Mayfly Nymphs Research Articles

Macrophyte‐specific effects on epiphyton quality and quantity and resulting effects on grazing macroinvertebrates

Abstract Aquatic macrophytes can have a significant impact on their associated community of epiphytic algae and bacteria through the provisioning of structural habitat complexity through different growth forms, the exudation of nutrients and the release of allelochemicals. In turn, this effect on epiphytic biofilm biomass and nutrient content has a potential effect on the macroinvertebrates that depend on epiphyton as a food source. We studied the effect of living macrophytes and their growth form on biofilm development in a semi‐controlled replicated microcosm experiment. Conditions of a nutrient‐poor water layer and nutrient‐rich sediment were created to study the effects of nutrient exudation by living macrophytes. We compared biofilm quantity and quality on structurally simple (Vallisneria spiralis) versus complex (Egeria densa) living plants and artificial analogues. Subsequently, the biofilm that had developed on the plants was fed, in a laboratory growth experiment, to two species of macroinvertebrate grazers (the snail Haitia acuta and the mayfly nymph Cloeon dipterum). This enabled us to assess if and how the macrophyte‐induced effects on the epiphyton can influence macroinvertebrate grazers. Living macrophytes were found to have a significant effect on epiphytic algal cover, which was mostly expressed by a lower cover on living macrophytes compared to their artificial analogues. Additionally, epiphyton cover on artificial macrophytes was found to be higher on complex structures compared to simple ones, yet this was not observed on living macrophytes. Plant specific traits, such as the release of allelopathic substances, competition for nutrients and DIC, and the amount of CaCO3 deposition on plant surfaces might explain these results. The density of epiphytic bacteria was found to be negatively correlated with biofilm Ca content from macrophytes in every treatment except living E. densa, which differed in leaf anatomy from the other plants by possessing polar leaves. Furthermore, biofilm on living macrophytes had lower C:N:P molar ratios compared to that on artificial plants, which is likely to be explained by nutrient exudation by the living plants. Although it was expected that a more nutritious biofilm would lead to increased grazer growth, this was observed only for H. acuta on E. densa. Because biofilm quantity was not a limiting factor, this lack of effect may be caused by compensatory feeding. It can be concluded that, depending on their traits, living macrophytes can have a positive effect on macroinvertebrate grazers by providing a large surface area for colonisation by epiphytic algae and bacteria, by improving biofilm stoichiometry and by stimulating bacterial growth.

Mayfly ecological traits in a European karst spring: species, microhabitats and life histories

Despite the recent increase in the number of mayfly studies in karst freshwater habitats, their biology and ecology in springs are still poorly characterized. Therefore, we studied mayfly assemblages in a European karst rheocrene spring at five microhabitats monthly over a one-year period. Three species were recorded: Baetis alpinus (Pictet, 1843), Baetis rhodani (Pictet, 1843) and Rhithrogena braaschi (Jacob, 1974). The latter species represents a new record for the fauna of Bosnia and Herzegovina. All three species inhabited all studied microhabitats but with varying abundance. Individual species were associated with a specific substrate type and/or water velocity and/or water depth. The grazer/scraper Rh. braaschi was most common at microhabitats with inorganic substrate (cobbles, mixture of pebbles and sand), moderate water velocity and higher water depth. The rheophilic grazer/scraper and gatherer/collector B. alpinus was most common at microhabitats with mosses and highest water velocity. The grazer/scraper and gatherer/collector B. rhodani was recorded at all microhabitats, yet due to its preference for moderate water velocity, the highest number of individuals were collected from cobbles. We recorded movements of mayfly nymphs among the available microhabitats during their life cycles, due likely to their dietary requirements and search for suitable refugia. Baetis alpinus has a bivoltine, B. rhodani polyvoltine and Rh. braaschi univoltine life cycle with a long emergence period. The results presented here contribute to the knowledge of spring and mayfly ecology.

