Stream Assemblages Research Articles

Comparative analysis of habitat structure and macroinvertebrate assemblages in headwater streams of Odzi sub-catchment, Chimanimani District, Zimbabwe, post Cyclone Idai-induced flooding

Flooding results in short and long-term modifications of aquatic ecosystem structure and biodiversity. Cyclone Idai, which ravaged through Zimbabwe in 2019, had devastating consequences on aquatic ecosystems. However, the extent of habitat modification and consequent biodiversity shifts are unknown. This study focuses on the comparative analysis of (i) habitat structure and (ii) macroinvertebrate assemblages in headwater streams of the Odzi sub-catchment, Chimanimani District, Zimbabwe, specifically examining the conditions post-Cyclone Idai-induced flooding. Field sampling was conducted in the dry season (September−November) 2019 and wet season (January−March) 2020. Headwater streams of the Murare (first order), Umvumvumvu (first and second order) and Nyanyadzi (first and second order) rivers were sampled. Habitat assessment was done following the Benthic Macroinvertebrate Monitoring Protocol Implementation Plan. Selected water variables were measured using appropriate probes. Macroinvertebrate assemblage data were collected using the South African Scoring System (SASS 5) protocol. Spatiotemporal variations in water quality, habitat structure and macroinvertebrate metrics were assessed using two-way ANOVA, ANOSIM and SIMPER. Significant spatiotemporal heterogeneity (p < 0.05) was detected in temperature, turbidity, conductivity and total dissolved solids, velocity and depth regimes, channel flow status, sediment deposition, channel alteration and frequency of riffles for the three rivers. Habitat quality ascending hierarchical order was: Umvumvumvu > Murare > Nyanyadzi after Cyclone Idai induced flooding. The highest macroinvertebrate composition diversity was detected in Murare River, the least flood-affected stream. The largest dissimilarity (ANOSIM, 75.3%) was between the Umvumvumvu and Nyanyadzi rivers. Macroinvertebrate community structure differed significantly because of species uniqueness and heterogenous tolerance to changes in environmental conditions after flooding. Flooding intensity and duration induces dissimilar environmental tolerances and persistent macroinvertebrates communities in lotic systems across local catchment scales. Long-term assessment of water quality impairment, resilient functional feeder groups and rifflescale physical habitat structure are imperative for optimised micro-scale conservation of macroinvertebrates in headwater streams prone to flash flooding.

Habitat Diversity Mitigates the Impacts of Human Pressure on Stream Biodiversity.

Recent decades have witnessed substantial changes in freshwater biodiversity worldwide. Although research has shown that freshwater biodiversity can be shaped by changes in habitat diversity and human-induced pressure, the potentials for interaction between these drivers and freshwater biodiversity at large spatial extents remain unclear. To address these issues, we employed a spatially extensive multitrophic fish and insect database from 3323 stream sites across the United States, to investigate the ability of habitat diversity to modulate the effect of human pressure on the richness and abundance of fish and insects. We found evidence that high levels of habitat diversity were associated with increased richness and abundance of fish and insects (including whole-assemblage and individual trophic guilds). We also show that the effects of human pressure on the richness and abundance of fish and insects tend to become positive at high levels of habitat diversity. Where habitat diversity is low, human pressure strongly reduces insect richness and abundance, whereas these reductions are attenuated at high levels of habitat diversity. Structural equation modeling revealed that human pressure reduced habitat diversity, indirectly negatively affecting the richness and abundance of fish and insects. These findings illustrate that, in addition to promoting greater fish and insect biodiversity, habitat diversity may mitigate the deleterious effects of human pressures on these two stream assemblages. Overall, our study suggests that maintaining high levels of habitat diversity is a useful way to protect freshwater biodiversity from ongoing increases in human pressure. However, if human pressures continue to increase, this will reduce habitat diversity, further threatening stream assemblages.

