Midge Chaoborus Research Articles

Predator‐induced plasticity in relation to prey body size: A meta‐analysis of Daphnia experiments

Abstract Predator‐induced plasticity is an adaptive response inprey to predation risks. Considering that size‐selective predation affects the body‐size distribution of prey populations, we hypothesised that the body size of species determines their expression of predator‐induced plasticity. However, as a result of variations in expression among species, an integrated understanding of the relationships between traits remains lacking. We considered the predator‐induced plasticity of Daphnia species separately for their body size, defensive morphology and life‐history traits. The aim of this study was to compare the predator‐induced plasticity of Daphnia against size‐selective predators: phantom midge Chaoborus larvae and fish. This meta‐analysis included 75 studies and nine plasticity traits for 15 Daphnia species. Daphnia were analysed separately according to phylogeny (subgenera Ctenodaphnia, Daphnia and Hyalodaphnia) and body size (large >3.0 mm, medium 2.0 mm and small 1.0 mm). Size‐dependent analyses showed that at least three of the nine plasticity traits were expressed in Daphnia against fish. Among the three subgenera, Daphnia induced the greatest plasticity against both predators (five key traits against Chaoborus and four against fish). The relationship between size and age at first reproduction showed that Daphnia exhibited different degrees of plasticity against Chaoborus and fish. Daphnia had only one set of life‐history response to fish, namely, decreased size at maturity and early reproduction. By contrast, Daphnia exhibited three sets of life‐history responses to Chaoborus larvae: decreased size and delayed reproduction, increased size and delayed reproduction, and increased size and early reproduction. Overall, predator‐induced plasticity was expressed well in small and medium‐sized Daphnia, and was more evident in small Daphnia than would be expected from size‐selective predation. This study shows that the body size of Daphnia is a key trait influencing its plasticity expression and evolution. We detected novel pattern among life‐history traits, but found no strong associations between morphological defences and life‐history traits. We suggest that prey size, predation preference and body size are important factors for understanding and explaining the evolution of phenotypic plasticity.

Uptake and Transfer of Polyamide Microplastics in a Freshwater Mesocosm Study

Steadily increasing inputs of microplastics pose a growing threat to aquatic fauna, but laboratory studies potentially lack realism to properly investigate its effects on populations and ecosystems. Our study investigates the trophic and ontogenetic transfer of microplastics in a near-natural exposure scenario. The controlled outdoor freshwater mesocosms were exposed to polyamide (PA) 5–50 µm in size in concentrations of 15 and 150 mg L−1 and a control without microplastic addition. To verify the uptake of particles via the food chain, larvae and imagines of the midges Chaoborus crystallinus and C. obscuripes were examined, which feed on zooplankton during their larval stage. Larvae were captured after 117 days and imagines were caught in emergence traps that were emptied weekly. To detect the microparticles within the organisms, 200 larvae and 100 imagines per application were macerated and treated with fluorescent dye before investigation under a fluorescent microscope. We could detect up to 12 PA particles per individual larvae, while nearly no plastic was found in the imagines. This shows that, while Chaoborus sp. takes up microplastics via predation, most of the pollutant is egested through regurgitation and remains in the water, where it can further accumulate and potentially harm other organisms.

Toxic Effects of Fine Plant Powder Impregnated With Avermectins on Mosquito Larvae and Nontarget Aquatic Invertebrates.

The toxic effects of an avermectin-impregnated fine plant powder (AIFP) against larval Aedes aegypti L. (Diptera: Culicidae), Culex modestus Ficalbi (Diptera: Culicidae), and Anopheles messeae Falleroni (Diptera: Culicidae), as well as selected nontarget aquatic invertebrates, were studied under laboratory conditions. The possibility of trophic transfer of avermectins (AVMs) through the food chain and their toxic effects on predaceous species fed AIFP-treated mosquito larvae was also evaluated. Among mosquitoes, Anopheles messeae were the most sensitive to AIFP, while Cx. modestus exhibited the least sensitivity to this formulation. Among nontarget aquatic invertebrates, the greatest toxicity of AIFP was observed for benthic species (larval Chironomus sp. Meigen (Diptera: Chironomidae), whereas predators (dragonflies, water beetles, and water bugs) exhibited the lowest AIFP sensitivity. AIFP sensitivity of the clam shrimp Lynceus brachyurus O. F. Muller (Diplostraca: Lynceidae), the phantom midge Chaoborus crystallinus De Geer (Diptera: Chaoboridae), and the mayfly Caenis robusta Eaton (Ephemeroptera: Caenidae) was intermediate and similar to the sensitivity of the mosquito Cx. modestus. However, these nontarget species were more resistant than An. messeae and Ae. aegypti. Solid-phase extraction of mosquito larvae treated with AIFP and subsequent high-performance liquid chromatography (HPLC) analysis of the extracts revealed an AVM concentration of up to 2.1 ± 0.3 μg/g. Feeding the creeping water bug Ilyocoris cimicoides L. (Hemiptera: Naucoridae) on the AIFP-treated mosquito larvae resulted in 51% mortality of the predaceous species. But no toxicity was observed for Aeshna mixta Latreille (Odonata: Aeshnidae) dragonfly larvae fed those mosquito larvae. The results of this work showed that this AVM formulation can be effective against mosquito larvae.

