short-term growth and long-term resilience in native versus non-native sites, offers insight into potential mechanisms driving these trends, and takeaways on site specific management decisions for successful coral outplanting success.

This study assesses the spatial dynamics of heavy metals and associated trace elements in the water and sediment of the Slana River approximately one and half year after an environmental accident and river contamination caused by mining effluent. Using PCA and standardized environmental indices (CF, PLI), we modelled the distribution of contaminants across the macro-gradient of the river and within the micro-gradient surrounding the source of pollution. We found that although the situation in the water column has improved and stabilized, the sediment remains the primary reservoir of trace elements, including toxic arsenic, with the highest concentrations recorded near the source and in its immediate vicinity. Although the concentration of primary mining indicators decreases relatively rapidly along the stream, this is systematically offset by the accumulation of other elements, including sulphur and aluminium. As a result of these geochemical processes, the total pollution load index (PLI) remains statistically unchanged along the entire stream, but indicates a chronic, spatially uniform (PLI = 1.06-1.16) toxicological burden on the ecosystem.

Zoos and public aquariums serve as essential hubs for wildlife conservation, public education, and scientific research; however, the success of these missions depends upon maintaining high animal welfare standards despite constant human presence. A primary concern is the 'visitor effect': the alteration of animal behavior due to human presence. While this phenomenon is well-documented in captive mammals and has been explored in chondrichthyes, it remains largely unexamined in teleost fish, despite evidence of their sensitivity to human stimuli in natural environments. This study addresses this knowledge gap by investigating the behavioral responses of 13 teleost species to varying levels of crowd density, direct human solicitation, and ambient noise. Our multivariate analysis reveals that visitor density and visitor-induced disturbances are significant drivers of behavioral change, with species identity acting as the primary source of variance. We observed high inter-taxonomic variability: while several species (including Euxiphipops sextriatus, Dascyllus aruanus, and Zebrasoma flavescens) showed marked sensitivity through significant alterations in stress-coping, exploration, and aggression, others remained behaviorally stable. Furthermore, acoustic analysis indicates a complex soundscape where visitor density correlates with increased sound amplitude, particularly in the 100 Hz to 400 Hz range, a critical band for teleost hearing suggesting that visitor-induced noise is distinct from the aquarium's technical background noise. These findings underscore that the 'visitor effect' is not a uniform phenomenon but a complex interaction shaped by species-specific sensitivity and distinct anthropogenic stressors. Our results highlight the necessity of incorporating species-specific behavioral data and acoustic monitoring into welfare management protocols to better mitigate the impact of human presence on captive fish populations.

Riverine and riparian food webs are connected via 'allochthonous' resource flows from neighboring ecosystems. These resources, such as terrestrial leaf litter, contribute to benthic macroinvertebrate diets, supporting higher trophic levels. While allochthony occurs in streams globally, its sensitivity to broad environmental gradients remains poorly understood. We explored the drivers of allochthony across six river basins within the contiguous United States, including climate, stream size, and flow permanence. We used Bayesian mixing models to estimate macroinvertebrate dietary proportions in four functional feeding groups. Air temperature best predicted allochthony, with consumers relying less on allochthonous resources with increasing temperature. Our models indicate that macroinvertebrate diets become primarily autochthonous at approximately 15{degrees}C mean annual air temperature, with leaf litter-consuming shredders showing a slightly higher threshold for this shift. We also found increased allochthony in smaller, non-perennial streams. These findings highlight the complexity of stream allochthony and responses to multi-scale environmental factors.

Aim To investigate how repeated historical connections between continental islands and the mainland have shaped the phylogeographic structure and genetic diversity of populations, using the widespread water strider Aquarius paludum as a model. Location Japan Taxon Water strider Aquarius paludum (Insecta: Hemiptera: Gerridae) Methods We analysed mitochondrial (COI and COII) and nuclear (ITS1) DNA sequences from populations across the Japanese archipelago and the Eurasian continent. Phylogenetic and population genetic analyses were used to reconstruct phylogeographic structure and infer demographic history. Results Western Japanese populations exhibited nucleotide diversity comparable to that of continental populations despite their insular distribution. Bayesian phylogenetic analyses identified two major mitochondrial haplogroups (A and B) that frequently co-occurred across the Japanese archipelago. Haplogroup A, which is rare on the Eurasian continent, occurred at high frequency in Japan and showed pronounced isolation by distance, whereas haplogroup B showed only weak but significant isolation by distance and was significantly more frequent in populations closer to the coast. These contrasting spatial patterns within species indicate distinct demographic histories for the two mitochondrial lineages. Main conclusion Repeated colonization from the Eurasian continent and the long-term coexistence of mitochondrial lineages with different demographic histories have shaped the pattern of genetic diversity of A. paludum in the Japanese archipelago. Our findings exemplify how continental islands can accumulate genetic diversity through lineage accumulation and secondary contact, which produces an intraspecific phylogeographic pattern comparable to those observed during an early phase of the taxon cycle between species.

The Peruvian anchovy (Engraulis ringens) is a small pelagic fish. It is the largest singlespecies fishery in the world and it is used mainly for the production of fishmeal and fish oil. The Peruvian hake (Merluccius gayi) is a predatory demersal fish that is valued for direct human consumption, mainly as frozen products. In this study, I compared the response of both species to certain fishing mortality scenarios using a climatological set-up of the multispecies model OSMOSE for the northern Humboldt Current System. I observed that hake landings benefit from a decreased fishing pressure. In addition, the resilience of the anchovy fishery may increase if a higher threshold for their minimum catch size was implemented. The results of this study provide insights into better management strategies that could be beneficial for the two species based on their life-strategies.

