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This book, like anuran biology itself, is a grand study in variation, the importance of which, as noted by Dodd in his second edition of I Frogs of the United States and Canada i , is so often not appreciated by researchers. The section on frogs in North American culture provides an interesting layer of awareness of what ancient and contemporary brothers and sisters in humanity saw as important in fellow life forms that were a part of their daily lives. Anuran biology is the better for this publication. [Extracted from the article]

Organisms that move across ecosystem boundaries connect food webs in apparently disparate locations. As part of their life cycle, aquatic insects transition from aquatic larvae to terrestrial adults, thereby linking freshwater ecosystem processes and terrestrial insectivore dynamics. These linkages are strongly affected by contamination of freshwater ecosystems, which can reduce production of adult aquatic insects (i.e., emergence), increase contaminant concentrations in adult insect tissues, and alter contaminant flux to terrestrial ecosystems. Despite the potential impact of contaminants on adult aquatic insects, little is known about predicting these effects. Here, I develop a heuristic model based on contaminant properties and ecotoxicological principles to predict the effects of various classes of aquatic contaminants on adult aquatic insects and discuss implications for terrestrial insectivores living near contaminated freshwaters. The main finding is that contaminant classes vary greatly in how their biologically-mediated effects on aquatic insects affect terrestrial insectivores. Highly bioaccumulative contaminants that are well retained during metamorphosis, like polychlorinated biphenyls (PCBs), are often non-toxic to aquatic insect larvae at concentrations commonly found in the environment. Such contaminants flux from aquatic ecosystems in large quantities in the bodies of emerging adult aquatic insects and expose terrestrial insectivores to toxic levels of pollution. On the other hand, contaminants that are less bioaccumulative, excreted during metamorphosis, and more toxic to insects, like trace metals, tend to affect terrestrial insectivores by reducing production of adult aquatic insects on which they prey. Management applications of this model illustrate type and severity of risk of aquatic contaminants to consumers of adult aquatic insects. [ABSTRACT FROM AUTHOR]

Identifying traits that underlie variation in individual performance of consumers (i.e., trait utility) can help reveal the ecological causes of population divergence and the subsequent consequences for species interactions and community structure. Here, we document a case of rapid divergence (over the past 100 generations, or ∼150 years) in foraging traits and feeding efficiency between a lake and stream population pair of threespine stickleback. Building on predictions from functional trait models of fish feeding, we analyzed foraging experiments with a Bayesian path analysis and elucidated the traits explaining variation in foraging performance and the species composition of ingested prey. Despite extensive previous research on the divergence of foraging traits among populations and ecotypes of stickleback, our results provide novel experimental evidence of trait utility for jaw protrusion, gill raker length, and gill raker spacing when foraging on a natural zooplankton assemblage. Furthermore, we discuss how these traits might contribute to the differential effects of lake and stream stickleback on their prey communities, observed in both laboratory and mesocosm conditions. More generally, our results illustrate how the rapid divergence of functional foraging traits of consumers can impact the biomass, species composition, and trophic structure of prey communities. [ABSTRACT FROM AUTHOR]

Conservation scientists have adapted conservation planning principles designed for protection of habitats ranging from terrestrial to freshwater ecosystems. We applied current approaches in conservation planning to prioritize California watersheds for management of biodiversity. For all watersheds, we compiled data on the presence/absence of herpetofauna and fishes; observations of freshwater-dependent mammals, selected invertebrates, and plants; maps of freshwater habitat types; measures of habitat condition and vulnerability; and current management status. We analyzed species-distribution data to identify areas of high freshwater conservation value that optimized representation of target taxa on the landscape and leveraged existing protected areas. The resulting priority network encompasses 34% of the area of California and includes ≥10% of the geographic range for all target taxa. High-value watersheds supported nontarget freshwater taxa and habitats, and focusing on target taxa may provide broad conservation value. Most of the priority conservation network occurs on public lands (69% by area), and 46% overlaps with protected areas already managed for biodiversity. A significant proportion of the network area is on private land and underscores the value of programs that incentivize landowners to manage freshwater species and habitats. The priority conservation areas encompass more freshwater habitats/ha than existing protected areas. Land use (agriculture and urbanization), altered fire regimes, nonnative fish communities, and flow impairment are the most important threats to freshwater habitat in the priority network, whereas factors associated with changing climate are the key drivers of habitat vulnerability. Our study is a guide to a comprehensive approach to freshwater conservation currently lacking in California. Conservation resources are often limited, so prioritization tools are valuable assets to land and water managers. [ABSTRACT FROM AUTHOR]

Natural and human-related landscape features influence the ecology and water quality of lakes. Summarizing these features in a hydrologically meaningful way is critical to understanding and managing lake ecosystems. Such summaries are often done by delineating watershed boundaries of individual lakes. However, many technical challenges are associated with delineating hundreds or thousands of lake watersheds at broad spatial extents. These challenges can limit the application of analyses and models to new, unsampled locations. We present the Lake-Catchment (LakeCat) Dataset (https://www.epa.gov/national-aquatic-resource-surveys/lakecat) of watershed features for 378,088 lakes within the conterminous USA. We describe the methods we used to: 1) delineate lake catchments, 2) hydrologically connect nested lake catchments, and 3) generate several hundred watershed-level metrics that summarize both natural (e.g., soils, geology, climate, and land cover) and anthropogenic (e.g., urbanization, agriculture, and mines) features. We illustrate how this data set can be used with a random forest model to predict the probability of lake eutrophication by combining LakeCat with data from US Environmental Protection Agency’s National Lakes Assessment (NLA). This model correctly predicted the trophic state of 72% of NLA lakes, and we applied the model to predict the probability of eutrophication at 297,071 unsampled lakes across the conterminous USA. The large suite of LakeCat metrics could be used to improve analyses of lakes at broad spatial extents, improve the applicability of analyses to unsampled lakes, and ultimately improve the management of these important ecosystems. [ABSTRACT FROM AUTHOR]

The gas-exchange rate between streams and the atmosphere is needed to measure in-stream ecological processes and C processing in rivers and streams. Current methods include empirical relationships to hydraulics, direct injection of a tracer gas, and modeling based on O2 or C diel curves. All existing methods have strengths and drawbacks and most are limited to point measurements or are unable to measure diel variation in exchange rate. Researchers continue to search for better techniques, particularly for steep streams with high rates of gas exchange and low primary productivity. We present the O2−C (OC) method for calculating gas-exchange rates via simultaneous measurement of O2 and dissolved inorganic C (DIC). Gas-exchange rates are calculated by solving the combined stream transport equation for O2 and DIC. The output is a time-series of aeration rates at the same sampling frequency as the input O2 and C data. Field tests in a 4th-order montane stream in Oregon, USA, indicate that the method is suitable for stream reaches with high downstream gas-concentration gradients and saturation deficits. The mean modeled aeration rate adjusted to 17°C (3.25/h) agreed well with the value of 3.22/h from direct gas injection. Net ecosystem production calculated with the modeled aeration rate (−1.69 g O2 m−2 d−1) was consistent with the result obtained with direct gas injection (−1.60 g O2 m−2 d−1). An assumption of the model is a constant respiration quotient, but results indicated that the respiration quotient may be time variable. Sensitivity analysis indicated that application of the OC method is limited to reaches with a suitable change in combined O2 and CO2 concentration ≥ ∼4 μmol/L and combined O2 and CO2 saturation deficits ≈ 4 μmol/L, characteristic of smaller gaining streams. Preliminary application of the OC method indicates it could be useful to practitioners interested in continuous measurement of gas-exchange rates. [ABSTRACT FROM AUTHOR]

