Showing papers in "Hydrobiologia in 2019"

Prospects and challenges of environmental DNA (eDNA) monitoring in freshwater ponds

Abstract: Environmental DNA (eDNA) analysis is a rapid, non-invasive, cost-efficient biodiversity monitoring tool with enormous potential to inform aquatic conservation and management. Development is ongoing, with strong commercial interest, and new uses are continually being discovered. General applications of eDNA and guidelines for best practice in freshwater systems have been established, but habitat-specific assessments are lacking. Ponds are highly diverse, yet understudied systems that could benefit from eDNA monitoring. However, eDNA applications in ponds and methodological constraints specific to these environments remain unaddressed. Following a stakeholder workshop in 2017, researchers combined knowledge and expertise to review these applications and challenges that must be addressed for the future and consistency of eDNA monitoring in ponds. The greatest challenges for pond eDNA surveys are representative sampling, eDNA capture, and potential PCR inhibition. We provide recommendations for sampling, eDNA capture, inhibition testing, and laboratory practice, which should aid new and ongoing eDNA projects in ponds. If implemented, these recommendations will contribute towards an eventual broad standardisation of eDNA research and practice, with room to tailor workflows for optimal analysis and different applications. Such standardisation will provide more robust, comparable, and ecologically meaningful data to enable effective conservation and management of pond biodiversity.

Impacts of increasing salinity and inundation on rates and pathways of organic carbon mineralization in tidal wetlands: a review

Abstract: To improve our understanding of the carbon cycling response to imminent sea-level rise and saltwater intrusions, we review the existing literature on the likely effects of the increasing salinity and inundation on organic carbon mineralization in tidal wetlands. Enhanced salinity and inundation will reduce the pool of the organic carbon substrate, but may expand that of microbes with strong capacities for carbon metabolism. Sulfate availability increases with the increasing salinity, while availability of other electron acceptors, e.g., oxygen, nitrate, ferric oxides, and carbon dioxide, could transiently increase but would ultimately fall with the increasing salinity and inundation. The changing electron acceptor pattern may result in microbial sulfate reduction predominating over other carbon mineralization pathways. Data derived from natural salinity and inundation gradients suggest clear negative effects of salinity and inundation on production rates or emission fluxes of carbon dioxide and methane. However, results for brackish wetlands are conflicting, probably due to their unique geographic location. Salinity and inundation exert their influence on organic carbon mineralization through sulfate enrichment, elevating ionic and osmotic stress and decreasing oxygen concentrations and redox conditions, among other biogeochemical changes. Future studies should address the combined effects of salinity and inundation on carbon biogeochemistry in low-level salinity tidal wetlands.

Oil pollution in the North Sea: the impact of governance measures on oil pollution over several decades

Abstract: Oil pollution entering the marine environment has been an issue of concern for many decades. It can come from riverine or land-based sources, accidental and intentional discharges from ships, or as a by-product of offshore oil extraction. Growing awareness of the impact of oil pollution on the marine environment has led, since the late 1960s, to the introduction of measures to reduce or eliminate pollution from shipping and the offshore oil industry. A framework for environmental protection of the North Sea has developed over many decades through international agreements, regional cooperation, and national measures, while education has also played an important role with modern-day sailors being given due training to understand that dumping waste at sea is illegal in many areas, and is harmful to the marine environment. This paper presents data on trends in pollution from ships and oil installations. While significant reductions in oil pollution have been identified over more than two decades, there remain some areas where action is needed to reduce inputs still further, especially from oil and gas platforms. This paper illustrates that international cooperation can result in a reduction in marine pollution leading to a cleaner environment.

Dynamics of cyanobacteria blooms are linked to the hydrology of shallow Florida lakes and provide insight into possible impacts of climate change

Abstract: Analysis of an 18-year dataset from seven shallow lakes in Florida provides evidence of hydrologic factors controlling dynamics of cyanobacteria blooms. Depth was the most important variable, and there was a synergistic effect with flushing. When the lakes were deep, rainfall led to water discharges and disruption of stagnant conditions that maintained blooms. Factors commonly associated with bloom formation (temperature) or suppression (high organic color, which can be a light-limiting factor) did not play a significant role. A conceptual model illustrates how blooms are regulated. First, the presence of bloom-forming species, high concentrations of nutrients, and lack of large zooplankton create a potential for blooms. Second, climate cycles influence yearly rainfall, resulting in wet years and droughts that affect lake water level and volume. This either stimulates blooms (drought, shallow) or suppresses them (wet, deep). Finally, proximal drivers such as a rain events and a flush of water suppress blooms. The results illustrate how climate variability and weather can control cyanobacteria blooms by affecting several processes long known to influence bloom formation, and provide insight into how climate change might affect occurrence of blooms in nutrient-enriched shallow lakes.

