Search

Metacommunity theory predicts that the relative importance of regional and local processes structuring communities will change over ecological succession. Determining effects of these processes on taxonomic and evolutionary diversity in spatially structured freshwater habitats of different successional stages may greatly improve understanding of the maintenance of diversity across temporal and spatial scales. In this study, we evaluated crayfish diversity at local and regional scales in pond metacommunities undergoing secondary succession from beaver (Castor canadensis) disturbance. Following theoretical predictions from metacommunity ecology of the increasing importance of local processes over succession, we hypothesised a decline in crayfish local and β diversity over succession from stronger local structuring as the older ponds may provide less suitable habitat than streams.Crayfish species and phylogenetic diversity were evaluated in beaver pond metacommunities and reference headwater streams located in three catchment regions. DNA sequences from the mitochondrial cytochrome oxidase I gene were used to assign crayfish to species for community and phylogenetic diversity tests. Local and β diversity were contrasted across beaver ponds ranging in age from 24 to 70 years and as a function of metacommunity processes.Counter to predictions, local species diversity among streams and the successional stages of ponds categorised by age class (24–39 years; 42–57 years; 60–70 years) did not differ, but community and phylogenetic convergence occurred in the oldest pond ecosystems. Crayfish community composition differed between the youngest and oldest ponds, resulting from higher abundance in the youngest ponds and community convergence in the oldest ponds. The association between community composition and the environment was strongest in streams and decoupled with pond age. In contrast, the correlation between intraspecific haplotype composition and the environment increased over succession. Among the three metacommunities, the regional crayfish species diversity arose from a combination of the temporal and environmental drivers from beaver‐constructed ecosystems and dispersal limitation within catchments.This study represents the first investigation of the taxonomic and phylogenetic diversity response to the successional stages of beaver pond metacommunities. The detection of differential crayfish composition and haplotype sorting to pond age suggests a role for local structuring and further indicates that future studies should acknowledge succession in shaping species diversity at local and regional scales. Dispersal limitation within catchment regions probably contributes to the evolution of crayfish species diversity in metacommunities and the overall maintenance of biodiversity.The results support a transition in community and freshwater ecology from a recent emphasis on spatial processes towards the integration of temporal drivers to better identify regulators of taxonomic and phylogenetic diversity across scales. [ABSTRACT FROM AUTHOR]

Identifying the most important factors affecting population growth in animal life cycles is an important tool of species conservation. Delta Smelt (Hypomesus transpacificus), an annual fish endemic to the San Francisco Estuary in California (USA), has been provided legal protection since 1993 but 30 years later exists in a conservation‐reliant state on the brink of extinction. Despite considerable controversies about what factors are most responsible for the species' decline, no population growth rate sensitivity comparisons between the most important factors regulating growth have been done. Nor has anyone attempted to quantitatively identify habitat conditions needed to support positive population growth. We developed a set of stage‐structured population models to link habitat indices regulating recruitment of new generations of fish as they metamorphosed into juveniles and the subsequent survival of those fish over several seasons until they reached adulthood. These models are used to quantify drivers of growth rate variation over 30 years. Several complimentary sensitivity analyses indicated freshwater outflow to the estuary during summer had the largest potential to change population growth. Multiple habitat metrics (e.g., food availability, temperature) influencing recruitment and life stage specific survival rates across different seasons interacted in nonlinear ways to determine habitat conditions and water management targets associated with positive population growth. We discuss the implications for freshwater management, Delta Smelt conservation, and the challenges climate change poses for co‐implementation of these two societal priorities. [ABSTRACT FROM AUTHOR]

The EU Nature Restoration Law represents an important opportunity for freshwater habitat restoration and, consequently, freshwater biodiversity protection. However, a number of challenges must be anticipated in its implementation, which may compromise its success. Some aspects, particularly those relating to freshwater ecosystems, require more clarification. We use riverine ecosystems to illustrate existing ambiguities in the proposed legislation and the potential consequences of leaving these aspects open to interpretation during the implementation process. We also discuss potential solutions to these problems which could help ensure that the law's objectives are met. We argue that river network structure and connectivity dimensions, which result into river meta‐ecosystems, must be explicitly considered. For that purpose, we ask for clear definitions of the critical terms "free‐flowing rivers," "barriers," and "reference areas." In addition, we recommend developing methods for integrated assessment of connectivity across river networks. As a key property of river ecosystems, this must be used to prioritize actions to increase the length and number of free‐flowing rivers. Adequate restoration planning at larger spatial scales will benefit from a meta‐ecosystem perspective and accurate representation of aquatic‐terrestrial linkages, which will significantly improve the efficacy of restoration efforts. Furthermore, stakeholder and citizen engagement offer important opportunities at local, national, and European scales, and should be fostered to ensure inclusive decision‐making. The conservation challenges outlined here are particularly important for rivers, but they also have implications for other ecosystems. These considerations are useful for policymakers, conservationists, and other stakeholders involved in the Nature Restoration Law and related policy initiatives. This article is categorized under:Water and Life > Stresses and Pressures on EcosystemsWater and Life > Conservation, Management, and AwarenessHuman Water > Water Governance [ABSTRACT FROM AUTHOR]

Aim: Biotic interchanges between Africa, India, and Eurasia are central to explaining the present‐day distribution and diversity of freshwater organisms across these landmasses. Synbranchiformes is a diverse and species‐rich clade of freshwater acanthomorph fishes found on all southern continents except Antarctica, and include eel‐ and perch‐like, air‐breathing and non‐air‐breathing fishes. Lacking a comprehensive and resolved phylogeny of the entire clade, contemporary interpretations of synbranchiform biogeography invoke scenarios as disparate as Gondwanan vicariance and pan‐global rafting to explain their modern‐day distribution. Here, we study their biogeographic history of continental dispersal events and test whether these are associated with increases in lineage diversification. Location: Asia, India, Africa freshwater habitats. Taxon: Synbranchiformes (gouramis, snakeheads, swamp eels, and relatives). Methods: We used nearly 1000 ultra‐conserved elements (UCEs) and Sanger‐sequenced genes to infer a phylogeny with representatives of all major synbranchiform lineages and nearly two‐thirds of its known species diversity. Incorporating fossil calibrations, we inferred a time‐calibrated phylogeny to which we apply Bayesian methods of ancestral area reconstruction and test for diversification rate shifts. Results: Analyses of UCE data provide a resolved phylogeny for major synbranchiform lineages. Divergence times support a most recent common ancestor of the entire clade approximately 79.2 million years ago. We infer significant increases in lineage diversification in both the spiny eels (Mastacembelidae) and the genus Betta (Osphronemidae). Main Conclusions: Our results reject the hypothesis of Gondwanan vicariance explaining synbranchiform biogeography. Instead, our analyses reconstruct a southeast Asian origin of the entire clade and independent dispersal events to other continents by snakeheads, anabantids, and spiny eels, with no signal of elevated lineage diversification occurring after these invasions. Higher lineage diversification rates in spiny eels pre‐date their arrival to Africa, while the high diversification rates observed in Betta were initiated prior to the flooding of insular Sundaland in southeast Asia. [ABSTRACT FROM AUTHOR]

In freshwater habitats, aerobic animals and microorganisms can react to oxygen deprivation by a series of behavioural and physiological changes, either as a direct consequence of hindered performance or as adaptive responses towards hypoxic conditions. Since oxygen availability can vary throughout the water column, different strategies exist to avoid hypoxia, including that of active 'flight' from low‐oxygen sites. Alternatively, some organisms may invest in slower movement, saving energy until conditions return to more favourable levels, which may be described as a 'sit‐and‐wait' strategy. Here, we aimed to determine which, if any, of these strategies could be used by the freshwater ciliate Tetrahymena thermophila when faced with decreasing levels of oxygen availability in the culture medium. We manipulated oxygen flux into clonal cultures of six strains (i.e. genotypes) and followed their growth kinetics for several weeks using automated image analysis, allowing to precisely quantify changes in density, morphology and movement patterns. Oxygen effects on demography and morphology were comparable across strains: reducing oxygen flux decreased the growth rate and maximal density of experimental cultures, while greatly expanding the duration of their stationary phase. Cells sampled during their exponential growth phase were larger and had a more elongated shape under hypoxic conditions, likely mirroring a shift in resource investment towards individual development rather than frequent divisions. In addition to these general patterns, we found evidence for intraspecific variability in movement responses to oxygen limitation. Some strains showed a reduction in swimming speed, potentially associated with a 'sit‐and‐wait' strategy; however, the frequent alteration of movement paths towards more linear trajectories also suggests the existence of an inducible 'flight response' in this species. Considering the inherent costs of turns associated with non‐linear movement, such a strategy may allow ciliates to escape suboptimal environments at a low energetic cost. [ABSTRACT FROM AUTHOR]

