Distribution Of Fish Communities Research Articles

Spatial Distribution Patterns and Beta Diversity of Fish Communities in a Tropical River Basin of Deccan Plateau

ABSTRACTRiverine ecosystems exhibit significant spatial variations in their communities, and understanding of these variances is vital to comprehend the mechanisms that maintain biodiversity. This study was conducted to understand pattern of distribution and beta diversity of fish communities in the Bhima River basin in the Deccan Plateau region of India. Fish distribution data from 59 sites across 11 rivers of the Bhima River basin were collected, and pair‐wise βDissimilarity and site‐wise local contribution to beta diversity (LCβDSorensen) and its components (LCβDTurnover and LCβDNestedness) were calculated. Power function regression was analysed to understand the decay in community similarity with geographical and environmental distances. Redundancy analysis was performed to investigate the relationship between fish distribution and environmental variables. Results indicated that species richness declined with increasing longitude from west to east. A negative relationship was observed between species richness and LCβDSorensen. LCβDTurnover formed Ո‐shaped curve at both ends of the species richness gradient, while LCβDNestedness values exhibited Ս‐shaped curve. No significant difference between mean LCβDTurnover and mean LCβDNestedness across the sites was observed. The distance decay relationship between community similarity and both geographical and environmental distances follows the power law shape, and the slope of this relationship flattened with increasing distance. Precipitation, topography, temperature variation and dissolved oxygen played a pivotal role in shaping fish assemblages. This study provides insight into the spatial distribution of fish communities in the Bhima River basin, which will be helpful to comprehend the ordination of biodiversity in the riverine ecosystem of the Deccan Plateau region.

Unveiling the effects of environmental factors and Yellow River inputs on the ichthyoplankton community structure in typical bays

To unravel the effects of environmental factors on fishery resources in the bay, we conducted six biological and environmental surveys in the Laizhou Bay between 2013 and 2020. The findings of our study illuminated several key aspects: (1) The annual discharge of water and sediment from the Yellow River to Laizhou Bay exhibited notable variations, while concurrently, environmental factors including temperature, salinity, and suspended particle matter underwent fluctuations, yet remained within a relatively stable range overall. (2) A total of 8318 eggs and larvae belonging to 10 orders, 16 families, and 19 genera were collected. Significant interannual fluctuations had been documented in the species composition, abundance, and biodiversity of ichthyoplankton. Notably, both Shannon-Wiener diversity index and Pielou evenness index were significantly negatively correlated with suspended particle matter concentration. (3) The water and sediment discharge significantly positively correlated with the number of cold-temperature species. However, the sediment input negatively correlated with the number of continental shelf benthopelagic fish. (4) Redundancy and correlation analyses confirmed the strong link between spatial and temporal distribution of fish communities and environmental factors, with salinity and dissolved oxygen key for ichthyoplankton abundance. Our research offers a scientific foundation for targeted fishery protection and management, which is crucial for preserving the ecological functions of spawning grounds in the bay.

Groundwater Springs Influence Fish Community Distribution and Trout Condition across a Longitudinal Gradient in a Coldwater Catchment in Southeastern Minnesota, USA

Groundwater Springs Influence Fish Community Distribution and Trout Condition across a Longitudinal Gradient in a Coldwater Catchment in Southeastern Minnesota, USA

Land use characteristics affect the sub-basinal scale urban fish community identified by environmental DNA metabarcoding