The large-scale impact of offshore wind farm structures on pelagic primary productivity in the southern North Sea

Abstract: The increasing demand for renewable energy is projected to result in a 40-fold increase in offshore wind electricity in the European Union by 2030. Despite a great number of local impact studies for selected marine populations, the regional ecosystem impacts of offshore wind farm (OWF) structures are not yet well assessed nor understood. Our study investigates whether the accumulation of epifauna, dominated by the filter feeder Mytilus edulis (blue mussel), on turbine structures affects pelagic primary productivity and ecosystem functioning in the southern North Sea. We estimate the anthropogenically increased potential distribution based on the current projections of turbine locations and reported patterns of M. edulis settlement. This distribution is integrated through the Modular Coupling System for Shelves and Coasts to state-of-the-art hydrodynamic and ecosystem models. Our simulations reveal non-negligible potential changes in regional annual primary productivity of up to 8% within the OWF area, and induced maximal increases of the same magnitude in daily productivity also far from the wind farms. Our setup and modular coupling are effective tools for system scale studies of other environmental changes arising from large-scale offshore wind farming such as ocean physics and distributions of pelagic top predators.

Deeper knowledge of shallow waters: reviewing the invertebrate fauna of southern African temporary wetlands

Abstract: Temporary lentic wetlands are becoming increasingly recognised for their collective role in contributing to biodiversity at the landscape scale. In southern Africa, a region with a high density of such wetlands, information characterising the fauna of these systems is disparate and often obscurely published. Here we provide a collation and synthesis of published research on the aquatic invertebrate fauna inhabiting temporary lentic wetlands of the region. We expose the poor taxonomic knowledge of most groups, which makes it difficult to comment on patterns of richness and endemism. Only a few groups (e.g. large branchiopods, ostracods, copepods and cladocerans) appear to reach higher richness and/or endemicity in temporary wetlands compared to their permanent wetland counterparts. IUCN Red List information is lacking for most taxa, thus making it difficult to comment on the conservation status of much of the invertebrate fauna. However, except for a few specialist groups, many of the taxa inhabiting these environments appear to be habitat generalists that opportunistically exploit these waterbodies and this is hypothesised as one of the reasons why endemism appears to be low for most taxa. Given that taxonomy underpins ecology, the urgent need for more foundational taxonomic work on these systems becomes glaringly apparent.

Phytoplankton species interactions and invasion by Ceratium furcoides are influenced by extreme drought and water-hyacinth removal in a shallow tropical reservoir

Abstract: This study explored the interactions of phytoplankton species during the invasion of Ceratium furcoides and the environmental variables that contributed to its establishment and ecological success in a shallow eutrophic reservoir (Garcas Reservoir, southeast Brazil), which has been monitored monthly for 20 years (1997–2017). The Ceratium furcoides invasion in September 2014 was preceded by disturbance events (macrophyte removal and a historical drought period), which disrupted the dominance of cyanobacteria by modifying resource availability (high water transparency and soluble reactive phosphorus concentrations) and recruiting other species. Ceratium blooms at the water surface were preceded by high abundance near the bottom, suggesting the importance of the propagule bank. However, the pattern of Ceratium-Microcystis coexistence that is usually recorded in temperate lakes was not observed. Instead, Ceratium replaced Cylindrospermopsis raciborskii in mixing periods with high light and nitrogen availabilities, significantly influencing the abundance of Trachelomonas spp. Flagellated forms became dominant in the Garcas Reservoir, due to the higher water transparency and relatively lower water-column stability, and alternative states between Ceratium-Trachelomonas in mixing periods and Microcystis-Cryptomonas in stratified periods have been repeated. Since then, cyanobacterial dominance ceased, and the “skillful” Ceratium apparently has come to stay, influencing interactions among phytoplankton species.

Widespread colonisation of Tanzanian catchments by introduced Oreochromis tilapia fishes: the legacy from decades of deliberate introduction

Abstract: From the 1950s onwards, programmes to promote aquaculture and improve capture fisheries in East Africa have relied heavily on the promise held by introduced species. In Tanzania these introductions have been poorly documented. Here we report the findings of surveys of inland water bodies across Tanzania between 2011 and 2017 that clarify distributions of tilapiine cichlids of the genus Oreochromis. We identified Oreochromis from 123 sampling locations, including 14 taxa restricted to their native range and three species that have established populations beyond their native range. Of these three species, the only exotic species found was blue-spotted tilapia (Oreochromis leucostictus), while Nile tilapia (Oreochromis niloticus) and Singida tilapia (Oreochromis esculentus), which are both naturally found within the country of Tanzania, have been translocated beyond their native range. Using our records, we developed models of suitable habitat for the introduced species based on recent (1960–1990) and projected (2050, 2070) East African climate. These models indicated that presence of suitable habitat for these introduced species will persist and potentially expand across the region. The clarification of distributions provided here can help inform the monitoring and management of biodiversity, and inform policy related to the future role of introduced species in fisheries and aquaculture.