A simple molecular assay differentiates two burrowing mayfly species, Hexagenia limbata and H. rigida (Ephemeroptera: Ephemeridae), in western Lake Erie

Abstract Burrowing mayflies (Hexagenia spp.) are important indicators of mesotrophic water conditions, and have been studied for several decades in conjunction with the changing trophic status of western Lake Erie. However, most studies on the biology of burrowing mayflies have failed to differentiate between immature H. limbata and H. rigida, the life stages that are most commonly collected. We developed a simple molecular assay to facilitate species-level identification of the two mayflies as an easier alternative to sequencing the COI gene. We analyzed a total of 152 cytochrome c oxidase, subunit I barcoding sequences from the Barcode of Life Data System (BOLD) for these mayfly species and developed a diagnostic primer set. We tested our primers on 46 random burrowing Lake Erie mayfly nymphs using both conventional PCR and qPCR. Results of the two methods were consistent and unambiguous. Sequencing of the COI barcoding region in the mayflies confirmed that the PCR assays correctly identified mayflies in all cases. Our assay is simple and effective, and will facilitate species-level identification of burrowing mayflies in future studies on their biology where the two species co-occur.

First record of trichomycetes associated with aquatic insects from Colombian Moorland and Andean forests

This paper discusses new findings relating to the first known diversity of trichomycete gut symbionts from Colombia. All species were associated with aquatic insects in the orders Diptera and Ephemeroptera collected from various localities in the tropical Eastern Ridge of Santander. Among the reported taxa, we describe two new species, Gauthieromyces colombiensis (Harpellales), phenotypically similar to the European G. microsporus, and Paramoebidium santanderensis (Amoebidiales) characterized by retaining the cystospore attached to the growing thallus after germination. Both taxa were found in the hindgut of mayfly nymphs. We also provide 17 new geographic records of trichomycetes for Colombia. Taxonomic and biogeographic implications of these records are discussed.

Evaluation of lower Green Bay benthic fauna with emphasis on re-ecesis of Hexagenia mayfly nymphs

Abstract The last historic Hexagenia specimen in lower Green Bay was officially recorded in 1955. Field surveys and Hexagenia viability studies were completed to determine if lower Green Bay could support Hexagenia re-ecesis and where in the bay egg stocking could best be accomplished. The invertebrate field data were compared with historical population data based on earlier published studies in the 1950s, 1970s and 1990s to determine the bay's ecological trajectory to better understand the re-ecesis success potential of Hexagenia. No native Hexagenia were observed during this study. Deep water invertebrate diversity within the upper lower bay appears to be improving, whereas the diversity along the lower mid-bay may be deteriorating. Shallower, nearshore samples indicated a better condition with Caenis mayflies sparsely present, amphipods, isopods, gilled snails, odonates, oligochaetes, chironomids, and meiofauna present. These results suggested improved conditions shoreward versus degraded conditions deeper. Hexagenia egg viability and neonate growth indicated Hexagenia could successfully inhabit in situ Green Bay nearshore (

The Wood-Boring Trace Fossil <i>Asthenopodichnium</i> from Palaeocene Sediments of the Barmer Hill Formation, Western Rajasthan, India

The present study documents the wood-boring trace fossil Asthenopodichnium from the Palaeocene sediments of the Barmer Hill Formation (BHF) in the Barmer Basin, Western Rajasthan, India. The Asthenopodichnium trace fossils are loosely to tightly packed, pouch-like burrows or almond-shaped structures identified as Asthenopodichnium lignorum , whereas lozenge and J-shaped structures are designated as Asthenopodichnium lithuanicum . The A. lignorum trace markers are considered to be the feeding and dwelling burrows produced by wood-rotting fungi, whereas A. lithuanicum are interpreted as feeding and dwelling burrows produced by Mayfly nymphs and larvae. The sedimentological and palaeontological studies of trace fossil-bearing horizons of BHF suggest freshwater fluvial sedimentary environment with humid to sub-humid climate.

Modeling Mayfly Nymph Length Distribution and Population Dynamics Across a Gradient of Stream Temperatures and Stream Types

We analyze a process-based temperature model for the length distribution and population over time of mayfly nymphs. Model parameters are estimated using a Markov Chain Monte Carlo parameter estimation method utilizing length distribution data at five different stream sites. Two different models (a standard exponential model and a modified Weibull model) of mayfly mortality are evaluated, where in both cases mayfly length growth is a function of stream temperature. Based on model-data comparisons to the modeled length distribution and the Bayesian Information Criterion, we found that approaches that length distribution data can reliably estimate 2–3 model parameters. Future model development could include additional factors include such as upstream environmental factors, abiotic conditions, interspecific competition, predation, or stream salinity. Outputs of this model could be applied to predict mayfly emergence across a geographic domain or to forecast mayfly population responses to climate change.