Macroinvertebrate, algal and diatom assemblages respond differently to both drying and wetting transitions in non‐perennial streams

Abstract Biological assemblages in streams are influenced by hydrological dynamics, particularly in non‐perennial systems. Although there has been increasing attention on how drying impacts stream organisms, few studies have investigated how specific characteristics of drying and subsequent wetting transitions influence biotic responses via resistance and resilience traits. Here, we characterized how hydrologic metrics, including those quantifying drying and wetting transitions as well as dry and wet phases, alter diversity and composition of three aquatic assemblages in non‐perennial streams in southern California: benthic macroinvertebrates, soft‐bodied algae and diatoms. We found that flow duration prior to sampling was correlated with variation in macroinvertebrate and soft‐bodied algal assemblage composition. The composition and richness of diatom assemblages, however, were predominantly influenced by the drying start date prior to sampling. Contrary to other studies, the duration of the dry phase prior to sampling did not influence the composition or richness of any assemblage. Although our study was conducted within a region in which each assemblage experienced comparable environmental conditions, we found no single hydrologic metric that influenced all assemblages in the same way. The hot‐summer Mediterranean climate of southern California likely acts as a strong environmental filter, with taxa in this region relying on resistance and resilience adaptations to survive and recolonize non‐perennial streams following wetting. The different responses of algal and diatom assemblages to hydrologic metrics suggest greater resilience to drying and wetting events, particularly for primary producers. As drying and wetting patterns continue to change, understanding biodiversity responses to hydrologic metrics could inform management actions that enhance the ecological resilience of communities in non‐perennial streams. In particular, the creation and enhancement of flow regimes in which natural timing and duration of dry and wet phases sustain refuges that support community persistence in a changing environment.

Diatom assemblages in glacial-fed streams of Italian Western Alps

ABSTRACT The rate of glacier retreat has recently increased, with changes in the glacier discharge, river flow and water characteristics, creating specific environmental conditions for highly specialized organisms. We here investigated diatom communities in glacier-fed rivers of the Valle d’Aosta region (NW-Italy), analyzing data collected between 2010 and 2019 for the WFD monitoring programs. We present a complete checklist of the species inhabiting this region, many of which are classified as endangered in the diatom Red List. We found significant differences between sites with different catchment glacier cover (CGC), in terms of taxonomic composition, ecological guilds and abundance of Red List taxa. In particular, we observed a significant increase in species richness with the decrease in CGC, as well as significant differences in terms of taxonomic composition. We highlighted the role of Achnanthidium lineare as an indicator species for streams with the highest glacial influence, together with Hannaea arcus, Eucocconeis laevis and other oligotrophic low profile species that are well adapted to physical stress induced by glacier runoff. On the other hand, streams with lower glacial influence were characterized by motile species mostly belonging to the genera Navicula and Nitzschia, due to the nutrient increase. Didymosphenia geminata was recorded in streams with marginal glacier cover; recently observed blooms indicate that conditions may become increasingly favorable for the spread of this species in Alpine environments, as glaciers retreat. The abundance of Red List diatoms increased significantly with increasing glacier cover suggesting that glacier-fed rivers are niches for the conservation of diatom biodiversity.

Odonata in the brazilian Cerrado: Influence of environmental and spatial factors on dragonfly and damselfly assemblages

Environmental and spatial variables can act as filters in species distribution, thereby structuring biological communities. Our study aims to analyze the effects of environmental and spatial factors on the structuring of Odonata assemblages in Cerrado. Testing the hypotheses: (1) the structuring of Odonata larvae and adult assemblages is more influenced by the environment than by space; and (2) the structuring of larvae and adult assemblages of the suborder Anisoptera is more influenced by the environment, while Zygoptera is more influenced by space. We measured physicochemical variables (dissolved oxygen, pH, conductivity and temperature) and Habitat Integrity Index. Data analysis involved the coverage-based rarefaction and extrapolation method, Partial Redundancy Analysis (RDAp), and Principal Coordinates of Neighbor Matrices. Thirteen streams were sampled, collecting 1204 specimens. The sampling effort for larvae showed an efficiency of 98 %, and for adults, 85 %. According to RDAp, the composition for larvae was explained solely by environmental factors, while for adults, there was an explanation by the environment for Anisoptera and by both environmental and spatial factors for the order and Zygoptera. The results highlight the joint influence of environmental and spatial factors on the configuration of adult and larval Odonata assemblages in Cerrado streams. A variety of responses, each corresponding to the specific object of analysis, is evident, driven by divergent eco-physiological characteristics among suborders. These nuances reflect the inherent complexity of the ecology of these aquatic insects, emphasizing the importance of considering both environmental and spatial factors when investigating the dynamics of Odonata communities at different developmental stages.