The heterogeneity of urban landscapes has effects on the environmental characteristics and fish composition of individual urban streams, even within a single water system. It is, therefore, imperative to assess the influence of physiochemical properties on urban streams by analyzing the spatial distribution of fish communities at the local scale. However, conventional fish surveys encounter time and labor constraints when selecting and surveying dense sampling points under 2 km in stream networks. In this study, environmental DNA (eDNA) metabarcoding was used as an innovative survey methodology to identify the effects of land use and stream order on fish composition and tolerance guild in an urban area. The eDNA sampling was conducted in 31 sites of the Anyang stream network in Korea, including part of the stream undergoing ecological restoration. The eDNA survey detected 12 of 17 species (70.6%) that appeared in the historical data, and 12 of 18 species (66.7%) identified in a conventional field survey with kick nets and casting nets. The proportions of urban area, forest and grassland were positively correlated with abundance (p < 0.05) and richness (p < 0.05) in multiple regression analyses, while the proportion of agricultural area showed a negative correlation (p < 0.05). For abundance, richness, and diversity within the fish community from first- to third-order streams, there was a significant decrease in sensitive species (p < 0.05) alongside a significant increase in tolerant species (p < 0.01) across all three indices. The results of this study highlight variations in fish composition across sites within the local scale of the urban stream network, underscoring the need for detailed monitoring to understand the ecological function of urban streams.

Fish communities and diversity in river ecosystems on the Qinghai-Tibet Plateau revealed by environmental DNA (eDNA) method

The Qinghai-Tibet Plateau (QTP) serves as the source of many large rivers in Asia, and also serves as a natural habitat for rare wildlife and a genetic reservoir for plateau species. The exceptional ecological environment of the QTP has fostered diverse fish species. However, due to climate change and human activities, fish species in this area are facing serious threats, while large spatial scale investigation is a big challenge. Environmental DNA (eDNA) metabarcoding, as an innovative monitoring technology, offers a simple, fast, and environmentally friendly approach to explore fish communities on the QTP. This study utilized eDNA technology to assess the diversity, composition, and potential environmental influences of riverine fish communities across the QTP. A total of 90 fish species were identified belonging to 79 genera, 34 families, and 18 orders. The dominant species were Schizothorax chongi, Gymnocypris przewalskii, Carassius carassius, and Botia striata. PCoA and ADONIS indicated significant differences among fish community in different river basins of the Qinghai-Tibet Plateau. Canonical correspondence analysis (CCA) revealed that the ratio of SRP to TP, average NDVI, average elevation, and proportion of bare land significantly influenced the distribution of fish community. This study provided a novel monitoring method and insight for fish communities and implied potential species invasion on the QTP.

Environmental DNA unveiling the fish community structure and diversity features in the Yangtze River basin

Fish, as top predators in aquatic ecosystems, play an important role in maintaining the structure and functioning of these ecosystems, making their diversity a topic of great interest. This study focused on the Yangtze River Basin to investigate the fish community structure and diversity using environmental DNA (eDNA) technology. The results showed that a total of 71616 fish operational taxonomic units (OTUs) and 90 fish belonging to 23 families were detected, with the Cyprinidae family being the dominant group, followed by the Cobitidae, Amblycipitidae, etc. Compared to historical traditional morphological fish surveys, the quantity of fish detected using eDNA was relatively low, but the overall distribution pattern of fish communities was generally consistent. The highest fish Shannon-Wiener diversity index in the Yangtze River Basin sites reaches 2.60 with an average value of 1.25. The fish diversity index was higher in the downstream compared to the middle and upstream regions, and there were significant differences among different sampling sites. Significant environmental factors influencing α-diversity included chlorophyll-a, chemical oxygen demand, dissolved oxygen, total nitrogen, and elevation. Non-metric multidimensional scaling (NMDS) analysis revealed significant differences in fish community composition between the upstream and middle/lower reaches of the Yangtze River, while the composition of fish communities in the middle and lower reaches was more similar. Redundancy analysis (RDA) indicated that total organic carbon (TOC) was positively correlated with fish community distribution in the upstream, while water temperature and NO3–N were negatively correlated with fish distribution in the upstream. NH3–N and CODMn were negatively correlated with fish distribution in the middle and downstream regions, indicating a relatively severe water pollution in these areas. Additionally, fish communities in the Yangtze River displayed a typical distance decay pattern.

Structure and Distribution of Fish Community in the Middle of Hamrin Dam Lake

Structure and Distribution of Fish Community in the Middle of Hamrin Dam Lake

Impacts of Strong ENSO Events on Fish Communities in an Overexploited Ecosystem in the South China Sea.