Evaluating factors driving population densities of mayfly nymphs in Western Lake Erie

Abstract Mayfly ( Hexagenia spp.) nymphs have been widely used as indicators of water and substrate quality in lakes. Thermal stratification and the subsequent formation of benthic hypoxia may result in nymph mortality. Our goal was to identify potential associations between recent increases in temperature and eutrophication, which exacerbate hypoxic events in lakes, and mayfly populations in Lake Erie. Nymphs were collected during April–May 1999–2014. We used wind and temperature data to calculate four measures of thermal stratification, which drives hypoxic events, during summers of 1998–2013. Bottom trawl data collected during August 1998–2013 were used to estimate annual biomass of fishes known to be predators of mayfly nymphs. We used Akaike's Information Criterion to identify the best one- and two-predictor regression models of annual population densities ( N /m 2 ) of age-1 and age-2 nymphs, in which candidate predictors included the four measures of stratification, predator fish biomass, competition, and population densities of age-2 (for age-1) and age-1 (for age-2) nymphs from the previous year. Densities of both age classes of nymphs declined over the time series. Population densities of age-1 and age-2 nymphs from the previous year best predicted annual population densities of nymphs of both age classes. However, hypoxic conditions (indicated by stratification) and predation both had negative effects on annual population density of mayflies. Compared with predation, hypoxia had an inconsistent effect on annual nymph density. The increases in temperature and eutrophication in Lake Erie, which exacerbate hypoxic events, may have drastic effects on the mayfly populations.

Do Mining Activities Significantly Affect Feeding Behavior of Freshwater Benthic Macroinvertebrates? A Case Study in South Sardinia (Italy)

We investigated the cascading effects of chemical contaminants on alder leaf detritus quality and the exploitation of this feeding resource by benthic macroinvertebrates (isopods, gastropods, and mayfly nymphs). Trophic behavior and energetics of benthic macroinvertebrates were used to evaluate the effects of contaminants on detritus exploitation. A two-way factorial nested experimental design was used to statistically quantify how leaf detritus origin (polluted and unpolluted streams) and the pollution level of the site selected for microbial conditioning of the detritus could affect the feeding resource quality for aquatic benthic macroinvertebrates, as measured by their trophic behavior (i.e. food selection) and exploitation (i.e. food ingestion). Alder leaves collected from a polluted stream in a former mining area (South-Sardinia, Italy) had Cd, Pb, and Zn concentrations up to 10 times that of leaves collected from an unpolluted stream. When benthic macroinvertebrates were given the option to choose, they all selected leaves from the unpolluted stream and/or those conditioned in the unpolluted stream. Ingestion rates were also significantly affected by both considered factors: leaf origin and conditioning. In addition, synergistic effects strongly increased the chemical contaminant stress on the leaf detritus quality. These results show that the terrestrial component of land–water ecotones affected by mining can be a relevant indirect pathway of chemical stress to benthic macroinvertebrate species.

Strategies of ionoregulation in the freshwater nymph of the mayfly Hexagenia rigida.

This study investigated ionoregulatory strategies used by freshwater (FW) nymphs of the mayfly Hexagenia rigida Like other FW organisms, H. rigida nymphs maintain hemolymph ion levels (in mmoll-1: Na+ ∼102; Cl- ∼84; K+ ∼6; pH ∼7.35) far in excess of their surroundings. This appears to be accomplished by the combined actions of the alimentary canal, Malpighian tubules (MTs) and tracheal gills. The alimentary canal contributes in a region-specific manner, a view supported by: (1) spatial differences in the activity of basolateral Na+/K+-ATPase (NKA) and apical V-type H+-ATPase (VA) and (2) region-specific Na+ and K+ flux rates. Both indicate a prominent role for the hindgut (rectum) in K+ reabsorption. MTs also exhibit region-specific differences in Na+ and K+ flux rates that are coupled with an organized but tortuous architecture. NKA and VA activities were highest in MTs versus all other organs examined. Tracheal gills were found to be sites of Na+ uptake, but no difference in Na+ uptake was found between gills taken from different regions of the abdomen or spatially along individual gills. This is likely because each gill exhibited a dense population of NKA and/or VA immunoreactive cells (putative ionocytes). Data provide new insight into how FW mayfly nymphs regulate salt and water balance using the alimentary canal, MTs and tracheal gills as well as the first direct evidence that tracheal gills acquire ions from FW.

