Bending the curve: Simple but massive conservation action leads to landscape-scale recovery of amphibians.

Success stories are rare in conservation science, hindered also by the research-implementation gap, where scientific insights rarely inform practice and practical implementation is rarely evaluated scientifically. Amphibian population declines, driven by multiple stressors, are emblematic of the freshwater biodiversity crisis. Habitat creation is a straightforward conservation action that has been shown to locally benefit amphibians, as well as other taxa, but does it benefit entire amphibian communities at large spatial scales? Here, we evaluate a landscape-scale pond-construction program by fitting dynamic occupancy models to 20 y of monitoring data for 12 pond-breeding amphibian species in the Swiss state Aargau, a densely populated area of the Swiss lowlands with intensive land use. After decades of population declines, the number of occupied ponds increased statewide for 10 out of 12 species, while one species remained stable and one species further declined between 1999 and 2019. Despite regional differences, in 77% of all 43 regional metapopulations, the colonization and subsequent occupation of new ponds stabilized (14%) or increased (63%) metapopulation size. Likely mechanisms include increased habitat availability, restoration of habitat dynamics, and increased connectivity between ponds. Colonization probabilities reflected species-specific preferences for characteristics of ponds and their surroundings, which provides evidence-based information for future pond construction targeting specific species. The relatively simple but landscape-scale and persistent conservation action of constructing hundreds of new ponds halted declines and stabilized or increased the state-wide population size of all but one species, despite ongoing pressures from other stressors in a human-dominated landscape.

Hydromorphological degradation modifies long-term macroinvertebrate responses to water quality and climate changes in lowland rivers.

Due to decades of persistent anthropogenic pressures, lowland rivers represent one of the most severely impaired habitats in Europe. Despite improved water quality, novel stressors, particularly climate change, are emerging with most lowland rivers suffering from past hydromorphological degradation. We aim to elucidate how such degradation alters the biological response in multiple-stressor environments, as this has rarely been considered in studies documenting long-term development of anthropogenically impacted rivers. Here, benthic macroinvertebrates, water quality and hydroclimatic variables were monitored over a period of two decades in nine of the largest Czech rivers. Detailed data on hydromorphological degradation allowed us to track distinct patterns in rivers with high and low levels of degradation. Temporal changes in environmental variables showed similar patterns in both site groups, characterised by reduced organic and nutrient pollution but increased hydroclimatic and salinity stress. 150 % increase in total abundance, especially in abundance and richness of sediment-dwelling and non-native taxa was found in both site groups. While the increase in abundance was due to improved water quality and rising water temperature, the longer duration of minimal flows had a negative effect on species richness, hampering species gain particularly at highly degraded sites. Our results provide novel evidence that degree of hydromorphological degradation modifies long-term macroinvertebrate responses to anthropogenic pressures. Less degraded sites displayed several favourable changes, such as 27 % increase in total and 23 % increase in potamal indicator richness, and stabilisation of the assemblages with few functional changes. In contrast, highly degraded sites experienced 9 % reduction in evenness, 235 % increase in proportion of non-native taxa and functional reorganisation, changes congruent with continuous deterioration. While overall water quality at studied sites has improved, consequences of climate change and high degree of hydromorphological degradation limit biotic recovery in multiple-stressor lowland rivers.

Microplastic exposure is associated with epigenomic effects in the model organism Pimephales promelas (fathead minnow).