Effects of nutrient limitation, salinity increase, and associated stressors on mangrove forest cover, structure, and zonation across Indian Sundarbans

Abstract: Anthropogenic coastal activities and natural stressors aggravate degradation of small coastal patches of mangroves, which in turn destroy local resilience of mangrove forests in the Indian Sundarbans, the continuous mangrove habitat that spans between India and Bangladesh. We conducted an analytical survey across 19 shoreline mangrove fringes spanning the Sundarbans, including both healthy and disturbed forests, and evaluated ninety-five 60-cm composite sediment cores across a degradation and salinity gradient from ~ 4 to ~ 12 ppt. Increased salinity and anoxicity greatly inhibited nutrient cycling and release by microbial decomposers, subsequently resulting in nutrient-poor soil as a condition of degradation. Nutrient limitation, salinity rise, anoxicity increase, and sulfide build-up negatively controlled forest structure causing declines of forest coverage from ~ 98 to ~ 11%. In addition, the tide-dominated salinity gradient controlling species zonation was disrupted in disturbed forests with salinity-sensitive species gradually disappearing. An obvious change in species distribution is anticipated while salt-sensitive Heritiera fomes, Xylocarpus spp., and Phoenix paludosa failed to cope with increased salinity, evident by their absence from many forests. Excoecaria agallocha and Avicennia spp. acclimated well and expanded freely into degraded forests across the Sundarbans. Overall, our study strongly establishes salinity intrusion as primary mechanism for mangrove degradation.

Fishers’ local ecological knowledge indicate migration patterns of tropical freshwater fish in an Amazonian river

Abstract: The local ecological knowledge (LEK) of fishers may help to fill the knowledge gaps about migration of tropical fish. We investigated fishers’ LEK on migratory patterns of seven fish species along 550 km of the Tapajos River, in the Brazilian Amazon. We interviewed 270 fishers individually in four stretches of this river. The interviewed fishers indicated that three fish species do not migrate over long distances, while four fish species perform migrations, usually longitudinal migration from downstream to upstream reaches. Fishers also mentioned an increase in size of a large catfish species in the upstream stretches of the studied river, indicating the potential occurrence of spawning adults there. These results from fishers’ knowledge indicated that planned dams in the upstream reaches of the Tapajos River will threaten migratory fishes, small-scale fisheries and food security. Fishers’ LEK on fish migration contributed to raise testable biological hypotheses about fish spawning and feeding grounds, as well as the occurrence of distinct populations along the river. The analysis of the LEK of many fishers at several sites over a broad range is a cost-effective source of information on fish migration, supporting environmental impact assessment, fisheries management, and conservation in this and other tropical rivers.

Environmental factors influence the detection probability in acoustic telemetry in a marine environment: results from a new setup

Abstract: Acoustic telemetry is a commonly applied method to investigate the ecology of marine animals and provides a scientific basis for management and conservation. Crucial insight in animal behaviour and ecosystem functioning and dynamics is gained through acoustic receiver networks that are established in many different environments around the globe. The main limitation to this technique is the ability of the receivers to detect the signals from tagged animals present in the nearby area. To interpret acoustic data correctly, understanding influencing factors on the detection probability is critical. Therefore, range test studies are an essential part of acoustic telemetry research. Here, we investigated whether specific environmental factors (i.e. wind, currents, waves, background noise, receiver tilt and azimuth) influence the receiver detection probability for a permanent acoustic receiver network in Belgium. Noise and wind speed in relation to distance, the interaction of receiver tilt and azimuth and current speed were the most influential variables affecting the detection probability in this environment. The study indicated that there is high detection probability up to a distance of circa 200 m. A new setup, making use of features that render valuable information for data analysis and interpretation, was tested and revealed general applicability.