Water crickets of the subfamily Haloveliinae are semi‐aquatic bugs occurring in freshwater and marine habitats throughout the Indo‐Australian region, presently including six genera with more than 80 extant species. Whether lineage diversification in Haloveliinae is associated with the utilization of new ecological niches caused by transition events between freshwater and marine habitats remains poorly understood. We investigate the evolutionary history of Haloveliinae using large‐scale phylogenomic datasets and a set of novel redefined morphological characters based on 24 ingroup taxa representing all recognized genera. Our phylogenetic results based on the novel datasets definitively indicate that the freshwater genus Strongylovelia Esaki as currently defined is paraphyletic and supports the establishment of a new genus: Metavelia gen. nov., including three congeneric species: Metavelia patiooni comb. nov. (type species), Metavelia priori comb. nov. and Metavelia albicolli comb. nov. Reconstruction of ancestral habitats suggests a freshwater origin for the Haloveliinae. Divergence time estimations reveal that the origin of the monophyletic marine clade occurred at around 83 Ma (95% highest posterior density: 71–98 Ma) in the Late Cretaceous, involving a single transition event from freshwater to marine habitats. This time coincides with the period of high global sea levels in the Late Cretaceous. During this period, the marine incursions caused by the massive sea level rise flooded the continental margins, especially in Southeast Asia, where ancestral Haloveliinae were probably distributed. The appearance of new marine habitats after the marine incursions (e.g., intertidal, mangroves and estuarine) probably led to a subsequent establishment and diversification of the marine lineages. [ABSTRACT FROM AUTHOR]

The morphology, morphogenesis, and molecular phylogeny of a new metopid ciliate, Castula specialis sp. nov., comprising three strains from geographically distant (China, Mexico, Czech Republic) anoxic freshwater habitats, were studied based on microscopic observation of live and protargol‐stained specimens as well as SSU rRNA gene sequence data. The new species is characterized as follows: size in vivo 105–220 × 25–70 μm, body oblong to elongated ellipsoidal and asymmetrical; preoral dome distinctly projecting beyond the body; 32–46 adoral membranelles; 31–52 somatic kineties; and 4–7 setae. This study brings the first morphogenetic investigation of a member of the genus Castula. The morphogenesis of the type population (China) of the new species proceeds as in Metopus spp. comprising drastic changes in body shape and a pleurotelokinetal stomatogenesis; however, the main difference is the origin of the opisthe's paroral membrane that derives from all perizonal rows and some adjacent dome kineties. Phylogenetically, the genus Castula is paraphyletic. [ABSTRACT FROM AUTHOR]

Pharmaceuticals and personal care products (PPCPs) are released from multiple anthropogenic sources and thus have a ubiquitous presence in the environment. The environmental exposure and potential effects of PPCPs on biota and humans has aroused concern within the scientific community and the public. Risk assessments are commonly conducted to evaluate the likelihood of chemicals including PPCPs that pose health threats to organisms inhabiting various environmental compartments and humans. Because thousands of PPCPs are currently used, it is impractical to assess the environmental risk of all of them due to data limitations; in addition, new PPCPs are continually being produced. Prioritization approaches, based either on exposure, hazard, or risk, provide a possible means by which those PPCPs that are likely to pose the greatest risk to the environment are identified, thereby enabling more effective allocation of resources in environmental monitoring programs in specific geographical locations and ecotoxicological investigations. In the present review, the importance and current knowledge concerning PPCP occurrence and risk are discussed and priorities for future research are proposed, in terms of PPCP exposure (e.g., optimization of exposure modeling in freshwater ecosystems and more monitoring of PPCPs in the marine environment) or hazard (e.g., differential risk of PPCPs to lower vs. higher trophic level species and risks to human health). Recommended research questions for the next 10 years are also provided, which can be answered by future studies on prioritization of PPCPs. Environ Toxicol Chem 2024;43:488–501. © 2022 SETAC [ABSTRACT FROM AUTHOR]

Urbanisation continues to increase at an alarming rate and its effects on the natural environment are very profound now more than ever. Moreover, studies on terrestrial urban landscapes seems to be more than that on urban freshwater habitats. Furthermore, studies have shown that the Odonata are effective indicators of the effects of urbanisation on freshwater habitats. However, not much is known about their responses to urbanisation in sub-Saharan Africa, especially given the unique set of conditions that characterise the area. Therefore, this study was conducted to investigate differences in Odonata responses, measured as the proportion of habitat generalists, to three levels of habitat disturbance in the Cape Coast Metropolis of Ghana. Results showed that Phaon camerunensis was a potential indicator of habitat disturbance. Also, differences in habitat disturbance significantly affected Odonata composition. The most important variables that influenced Odonata responses were the individual and interaction effects of altitude and preservation of riparian vegetation. Therefore, conservation strategies that are targeted at reducing the impacts of urbanisation on Odonata must focus on these variables. [ABSTRACT FROM AUTHOR]

The Squaretail mullet, Ellochelon vaigiensis, is a commercial fish species distributed throughout the Indo‐Pacific region. This species tolerates wide variations in salinity, having been reported from both freshwater and marine habitats. Although economically significant, there is little information on its reproduction, especially in the Vietnamese Mekong Delta (VMD), where it is heavily extracted. Our study elucidates the breeding pattern, seasonality, first length at maturity, as well as potential and relative fecundity of this species. Fish specimens were collected by trawl nets from November 2020 to October 2021 at four estuarine sites within the VMD. We found this species to be a synchronous spawner, with peaks in reproductive activity from June to September. In the populations we surveyed, there was significant dominance of males (1.26:1.00) based on 942 fish samples (526 males and 416 females). The length at 50% maturity for females was significantly higher than for males at all sites and ranged from 10.6 to 19.3 cm. The diameter of the eggs examined for this species exhibited slight variation, from 0.43 to 0.54 mm. The potential fecundity ranged from 246,254 ± 35,878 to 411,970 ± 54,370 eggs, corresponding to female length and weight of 26.7–32.6 cm and 102.97–234.19 g, respectively. Relative fecundity values were highest at Thanh Phu, Ben Tre (6388 ± 605 eggs), and Dong Hai, Bac Lieu (6461 ± 637 eggs), followed by Tran De, Soc Trang (4729 ± 408), and were found to be lowest at Duyen Hai, Tra Vinh (3117 ± 223 eggs). Information on reproductive behavior in this species has far‐reaching impacts on sustainable extractions, stock conservation, and aquaculture. [ABSTRACT FROM AUTHOR]

The continued loss of freshwater habitats poses a significant threat to global biodiversity. We reviewed the extinction risk of 166 freshwater aquatic and semiaquatic mammals—a group rarely documented as a collective. We used the International Union for the Conservation of Nature Red List of Threatened Species categories as of December 2021 to determine extinction risk. Extinction risk was then compared among taxonomic groups, geographic areas, and biological traits. Thirty percent of all freshwater mammals were listed as threatened. Decreasing population trends were common (44.0%), including a greater rate of decline (3.6% in 20 years) than for mammals or freshwater species as a whole. Aquatic freshwater mammals were at a greater risk of extinction than semiaquatic freshwater mammals (95% CI –7.20 to –1.11). Twenty‐nine species were data deficient or not evaluated. Large species (95% CI 0.01 to 0.03) with large dispersal distances (95% CI 0.03 to 0.15) had a higher risk of extinction than small species with small dispersal distances. The number of threatening processes associated with a species compounded their risk of extinction (95% CI 0.28 to 0.77). Hunting, land clearing for logging and agriculture, pollution, residential development, and habitat modification or destruction from dams and water management posed the greatest threats to these species. The basic life‐history traits of many species were poorly known, highlighting the need for more research. Conservation of freshwater mammals requires a host of management actions centered around increased protection of riparian areas and more conscientious water management to aid the recovery of threatened species. [ABSTRACT FROM AUTHOR]

The impacts of climate change are widespread and threaten natural systems globally. Yet, within regions, heterogeneous physical landscapes can differentially filter climate, leading to local response diversity. For example, it is possible that while freshwater lakes are sensitive to climate change, they may exhibit a diversity of thermal responses owing to their unique morphology, which in turn can differentially affect the growth and survival of vulnerable biota such as fishes. In particular, salmonids are cold‐water fishes with complex life histories shaped by diverse freshwater habitats that are sensitive to warming temperatures. Here we examine the influence of habitat on the growth of sockeye salmon (Oncorhynchus nerka) in nursery lakes of Canada's Skeena River watershed over a century of change in regional temperature and intraspecific competition. We found that freshwater growth has generally increased over the last century. While growth tended to be higher in years with relatively higher summer air temperatures (a proxy for lake temperature), long‐term increases in growth appear largely influenced by reduced competition. However, habitat played an important role in modulating the effect of high temperature. Specifically, growth was positively associated with rising temperatures in relatively deep (>50 m) nursery lakes, whereas warmer temperatures were not associated with a change in growth for fish among shallow lakes. The influence of temperature on growth also was modulated by glacier extent whereby the growth of fish from lakes situated in watersheds with little (i.e., <5%) glacier cover increased with rising temperatures, but decreased with rising temperatures for fish in lakes within more glaciated watersheds. Maintaining the integrity of an array of freshwater habitats—and the processes that generate and maintain them—will help foster a diverse climate‐response portfolio for important fish species, which in turn can ensure that salmon watersheds are resilient to future environmental change. [ABSTRACT FROM AUTHOR]