Microplastics have evolutionary and ecological impacts across species, affecting organisms' development, reproduction, and behavior along with contributing to genotoxicity and stress. As plastic pollution is increasing and ubiquitous, gaining a better understanding of organismal responses to microplastics is necessary. Epigenetic processes such as DNA methylation are heritable forms of molecular regulation influenced by environmental conditions. Therefore, determining such epigenetic responses to microplastics will reveal potential chronic consequences of this environmental pollutant. We performed an experiment across two generations of fathead minnows (Pimephales promelas) to elucidate transgenerational epigenetic effects of microplastic exposure. We exposed the first generation of fish to four different treatments of microplastics: two concentrations of each of pre-consumer polyethylene (PE) and PE collected from Lake Ontario. We then raised the first filial generation with no microplastic exposure. We used enzymatic methylation sequencing on adult liver tissue and homogenized larvae to evaluate DNA methylation differences among treatments, sexes, and generations. Our findings show the origin of the plastic had a larger effect in female minnows whereas the effect of concentration was stronger in the males. We also observed transgenerational effects, highlighting a mechanism in which parents can pass on the effects of microplastic exposure to their offspring. Many of the genes found within differentially methylated regions in our analyses are known to interact with estrogenic chemicals associated with plastic and are related to metabolism. This study highlights the persistent and potentially serious impacts of microplastic pollution on gene regulation in freshwater systems.

A global agenda for advancing freshwater biodiversity research.

Global freshwater biodiversity is declining dramatically, and meeting the challenges of this crisis requires bold goals and the mobilisation of substantial resources. While the reasons are varied, investments in both research and conservation of freshwater biodiversity lag far behind those in the terrestrial and marine realms. Inspired by a global consultation, we identify 15 pressing priority needs, grouped into five research areas, in an effort to support informed stewardship of freshwater biodiversity. The proposed agenda aims to advance freshwater biodiversity research globally as a critical step in improving coordinated actions towards its sustainable management and conservation.

Prioritizing conservation in sub-Saharan African lakes based on freshwater biodiversity and algal bloom metrics.

As agricultural land use and climate change continue to pose increasing threats to biodiversity in sub-Saharan Africa, efforts are being made to identify areas where trade-offs between future agricultural development and terrestrial biodiversity conservation are expected to be greatest. However, little research so far has focused on freshwater biodiversity conservation in the context of agricultural development in sub-Saharan Africa. We aimed to identify lakes and lake areas where freshwater biodiversity is most likely to be affected by eutrophication and Harmful Algal Blooms (i.e., when algae multiply to the extent that they have toxic effects on people and freshwater fauna), some of the most important emerging threats to freshwater ecosystems worldwide, especially with the onset of climate change. Using novel remote-sensing techniques, we identified lakes that demonstrated high biodiversity and algal bloom levels. We calculated the richness of freshwater species and the normalized difference chlorophyll index (NDCI) to prioritize lakes in Ghana, Ethiopia, Zambia, and bordering countries, of high priority for conservation. We identified 169 priority lakes and lake areas for conservation, based on high levels of biodiversity exposed to potentially harmful algal blooms. Zambia had the most lakes identified as conservation priorities (76% of its small lakes and five 100-km2 areas in large lakes). Many of the conservation priority lakes and lake areas identified in this study were in transboundary watersheds; thus, collaborative water resource management and conservation at the watershed scale is needed. The use of remote-sensing tools to prioritize freshwater systems for conservation according to algal-bloom risk is vital in remote, undersampled world regions, especially given the increasing threat posed to freshwater biodiversity by rapidly expanding agriculture and climate change.

