Aquatic Community Composition Research Articles

Holocene palaeoecological changes in a transitional climate zone of western-central Mexico: The pollen and non-pollen palynomorphs record

The Alberca de Tacámbaro (AT) is located at a transitional zone between tropical and temperate climates at the core of the North American Monsoon area. This location features a mosaic vegetation comprising pine-oak forests and tropical dry forests. Currently there is no information regarding the dynamics or evolution during the Holocene of these vegetation types. The palynological record of the last 9400 years BP preserved in the lacustrine sequence of the AT was used to document changes in the composition of terrestrial and aquatic communities, evenness, and rate of change. Pinus and Quercus forests dominated the terrestrial palynological record, but mesophytic forests were also recorded throughout the sequence. Four tropical dry forest taxa assemblage expansions were identified at 9200 to 8420 yr BP; 5900 to 5230 yr BP; 3100 to 2800 yr BP; and 2300 to 2000 yr BP. These phases correlated with times of reduced North American Monsoon intensity, suggesting that these communities thrived during drought periods. Variations in non-pollen palynomorphs were synchronic with the lithostratigraphic, geochemical data as well as with the terrestrial changes. During the Meghalayan, compositional shifts in the vegetation and increases in the herbaceous elements indicated human impact, while aquatic taxa, suggested eutrophic and warmer conditions in the lake. By examining the history of this vegetation mosaic, the data on temporal vegetation dynamics during the Holocene offered clues about the response to ongoing global warming and how climate change will likely shape plant communities in western-central Mexico.

Developing a European aquatic macrophyte transfer function for reconstructing past lake-water chemistry

Quantitative paleoecological reconstructions using biological proxies, such as diatoms, Cladocera, and chironomids, have revolutionized paleolimnology and have greatly contributed to the understanding of the past local and regional environmental changes, as well as to nature conservation. While macrophytes are good ecological indicators, they have rarely been used to reconstruct past lake-water chemistry. The present study investigates which environmental variable best explains aquatic plant community composition in Finnish, Polish, and Swedish lakes for its further use in quantitative paleoenvironmental reconstructions. The method involved the creation of a modern macrophyte-environment calibration dataset, calculation of modern calibration functions using simple averaging regression, and final reconstruction of past environmental conditions in Lake Linówek (NE Poland) from a fossil assemblage using weighted averaging calibration. The data demonstrate that conductivity and alkalinity best explained macrophyte community composition in our dataset. Species “optima” for alkalinity were influenced by the presence/absence of carbon concentrating mechanisms (CCMs), enabling the utilization of HCO3− as a carbon source. Quantitative paleoenvironmental reconstruction indicates that past water conductivity and alkalinity fluctuated depending on internal lake processes and the supply of basic ions to the lake from the catchment related to climate and soil development in the watershed during the late Glacial (∼14,500–11,700 calibrated years before the present; cal BP) and the Holocene (11,700 cal BP–recent). We conclude that macrophytes can be successfully used for past lake-water chemistry reconstruction. Furthermore, calculated modern calibration functions for conductivity and alkalinity can be used in nature conservation for determining habitat requirements of numerous endangered macrophyte species as a basis for successful (re)introductions.

Non-native amphipods reach higher maximum swimming velocities than natives

The invasion of non-native amphipods often leads to severe changes in the composition of aquatic communities and may also result in the local replacement of native species. Particularly, a lower risk of being preyed upon resulting from high swimming velocities can be an advantage in interspecific competition. Furthermore, as swimming velocities are ecologically important, they are often used in ecotoxicological studies to estimate effects of different stressors. However, knowledge on swimming velocities of native and non-native amphipods is still rather limited. We experimentally investigated the maximum swimming velocities of three native and three non-native amphipods via video analyses in the laboratory. Results showed that non-native species reach higher maximum swimming velocities compared to natives probably leading to a higher predation success and reduced risk of being preyed upon. Additionally, body length correlates positively with swimming velocities, except for the invader Dikerogammarus villosus. As D. villosus can be cannibalistic, the high swimming velocities of the small individuals may reduce the intraspecific predation and may increase the survival rates of smaller specimen. Hence, knowledge about the swimming velocities of species contribute to the understanding of interspecific competition among species and might support explanation approaches for the success of invasive species. Furthermore, it provides baselines for ecotoxicological studies of stressor impacts.