Intensively monitored watershed (IMW) studies, the intent of which is to quantify habitat restoration effects on salmonid populations, have been underway in the Pacific Northwest, USA, for more than two decades. Lack of population‐level response to habitat improvements by target species in some IMWs may be related to incomplete knowledge of factors regulating fish abundance, excessively prolonged restoration application periods, underappreciation of natural environmental and population variability, failure to carry out restoration at a sufficiently large scale within a watershed, lack of sufficient time to document a posttreatment response, or an actual failure of the restoration activities in those locations to achieve population recovery objectives. However, knowledge gained from IMWs has yielded important insight into (1) the long‐term responses of salmon and steelhead Oncorhynchus mykiss to different types of restoration and (2) the importance of placing freshwater habitat improvements in the context of changes in anadromous salmonid survival and growth during other life history stages. Scientists, funding organizations, and policymakers should appreciate the potential value of IMWs as long‐term barometers of the status of salmon populations and their habitats in watersheds where restoration activities are occurring. This requires a commitment to prolonged monitoring and an acknowledgment that environmental recovery after habitat restoration may take decades. [ABSTRACT FROM AUTHOR]

Free‐living litostomatean ciliates, prominent microeukaryote predators commonly encountered in freshwater and marine habitats, play vital roles in maintaining energy flow and nutrient cycles. Nevertheless, understanding their biodiversity and phylogenetic relationships remains challenging due to insufficient morphological information and molecular data. As a new contribution to this group, three haptorian ciliates, including two new species (Actinobolina bivacuolata sp. nov. and Papillorhabdos foissneri sp. nov.) and the insufficiently described type species, Actinobolina radians, were isolated from wetlands around Lake Weishan, China and investigated by a combination of living morphology, stained preparations, and 18S rRNA gene sequence data. An illustrated key of the valid species within the two genera is provided. In addition, we reveal the phylogenetic positions of these two genera for the first time. Although they differ in all key morphologic characters such as general appearance (ellipsoidal with numerous tentacles vs. cylindrical), extrusomes (stored in tentacles vs. anchored to pellicle), circumoral kinety (present vs. absent), composition of somatic kineties (kinetosome clusters vs. monokinetids), and number of dorsal brush rows (1 vs. 4), they both cluster in a fully supported clade in the phylogenetic tree, which indicates that the biodiversity and additional molecular markers of this group need further exploration. [ABSTRACT FROM AUTHOR]

Aim: Human activities have introduced numerous non‐native species (NNS) worldwide. Understanding and predicting large‐scale NNS establishment patterns remain fundamental scientific challenges. Here, we evaluate if NNS composition represents a proportional subset of the total species pool available to invade (i.e. total global biodiversity), or, conversely, certain taxa are disproportionately pre‐disposed to establish in non‐native areas. Location: Global. Time period: Present day. Major taxa studied: Global diversity. Methods: We compiled one of the most comprehensive global databases of NNS (36,822 established species) to determine if NNS diversity is a representative proportional subset of global biodiversity. Results: Our study revealed that, while NNS diversity mirrors global biodiversity to a certain extent, due to significant deviance from the null model it is not always a representative proportional subset of global biodiversity. The strength of global biodiversity as a predictor depended on the taxonomic scale, with successive lower taxonomic levels less predictive than the one above it. Consequently, on average, 58%, 42% and 28% of variability in NNS numbers were explained by global biodiversity for phylum, class and family respectively. Moreover, global biodiversity was a similarly strong explanatory variable for NNS diversity among regions, but not habitats (i.e. terrestrial, freshwater and marine), where it better predicted NNS diversity for terrestrial than for freshwater and marine habitats. Freshwater and marine habitats were also greatly understudied relative to invasions in the terrestrial habitats. Over‐represented NNS relative to global biodiversity tended to be those intentionally introduced and/or 'hitchhikers' associated with deliberate introductions. Finally, randomness is likely an important factor in the establishment success of NNS. Main conclusions: Besides global biodiversity, other important explanatory variables for large‐scale patterns of NNS diversity likely include propagule and colonization pressures, environmental similarity between native and non‐native regions, biased selection of intentionally introduced species and disparate research efforts of habitats and taxa. [ABSTRACT FROM AUTHOR]

Herbicides are important, ubiquitous environmental contaminants, but little is known about their interaction with bacterial aquatic communities. Here, we sampled a protected natural freshwater habitat and characterised its microbiome in interaction with herbicides. We evolved the freshwater microbiomes in a microcosm assay of exposure (28 days) to flufenacet and metazachlor at environmental concentrations of 0.5, 5 and 50 μg L−1. Inhibitory effects of herbicides were exemplarily assessed in cultured bacteria from the same pond (Pseudomonas alcaligenes, Paenibacillus amylolyticus and Microbacterium hominis). Findings were compared to long‐term concentrations as provided by local authorities. Here, environmental concentrations reached up to 11 μg L−1 (flufenacet) and 76 μg L−1 (metazachlor). Bacteria were inhibited at minimum inhibitory concentrations far above these values; however, concentrations of 50 μg L−1 of flufenacet resulted in measurable growth impairment. While most herbicide‐exposed microcosm assays did not differ from controls, Acidobacteria were selected at high environmental concentrations of herbicides. Alpha‐diversity (e.g., taxonomic richness on phylum level) was reduced when aquatic microbiomes were exposed to 50 μg metazachlor or flufenacet. One environmental strain of P. alcaligenes showed resistance to high concentrations of flufenacet (50 g L−1). In total, this study reveals that ecologic imbalance due to herbicide use significantly impacts aquatic microbiomes. [ABSTRACT FROM AUTHOR]

We explored the distribution, metabolic and antagonistic activities of Carnobacterium maltaromaticum, isolated from freshwater locations in Denmark during winter or early spring. This species was widely distributed in such habitats although it was relatively rare in low pH locations. Isolates possessed a diverse metabolism, potentially enabling functional capacities independent of habitat. The intraspecies competition showed a relatively high degree of mostly low‐intensity interactions, which overall were not correlated with phylogeny or location. Only a few isolates exhibited broad‐spectrum inhibition activity, targeting species from other genera and families, including one isolate that exhibited a broad inhibitory activity due to H2O2 production. Bioinformatic analyses revealed that the frequency of bacteriocinogenic systems was low, and only one unmodified bacteriocin, piscicolin 126, correlated with phenotypic antagonistic activity. Furthermore, most potential bacteriocin gene complexes were not complete. Overall, this study showed C. maltaromaticum to be a generalist (nomadic) species with a constant presence in freshwater habitats, especially those with pH values >5. General metabolic properties did not suggest a strong degree of adaptation to the freshwater environment, and bacteriocin‐mediated antagonistic activities appeared to play a minimal ecological role. [ABSTRACT FROM AUTHOR]

Simple filamentous cyanobacteria comprise a diverse and polyphyletic group of species, primarily in the orders Leptolyngbyales and Oscillatoriales, that need more sampling to improve their taxonomy. Oceanic islands, such as the Azores archipelago, present unique habitats and biogeographic conditions that harbor an unknown range of diversity of microorganisms. Filamentous cyanobacteria isolated from aquatic habitats in the Azores and maintained in the BACA culture collection were described using morphology, both light and transmission electron microscopy, ecology, and genetic data of the 16S rRNA gene sequences and 16S–23S Internal Transcribed Spacer (ITS) rRNA region secondary structure. Our analyses revealed two new monophyletic genera: Tumidithrix elongata gen. sp. nov. (Pseudanabaenaceae) and Radiculonema aquaticum gen. sp. nov. (Leptolyngbyaceae). In addition, two new species Leptodesmis lacustris sp. nov. (Leptolyngbyaceae) and Pycnacronema lacustrum sp. nov. (Wilmottiaceae) are reported as the first aquatic species for these genera. The description of these new taxa and the genetic study of an isolate of Leptodesmis alaskaensis from the Azores followed the polyphasic approach, identifying diacritical features. Our results reinforce the need for taxonomic studies on cyanobacteria from less‐studied habits and geographic regions, which have a potential for new taxa description. [ABSTRACT FROM AUTHOR]