Priorización de la Conservación en los Lagos Sub-Saharianos con base en Medidas de Biodiversidad de Aguas Dulces y Floración de Algas Resumen Conforme el cambio climático y el uso de suelo para cultivos siguen representando amenazas crecientes para la biodiversidad en la región sub-sahariana de África, se están realizando esfuerzos para identificar las áreas en donde se espera que sucedan las mayores compensaciones entre el desarrollo agrícola venidero y la conservación de la biodiversidad terrestre. Sin embargo, pocas investigaciones se han centrado en la conservación de la biodiversidad de aguas dulces dentro del contexto del desarrollo agrícola en esta región de África. Nos enfocamos en localizar las áreas en donde sea más probable que la biodiversidad de aguas dulces se vea afectada por la eutrofización y las floraciones de algas (es decir, cuando las algas se multiplican a tal grado que tienen efectos tóxicos sobre las personas y la fauna de agua dulce), dos de las amenazas emergentes más importantes para los ecosistemas de agua dulce en todo el mundo debido al cambio climático. Mediante técnicas novedosas de teledetección identificamos los lagos que se traslapaban con áreas de gran biodiversidad y floraciones de algas. Calculamos la riqueza de especies de agua dulce y el índice de diferencia normalizada de clorofila (IDNC) para identificar los lagos de suma importancia para la conservación en Ghana, Etiopía, Zambia y sus países fronterizos. Identificamos 169 áreas prioritarias para la conservación con base en los niveles elevados de biodiversidad expuestos a las floraciones de algas potencialmente dañinas. Zambia tuvo la mayor cantidad de lagos identificados como prioridades de conservación (76% de sus lagos pequeños y cinco áreas de 100 km2 en los grandes lagos). Las amenazas para la biodiversidad de agua dulce estuvieron presentes a nivel de cuenca, con frecuencia con una extensión más allá de las fronteras políticas de un país; por lo tanto, se requiere que el manejo de recursos hídricos y la conservación sean esfuerzos colaborativos a nivel de cuenca. El uso de herramientas de teledetección para priorizar la conservación de los sistemas de agua dulce de acuerdo con el riesgo de floración de algas es vital en las regiones remotas y poco muestreadas del mundo, especialmente debido a la amenaza creciente que representan el cambio climático y la expansión agrícola para la biodiversidad de agua dulce.

Comparison of markers for the monitoring of freshwater benthic biodiversity through DNA metabarcoding.

Metabarcoding of bulk or environmental DNA has great potential for biomonitoring of freshwater environments. However, successful application of metabarcoding to biodiversity monitoring requires universal primers with high taxonomic coverage that amplify highly variable, short metabarcodes with high taxonomic resolution. Moreover, reliable and extensive reference databases are essential to match the outcome of metabarcoding analyses with available taxonomy and biomonitoring indices. Benthic invertebrates, particularly insects, are key taxa for freshwater bioassessment. Nevertheless, few studies have so far assessed markers for metabarcoding of freshwater macrobenthos. Here we combined in silico and laboratory analyses to test the performance of different markers amplifying regions in the 18S rDNA (Euka02), 16S rDNA (Inse01) and COI (BF1_BR2-COI) genes, and developed an extensive database of benthic macroinvertebrates of France and Europe, with a particular focus on key insect orders (Ephemeroptera, Plecoptera and Trichoptera). Analyses on 1,514 individuals representing different taxa of benthic macroinvertebrates showed very different amplification success across primer combinations. The Euka02 marker showed the highest universality, while the Inse01 marker showed excellent performance for the amplification of insects. BF1_BR2-COI showed the highest resolution, while the resolution of Euka02 was often limited. By combining our data with GenBank information, we developed a curated database including sequences representing 822 genera. The heterogeneous performance of the different primers highlights the complexity in identifying the best markers, and advocates for the integration of multiple metabarcodes for a more comprehensive and accurate understanding of ecological impacts on freshwater biodiversity.

The role of anthropogenic habitats in freshwater mussel conservation.

Anthropogenic freshwater habitats may provide undervalued prospects for long-term conservation as part of species conservation planning. This fundamental, but overlooked, issue requires attention considering the pace that humans have been altering natural freshwater ecosystems and the accelerated levels of biodiversity decline in recent decades. We compiled 709 records of freshwater mussels (Bivalvia, Unionida) inhabiting a broad variety of anthropogenic habitat types (from small ponds to large reservoirs and canals) and reviewed their importance as refuges for this faunal group. Most records came from Europe and North America, with a clear dominance of canals and reservoirs. The dataset covered 228 species, including 34 threatened species on the IUCN Red List. We discuss the conservation importance and provide guidance on how these anthropogenic habitats could be managed to provide optimal conservation value to freshwater mussels. This review also shows that some of these habitats may function as ecological traps owing to conflicting management practices or because they act as a sink for some populations. Therefore, anthropogenic habitats should not be seen as a panacea to resolve conservation problems. More information is necessary to better understand the trade-offs between human use and the conservation of freshwater mussels (and other biota) within anthropogenic habitats, given the low number of quantitative studies and the strong biogeographic knowledge bias that persists.