Weak congruence between biological assemblages of streams and their relationship with the environmental gradient in the Cerrado–Amazon transition area, Brazil

Weak congruence between biological assemblages of streams and their relationship with the environmental gradient in the Cerrado–Amazon transition area, Brazil

The role of the environment and connectivity on multiple facets of local fish diversity in tropical headwater streams

Abstract The identification of multiple facets of biodiversity (e.g., phylogenetic and functional) can help to understand how evolutionary and ecological mechanisms shape the assembly of biological communities. Here, we employed multiple regressions and variance partitions to investigate the effects of environmental conditions, connectivity and space on aspects of the functional and phylogenetic facets of fish fauna in tropical headwater streams of the Xingu River basin, in Eastern Amazonia. We found that the functional and phylogenetic diversities of fish communities are related to local environmental conditions and stream connectivity in the drainage network, with marked differences occurring between the rainy and dry periods. Furthermore, we discovered that functional uniqueness was influenced mainly by environmental factors, whereas phylogenetic uniqueness had a more complex relationship with the influence of local environmental factors and connectivity. Our findings indicate that the fish assemblages of small headwater streams of the Xingu River basin share a close phylogenetic history. This is probably because of the climatic and environmental stability experienced by Amazonian ichthyofauna over evolutionary time. Our findings emphasise the role of niche‐based processes in shaping the unique functional composition of fish assemblages in headwater streams, and highlight the importance of environmental heterogeneity in maintaining the ecological integrity of these freshwater ecosystems.

Effects of cattle intrusion on environmental conditions and fish assemblages of temperate neotropical prairie streams

Effects of cattle intrusion on environmental conditions and fish assemblages of temperate neotropical prairie streams

Fish beta diversity associated with hydrologic and anthropogenic disturbance gradients in contrasting stream flow regimes

Understanding the role of hydrologic variation in structuring aquatic communities is crucial for successful conservation and sustainable management of native freshwater biodiversity. Partitioning beta diversity into the additive components of spatial turnover and nestedness can provide insight into the forces driving variability in fish assemblages across stream flow regimes. We examined stream fish beta diversity across hydrologic and anthropogenic disturbance gradients using long-term (1916–2016) site occurrence records (n = 17,375) encompassing 252 species. We assessed total beta diversity (Sørensen dissimilarity), spatial turnover, and nestedness of fish assemblages in contrasting stream flow regimes across a gradient of decreasing flow stability: groundwater stable (n = 77), groundwater (n = 67), groundwater flashy (n = 175), perennial runoff (n = 141), runoff flashy (n = 255), and intermittent (n = 63) streams. Differences in total beta diversity among the stream flow regimes were driven predominantly (>86 %) by spatial turnover (i.e. species replacement) as opposed to nestedness (i.e. species loss or gain). Total fish beta diversity and spatial turnover were highest in streams with intermediate flow stability (groundwater flashy), while more flow-stable streams (groundwater stable and groundwater) had lower turnover and higher nestedness. Species turnover was also strongly associated with seasonal variation in hydrology across all flow regimes, but these relationships were most evident for assemblages in intermittent streams. Distance-based statistical comparisons showed significant correlations between beta diversity and anthropogenic disturbance variables, including dam density, dam storage volume and water withdrawals in catchments of groundwater stable streams, while hydrologic variables were more strongly correlated with beta diversity in streams with runoff-dominated and flashy flow regimes. The high spatial turnover of species implies that fish conservation actions would benefit from watershed-focused approaches targeting multiple streams with wide spatial distribution, as opposed to simply focusing on preserving sites with the greatest number of species.

Near-natural streams: Spatial factors are key in shaping multiple facets of zooplankton α and β diversity