Limited hybridization between introduced and critically endangered indigenous tilapia fishes in Northern Tanzania

Abstract: Hybridization between introduced and indigenous species can lead to loss of unique genetic resources and precipitate extinction. In Tanzania, the Nile tilapia (Oreochromis niloticus) and blue-spotted tilapia (Oreochromis leucostictus) have been widely introduced to non-native habitats for aquaculture and development of capture fisheries. Here, we aimed to quantify interspecific hybridization between these introduced species and the indigenous species Oreochromis esculentus, Oreochromis jipe and Oreochromis korogwe. In the Pangani basin, several hybrids were observed (O. niloticus × O. jipe, O. leucostictus × O. jipe, O. niloticus × O. korogwe), although hybrids were relatively uncommon within samples relative to purebreds. Hybrids between the native O. jipe × O. korogwe were also observed. In the Lake Victoria basin, no evidence of hybrids was found. Analysis of body shape using geometric morphometrics suggested that although purebreds could be discriminated from one another, hybrids could not be readily identified on body and head shape alone. These results provide the first evidence of hybridization between the introduced species and the Critically Endangered O. jipe in Tanzania. Given uncertainty regarding benefits of introduced species over large-bodied indigenous species in aquaculture and capture fisheries, we suggest that future introductions of hybridization-prone species should be carefully evaluated.

Effectiveness of catchment erosion protection measures and scale-dependent response of stream biota

Abstract: Many rivers in Central Europe are heavily affected by increased sedimentation due to erosion from agricultural land. High fine sediment loads can clog the interstitial system, increase turbidity, limit light penetration and potentially reduce primary productivity with negative impacts on stream biota such as reduced abundance and diversity. In this study, the effects of different erosion protection measures on instream sedimentation and the communities of fishes, macroinvertebrates and periphyton were evaluated. The erosion protection measures in the catchment successfully reduced the fine-sediment and nutrient input into the river system resulting in positive effects on interstitial habitat quality and the species assemblage of the assessed biota. The single taxonomic groups differed in their response both to catchment-related and instream-related variables. Fish community composition was best explained by catchment-scale variables, while periphyton and macroinvertebrate assemblage structure was significantly governed by instream-scale variables. For increasing restoration success, a combination of measures in the catchment area with structure-enhancing measures within the stream is necessary. The results also suggest that an integrative assessment of abiotic and biotic variables in monitoring increases the detectability of effects on the instream scale.

Extreme drought favors potential mixotrophic organisms in tropical semi-arid reservoirs

Abstract: Climate change is affecting the global hydrological cycle and is causing drastic changes in the freshwater hydrological regime. Water level (WL) reduction caused by drought tends to increase the concentration of nutrients favoring the dominance of cyanobacteria. We hypothesized that the WL reduction favors the dominance of cyanobacteria at regular dry conditions, but at extremely dry events mixotrophic algae would thrive because of light limitation due to increased resuspension of sediments on the water column. To test our hypothesis, we compared phytoplankton traits and water quality variables between two sets of reservoirs located in two watersheds with contrasting precipitation regimes within the Brazilian semi-arid. The reservoirs were compared in a dry period and in an extremely dry period to evaluate the response of the variables to an extreme drought. Drought intensification decreased the reservoirs’ WL and water transparency and increased the total phosphorous. Cyanobacteria dominated in the dry period, and the contribution of mixotrophic algae increased in the extremely dry period. Thus, phytoplankton with mixotrophic potential was favored by the extreme drought. This result suggests that this can be one possible scenario for phytoplankton communities in reservoirs of semi-arid regions if extreme droughts become more frequent because of climate change.

Brown trout ( Salmo trutta L.) high genetic diversity around the Tyrrhenian Sea as revealed by nuclear and mitochondrial markers

Abstract: The brown trout (Salmo trutta L.) is widely distributed all around Europe but its natural diversity is threatened by massive stocking with Atlantic domestic strains. Describing the remaining natural genetic diversity and the proportion of domestic hatchery strains in rivers is a prerequisite for smart conservation. The high genetic diversity of brown trout populations around the Tyrrhenian Sea is well known. Use of twelve microsatellites has allowed description of the natural genetic structure of populations and detection of the consequences of stocking. Mitochondrial DNA control region sequences and the LDH-C1* gene enabled placement of each population into one of the six mitochondrial and two allozymic known evolutionary lineages. The Corsican populations showed low intra-population genetic diversity but an exceptionally high level of inter-population differentiation. More southern Tyrrhenian regions exhibited opposite pattern of diversity, partly due to the Atlantic domestic introgression. Globally, the natural structure outlines two north–south clines: high inter-population differentiation and predominance of the Adriatic lineage in the north, but lower inter-population differentiation and the presence of the natural Atlantic lineage in the south. In addition, the Tyrrhenian region is the contact zone between the widespread Adriatic lineage and a local natural Atlantic lineage probably coming from North Africa through the Strait of Gibraltar.