The Klebsormidiophyceae are a class of green microalgae observed globally in both freshwater and terrestrial habitats. Morphology‐based classification schemes of this class have been shown to be inadequate due to the simple morphology of these algae, the tendency of morphology to vary in culture versus field conditions, and rampant morphological homoplasy. Molecular studies revealing cryptic diversity have renewed interest in this group. We sequenced the complete chloroplast genomes of a broad series of taxa spanning the known taxonomic breadth of this class. We also sequenced the chloroplast genomes of three strains of Streptofilum, a recently discovered green algal lineage with close affinity to the Klebsormidiophyceae. Our results affirm the previously hypothesized polyphyly of the genus Klebsormidium as well as the polyphyly of the nominal species in this genus, K. flaccidum. Furthermore, plastome sequences strongly support the status of Streptofilum as a distinct, early‐diverging lineage of charophytic algae sister to a clade comprising Klebsormidiophyceae plus Phragmoplastophyta. We also uncovered major structural alterations in the chloroplast genomes of species in Klebsormidium that have broad implications regarding the underlying mechanisms of chloroplast genome evolution. [ABSTRACT FROM AUTHOR]

Alternative migratory tactics in salmonids reflect the large observed interindividual variation in spatial behaviour which may range from strict freshwater residency to uninterrupted anadromy. In Salvelinus, sea migrations are performed during the ice‐free period as freshwater overwintering is thought to be obligatory due to physiological constraints. As a result, individuals can either migrate the next spring or remain in freshwater, as anadromy is generally considered facultative. In Arctic charr (Salvelinus alpinus), skipped migrations are known to occur, but limited data are available regarding their frequencies within and among populations. Here, the authors used an otolith microchemistry approach relying on strontium (88Sr) to infer movements between freshwater and marine habitats, and annual oscillations in zinc (64Zn) to help with age identification. They determined the age‐at‐first‐migration and the occurrence of subsequent annual migrations in two Nunavik Arctic charr populations sampled in Deception Bay (Salluit) and river systems linked to Hopes Advance Bay (Aupaluk), northern Québec, Canada. The mode for age‐at‐first‐migration was 4+ for both populations, although it exhibited large variation (range: 0+ to 8+). Skipped migrations constituted a rare event, as 97.7% and 95.6% of the examined Arctic charr at Salluit (n = 43, mean age = 10.3 ± 2.0 years) and Aupaluk (n = 45, mean age = 6.0 ± 1.9 years), respectively, were found to have performed uninterrupted annual migrations after initiation of the behaviour. The consistency of the annual migrations suggests that the tactic is sufficiently fitness rewarding to be maintained under current environmental conditions. From a fisheries management perspective, these repeated migrations combined with low site fidelity in this species may lead to large interannual variations in abundance at the local scale, which may represent a challenge for monitoring Arctic charr demographics on a river‐by‐river basis. [ABSTRACT FROM AUTHOR]

Explaining the mechanisms underlying spatial and temporal variation in community composition is a major challenge. Nevertheless, the processes controlling temporal variation at a site (i.e. temporal β‐diversity, including its turnover and nestedness components) are less understood than those affecting variation among sites (i.e. spatial β‐diversity). Short‐term temporal turnover (e.g. throughout an annual cycle) is expected to correlate positively with seasonal environmental variability and landscape connectivity, but also species pool size (γ‐diversity). We use the megadiverse Amazonian freshwater ichthyofauna as a model to ask whether seasonality and landscape connectivity drive variation in temporal species turnover among geomorphological habitat types, while accounting for between‐habitat variation in γ‐diversity. We collected 11 397 fish representing 260 species during a year‐long sampling program from an area containing the lowland Amazon's four major geomorphological habitat types: rivers, floodplains, terra firme streams, and shield streams. River‐floodplain systems exhibit strong but predictable seasonality (via a high‐amplitude annual flood pulse), high connectivity, and high species richness with many rare species. Terra firme and shield streams exhibit low seasonality, low connectivity, and low species richness with proportionally fewer rare species. Based on these parameters we predicted that river‐floodplain systems should have higher temporal turnover than stream systems. Using a null model approach combined with β‐deviation calculations, we confirmed that rivers and floodplains do exhibit higher turnover (but not nestedness) than terra firme and shield streams, even when controlling for the potentially confounding effect of higher species richness in river‐floodplain systems. All habitats exhibit low temporal nestedness, indicating that short‐term changes in community composition result primarily from temporal species turnover. Our results provide a timely reminder that efforts to conserve the Amazon's threatened aquatic biodiversity should account for the distinct temporal dynamics of habitat types and variation in hydrological seasonality. [ABSTRACT FROM AUTHOR]

Artificial light at night (ALAN) is a pervasive and growing issue worldwide. ALAN disrupts the physiology and natural crepuscular and nocturnal behavior of organisms, with widely observed effects on insects. Mosquitoes (Diptera: Culicidae) are disease vectors that evaluate and select freshwater habitats as oviposition sites. This behavior has both ecological and epidemiological implications. However, it is unknown how ALAN affects mosquito oviposition. We compared oviposition rates in outdoor mesocosms exposed to light‐emitting diodes (LED, 3000 K, ca. 13 lux) with dark controls. We assayed the oviposition behavior of natural populations of mosquitoes by quantifying mosquito eggs (Culex restuans Theobald and Ochlerotatus japonicus Theobald) deposited in the experimental mesocosms over 7 days. Mosquitoes had species‐specific responses to ALAN. Mean cumulative Cx. restuans egg raft deposition was greater in control pools than in ALAN pools (21 vs. 10 eggs). We observed no response of Oc. japonicus, potentially reflecting the risk associated with the alternative oviposition strategies of the two species (eggs rafts vs. skip oviposition). Our results show that ALAN has species‐specific effects on organisms, thereby complicating our understanding of the behavioral and potential ecological and epidemiological effects of this novel anthropogenic stressor. [ABSTRACT FROM AUTHOR]

Studies on host–parasite systems that have experienced distributional shifts, range fragmentation, and population declines in the past can provide information regarding how parasite community richness and genetic diversity will change as a result of anthropogenic environmental changes in the future. Here, we studied how sequential postglacial colonization, shifts in habitat, and reduced host population sizes have influenced species richness and genetic diversity of Corynosoma (Acanthocephala: Polymorphidae) parasites in northern European marine, brackish, and freshwater seal populations. We collected Corynosoma population samples from Arctic, Baltic, Ladoga, and Saimaa ringed seal subspecies and Baltic gray seals, and then applied COI barcoding and triple‐enzyme restriction‐site associated DNA (3RAD) sequencing to delimit species, clarify their distributions and community structures, and elucidate patterns of intraspecific gene flow and genetic diversity. Our results showed that Corynosoma species diversity reflected host colonization histories and population sizes, with four species being present in the Arctic, three in the Baltic Sea, two in Lake Ladoga, and only one in Lake Saimaa. We found statistically significant population‐genetic differentiation within all three Corynosoma species that occur in more than one seal (sub)species. Genetic diversity tended to be high in Corynosoma populations originating from Arctic ringed seals and low in the landlocked populations. Our results indicate that acanthocephalan communities in landlocked seal populations are impoverished with respect to both species and intraspecific genetic diversity. Interestingly, the loss of genetic diversity within Corynosoma species seems to have been less drastic than in their seal hosts, possibly due to their large local effective population sizes resulting from high infection intensities and effective intra‐host population mixing. Our study highlights the utility of genomic methods in investigations of community composition and genetic diversity of understudied parasites. [ABSTRACT FROM AUTHOR]

Climate change is affecting freshwater habitats worldwide through multiple, interacting pressures that influence the survival, distribution, and persistence of freshwater organisms. Temporary freshwater habitats, or those that dry seasonally, can exhibit wide‐ranging variability in temperature and drying regimes. Aquatic organisms with complex life cycles (e.g., aquatic and terrestrial life stages) often rely on temporary freshwaters to complete their life cycles and have specific adaptations to cope with these dynamic environments. However, climate change is altering the temperature and drying regime of many temporary freshwater habitats worldwide, often resulting in warmer habitats available for shorter durations of time. The ways in which climate‐mediated changes to temporary freshwaters affect development and life history of aquatic organisms, particularly those with complex life cycles, remains poorly understood.We investigated larval development, growth, survival, and relationships among them for two amphibian species, wood frogs (Lithobates sylvaticus) and spring peepers (Pseudacris crucifer), in response to warming and drying in a mesocosm experiment. Over 13 weeks in the spring and summer of 2019, we manipulated temperature and water levels in 48 outdoor pond mesocosms to produce four treatments: control (ambient conditions), drying alone, warming alone, and drying + warming. We predicted reduced survival, body size, and time to metamorphosis for both species in response to warming and drying, with the effect being stronger on wood frogs due to their more specialised habitat use and shorter breeding period.Warming treatments were on average 2°C higher than controls, and drying treatments decreased water depth by 2.5 cm each week. We found that warming temperature shortened larval time to metamorphosis, and drying decreased body size at metamorphosis. Surprisingly, we also found that, across all treatment groups, individuals with early metamorphosis tended to be larger in size and from mesocosms with generally higher survival.Our study indicates that warming and drying may act independently on different developmental responses for amphibians. Our results echo recent calls for a better understanding of the nuanced, often unpredictable, relationships among climate‐mediated environmental pressures and the developmental traits they influence, particularly for organisms with complex life cycles that depend upon dynamic habitat for growth and survival. Understanding these relationships and the mechanisms that drive them will be key to predicting the response of freshwater organisms to climate change. [ABSTRACT FROM AUTHOR]