The ability to model freshwater stream habitat and species distributions is limited by the spatially sparse flow data available from long-term gauging stations. Flow data beyond the immediate vicinity of gauging stations would enhance our ability to explore and characterize hydrologic habitat suitability. The southeastern USA supports high aquatic biodiversity, but threats, such as landuse alteration, climate change, conflicting water-resource demands, and pollution, have led to the imperilment and legal protection of many species. The ability to distinguish suitable from unsuitable habitat conditions, including hydrologic suitability, is a key criterion for successful conservation and restoration of aquatic species. We used the example of the critically endangered Tar River Spinymussel (Parvaspina steinstansana) and associated species to demonstrate the value of modeled flow data (WaterFALL™) to generate novel insights into population structure and testable hypotheses regarding hydrologic suitability. With ordination models, we: 1) identified all catchments with potentially suitable hydrology, 2) identified 2 distinct hydrologic environments occupied by the Tar River Spinymussel, and 3) estimated greater hydrological habitat niche breadth of assumed surrogate species associates at the catchment scale. Our findings provide the first demonstrated application of complete, continuous, regional modeled hydrologic data to freshwater mussel distribution and management. This research highlights the utility of modeling and data-mining methods to facilitate further exploration and application of such modeled environmental conditions to inform aquatic species management. We conclude that such an approach can support landscape-scale management decisions that require spatial information at fine resolution (e.g., enhanced National Hydrology Dataset catchments) and broad extent (e.g., multiple river basins). [ABSTRACT FROM AUTHOR]

Introduction of nonnative salmonids into fishless aquatic ecosystems often can have negative effects on these ecosystems. Amphibians appear to be particularly susceptible to the introduction of trout. Nonnative Rainbow Trout (Oncorhynchus mykiss) have been introduced to Mexico, including to streams in the mountains around Mexico City that are home to several endemic Mexican amphibians. We examined the effect of Rainbow Trout on the distributions of 2 endemic Mexican amphibians, Ambystoma altamirani and Hyla plicata, in the Sierra de Las Cruces. Ambystoma altamirani was never found at sites with Rainbow Trout, and H. plicata was observed only once at sites with Rainbow Trout. Stream site characteristics, for the most part, did not vary among streams occupied by different species, suggesting environmental variables were not primarily responsible for the species distributions. Our results provide strong circumstantial evidence that the introduction of Rainbow Trout in streams in the Sierra de Las Cruces has a negative effect on the distribution of native Mexican amphibians. [ABSTRACT FROM AUTHOR]

Pond hydroperiod and other aspects of environmental heterogeneity play important roles in metacommunity organization in freshwater systems. We examined tadpole species richness and dissimilarities among assemblages at different hydroperiods (3, 7, and 13 mo) in highland ponds in the Araucaria moist forest ecoregion of southern Brazil. We also investigated whether β diversity components changed in accordance with spatial and environmental factors. We sampled tadpoles at 18 ponds between September 2012 and April 2013. Tadpole species richness was lower in permanent than in temporary ponds, but pond hydroperiod was not associated with tadpole abundance and species dissimilarities. β diversity was almost completely caused by species replacement associated with pond area, presence of predatory fish, and type of margin. Despite its small contribution, the nestedness component was associated with water depth and geographic patterns. Our study suggests that tadpole communities in the highlands of Araucaria moist forests are niche structured. [ABSTRACT FROM AUTHOR]

Finding remnant populations of species that are of conservation concern can be difficult, particularly in aquatic habitats. Models of ecological niches can aid in the discovery of refuges. Remnant populations of native freshwater mussels (unionids) have been found in Lakes Erie and St Clair. Our goals were to predict undiscovered refuges in Lake Ontario based on habitat analysis from Lake Erie and to conduct surveys to test those predictions. We built a presence-only model on environmental data including attributes of the benthic zone and shoreline where mussels occurred in Lake Erie. We found a link between small- and large-scale variables related to unionid persistence. Bathymetry, fetch, and shoreline geomorphology contributed most to the model. These variables correspond to local-scale environmental factors important for unionid survival, including presence of vegetation and substrate composition, which explained ∼22% of the variance in presence, abundance, and richness. The model predicted that 0.8% of the near-shore area of Lake Ontario should be habitat for unionids. In surveys at 34 locations on the USA shore of Lake Ontario, we found 1800 unionids of 11 species and showed that areas <500 m from predicted good habitat contained significantly more individuals than near-shore areas not identified as good habitat. We were able to predict new refuges in Lake Ontario successfully even though mussel assemblages differed between Lakes Erie and Ontario, a result signifying generality of our model for conservation approaches to freshwater mussels. [ABSTRACT FROM AUTHOR]

Disturbance in lotic ecosystems strongly influences which animals can survive and how those ecosystems function. Flow disturbances physically remove animals and periphyton, but it is unclear whether physical removal of individuals or the loss of food is the principal driver of effects of flow disturbances on invertebrate communities. Invertebrates possess traits that help them withstand high flows or recolonize rapidly after floods. At light-limited, closed-canopy sites, periphyton biomass should be unaffected by disturbances, so disturbance should affect invertebrate community trait composition by direct removal of animals. At open-canopy sites, disturbance should affect trait composition by both removing individuals and reducing periphyton food resources. We investigated whether a trait-based approach could elucidate drivers of effects of flow disturbance on benthic invertebrate communities and better identify potential mechanistic linkages. We sampled 10 autotrophic streams that differed in substrate-disturbance regime and varied from 100 to 0% canopy cover. We sampled 2 sites per stream, 1 in forest (closed-canopy) and 1 downstream in low-intensity agricultural grassland (open-canopy). Regardless of canopy, in streams with greater substrate disturbance, the proportion of individuals that respired with a plastron increased and proportions of individuals having 2 aquatic life stages or that were filter-feeders decreased. At open-canopy sites, the proportion of collector-gatherers with flattened bodies increased with increased substrate disturbance and decreased periphyton biomass, and the proportion of taxa having high body flexibility and 2 aquatic life stages increased with decreased substrate disturbance and increased periphyton biomass. Trait composition of these mountain stream invertebrate communities is strongly influenced by physical removal via substrate movement and by reduced periphyton resources. [ABSTRACT FROM AUTHOR]