Towards a cohesive strategy for the conservation of the United States’ diverse and highly endemic crayfish fauna

Abstract: Freshwater biodiversity of the United States has long been recognized for its high level of species richness. The US crayfish fauna is richer than that found in any other country or continent in the world. Crayfishes are critically important members of freshwater ecosystems and have long been utilized for human consumption. Combined, these factors argue for effective conservation. When compared to other diverse aquatic groups such as fishes or unionid mussels, conservation efforts for US crayfishes are lacking. We review here, knowledge gaps that prevent effective conservation and past and ongoing crayfish conservation and management activities. We conclude by proposing a strategy of actions to improve the conservation standing of this important group of organisms. These action items include improved outreach efforts, funding and research to fill numerous knowledge gaps, and the inclusion of crayfishes in broader scale aquatic conservation activities.

The Ecological Importance of Unregulated Tributaries to Macroinvertebrate Diversity and Community Composition in a Regulated River

Abstract: In regulated rivers, dams alter longitudinal gradients in flow regimes, geomorphology, water quality and temperature with associated impacts on aquatic biota. Unregulated tributaries can increase biodiversity in regulated environments by contributing colonists to the main channel and creating transitional habitats at a stream junction. We assessed whether unregulated tributaries influence macroinvertebrate communities in two mainstem rivers during summer low-flows. Three tributary junctions of upland cobble-gravel bed streams were surveyed in an unregulated and a regulated river in the Sierra Nevada Mountains, California, USA. We found distinct physical habitat conditions and increased macroinvertebrate abundance and diversity in unregulated tributaries on the regulated river, but macroinvertebrate diversity did not increase downstream of tributary junctions as predicted. On the unregulated river, macroinvertebrate diversity was similar in upstream, downstream and unregulated tributary sites. Our findings highlight that unregulated tributaries support high macroinvertebrate diversity and heterogeneous communities compared to the mainstem sites in a regulated river, and thus likely support ecological processes, such as spill-over predation, breeding and refugia use for mobile taxa. We suggest unregulated tributaries are an integral component of river networks, serving as valuable links in the landscape for enhancing biodiversity, and should be protected in conservation and management plans.

Phylogenomics of pike cichlids (Cichlidae: Crenicichla ) of the C. mandelburgeri species complex: rapid ecological speciation in the Iguazú River and high endemism in the Middle Paraná basin

Abstract: The Crenicichla mandelburgeri species complex from the Middle Parana basin is a diverse group of cichlid species and contains all known ecomorphs found within the entire genus Crenicichla. Here, we study the phylogenetic relationships within the C. mandelburgeri species complex using ddRAD sequencing with focus on its two candidate species flocks endemic to the Iguazu and Urugua-i Rivers, and on two putative sympatric species in the Piray Guazu River. These species flocks include four and three syntopic species, respectively, which are strongly adapted to different trophic niches and include derived ecomorphs of Crenicichla (molluscivores, a periphyton grazer, and a crevice-feeding thick-lipped invertivore). Our phylogenomic analyses strongly support monophyly and rapid diversification of the Iguazu species flock, but reveal more complex evolutionary histories in the Urugua-i and Piray Guazu tributaries. Most species in the Middle Parana, including one species in the Urugua-i and both species in the Piray Guazu show cytonuclear discordance, and in both of these tributaries, we also found hybridization in one of the resident species. Population-level analyses reveal complete isolation of the Iguazu species and coupled with their dramatic ecological diversity, this radiation exemplifies characteristics of a species flock that arose via ecological speciation.

Utility of eDNA and occupancy models for monitoring an endangered fish across diverse riverine habitats

Abstract: Environmental DNA (eDNA) studies show great promise for non-invasive surveys of aquatic organisms, but should account for imperfect detection and the influences of biotic and abiotic conditions on detection. We evaluated an eDNA protocol for Roanoke logperch (RLP) Percina rex, an endangered fish of the eastern United States occupying habitats ranging from cold, clear creeks to warm, turbid rivers. We assayed water samples from streams presumed likely to be occupied or unoccupied by RLP based on previous fish surveys. Data were analyzed using multi-scale occupancy models that estimated occurrence and detection probability at the scales of sites, replicate water filters, and replicate PCR reactions, and environmental influences on these probabilities. We detected RLP eDNA at 11 of 12 sites in occupied streams and no sites in presumed-unoccupied streams. In best-supported models, detection was positively related to an index of fish density, whereas other environmental factors had no consistent effects. This approach had a higher detection rate and lower sensitivity to sampling conditions than traditional techniques like snorkeling and electrofishing, suggesting it could provide a powerful tool for assessing the distribution of this and other rare fishes that occur across a wide range of fluvial habitats.

