Littoral Habitats Research Articles

Conservation biology of three threatened Limonium species endemic to Zakynthos Island (Ionian Islands, Greece)

Abstract Knowledge of the life history traits, reproductive biology and demography of rare species is fundamental for their conservation, yet plant population monitoring is uncommon. The restricted ranges of the Limonium species endemic to the Mediterranean area, combined with the vulnerability of their specialized littoral habitats, indicate the need for appropriate conservation measures. We evaluate the conservation status and estimate the future extinction risk of three Limonium species endemic to Zakynthos Island in the Ionian Islands, Greece (Limonium korakonisicum, Limonium phitosianum and Limonium zacynthium) using 5 years of monitoring data. We compile information on their geographical distribution, population dynamics, reproductive biology and genetic diversity. Population sizes and survival rates of seedlings exhibited marked annual fluctuations, although fecundity and relative reproductive success remained high throughout the monitoring period. We observed a dominance of mature individuals in all three species, indicating their increased tolerance to salinity. Three subpopulations each of L. phitosianum and L. zacynthium were genotyped using five microsatellite loci. The observed number of alleles and the low gene flow value potentially indicate reduced genetic diversity, inbreeding, and limited gene flow within and among subpopulations of both species. Based on the IUCN categories and criteria, we assess L. korakonisicum as Critically Endangered, L. phitosianum as Near Threatened and L. zacynthium as Endangered. Population viability analyses predict that, among the three species, L. zacynthium will face the highest risk of extinction within the next 50 years. Knowledge of the biology of these species provides data essential for identifying critical factors for their survival and for proposing targeted conservation measures.

Nutrients limiting the growth of planktonic and benthic-littoral primary producers in Patagonian Andean Lakes

In this work, we assess differences in nutrient limitation (nitrogen and phosphorus) between benthic-littoral (in the littoral habitat) and planktonic (in the epi-pelagic habitat) primary producers of seven Patagonian Andean lakes in southern South America. We conducted nutrient enrichment experiments using nitrate, ammonium, and phosphate to identify which nutrient(s) restrict primary producers’ growth in each lake habitat. Also, we determined the concentration of dissolved inorganic nitrogen (DIN), soluble reactive phosphorous (SRP), and the nitrogen to phosphorous ratio (DIN:SRP) at the littoral and epi-pelagic habitats of each lake. For all the lakes, benthic-littoral primary producers were limited by nitrogen, while planktonic primary producers in the epi-pelagic habitat were colimited by nitrogen and phosphorus. Our study is the first to show that different nutrients limit the growth of benthic-littoral and planktonic primary producers in Patagonian Andean lakes. This contributes to our understanding of lake ecology in a region where there is limited information on benthic-littoral habitats. This is important because globally, there is an increase in periphyton blooms in the benthic-littoral habitats of oligotrophic lakes, while the pelagic habitats remain unchanged. Additionally, we found nutrient concentrations in the lakes are up to 7.4 times higher than those described in previous studies, which may be related to anthropogenic impact and natural events. If nutrient levels continue to increase, algal blooms in Patagonian Andean lakes may become a regional issue, especially in the benthic-littoral habitats.

Field kinematics of intermittent swimming in bluegill sunfish (Lepomis macrochirus)—pelagic locomotion and littoral maneuverability

Abstract Objectives Locomotion is essential for the survival of animals. Fishes have evolved mechanisms to minimize the cost of transport. For example, Bluegill Sunfish (Lepomis macrochirus) employ intermittent swimming, which involves swimming at relatively slow speeds with short propulsive bursts alternating with gliding episodes. This typically involves axial undulation powered by slow-twitch muscle, either with or without pectoral fin usage. The propulsive bursts are at higher tailbeat frequencies than observed for a given average speed with constant propulsion, and muscle physiology experiments show that the propulsive bursts produce relatively high power, while the glide reduces fatigue relative to continuous activity. However, Bluegill encounter complex 3D in-shore habitats, in which an intermittent swimming gait may enable successful capture of habitat-specific prey. Methods Field observations of Bluegill Sunfish were made via underwater videography in Lake Waban, Massachusetts. Key Findings In both pelagic and littoral habitats, Bluegill employed intermittent swimming. This provided the maneuverability and muscle activity needed to capture prey items suspended in the water column and enabled effective prey detection and maneuverability for feeding on sessile invertebrates in dense vegetation. Radio telemetry studies demonstrated that bluegill moved regularly between the pelagic and the littoral. Conclusion In both zones, intermittent swimming may provide both energetic and foraging advantages.