Climate change and human impacts on aquatic communities at Etoliko Lagoon in western Greece

The Etoliko Lagoon in western Greece has experienced extensive human modification since the 20th century, both on the surrounding land and in the aquatic environment. To examine human impacts and disentangle climatic from anthropogenic changes, we present a suite of biomarker records that span the past two centuries (∼1790–2011). Specifically, we use terrigenous (n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and phytosterols) and aquatic (dinosterol, brassicasterol, cholesterol, and stigmasterol) biomarkers to document changes in nutrient inputs, combustion, and algal productivity. During most of the 19th and 20th centuries, aquatic communities respond to temperature, forced mainly by solar irradiance and volcanic activity, and precipitation, controlled largely by summer and winter North Atlantic Oscillation (NAO) patterns that determine freshwater runoff. PAHs illustrate the acceleration of coal combustion during the 1800s, and declining concentrations since the 1950s correspond to the implementation of emission controls and reductions in rainfall that likely inhibited PAH transport. As human pressures increased in the late 1900s and water column anoxia grew, the absence of a clear human waste and eutrophication signal suggests that other factors also contributed to limited oxygen availability. Overall, environmental degradation of the late 20th and early 21st centuries is clear and can be attributed to a combination of especially arid conditions and human interferences that altered lagoon hydrography, trophic state, and aquatic community composition.

A bacteria-based index of biotic integrity indicates aquatic ecosystem restoration

Intensive ecological interventions have been carried out in highly polluted shallow lakes to improve their environments and restore their ecosystems. However, certain treatments, such as dredging polluted sediment and stocking fish, can impact the aquatic communities, including benthos and fishes. These impacts can alter the composition and characteristics of aquatic communities, which makes community-based ecological assessments challenging. Here we develop a bacteria-based index of biotic integrity (IBI) that can clearly indicate the restoration of aquatic ecosystems with minimal artificial interventions. We applied this method to a restored shallow lake during 3-year intensive ecological interventions. The interventions reduced nutrients and heavy metals by 27.1% and 16.7% in the sediment, while the total organic carbon (TOC) increased by 8.0% due to the proliferation of macrophytes. Additionally, the abundance of sulfur-related metabolic pathways decreased by 10.5% as the responses to improved ecosystem. The score of bacteria-based IBI, which is calculated based on the diversity, composition, and function of benthic bacterial communities, increased from 0.62 in 2018 to 0.81 in 2021. Our study not only provides an applicable method for aquatic ecological assessment under intensive artificial interventions but also extends the application of IBI to complex application scenarios, such as ecosystems with significantly different aquatic communities and comparisons between different basins.

Effects of river regulation on aquatic invertebrate community composition: A comparative analysis in two southern African rivers.

While natural floods play a crucial role in shaping the composition of aquatic communities, the most rivers worldwide are regulated or dammed for anthropogenic purposes, resulting in alterations to the biological and chemical composition of these ecosystems. Studies have demonstrated various negative effects of river regulation on aquatic invertebrate communities globally. However, there is a scarcity of research in Africa, despite its vulnerability to anthropogenic impacts. This study aimed to compare aquatic invertebrate communities in the Phongolo River, an impacted regulated river, and the Usuthu River, a less impacted unregulated river, in South Africa. It further aimed to ascertain whether Lake Nyamithi, a naturally saline lake receiving water from both of the aforementioned systems, exhibited a stronger similarity to one of the two rivers in terms of its aquatic invertebrate composition. Aquatic invertebrate and water samples were collected from 2012 to 2018 over several surveys. The Usuthu River demonstrated a diverse and sensitive aquatic invertebrate community, emphasising its high conservation value. The Phongolo River demonstrated effects of anthropogenic impact, with taxa more resilient to changes in water quality and flow compared to the Usuthu River. Mismanagement and excessive water use may lead to the loss of any remaining sensitive aquatic invertebrate communities in this river. The presence of invasive molluscan in the Phongolo River and Lake Nyamithi also poses a threat to the native aquatic invertebrate communities. These invasive species are currently absent from the Usuthu River although other invasive species, such as the Australian redclaw crayfish, are found in both river systems. Lake Nyamithi displayed a unique aquatic invertebrate community, distinct from both rivers and their floodplains. This study provides important baseline information on the Usuthu River's aquatic invertebrates and emphasises the need to maintain adequate water flow in rivers and floodplains to protect biodiversity and sensitive species.