Emergence of steeply stratified permafrost thaw ponds changes zooplankton ecology in subarctic freshwaters

ABSTRACT Climate change and associated permafrost thaw are creating new shallow waterbodies in vast regions of the circumpolar Arctic. These thaw ponds are characterized by high concentrations of colored dissolved organic matter originating from the degrading watershed, inducing a strong vertical thermal and oxygen (O2) stratification. We investigated the zooplankton community and biomass in eight subarctic thaw ponds and evaluated how zooplankton respond to this stratification. In a subset of three ponds, we further examined how other environmental variables, including essential fatty acids (EFA) concentration and phytoplankton, bacteria, and larval phantom midge Chaoborus biomass stratify and contribute to the vertical distribution of zooplankton in this increasingly common type of arctic freshwater system. The zooplankton community was extremely abundant in all ponds (up to 3,548 ind L−1) and dominated mainly by rotifers (35–93 percent of the biomass). Most zooplankton aggregated at the interface between the shallow well-oxygenated mixed surface layer and the deeper hypoxic but algal-rich stratified layer, and their distribution was affected by a combination of O2, Chaoborus, phytoplankton, and EFA that were supplied from opposite directions. Our findings show how water column stratification deeply affects the ecology of planktonic organisms in circumpolar freshwaters and indicate Arctic zooplankton species composition is expected to deeply change with the ongoing warming and browning.

Differential Interaction Strengths and Prey Preferences Across Larval Mosquito Ontogeny by a Cohabiting Predatory Midge.

Understandings of natural enemy efficacy are reliant on robust quantifications of interaction strengths under context-dependencies. For medically important mosquitoes, rapid growth during aquatic larval stages could impede natural enemy impacts through size refuge effects. The identification of biocontrol agents which are unimpeded by ontogenic size variability of prey is therefore vital. We use functional response and prey preference experiments to examine the interaction strengths and selectivity traits of larvae of the cohabiting predatory midge Chaoborus flavicans (Meigen 1830) (Diptera: Chaoboridae) towards larval stages of the Culex pipiens (Diptera: Culicidae) mosquito complex. Moreover, we examine the influence of search area variation on selectivity traits, given its importance in consumer-resource interactions. Chaoborids were able to capture and consume mosquito prey across their larval ontogeny. When prey types were available individually, a destabilizing Type II functional response was exhibited towards late instar mosquito prey, whereas a more stabilizing Type III functional response was displayed towards early instars. Accordingly, search efficiencies were lowest towards early instar prey, whereas, conversely, maximum feeding rates were highest towards this smaller prey type. However, when the prey types were present simultaneously, C. flavicans exhibited a significant positive preference for late instar prey, irrespective of water volume. Our results identify larval chaoborids as efficacious natural enemies of mosquito prey, with which they frequently coexist in aquatic environments. In particular, an ability to prey on mosquitoes across their larval stages, coupled with a preference for late instar prey, could enable high population-level offtake rates and negate compensatory reductions in intraspecific competition through size refuge.