Restoration of natural processes in ecosystems is key to mitigate the biodiversity crisis. Here, we evaluate 20 Danish stream‐valley restoration projects—mainly by rewetting—in terms of successful restoration of natural wetland habitats. We used quadratic discriminant analysis and generalized linear models to compare 80 vegetation plots from the restoration projects with >60,000 natural or semi‐natural wetland reference plots. We modeled the influence of time since restoration, grazing, rewetting, and nutrient availability on (1) the probability that study plots belong to natural habitats and (2) their richness of high‐quality‐habitat indicator species. The probability of a restored wetland having developed into a natural wetland habitat—such as an alkaline fen—was generally below 10%. Also, we found only half as many indicator species in restored wetlands than in reference wetlands and we demonstrated that the number of characteristic alkaline fen species did not deviate from what could be expected under the prevailing nutrient conditions. We found a negative effect of soil nutrient availability on the number of high‐quality‐habitat indicator species and the lowest probability of plots being natural wetlands in the most nutrient rich plots. The effect of grazing was only positive in the first years after restoration and only in the most nutrient rich plots, while the effect of rewetting sites to historical hydrological conditions was generally negative. Our findings suggest that unnaturally high nutrient availability is probably the core limiting factor for successful restoration of natural wetlands and their associated plant diversity. [ABSTRACT FROM AUTHOR]

Remote sensing technology offers the ability to derive information on freshwater fish habitats across broad geographic areas and has the potential to transform approaches to monitoring. However, the numerous platforms, sensors and analytical software that are available may overwhelm those interested in utilizing this important technology and thus limit its broad application and uptake. Our review is intended to shed light on the capacity of this technology to transform freshwater fish habitat monitoring by examining the fundamental characteristics of the major remote sensing technologies that have been used for characterizing freshwater habitats, conducting a systematic literature review of studies that have used remote sensing technologies to characterize freshwater fish habitats and, highlighting some of the key habitat features, fish species and regions, that have been examined. Lastly, we identify the relative strengths and weaknesses of the various remote sensing technologies that can be used, recommend future research that could help improve the use of these technologies, and, provide a series of important considerations for those who are interested in utilizing these technologies for freshwater fish habitat characterization. [ABSTRACT FROM AUTHOR]

Research in freshwater ecosystems has always had a strong focus on ecological interactions. The vast majority of studies, however, have investigated trophic interactions and food webs, overlooking a wider suite of non‐trophic interactions (e.g. facilitation, competition, symbiosis and parasitism) and the ecological networks they form.Without a complete understanding of all potential interactions, ranging from mutualistic through to antagonistic, we may be missing important ecological processes with consequences for ecosystem assembly, structure and function. Ecological networks can be constructed at different scales, from genes to ecosystems, but also local to global, and as such there is significant opportunity to put them to work in freshwater research.To expand beyond food webs, we need to leverage technological and methodological advances and look to recent research in marine and terrestrial systems—which are far more advanced in terms of detecting, measuring and contextualising ecological interactions.Future studies should look to emerging technologies to aid in merging the wide range of ecological interactions in freshwater ecosystems into networks to advance our understanding and ultimately increase the efficacy of conservation, management, restoration and other applications. [ABSTRACT FROM AUTHOR]

Instream barriers remain ubiquitous threats to freshwater species and their habitats. Decisions regarding barrier removal are often aimed at maximizing habitat area and connectivity for freshwater fish; yet can be challenging due to the sheer number of barriers, uncertainty in species presence, abundance, and habitat quality, as well as limited budgets alongside high costs of restoration. Here, we apply systematic conservation planning to prioritize in‐stream barrier removal aimed at restoring habitat connectivity for 14 populations of wild Pacific salmon in the lower Fraser River, Canada's most productive salmon‐bearing river. To understand how priorities change when stream quality is considered, we contrast scenarios that maximize habitat extent with scenarios that include four indicators of habitat quality. Region‐wide, approximately 64% of naturally accessible stream length is currently blocked by barriers. We estimate approximately 75% of this alienated habitat (over 1600 km of stream), could have full access restored with an investment of $200 million CAD, whereas 60% could be restored for half this amount. When stream quality was considered within the optimization, priorities for barriers removal shifted away from urbanized floodplain valleys towards less developed areas. The spatial shift in priorities meant that species like chum salmon (Oncorhynchus keta) would see less restored habitat. To inform barrier removal strategies using these model scenarios, an iterative and adaptive approach will be required that includes the values and priorities of rights and titleholders. Continuous improvement in data quality, accuracy, and feedback from monitoring as barriers are restored is also crucial. [ABSTRACT FROM AUTHOR]

Louisiana is facing a land loss crisis with 5,000 km2 lost since the 1930s, and another 10,000 km2 may disappear over the next 50 years. In response, the state developed a Comprehensive Master Plan for a Sustainable Coast, which includes predictions for how wildlife species respond to futures with or without restoration action. However, the 2017 Master Plan did not include a bird species representative of brackish or freshwater wetland habitats. Our objective therefore was to evaluate the potential for the Bald Eagle (Haliaeetus leucocephalus) to serve as an indicator of freshwater wetland health, and to develop a model to predict Bald Eagle responses to land cover change 20 and 50 years into the future, with or without restoration action. Using nest location data collected by the Louisiana Department of Wildlife and Fisheries from the Barataria Basin, we modeled the relationship between Bald Eagle nest occurrence and land cover using boosted regression trees. Model performance was strong, explaining 54.4 ± 0.1% of the deviance in nest occurrence, and showed that Bald Eagle nests were more common in areas with greater fresh forested wetland, freshwater marsh, and flotant marsh land cover. Future suitability for nesting Bald Eagles was higher in 20 and 50 years with restoration action compared to without, although suitability in both years was lower than contemporary suitability, regardless of restoration action. Our model suggests that comprehensive restoration action is needed, including the implementation of Mississippi River diversions, to sustain high densities of nesting Bald Eagles in coastal Louisiana. [ABSTRACT FROM AUTHOR]

Passive acoustic monitoring has been used for decades as a non‐invasive tool for quantifying biodiversity in terrestrial and marine ecosystems. Recently, there has been increased interest in the potential for the method to survey freshwater biodiversity. Fundamental aspects of freshwater soundscape phenology, however, often remain poorly understood, despite their importance for suitable survey design.To gain a greater understanding of daily acoustic variation in aquatic insect‐dominated temperate pond soundscapes, 840 hr of underwater sound recordings were collected from five ponds in the southwest of the U.K. We calculated six commonly used acoustic indices to investigate diel trends and evaluated the suitability of each acoustic index to identify biologically complex pond soundscapes. In addition, macroinvertebrates were collected from each pond to investigate potential drivers of diel soundscape variation.The ponds studied possessed clear patterns of daily acoustic variation, with acoustic activity typically peaking between 02:00 and 04:00 and around the solar noon. Acoustic Entropy showed the greatest variation between day and night soundscapes and was best suited for detecting overall daily acoustic variation in the study ponds. However, the Normalised Difference Soundscape Index and the Bioacoustic Index captured strong diel variation in aquatic insect‐dominated soundscapes. Furthermore, we calculated that a minimum hydrophone deployment time of 24 hr is required to ensure that soundscape variation is adequately captured.This study provides an increased understanding of daily acoustic variation in insect‐dominated temperate pond soundscapes, enabling us to provide guidelines for the design and implementation of future passive acoustic monitoring surveys. We suggest that a minimum of 24 hr is required to adequately capture pond soundscape variation. This will increase the chance of detecting key soniferous species in the soundscape and enable more accurate assessments of temperate pond soundscapes. [ABSTRACT FROM AUTHOR]