The ecological effects of invading adult zebra and quagga mussels (Dreissena polymorpha and Dreissena bugensis, respectively) are well-documented worldwide, but the ecology and fate of their veliger larvae are poorly understood. We addressed potential errors encountered when estimating veliger biomass. Faced with uncertainty surrounding an established length-mass relationship for veligers, we developed a new dry mass relationship that works for both fresh and formalin-preserved animals. We used this new equation to estimate that veliger dry biomass averaged 74 ± 0.6% of the values obtained from the established equation. Therefore, researchers who assumed the established equation yielded wet mass and applied correction factors of 10 to 50% would have underestimated biomass. Use of coarse-mesh nets also leads to underestimates of biomass. We found that 153-µm-mesh nets captured only 3 to 27% of individuals, or 10 to 66% of veliger biomass captured in 64-μm-mesh nets. We also examined temporal trends, seasonality, and relative contribution of veliger larvae to total zooplankton biomass at several Laurentian Great Lake long-term monitoring sites in Ontario, Canada. Based on the new equation, veliger biomass generally increased from 2008 to 2014, with May to October means of 1 to 27 mg/m3 in Lake Ontario, Georgian Bay, and Lake Erie, or up to 39% of total zooplankton biomass. Veligers were present for most of the sampling season, but abundance peaked in August and September. In contrast, crustacean biomass has declined markedly in Lake Ontario since the 1990s. Given their dominance across many sites, accurate depiction of veliger dry mass may partially offset the observed losses in crustacean biomass to the pelagic food web following P control and the dreissenid invasion of the Great Lakes. [ABSTRACT FROM AUTHOR]

Like many aggregating animals, unionid mussels occurring at high densities can create patches or ‘hotspots’ of biogeochemical activity directly through nutrient regeneration and material flux and indirectly by movement of sediments through physical activities of the organism. We examined the effect of unionid mussels and nutrient limitation on denitrification and nitrification rates across a gradient of ambient mussel diversity and density in the Kiamichi River, Oklahoma, USA. We incubated pooled sediment samples and measured denitrification rates (with amendments of N as KNO3, C as dextrose, N and C together, and no amendment), nitrification rates, and pore-water chemistry at each site. Mussel biomass and alleviation from N limitation influenced denitrification rates. In unamended sediments, denitrification rates decreased with increasing mussel densities, and were not limited by N or C. However, sediments with mussels had higher denitrification rates with the addition of N. Nitrification rates were not correlated with mussel biomass, but rates did increase marginally with the proportion of Actinonaias ligamentina (a relatively more mobile species) in each mussel bed. Pore-water concentrations of NO3− and NH4+ were highest at high-mussel-biomass sites. Our study builds on existing evidence of the importance of unionid mussels in nutrient cycling in streams, by relating their effects to organism biomass and alleviation from nutrient limitation. The N limitation of denitrification rates found in our study may mean that mussel beds become denitrification hotspots given anticipated increases in nutrient availability. However, the continued decline of these organisms probably will reduce the denitrification capacity of mussel beds. [ABSTRACT FROM AUTHOR]

Subsidies across aquatic-terrestrial boundaries can alter consumer distributions and physiology. The importance of subsidies is a function of export quantity and of their physiological significance and relative scarcity in the recipient system. Aquatically derived long-chain polyunsaturated fatty acids (LC-PUFAs) are physiologically essential, relatively rare in terrestrial habitats, and can enhance immune function. We explored fatty-acid profiles and immune function of Tigrosa georgicola wolf spiders in wetland and upland habitats. Wetland spiders had higher tissue levels of aquatically derived LC-PUFAs and elevated immune function (measured as encapsulation of parasites) compared to upland spiders. Whether increased encapsulation activity translates into greater survival is unclear, but our results suggest that aquatically derived nutrients, such as LC-PUFAs, may benefit organisms exploiting freshwater habitats. Furthermore, these patterns suggest that such aquatic-terrestrial subsidies may shape parasite-host interactions in surrounding ecological communities. [ABSTRACT FROM AUTHOR]

Intrinsic ecological characteristics of Mediterranean wetlands make them excellent sites for studying biodiversity, but these wetlands have been studied much less frequently than temperate lakes. The invertebrates that inhabit them, and zooplankton specifically, play important roles in these wetlands. We compared the ability of taxon- and size-based analyses of the zooplankton community to predict the influence of environmental variables. We sampled environmental variables and zooplankton at 7Mediterraneanwetlands in the Iberian Peninsula (southern Spain)monthly along 1 hydroperiod cycle (2009-2010). We used 3 arrays for classifying the zooplankton community: 1) species occurring in >5% of the samples, 2) coarse-level taxa easily identified by a nonexpert (large branchiopods, small branchiopods, calanoid copepods, cyclopoid copepods, and harpacticoid copepods), and 3) 4 body-size classes (<1, 1-2.5, 2.5-10, and >10 mmin length). We used permutational analysis of variance (PERMANOVA) and canonical correspondence analysis (CCA) to test our hypotheses. Communities differed significantly among wetlands, and body size (55.8% of explained variance) was more useful than taxonomic composition (common taxa: 24.4%, coarselevel taxa: 26.5% of explained variance) for rapid assessment of the influence of the environmental variables on zooplankton community in temporary wetlands. [ABSTRACT FROM AUTHOR]

Scaling aquatic ecosystem processes like nutrient removal is critical for assessing the importance of streams and rivers to watershed nutrient export. We used pulse NH4+ enrichment experiments and measured net NH4+ uptake in 7 streams throughout a mountainous tropical river network in Puerto Rico to assess spatial variability in NH4+ uptake and to infer the physical, chemical, and biological characteristics that most influence its variation. Across 14 experiments, NH4+ uptake velocity (vf) ranged from 0.3 to 8.5 (mean 5 2.7) mm/min and was positively related to algal biomass standing stock, measured as chlorophyll a. On average, 49% of experimentally added NH4+ was immediately transformed to NO 3-, suggesting that nitrification can rival microbial and algal assimilation as a fate of streamwater NH4+. We considered the implications of our empirical results at the river-network scale based on a simple mass-balance model parameterized for the Río Mameyes watershed. Most catchment NH4+ inputs are delivered to 1st-order streams. Therefore, model results indicated that high NH4+ uptake rates in headwater streams limit NH4+ inputs to downstream reaches, thereby decreasing the role of larger streams in NH4+ removal at the river-network scale. In-stream nitrification resulted in additional NO3- inputs, which were more likely than NH4+ to be transported downstream because of lower biological demand for NO3- relative to NH4+. Given our estimates of catchment N loading to streams and rivers, we estimated that 39% of modeled watershed NO3- export was produced within the river network by nitrification. Together, these results suggest that streams and rivers can significantly transform the N load from their catchments. [ABSTRACT FROM AUTHOR]

Parasites may mediate ecosystem functioning through a number of direct and indirect mechanisms, but the importance of parasitism at the ecosystem scale is poorly understood. Measuring the density of free-living and parasitic consumers in units that are directly comparable provides a first step toward understanding the importance of parasitism to ecosystem processes. I sampled 2 streams in the New Jersey Pine Barrens seasonally for 1 y to measure the biomass density of all major consumer groups, including macroparasites infecting fish and macroinvertebrates. Parasites made up a small percentage of consumer biomass in Pine Barrens streams, representing just 0.00643 to 0.00733% of total consumer biomass annually. These low values contrast with higher estimates from other aquatic ecosystems, where parasite biomass exceeds that of some free-living consumers. The mean biomass densities of all consumer groups differed significantly between the 2 streams, perhaps because of stream characteristics, such as productivity or pH. Comparison of parasite biomass density in these 2 streams with that in 3 other types of aquatic ecosystems reveals substantial variation both within and among ecosystem types. Methodological differences among published studies complicate comparisons of parasite biomass across ecosystems. I reviewed the methods used in previous studies on parasite biomass and argue for a consistent and transparent method for future research. Comparing the biomass of free-living and parasitic consumers is a first step toward understanding the ecosystem-level importance of parasitism, but more work is needed to understand the specific mechanisms by which parasites influence ecosystem processes and the magnitude of parasite effects. [ABSTRACT FROM AUTHOR]