Elusive enemies: Consumptive and ovipositional effects on mosquitoes by predatory midge larvae are enhanced in dyed environments

Mosquito-borne disease incidences continue to proliferate and cause enormous mortality and debilitation rates. Predatory natural enemies can be effective in population management strategies targeting medically-important mosquito species. However, context-dependencies and target organism behavioural responses can impede or facilitate biological control agents. Black pond dye has been shown to be a strong mosquito oviposition attractant, and could potentially be used alongside predatory agents to create mosquito population sink effects. Here, we thus examine the predatory impact of larvae of the non-biting chaoborid midge Chaoborus flavicans towards larvae of the West Nile virus vector mosquito complex Culex pipiens in the presence and absence of black pond dye. We then examine the ovipositional responses of C. pipiens to predation risk and dye in laboratory-, semi-field- and field-based trials. Larval C. flavicans exhibited potentially population destabilising type II functional responses towards mosquito larvae irrespective of the presence of pond dye. Neither consumption rates nor functional response parameters (attack rates, handling times) were significantly influenced by the presence of dye, indicating a use of hydromechanics to detect mosquito prey by chaoborids. Wild-caught adult C. pipiens did not avoid predatory chaoborids when ovipositing, however they were significantly more attracted to oviposit in dye-treated water regardless of the presence of predators. We thus demonstrate high predatory impact towards mosquito larvae by non-biting chaoborid midges during their predaceous aquatic larval stages, and proliferations of such predators may assist or augment control efforts for mosquitoes. Our results suggest a lack of influence of predatory dipterans on oviposition selectivity by C. pipiens mosquitoes, and that pond dye may enhance the efficacy of select predatory biological control agents through the creation of population sinks, characterised by high rates of oviposition and subsequent predation.

Effects of water browning on freshwater biodiversity: the case of the predatory phantom midge Chaoborus nyblaei

Water browning, due to increased runoff of terrestrial dissolved organic carbon (DOC), has recently gained considerable attention. While it is well settled how browning affects light regime and thereby aquatic primary production, other impacts on the aquatic biota is less explored. Water browning shelters against UV radiation, and may thus benefit range expansion of UV sensitive organisms, such as midges. We mapped occurrence of Chaoborids in 148 subalpine and alpine ponds in Norway, and identified an apparent threshold for their presence around 3 mg total organic carbon (TOC) l−1. The field study was complemented with laboratory experiments on Chaoborus nyblaei (Zetterstedt, 1838), to test if this species is able to identify and select water colour (concentrations of DOC) for oviposition. Number of egg rafts on brown water tanks was significantly higher than in clear water tanks, indicating that C. nyblaei performs oviposition habitat selection. Chaoborids are effective predators in planktonic habitats, and our findings support the hypothesis that climate change may cascade through the ecosystem and promote range shifts of species due to alternated habitat frame conditions.

Phenotypic plasticity in three Daphnia genotypes in response to predator kairomone: evidence for an involvement of chitin deacetylases.

The genetic background of inducible morphological defences in Daphnia is still largely unknown. Dissolved infochemicals from the aquatic larvae of the phantom midge Chaoborus induce so-called 'neck-teeth' in the first three post-embryonic stages of Daphnia pulex This defence has become a textbook example of inducible defences. In a target gene approach, by using three Daphnia genotypes which show a gradient of neck-teeth induction in response to equal amounts of kairomone, we report a high correlation of neck-teeth induction in Daphnia pulex and relative gene expression of two chitin deacetylases. Further, previous studies suggested genes from both the juvenoid and the insulin hormone signalling pathways as well as several morphogenetic genes downstream to be responsible for neck-teeth induction in D. pulex However, these data were not supported by our study. None of the three D. pulex clones showed an upregulation of these previously proposed candidate genes as a response to predator kairomone, which is interpreted as the result of refined methods used for both RNA sampling and kairomone enrichment yielding unambiguous results compared with earlier studies. The assessment of a clonal gradient of Daphnia in the presence and absence of infochemicals provides a promising approach to identify further genes involved in the induction of morphological defences by correlating gene expression and morphology.

Temporal population dynamics of the phantom midge Chaoborus crystallinus and its influence on the zooplankton community

The predatory larvae of the phantom midge Chaoborus are considered a key factor for zooplankton community structure in freshwater ecosystems. This study analysed C. crystallinus population dynamics and its influence on the zooplankton community structure in ponds by means of different methods of multivariate statistics based on data collected from 19 mesocosm studies over a period of 14 years. Usually, there were three Chaoborus generations per year in the evaluated studies. According to redundancy analysis the population structure of C. crystallinus varied significantly between years and seasons (within a year). Ordination analysis indicated that C. crystallinus had a significant long-term impact on the zooplankton community structure but this impact was weak when compared to time-related factors. The fourth larval stage had the greatest influence on the zooplankton community. C. crystallinus promoted high densities of rotifers and reduced the abundance of small crustaceans (copepods and small cladocerans). The abundance of large cladocerans such as daphnids was unaffected by the number of C. crystallinus larvae. There was no indication that the predatory impact of C. crystallinus on zooplankton substantially influenced phytoplankton. This study provides new findings to a better understanding of impacts on the pelagic food web related to Chaoborus predation.