Mangroves dramatically increase carbon storage after 3 years of encroachment

Abstract: In North America, the dynamic ecotonal boundary between mangrove and salt marsh is currently fluctuating in response to freeze-free winters, which can cause rapid alterations in a number of wetland processes and attributes. Permanent plots were established in pure salt marsh habitat along the Atlantic coast of Florida in 2015, and by 2018, mangrove saplings had encroached into plots. In this study, above- and belowground biomass measurements and soil C in the top 10-cm soil profile were quantified in 2018 and compared to 2015 data to better understand the effects of mangrove encroachment on C storage in salt marsh habitat. Plant and soil fractions were tested for δ13C stable isotopic signatures to elucidate soil C sources. In 3 years, mangrove biomass increased dramatically and soil C doubled in pure salt marsh plots, consequently increasing total C in the system. Soil organic matter increased, while there was no change in soil C:N. δ13C values suggest that soil C was derived mainly from salt marsh soil organic matter, especially that of belowground, rather than aboveground biomass. These results provide real-time, quantitative data on the encroachment of mangroves into salt marshes over a relatively short period of time.

Cyanobacteria dominance drives zooplankton functional dispersion

Abstract: Accelerated eutrophication reduces water quality and shifts plankton communities. However, its effects on the aquatic food web and ecosystem functions remain poorly understood. Within this context, functional ecology can provide valuable links relating community traits to ecosystem functioning. In this study, we assessed the effects of eutrophication and cyanobacteria blooms on zooplankton functional diversity in a tropical hypereutrophic lake. Phytoplankton and zooplankton communities and limnological characteristics of a tropical Brazilian Lake (Southeast, Brazil) were monitored monthly from April 2013 to October 2014. Lake eutrophication indicators were total phosphorus, total chlorophyll-a, and chlorophyll-a per group (blue, green, and brown). The variation of major phytoplankton taxonomic group biomass was calculated and used as a proxy for changes in phytoplankton composition. Zooplankton functional diversity was assessed through functional dispersion and the community-weighted mean trait value. Regressions were performed between the lake eutrophication indicators, the phytoplankton biomass variation, and zooplankton functional dispersion. Our results suggest that eutrophication and cyanobacterial dominance change the composition of zooplankton traits and reduce functional dispersion, leading to zooplankton niche overlap. These findings are important because they provide a meaningful view of phytoplankton-zooplankton trophic interactions and contribute to an improved understanding their functional effects on aquatic ecosystems.

Estimating stable isotope turnover rates of epidermal mucus and dorsal muscle for an omnivorous fish using a diet-switch experiment

Abstract: Stable isotope (SI) analysis studies rely on knowledge of isotopic turnover rates and trophic-step discrimination factors. Epidermal mucus (‘mucus’) potentially provides an alternative SI ‘tissue’ to dorsal muscle that can be collected non-invasively and non-destructively. Here, a diet-switch experiment using the omnivorous fish Cyprinus carpio and plant- and fish-based formulated feeds compared SI data between mucus and muscle, including their isotopic discrimination factors and turnover rates (as functions of time T and mass G, at isotopic half-life (50) and equilibrium (95)). Mucus isotope data differed significantly and predictively from muscle data. The fastest δ13C turnover rate was for mucus in fish on the plant-based diet ( $$T_{50}$$ : 17 days, $$T_{95}$$ : 74 days; $$G_{50}$$ : 1.08(BM), $$G_{95}$$ : 1.40(BM)). Muscle turnover rates were longer for the same fish ( $$T_{50}$$ : 44 days, $$T_{95}$$ : 190 days; $$G_{50}$$ : 1.13(BM), $$G_{95}$$ : 1.68(BM)). Longer half-lives resulted in both tissues from the fish-based diet. δ13C discrimination factors varied by diet and tissue (plant-based: 3.11–3.28‰; fishmeal: 1.28–2.13‰). Mucus SI data did not differ between live and frozen fish. These results suggest that mucus SI half-lives provide comparable data to muscle, and can be used as a non-destructive alternative tissue in fish-based SI studies.

Influence of salt marsh canopy on black mangrove (Avicennia germinans) survival and establishment at its northern latitudinal limit

Abstract: As annual minimum temperatures increase due to climate change, species once constrained by minimum temperatures are expanding poleward. Avicennia germinans (black mangrove), a freeze-intolerant tree, has been expanding northward into salt marsh-grass-dominated communities. Distribution and colonization dynamics of A. germinans are crucial for understanding changes in coastal habitats and ecosystem structure and function along the Gulf of Mexico Coast (USA). We transplanted A. germinans seedlings and propagules into salt marsh plots of S. alterniflora, half of which had the canopy removed, along a latitudinal gradient that spanned locations within and outside of A. germinans’ current range limits (29°7′20″N to 30°23′41″N). Plot microclimate and transplant survival and growth were monitored for 2 years. Canopy removal resulted in lower minimum temperatures and longer cumulative freeze duration. Seedling survival was greatest at the southernmost site; however, seedling growth was reduced in plots with the canopy intact, as hypothesized. Seedling survival at northern sites was limited to plots with the S. alterniflora canopy intact. Propagules survived and established at all sites in the second year, although there was no S. alterniflora canopy effect on propagule survival and establishment. Our results illustrate the complexity of ecological interactions between herbaceous marsh species and mangroves at the species’ range limit.