Environmental and ecological drivers of eye size variation in a freshwater predator: A trade‐off between foraging and predation risk

Abstract Variations in the size and shape of the eye have been observed in many species of fish. As eye size is positively related to visual acuity, larger eyes should favour foraging and detection of predators. However, few studies have examined the variation in eye morphology in relation to the complexity of lake conditions, including environmental perturbation and spatial variation in predation and competition. Such tests are especially important as the degrading of the visual climate is expected due to climate change, where browning, turbidity and variations in structural complexity should set different demands for visual acuity of foraging fish under predation risk. In this study, we tested the variation of the eye size among 667 individuals of an aquatic predator perch, Perca fluviatilis, from littoral and pelagic habitats of 14 lakes. We used Secchi depth to assess the effects of the visual climate of our lake systems, as fish foraging is highly related to visual conditions, and studied eye size variation in relation to the contribution of the pelagic resources to an individual's diet and the risk of predation. Secchi depth, the pelagic contribution to the diet and the percentage of piscivores had significant effects on eye size. These variable outcomes suggest that the lake environment in terms of visual climate, predation landscape and diet are major factors of eye size variation in this generalist predator. As many fish species trade off foraging against predation risk, future studies will show whether the complexity of intra‐ and interspecific interactions contribute to the variation in eye size in freshwater fish. Read the free Plain Language Summary for this article on the Journal blog.

Year-round sampling of the fish community in a boreal lake: differences between summer and winter influence estimates of species composition, catch, and fish size.

Boreal lakes experience pronounced seasonal variation in abiotic factors, especially light, temperature, and oxygen. A deep boreal humic lake was sampled year-round to test putative changes in total fish catch, species composition, catch-per-unit-effort (CPUE), habitat use, fish size, and condition. Monthly sampling was conducted in Lake Pääjärvi, southern Finland, during one full year in 2020-2021 as well as in March and August 2021 and 2022. The fish community was dominated by cyprinid species in all months, but the percentage of percid fish caught increased during the warm summer period. Most fish were caught in littoral habitats and the highest catches occurred in summer, but some species (e.g., ruffe, Gymnocephalus cernua, and pikeperch, Sander lucioperca) remained abundant in the winter catch. The body size of fish was larger in the winter catch, while condition factor was higher in summer for most species. Fish species proportions in total catch, CPUE, and average size of fish were closest to the annual mean values in September, which may be used as the optimal period to monitor fish communities of similar deep boreal lakes. Our findings highlight the need for year-round research to reveal the impacts of rising temperatures and diminishing ice-covered periods in fish communities and lake food webs.

Identification of fish behaviours in littoral habitats of Lake Buyo (south-west Ivory Coast) using video surveillance

Video surveillance is a non-extractive and less disruptive method of observing fish in their natural environment. Increasingly used, this technique makes it possible to describe the behaviour of fish in their habitat. In Côte d'Ivoire, the use of waterproof cameras for ichthyological purposes is still not widespread. This study proposes to use video surveillance to identify the different behaviours performed by fish in the littoral habitats of the Buyo dam lake. The objective is to know the mode how fish use the littoral habitats of Lake Buyo in order to provide managers with important data for developing programmes to preserve and manage these environments. Four unbaited camera systems were deployed at each station between 7 am and 6 pm. In the laboratory, various criteria were used to identify the behaviour of the fish. The results show that 8 species of fish frequented the littoral habitats of Lake Buyo to feed, reproduce and protect themselves from predators. Feeding (62.70%) was the most frequently observed activity, followed by reproduction (32.32%). The Dera and Pk15 stations recorded the highest number of species and behaviours. These behaviours varied according to species; Coptodon zillii stood out by displaying the highest average frequency (32.12 activities/day) of all types of behaviour observed in fish. The data from this study are essential for developing strategies to effectively conserve coastal areas in order to ensure the long-term survival of the species.