Prey-induced vertical migration in Chaoborus larvae under different predator and light regimes

For freshwater prey like Daphnia and larvae of Chaoborus, it is well documented that they adjust their residence depth in the water column in response to predator kairomones in order to decrease encounter probability with the respective predator. Despite the importance of infochemicals in predator–prey interactions, it has not been tested if predators adjust their residence depth in response to infochemicals released by prey. Here, we use an indoor system with a stratified water column and show that the predatory phantom midge Chaoborus prefers strata with Daphnia incubation water over strata with control water. Further, the chemically mediated effect of a top predator (fish) on this system was shown to be light dependent with Chaoborus avoiding prey-conditioned water when it also contained fish kairomone in brighter surface water, but not in deeper and thus darker water layers. The foraging kairomone released by Daphnia can be extracted from incubation water via C18-based solid-phase extraction. These results add another dimension to the steering role of infochemicals in predator–prey interactions in zooplankton.

Uptake and subcellular distributions of cadmium and selenium in transplanted aquatic insect larvae.

We transplanted larvae of the phantom midge Chaoborus punctipennis from a lake having lower concentrations of Cd and Se (Lake Dasserat) to a more contaminated lake (Lake Dufault) located near a metal smelter in Rouyn-Noranda, Quebec. Transplanted individuals were held in mesh mesocosms for up to 16 days where they were fed with indigenous contaminated zooplankton. Larval Cd and Se burdens increased over time, and came to equal those measured in indigenous C. punctipennis from contaminated Lake Dufault. Larval Se burdens increased steadily, whereas those of Cd showed an initial lag phase that we explain by a change in the efficiency with which this insect assimilated Cd from its prey. We measured Cd and Se in subcellular fractions and found that larvae sequestered the majority (60%) of the incoming Cd in a detoxified fraction containing metal-binding proteins, whereas a minority of this nonessential metal was in sensitive fractions (20%). In contrast, a much higher proportion of the essential element Se (40%) was apportioned to metabolically active sensitive fractions. Larvae took up equimolar quantities of these elements over the course of the experiment. Likewise, Cd and Se concentrations in wild larvae were equimolar, which suggests that they are exposed to equimolar bioavailable concentrations of these elements in our study lakes.

Feeding efficiency of planktivores under disturbance, the effect of water colour, predation threat and shoal composition

The consumption of phantom midge Chaoborus flavicans larvae by Perca fluviatilis showed clear response to water colour, predation threat and shoal composition with the most significant negative effect for water colour. In the case of Rutilus rutilus, no similar combined response was observed and the total prey consumption was significantly negatively affected by predation threat of Esox lucius. The results suggest that differences in life-history traits may result in disparity in species-specific responses to disturbance.

Effects of Sedimentation on the Profundal Benthic Macroinvertebrates of a Great Plains Reservoir

Reservoir sedimentation has become a large and pervasive problem throughout the entire United States. Sedimentation gradually destroys and eliminates the services for which reservoirs were constructed (flood protection, water storage, and recreation), yet sedimentation is also an ecological problem. Organisms that depend on the deep parts of lakes cannot survive if their habitats are being buried by sediments. Perry Lake, in northeastern Kansas, has lost 23% of its original volume. Sediment thicknesses (depth of sediment accrued since lake formation) in the main lake range from 2–140cm, and upper portions of the lake have become unnavigable. To measure the effect of sedimentation the diversity and density of profundal invertebrate macrofauna were sampled. Thirteen taxa were collected and assemblages were dominated by oligochaetes, midges (chironomidae), and the Phantom Midge Chaoborus. No significant associations between sediment thickness and invertebrate metrics were found, however sediment size was cor...

Rapid swimming and escape movements in the aquatic larvae and pupae of the phantom midge Chaoborus crystallinus.