Multiple co-occurrent alien invaders constrain aquatic biodiversity in rivers.

A greater understanding and effective management of biological invasions is a priority for biodiversity conservation globally. Many freshwater ecosystems are experiencing the colonization and spread of multiple co-occurrent alien species. Here the implications of both the relative abundance and richness of alien invaders on aquatic macroinvertebrate taxonomic and functional richness, ecosystem quality, and functional redundancy are assessed using long-term data from rivers in England. Based on the most common aquatic invaders, results indicated that their richness, rather than abundance, was the most important factor negatively affecting aquatic macroinvertebrate biodiversity. However, the response of functional redundancy was negatively affected by invader abundance at the river basin scale. The response of communities varied as the number of invading taxa increased, with the most marked reductions following the colonization of the first few invaders. Results indicate that different facets of multiple biological invasions influence distinct aspects of aquatic biodiversity. Preventing the establishment of new invaders and limiting invader taxa richness within a community should therefore be a conservation priority. These findings will assist river scientists in understanding mechanisms driving changes in biodiversity and facilitate the testing of ecological theories while also ensuring environmental managers and regulators can prioritize conservation / management opportunities.

Is there enough water? How bearish and bullish outlooks are linked to decision maker perspectives on environmental flows.

Policies that mandate environmental flows (e-flows) can be powerful tools for freshwater conservation, but implementation of these policies faces many hurdles. To better understand these challenges, we explored two key questions: (1) What additional data are needed to implement e-flows? and (2) What are the major socio-political barriers to implementing e-flows? We surveyed water and natural resource decision makers in the semi-arid Red River basin, Texas-Oklahoma, USA, and used social network analysis to analyze their communication patterns. Most respondents agreed that e-flows can provide important benefits and identified the same data needs. However, respondents sharply in their beliefs on other issues, and a clustering analysis revealed two distinct groups of decision makers. One cluster of decision makers tended to be bearish, or pessimistic, and believed that: current flow conditions are not adequate, there are many serious socio-political barriers to implementation, water conflicts will likely increase in the future, and climate change is likely to exacerbate these issues. The other cluster of respondents was bullish, or optimistic: they foresaw fewer future water conflicts and fewer socio-political barriers to implementation. Despite these differences, both clusters largely identified the same data needs and barriers to e-flows implementation. Our social network analysis revealed that the frequency of communication between clusters was not significantly different than the frequency of communication within clusters. Overall, our results suggest that the different perspectives of decision-makers could complicate efforts to implement e-flows and proactively plan for climate change. However, there are opportunities for collaboration on addressing common data needs and barriers to implementation. Overall, our study provides a key socio-environmental perspective on e-flows implementation from a semi-arid and socio-politically complex river basin and contextualizes the many challenges facing e-flows implementation in river basins globally.

Freshwater fish diversity hotspots for conservation priorities in the Amazon Basin.

Conserving freshwater habitats and their biodiversity in the Amazon Basin is a growing challenge in the face of rapid anthropogenic changes. We used the most comprehensive fish-occurrence database available (2355 valid species; 21,248 sampling points) and 3 ecological criteria (irreplaceability, representativeness, and vulnerability) to identify biodiversity hotspots based on 6 conservation templates (3 proactive, 1 reactive, 1 representative, and 1 balanced) to provide a set of alternative planning solutions for freshwater fish protection in the Amazon Basin. We identified empirically for each template the 17% of sub-basins that should be conserved and performed a prioritization analysis by identifying current and future (2050) threats (i.e., degree of deforestation and habitat fragmentation by dams). Two of our 3 proactive templates had around 65% of their surface covered by protected areas; high levels of irreplaceability (60% of endemics) and representativeness (71% of the Amazonian fish fauna); and low current and future vulnerability. These 2 templates, then, seemed more robust for conservation prioritization. The future of the selected sub-basins in these 2 proactive templates is not immediately threatened by human activities, and these sub-basins host the largest part of Amazonian biodiversity. They could easily be conserved if no additional threats occur between now and 2050.