Effects of freshwater eutrophication on species and functional beta diversity of periphytic algae

Abstract: Studies about beta diversity and environmental heterogeneity have shown that the strength of the environmental filtering effect may decrease with the increasing scale. These empirical results have related eutrophic aquatic environments to higher values of beta diversity, but never to dissimilarity of species and functional traits of periphytic algae. We tested the hypotheses that periphytic algae have higher dissimilarity of both species and functional traits in eutrophic environments, and that these dissimilarities are related to environmental dissimilarity. To this end, we used richness, density, and four functional traits of periphytic algae and local limnological data from wetlands in the Brazilian savanna (Cerrado). We analyzed the beta diversity and the relationship of species and functional dissimilarities with the environmental dissimilarity and geographic distances. Our hypothesis was confirmed for functional traits dissimilarity and for the importance of the environmental dissimilarity for both species and functional beta diversity. The cultural eutrophication led to a functional homogenization in urban wetlands, which indicates the establishment of species with similar ecological requirements, and consequently, similar ‘roles’ in the ecosystem, and also that sensitive species may have been replaced by tolerant species, leading to declining biodiversity.

The role of recurrent dewatering events in shaping ecological niches of scrapers in intermittent Alpine streams

Abstract: Several Alpine streams are currently changing from perennial to intermittent systems with expected detrimental consequences on benthic invertebrates, through the alteration of hydrological conditions, substrate composition, and trophic resources. We examined the ecological niche of three phylogenetically-related scraper macroinvertebrates, namely Ecdyonurus, Epeorus, and Rhithrogena (Ephemeroptera, Heptageniidae) experiencing recurrent summer dewatering events in perennial and intermittent stretches in 13 Alpine streams. We evaluated the overlap among the ecological niches of the three examined taxa in terms of hydraulic stress, substrate coarseness, and total primary production and we investigated their ecological preferences in perennial and intermittent sites. Our results showed a broad overlap of their ecological niches, suggesting exploitative competition among the examined taxa. Their ecological niches were smaller in intermittent than perennial sites, pointing out a reduction of available microhabitats. All groups were favored by substrate coarseness and total primary production in reach types, while the hydraulic stress showed an opposite effect in perennial (negative) and intermittent (positive) sites. Overall, our results emphasize how stream physical parameters play a key role in determining the ecological niche of Heptageniidae and underline how benthic communities in intermittent sections of previously perennial Alpine streams are currently under pressure.

Water temperature dynamics and the prevalence of daytime stratification in small temperate shallow lakes

Abstract: Small lakes are understudied compared to medium- and large-sized lakes, but have recently received increased attention due to their abundance and importance for global scale biogeochemical cycles. They have close terrestrial contact, extensive environmental variability, and support high biodiversity among them. Temporal and spatial variability of water temperature, oxygen, and stratification–mixing dynamics were examined during a year in nine small Danish lakes. We found that diel mean surface water temperatures were similar among lakes while the diel range decreased with increasing water depth. Vertical temperature stratification occurred on 47% of the days during the entire year and 64% of summer days, usually with daytime stratification and nocturnal convective mixing. The probability of daytime stratification increased with higher incident irradiance, higher air temperature, and lower wind speed. During spring, daytime stratification caused differences in oxygen saturation between surface and bottom waters. These findings offer new insights on the high variability of water temperature and oxygen in time and space in small temperate shallow lakes. The variable water temperature and the regular stratification–mixing processes will have a pronounced influence on biogeochemical cycles. Also, these features are expected to affect the performance and evolutionary process of organisms associated with small lakes.