Minor effect of wind exposure and littoral slope on macrophyte characteristics in non-impacted lowland lakes of Poland.

Aquatic vegetation is a reliable indicator of the ecological condition of surface waters. Abundance, composition and spatial structure of aquatic communities are shaped by an array of factors, which include both natural abiotic features of an ecosystem and external influences. We investigated whether the physical features, i.e., wind exposure and slope of the lake basin, have a significant impact on the taxonomic composition and spatial structure of macrophyte communities from non-impacted, highly alkaline, lowland lakes of the European plains (Poland). We further examined whether these features can affect the classification of the ecological status of lakes assessed in accordance with the Water Framework Directive requirements. Morphological, botanical and physicochemical data from 260 transects in 16 non-disturbed lakes of Polish lowlands surveyed in the years 2011-2016 were analysed. For each transect, littoral slope and wind exposure were calculated. Additionally, the total phosphorus concentration was used as a proxy of water trophy. The relationships between environmental variables and macrophyte indices as well as the syntaxonomic composition of aquatic and rush vegetation (dependent variables) were analysed using multidimensional ordination techniques (redundancy analysis, variation partitioning and indicator values), correlation and regression analysis. Among the three analysed environmental factors (littoral slope, wind exposure and water trophy), in almost all cases the latter explained the highest variance in the macrophyte community, while the contribution of the first two was at most moderate, weak or usually statistically insignificant. However, lakes with steeper slopes were more frequently inhabited by stoneworts and had better ecological status than those with a gentle littoral shape. This may be attributed to the links between lake morphometry and rate of eutrophication, with deep lakes supporting more effective dilution of substances. Furthermore, lower light requirements of charophytes than of higher plants and the capacity to growth in unstable sediments facilitate charophyte establishment in deeper and steeper parts of the littoral over higher plants. Our findings suggest that in lowland lakes with relatively small areas, moderate depths and low wind exposure typical of European plains, slopes and weaving do not hamper vegetation development and do not negatively affect the macrophyte assessment of ecological status. In such ecosystems, eutrophication seems to be a more important factor determining aquatic vegetation than physical features.

The role of turnover in structuring subterranean aquatic communities in Southeastern Brazil.

Similarly to other animal communities, the diversity of subterranean aquatic fauna is influenced by several factors and processes, such as habitat fragmentation, dispersion, environmental heterogeneity, and physical and chemical water characteristics. Here, we studied cave aquatic communities of the Alto Ribeira hydrographic basin, regarding troglobitic and non-troglobitic species, located in a single karst area to evaluate the influence of sub-basins in fauna differentiation. We investigated how abiotic variables (flow, electrical conductivity, temperature, pH, and substrate) influence the fauna composition and the contribution of beta diversity components (nestedness and turnover) in explaining communities' dissimilarities. Fauna composition differed between sub-basins, as most species did not co-occur in different caves. Caves with higher flow and substrate diversity were the richest. In addition, each cave community was influenced by a unique set of abiotic variables. Dissimilarity among caves was mainly explained by turnover, and our findings suggest the restricted species distribution could be due to ecological (e.g., limited dispersion capacity, tolerance to abiotic variables), hydrogeological (e.g., dispersion barriers, isolation of sub-basins), and historical (e.g., colonization, paleoclimatic events) factors and processes. Therefore, different elements are responsible for determining the composition of cave aquatic communities in different sub-basins, reflecting the variability within a single karst area.

Engineering aquatic plant community composition on floating treatment wetlands can increase ecosystem multifunctionality