Puntos Calientes de Diversidad de Peces de Agua Dulce para las Prioridades de Conservación en la Cuenca del Amazonas Resumen Cada día, la conservación de los hábitats de agua dulce y su biodiversidad en la cuenca del Amazonas es un reto creciente de cara a los rápidos cambios antropogénicos. Usamos la base de datos de presencia de peces más completa que existe (2,355 especies válidas; 21,248 puntos de muestreo) y tres criterios ecológicos (carácter irremplazable, representatividad y vulnerabilidad) para identificar los puntos calientes de biodiversidad con base en seis patrones de conservación (tres proactivos, uno reactivo, uno representativo y uno balanceado) y así proporcionar un conjunto de soluciones alternativas para la planeación de la protección de peces de agua dulce en la cuenca del Amazonas. Identificamos para cada patrón de manera empírica el 17% de las subcuencas que deberían conservarse y realizamos un análisis de priorización identificando amenazas actuales y a futuro (2050) (es decir, grado de deforestación y fragmentación del hábitat causado por presas). Dos de nuestros tres patrones proactivos tuvieron alrededor del 65% de su superficie cubierta por áreas protegidas; niveles altos de carácter irremplazable (60% de especies endémicas) y de representatividad (71% de la fauna ictiológica del Amazonas); y una vulnerabilidad baja actual y a futuro. Entonces, estos dos patrones parecen estar más completos para la priorización de la conservación. El futuro de las subcuencas en estos dos patrones proactivos no está amenazado por las actividades humanas a corto plazo. Además, estas subcuencas albergan la mayor parte de la biodiversidad amazónica. Se podrían conservar fácilmente si ninguna amenaza adicional sucede entre ahora y el 2050.

Rainforest metropolis casts 1,000-km defaunation shadow.

Tropical rainforest regions are urbanizing rapidly, yet the role of emerging metropolises in driving wildlife overharvesting in forests and inland waters is unknown. We present evidence of a large defaunation shadow around a rainforest metropolis. Using interviews with 392 rural fishers, we show that fishing has severely depleted a large-bodied keystone fish species, tambaqui (Colossoma macropomum), with an impact extending over 1,000 km from the rainforest city of Manaus (population 2.1 million). There was strong evidence of defaunation within this area, including a 50% reduction in body size and catch rate (catch per unit effort). Our findings link these declines to city-based boats that provide rural fishers with reliable access to fish buyers and ice and likely impact rural fisher livelihoods and flooded forest biodiversity. This empirical evidence that urban markets can defaunate deep into rainforest wilderness has implications for other urbanizing socioecological systems.

Climate warming reduces fish production and benthic habitat in Lake Tanganyika, one of the most biodiverse freshwater ecosystems.

Warming climates are rapidly transforming lake ecosystems worldwide, but the breadth of changes in tropical lakes is poorly documented. Sustainable management of freshwater fisheries and biodiversity requires accounting for historical and ongoing stressors such as climate change and harvest intensity. This is problematic in tropical Africa, where records of ecosystem change are limited and local populations rely heavily on lakes for nutrition. Here, using a ∼1,500-y paleoecological record, we show that declines in fishery species and endemic molluscs began well before commercial fishing in Lake Tanganyika, Africa's deepest and oldest lake. Paleoclimate and instrumental records demonstrate sustained warming in this lake during the last ∼150 y, which affects biota by strengthening and shallowing stratification of the water column. Reductions in lake mixing have depressed algal production and shrunk the oxygenated benthic habitat by 38% in our study areas, yielding fish and mollusc declines. Late-20th century fish fossil abundances at two of three sites were lower than at any other time in the last millennium and fell in concert with reduced diatom abundance and warming water. A negative correlation between lake temperature and fish and mollusc fossils over the last ∼500 y indicates that climate warming and intensifying stratification have almost certainly reduced potential fishery production, helping to explain ongoing declines in fish catches. Long-term declines of both benthic and pelagic species underscore the urgency of strategic efforts to sustain Lake Tanganyika's extraordinary biodiversity and ecosystem services.