To better understand how fish communities respond to environmental changes under extreme climate events, we examine changes in fish communities in Beibu Gulf during strong El Niño and La Niña events. Strong La Niña and El Niño events affect the composition, abundance, and distribution of fish communities in Beibu Gulf. Fish community distribution and composition change before and after La Niña and El Niño events, and dominant species within them change with stable fishing intensity. The abundance and distribution of small pelagic fish such as Japanese jack mackerel (Trachurus japonicus) and Japanese scad (Decapterus maruadsi) are the most affected. Using a generalized additive model (GAM), we explore relationships between the abundance of T. japonicus and D. maruadsi and a suite of environmental variables. The GAM results revealed that sea surface salinity and sea surface temperature best explain changes in catch per unit effort of these two species during a La Niña event; depth, sea surface temperature, and mixed layer depth during an El Niño event. The results obtained in this study will offer support for implementing more-accurate, scientific fisheries management measures.

Assessment of Aquatic Ecological Health Based on the Characteristics of the Fish Community Structures of the Hun River Basin, Northeastern China

Long-term ecological restoration can restore aquatic ecosystems to a certain extent and alleviate the crisis of freshwater fish biodiversity. In order to explore the fish community distribution patterns and key factors after ecological restoration and the health status of the watershed, fish and environmental data were collected from 39 sampling points in the Hun River Basin in the spring and autumn of 2021. A total of 51 fish species belonging to 11 families and 37 genera were collected during the survey, and the dominant species were Rhynchocypris lagowskii, Zacco platypus, Carassius auratus and Pseudorasbora parva. Compared with the results of past studies, the number of fish species has increased. The study found that the distribution of fish along the longitudinal gradient of the watershed showed obvious spatial differences and was divided into two groups. The results of canonical correspondence analysis (CCA) showed that agricultural land, urban land and grassland were the key factors for the spatial variation in fish communities in the Hun River Basin. The results of the F-IBI evaluation showed that the health status of the Hun River was fair or above fair, among which healthy, good, fair, poor and bad points accounted for 5.13%, 30.77%, 33.33%, 25.64% and 5.13%, respectively. The upper and middle reaches of the Hun River Basin were in better health, while the lower reaches were in poorer health, which was mainly affected by the intensity of human activities in different regions. This study will help watershed managers to make targeted restoration and protection measures for different regions.

Fish Biomonitoring and Ecological Assessment in the Dianchi Lake Basin Based on Environmental DNA

Fish are among the main target groups when conducting biomonitoring and ecological assessment of aquatic environments. Environmental DNA (eDNA) metabarcoding provides a unique opportunity to enhance biomonitoring throughput, precision, and standardization. However, few fish monitoring studies based on eDNA metabarcoding have been conducted at the basin scale. Taking Dianchi Lake and the three inflowing rivers (Panlong River, Baoxiang River, and Chai River) as research objects, this study monitored fish diversity via eDNA metabarcoding, and the Fish Index of Biological Integrity (F-IBI) was constructed and applied for the ecological assessment of the aquatic environment. Here, we detected 41 species belonging to 9 orders, 15 families, and 35 genera in the sampling areas, including 17 native fish species such as Hemiculter leucisculus, Cyprinus carpio, and Silurus soldatovi. Distinct diversity patterns were observed among Dianchi Lake and the three inflowing rivers. Particularly, the fish diversity of Panlong River was richer than that of Dianchi Lake, Baoxiang River, and Chai River. Water temperature (WT), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) significantly influenced the distribution of fish communities in most sampling sites of the Dianchi Lake basin (p &lt; 0.05). Moreover, according to the F-IBI assessment system, 25% of the sampling sites were defined as ‘fine’ or above, and 75% were ‘impaired’ or below. This study provided insights into the ecological restoration and precise management of the aquatic environment of the Dianchi Lake basin.