Phytoremediation using floating treatment wetlands (FTWs) is an emerging nature-based solution for freshwater restoration. However, the potential to design these systems by manipulating macrophyte community composition to provide multiple ecosystem services remains unexplored. Using a tank experiment, we simulated aquatic environments impacted by multiple pollutants and employed a comparative ecological approach to design emergent macrophyte communities using the trait of plant stature (plant height) to structure communities. Ecosystem functions were quantified, and a threshold-based method used to compute an ecosystem multifunctionality index that was weighted based on three different management-driven restoration objectives: equal importance, phytoremediation, and regulation and cultural services. Across all restoration scenarios, ecosystem multifunctionality was higher when community types performed more diverse functions. Small emergent plant communities outperformed all other community types due to their increased provision of both regulation and maintenance, cultural, and provisioning services. Conversely, large emergent communities that are more typical candidates for phytoremediation had the highest levels of multifunctionality only when function was lower. Arranging emergent macrophytes in mixed-statured communities led to intermediate or poorer performance both in terms of multifunctionality and specific functions, suggesting that diversity on the plant stature axis leads to negative plant interactions and represents a ‘worst of both worlds’ combination. Employing comparative ecology to generalise plant selection by stature demonstrates that large emergent macrophytes are more likely to better deliver provision-based services, while small emergent communities can provide additional benefits from cultural and regulatory services. Selecting macrophytes for FTWs employed in freshwater restoration by stature is a simple and widely applicable approach for designing plant communities with predictable outcomes in terms of (multiple) ecosystem service provision and highlights the need for environmental managers to closely align restoration objectives with potential community types.

Meta-analysis of the thermal pollution caused by coastal nuclear power plants and its effects on marine biodiversity

The rise in seawater temperature due to industrial activities is one of the main threats to marine biodiversity. In nuclear power plants, large volumes of water are used for their operation, returning to the ecosystem at higher temperatures. A global meta-analysis was performed to evaluate the thermal effects caused by coastal nuclear power plants on marine organisms. We found 853 articles of which, 99 were included in the qualitative analysis and 75 in the meta-analysis. The meta-analysis showed an increase of 4.38 °C in water temperature near the outfall, and the temperature variation of each study was found to be associated with the power plant latitudes. The main effects on organisms were related to changes in the structure and composition of aquatic communities, with species abundance, distribution, dominance, and density being the most cited ones. Among the affected groups, photosynthesizing microorganisms were the most cited, potentially contributing to shifts in ecosystem dynamics.

Development and validation of targeted environmental DNA (eDNA) metabarcoding for early detection of 69 invasive fishes and aquatic invertebrates

AbstractInvasive species are of concern due to their impacts on ecosystems and economies, but they pose significant control challenges. Environmental DNA (eDNA) is a powerful tool in the detection of aquatic organisms at low densities due to high detection sensitivity and relative ease of sample collection. Aquatic eDNA analyses have increased worldwide and are generally either applied to few target species (quantitative PCR), or for broad taxonomic applications (metabarcoding). Here, we describe the development and testing of a hybrid approach that utilized high‐sensitivity PCR primer sets and high‐throughput sequencing (HTS), referred to as targeted metabarcoding, to detect 69 fishes and invertebrates. We identified target species based on reports of globally important invasive species and developed two independent PCR primers for each species (CO1 and a second mtDNA region). We assessed sensitivity and eDNA interference for all 138 primers (2 per species and 69 species) using standard end‐point PCR and tested them on 10 eDNA samples spiked with various amounts of one or more of the target species DNA. The sensitivity of the 138 primer sets ranged between 1.5 × 10−5 and 2.64 ng template DNA (mean = 0.069 ng). Primers were also tested for interference effects using plankton eDNA to simulate field conditions. The inclusion of interfering plankton DNA reduced the sensitivity for most primer sets by one or more orders of magnitude (range 0–3). Overall, our targeted metabarcoding resulted in the detection of ~98% of species in the DNA spiked samples, and perhaps more importantly, the HTS read count was positively related to the quantity of spiked DNA (p < 0.002). We envision this technique being particularly useful for the early detection of species at low population densities; however, there are diverse applications of targeted metabarcoding for monitoring aquatic community composition and to quantify ecosystem change and health.

Next-Generation High-Throughput Sequencing to Evaluate Bacterial Communities in Freshwater Ecosystem in Hydroelectric Reservoirs.