Impacts of hydrologic management on the eutrophication of shallow lakes in an intensive agricultural landscape (Saskatchewan, Canada)

Abstract Hydrologic management of shallow lakes is often undertaken to prevent fluctuations in lake level, and to ensure sufficient water volume for economic, domestic, and recreational uses, but there is inconsistent evidence of whether lake‐level stabilisation through hydrological management promotes or hinders eutrophication. Here we used multi‐proxy paleolimnological assessments of water quality (sedimentary carbon, nitrogen, total phosphorus, fossil pigments), and zooplankton community ecology (fossil Cladocera assemblages), combined with Landsat‐derived estimates of lake surface area in two shallow eutrophic lakes, in the Prairies of southern Saskatchewan, Canada, to quantify how 8 decades of contrasting hydrological management strategies (continuous or intermittent) affect primary production and phytoplankton composition. Analysis revealed that irregular hydrological management of Pelican Lake led to sharp increases in primary production concomitant with lake‐level decline. In contrast, continuously managed Buffalo Pound Lake, a drinking water reservoir for regional cities, exhibited slow, persistent eutrophication over decades despite active regulation of water levels. In both lakes, strong correlations of δ 15N values with pigments from diazotrophic cyanobacteria (canthaxanthin) showed that N2‐fixation increased during eutrophication irrespective of the timing of change. Finally, variation in fossil cladoceran density and composition reflected changes in pelagic and littoral habitats (e.g., reduced macrophyte cover) due to changes in both lake level and water quality. Basin comparison shows that while hydrologic management can moderate water quality degradation due to lake‐level change, it does not prevent eutrophication when nutrient influx remains high. Given that regional water availability is forecast to decline in coming decades, we anticipate that continued hydrological management will be unavoidable and will be unable to improve water quality unless nutrient influx is also controlled.

Thermal habitat fragmentation in stratified lakes induces resource waves that brook charr track across seasons

The spatial configuration of thermal habitats constrains the thermoregulatory performance of ectotherms. Thermal landscapes also vary through time, which is particularly relevant in seasonal environments such as temperate lakes. Indeed, elevated temperatures in the epilimnion of dimictic lakes during summer could substantially reduce the use of this habitat by cold‐stenothermic fish during the stratified period. The main objective of this study was to evaluate whether thermal habitat fragmentation in stratified lakes modulates accessibility to resources that brook charr, Salvelinus fontinalis, which is a mobile consumer, can track across seasons. More specifically, we hypothesize that reduced access to the littoral habitat during summer enhances foraging opportunities in this habitat during winter. We used an automatic acoustic telemetry system offering full coverage of the lake to continuously record brook charr locations across seasons, and we estimated zoobenthos abundances in the littoral habitat using image processing and semi‐automatic classification. While brook charr concentrate in the metalimnion of the pelagic habitat in summer, most individuals in winter shift to a shallow bay that is unexploited in summer due to thermal constraints. In this habitat, zoobenthos abundance is more than twice as high at the end of the summer compared to littoral habitats close to the thermal refuge in the pelagic habitat. Surprisingly, brook charr showed strong within‐lake site fidelity between two consecutive summers, which suggests that spatial memory could be a key driver of seasonal habitat use in this lacustrine population. Overall, our results suggest that thermal barriers create fragmentation between littoral and pelagic habitats that in turn produces resource opportunities that brook charr can track across seasons.