Diversity, abundance and distribution of fish community in the Mangroves of the MPA of Niamone-Kalounayes (Casamance, Senegal)

Diversity, abundance and distribution of fish community in the Mangroves of the MPA of Niamone-Kalounayes (Casamance, Senegal)

Projected stream fish community risk to climate impacts in the Northeastern and Midwestern United States

Climate change is expected to alter stream fish habitat potentially leading to changes in the composition and distribution of fish communities. In the Northeastern and Midwestern United States we identified the distribution and characteristics of those fish communities most and least at risk of experiencing changes in climate which deviate from the climate they are associated with. We classified stream fish communities based on a suite of climate and environmental variables with multivariate regression trees under both recent and future conditions based on eight climate models. Our findings showed that some areas, such as the majority of the Illinois, Wisconsin, and Iowa), have high levels of risk of change in stream class, while much of Kentucky, West Virginia, Virginia, Pennsylvania, Eastern Ohio, Southern Michigan, and the Atlantic Coast are at relatively low risk. Stream class shifts ranged from over 75% of segments lost (associated with cooler temperatures) to gains of over 40% (associated with warmer temperatures). Common warmwater species such as green sunfish (Lepomis cyanellus), bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides) are expected to have the largest net gains in associated stream classes, while species associated with cooler streams such as Southern redbelly dace (Chrosomus erythrogaster), slimy sculpin (Cottus cognatus), and Eastern blacknose dace (Rhinichthys atratulus) were expected to experience the largest proportional losses. By pairing our climate risk predictions with other stressors such anthropogenic land use, habitat fragmentation, and water quality impairment, we identified opportunities for preservation (low risk due to all threats), restoration (low risk due to climate, high risk due to other stressors), and adaptation (high climate risk with low risk from other stressors). Understanding which communities are at risk due to climate change will aid in developing adaptation strategies to help sustain them in the future.

基于环境DNA宏条形码技术的秦淮河生物多样性研究

秦淮河是南京的母亲河, 其生物多样性受城市化进程影响面临严重威胁, 而物种资源调研是生物多样性保护的基础。环境DNA宏条形码技术较形态学监测是一种简单高效、灵敏度高的新型监测技术。为探究秦淮河浮游生物、底栖动物及鱼类的生物多样性, 于2019年7月, 采用环境DNA宏条形码技术对其进行了探究, 并分析了秦淮河上下游间的差异及环境因子对其群落结构的影响。结果表明: 秦淮河共监测到浮游动物13属22种407个操作分类单元(Operational Taxonomic Units, OTUs), 浮游植物85属60种4445个OTUs, 底栖动物16属17种212个OTUs, 鱼类53属44种1663个OTUs。其中浮游动物以游泳轮虫目(Ploima)和双甲目(Diplostraca)为主, 共占浮游动物63.37%, 浮游植物以隐藻门(Cryptomonas)和褐藻门(Ochrophyta)为主, 共占浮游植物88.11%, 底栖动物中节肢动物门(Arthropoda)占比最高, 达91.67%, 鱼类中鲤形目(Cypriniformes)占比最高, 达69.99%。与秦淮河历史形态学监测数据相比, 环境DNA宏条形码技术在物种丰度鉴定方面显著高于传统形态学鉴定的物种丰度。通过主坐标分析和PERMANOVA检验, 发现秦淮河下游、上游南支和上游北支间有极显著差异(P < 0.001)。其中浮游动物、浮游植物和底栖动物受分组影响更大, 分组对鱼类的影响相对较小。下游α多样性较上游更为贫乏, 上游南支(南京)α多样性较上游北支(句容)更丰富。浮游生物和底栖动物均表现出了明显的随距离增加而衰减的趋势。冗余分析表明, 较低营养级的生物对环境因子的变化更为敏感, 浮游生物和底栖动物的主要影响因子为总氮、总有机碳、总磷、氨氮、化学需氧量和溶解氧。鱼类的影响因子为溶解氧、总有机碳、总氮、总磷和化学需氧量。研究通过对秦淮河生物多样性的调研, 可为秦淮河的生物多样性保护提供理论参考。;Qinhuai River is the mother river of Nanjing, and its biodiversity is seriously threatened by the process of urbanization. The survey of species resources is the basis of biodiversity protection. Compared with morphological monitoring, the environmental DNA metabacroding is a simple, efficient and sensitive new monitoring technology. In order to explore the biodiversity of plankton, zoobenthos and fish in Qinhuai River, the environmental DNA metabacroding was used to explore it in July 2019, the differences between upstream and downstream of Qinhuai River were analyzed, and the relationship between the community composition of Qinhuai River and environmental variables was evaluated. The results showed that a total of 13 genus, 22 species and 407 operational taxonomic units (OTUs) of zooplankton, 85 gennus, 60 species and 4445 OTUs of phytoplankton, 16 genus, 17 species and 212 OTUs of zoobenthos, 53 genus, 44 species and 1663 OTUs were detected through the environmental DNA metabacroding. Among them, Ploima and Diplostraca, accounting for 63.37%, were dominant species in zooplankton community at the order level. The most abundant species in phytoplankton community at the phylum level were Cryptomonas and Ochrophyta, accounting for 88.11%. The zoobenthos were dominated by Arthropoda at the phylum level, which accounted for 91.67%. The Cypriniformes accounting for 69.99%, were dominants in fish of different samples at the order level. Compared with the historically morphological monitoring data of Qinhuai River, the environmental DNA metabarcoding technique was more powerful than the morphological method in assessment of species richness. Through the principal coordinate analysis (PCoA) and PERMANOVA test, a significant difference (P < 0.001) was found among downstream, the south branch of upstream and the north branch of upstream of Qinhuai River. Zooplankton, phytoplankton and zoobenthos were more affected by the group of sites than fish. Alpha(α) diversity of downstream in Qinhuai River was poorer than that of upstream, and Alpha(α) diversity of the south branch of upstream (Nanjing) was richer than that of the north branch (Jurong). All of the taxa of Qinhuai River except fish showed strong relationship between geographical distance (km) and biotic community similarity based on Bray-Curtis distance. Redundancy analysis (RDA) showed that organisms with lower trophic levels were more sensitive to changes in the environmental factors. The main influencing factors in plankton and zoobenthos community distribution were total nitrogen (TN), total organic carbon (TOC), total phosphorus (TP), ammonia nitrogen (NH₃-N), chemical oxygen demand (COD) and dissolved oxygen (DO). While the key factors in fish community distribution were DO, TOC, TN, TP and COD. Our results can provide a theoretical reference for the protection of the biodiversity of Qinhuai River.