Ocurrencia de nemátodos en ninfas de Ephemeroptera en una quebrada de bosque tropical lluvioso

Nematodes are common symbionts of aquatic insects. Here, we assessed the presence of nematodes in mayfly nymphs (Ephemeroptera), evaluated their prevalence in the population, and determined factors associated with nematode presence. Mayflies were collected (n = 130) from three stream habitats (riffles, pools, and boulders) using a D net, in Prieta stream, El Verde Field Station, Puerto Rico. Mayflies were dissected and nematode presence was determined under a light microscope (4 x and 10 x). Nematode prevalence was 50 %. Nematodes were not identified beyond Phylum level, but we were able to eliminate various groups as infective agents (Nematoda: Mermithidae and Nematomorpha: Gordiida). They were mostly found in the abdomen, head or thorax of mayflies. There were differences in infection among taxa, Neohagenulus was the group with the highest proportion of infection. Mayfly body shape, feeding strategy, or activity potentially explain differences in infection among taxa. There were no differences in infection among habitats, but mayflies were less abundant in riffles; and there was no relation between mayfly body length and the number of nematodes present. To our knowledge, this is the first report of a nematode present in mayfly nymphs in Puerto Rico.

A depth-adjusted ambient distribution approach for setting numeric removal targets for a Great Lakes Area of Concern beneficial use impairment: degraded benthos.

We compiled macroinvertebrate data collected from 1995 to 2014 from the St. Louis River Area of Concern (AOC) of Lake Superior. Our objective was to define depth-adjusted cutoff values for benthos condition classes to provide an analytical tool for quantifying progress toward achieving removal targets for the degraded benthos beneficial use impairment. We used quantile regression to model the limiting effect of depth on selected benthos metrics, including taxa richness, percent non-oligochaete individuals, combined percent Ephemeroptera, Trichoptera, and Odonata individuals, and density of ephemerid mayfly nymphs (Hexagenia). We created a scaled trimetric index from the first three metrics. Metric values above the 75th percentile quantile regression model prediction were defined as being in relatively excellent condition in the context of the degraded beneficial use impairment for that depth. We set the cutoff between good and fair condition as the 50th percentile model prediction, and we set the cutoff between fair and poor condition as the 25th percentile model prediction. We examined sampler type, geographic zone, and substrate type for confounding effects. Based on these analyses we combined data across sampler types and created separate models for each of three geographic zone. We used the resulting condition-class cutoff values to determine the relative benthic condition for three adjacent habitat restoration project areas. The depth-limited pattern of ephemerid abundance we observed in the St. Louis River AOC also occurred elsewhere in the Great Lakes. We provide tabulated model predictions for application of our depth-adjusted condition class cutoff values to new sample data.

Alteration of physico-chemical and microbial properties in freshwater substrates by burrowing invertebrates

The hyporheic interstitial provides habitat for many different organisms – from bacteria to burrowing invertebrates. Due to their burrowing and sediment reworking behaviour, these ecosystem engineers have the potential to affect hyporheic processes such as respiration and nutrient cycling. However, there is a lack of studies that characterize the interactions between bioturbators, physico-chemical habitat properties and microbial communities in freshwater substrates. In a standardized laboratory experiment, we investigated the effects of three functionally different bioturbators, duck mussels (Anodonta anatina, Linnaeus 1758), mayfly nymphs (Ephemera danica, Müller 1764) and tubificid worms (Tubifex tubifex, Müller 1774), on the physico-chemical conditions and bacterial communities in hyporheic substrates. We hypothesized that different invertebrates distinctly alter habitat conditions and thus microbial community composition, depending on the depth and the manner of burrowing. A. anatina and E. danica caused an increase in interstitial oxygen concentration, whereas strong declines in oxygen concentration and redox potential were detected in the T. tubifex treatment. These effects on physico-chemical habitat properties were even detectable in open water. Mussels and tubificid worms also significantly influenced the composition of bacterial communities in the hyporheic zone. A loss or replacement of bioturbators in stream ecosystems due to anthropogenic habitat alterations is expected to result in shifts in microbial community compositions, with effects on nutrient fluxes, pollutant degradation and benthic food webs. An understanding of the effects of functionally different native and invasive bioturbators is crucial to predict changes in stream ecosystem functioning.