The freshwater isopod Asellus aquaticus is an important decomposer of leaf detritus, and its diverse gut microbiome has been depicted as key contributors in lignocellulose degradation as of terrestrial isopods. However, it is not clear whether the individual‐level microbiome profiles in the isopod digestive system across different habitats match the implied robust digestion function of the microbiome. Here, we described the bacterial diversity and abundance in the digestive system (hindgut and caeca) of multiple A. aquaticus individuals from two contrasting freshwater habitats. Individuals from a lake and a stream harboured distinct microbiomes, indicating a strong link between the host‐associated microbiome and microbes inhabiting the environments. While faeces likely reflected the variations in environmental microbial communities included in the diet, the microbial communities also substantially differed in the hindgut and caeca. Microbes closely related to lignocellulose degradation are found consistently more enriched in the hindgut in each individual. Caeca often associated with taxa implicated in endosymbiotic/parasitic roles (Mycoplasmatales and Rickettsiales), highlighting a complex host–parasite–microbiome interaction. The results highlight the lability of the A. aquaticus microbiome supporting the different functions of the two digestive organs, which may confer particular advantages in freshwater environments characterized by seasonally fluctuating and spatially disparate resource availability. [ABSTRACT FROM AUTHOR]

The salinity gradient separating marine and freshwater environments is a major ecological divide, and the mechanisms by which most organisms adapt to new salinity environments are poorly understood. Diatoms are a lineage of ancestrally marine microalgae that have repeatedly colonized and diversified in freshwaters. Cyclotella cryptica is a euryhaline diatom found in salinities ranging from fully freshwater to fully marine, thus providing a powerful system for understanding the genomic mechanisms for mitigating and acclimating to low salinity. To understand how diatoms mitigate acute hypo‐osmotic stress, we abruptly shifted C. cryptica from seawater to freshwater and performed transcriptional profiling during the first 10 h. Freshwater shock dramatically remodelled the transcriptome, with ~50% of the genome differentially expressed in at least one time point. The peak response occurred within 1 h, with strong repression of genes involved in cell growth and osmolyte production, and strong induction of specific stress defence genes. Transcripts largely returned to baseline levels within 4–10 h, with growth resuming shortly thereafter, suggesting that gene expression dynamics may be useful for predicting acclimation. Moreover, comparison to a transcriptomics study of C. cryptica following months‐long acclimation to freshwater revealed little overlap between the genes and processes differentially expressed in cells exposed to acute stress versus fully acclimated conditions. Altogether, this study highlights the power of time‐resolved transcriptomics to reveal fundamental insights into how cells dynamically respond to an acute environmental shift and provides new insights into how diatoms mitigate natural salinity fluctuations and have successfully diversified across freshwater habitats worldwide. see also the Perspective by Gust Bilcke and Shiho Kamakura [ABSTRACT FROM AUTHOR]

As the global climate is changing, average water temperatures and the supply of CO2 to water bodies are increasing. To determine how the effects of these changes on freshwater communities interact, we ran a month‐long factorial mesocosm experiment, in which we manipulated water temperature (heated, ambient) and pCO2 (preindustrial, ambient, future). We found that the total phytoplankton biomass responded positively to the pCO2 and temperature treatments but no interactive effects were detected. Green algae were positively affected by temperature and, over the course of the experiment, responded to pCO2 first positively, then negatively. Heterokonts, on the other hand, were unaffected by temperature but responded positively to pCO2. pCO2 enrichment also led to increases in seston C : N stoichiometry, although the experiment ended before we could observe any effects of pCO2 on the zooplankton community composition. Warming caused shifts in zooplankton community composition, primarily through higher abundances of the cladoceran Bosmina longirostris and the rotifer Conochilus unicornis, and lower abundances of the rotifer Polyarthra vulgaris. We found that, in contrast to the effects of temperature, which can be explained by temperature‐dependent plankton growth curves, the responses of algal groups to pCO2 enrichment were difficult to anticipate, despite the availability of priors from previous pCO2 enrichment experiments in the same lake mesocosms. We conclude that climate change‐induced increases in aquatic pCO2 and temperatures are likely to affect pelagic ecosystems, though further research in freshwater systems is needed before generalized claims regarding the simple and interactive effects of pCO2 can be made. [ABSTRACT FROM AUTHOR]

Invasive non‐native species and climate change are two of the greatest pressures facing freshwater communities; however, how they interact to impact ecosystem function remains poorly understood despite the potential for impacts on key functional behaviours, such as detritivory, which could have wide‐reaching impacts. We quantified the rates of detrital processing and survival of one U.K. native (Gammarus pulex) and two invasive non‐native (Dikerogammarus villosus and Dikerogammarus haemobaphes) freshwater amphipod species, across three temperatures (8°C, 14°C, and 20°C), and three leaf diets of varying resource quality (oak, sycamore, and alder) in laboratory microcosms. We also compared amphipod survival across the different temperature and diet treatments. Rates of detrital processing varied between the native and invasive non‐native amphipod species, with native G. pulex having a faster processing rate than both invasive non‐native species at the lower temperatures. However, as the temperature treatments increased, between‐species differences decreased, while the effects of leaf diets became more apparent. Although the survival probability did not vary with amphipod species, amphipod survival was higher at lower temperatures and in treatments containing higher quality leaf diets. We propose that the invasive non‐native Dikerogammarus species will affect native communities through lower rates of detrital processing; however, this impact may change under predicted climatic warming and be increasingly similar to native amphipod species. [ABSTRACT FROM AUTHOR]

Salmon‐lice have the potential to change the behaviour and growth of their salmonid host species. Here, the baseline infection levels of salmon‐lice of post‐smolts (n = 815) and veteran migrants (n = 875) of sea‐run Arctic charr (Salvelinus alpinus Linnaeus, 1758) were monitored over two successive years in a sub‐Arctic Norwegian fjord without farming of salmonids. All Arctic charr were collected after the sea‐migration period from a trap placed in the river, ascending to their overwintering freshwater habitat (Lake Laksvatn). The sea‐lice infection showed a stable infection across the 2 years while increasing through the migration period and with the size of the wild sea‐run Arctic charr. The prevalence of sea‐lice infection was intermediate to high, and the intensities of sea‐lice infections observed were generally modest, although some individuals had high infections. The relatively high infection of salmon‐lice highlights the potential detrimental effects these parasites can have at both the individual and population level of such endangered sub‐Arctic life‐history strategies. A comparative study should be performed in fjords with aquaculture activity as focal points for salmon‐lice, to investigate the impact farming have on sea‐run Arctic charr populations. [ABSTRACT FROM AUTHOR]

Freshwater habitats are experiencing two to three times the rate of biodiversity loss of terrestrial and marine habitats. As status quo actions within the conservation community are not reversing the downward trajectory for freshwater biodiversity, we propose four actions to shift the narrative such that freshwater biodiversity is no longer invisible and overlooked, but rather explicitly recognized, valued, and protected: (1) Reshape our relationship with freshwater habitats and biodiversity, (2) Appreciate indigenous knowledge systems relating to freshwater habitats, (3) Connect science more directly to action, and (4) Elevate freshwater habitats as a unique "domain" that requires explicit recognition in conservation planning (RACE). We highlight roles that both freshwater scientists and the wider conservation community can play in implementing the four actions such that the "RACE" can be won. [ABSTRACT FROM AUTHOR]

Microsporidia are a large group of obligate intracellular eukaryotic parasites related to fungi primarily known as parasites of vertebrates and invertebrates. They are well described as parasites of organisms of interest (e.g., edible fish and crustaceans, honeybees, bioindicators such as daphnia, humans) on which they can have an important impact (e.g., reduced survival or fecundity and sex ratio distortion). However, their diversity in aquatic environments, especially in marine ecosystems, has been greatly understudied since they are not targeted by classical eukaryotic primers used in metabarcoding studies. Moreover, little is known about their hosts among protists or microzooplankton and therefore about their impact on the trophic food web functioning. In this work, we sampled 15 different sites across marine and freshwater environments, size‐fractioned the samples, and used microsporidian specific primers associated with metabarcoding to study the microsporidian diversity (and the associated spatial variation). Co‐occurrence networks as well as tyramide signal amplification‐fluorescent in situ hybridization were used to link potential hosts (planktonic eukaryotes < 150 μm) and Microsporidia diversity. Our analysis unraveled a large microsporidian diversity which was widely divergent between the two environments studied. In both of them, an important part of this diversity was not affiliated to a genus, suggesting an important reservoir of new microsporidian species and thus new hosts among planktonic eukaryotes. Co‐occurrence networks and fluorescence microscopy showed for the first‐time associations between Microsporidia and dinoflagellates in freshwater and marine environments. [ABSTRACT FROM AUTHOR]