A first attempt at a holistic analysis of various influencing factors on the fish fauna in the Eastern European Alps

Fish are some of the most threatened vertebrates in the world due to their often-sensitive response to environmental changes. Major land-use changes in the European Alps have direct and indirect impacts on fish communities, and these impacts are expected to increase in the future. Therefore, the identification of factors that are associated with the distribution of fish communities is of great importance to develop guidelines for management, precautions and sustainable use of running waters. In this study, the relationship of various factors – landscape structure and land use, topography, morphology, hydrology, physical and chemical water characteristics, hormonally active substances, pesticides, food availability, fisheries and piscivores birds – with fish assemblages are analysed. Field data from 81 stream sections from 2001 metres above sea level (m.a.s.l.) down to 219 m.a.s.l. are used in the study. The results reveal that the number of fish species has a strong association with topographic characteristics in the catchment area as well as with landscape configuration. Fish abundance and biomass are associated mostly with land-use type, hydrology, morphology as well as topography. In addition, there are indirect connections between fish abundance and biomass through land-use type, topography, water properties and hydromorphology. The results clearly indicate that not a single factor, but a multitude of factors are associated with the fish communities in the Eastern European Alps.

The functional composition of nearshore fish communities demonstrated by trait analysis: Response to environmental gradients

There is limited understanding on nearshore fish community functioning in relation to changing environmental gradients. To address this, we investigated the trait composition of fish communities in five regions along the Portuguese coast during 4 years. Northern regions were characterized by higher Chlorophyll-α and small-sized species with short lifespans. The southernmost region was characterized by warmer waters, more intense upwelling events and typical warm-water species. Higher species richness and functional redundancy at the southernmost region suggested that in case of potential species loss, community functioning would be less affected in this region, and thus, a certain level of community resilience is maintained. The central region presented lower functional redundancy and high functional richness, which indicated the presence of rare species with rare traits, suggesting a more vulnerable community. This information on the nearshore fish community distribution may be particularly important towards managing coastal ecosystems in response to changing environmental conditions.