In near-natural basins, zooplankton are key hubs for maintaining aquatic food webs and organic matter cycles. However, the spatial patterns and drivers of zooplankton in streams are poorly understood. This study registered 165 species of zooplankton from 147 sampling sites (Protozoa, Rotifers, Cladocera and Copepods), integrating multiple dimensions (i.e., taxonomic, functional, and phylogenetic) and components (i.e., total, turnover, and nestedness) of α and β diversity. This study aims to reveal spatial patterns, mechanisms, correlations, and relative contribution of abiotic factors (i.e., local environment, geo-climatic, land use, and spatial factors) through spatial interpolation (ordinary kriging), mantel test, and variance partitioning analysis (VPA). The study found that α diversity is concentrated in the north, while β diversity is more in the west, which may be affected by typical habitat, hydrological dynamics and underlying mechanisms. Taxonomic and phylogenetic β diversity is dominated by turnover, and metacommunity heterogeneity is the result of substitution of species and phylogeny along environmental spatial gradients. Taxonomic and phylogenetic β diversity were strongly correlated (r from 0.91 to 0.95), mainly explained by historical/spatial isolation processes, community composition, generation time, and reproductive characteristics, and this correlation provides surrogate information for freshwater conservation priorities. In addition, spatial factors affect functional and phylogenetic α diversity (26%, 28%), and environmental filtering and spatial processes combine to drive taxonomic α diversity (10%) and phylogenetic β diversity (11%). Studies suggest that spatial factors are key to controlling the community structure of zooplankton assemblages in near-natural streams, and that the relative role of local environments may depend on the dispersal capacity of species. In terms of diversity conservation, sites with high variation in uniqueness should be protected (i) with a focus on the western part of the thousand islands lake catchment and (ii) increasing effective dispersal between communities to facilitate genetic and food chain transmission.

Quantification of large-spatial scale and in-stream factors affecting the structure of benthic macroinvertebrate communities in mountain streams

Habitat diversity plays a crucial role in shaping the structure and distribution of benthic macroinvertebrate communities. However, few studies have investigated the concurrent effects of such drivers operating at different spatial scales in mountain streams. Here, we assessed which environmental factors at different spatial scales, related to stream/river type and substrate, influence the diversity of benthic macroinvertebrate assemblages in mountain streams and rivers. Within the framework of the aquatic investigations of the Biodiversity Monitoring South Tyrol (BMS) – a newly-established, regional-based, long-term biodiversity monitoring program – benthic macroinvertebrates and a set of environmental factors describing water quality, stream/river hydromorphology and in-stream habitat characteristics were collected and analysed. The variation in total density, taxonomic richness, Shannon evenness and % Ephemeroptera–Plecoptera–Trichoptera taxa of stream benthic macroinvertebrates was assessed at multi-scale habitat levels, in 48 sampling sites across the mountainous region of the Autonomous Province of Bolzano/Bozen (Italy). The effects of stream/river type, substrates and different environmental factors on community composition of benthic macroinvertebrates were quantified, using a stepfoward Redundancy Analysis (RDA) and generalized additive models (GAMs). In addition, we performed an Indicator Value analysis to detect taxa that were significantly associated with a specific substrate and/or stream/river type. Overall, we observed significant differences in benthic biological metrics among both stream/river and substrate types. We also found at least one indicator taxa for each stream/river type, with environmental factors acting at reach and large-spatial scale – temperature, stream channel stability, elevation – being the key drivers in shaping macroinvertebrate distribution patterns in the analysed mountain rivers. While significant differences in macroinvertebrate community structures were found among substrates, the influence of stream/river type conditions was particularly evident. Apart from ranking environmental variables worth including in a long-term aquatic biodiversity monitoring program in mountain areas, our study provides a baseline for practical applications. For instance, depending on the desired outcome of habitat heterogeneity restoration, it can suggest the optimal scale (landscape vs. reach vs. patch) for prioritizing in-field interventions.

Autecology of the extant ostracod fauna of Lake Ohrid and adjacent waters - a key to paleoenvironmental reconstruction