Resource quantity (i.e. organic matter; OM) is a main driver of the prevailing energy pathway in freshwater food webs. The OM pool is mainly composed of allochthonous material, a primary resource for freshwater consumers. Contrastingly, small amounts of autochthonous OM (i.e. algae) can subsidize aquatic communities due to its higher nutritional quality. To date, there is no consensus about the relative importance of allochthonous and autochthonous OM for freshwater food webs or the environmental factors driving their relative importance. We fill this gap by evaluating the relative importance of allochthonous and autochthonous OM sources for freshwater food webs on a global scale through a meta‐analytical approach. We gathered the outcome of stable isotope mixing models of 2789 cases from 58 published studies and calculated a response ratio between the mean contributions of allochthonous and autochthonous OM for freshwater consumers. Using mixed‐effect models and a multimodel inference approach, we tested the influence of latitude, habitat type, ecosystem size, climate and terrestrial productivity over the response ratio. The relative contribution of autochthonous OM was higher in lotic systems. In lentic systems, increasing terrestrial productivity increased the relative contribution of autochthonous OM, while increasing precipitation and temperature seasonality reduced this relative contribution. We suggested that factors increasing terrestrial productivity might also boost autochthonous OM in these systems, while precipitation increases the transport of allochthonous OM to freshwater habitats. We did not find any relationship between environmental factors and the relative contribution of autochthonous OM for lotic systems. We concluded that the relative contribution of allochthonous and autochthonous energy sources to freshwater food webs differs between lotic and lentic ecosystems and it is dependent on multiple environmental factors. [ABSTRACT FROM AUTHOR]

The presence of submerged macrophytes is a desired environmental target for coastal freshwater ecosystems. Maintaining a rich community of these species can be challenging as salinisation by sea‐level rise poses an increasing threat to ecosystem integrity.We tested the effect of salinisation on the growth and germination of freshwater macrophytes experimentally using field sediment. In a 56‐day experiment, a macrophyte community was exposed to salinity treatments representing seasonal water management scenarios (a decreasing salinity from 1,500 to 300 mg NaCl/L, a stable salinity of 300 mg NaCl/L, an increasing salinity from 300 to 1,500 mg NaCl/L and a stable salinity of 1,500 mg NaCl/L), crossed with treatments simulating periodic turbidity pulses.All species except Elodea nuttallii grew poorly on the saline and eutrophic sediment, reflecting the challenges of growth in eutrophic coastal systems. Surprisingly, the highest community biomass was achieved in the salinity scenario of 1,500 mg NaCl/L.In a second experiment, field‐collected sediments were incubated at 300 and 1,500 mg NaCl/L salinity (representing summer and winter scenarios), and the germination capacity of the existing seedbank was quantified.Most germinated seedlings did not reach maturity irrespective of salinity treatment. This indicated that sediment salinity, rather than water column salinity, determined seedling establishment success. Interestingly, the established species were characteristic of freshwater habitats, thus indicating maladaptation of the seedbank.Our results show that a mismatch between the high salinity level of eutrophic sediment and the overlaying freshwater may hamper macrophyte growth. Furthermore, target species in coastal eutrophic freshwaters should be evaluated carefully. Elodea nuttalli, which has a wide tolerance range for nutrients and salinity, outperformed other macrophyte species in our study. Thus, species with similar traits may be most successful in establishing macrophyte stands in coastal eutropic wetlands. [ABSTRACT FROM AUTHOR]

Three novel strains in Calotrichaceae from tropical habitats were isolated and characterized with regard to their morphology, phylogenetic placement, and secondary structures of conserved domains in the 16S‐23S internal transcribed spacer (ITS). The strains fell into two clades formerly identified as Calothrix from freshwater and brackish habitats. Based on both morphology and ecology, they differed from the type species of Calothrix, C. confervicola, which is marine, has wide trichomes with short cells, and narrows abruptly to a hyaline hair. The first clade grouped species with heteropolar filaments widened at the base and narrowed gradually toward the apex but not ending in a hair, with basal heterocytes that are formed in series as the apically placed heterocytes senesce; this clade is being named Fulbrightiella gen. nov., with two named species, F. bharadwajae sp. nov. and F. oahuensis sp. nov. The second clade was comprised of a single species with isopolar trichomes that are untapering as hormogonia, but which widen midfilament and taper toward both ends following growth. These trichomes develop pairs of heterocyte mid‐filament, causing fragmentation into heteropolar trichomes with basal heterocytes and ends that taper, but not to a hair. This clade consists of a single species at present, Sherwoodiella mauiensis. With this action, four clades in the Calotrichaceae have been named: Macrochaete, Dulcicalothrix, Fulbrightiella, and Sherwoodiella. Calothrix sensu stricto is truly marine, morphologically distinct, and unsequenced; finding and sequencing the generitype for Calothrix remains as the most important and unfinished task in the revision of the Calotrichaceae. [ABSTRACT FROM AUTHOR]

Aerobic anoxygenic photoheterotrophic (AAP) bacteria represent a functional group of prokaryotic organisms that harvests light energy using bacteriochlorophyll‐containing photosynthetic reaction centers. They represent an active and rapidly growing component of freshwater bacterioplankton, with the highest numbers observed usually in summer. Species diversity of freshwater AAP bacteria has been studied before in lakes, but its seasonal dynamics remain unknown. In this report, we analysed temporal changes in the composition of the phototrophic community in an oligo‐mesotrophic freshwater lake using amplicon sequencing of the pufM marker gene. The AAP community was dominated by phototrophic Gammaproteobacteria and Alphaproteobacteria, with smaller contribution of phototrophic Chloroflexota and Gemmatimonadota. Phototrophic Eremiobacteriota or members of Myxococcota were not detected. Interestingly, some AAP taxa, such as Limnohabitans, Rhodoferax, Rhodobacterales or Rhizobiales, were permanently present over the sampling period, while others, such as Sphingomonadales, Rhodospirillales or Caulobacterales appeared only transiently. The environmental factors that best explain the seasonal changes in AAP community were temperature, concentrations of oxygen and dissolved organic matter. [ABSTRACT FROM AUTHOR]

Despite significant population declines and targeted European Union regulations aimed at Anguilla anguilla conservation, little attention has been given to their status at their easternmost range. This study applies wide‐scale integrated monitoring to uncover the present‐day eel distribution in Cyprus' inland freshwaters. These are subject to increasing pressures from water supply requirements and dam construction, as seen throughout the Mediterranean. We applied environmental DNA metabarcoding of water samples to determine A. anguilla distribution in key freshwater catchments. In addition, we present this alongside 10 years of electrofishing/netting data. Refuge traps were also deployed to establish the timing of glass eel recruitment. These outputs are used together, alongside knowledge of the overall fish community and barriers to connectivity, to provide eel conservation and policy insights. This study confirm the presence of A. anguilla in Cyprus' inland freshwaters, with recruitment occurring in March. Eel distribution is restricted to lower elevation areas, and is negatively associated with distance from coast and barriers to connectivity. Many barriers to connectivity are identified, though eels were detected in two reservoirs upstream of dams. The overall fish community varies between freshwater habitat types. Eels are much more widespread in Cyprus than previously thought, yet mostly restricted to lowland intermittent systems. These findings make a case to reconsider the requirement for eel management plans. Environmental DNA‐based data collected in 2020 indicate that "present‐day" eel distribution is representative of 10‐year survey trends. Suggesting that inland freshwaters may act as an unrealized refuge at A. anguilla's easternmost range. Conservation efforts in Mediterranean freshwaters should focus on improving connectivity, therefore enabling eels to access inland perennial refugia. Thus, mitigating the impact of climate change and the growing number of fragmented artificially intermittent river systems. [ABSTRACT FROM AUTHOR]

Color polymorphism can be maintained in natural populations by natural selection or sexual selection. In this study, we use two different approaches to test which of these evolutionary mechanisms may explain the presence of color polymorphism in the Cuban Limia (Limia vittata), an endemic livebearing fish from Cuba. First, we investigate the role of sexual selection using traditional binary choice tests looking at both female and male preferences relative to varying degrees of black spotting in stimulus mates. Second, we assess the role of natural selection by analyzing the frequency and geographic distribution of black‐spotted and nonspotted morphs of L. vittata in natural populations from Cuba. The frequency of black‐spotted morphs is significantly higher in brackish and saltwater environments compared with freshwater habitats, which could be related to higher predation pressure in coastal ecosystems compared with purely freshwater environments. Our results suggest that habitat variation is the most important factor in maintaining color polymorphism in L. vittata. Salinity levels could be indirectly responsible for maintaining different color morphs in this species, likely due to the regulatory effect of saline gradients on predation regimes. [ABSTRACT FROM AUTHOR]

The context and cause of adaptive radiations have been widely described and explored but why rapid evolutionary diversification does not occur in related evolutionary lineages has yet to be understood. The standard answer is that evolutionary diversification is provoked by ecological opportunity and that some lineages do not encounter the opportunity. Three‐spined sticklebacks on the Scottish island of North Uist show enormous diversification, which seems to be associated with the diversity of aquatic habitats. Sticklebacks on the neighboring island of South Uist have not been reported to show the same level of evolutionary diversity, despite levels of environmental variation that we might expect to be similar to North Uist. In this study, we compared patterns of morphological and environmental diversity on North and South Uist. Ancestral anadromous sticklebacks from both islands exhibited similar morphology including size and bony "armor." Resident sticklebacks showed significant variation in armor traits in relation to pH of water. However, North Uist sticklebacks exhibited greater diversity of morphological traits than South Uist and this was associated with greater diversity in pH of the waters of lochs on North Uist. Highly acidic and highly alkaline freshwater habitats are missing, or uncommon, on South Uist. Thus, pH appears to act as a causal factor driving the evolutionary diversification of stickleback in local adaptation in North and South Uist. This is consistent with diversification being more associated with ecological constraint than ecological opportunity. [ABSTRACT FROM AUTHOR]