Rapid locomotion in the aquatic larvae and pupae of the phantom midge Chaoborus crystallinus was analysed. A 10-mm long larva moved sporadically by rapidly curling into a tight circle and then unfurling. The most common movement (70% of all movements) was a body rotation of 332±22 deg (mean ± s.d.) that lasted 63±19 ms and reached a peak velocity of 0.07±0.02 m s(-1). If the head unfurled earlier in the cycle, the rotation was smaller and the larva dived downwards. A distinct category of single rotations of approximately 180 deg (8%) resulted in a larva finishing with its head pointing in the opposite direction. A sequence of rotational movements (22%) resulted in more extensive displacements. The area of the tail fan was reduced by folding during part of a cycle. It was made of a row of 26 radiating filaments with interlacing hairs between adjacent filaments and resilin at their ventral midline articulations with the body. The fan sprang back passively to its splayed position after being forcibly folded. Reducing the area of the fan by 80% decreased angular rotation and impaired stability so that 33% of movements ended with the body upside down. A 6 mm long pupa also moved by curling and unfurling motions of the head and tail that lasted 215±19 ms and generated slower velocities of 0.03±0.01 m s(-1). The pupal tail fan was membranous, oriented differently, had resilin at its articulations and its area could be changed.

Dystrophy in determining midge community composition in boreal lakes

Brown-water dystrophic lakes have several limnological characteristics that clearly separate them from clear-water oligotrophic and murky eutrophic lakes. In this study, I examined the sedimentary midge (Nematocera) assemblages from 30 shallow boreal lakes of varying humic status to test the influence of dystrophy on community composition. The results indicate differing community assemblages between oligohumic and humic lakes. Several taxa were restricted to clear-water lakes, whereas dystrophic lakes also had their characteristic taxa, which were rare or absent in the clear-water lakes. The most common and abundant nematocerans having statistically significant indicator values for dystrophy were chironomids Zalutschia zalutschicola-type, Tanytarsus mendax-type, and Cladotanytarsus mancus-type, together with the phantom midge Chaoborus flavicans. These results indicate that the level of dystrophy plays a significant role in determining midge distribution in boreal lakes. Therefore, consideration of differences in humic conditions is crucial to contemporary midge-based environmental assessments and long-term paleolimnological investigations, because temporal changes in the humic state may have occurred.

Behavioural responses of freshwater zooplankton vary according to the different alarm signals of their invertebrate predators

Single behavioural interactions between two freshwater planktonic crustaceans and invertebrate predators from different zones of the common environment were studied. The planktonic prey organisms were the cladoceran Ceriodaphnia dubia and the copepod Notodiaptomus conifer. The three invertebrate predators were the shrimp Macrobrachium borellii, the crab Trichodactylus borellianus and the larva of the dipteran midge Chaoborus. Feeding experiments were first performed to document the effects of exposure time and prey density on predation. All the selected predators fed on C. dubia and N. conifer, and predation rates were dependent on prey density and exposure time. The ability of microcrustaceans to modify their swimming and avoidance behaviour when faced with cues from each predator was then analysed. The cladoceran was more vulnerable to decapod predation, whereas the prey microcrustaceans were taken equally by the dipteran larvae. The analysis showed that the microcrustaceans detected the presence of at least one invertebrate predator through the predator alarm signals. The cladoceran responded to chemical signals from the three predators but copepods modified their behaviour only in the presence of infochemicals of M. borellii. The different outcomes suggest that macrocrustaceans have different vulnerabilities when faced with the same predator and so have evolved specific and different strategies to reduce invertebrate predation.

Community structure in boreal lakes with recurring blooms of the nuisance flagellate Gonyostomum semen

Blooms of the nontoxic raphidophyte Gonyostomum semen have shown a recent increase in frequency and distribution in the Fennoscandian region. Due to large cell size and several grazer-avoidance strategies, G. semen is hypothesized to be inedible for most zooplankton species and therefore may constitute a bottleneck for the transfer of energy and nutrients in pelagic food webs. Repression of other phytoplankton through increased competition and induced mortality could further exacerbate this effect. In a field study of four lakes with recurring blooms of G. semen and four lakes without blooms, we found significant differences in community structure between the two lake groups during the bloom period. Bloom-lakes had lower biovolumes of small chrysophytes and chlorophytes and zooplankton assemblages were predominated by small, potentially bacterivorous cladocerans, suggesting a limited availability of edible phytoplankton and an increased importance of microbial pathways during G. semen blooms. Low biovolumes of large cladocerans in bloom-lakes may be due to interference of G. semen with filter feeding. Moreover, high abundances of the phantom midge Chaoborus flavicans in bloom-lakes suggest that the flow of energy and nutrients is directed more towards this invertebrate predator than fish. This could have negative impacts on fish populations, especially if bloom periods are prolonged.