The quality of aquatic ecosystems is a major public health concern. The assessment and management of a freshwater system and the ecological monitoring of microorganisms that are present in it can provide indicators of the environment and water quality to protect human and animal health. with bacteria is. It is a major challenge to monitor the microbiological bacterial contamination status of surface water associated with anthropogenic activities within rivers and freshwater reservoirs. Understanding the composition of aquatic microbial communities can be beneficial for the early detection of pathogens, improving our knowledge of their ecological niches, and characterizing the assemblages of microbiota responsible for the degradation of contaminants and microbial substrates. The present study aimed to characterize the bacterial microbiota of water samples collected alongside the Madeira River and its small tributaries in rural areas near the Santo Antonio Energia hydroelectric power plant (SAE) reservoir in the municipality of Porto Velho, Rondonia state, Western Brazil. An Illumina 16s rRNA metagenomic approach was employed and the physicochemical characteristics of the water sample were assessed. We hypothesized that both water metagenomics and physicochemical parameters would vary across sampling sites. The most abundant genera found in the study were Acinetobacter, Deinococcus, and Pseudomonas. PERMANOVA and ANCOM analysis revealed that collection points sampled at the G4 location presented a significantly different microbiome compared to any other group, with the Chlamidomonadaceae family and Enhydrobacter genus being significantly more abundant. Our findings support the use of metagenomics to assess water quality standards for the protection of human and animal health in this microgeographic region.

Seasonal and spatial dynamics of the aquatic insect communities of an intermittent Mediterranean river

Although intermittent rivers are present in all climate regions, their biodiversity and ecosystem functions were largely overlooked in the past. Recently, considerable effort has been made to improve our understanding of these, however, many data gaps still remain. We conducted a study to improve knowledge of the community patterns and processes in intermittent rivers in the Dinaric Western Balkan ecoregion. We studied spatial and temporal variation of aquatic insect community composition and structure in the intermittent Krčić River over two seasons (June and December) in three river sections (spring, upper/middle and lower reaches), encompassing dominant microhabitats (phytal, boulders, cobbles, sand and xylal). Community was primarily composed of aquatic insects (92 % of the community) and seasonality was inferred as the most important factor determining its composition, diversity and abundance. This was also supported by the ecological trait information, i.e. trophic and dispersal-related community structure. The most diverse and abundant insect group were the under-investigated chironomids, thus, we discussed tolerance and intermittency indicator potential of some of these taxa. By providing new insights into temporal and spatial dynamics of aquatic insect communities, a major bioindicator component of the macroinvertebrate community used in water quality monitoring in intermittent rivers, our data support development of the intermittent river-specific and adequate management and monitoring procedures.

Effects of wind-wave disturbance and nutrient addition on aquatic bacterial diversity, community composition, and co-occurrence patterns: A mesocosm study

Wind-wave disturbance and nutrient input are the major environmental factors that shape bacterial diversity and community composition in lakes. However, knowledge of bacteria as bio-indicators' synergistic response to disturbance patterns and nutrient addition is still poor. To address this knowledge gap, we conducted a mesocosm experiment over 21 days, and collected 90 water samples from tanks under six different patterns of disturbance and nutrient addition; we explored the bacterial communities using high-throughput 16S rRNA gene sequencing. We found significantly increased bacterial diversity in continuously disturbed conditions and in intermittently disturbed conditions, and significantly decreased bacterial diversity under the synergistic effect of disturbances and nutrients. Bacterial community composition (BCC) under conditions of disturbance and nutrient addition exhibited different variations. However, there were no significant differences in BCC between continuously and intermittently disturbed mesocosms. Co-occurrence networks analysis showed that the proportion of positive correlations among edges in nutrient addition conditions were significantly higher than that in disturbed condition, indicating that nutrient input may increase the proportion of niche overlap, and enhance positive interactions among bacteria. Meanwhile, the co-occurrence patterns between algal and bacterial communities suggested shared environmental preferences or potential interactions among these two groups. Our study provides a new insight into the restoration of shallow eutrophic lake ecosystems. Moreover, the different distribution patterns of bacterial community act as ecological indicators of response to disturbances and nutrient input.

Substrate diversity affects carbon utilization rate and threshold concentration for uptake by natural bacterioplankton communities

Persistence of dissolved organic matter (DOM) in aquatic environments may in part be explained by high diversity and low concentrations of carbon substrates. However, changes in dissolved substrate quality can modify aquatic bacterial community composition and rate of carbon uptake. The aim of this study was to test if the presence of multiple simple substrates affects the turnover of organic carbon. Natural bacterial communities were grown in continuous cultures supplied with either individual carbon substrates—salicylic acid (SA), tryptophan (Trp) or tyrosine (Tyr)—or a combination of the 3 substrates. Concentrations were tracked using fluorescence spectroscopy, and steady-state concentrations of a few nanomolar were reached. Bacterial growth efficiency was dependent on which carbon sources were present and reached an intermediate level in the combined treatment. The bacterial community maintained steady-state concentrations of Trp that were lower in the combined treatment than in the individual substrate treatment. In addition, steady-state concentrations were reached faster during growth on combined carbon substrates, although the maximum utilization rate of each individual compound was lower. However, the steady-state concentration of total carbon (sum of carbon content of SA, Trp and Tyr) was higher in the combined culture than in the individual substrate treatments, and seemed to be determined by the carbon substate for which the bacteria had the lowest affinity. The results from this study indicate that persistence of dissolved organic carbon can in part be explained by vast substrate diversity, which raises the threshold concentration for utilization by natural bacterial communities.