Synthesizing the role of epigenetics in the response and adaptation of species to climate change in freshwater ecosystems.

Freshwater ecosystems are amongst the most threatened ecosystems on Earth. Currently, climate change is one of the most important drivers of freshwater transformation and its effects include changes in the composition, biodiversity and functioning of freshwater ecosystems. Understanding the capacity of freshwater species to tolerate the environmental fluctuations induced by climate change is critical to the development of effective conservation strategies. In the last few years, epigenetic mechanisms were increasingly put forward in this context because of their pivotal role in gene-environment interactions. In addition, the evolutionary role of epigenetically inherited phenotypes is a relatively recent but promising field. Here, we examine and synthesize the impacts of climate change on freshwater ecosystems, exploring the potential role of epigenetic mechanisms in both short- and long-term adaptation of species. Following this wrapping-up of current evidence, we particularly focused on bringing together the most promising future research avenues towards a better understanding of the effects of climate change on freshwater biodiversity, specifically highlighting potential molecular targets and the most suitable freshwater species for future epigenetic studies in this context.

Assessing threats of non-native species to native freshwater biodiversity: Conservation priorities for the United States.

Non-native species pose one of the greatest threats to native biodiversity, and can have severe negative impacts in freshwater ecosystems. Identifying regions of spatial overlap between high freshwater biodiversity and high invasion pressure may thus better inform the prioritization of freshwater conservation efforts. We employ geospatial analysis of species distribution data to investigate the potential threat of non-native species to aquatic animal taxa across the continental United States. We mapped non-native aquatic plant and animal species richness and cumulative invasion pressure to estimate overall negative impact associated with species introductions. These distributions were compared to distributions of native aquatic animal taxa derived from the International Union for the Conservation of Nature (IUCN) database. To identify hotspots of native biodiversity we mapped total species richness, number of threatened and endangered species, and a community index of species rarity calculated at the watershed scale. An overall priority index allowed identification of watersheds experiencing high pressure from non-native species and also exhibiting high native biodiversity conservation value. While priority regions are roughly consistent with previously reported prioritization maps for the US, we also recognize novel priority areas characterized by moderate-to-high native diversity but extremely high invasion pressure. We further compared priority areas with existing conservation protections as well as projected future threats associated with land use change. Our findings suggest that many regions of elevated freshwater biodiversity value are compromised by high invasion pressure, and are poorly safeguarded by existing conservation mechanisms and are likely to experience significant additional stresses in the future.

Vulnerability of European freshwater catchments to climate change.

Climate change is expected to exacerbate the current threats to freshwater ecosystems, yet multifaceted studies on the potential impacts of climate change on freshwater biodiversity at scales that inform management planning are lacking. The aim of this study was to fill this void through the development of a novel framework for assessing climate change vulnerability tailored to freshwater ecosystems. The three dimensions of climate change vulnerability are as follows: (i) exposure to climate change, (ii) sensitivity to altered environmental conditions and (iii) resilience potential. Our vulnerability framework includes 1685 freshwater species of plants, fishes, molluscs, odonates, amphibians, crayfish and turtles alongside key features within and between catchments, such as topography and connectivity. Several methodologies were used to combine these dimensions across a variety of future climate change models and scenarios. The resulting indices were overlaid to assess the vulnerability of European freshwater ecosystems at the catchment scale (18 783 catchments). The Balkan Lakes Ohrid and Prespa and Mediterranean islands emerge as most vulnerable to climate change. For the 2030s, we showed a consensus among the applied methods whereby up to 573 lake and river catchments are highly vulnerable to climate change. The anthropogenic disruption of hydrological habitat connectivity by dams is the major factor reducing climate change resilience. A gap analysis demonstrated that the current European protected area network covers <25% of the most vulnerable catchments. Practical steps need to be taken to ensure the persistence of freshwater biodiversity under climate change. Priority should be placed on enhancing stakeholder cooperation at the major basin scale towards preventing further degradation of freshwater ecosystems and maintaining connectivity among catchments. The catchments identified as most vulnerable to climate change provide preliminary targets for development of climate change conservation management and mitigation strategies.