Predators control prey populations and influence communities and the functioning of ecosystems through a combination of consumptive and nonconsumptive effects. These effects can be locally confined to one ecosystem but can also be extended to neighboring ecosystems. In this study, we investigated the nonconsumptive effects of terrestrial avian predators on the communities of aquatic invertebrates inhabiting bromeliads and on the functioning of these natural ecosystems. Bromeliads with stuffed birds placed nearby showed a decrease in aquatic damselfly larvae abundance and biomass, and we can infer that these changes were caused by antipredator responses. These larvae, which are top predators in bromeliad ecosystems, changed the composition of the entire aquatic invertebrate community. While total species richness, mesopredator richness, and shredder abundance increased in the presence of birds, scraper biomass decreased, possibly as a consequence of the increase in mesopredator richness. High scraper biomass in the absence of birds may have accelerated detrital decomposition, making more nutrients available for bromeliads, which grew more. These results show that nonconsumptive effects triggered by terrestrial predators can cascade down to lower trophic levels and dramatically affect the functioning of aquatic ecosystems, which can in turn alter nutrient provision to terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Submerged aquatic vegetation (SAV) in the Chesapeake Bay is well below half of its historic levels, largely due to excessive nutrient and sediment loads degrading water quality. SAV provides important ecosystem functions, many of which are beneficial to local residents. To understand the implicit value residents place on SAV and the ecosystem services it provides, we undertake a hedonic property value study using residential transactions in 11 Maryland counties adjacent to the Chesapeake Bay. These data are matched to highresolution maps of SAV coverage. We pose a quasi-experimental comparison and examine how the prices of homes near the waterfront vary with the presence of SAV. On average, waterfront and near-waterfront homes within 200 meters of the shore sell at about a 6.5% premium when SAV is present. Applying these estimates to the 185,000-acre SAV attainment goal suggests total property value gains on the order of $436 million. [ABSTRACT FROM AUTHOR]

Visual estimates of habitat features are often used in aquatic ecology because of their relatively low cost, ease of collection, and minimal equipment requirements. However, the precision and accuracy of these methods have rarely been quantified. We assessed the precision and accuracy of visual estimates of aquatic habitat features by comparing independent estimates made by 4 observers and by comparing observer estimates with values based on more thorough and objective methods (measured). Percent areal cover and % water-column cover of aquatic macrophytes and algae, aquatic macrophyte and algal species richness, and % composition of river substrates (mud, sand, and gravel) were estimated at 50 points for each of 3 strata in the Niagara River (wetland, water depth ≤1.0 m, and water depth >1.0-2.0 m). Estimates between pairs of observers differed on average by 10% for areal cover, 9% for water column cover, 0.79 for species richness, 11% for mud, 11% for sand, and 3% for gravel. Mean absolute differences (MADs) of observer estimates from measured values were 16% for water-column cover, ~1.6 species for species richness, 20% for mud, 20% for sand, and 5% for gravel. Visual estimates of the aquatic habitat features examined were relatively precise (i.e., repeatable among observers) but often inaccurate (i.e., biased from the measured values). If visual estimates are implemented, we recommend training of observers based on samples with known values to provide more accurate and precise estimates. [ABSTRACT FROM AUTHOR]

Stable-isotope analysis is widely used in aquatic ecosystem studies to evaluate trophic structure and resource dynamics. Because ƍ15N values vary in freshwater systems, e.g., reflecting variations in land use, suitable baseline indicators must be specified. Few investigators have identified specific baseline organisms based on thorough and methodical screening. We screened for baseline organisms in temperate lotic waters based on 4 criteria: 1) baseline organisms should be easy to collect, 2) within-site variation in ƍ15N levels should be low, 3) ƍ15N should reflect land use, and 4) trophic position (TP) of consumers calculated from the baseline should be independent of system-specific ƍ15N variability as long as no systematic change in food consumption occurred. We investigated individual taxa and bulked groups representing different feeding modes as baselines. We found that Simuliidae, a sestonic filter feeder, fulfilled all criteria. Furthermore, TP estimates of 2 common fishes that were based on the Simuliidae or grouped filterers as baselines were the only estimates in our study that were independent of landuse changes. In addition, the diet of these fishes did not change across land use as based on stableisotope mixing-model analysis. Simuliidae also had the lowest within-site variation, i.e., the lowest trophic level range, probably a result of uniform feeding behavior. Therefore, Simuliidae and grouped filterers could be suitable baseline indicators in future studies. We recommend minimizing ƍ15N variability in and among systems because the precise, complex choice, timing, or proportions of food sources consumed cannot be mimicked. We also promote combining TP estimation andmixing-model analyses as a strong tool in studies of streamfood webs. [ABSTRACT FROM AUTHOR]

The fate and transport of triclosan (5-chloro-2-[2,4-dichlorophenoxy]phenol), a widely used antimicrobial agent in personal care products, in aquatic ecosystems is a growing environmental concern. At ecosystem scales, triclosan potentially interacts with co-occurring nutrient stressors to affect overall biogeochemical cycling through consumer-mediated nutrient recycling pathways. We examined N- and P-excretion rates of snails (Physella spp.) in 12 outdoor experimental stream mesocosms dosed with 3 P treatments crossed with 3 triclosan treatments and a methanol carrier control. Snail N- and P-excretion rates increased with decreasing periphyton C: N and C: P ratios across the P-enrichment gradient. N- and P-excretion rates were significantly higher in the high-triclosan than in the methanol control treatments on day 14, but only in high-P-enrichment streams. However, methanol had positive effects on N- and P-excretion rates in low- and high-P-enrichment treatments compared to nonsolvent controls, but no effect at background P concentrations. Multiple inferences can be drawn from our study. First, whereas many investigators have confirmed that using methanol as a carrier below established regulatory levels does not influence laboratory and mesocosm ecotoxicology responses, our results suggest that low-level methanol concentrations can influence measures of ecosystem function. Second, higher use of triclosan and other antimicrobial agents in commercial products coupled with predicted urbanization and surfacewater shortages in the future have the potential to increase triclosan concentrations and shift patterns in consumermediated nutrient cycling in aquatic systems because of interactive effects of antimicrobial agents and nutrient enrichment. [ABSTRACT FROM AUTHOR]