Heterogenous Impact of Water Warming on Exotic and Native Submerged and Emergent Plants in Outdoor Mesocosms.

Some aquatic plants present high biomass production with serious consequences on ecosystem functioning. Such mass development can be favored by environmental factors. Temperature increases are expected to modify individual species responses that could shape future communities. We explored the impact of rising water temperature on the growth, phenology, and metabolism of six macrophytes belonging to two biogeographic origins (exotic, native) and two growth forms (submerged, emergent). From June to October, they were exposed to ambient temperatures and a 3 °C warming in outdoor mesocosms. Percent cover and canopy height were favored by warmer water for the exotic emergent Ludwigia hexapetala. Warming did not modify total final biomass for any of the species but led to a decrease in total soluble sugars for all, possibly indicating changes in carbon allocation. Three emergent species presented lower flavonol and anthocyanin contents under increased temperatures, suggesting lower investment in defense mechanisms and mitigation of the stress generated by autumn temperatures. Finally, the 3 °C warming extended and shortened flowering period for L. hexapetala and Myosotis scorpioides, respectively. The changes generated by increased temperature in outdoor conditions were heterogeneous and varied depending on species but not on species biogeographic origin or growth form. Results suggest that climate warming could favor the invasiveness of L. hexapetala and impact the structure and composition of aquatic plants communities.

The daily effect is more important than the diurnal effect when shaping photosynthetic picoeukaryotes (PPEs) communities in Lake Taihu at a small temporal scale.

As major primary producers in aquatic systems, the diversity and community composition dynamics of photosynthetic picoeukaryotes (PPEs) have been investigated in recent years. Here, we explored the 3-day diurnal succession of the PPE community in a highly eutrophic lake in early spring using a combination of flow cytometric sorting and high-throughput sequencing. Our results showed that the PPEs were the dominant group of autotrophic picophytoplankton, although they had relatively low diversity and were dominated by the Stephanodiscaceae family in early spring in Lake Taihu. Furthermore, PPE abundance was significantly higher at night than during the day, probably due to their high specific rate of carbon uptake during the day and rapid proliferation at night. Several environmental variables had a significant influence on the PPE community composition, and the daily effect was more important than the diurnal effect when shaping the PPE community in Lake Taihu at a temporal scale of 3 days. Furthermore, based on the variation partitioning analysis (VPA), the relative importance of abiotic factors (deterministic processes) to short-term succession was low, explaining only 20.44% of the PPE community variation. We therefore conclude that stochastic processes determined PPE community assembly over a short temporal scale based on a neutral community model (NCM).

Decomposition of leaf litter mixtures in streams: effects of component litter species and current velocity

The effects of mixing different leaf litter species on litter decomposition in streams have received considerable attention in recent years. However, contrasting results have been reported and the mechanisms behind the effects of litter diversity have been poorly examined. We compared the decomposition rates and associated fungi for two contrasting litter species, when incubated individually and in mixture, at two different current velocities. Coarse-mesh bags with alder litter individually, oak litter individually and with a mixture of both were incubated in a forest headwater stream over 32 days, under fast or slow current velocities. We determined litter decomposition rates, microbial oxygen consumption rates, and aquatic hyphomycete sporulation rates, species richness and community composition; litter species in the mixture were processed individually. Our results provided weak evidences for diversity effects on leaf litter decomposition. Generally, litter decomposition was unaffected by mixing contrasting litter species, with litter species in the mixture decomposing at the same rate as when incubated individually at both current velocities. The same pattern was observed for microbial variables. Decomposition rates and microbial colonization and activity depended primarily on the traits of the target litter species and were not affected by those of the companion species. However, litter-mixing effects were detected on oak litter at late decomposition stages under fast current velocity conditions, suggesting that both current velocity and the incubation time might influence diversity effects on litter decomposition in streams. This finding contributes to explain the lack of litter-mixing effects reported previously by many studies.