Mysis segerstralei, an unexpected but important prey for resident Arctic charr (Salvelinus alpinus) in a Svalbard lake

Mysis segerstralei is distributed over a wide geographic area and in habitats with a variety of salinity conditions, including marine and brackish waters around Svalbard. The species has seldom been found in freshwater lakes, and the discovery of M. segerstralei in Lake Pulmankijärvi at the border between Northeastern Norway and Finland, may represent the single known freshwater occurrences in western Europe. Svalbard lake systems are characterized by very low water temperatures, long-term ice cover, and low levels of nutrients. Food is thus limited, and chironomids generally dominate the stomach contents in Arctic charr, the only freshwater fish species on Svalbard. Based on several surveys in more than 30 of Svalbard lakes over many decades, M. segerstralei has only been found as food for Arctic charr in Lake Vårfluesjøen. In a later fishery survey, we studied the diet of Arctic charr in this lake. The stomach contents from Arctic charr sampled in the profundal habitats were dominated by M. segerstralei, but the species was also among the most frequent prey items in the littoral and pelagic habitats. This unexpected occurrence of M. segerstralei demonstrates the high importance of mysids even in a low-productive, High Arctic lake.

Filling gaps in the Webbnesia marine diversity: The madeiran sponge fauna

Despite few pioneering works in the late XIX and early XX century, the poriferan fauna of Madeira has remained mostly unexplored until today, Madeira being one of the least studied eastern Atlantic archipelagos in terms of its sponge diversity. After a thorough analysis of both new material collected by SCUBA diving as well as a literature research, 140 sponge species are known to occur in the Madeira archipelago. From the 56 species identified by both collected material and pictures, approximately 60% (34 species) are new records for the Archipelago. These 34 new records were found associated with littoral rocky substrates and, to a lesser extent, caves, rhodolith beds and wrecks, within a depth range of 10–35 m depth. Our records also contain several Mediterranean species that have not been previously recorded in the North Atlantic, several North-east Atlantic species whose presence in Madeira marks their southernmost limit of occurrence, as well as elements from the subtropical West African fauna. Amongst the new additions to its sponge fauna there are the first records of Homomscleromorpha, with at least three Oscarella species noted, as well as a new species of Hemimycale (Demospongiae, Poecilosclerida). Yet, this is still an underestimation of Madeira's real sponge diversity. Data on Madeiran sponge fauna is still skewed towards shallow and littoral habitats, with other less accessible environments, such as caves, rhodolith beds or the deep sea, remaining largely unexplored. Similarly, complex poriferan groups (e.g. calcareans, haplosclerids, tetractinellids, hymedesmids) have only been partially studied, and their true diversity remains unknown. Finally, due to a lack of prior baseline it is difficult to conclude if some newly recorded species are non-indigenous, range-expanding or simply previously overlooked native species. However, it is now clear that two previously thought non-indigenous species, Mycale (Carmia) senegalensis and Prosuberites longispinus are in fact native to the Archipelago, their prior status as non-indigenous arising from the lack of prior confirmation of their presence outside of port facilities.

Drivers of macroinvertebrate assemblages in littoral and pelagic habitats of a large shallow lake: implications for bioassessment

Drivers of macroinvertebrate assemblages in littoral and pelagic habitats of a large shallow lake: implications for bioassessment

Sport fish movement responses to a littoral zone coarse woody habitat addition

AbstractObjectiveFish movements and distributions throughout an ecosystem are important for understanding ecological interactions, conservation, and management. Coarse woody habitat (CWH) additions are a popular habitat enhancement tool that can influence movements and distributions of fishes; however, behavioral responses in relation to CWH additions are understudied. The objectives of our study were to test for changes in habitat use and behavioral responses of Muskellunge Esox masquinongy, Smallmouth Bass Micropterus dolomieu, and Walleye Sander vitreus to CWH additions in a small inland northern lake over 3 years and to evaluate two common forms of fish tracking to estimate daily movement of these fishes.MethodsWe used passive integrated transponder tag data collected continuously at 10 littoral sites and radiotelemetry data collected biweekly during the summer–fall months prior (2017) and following (2018–2019) CWH addition to examine movement behaviors and estimate daily probability of movement for the three species among lake habitats using multistate models.ResultWalleye were the most likely to remain near CWH, followed by Smallmouth Bass and Muskellunge. All species were more likely to move away from the modified and unmodified littoral zones and were more likely to remain in the offshore zone. Increased movement of fish may be in response to CWH creating a refuge for forage fish and subsequent increases in prey search times.ConclusionOur results suggest that CWH additions may alter established species‐specific annual movements, distributions, and habitat use to differing degrees in ecosystems, as our results differ from other CWH studies. Methodologically, radio‐tagging was most effective for offshore tracking but most labor intensive. Novel passive integrated transponder arrays (less labor intensive once installed) worked well to monitor movement between habitat types in shallow littoral areas. Long‐term monitoring of behavioral changes will be essential to assessing the stability changes caused by these habitat alterations.