The effects of pharmaceuticals on aquatic ecosystems are the subject of increasing environmental concern. Of particular interest are a suite of drugs known as selective serotonin reuptake inhibitors (SSRIs), commonly prescribed to treat depression. SSRIs are now detected in the environment worldwide, but their effects on ecosystems are not well understood. We conducted replicated experiments testing for an ecosystem effect of SSRIs in streams. We used artificial stream mesocosms to expose natural biofilms and aquatic insect communities to concentrations (20 µg/L) of fluoxetine or citalopram or a mix of both (totaling 40 µg/L). These concentrations are the lowest found to have an effect on aquatic invertebrates in other studies. Treatments suppressed gross primary production by 29% and community respiration by ≥43% on rock biofilms but did not affect algal biomass or whole-stream metabolism. A common group of dipteran midges emerged earlier in all SSRI treated streams compared with the controls. Total biomass of emerged adults at day 14 was greater in the SSRI-exposed streams, suggesting that fluoxetine and citalopram may influence developmental processes in some stream insects. Ecosystem function and invertebrate population dynamics are sensitive to pharmaceuticals. Our study demonstrates that chronic exposure to fluoxetine and citalopram has the potential to affect aquatic biota and ecosystem function. [ABSTRACT FROM AUTHOR]

Anthropogenic river fragmentation has the potential to alter fish population structure and diversity, but it can be difficult to infer whether observed effects reflect the obstruction of fish movement or population responses to altered flow regimes or habitat structure concomitant with fragmentation. We addressed the influence of habitat fragmentation on the European Chub (Squalius cephalus), a large-bodied fish with strong swimming ability that is a ubiquitous habitat generalist that occurs at high densities in lentic and lotic habitats. European Chub populations have never been stocked and are little affected by habitat alterations. Thus, they are good sentinels for the effects of fragmentation per se. We used microsatellite genotyping of 1726 fish from 38 sites to compare the genetic structure and diversity of European Chub populations from 3 Swiss midland rivers that are unequally affected by man-made fragmentation. The Thur is unfragmented, the adjacent Glatt is strongly fragmented by tall barriers, and the Broye is fragmented by a large number of low barriers that are individually traversable. European Chub from the Thur possessed the highest allelic diversity overall and showed no significant isolation-by-distance and only a weak nonsignificant upstream decline in genetic diversity. European Chub from the Glatt were less genetically diverse and showed significant isolation-by-distance that was explicable by existing barriers and the presence of a lake in the system and a steep upstream decline of allelic diversity. European Chub from the Broye showed no genetic substructure, suggesting that barriers of low height, even when numerous, had little effect on population connectivity. The detectable effects of anthropogenic fragmentation of rivers on a highly mobile fish like the European Chub suggests that less mobile species, such as habitat specialists or small benthic species, are potentially more vulnerable to isolation. [ABSTRACT FROM AUTHOR]

Benthic biofilms have multiple functions in stream and river ecosystems, and their growth and productivity are often limited by dissolved inorganic nutrient availability, particularly N or P. We deployed nutrient diffusing substrata (NDS) in 5 rivers in each of 3 regions: the Mountain West, the Arid West, and the Midwest, to assess regional and seasonal variation in nutrient limitation of river biofilms and to quantify which environmental factors control nutrient limitation. We constructed NDS with either inorganic or organic substrata to compare nutrient limitation of autotrophic and heterotrophic biofilms, and we explored inorganic N preference of biofilms by comparing results of NO3 - and NH4 + amendments. During summer deployments, autotrophic and heterotrophic biofilms in Mountain Western rivers were commonly limited by N or colimited by N and P, whereas nutrient limitation was less common in Arid Western and Midwestern rivers. We deployed NDS seasonally in Midwestern rivers and found no obvious seasonal patterns of nutrient limitation, probably because background nutrient concentrations were consistently high. Heterotrophic biofilm responses in Midwestern rivers suggested a preference for NO3 - over NH4 +. The magnitude of the autotrophic biofilm response, calculated as response ratios for gross primary production and chlorophyll a, were inversely related to % developed lands in the surrounding watershed and background NO3 - availability, whereas heterotrophic response ratios were related to river temperature. Patterns of nutrient limitation for autotrophic biofilms in rivers were similar to those in headwater streams, suggesting that biofilms in lotic ecosystems of varying size are similarly sensitive to nutrient amendments from the landscape. Clarifying the nutrient-limitation status of autotrophic and heterotrophic biofilms across a variety of rivers expands our understanding of nutrient limitation in lotic ecosystems and enables improved management of autotrophic and heterotrophic biofilms. [ABSTRACT FROM AUTHOR]

Fire is a prevalent feature of many landscapes and has numerous and complex effects on geological, hydrological, ecological, and economic systems. In some regions, the frequency and intensity of wildfire have increased in recent years and are projected to escalate with predicted climatic and landuse changes. In addition, prescribed burns continue to be used in many parts of the world to clear vegetation for development projects, encourage desired vegetation, and reduce fuel loads. Given the prevalence of fire on the landscape, authors of papers in this special series examine the complexities of fire as a disturbance shaping freshwater ecosystems and highlight the state of the science. These papers cover key aspects of fire effects that range from vegetation loss and recovery in watersheds to effects on hydrology and water quality with consequences for communities (from algae to fish), food webs, and ecosystem processes (e.g., organic matter subsidies, nutrient cycling) across a range of scales. The results presented in this special series of articles expand our knowledge of fire effects in different biomes, water bodies, and geographic regions, encompassing aquatic population, community, and ecosystem responses. In this overview, we summarize each paper and emphasize its contributions to knowledge on fire ecology and freshwater ecosystems. This overview concludes with a list of 7 research foci that are needed to further our knowledge of fire effects on aquatic ecosystems, including research on: 1) additional biomes and geographic regions; 2) additional habitats, including wetlands and lacustrine ecosystems; 3) different fire severities, sizes, and spatial configurations; and 4) additional response variables (e.g., ecosystem processes) 5) over long (>5 y) time scales 6) with more rigorous study designs and data analyses, and 7) consideration of the effects of fire management practices and policies on aquatic ecosystems. [ABSTRACT FROM AUTHOR]

The Grand River is a 7th-order 300-km river draining the largest watershed (6800 km²) in southern Ontario, Canada. The watershed has experienced large landuse changes during a period >100 y, resulting in increasing agricultural and urban nutrient inputs to the river. As a result, the Grand River is highly degraded from its source to mouth. We studied longitudinal and temporal changes in aquatic community metabolism (photosynthesis and respiration) and O2 gas exchange over 3 seasons using O2 and d18O-O2. Diel changes in O2 saturation were >50 percentage points along the river. In some parts, the diel O2 change was >10 mg/L. Strong daily variation in d18O-O2, up to 22‰, was observed at all 23 sampling sites in the river. Despite consistently high nutrient levels and high productivity from headwaters to mouth, wastewater treatment plant (WWTP) effluents strongly affected O2 saturation in all seasons. Modifications to river flow or nutrient inputs that affect the O2 gas-exchange coefficient or O2 demand could exacerbate current nighttime hypoxia problems. Strong diel variability in O2 may not directly indicate changes in metabolic rates because changes in gas-exchange coefficients alone are enough to mask changes in metabolic rates. Photosynthetic rates immediately downstream of WWTPs did not increase because nutrients were already high because of agricultural nutrient loading upstream of WWTPs. As a result, WWTP nutrients were exported downstream rather than used immediately below the WWTPs and the zone of impact from WWTP nutrients extended farther downstream than would otherwise be expected. O2 is the measure used by ecosystem managers, but metabolism and gas exchange must be managed to achieve the desired O2 outcomes. [ABSTRACT FROM AUTHOR]