The use of environmental DNA in monitoring aquatic biodiversity for conservation: a review of challenges and opportunities

Evidence-based decision-making in conservation and natural resource management is often constrained by lack of robust biodiversity data. Technology offers opportunities for enhanced data collection, with satellite-based remote sensing increasingly complemented by Earth-based sensors such as camera traps, acoustic recording devices and drones. In aquatic as well as terrestrial systems, environmental DNA is increasingly promoted as a tool to monitor species diversity and community composition. But if conservationists and natural resource managers are to know when to use eDNA, they need to understand its relative advantages and disadvantages, and when it can be used with or instead of other tools. In this paper, I expand on two recent publications (Stephenson 2020; Stephenson et al. 2020) to review lessons learned from the application of eDNA, especially metabarcoding, to the monitoring of aquatic biodiversity for conservation and to identify factors affecting its relevance and applicability. Over the past decade there have been many advances in technological solutions for biodiversity monitoring. eDNA and various remote sensing tools offer opportunities to create the enabling conditions for enhanced biodiversity monitoring, and are becoming cheaper and easier to use for scientists, public and private sector resource managers, and citizen scientists. Nonetheless, a number of challenges need to be addressed to, for example, improve the standardisation of tool use and to enhance capacity for the use, storage, sharing and analysis of huge volumes of data, especially in high-biodiversity countries. More studies comparing the relative efficiency and cost-effectiveness of different tools with different species in different habitats would help managers choose the right tools for their needs and capacity and better integrate them into monitoring schemes. eDNA is becoming the go-to option for the monitoring of aquatic species diversity and community composition and has also proven successful in some terrestrial settings. eDNA is especially useful for monitoring species that are in low densities or difficult to observe with traditional observer-based methods; indeed, several studies show eDNA metabarcoding techniques have a much better detection probability overall for taxa such as amphibians and fish. In some cases, eDNA has been shown to complement other tools when used together, by either increasing animal detection probabilities or increasing the number of indicators that can be measured at one site. This suggests that, in future, more effort should be made to test the effectiveness of integrating eDNA with one or more other tools to enhance the efficiency and effectiveness of measuring indicators and to increase the diversity of species detected. For example, eDNA could be combined with camera traps for monitoring vertebrates visiting waterholes. Testing multiple tools would also provide better opportunity to quantify when and how traditional observer-based methods can complement the technological solutions and when they are more cost-effective. However, it is noteworthy that, in general, the taxa for which data are most lacking, such as invertebrates, plants and fungi, are still those less easily monitored by eDNA and other new technologies. This suggests a focus only on technological solutions for biodiversity monitoring may perpetuate existing taxonomic data biases. I conclude by discussing the international policy context and the relevance of eDNA for monitoring global biodiversity indicators. Several opportunities exist to integrate eDNA into monitoring programmes to measure government, business and civil society contributions towards delivery of the post-2020 global biodiversity framework and the Sustainable Development Goals.

Different scales determine the occurrence of aquatic macrophyte species in a tropical stream

Distributions of aquatic macrophyte species are commonly associated with water chemistry characteristics. However, other environmental factors that can lead to the occurrence of aquatic plants in lotic ecosystems, such as dynamic habitats linked to the surrounding landscape, have been underestimated. This study aims to evaluate landscape features that may influence the occurrence of species of euhydrophyte aquatic macrophytes in a tropical river basin. We assessed the occurrence of the following seven species: Egeria densa, Cabomba furcata, Potamogeton pusillus, Potamogeton polygonus, Utricularia foliosa, Pistia stratiotes and Salvinia molesta. We also measured environmental variables related to three spatial scales, local (limnological), channel and riparian landscape, along 25.5 Km of the Itanhaém River basin (São Paulo, Brazil). We found that local (limnological) and channel characteristics were important variables in determining the occurrence of aquatic macrophyte species while the landscape scale had little influence on species composition. Channel depth and margin slope were especially relevant abiotic variables in explaining the occurrence of four of the species but not P. pusillus, P. polygonus and U. foliosa. Our results highlight the importance of channel morphology for understanding aquatic plant occurrence and community composition in tropical rivers.