Fish Ecology of the Alto Madre de Dios River Basin (Peru): Notes on Electrofishing Surveys, Elevation, Palm Swamp and Headwater Fishes

Our study analyzes the distribution of fish communities related to the environmental variables of the Alto Madre de Dios River, an Andean-Amazon watershed of southern Peru, between 300 and 2811 m a.s.l. within the Manu Biosphere Reserve. We provide new ecological and diversity data on fishes for these poorly studied rivers and new data for palm swamp habitats. With electric fishing techniques, we collected a total of 1934 fish specimens belonging to 78 species, 42 genera and 15 families. To assess main patterns of diversity we combined SIMPER and ANOSIM with canonical correspondence analysis to obtain an overview of the community structure of fish and their distribution related to aquatic habitats. Our results show an important shift on fish diversity at 700 m a.s.l. separating headwater and middle-lowland communities. Electrofishing was a hindrance due to the depth, flow and low conductivity of the rivers, but also allowed us to capture fish not observed with other techniques. We also compared the use of elevation with slope as an alternative variable for statistical analysis. Our results show that slope offers a solid and equivalent explanation for fish distribution variability, avoids redundance, and instead of giving geographical data offers ecologically solid information.

The Effect of Laver-Farming on the Distribution of Copepod Community in the West Coast of Korea

Kim, S,-K.; Kim, J.-C., and Choi, J.-Y., 2020. The effect of laver-farming on the distribution of copepod community in the west coast of Korea. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Geospatial Research of Coastal Environments. Journal of Coastal Research, Special Issue No. 102, pp. 63-68. Coconut Creek (Florida), ISSN 0749-0208.To understand the effect of farms on copepod communities in the coastal marine environment, this study investigated the environmental variables and copepod communities in June 2016 in the coastal region adjacent to the Geum River estuary. Copepod communities were more abundant in laver farms than in areas not covered by laver farms, due to the availability of various food sources and low predation risks. Although laver farms had low abundance (cells/mL) of phytoplankton, they were observed to have high species diversity. This provides an environment in which a variety of food items is available for copepod communities. Moreover, fishes were more abundant in the areas not occupied by farms than in laver farms. the complex habitat structure created by abundant laver, as well as frequent human interference in laver farms, has a negative impact on the distribution of fish communities. However, the abundance of copepod communities in laver farms is important for a continuous supplement to the diet of fishes in the marine environment, where food sources are likely to be depleted. Thus, the positive effects of laver farms on copepod communities can greatly contribute to the population growth of fishes and to the sustainability of copepod communities in the coastal marine environment. However, the artificial disturbances that frequently occur in laver farms are likely to lead to eutrophication and various types of water pollution in the coastal marine environment, so proper control and management of human activity are required.

Space-time dynamics in monitoring neotropical fish communities using eDNA metabarcoding

The biodiverse Neotropical ecoregion remains insufficiently assessed, poorly managed, and threatened by unregulated human activities. Novel, rapid and cost-effective DNA-based approaches are valuable to improve understanding of the biological communities and for biomonitoring in remote areas. Here, we evaluate the potential of environmental DNA (eDNA) metabarcoding for assessing the structure and distribution of fish communities by analysing water and sediment from 11 locations along the Jequitinhonha River catchment (Brazil). Each site was sampled twice, before and after a major rain event in a five-week period and fish diversity was estimated using high-throughput sequencing of 12S rRNA amplicons. In total, 252 Molecular Operational Taxonomic Units (MOTUs) and 34 fish species were recovered, including endemic, introduced, and previously unrecorded species for this basin. Spatio-temporal variation of eDNA from fish assemblages was observed and species richness was nearly twice as high before the major rain event compared to afterwards. Yet, peaks of diversity were primarily associated with only four of the locations. No correlation between β-diversity and longitudinal distance or presence of dams was detected, but low species richness observed at sites located near dams might that these anthropogenic barriers may have an impact on local fish diversity. Unexpectedly high α-diversity levels recorded at the river mouth suggest that these sections should be further evaluated as putative “eDNA reservoirs” for rapid monitoring. By uncovering spatio-temporal changes, unrecorded biodiversity components, and putative anthropogenic impacts on fish assemblages, we further strengthen the potential of eDNA metabarcoding as a biomonitoring tool, especially in regions often neglected or difficult to access.