Food webs in isolation: The food-web structure of a freshwater reservoir with armoured shores in a former coastal bay area

Many shallow coastal bays have been closed off from the sea to mitigate the risk of flooding, resulting in coastal reservoir lakes with artificial armoured shorelines. Often these enclosed ecosystems show a persistent decline in biodiversity and ecosystem services, which is likely reflected in their food-web structure. We therefore hypothesize that the food webs of coastal reservoir lakes with armoured shorelines (1) consist of relatively few species with a low food-web connectance and short food chains, and (2) are mainly fuelled by autochthonous organic matter produced in the pelagic zone. To investigate these two hypotheses, we used stable-isotope analysis to determine the food-web structure of lake Markermeer (The Netherlands), a large reservoir lake with armoured shorelines in a former coastal bay area. Contrary to expectation, connectance of the food web in lake Markermeer was comparable to other lakes, while food-chain length was in the higher range. However, the trophic links revealed that numerous macroinvertebrates and fish species in this constructed lake exhibited omnivorous feeding behaviour. Furthermore, in line with our second hypothesis, primary consumers heavily relied on pelagically derived organic matter, while benthic primary production exerted only a minor and seasonal influence on higher trophic levels. Stable-isotope values and the C:N ratio of sediment organic matter in the lake also aligned more closely with phytoplankton than with benthic primary producers. Moreover, terrestrial subsidies of organic matter were virtually absent in lake Markermeer. These findings support the notion that isolation of the lake through shore armouring and the lack of littoral habitats in combination with persistent resuspension of sediments have affected the food web. We argue that restoration initiatives should prioritize the establishment of land-water transition zones, thereby enhancing habitat diversity, benthic primary production, and the inflow of external organic matter while preserving pelagic primary production.

Late Quaternary ostracode stratigraphy of Mono Lake (California, USA): evidence for benthic ecosystem sensitivity to climate change

ABSTRACTThe response of aquatic ecosystems in the Sierra Nevada (California, USA) to late Quaternary hydroclimate changes remains mostly unknown. Mono Lake, a large endorheic lake just east of the Sierra Nevada, contains an expanded archive of laminated sediments that can be used to examine the response of benthos to environmental changes. Fossil ostracodes from a radiocarbon‐dated core were used to examine paleoecologic changes from ~16.6 to 4.3k cal a bp. Seven species were identified, with the co‐occurrence of Limnocythere ceriotuberosa and Limnocythere staplini indicating a large SO42−‐rich lake in the Pleistocene. The Younger Dryas was complex, with Fabaeformiscandona caudata reflecting a cold and deep lake ~13.0–12.2k cal a bp, followed by an interval of extensive littoral habitat from ~12.2–11.6k cal a bp. Ostracode diversity, valves g–1 and the ratio of adult:juvenile valves declined after ~10.7k cal a bp due to regression, altered hydrochemistry and seasonal anoxia. Strong seasonality during the Early Holocene is suggested by the presence of reworked ostracodes and macrocharcoal, delivered to Mono Lake by erosion of ancient lake beds in the basin. A depauperate ostracode fauna in the Middle Holocene suggests a strong sensitivity to drought in this ecosystem, which has implications for biodiversity in the future.