Evolutionary theory predicts that different selective regimes may contribute to divergent evolution of body size and growth rate among populations, but most studies have focused on allopatric populations. Here, we studied five sympatric subpopulations of anadromous northern pike (Esox lucius) in the Baltic Sea subjected to allopatric habitats for a short period of their life cycle due to homing behavior. We report differences in adult body size among subpopulations that were in part due to variation in growth rate. Body size of emigrating juveniles also differed among subpopulations, and differences remained when individuals were reared in a common environment, thus indicating evolutionary divergence among subpopulations. Furthermore, a QST-FST comparison indicated that differences had evolved due to divergent selection rather than genetic drift, possibly in response to differences in selective mortality among spawning habitats during the allopatric life stage. Adult and juvenile size were negatively correlated across subpopulations, and reconstruction of growth trajectories of adult fishes suggested that body size differences developed gradually and became accentuated throughout the first years of life. These results represent rare evidence that sympatric subpopulations can evolve differences in key life-history traits despite being subjected to allopatric habitats during only a very short fraction of their life. [ABSTRACT FROM AUTHOR]

In terrestrial and aquatic ecosystems, organisms directly affect nutrient storage and cycling by sequestering nutrients via growth and remineralizing nutrients via excretion and egestion. Therefore, species introductions and extirpations can profoundly affect nutrient storage and remineralization rates, and present a challenge for conserving ecosystem function in fresh waters. The literature of consumer-driven nutrient dynamics is growing rapidly, but studies of consumer effects on nutrient storage and remineralization across species and among ecosystems are limited. We compared the effects of 3 grazing taxa, nonnative armored catfish in Mexican streams, native mussels in Oklahoma streams, and native tadpoles in Panamanian streams, on nutrient storage and remineralization. We examined interactions among organismal stoichiometry and biomass, nutrient storage, remineralization rates, and ecosystem size across these 3 groups following species decline (tadpoles and mussels) or introduction (armored catfish) to gain a better understanding of organism-specific effects on nutrient dynamics among freshwater ecosystems. Collectively, our results suggest that the ecosystem-level effect of consumer-driven nutrient dynamics is strongly influenced by environmental variables and is taxon specific. Major changes in biomass of stoichiometrically distinctive organisms can lead to subsequent changes in the flux and storage of elements in an ecosystem, but the overall effect of aquatic animals on nutrient dynamics also is determined by discharge and nutrient-limitation patterns in streams and rivers. [ABSTRACT FROM AUTHOR]

The current and future direction of aquatic ecological research leans toward addressing questions that cover multiple scales and levels of complexity. Historically, the ability to do comparative aquatic research across large spatial and temporal scales has been impeded by a lack of comparable measurements, standard methods, and a well organized data management and retrieval system. The National Ecological Observatory Network (NEON) is the first continental-scale ecological observation system designed to collect and provide freely available data on the drivers and responses of ecological change. In this paper, we describe past and present attempts to work across multiple scales in aquatic ecology, and the potential use of NEON aquatics data and infrastructure by researchers to integrate and expand ecological research programs and address novel ecological questions. [ABSTRACT FROM AUTHOR]

Foraminifera are commonly defined as marine testate protists, and their diversity is mainly assessed on the basis of the morphology of their agglutinated or mineralized tests. Diversity surveys based on environmental DNA (eDNA) have dramatically changed this view by revealing an unexpected diversity of naked and organic-walled lineages as well as detecting foraminiferal lineages in soil and freshwater environments. Moreover, single-cell analyses have allowed discrimination among genetically distinctive types within almost every described morphospecies. In view of these studies, the foraminiferal diversity appeared to be largely underestimated, but its accurate estimation was impeded by the low speed and coverage of a cloning-based eDNA approach. With the advent of high-throughput sequencing (HTS) technologies, these limitations disappeared in favor of exhaustive descriptions of foraminiferal diversity in numerous samples. Yet, the biases and errors identified in early HTS studies raised some questions about the accuracy of HTS data and their biological interpretation. Among the most controversial issues affecting the reliability of HTS diversity estimates are (1) the impact of technical and biological biases, (2) the sensitivity and specificity of taxonomic sequence assignment, (3) the ability to distinguish rare species, and (4) the quantitative interpretation of HTS data. Here, we document the lessons learned from previous HTS surveys and present the current advances and applications focusing on foraminiferal eDNA. We discuss the problems associated with HTS approaches and predict the future trends and avenues that hold promises for surveying foraminiferal diversity accurately and efficiently. [ABSTRACT FROM AUTHOR]

Metagenomic sequencing now represents a common, powerful approach for investigating diversity and functional relationships in marine ecosystems. Highthroughput datasets generated from random fragments of environmental DNA can provide a less biased view of organismal abundance (versus PCR-based amplicon sequencing) and enable novel exploration of microbial genomes by recovering genome assemblies from uncultured species, identifying ecological functions, and reconstructing metabolic pathways. This review highlights the current state of knowledge in marine metagenomics, focusing on biological insights gained from recent environmental studies and detailing commonly employed methods for data collection and analysis. [ABSTRACT FROM AUTHOR]

The chironomid Benthic Quality Index (BQI) is a widely used metric in assessments of lake status. The BQI is based on 7 indicator taxa, which like most profundal fauna, often occur sporadically in low densities. Hence, a major weakness of the index is that it cannot be calculated when indicator taxa are not captured. Thus, an extension of the BQI that incorporates more macroinvertebrate taxa is desirable. We used 2 statistical approaches (Detrended Correspondence Analysis and Weighted Averaging) to estimate new benthic quality indicator scores for profundal macroinvertebrate taxa and to construct modified BQIs called Profundal Invertebrate Community Metrics (PICMs). We calibrated the PICMs and evaluated their bioassessment performance with macroinvertebrate and environmental data from 735 lake basins in Finland. Both PICMs included 70 taxa and could be calculated for a substantially greater proportion (99.5%) of sites than the original BQI (83.5%). Compared to the BQI, the PICMs were more strongly correlated with whole-community variation and were more predictable from environmental factors independent of human activities in undisturbed reference lakes. PICMs were more specific in identifying undisturbed lakes and more sensitive in discriminating nonreference from reference lakes. The strength of relationships to total P concentration was equal among indices. These results suggest that the extension of BQI to incorporate more taxa will increase generality, accuracy, and representativeness of lake profundal macroinvertebrate assessment. [ABSTRACT FROM AUTHOR]