Understanding the ecology of bioindicators such as ostracods is essential in order to reconstruct past environmental and climate change from analysis of fossil assemblages preserved in lake sediment cores. Knowledge of the ecology of ancient Lake Ohrid’s ostracod fauna is very limited and open to debate. In advance of the Ohrid ICDP-Drilling project, which has potential to generate high-resolution long-term paleoenvironmental data of global importance in paleoclimate research, we sampled Lake Ohrid and a wide range of habitat types in its surroundings to assess 1) the composition of ostracod assemblages in lakes, springs, streams, and short-lived seasonal water bodies, 2) the geographical distribution of ostracods, and 3) the ecological characteristics of individual ostracod species. In total, 40 species were collected alive, and seven species were preserved as valves and empty carapaces. Of the 40 ostracod species, twelve were endemic to Lake Ohrid. The most common genus in the lake was Candona, represented by 13 living species, followed by Paralimnocythere, represented by five living species. The most frequent species was Cypria obliqua. Species with distinct distributions included Heterocypris incongruens, Candonopsis kingsleii, and Cypria lacustris. The most common species in shallow, flooded areas was H. incongruens, and the most prominent species in ditches was C. kingsleii. C. lacustris was widely distributed in channels, springs, lakes, and rivers. Statistical analyses were performed on a “Lake Ohrid” dataset, comprising the subset of samples from Lake Ohrid alone, and an “entire” dataset comprising all samples collected. The unweighted pair group mean average (UPGMA) clustering was mainly controlled by species-specific depth preferences. Canonical Correspondence Analysis (CCA) with forward selection identified water depth, water temperature, and pH as variables that best explained the ostracod distribution in Lake Ohrid. The lack of significance of conductivity and dissolved oxygen in CCA of Ohrid data highlight the uniformity across the lake of the well-mixed waters. In the entire area, CCA revealed that ostracod distribution was best explained by water depth, salinity, conductivity, pH, and dissolved oxygen. Salinity was probably selected by CCA due to the presence of Eucypris virens and Bradleystrandesia reticulata in short-lived seasonal water bodies. Water depth is an important, although indirect, influence on ostracod species distribution, which is probably associated with other factors such as sediment texture and food supply. Some species appeared to be indicators for multiple environmental variables, such as lake level and water temperature.

Water quality, habitat, and fish assemblage relationships in middle-order agriculture and forest streams of the Mississippi Alluvial Plain

BackgroundAgriculture has greatly influenced water quality, habitats, and fish assemblages in streams of the Mississippi Alluvial Plain (MAP) ecoregion. However, MAP streams have historically been understudied compared to streams in other agricultural regions of the USA. In this study, water quality, habitat, and fish assemblage composition were assessed seasonally (spring, summer, and fall) in eight representative MAP streams located across three U.S. states. The study design included four streams containing highly agricultural watersheds (herein termed “agriculture” streams) and four streams containing mostly forested watersheds (herein termed “forest” streams), which were intended to represent reference conditions for MAP streams.ResultsIn general, forest streams contained significantly better instream and riparian habitats than agriculture streams (P = 0.010–0.040) whereas agriculture streams contained significantly greater levels of primary nutrients (P < 0.001–0.010). Differences between agriculture and forest streams with respect to other physical and chemical variables were intermittent and season dependent. Fish assemblages in agriculture and forest streams were structured primarily along an environmental gradient reflecting instream habitat conditions, water nutrient concentrations, and benthic chlorophyll-a production. Structurally, fish assemblages in both stream types contained many regionally common species, though some species appeared to exhibit affinities for a particular stream type. Functionally, fish assemblages in agriculture streams contained more tolerant species, more omnivores, and fewer insectivores compared to forest stream assemblages, which were nearly all insectivores. Overall, one-third of the fish specimens collected in forest streams classified as intolerant species.ConclusionsOur results suggested that stream water quality, habitat, and fish assemblages differed between agriculture and forest streams in the MAP, with fish assemblages exhibiting both structural and functional differences. Results were consistent with a larger body of literature from smaller, headwater streams whereby land-use changes (e.g., row-crop agriculture) impacted the physical, chemical, and biological characteristics of stream ecosystems. Results further highlight the importance of land use management and its effects on habitat diversity in stream ecosystems, and that protecting the few remaining undisturbed or less-disturbed streams should be a priority.

Water mites and their use as bioindicators of water quality conditions: a Pennsylvania case study

Water mites (Acariformes: Hydrachnidia) are one of the planet's most diverse and abundant groups of aquatic arthropods. With more than 7,500 described species, water mites have been documented in nearly every known freshwater environment. In lotic systems, water mites are commonly found in fast-flowing, riffle-run stream habitats, where one square meter of substrate can contain as many as 5,000 individual mites representing more than 50 species, 30 genera, and all 8 superfamilies. Despite their widespread distribution, relative diversity, and abundance, water mites have been widely neglected in freshwater biomonitoring efforts. However, several studies across the globe have found that water mites can be used as successful bioindicators of water quality conditions. Thus, the following study provides one of the first detailed examinations of lotic water mites and their bioindicator potential in North America. We sampled water mites from sites along 'attaining' (unpolluted) and agriculturally 'impaired' (polluted) riffle-run stream habitats and compared their assemblages to other physicochemical and benthic macroinvertebrate metrics used to quantify water quality in Pennsylvania. In total, we collected 9,139 individual water mites representing 5 superfamilies, 9 families, and 14 genera from both attaining (n = 13) and impaired (n = 13) streams. Similar to other global studies, we found significant differences between the water mite assemblages of attaining and impaired streams, with attaining streams having greater richness and diversity of water mites. Our data shows that several mite taxa are associated with biological and physicochemical conditions of water quality, where some known sensitive taxa are increasingly dominant in attaining streams and less dominant in impaired streams. Conversely, some pollution-tolerant taxa dominance increases in impaired streams while sensitive taxa abundance declines. These findings illustrate that water mites vary in their sensitivity to pollution and are suitable bioindicator species whose inclusion in biomonitoring assessments will increase assessment accuracy.