Sperm competition can occur when sperm from two or more males compete for fertilization of a batch of eggs. While it has been extensively studied in internal fertilizers, it remains poorly under-stood in external fertilizers. To investigate how sperm competition affects fertilization under sperm limitation, we conducted controlled experiments on two sea urchin species: Paracentrotus lividus and Dendraster excentricus. Eggs from a single female were exposed to sperm from three individ-ual males separately (non-competitive treatment) or to a pooled sample from three males (competi-tive treatment). We measured fertilization success as proportion of eggs fertilized after two hours and assessed sperm motility as percentage of motile sperm and curvilinear velocity. For P. lividus , we estimated the sperm concentrations where fertilization success was 50% of maximum observed fertilization success (F50), and the fertilization efficiency of the sperm (Fe), i.e. the likelihood that a sperm - egg encounter results in a fertilizing contact, using the fertilization kinetics model of Styan (1998). For D. excentricus, fertilization success was measured at a sperm concentration expected to produce 50% fertilization success. Sperm competition reduced fertilization success and increased F50 compared to non-competitive treatments, suggesting antagonistic effects that may compromise fertilization under sperm-limited conditions in external fertilizers.

The most studied symbiosis between land vertebrates and algae, is the one between Ambystoma maculatum and Oophila amblystomatis, where the latter colonizes the amphibian''s eggs. Although clear benefit given by algal growth for the salamander embryo has been observed, mutualism is not widely accepted. Mutualistic hypotheses posit benefits from the host to the algae which include protection, N- and C-sources, but no experimental evidence has been obtained. In fact, recent studies suggest that the algae are stressed during this relationship and propose fermentation rather than photosynthesis as main driver for algal growth. In this work, we analyzed embryonic host developmental rate, algal and embryo growth and photosynthetic function of eggs housed at different light intensities. We provide evidence that photosynthetic growth is the main driver for Oophila and that higher algal growth yields faster developmental rate and embryo size. Also, we provide strong evidence that rates of photosynthetic electron transport (and the concomitant O2 evolution) must be higher than those of consumption by the embryo for this symbiosis to be mutualistic. Since photosynthetic rate is dependent on light, this work illustrates the importance of light intensity in this symbiotic relationship.

Animal movements can transport materials across ecosystem boundaries, while simultaneously modifying habitats through physical engineering. We integrated GPS telemetry, camera trapping, sediment measurements and physicochemical sampling of ponds on Santa Cruz Island, Galapagos, to evaluate how giant tortoises connect and shape terrestrial and freshwater ecosystems. Telemetry revealed 2,254 visits by 21 tortoises to 12 ponds, with visits lasting up to 21.38 h and showing strong seasonal and diel variation, while camera traps showed peak pond use in January and during early morning and late afternoon. Greater tortoise abundance was associated with higher ammonium, dissolved organic carbon and total phosphorus concentrations, while ponds with persistently greater tortoise abundance had higher total suspended solids. Departing tortoises carried a mean 505.9 g of sediment, yielding a conservative potential export of 8.20 kg per tortoise per year and tens of tonnes annually. These findings identify giant tortoises as mobile zoogeochemical engineers linking terrestrial and freshwater ecosystems through physical and biogeochemical pathways.

Extensive green roofs are an important component of urban green infrastructure. However, harsh rooftop conditions, including shallow substrates, high temperatures and limited water availability, considerably restrict plant selection. Although extensive green roofs are traditionally dominated by succulent species, increasing attention has been directed towards annual plants because of their rapid establishment, developmental plasticity and potential contribution to vegetation diversity. This review aimed to identify annual plant species introduced on extensive green roofs and to characterize the functional traits most frequently associated with their establishment under rooftop conditions. In addition, the review examined the geographical distribution and methodological characteristics of existing studies and identified species with potential for application under temperate climatic conditions. A total of 22 studies published between 2015 and 2025 were analyzed, comprising 100 annual species representing 29 plant families. The reviewed studies showed a clear geographical bias towards Mediterranean and arid regions, whereas temperate climates were considerably underrepresented. Among species occurring in Central Europe, ruderal life strategies, drought avoidance, efficient dispersal mechanisms, low plant height and prolonged flowering were the most frequently observed functional characteristics, while seed mass and specific leaf area (SLA) exhibited substantial interspecific variation. These findings suggest that functional traits, rather than taxonomic affiliation alone, provide a useful framework for selecting annual species for extensive green roofs. The review also highlights the need for long-term studies conducted under temperate climatic conditions to improve evidence-based plant selection and support the development of resilient and multifunctional green roof vegetation.

Hormesis is an important consideration in chemical risk assessment across most aquatic environments. Evidence suggests that hormetic responses are shaped by organismal physiological processes. Accordingly, predictions of hormesis under environmentally realistic conditions should account for physiological traits. Yet the role of these traits remains largely unexplored. This study investigated how baseline growth rate modulates antibiotic responses in the harmful cyanobacterium Microcystis and the underlying mechanisms. Results showed that at an antibiotic concentration of 200 ng L-1 (representing environmental concentration levels), slow-growing Microcystis populations exhibited an obvious growth enhancement more than 4-fold greater than that of fast-growing populations, and this enhancement was positively correlated with cellular reserves. A baseline growth rate below 0.19 day-1 emerged as the threshold below which hormetic responses were consistently observed. This study provides pioneering insights into how organisms' physiological states influence pollutant-induced hormetic responses in aquatic environments. Our findings point to a central principle for extrapolation that laboratory-derived toxicological responses may not translate directly to the field unless key physiological traits of the organisms are explicitly considered. In this regard, baseline growth rate and energy reserves may be key physiological traits for reliably predicting toxic effects at the population level. This study also makes an initial attempt to conceptualize a physiology-anchored framework for strengthening risk assessment of low-level emerging contaminants.