Effects of multiple stressors on the distribution of fish communities in 203 headwater streams of Rhine, Elbe and Danube

Fishes in European rivers are threatened by manifold stressors such as structural degradation, water pollution, overexploitation, land-use changes in the catchment, invasive species and global processes including climate change. Identifying main stressors in a stream/river system is of utterly importance for efficiently utilizing the scarce funds for conservation measures in order to achieve the best possible outcome. Within 203 headwater streams of Rhine, Elbe and Danube, we quantified the relative influence of different environmental stressors (water chemistry, food availability (macroinvertebrates), terrestrial predators) and anthropogenic stressors (land use, structural modification of streams) on fish assemblages at different spatial scales based on multivariate biota-environment models. In our analyses, the predictor variables percentage of impoundments, crop farming (especially erosion-prone crops such as maize) and ground sealing in the catchments, the number of wastewater treatment plants and biogas plants in the catchments as well as structural modifications of river banks were most often identified as stressors influencing fish community composition. However, the effects of the stressors varied between the investigated survey-area scales (two different catchments sizes and riparian strips) and regionally (entire study area, major drainage systems, river catchments, stream sizes, geographical subregions). In most cases, fish community composition was simultaneously affected by multiple stressors, underpinning the need for a more holistic and ecosystem-based approach in freshwater conservation and restoration.

Limited dispersion and quick degradation of environmental DNA in fish ponds inferred by metabarcoding

Abstract:BackgroundEnvironmental DNA (eDNA) metabarcoding is a promising tool for rapid, non‐invasive biodiversity monitoring.AimsIn this study, eDNA metabarcoding is applied to explore the spatial and temporal distribution of fish communities in two aquaculture ponds and to evaluate the detection sensitivity of this tool for low‐density species alongside highly abundant species.Materials &amp; MethodsThis study was carried out at two artificially stocked ponds with a high fish density following the introduction and removal of two rare fish species.Results &amp; DiscussionWhen two rare species were introduced and kept at a fixed location in the ponds, eDNA concentration (i.e., proportional read counts abundance) of the introduced species typically peaked after two days. The increase in eDNA concentration of the introduced fish after 43 hrs may have been caused by increased eDNA shedding rates as a result of fish being stressed by handling, as observed in other studies. Thereafter, it gradually declined and stabilised after six days. These findings are supported by the highest community dissimilarity of different sampling positions being observed on the second day after introduction, which then gradually decreased over time. On the sixth day, there was no longer a significant difference in community dissimilarity between sampling days. The introduced species were no longer detected at any sampling positions on 48 hrs after removal from the ponds. eDNA is found to decay faster in the field than in controlled conditions, which can be attributed to the complex effects of environmental conditions on eDNA persistence or resulting in the vertical transport of intracellular DNA and the extracellular DNA absorbed by particles in the sediment. The eDNA signal and detection probability of the introduced species were strongest near the keepnets, resulting in the highest community variance of different sampling events at this position. Thereafter, the eDNA signal significantly decreased with increasing distance, although the signal increased slightly again at 85 m position away from the keepnets.ConclusionsCollectively, these findings reveal that eDNA distribution in lentic ecosystems is highly localised in space and time, which adds to the growing weight of evidence that eDNA signal provides a good approximation of the presence and distribution of species in ponds. Moreover, eDNA metabarcoding is a powerful tool for detection of rare species alongside more abundant species due to the use of generic PCR primers, and can enable monitoring of spatial and temporal community variance.