The imperiled fish fauna in the Nicaragua Canal zone.

Large-scale infrastructure projects commonly have large effects on the environment. The planned construction of the Nicaragua Canal will irreversibly alter the aquatic environment of Nicaragua in many ways. Two distinct drainage basins (San Juan and Punta Gorda) will be connected and numerous ecosystems will be altered. Considering the project's far-reaching environmental effects, too few studies on biodiversity have been performed to date. This limits provision of robust environmental impact assessments. We explored the geographic distribution of taxonomic and genetic diversity of freshwater fish species (Poecilia spp., Amatitlania siquia, Hypsophrys nematopus, Brycon guatemalensis, and Roeboides bouchellei) across the Nicaragua Canal zone. We collected population samples in affected areas (San Juan, Punta Gorda, and Escondido drainage basins), investigated species composition of 2 drainage basins and performed genetic analyses (genetic diversity, analysis of molecular variance) based on mitochondrial cytb. Freshwater fish faunas differed substantially between drainage basins (Jaccard similarity = 0.33). Most populations from distinct drainage basins were genetically differentiated. Removing the geographic barrier between these basins will promote biotic homogenization and the loss of unique genetic diversity. We found species in areas where they were not known to exist, including an undescribed, highly distinct clade of live bearing fish (Poecilia). Our results indicate that the Nicaragua Canal likely will have strong impacts on Nicaragua's freshwater biodiversity. However, knowledge about the extent of these impacts is lacking, which highlights the need for more thorough investigations before the environment is altered irreversibly.

Freshwater ecosystems and aquatic insects: a paradox in biological invasions.

Biological invasions have increased significantly in response to global change and constitute one of the major causes of biodiversity loss. Insects make up a large fraction of invasive species, in general, and freshwaters are among the most invaded ecosystems on our planet. However, even though aquatic insects dominate most inland waters, have unparalleled taxonomic diversity and occupy nearly all trophic niches, there are almost no invasive insects in freshwaters. We present some hypotheses regarding why aquatic insects are not common among aquatic invasive organisms, suggesting that it may be the result of a suite of biological, ecological and anthropogenic factors. Such specific knowledge introduces a paradox in the current scientific discussion on invasive species; therefore, a more in-depth understanding could be an invaluable aid to disentangling how and why biological invasions occur.

Threats and opportunities for freshwater conservation under future land use change scenarios in the United States.

Freshwater ecosystems provide vital resources for humans and support high levels of biodiversity, yet are severely threatened throughout the world. The expansion of human land uses, such as urban and crop cover, typically degrades water quality and reduces freshwater biodiversity, thereby jeopardizing both biodiversity and ecosystem services. Identifying and mitigating future threats to freshwater ecosystems requires forecasting where land use changes are most likely. Our goal was to evaluate the potential consequences of future land use on freshwater ecosystems in the coterminous United States by comparing alternative scenarios of land use change (2001-2051) with current patterns of freshwater biodiversity and water quality risk. Using an econometric model, each of our land use scenarios projected greater changes in watersheds of the eastern half of the country, where freshwater ecosystems already experience higher stress from human activities. Future urban expansion emerged as a major threat in regions with high freshwater biodiversity (e.g., the Southeast) or severe water quality problems (e.g., the Midwest). Our scenarios reflecting environmentally oriented policies had some positive effects. Subsidizing afforestation for carbon sequestration reduced crop cover and increased natural vegetation in areas that are currently stressed by low water quality, while discouraging urban sprawl diminished urban expansion in areas of high biodiversity. On the other hand, we found that increases in crop commodity prices could lead to increased agricultural threats in areas of high freshwater biodiversity. Our analyses illustrate the potential for policy changes and market factors to influence future land use trends in certain regions of the country, with important consequences for freshwater ecosystems. Successful conservation of aquatic biodiversity and ecosystem services in the United States into the future will require attending to the potential threats and opportunities arising from policies and market changes affecting land use.