Despite the ubiquitous nature of parasitism, how parasitism alters the outcome of host–species interactions such as competition, mutualism and predation remains unknown. Using a phylogenetically informed meta‐analysis of 154 studies, we examined how the mean and variance in the outcomes of species interactions differed between parasitized and non‐parasitized hosts. Overall, parasitism did not significantly affect the mean or variance of host–species interaction outcomes, nor did the shared evolutionary histories of hosts and parasites have an effect. Instead, there was considerable variation in outcomes, ranging from strongly detrimental to strongly beneficial for infected hosts. Trophically‐transmitted parasites increased the negative effects of predation, parasites increased and decreased the negative effects of interspecific competition for parasitized and non‐parasitized heterospecifics, respectively, and parasites had particularly strong negative effects on host species interactions in freshwater and marine habitats, yet were beneficial in terrestrial environments. Our results illuminate the diverse ways in which parasites modify critical linkages in ecological networks, implying that whether the cumulative effects of parasitism are considered detrimental depends not only on the interactions between hosts and their parasites but also on the many other interactions that hosts experience. [ABSTRACT FROM AUTHOR]

Neotropical freshwater habitats are particularly sensitive to degradation by human activity. Piscivorous semi‐aquatic freshwater megafauna inhabit both the terrestrial and aquatic mediums and thus may be good indicators of wetland habitat quality. However, the drivers of their space use at the terrestrial and aquatic landscape levels are not well understood. We studied the spatial behavior and habitat use of giant otters in Madre de Dios, Peru, inhabiting areas with variable levels of protection. We combined unmanned aerial vehicle (UAV) and satellite images to develop different terrestrial and water‐associated land cover variables. We tested the influence of these predictors on giant otter habitat use at multiple spatial scales, comparing used and available locations. Giant otters favored bank areas with dense forest canopy cover. In the aquatic medium, giant otters showed positive selection for open water and fallen logs and avoided floating vegetation. These findings may be explained by preference for optimal fish habitat to maximize foraging yield and bank areas that provide more cover from predators and higher quality denning locations. Variables developed from UAV images outperformed satellite‐derived variables. Despite recent signs of deforestation in lake banks in unprotected areas, spatial model predictions indicated that unprotected oxbow lakes did not differ in their habitat suitability from protected freshwater habitats. Management implications of our findings include identification of factors driving habitat suitability to guide policy and decisions regarding protection or restoration of oxbow lake ecosystems to support giant otter populations. In addition, we demonstrate that UAVs have value in complementing satellite‐derived images and providing a cost‐effective methodology to assess habitat quality for semi‐aquatic species at the land‐water interface. [ABSTRACT FROM AUTHOR]

N2‐fixing heterocytous cyanobacteria are considered to play a minor role in sustaining coastal microbial mat communities developing under normal marine to hypersaline conditions. Here, we investigated microbial mats growing under different salinities from freshwater mats of Giblin River (Tasmania) to metahaline and hypersaline mats of Shark Bay (Western Australia). Analyses of genetic (rRNA and mRNA) and biological markers (heterocyte glycolipids) revealed an unexpectedly large diversity of heterocytous cyanobacteria in all the studied microbial mat communities. It was observed that the taxonomic distribution as well as abundance of cyanobacteria is strongly affected by salinity. Low salinity favoured the presence of heterocytous cyanobacteria in freshwater mats, while mats thriving in higher salinities mainly supported the growth unicellular and filamentous non‐heterocytous genera. However, even though mRNA transcripts derived from heterocytous cyanobacteria were lower in Shark Bay (<6%) microbial mats, functional analyses revealed that these diazotrophs were transcribing a substantial proportion of the genes involved in biofilm formation and nitrogen fixation. Overall, our data reveal an unexpectedly high diversity of heterocytous cyanobacteria (e.g. Calothrix, Scytonema, Nodularia, Gloeotrichia, Stigonema, Fischerella and Chlorogloeopsis) that had yet to be described in metahaline and hypersaline microbial mats from Shark Bay and that they play a vital role in sustaining the ecosystem functioning of coastal‐marine microbial mat systems. [ABSTRACT FROM AUTHOR]

Nucleic acids released by organisms and isolated from environmental substrates are increasingly being used for molecular biomonitoring. While environmental DNA (eDNA) has received much attention, the potential of environmental RNA as a biomonitoring tool remains under‐explored. Several recent studies using paired DNA and RNA metabarcoding of bulk samples suggest that RNA might better reflect "metabolically active" parts of the community. However, such studies mainly capture organismal eDNA and eRNA. For larger eukaryotes, isolation of extra‐organismal RNA will be important, but viability needs to be examined in a field‐based setting. In this study we evaluate (a) whether extra‐organismal eRNA release from macroeukaryotes can be detected given its supposedly rapid degradation, and (b) if the same field collection methods for eDNA can be applied to eRNA. We collected eDNA and eRNA from water in lakes where fish community composition is well documented, enabling a comparison between the two nucleic acids in two different seasons with monitoring using conventional methods. We found that eRNA is released from macroeukaryotes and can be filtered from water and metabarcoded in a similar manner as eDNA to reliably provide species composition information. eRNA had a small but significantly greater true positive rate than eDNA, indicating that it correctly detects more species known to exist in the lakes. Given relatively small differences between the two molecules in describing fish community composition, we conclude that if eRNA provides significant advantages in terms of lability, it is a strong candidate to add to the suite of molecular monitoring tools. [ABSTRACT FROM AUTHOR]

Minnows of the genus Phoxinus are common and an often highly abundant fish species in Palearctic freshwater habitats. Phoxinus species have a complex evolutionary history, phylogenetic relationships are not well understood and there are a number of unresolved taxonomic problems. There are currently 23 different mitochondrial genetic lineages identified in the genus Phoxinus, 13 of which are recognized as valid species. The taxonomic status of these lineages requires resolution, including the degree to which they can interbreed. Suitable nuclear molecular markers for studies of population divergence and interbreeding between morphotypes and mitochondrial lineages are lacking for Phoxinus species. Therefore, the authors developed a set of microsatellite markers using genomic information from Phoxinus lumaireul and tested their suitability for this and two related species, Phoxinus krkae and Phoxinus marsilii. Out of 16 microsatellite candidate loci isolated, 12 were found to be in Hardy–Weinberg equilibrium when tested on two P. lumaireul senso lato populations. Seven loci amplified across the three species, enabling the study of intraspecific genetic diversity and population structure within P. marsilii and P. krkae. The markers were able to clearly resolve differences among the three tested species, including the recently described P. krkae, and are therefore suitable for the detection of introgression and hybridization among populations consisting of mixtures of two or more of P. lumaireul s. l., P. marsilii and P. krkae. [ABSTRACT FROM AUTHOR]

Aim: Biological invasions are a major threat to biodiversity in aquatic and terrestrial habitats. Insects represent an important group of species in freshwater and terrestrial habitats, and they constitute a large proportion of non‐native species. However, while many non‐native insects are known from terrestrial ecosystems, they appear to be less represented in freshwater habitats. Comparisons between freshwater and terrestrial habitats of invader richness relative to native species richness are scarce, which hinders syntheses of invasion processes. Here, we used data from three regions on different continents to determine whether non‐native insects are indeed under‐represented in freshwater compared with terrestrial assemblages. Location: Europe, North America, New Zealand. Methods: We compiled a comprehensive inventory of native and non‐native insect species established in freshwater and terrestrial habitats of the three study regions. We then contrasted the richness of non‐native and native species among freshwater and terrestrial insects for all insect orders in each region. Using binomial regression, we analysed the proportions of non‐native species in freshwater and terrestrial habitats. Marine insect species were excluded from our analysis, and insects in low‐salinity brackish water were considered as freshwater insects. Results: In most insect orders living in freshwater, non‐native species were under‐represented, while they were over‐represented in a number of terrestrial orders. This pattern occurred in purely aquatic orders and in orders with both freshwater and terrestrial species. Overall, the proportion of non‐native species was significantly lower in freshwater than in terrestrial species. Main conclusions: Despite the numerical and ecological importance of insects among all non‐native species, non‐native insect species are surprisingly rare in freshwater habitats. This is consistent across the three investigated regions. We review hypotheses concerning species traits and invasion pathways that are most likely to explain these patterns. Our findings contribute to a growing appreciation of drivers and impacts of biological invasions. [ABSTRACT FROM AUTHOR]