Subcellular metal partitioning in larvae of the insect Chaoborus collected along an environmental metal exposure gradient (Cd, Cu, Ni and Zn)

Larvae of the phantom midge Chaoborus are common and widespread in lakes contaminated by metals derived from mining and smelting activities. To explore how this insect is able to cope with potentially toxic metals, we determined total metal concentrations and subcellular metal partitioning in final-instar Chaoborus punctipennis larvae collected from 12 lakes situated along gradients in aqueous Cd, Cu, Ni and Zn concentrations. Concentrations of the non-essential metals Cd and Ni were more responsive to aqueous metal gradients than were larval concentrations of the essential metals Cu and Zn; these latter metals were better regulated and exhibited only 2–3-fold increases between the least and the most contaminated lakes. Metal partitioning was determined by homogenization of larvae followed by differential centrifugation, NaOH digestion and heat denaturation steps so as to separate the metals into operationally defined metal-sensitive fractions (heat-denaturable proteins (HDP), mitochondria, and lysosomes/microsomes) and metal-detoxified fractions (heat stable proteins (HSP) and NaOH-resistant or granule-like fractions). Of these five fractions, the HSP fraction was the dominant metal-binding compartment for Cd, Ni and Cu. The proportions and concentrations of these three metals in this fraction increased along the metal bioaccumulation gradient, which suggests that metallothionein-like proteins play an important role in metal tolerance of Chaoborus living in metal-contaminated environments. Likewise, a substantial proportion of larval Zn was in the HSP fraction, but its contribution did not increase progressively along the metal gradient. Despite the increases in Cd, Ni and Cu in the HSP fraction along the metal bioaccumulation gradient, some accumulation of non-essential metals (Cd and Ni) was observed in putative metal-sensitive fractions (e.g., HDP, mitochondria), suggesting that metal detoxification was incomplete. In the case of Cd, there appears to be a threshold body concentration of about 50nmolCdg−1 dry weight, above which Cd detoxification becomes more effective and below which Chaoborus does not “turn on” its detoxification machinery to the fullest extent. We speculate that acclimation or adaptation of Chaoborus to these highly metal-contaminated environments may have resulted in a capacity to tolerate some metal spillover without comprising essential biological functions such as growth and reproduction.

Long Term Effects of Climate on Two Pond Predators

This study assessed the influence of annual snowpack on long term changes in the predatory regime of four high elevation ponds in the mountains of northwest Wyoming. Over 36 y of observation, in two ponds the primary predator alternated between phantom midge Chaoborus americanus larvae and Diaptomus shoshone predatory copepods, whereas the predatory regime did not change in the other two shallower ponds. Switching of predators correlated with extreme amounts of winter snow, either high or low, which determined the depth at which drying or complete freezing of the pond occurred. Chaoborus americanus colonized ponds after the wettest years and disappeared after the driest years. The results provide an unusual long term perspective of the effects of weather on predator dominance.

Factors affecting methylmercury biomagnification by a widespread aquatic invertebrate predator, the phantom midge larvae Chaoborus

MeHg biomagnification by the phantom midge Chaoborus in relation to MeHg concentrations in their prey and its migratory behavior was investigated in two Canadian Precambrian Shield lakes. Three Chaoborus species with contrasted migratory behavior were collected in a fishless and a fish-inhabited lake. All species accumulated MeHg through their ontogenic development. In the lake inhabited by fish, all instars of Chaoborus punctipennis displayed a marked migratory behavior and were unable to biomagnify MeHg, whereas in the fishless lake, Chaoborus americanus and Chaoborus trivittatus biomagnified MeHg. Reduced biomagnification capacity of C. trivittatus, the coexisting species living with C. americanus, was also ascribed to a progressive vertical segregation with age. Growth dilution, amount and type of prey items or trophic position could not explain the different patterns of biomagnification. Our findings demonstrate that the most common invertebrate predator of temperate planktonic food webs can biomagnify mercury, contrarily to previous reports.