Old sins have long shadows: climate change weakens efficiency of trophic coupling of phyto- and zooplankton in a deep oligo-mesotrophic lowland lake (Stechlin, Germany)—a causality analysis

Abstract: Analysis of a long-term (1994–2014) data set of phytoplankton and zooplankton in the deep, dimictic, oligo-mesotrophic Lake Stechlin (Germany) revealed trend-like changes: phytoplankton biomass and resource use efficiency increased with proliferation of heterocytic cyanobacteria (Dolichospermum spp. and Aphanizomenon flos-aquae), and those of especially large-sized zooplankton (Eudiaptomus, Eurytemora) decreased. These reverse trends are clear eutrophication symptoms and suggest a long-term trophic decoupling with potential decrease in energy transport towards higher tropic levels. Total phosphorus increased significantly over time; however, there is no known external P load for Lake Stechlin. Causality analysis enabled us to identify the primary reason of the observed changes. According to the results, stronger and longer-lasting stratification (measured as relative water column stability) drove the observed changes and the gradual regime shift was initiated by an extreme weather event—both indicating that climate change has been the crucial driver of the planktic community in this lake. Our study also documents that there might be decadal delays between cause and consequences in aquatic food webs, supporting the essential importance of long-term monitoring efforts.

Trophic state assessment based on zooplankton communities in Mediterranean lakes

Abstract: Eutrophication assessment is made widely using Carlson Trophic State indices (TSI) [e.g. secchi disc depth (TSISD)] or phytoplankton biomass. Recently, two Carlson type indices using rotifers (TSIROT) and crustaceans (TSICR) were developed from Polish lakes. In the present study, both indices were applied to zooplankton communities from 16 Greek lakes, covering the entire trophic state spectrum, in order to test their application in a different climatic zone, the Mediterranean. The evaluation of the indices (TSIROT and TSICR) was made comparing the trophic state of each sampling/lake based on TSISD and mean summer phytoplankton biomass. Both indices increased across the eutrophication gradient but misclassify the trophic state. We propose a new index, TSIZOO, the average of the formulae TSIROT and TSICR which are significantly correlated with the eutrophication proxies. All three zooplanktonic indices can efficiently detect low (oligotrophic–mesotrophic) and high (eutrophic–hypertrophic) trophic state using the boundaries < 45 for TSIROT and TSIZOO and < 50 for TSICR. All zooplanktonic indices are promising and effective tools for monitoring and assessment of eutrophication of Mediterranean lakes when mean values are used. Still, TSIZOO should be preferred as the best index that correlated with eutrophication which had the best estimations.

Development of marine biofilm on plastic: ecological features in different seasons, temperatures, and light regimes

Abstract: Microorganisms are able to colonise abiotic surfaces in marine waters, supporting ecological and biogeochemical functions. In turn, environmental factors may determine the accrual and activity of microbial biofilms. The environment is subject to global climate change and pollution by plastic, and therefore we focused on the response of natural marine biofilm on common plastic items (bottles) to seasonality, increases in temperature, and light regime in experimental systems. Chlorophyll-a, prokaryotic abundance and replication frequency, organic matter (OM), and enzymatic activity were measured. Statistical analysis indicated that different environmental conditions modified the biofilms. Summer conditions favoured photoautotrophic organisms. The increase of photoautotrophic biomass could have caused the prokaryotic microorganisms’ lowest abundances. Temperature rise affected chlorophyll-a and increased hydrolytic activities, responsible for OM degradation, as also recorded in the absence of light. In winter, temperature variation led to a delayed increase of enzymatic activity, suggesting the need for a time lag to potentiate OM recycling. The correlations between prokaryotic abundance and the other variables highlighted tighter links in cases of temperature alteration. Our results indicated that a potential temperature increase, and light limitation due to plastic sinking in the water column, could modify the biofilm community, increasing the role of prokaryotic organisms.

Benthic diatom metacommunity across small freshwater lakes: driving mechanisms, β-diversity and ecological uniqueness

Abstract: In this study, driving forces and diversity patterns of a benthic diatom metacommunity across small freshwater lakes exhibiting environmental heterogeneity were investigated. Furthermore, local (LCBD) and species (SCBD) contributions to β-diversity and their driving parameters were assessed with abundance- and incidence-based analyses. Our results revealed that both spatial distance and environmental heterogeneity affected the community assembly, which corresponds most to the mass-effect (ME) concept. This theory was confirmed by high α-diversity of sampling sites; however, high overall β-diversity enhanced mainly by turnover contradicted the ME paradigm. LCBD indices were affected by environmental variables; furthermore, LCBD and LCBD in terms of species replacement showed a strong positive correlation. The ecologically most unique sites hosted relatively low species richness, and common species with intermediate-sized or broad niches contributed mostly to the regional β-diversity. However, abundance- and incidence-based calculations revealed different relationships of SCBD with the species’ total abundance and the number of occupied sites. Consequently, we favor the previous suggestions that comprehensive research focusing on conservation should incorporate the investigation of LCBD, SCBD, species-rich sites and also ecologically restricted species. Moreover, in assessing ecological uniqueness, both abundance and binary data sets should be considered since they might shed light on distinct patterns.