An individual-based model to predict the spatial distribution of northern pike, European perch and pikeperch from habitat use in a reservoir subject to water level fluctuations

Reservoirs are subject to artificial water level fluctuations leading to a degradation of the littoral habitats. This often results in reduced productivity and biological diversity, particularly for fish. The development of predictive tools of fish population dynamics linked to habitat characteristics can help to optimize management actions such as habitat restoration. We developed a spatially explicit individual-based model, the 3Plake model, which predicts the spatial distribution of three fish species, northern pike, European perch and pikeperch, over seasons and diel cycles according to their habitat use. The model was calibrated with an accurate description of habitat and high spatial and temporal resolution data of fish movements in a French reservoir. The model calibration is only based on a species-specific coefficient of habitat selectivity. It was chosen to (i) match the observed and simulated traveled hourly and daily distances and (ii) minimize a metric quantifying the distance between observed and simulated density maps. The 3Plake model correctly simulated the means of traveled distances and the species distributions along the year on the study reservoir. The minimal input required (HSI maps and maximum distance range) allows its easy implementation on other reservoirs and fish species. It could be used to assess the impact of habitat restoration or water level management scenarios on fish distribution.

A catalogue of the nematode slide collection from the late W.L. Nicholas held at National Research Collections Australia, CSIRO.

A catalogue is presented of the nematode slide collection of W.L. Nicholas, which is deposited in the National Research Collections Australia at CSIRO. This is the most extensive slide collection of free-living marine and estuarine nematodes from Australia to date, and consists of 553 putative species, collected across a wide range of Australias eastern and northern regions over the course of nearly 40 years. The collection contains mostly marine and estuarine free-living nematodes collected on coarse substrate in littoral habitats. The most abundant genera were Desmodora, Theristus, and Onyx. Most taxa were found rarely, being recorded only once, and repeated sampling at several sandy beach sites revealed only a small proportion of the fauna on more than one occasion. A significant proportion of the taxa were also found to be widespread, occurring on more than one occasion at more than one location, with Theristus sp., Onyx sp., and Viscosia sp. occurring in the greatest number of localities. The catalogue adds an additional 90 species and 160 genera to the documented fauna of Australian free-living nematodes verifiable by specimens in permanent collections. It thus provides a better framework for studying nematode biodiversity and biogeography in the region.

Response of yellow perch to water level fluctuations in oligotrophic, north‐temperate inland lakes

AbstractInformation on yellow perch Perca flavescens population dynamics and responses to various abiotic and biotic factors in oligotrophic, north‐temperate inland lakes is limited. Water level fluctuations are known to influence available habitat and biological communities within the littoral zones of lakes, yet research is lacking for yellow perch in Wisconsin. The goal of our study was to characterize yellow perch population‐level responses to natural water level fluctuations in four northern Wisconsin lakes using a 39‐year time series. On average, increasing water level periods correlated with lower mean fyke net and gill net relative abundances (catch‐per‐unit‐effort), though generally not statistically significant. Yellow perch mean relative weight varied among lakes and was significantly greater during increasing water level periods for all lakes except one. The lack of statistically significant findings potentially suggests a buffering mechanism of north‐temperate oligotrophic lakes due to their small surface area to volume ratios, relative lack of nutrients, and(or) littoral structural habitat compared to other systems (e.g., shallow eutrophic lakes). Our results suggest that natural water level fluctuations may not be an environmental concern for yellow perch populations in some north‐temperate oligotrophic inland lakes.

Littoral meiofauna community structure in San Julián bay, Santa Cruz province, Argentina