Insect emergence is a fundamental process in freshwaters. It is a critical life-history stage for aquatic insects and provides an important prey resource for terrestrial and aquatic consumers. Sticky traps are increasingly being used to sample these insects. The most common design consists of an acetate sheet coated with a nondrying adhesive that is attached to a wire frame or cylinder. These traps must be prepared at the deployment site, a process that can be time consuming and difficult given the vagaries of field conditions. Our goals were to develop a sturdy, low-cost sticky trap that could be prepared in advance, rapidly deployed and recovered in the field, and used to estimate the flight direction of insects. We used 150-mm Petri dishes with lids. The dishes can be coated cleanly and consistently with Tangle-Trap® adhesive. Deploying traps is simple and requires only a pole set near the body of water being sampled. Four dishes can be attached to the pole using Velcro and aligned in 4 different directions to enable quantification of insect flight direction. After sampling, Petri dishes can be taped closed, packed in boxes, and stored indefinitely. Petri traps are comparable in price to standard acetate sheet traps at ~US$0.50/directional deployment, but they require more space for storage than acetate sheet traps. However, a major benefit of Petri traps is that field deployment times are ⅓ those of acetate traps. Our study demonstrated that large Petri dishes are an ideal platform for sampling postemergent adult aquatic insects, particularly when the study design involves estimating flight direction and when rapid deployment and recovery of traps is critical. [ABSTRACT FROM AUTHOR]

A natural pH gradient caused by marine CO2 seeps off Vulcano Island (Italy) was used to assess the effects of ocean acidification on coccolithophores, which are abundant planktonic unicellular calcifiers. Such seeps are used as natural laboratories to study the effects of ocean acidification on marine ecosystems, since they cause long-term changes in seawater carbonate chemistry and pH, exposing the organisms to elevated CO2 concentrations and therefore mimicking future scenarios. Previous work at CO2 seeps has focused exclusively on benthic organisms. Here we show progressive depletion of 27 coccolithophore species, in terms of cell concentrations and diversity, along a calcite saturation gradient from Ωcalcite 6.4 to <1. Water collected close to the main CO2 seeps had the highest concentrations of malformed Emiliania huxleyi. These observations add to a growing body of evidence that ocean acidification may benefit some algae but will likely cause marine biodiversity loss, especially by impacting calcifying species, which are affected as carbonate saturation falls. [ABSTRACT FROM AUTHOR]

The tropical ocean environment is changing at an unprecedented rate, with warming and severe tropical cyclones creating obvious impacts to coral reefs within the last few decades and projections of acidification raising concerns for the future of these iconic and economically important ecosystems. Documenting variability and detecting change in global and regional climate relies upon high-quality observational records of climate variables supplemented, prior to the mid-19th century, with reconstructions from various sources of proxy climate information. Here we review how annual density banding patterns that are recorded in the skeletons of massive reef-building corals have been used to document environmental change and impacts within coral reefs. Massive corals provide a historical perspective of continuous calcification processes that pre-date most ecological observations of coral reefs. High-density stress bands, abrupt declines in annual linear extension, and evidence of partial mortality within the skeletal growth record reveal signatures of catastrophic stress events that have recently been attributed to mass bleaching events caused by unprecedented thermal stress. Comparison of recent trends in annual calcification with century-scale baseline calcification rates reveals that the frequency of growth anomalies has increased since the late 1990s throughout most of the world's coral reef ecosystems. Continuous coral growth histories provide valuable retrospective information on the coral response to environmental change and the consequences of anthropogenic climate change. Co-ordinated efforts to synthesize and combine global calcification histories will greatly enhance our understanding of current calcification responses to a changing ocean. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses the uses of molecular approaches in freshwater ecology.

The National Lakes Assessment (NLA) used relative and attributable risks to measure the apparent nationwide effects of excess N, reduced lakeshore habitat, and other stressors on planktonic assemblages in lakes. The risk measures, borrowed from human health research, use nontechnical language to compare the apparent effects of disparate lake stressors, thereby helping the public and policymakers identify stressors of greatest national concern. However, the investigators for the NLA and similar prior surveys of streams did not adjust their risk estimates of each stressor for possible confounding by other covarying stressors. As a result, the NLA point estimates overstate the risks of individual stressors and, thus, are unreliable for assessing their importance relative to that of closely related stressors. I used NLA data from 966 lakes to illustrate existing statistical methods of risk adjustment. Point estimates of adjusted relative risk for 7 stressor variables were 15 to 64% lower than unadjusted estimates. Adjusted attributable risks also were lower than unadjusted values, but for some stressors, they were very inconsistent across 3 adjustment methods. In addition, adjusted risk estimates used only part of the available data because each estimate was adjusted for many (6) covarying stressors. Closely related stressor variables (for example, N, P, and turbidity) can be combined into a bundle representing a broader type of stress (reduced water quality). For the NLA data, adjusted risk estimates for the stressor bundles (water quality and habitat) were more consistent across estimation methods and had lower relative uncertainty than estimates for their component stressors. In addition, closely related stressors with similar sources and modes of impact are more likely to be managed together rather than individually. For these reasons, I suggest evaluating stressor bundles in future aquatic surveys. [ABSTRACT FROM AUTHOR]

Premise of research. Tristyly is a floral polymorphism that is reliably reported from six flowering plant families. Populations of tristylous species often contain three floral morphs that differ reciprocally in stigma and anther height. Trimorphic incompatibility and a suite of ancillary pollen and stigma polymorphisms are commonly associated with sex organ trimorphism. Here, we investigate the tristylous syndrome of Pontederia subovata (Pontederiaceae), a little-known aquatic from southwest Brazil. Methodology. We conducted measurements of sex organ position, pollen size, pollen production, and stigmatic papillae length on the three floral morphs under glasshouse conditions and carried out a controlled pollination program to investigate whether P. subovata possesses a trimorphic incompatibility system and whether its expression varies among the floral morphs. Pivotal results. Pontederia subovata displays reciprocal stigma and anther heights and trimorphism in the size of pollen grains and the length of stigmatic papillae. Controlled pollinations provided evidence of trimorphic incompatibility: self- and intramorph crosses yielded significantly less seed than do intermorph crosses when pollen from anthers and stigmas of equivalent height were employed. However, trimorphic incompatibility was weakly expressed in the mid-styled morph when pollinations involved long-level anthers. The occurrence of stem-borne tubers is reported for the first time from Pontederiaceae. Conclusions. Our results confirm the presence of tristyly in P. subovata. The species has several features in common with other tristylous members of Pontederia, including striking variation in the strength of incompatibility among the floral morphs. We suggest that weak incompatibility in the mid-styled morph may provide reproductive assurance during colonization. Tuber formation in P. subovata probably evolved as an adaptation enabling persistence of genets during the marked dry season that characterizes the aquatic habitats in which the species occurs. [ABSTRACT FROM AUTHOR]

Disturbances often lead to changes in average values of community properties; however, disturbances can also affect the predictability of a community's response. We performed a meta-analysis to determine how response predictability, defined as among-replicate variance in diversity and community abundance, is affected by species removals, species invasions, nutrient addition, temperature increase, and habitat loss/fragmentation, and we further determined whether response predictability differed according to habitat and trophic role. Species removals and nutrient addition decreased response predictability, while species invasions increased response predictability. In aquatic habitats, disturbances generally led to a decrease in response predictability, whereas terrestrial habitats showed no overall change in response predictability, suggesting that differences in food web and ecosystem structure affect how communities respond to disturbance. Producers were also more likely to show decreases in response predictability, particularly following species removals, highlighting widespread destabilizing effects of species loss at the producer level. Overall, our results show that whether disturbances cause changes in response predictability is highly contingent on disturbance type, habitat, and trophic role. The nature of changes in response predictability—for example, strong decreases following species invasions and increases following species removals—will likely play a major role in how communities recover from disturbance. [ABSTRACT FROM AUTHOR]