Surviving global change: a review of the impacts of drought and dewatering on freshwater mussels.

The increase in the frequency and intensity of droughts and heatwaves caused by climate change poses a major threat to biodiversity. In aquatic systems, sedentary species such as freshwater mussels are generally considered more vulnerable to changes in habitat conditions than mobile species such as fish. As mussels provide important ecosystem services, understanding the impacts of drought on freshwater mussels is of particular importance for the management of overall functioning of aquatic ecosystems. We used a comprehensive literature search to provide a systematic overview of direct and indirect effects of drought on freshwater mussels (Bivalvia: Unionida) and an evaluation of mitigation strategies. We found that drought studies were concentrated mostly in the USA, with a focus on the Unionidae family. Topics ranged from the physiological effects of high temperatures, emersion, and hypoxia/anoxia to behavioural and reproductive consequences of drought and the implications for biotic interactions and ecosystem services. Studies spanned all levels of biological organization, from individual responses to population- and community-level impacts and ecosystem-wide effects. We identified several knowledge gaps, including a paucity of trait-based evaluation of drought consequences, limited understanding of thermal and desiccation tolerance at the species level, and the synergistic effects of multiple drought stressors on mussels. Although we found many studies provided suggestions concerning management of populations, habitat conditions, and anthropogenic water use, a systematic approach and testing of recommended mitigation strategies is largely lacking, creating challenges for managers aiming to conserve freshwater mussel communities and populations in light of climate change.

Multi-gene phylogeny of the primary freshwater crab genus Ptychophallus Smalley, 1964 (Pseudothelphusidae: Ptychophallinae) from the Neotropical region.

The diversity of primary freshwater crabs of Central America is underestimated and poorly known, specially when considering both Atlantic and Pacific drainages distribution. Among the family Pseudothelphusidae Ortmann, 1893, the genus Ptychophallus Smalley, 1964 was recently revised using morphological data and encompassing 14 valid species, which are distributed exclusively in Costa Rica and Panama. Despite the informative scenario constructed with this previous study, some uncertainties remained such as those related to the populations distributed along different drainages and the lack of complete information regarding the phylogenetic relationships among the species that belong to this genus. Our phylogenetic reconstruction based on multigenes revealed four lineages. Ptychophallus costaricensis, P. colombianus, P. lavallensis, P. montanus, and P. tumimanus are well-established species, while P. paraxanthusi, P. exilipes and P. tristani were recovered as non-monophyletic in some relationships. Ptychophallus tristani and P. paraxanthusi were determined to be close relatives one with other, but with some representatives showing no clear correspondence and positioning in the molecular phylogeny, which raised doubts about the validity as separate species and/or the accuracy of identifications for some GenBank sequences. Ptychophallus tumimanus and P. montanus are morphologically very similar, but they are positioned in distinct clades. The genetic results confirmed a previous proposal that P. barbillaensis is a junior synonym of P. uncinatus, and P. bilobatus is closely related to P. uncinatus. The findings revealed the presence of one peculiar lineage with one species from Costa Rica compound by the resurrected P. campylus and another species from Costa Rica, originally identified as "P. cf. exilipes"; its morphology, however, did not match with any other analyzed species, which requires further analysis. Finally, possible misidentification in some sequences deposited in the GenBank were detected and should be reviewed. The reconstructed molecular phylogeny for the genus that inhabits both Atlantic and Pacific drainages of Central America provides a better understanding of the knowledge on the evolution of freshwater crabs and represents key information that will serve as baseline for further taxonomic studies on the cryptic biodiversity of this group.