Biological barriers to restoration: testing the biotic resistance hypothesis in an upland stream recovering from acidification

The biotic resistance hypothesis provides one of several explanations for the limited biological recovery of streams recovering chemically from acidification. The hypothesis proposes that acidification has changed the presence, abundance and interactions among species in acidified streams to the extent that acid-sensitive colonists cannot re-invade even where acidity has ameliorated. As a first step in testing for biotic resistance in streams, we conducted a field experiment to determine whether the success (growth rate) of acid-sensitive recolonists (mayfly nymphs, Baetis rhodani) is reduced by competition with abundant acid-tolerant residents (stonefly nymphs, Leuctra inermis) in a chemically recovering Welsh stream (UK). Gut contents analysis revealed a marked overlap in resource use between the two species. However, when Baetis was exposed to several (0, 0.25, 0.5 and 1 times ambient) densities of its putative competitor, Leuctra, growth rates of the colonist were not affected by the residents at any of the densities tested. These results do not support the hypothesis that resident species constrain colonist populations by affecting growth rates through competition for limited resources or interference. Further work is required to assess whether independent and/or interactive ecological effects of other common residents might affect colonists in ecosystems recovering from past stressors.

Spatial and temporal trends in contaminant concentrations in Hexagenia nymphs following a coal ash spill at the Tennessee Valley Authority's Kingston Fossil Plant.

A dike failure at the Tennessee Valley Authority Kingston Fossil Plant in East Tennessee, United States, in December 2008, released approximately 4.1 million m(3) of coal ash into the Emory River. From 2009 through 2012, samples of mayfly nymphs (Hexagenia bilineata) were collected each spring from sites in the Emory, Clinch, and Tennessee Rivers upstream and downstream of the spill. Samples were analyzed for 17 metals. Concentrations of metals were generally highest the first 2 miles downstream of the spill, and then decreased with increasing distance from the spill. Arsenic, B, Ba, Be, Mo, Sb, Se, Sr, and V appeared to have strong ash signatures, whereas Co, Cr, Cu, Ni, and Pb appeared to be associated with ash and other sources. However, the concentrations for most of these contaminants were modest and are unlikely to cause widespread negative ecological effects. Trends in Hg, Cd, and Zn suggested little (Hg) or no (Cd, Zn) association with ash. Temporal trends suggested that concentrations of ash-related contaminants began to subside after 2010, but because of the limited time period of that analysis (4 yr), further monitoring is needed to verify this trend. The present study provides important information on the magnitude of contaminant exposure to aquatic receptors from a major coal ash spill, as well as spatial and temporal trends for transport of the associated contaminants in a large open watershed.

How oil palm cultivation is affecting mayfly assemblages in Amazon streams

The effects of the implantation of oil palm plantations on a series of environmental variables and the diversity and distribution of mayfly nymphs was investigated through a survey of 23 streams located in areas of plantation and natural forest in the eastern Amazon basin. Composition and richness of mayfly genera were compared among streams in order to verify which genera respond to the habitat disturbance gradient and determine thresholds for each variable. The genera number was higher in forest streams, although genus composition was similar between treatments. Only 9 of the 114 physical variables measured differed significantly between plantation and forest, and only three limnological variables were significantly different. Threshold Indicator Taxa ANalysis indicated that four genera were significantly associated with these variables. Of these, Miroculis and Ulmeritoides were associated with the largest number of variables. Given the different options available for use of soil in the Amazon basin, oil palm plantations appear to be one of the least deleterious for native fauna. In the Brazilian Amazon basin, government-sponsored zoning for the establishment of oil palm plantations as a strategy for the recuperation of degraded land thus appears to be a viable option for the reintegration of areas left damaged by agricultural activities, as long as the process is implemented adequately and monitored systematically. Also, legislation must be respected, in particular the permanent preservation of riparian zones, which may function as effective buffer zones to the runoff of pesticides and sediments.

Acute and chronic toxicity of neonicotinoids to nymphs of a mayfly species and some notes on seasonal differences.

Mayfly nymphs are among the most sensitive taxa to neonicotinoids. The present study presents the acute and chronic toxicity of 3 neonicotinoids (imidacloprid, thiacloprid, and thiamethoxam) to a mayfly species (Cloeon dipterum) and some notes on the seasonality of the toxicity of imidacloprid to C. dipterum and 5 other invertebrate species. Imidacloprid and thiamethoxam showed equal acute and chronic toxicity to a winter generation of C. dipterum, whereas thiacloprid was approximately twice as toxic. The acute and chronic toxicity of imidacloprid was much higher for the C. dipterum summer generation than for the winter one. The acute toxicity differs by a factor of 20 for the 96-h 50% effective concentration (EC50) and by a factor of 5.4 for the chronic 28-d EC50. Temperature had only a slight effect on the sensitivity of C. dipterum to imidacloprid because we only found a factor of 1.7 difference in the 96-h EC50 between tests performed at 10 °C and 18 °C. The difference in sensitivity between summer and overwintering generations was also found for 3 other insect species. The results indicate that if the use and environmental fate of the 3 neonicotinoids are comparable, replacing imidacloprid by another neonicotinoid might not reduce the environmental impact on the mayfly nymph C. dipterum. The results also show the importance of reporting which generation is tested because sensitivity values of insects in the summer might be underestimated by the experiments performed with neonicotinoids and an overwintering population.

