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.

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.

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.

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.

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.

Abstract: The role of environmental control and spatial structuring may vary depending on dispersal mode within a metacommunity in stream systems. However, as a result of high seasonal variation in environment conditions and phenological features, there might be considerable seasonal changes in the relative importance of structuring factors. The objective of this study was (i) to determine the relative role of structuring factors for aquatic macroinvertebrates with different dispersal mode groups which have seasonal variation in their dispersal capacity and (ii) to disentangle seasonal changes in metacommunity structuring. We sampled 50 stream sites of the Middle Danube Basin (Hungary) in spring and summer. We compared Distance–Decay Relationships between communities of different dispersal groups and distance measures, and then we used variation partitioning analysis and Moran’s eigenvector maps based on overland and watercourse distances to reveal structuring processes in both seasons. We found that metacommunities of all dispersal groups were influenced in both seasons mainly by environmental factors with additional impacts of the spatial components. Our findings suggest that metacommunities of taxa with temporally stable dispersal capacity have seasonally stable structuring processes, while the relative importance of structuring factors can vary seasonally in groups with seasonally changing dispersal capacity.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Abstract: The Asian clam, Corbicula fluminea, was introduced into North America in the 1920s—first observed in the Columbia River—and has expanded its range across the continent and into South America and Europe, yet little is known about its ecology and potential to impact food webs. To evaluate prey selectivity and feeding rates of C. fluminea, we conducted laboratory feeding experiments using water from two distinct Columbia River environments (unimpounded river and reservoir) during July and October 2016. The mean clearance rate on microplankton was 270 (± 53.6 SE) ml water clam−1 h−1 and mean ingestion rate was 2.45 (± 0.83 SE) µg C clam−1 h−1, although rates varied with season and location. In the reservoir in July, clams preferred diatoms and showed an avoidance of dinoflagellates and flagellates; during October in the unimpounded river, clams preferred flagellates while showing a significant avoidance of cyanobacteria. Diatoms were dominant at both sites, and were ingested by clams; however, clams ingested cyanobacteria at very low rates. Substantial consumption of microplankton such as diatoms and rejection of cyanobacteria by C. fluminea may provide competitive advantages to cyanobacteria, leading to microplankton community composition shifts and other changes to food webs in the Columbia River.

Abstract: We reviewed the literature pertaining to Brook Charr thermal habitat, one of Fry’s original species used in developing his scope for activity, to determine what guidance may be established for defining thermal habitat from the literature. The literature was surprisingly large, with 53 publications estimating Brook Charr thermal habitat. The laboratory-based optimal temperature estimates varied widely but were far more consistent when only acclimation-controlled studies were considered. Acclimation-controlled estimates of optimal temperature matched the peak of the aerobic scope curve published nearly 70 years ago. Confidence in defining optimal thermal habitat is strengthened for Brook Charr based on this match because the peak in aerobic scope has strong mechanistic links between physiology and thermal ecology. However, laboratory-based studies used only sub-adult Brook Charr and may underrepresent Brook Charr thermal habitat in nature due to ontogenetic differences in thermal preference. Optimal temperature estimates from aerobic scope or acclimation-controlled studies should be used to define thermal habitat boundaries for fish but should be treated with caution if based on sub adults. Population level sampling is needed to determine the generality of these literature-derived boundaries among Brook Charr populations.

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.

Abstract: Our objective was to evaluate the effect of environmental, spatial, and temporal predictors on different ecological approaches in phytoplankton metacommunity of two subtropical reservoirs. Our hypothesis was that the morphological structure, represented by morphological traits, would be related to both environmental and spatial factors, while the functional structure, represented by the physiological, ecological, and morphological traits, would be related to environmental factors. We also test the temporal factor for both approaches. Sampling was performed in two Brazilian subtropical reservoirs along six sampling periods. We applied the morphology-based functional classification (MBFG) and the classification based on functional group (FG) as surrogates to phytoplankton metacommunity and performed the partition variation to investigate the influences of different predictors. We found spatial and temporal variability of MBFG and FG, and although the metacommunity models presented weak relations, the environmental, spatial, and temporal processes appear to influence the phytoplankton morpho-functional structure along the longitudinal axis reservoirs. However, the relative importance of these processes seems to depend on the type of functional attribute evaluated since the MBFGs were related to the spatial and temporal predictor, while the FGs were associated with environmental, spatial, and temporal predictors.

Abstract: Intense sampling of an estuary can reveal relative spatial changes that are significant irrespective of whether or not the estuary is eutrophic, micro- or meso-tidal, disturbed, or restored. This ‘waterscape’ perspective is analogous to a landscape perspective. We collected monthly water samples in the Barataria Basin watershed from 1994 to 2016 at 37 stations along a 129 km transect from 1 km offshore to a freshwater stream. The average Chlorophyll a (Chl) concentration from 267 trips was supported from both nitrogen-fixing cyanobacteria in a freshwater lake and partially from nutrients in seaward sources. Estuarine salinity was correlated with the discharge of the nearby Mississippi River. The main form of N was as organic nitrogen, not inorganic forms that recycle quickly, making changes in inorganic nitrogen concentration an unreliable indicator of net denitrification or uptake. The total nitrogen (TN) and total phosphorus (TP) concentrations declined with dilution towards the coast, but not because of denitrification. The phytoplankton standing biomass reflected the TN:TP ratio in the water column and there was a significant rise in the variability of Chl concentration at 2–6 psu, which was otherwise unremarkably constant. These waterscape patterns and cautionary interpretations may be common to other estuaries.

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.