Pesticides play a critical role in maximizing yields of economically important crops and minimizing the human health threats of disease-carrying pests, but they often have collateral effects on nontarget species. We used a mesocosm study to address how the most commonly used insecticide in the USA, malathion, applied at low, ecologically relevant concentrations (20 and 110 µg/L) affects species interactions in aquatic communities. Unlike many community ecotoxicology studies, our study assessed how malathion affects both consumptive and nonconsumptive effects of predators. We also considered how the vertical distribution of predator cues and malathion (caused by potential stratification) affects species interactions. We found no evidence for vertical stratification of malathion, a result suggesting that exposure to the pesticide was uniform throughout the water column. Malathion was lethal to some primary consumers (cladocerans) at both concentrations and to top predators (dragonflies) at the highest concentration (110 µg/L). These lethal effects initiated density-mediated indirect effects in both cases. Malathion also may have decreased dragonfly foraging efficiency, resulting in increased tadpole survival (trait-mediated indirect effect), which decreased the resources used by tadpoles (periphyton). Collectively, our results show that malathion alters species interactions. However, we suggest that the degree to which pesticides affect aquatic communities will depend strongly on the species composition of communities. Therefore, the community-level consequences of pesticide exposure are likely to vary across the ecological landscape. [ABSTRACT FROM AUTHOR]

Aquatic research historically has focused on separate aquatic ecosystems (i.e., freshwater, estuarine, and marine). We argue that this separation into subdisciplines is artificial and may even be counterproductive. Instead, scientists should consider the physical linkages between different aquatic ecosystems and the many similarities in properties and processes among those ecosystems (conceptual linkages). The 4 papers in this J-NABS cluster demonstrate the value of integrating information from different aquatic ecosystems. For example, the papers illustrate that transformation and transportation of nutrients and energy physically and conceptually link all aquatic ecosystems and are facilitated by the characteristics of the medium that defines them all-- water. To promote the exchange of information within aquatic science, more interecosystem studies should be published in journals and books so that scientists will see parallels and linkages among freshwater, estuarine, and marine systems. Over the longer term, such studies would benefit from the funding and teaching of aquatic science as an integrated whole. [ABSTRACT FROM AUTHOR]

The fast-start escape response in fish is essential for predator avoidance, but almost nothing is known about whether sublethal concentrations of pollutants can impair this reflex. Ammonia, a pervasive pollutant of aquatic habitats, is known to have toxic effects on nervous and muscle function in teleost fish. Golden gray mullet (Liza aurata L.) were exposed for 24 h to sublethal ammonia concentrations in seawater (control, 400 μmoI L-1, or 1,600 μmol L-1 NH4Cl), and then their response to startling with a mechanical stimulus was measured with high-speed video. Initiation of the escape response was significantly slowed by ammonia exposure: response latency rose proportionally from <50 ms in controls to >300 ms at a concentration of 1,600 μmol L-1 NH4Cl. This indicates toxic effects on nervous function within the reflex arc. Impaired escape performance was also observed: maximum turning rate, distance covered, velocity, and acceleration were significantly reduced by >45% at a concentration of 1,600 μmol L-1 NH4Cl. This indicates toxic effects on fast-twitch glycolytic white muscle function, the muscle type that powers the fast-start response. These neuromotor impairments were associated with significant ammonia accumulations in venous plasma and white muscle and brain tissue. These results indicate that anthropogenic ammonia pollution in aquatic habitats may increase the vulnerability of fish to predation, especially by birds and mammals that are not affected by water ammonia concentrations. [ABSTRACT FROM AUTHOR]

The ETH Zürich hosted an art-science competition in which artists were asked to communicate scientific findings through various media (photo: CTR). This Bridges cluster is designed to bring the art-science perspective forward in the freshwater sciences, augment art-science interactions, and increase awareness for potential integration. [Extracted from the article]

During metamorphosis, most amphibians undergo rapid shifts in their morphology that allow them to move from an aquatic to a more terrestrial existence. Two important challenges associated with this shift in habitat are the necessity to switch from an aquatic to terrestrial mode of locomotion and changes in the thermal environment. In this study, I investigated the consequences of metamorphosis to the burst swimming and running performance of the European newt Triturus cristatus to determine the nature and magnitude of any locomotor trade- offs that occur across life-history stages. In addition, I investigated whether there were any shifts in the thermal dependence of performance between life-history stages of T. cristatus to compensate for changes in their thermal environment during metamorphosis. A trade-off between swimming and running performance was detected across life-history stages, with metamorphosis resulting in a simultaneous decrease in swimming and increase in running performance. Although the terrestrial habitat of postmetamorphic stages of the newt T. cristatus experienced greater daily fluctuations in temperature than the aquatic habitat of the larval stage, no differences in thermal sensitivity of locomotor performance were detected between the larval aquatic and postmetamorphic stages. The absence of variation across life-history stages of T. cristatus may indicate that thermal sensitivity may be a conservative trait across ontogenetic stages in amphibians, but further studies are required to investigate this assertion. [ABSTRACT FROM AUTHOR]

Overwintering habits of hatchling Blanding's turtles (Emydoidea blandingii) are unknown. To determine whether these turtles are able to survive winter in aquatic habitats, we submerged hatchlings in normoxic (155 mmHg Po2) and hypoxic (6 mmHg Po2) water at 4°C, recording survival times and measuring changes in key physiological variables. For comparison, we simultaneously studied hatchling softshell (Apalone spinifera) and snapping (Chelydra serpentina) turtles, which are known to overwinter in aquatic habitats. In normoxic water, C. serpentina and A. spinifera survived to the termination of the experiment (76 and 77 d, respectively). Approximately one- third of the E. blandingii died during 75 d of normoxic sub-mergence, but the cause of mortality was unclear. In hypoxic water, average survival times were 6 d for A. spinifera, 13 d for E. blandingii, and 19 d for C. serpentina. Mortality during hypoxic submergence was probably caused by metabolic acidosis, which resulted from accumulated lactate. Unlike the case with adult turtles, our hatchlings did not increase plasma calcium and magnesium, nor did they sequester lactate within the shell. Our results suggest that hatchling E. blandingii are not particularly well suited to hibernation in hypoxic aquatic habitats. [ABSTRACT FROM AUTHOR]

Examines the land-use changes in the Ipswich River watershed in Massachusetts. Background of the watershed; Influence of land-use legacy on the ecology of the watershed; Land use in the watershed.

Examines the photochemical and microbial degradation of dissolved organic carbon (DOC) in a headwater stream system. Samples from three sources with different levels of DOC; Photochemical degradation measured and labeled as total organic carbon concentration; Microbial activity labeled as bacterial productivity.