For the first time, standing stocks and community structure have been reported in San Julián Bay, located in the Santa Cruz province, toward the southern tip of South America, within the sub-Antarctic region. The mean density of the meiofauna found was 6724 individuals/10 cm2, with a high dominance of nematodes (97.69%). Multivariate studies (PERMANOVA) revealed two distinct meiofauna assemblages: one, in an upper littoral salt marsh habitat and other, in a medium to low soft bare sediment. In the middle of the bay —in front of San Julián city— salt marsh habitats had the highest meiofaunal density, while bare sediments (medium-low levels) were the lowest. The mean average in the salt marsh area was 12246 individuals/10 cm2, with nematodes being dominant followed by oligochaetes as the subdominant taxa. The mean average in bare sediments (medium to low levels) was 3962 individuals/10 cm2, with nematodes as dominant and turbellarians, mastigophorans and maxillopodos (harpacticoid copepods) as subdominant taxa. Bare sediments related to Patagonian mussel’s populations presented the lowest meiofauna densities. Diversity showed an opposite trend, with a maximum in medium-low levels and a minimum in salt-marshes habitat. Richness in number of taxa ranged from 8 to 12, with a total number of 18 taxa. Despite dominance of nematodes in meiofauna assemblages is known, maximum density found in San Julián bay is much higher than previously found for estuaries from north and mid-latitudes littoral sandy beaches and in the nearby region of the Straits of Magellan and Beagle Channel and other sub-Antarctic and Antarctic sites. On the other hand, the number of meiofauna taxa (no nematodes) is low, and its community structure differs from what has been reported in previous studies. The meiofauna taxa assemblages provide evidence that, in salt-marsh habitats, they have the highest densities, but the lowest diversity when compared with lower levels. This is likely due to adaptation problems of meiofauna communities to a semi-terrestrial habitat.

Unraveling trait‐based fish community assembly in tropical reservoirs

AbstractDamming of large rivers has promoted well‐documented ecosystem changes that constitute critical threats to freshwater fish biodiversity. However, it is unclear how trait–environment relationships drive community assembly in older (>50 years) tropical river‐reservoir systems. We assessed physical features filtering functional traits (RLQ and fourth‐corner approaches) in seven tropical reservoirs along a major river, in southeastern Brazil, and correlated taxonomic and functional counterparts of local and beta diversity to assess niche‐based assembly processes under prevailing environmental conditions (null model approach). Lower littoral habitat availability (smaller area, volume, and riverine influence) favored species inhabiting open areas that feed on the bottom (mostly migratory species). Downstream position (lower elevation and inflow of water from the mainstem) allowed migrators to enter the reservoirs and promoted environmental heterogeneity, favoring detritivores, invertivores, and carnivorous generalists. Total blocking of the main channel excluded most migratory species from reservoirs at upstream reaches, whereas higher riverine influence and hydrological stability (larger area, volume, and water residence time) favored small‐sized sedentary species (omnivores and piscivores with parental care, mostly non‐native species) in the littoral zone. Correlations differing from null expectations for alpha diversity and nestedness revealed that niche‐based processes support species richness and loss under higher riverine influence and hydrological stability. Our study supports the importance of physical features to set functional spaces available for fish species, but random processes that boost taxonomic differences between reservoirs, largely related to non‐native species introductions, are the primary drivers of fish assemblage structure in tropical reservoirs long‐term disconnected from riverine dynamics.

A Dataset of Non-Indigenous and Native Fish of the Volga and Kama Rivers (European Russia)

Fish in the Volga-Kama River System (the largest river system in Europe) are important as a crucial food source for local populations; fish have the highest trophic level among hydrobionts. The purpose of this research is to describe the diversity of non-indigenous and native fish in the Volga and Kama Rivers, in the European part of Russia. This dataset encompasses data from June 2001 to September 2021 and comprises 1888 records (36,376 individual observations) for littoral and pelagic habitats from 143 sampling sites, representing 52 species from 42 genera in 22 families. The dataset has a Darwin Core standard format and has been fully released in the Global Biodiversity Information Facility (GBIF) under CC-BY 4.0 International license. The data are validated with several international databases such as FishBase, Eschmeyer’s Catalog of Fishes, the Barcode of Life Data System, and the SAS.Planet geoinformations system. Newly established populations have been found for several species belonging to the following Actinopteri families: Alosidae, Anguillidae, Cichlidae, Ehiravidae, Gobiidae, Odontobutidae, Syngnathidae, and Xenocyprididae. Therefore, this dataset can be used in the particular taxon species distribution analysis, which are especially important for non-indigenous species.