Feeding peculiarities of the juveniles of the Atlantic salmon (Salmo salar L.) infected with the invasive parasite Gyrodactylus salaris in the Keret River

Extremely low feeding intensity was registered for the juveniles of Atlantic salmon inhabiting the Keret River (the White Sea basin) and infected with the invasive monogenean Gyrodactylus salaris. This was due to the asthenia observed during the summer period. The infected fingerlings and parrs were characterized by single specimens of the bottom invertebrates in their guts (larvae of caddis flies, nymphs of stoneflies and mayflies, and mollusks). The stomach filling index in these specimens was five to seven times lower comparing to the healthy individuals inhabiting the Ponoi and Kachkovka rivers (Kola Peninsula). About one-third of the infected fingerlings had empty guts, which was never observed for the juveniles of the wild populations of Atlantic salmon during the summer growth period in the rivers of Karelia and the Kola Peninsula.

Dissolved ions mediate body mass gain and predatory response of an invasive fish

Ecological impacts of invasive species are mediated by the environmental characteristics of the invaded habitats. The invasive round goby Neogobius melanostomus is a brackish-water adapted invader with high predatory and competitive impacts on native communities. We test the hypothesis that both body mass gain and predation rates of the round goby are reduced in low-dissolved ion waters in which they can establish, using calcium (Ca2+) as a focal ion of great importance to the physiology of aquatic animals. Round gobies were first acclimated for 36 days on a diet of shrimp pellets in either high (35 mg L−1) or low (12 mg L−1) Ca2+ concentration [Ca]. We then assessed the functional response (FR)—the relationship between predation rate and prey supply—of the round goby from high and low [Ca] on amphipod prey in either condition. Round gobies in high [Ca] consumed more pellets during the acclimation period and gained more mass compared to fish in low-[Ca] conditions. Functional response experiments revealed that round gobies at high-[Ca] levels for both acclimation and FR experiments had the highest predatory impact, whereas fish in low-[Ca] FR treatments had similarly low predation rates regardless of acclimation [Ca]. In a second experiment, non-acclimated round gobies had a higher FR on mayfly nymph prey at high [Ca] than fish at low-[Ca] levels. Our results indicate that the round goby has stronger ecological impacts in conditions that are more physiologically optimal for the species. Identifying key physico-chemical factors that mediate impacts of invaders would help prioritize habitats for management attention.

Sediment and water quality limit mayfly survivorship in an urban lake undergoing remediation

Onondaga Lake is a highly perturbed system undergoing a large-scale remediation effort. The benthic macroinvertebrate community in the lake is degraded and lacks mayfly diversity. The objective of this study was to assess the effects of Onondaga Lake water and sediment on survivorship of indicator mayfly species to determine the potential for colonization before and after remediation. We performed a survivorship experiment in situ by incubating mayfly nymphs, Stenonema femoratum, (n = 20) that were given either Onondaga Lake or reference lake sediment in Onondaga Lake or the reference lake. We repeated this study in the laboratory using burrowing mayflies, Hexagenia spp. (n = 100). S. femoratum that were incubated in Onondaga Lake with Onondaga Lake sediment yielded 0% survival after 24 h. On higher quality substrate, survival after 24 h increased to 80%, indicating that Onondaga Lake's sediment significantly decreased survival and that survivorship probability after sediment remediation may be increased. Water quality also negatively affected survival, however. Even when incubated on higher quality sediment in Onondaga Lake, no mayflies survived for 9 d. Similarly, in the lab, survivorship of Hexagenia nymphs after 15 d was significantly lower (52%) when exposed to both Onondaga Lake sediment and water compared to nymphs given reference sediment and water (88% survival). Results suggest that areas of the lake not included in sediment remediation plans may still be unsuitable for colonization of more sensitive benthic taxa and that areas undergoing sediment remediation may still not be suitable for sensitive species if water quality does not improve.