Influence of river channel typology on aquatic macroinvertebrate assemblages in tropical streams

Influence of river channel typology on aquatic macroinvertebrate assemblages in tropical streams

Constructed rock riffles increase habitat heterogeneity but not biodiversity in streams constrained by urban impacts

AbstractRiffles are heterogeneous habitats that support diverse assemblages in natural streams. They are often constructed as part of stream restoration practice, including in degraded urban stream ecosystems, despite larger scale limits to ecological state. Such restoration practices fail to consider ecological theory, and their outcomes have rarely been robustly monitored and assessed. We assessed the effects of constructed rock riffles on habitat heterogeneity and on macroinvertebrate assemblages in six urban streams (4%–32% effective imperviousness). We compared habitat heterogeneity, and taxon abundance and richness of the six streams before and after (1 and 5 years) riffle construction and in three control streams without riffles. Riffles increased habitat heterogeneity. In contrast, macroinvertebrate assemblages in all streams were dominated by tolerant, cosmopolitan, and invasive taxa before and after riffle construction. Riffles reduced the abundance and richness of tolerant taxa in less urbanized streams and increased their richness in more urban streams. These changes had no effect on measures of biodiversity. Urban stormwater runoff can affect the degree to which rock riffles increase habitat heterogeneity through sediment transport and increased physical disturbance. In highly urban streams, increased habitat heterogeneity is likely to primarily favor cosmopolitan species that can tolerate frequent chemical and physical disturbance. Riffle construction may reduce the abundance of cosmopolitan species and increase the abundance of more sensitive species, but only if catchment‐scale impacts of urban stormwater runoff are adequately controlled. Robust experiments such as this add to general understanding of the effectiveness of restoration practice, reducing the need for ubiquitous monitoring of restoration projects.

Agricultural land use affects the beta diversity of fish assemblages in subtropical headwater streams in China

Agricultural land use affects the beta diversity of fish assemblages in subtropical headwater streams in China

Connected headwaters: Indelible field evidence of dispersal by a diverse caddisfly assemblage up stream valleys to dry catchment boundaries

Abstract1. Integral to many ecological models is the notion that dispersal connects populations and communities in disparate locations. For stream insects, however, there is very little empirical information about which species and what proportion of the species in a community are likely to disperse, in what direction and how far they travel, and whether dispersal is successful in connecting populations and communities. This study examines whether species of caddisfly can disperse between catchments and potentially connect communities.2. We used a novel sampling design comprising five pairs of streams. Each stream in a pair flowed from the same boundary, but in opposite directions and into isolated catchments. We surveyed abundances of adult caddisflies on the catchment boundary (boundary species) where there was no water (Up location), and on two locations per stream (Middle, Down locations) where there was permanently flowing water (resident species). If caddisflies fly along the topographic features of stream valleys, then we expected to find adults on the ridge between catchments and, if dispersal is successful, stream communities in adjacent catchments should have similar species composition.3. Over 130 species of caddisfly (from 18 families) were collected. Approximately half of them occurred on at least one catchment boundary, and Up locations averaged almost 20 species. Boundary species included both the smallest‐ and largest‐bodied taxa and they were a near perfect subset of species in resident assemblages. However, boundary species were not simply the most common in resident assemblages. There was no evidence of sex‐biased dispersal. Unsurprisingly, assemblage composition varied across the landscape, within and among catchments. However, resident assemblages within stream pairs were significantly more similar to one another than unpaired streams in either the same or in different catchments.4. Our results suggest that a surprisingly diverse set of caddisflies disperse up to catchment boundaries and potentially connect streams on either side of catchment divides. Nevertheless, many other caddisfly species were never recorded at Up sites and hence may never or only rarely reach catchment boundaries.5. These outcomes suggest, firstly, that some caddisflies are capable of trans‐catchment dispersal but it is incorrect to assume that all caddisflies are good dispersers, as is often stated in the literature. Secondly, caddisfly assemblages in headwater streams may be less isolated than is often considered and the dendritic structure of stream networks may be less important for their distribution patterns than the proximity of tributaries in neighbouring catchments, in many landscapes. Trans‐catchment dispersal could ensure community connectivity and facilitate recovery after catchment‐wide extinctions.

Diversity of freshwater algal assemblages across the United States as revealed by DNA metabarcoding

AbstractAs freshwater algae respond strongly to environmental conditions, algal communities are routinely used as indicators of aquatic health. Algal bioassessments have historically relied upon microscopy‐based identifications that are typically slow, expensive, taxonomically restricted, and inconsistent across analysts and time. Metabarcoding of water column DNA (environmental DNA, or eDNA) can characterize assemblages more quickly, at lower cost, and with higher taxonomic precision than microscopy. As such, eDNA metabarcoding has the potential to improve bioassessments, but relationships between environmental conditions and eDNA‐derived algal assemblage composition need to be determined first. We performed metabarcoding of a plastid 23S rRNA gene region for 1230 freshwater eDNA samples collected from 51 lakes and 617 streams across the conterminous United States to test for assemblage‐wide patterns that may indicate ecological condition. Samples were collected by citizen, academic, and research scientists using a standardized commercial kit. This effort constitutes the largest published water column eDNA survey yet of algal diversity across freshwaters in the United States. We detected 14,943 algal exact sequence variants (ESVs) from 11 divisions. The richness and abundance of cyanobacteria was higher in lakes, while streams were dominated by diatoms. Nationwide, only 1% of variation in stream assemblages was explained by catchment integrity. The remaining, explicable 19% was associated with forest cover, stream order, elevation, and broad‐scale spatial variables. Nevertheless, select ESVs were candidate indicators of gradients in stream catchment integrity and possible eutrophication. Together, we show that algal eDNA metabarcoding has potential for measuring ecological condition relative to water quality. Yet, further sampling along anthropogenic gradients is needed before algal eDNA can be used for large‐scale biomonitoring in the United States. We also found that only 2% of algal ESVs could be assigned to U.S. morphospecies, highlighting the importance of building a more comprehensive reference sequence database to integrate existing morphospecies autecology with eDNA‐based bioassessments.

Relationships between reference site quality and baetid mayfly assemblages in mountainous streams of the Luvuvhu catchment, South Africa

With water quality deteriorating rapidly at a global scale, river sections suited to serve as reference sites are being increasingly lost. It thus becomes critical to develop rapid methods to confirm that previously monitored sites continue meet the requirements of reliable reference sites. In the absence of pristine sites, 9 near-natural sites, as defined by the Kleynhans (1996) classification, were used as reference sites for the Luvuvhu River catchment to compare the quality of physico-chemical factors against a biological metric. Baetid mayfly community structure at a site was chosen as an index of water quality, since this family is common in all types of freshwaters, highly diverse and adapted to unpolluted running water. Baetid larvae were sampled monthly from stones-in-current biotopes across 9 sites for over 1 year, between December 2016 and January 2018. A Spearman’s correlation test was used to evaluate the relationship between physico-chemical factors and identify redundant variables. Water quality standards were measured against the national water quality guidelines for aquatic ecosystems. We used a generalized linear model to determine the effect of physico-chemical variables on baetid species, and canonical correspondence analysis to show the relationships between baetid species, sites, and physico-chemical variables. A total of 3 039 individuals belonging to 12 mayfly species were recorded. Our findings indicated that while the physico-chemical factors were highly variable, they were within favourable ranges to reflect reference site conditions. While water temperature was the most important driver of baetid community structure in general, as it negatively affected their abundances, a subset of species (Pseudoponnota sp., Pseudocloeon sp., Acanthiops varius and Demoulinia crassi) showed clear responses to changes in TDS and stream width. We conclude that specific baetid species show good potential as biological indicators of reference sites and chronic water temperature stress, making assessment of reference sites easier.