Chaoborus Flavicans Research Articles

Acoustic scattering from a larval insect ( Chaoborus flavicans) at six echosounder frequencies: Implication for acoustic estimates of fish abundance

Acoustic scattering from Chaoborus flavicans larvae was studied in a virtually fishless lake using multi-frequency split-beam echosounders with 7° partly overlapping acoustic beams. Six echosounders simultaneously operating at 38, 70, 120, 200 and 364 and 710 kHz were employed. Zooplankton sampling, using a Schindler-Patalas trap, was used to identify the nature and composition of acoustic scatterers at five different depths and to establish a correlation between observed and acoustic volume density of Chaoborus. Chaoborus showed high scattering at 200 kHz (NASC > 30,000 m 2 nmi −2, Δ d = 10 m), but was virtually “invisible” at 38 kHz (NASC < 10 m 2 nmi −2, Δ d = 10 m). The remaining frequencies produced intermediate responses, resulting in a distinctive signature of the frequency response curve that ranged from Rayleigh to geometrical scattering, with a resonance around 200 kHz. The mean target strength ranged from −60.5 to −64.3 dB re 1 m 2 depending on body length. The correlation between the volume density of Chaoborus established from the direct sampling and the acoustic recordings was poor ( r 2 < 0.37), but agreement was found between density maxima. Although other zooplankton species were present and at higher densities, Chaoborus were identified as the source of the acoustic scattering. Chaoborus can represent a major error in acoustic estimates of fish densities obtained at higher echosounder frequencies, but not at lower frequencies (e.g. 38 kHz). The distinctive acoustic signature of Chaoborus demonstrates the usefulness of multi-frequency acoustics for species identification and discrimination. Acoustic methods selectively assess vertical distribution maxima for Chaoborus and size, but cannot reliably estimate abundance.

Determination of aerobic‐anaerobic metabolism‐related compounds in a Chaoborus flavicans population by infusion ion trap mass spectrometry of extracts of individual larvae

In a daily migration, the aquatic larvae of Chaoborus flavicans (a phantom midge) alternate oxygen-saturated and anoxic lake strata. To investigate this cycle, larvae were collected at a natural environment, and acetate, propionate, pyruvate, lactate, glycerol, phosphate, maleate, succinate, glucose and citrate were determined. Each larva was homogenized with 200 microL water and deproteinized with a spin-filter; 50 microL aliquots were mixed with 50 microL of a buffer containing 80 mM propylamine, 20 mM HCl and 0.06 mM 2,4-dihydroxybenzoic acid (internal standard) in methanol. The extracts were infused in an electrospray ionization ion-trap mass spectrometer. The limits of detection for the [M-H](-) peaks ranged from 2 microM for pyruvate and lactate to 200 microM for acetate and glycerol. The MS(2) ion-trap spectra obtained at pH 7 (ammonium acetate buffer) were used to distinguish maleate (cis-2-butenedioic), which gave [M-CO(2)-H](-) (m/z 71), from fumarate (trans-2-butenedioic), which showed first a loss of water yielding an instable peak at m/z 97. The compounds involved in the aerobic-anaerobic adjustment of the metabolism were revealed by linear discriminant analysis. Acetate, citrate, glucose, maleate (which decreased during the daytime), and particularly succinate (which increased), showed the maximal discrimination power between the day- and night-time samples.

Zooplankton of a flooded opencast sulphur mine

The zooplankton community of a flooded opencast sulphur mine was investigated during two years. The complicated physical and chemical relationships in this water-filled pit caused an atypical plankton assemblage. At the time of the investigation 20 species of rotifers, 6 of Cladocera, and 8 species of Copepoda were found. A single Ostracod and Chaoborus flavicans were also noted in the samples. Usually the epilimnion was monopolised by rotifers whereas the hypolimnion had a more diversified assemblage of rotifers, cladocerans and copepods. The result of clustering analysis indicated that each predator was associated with its own group of prey. Discrimination analyses showed weak seasonal differences in the zooplankton and three zones in the vertical profile – epilimnetic, upper hypolimnetic and anaerobic. Principal component analysis reduced the chemical parameters to the main contributors of conductivity (the main anions and cations) plus toxic sulphide and hydrogen sulphide. The animals were classified by the first two components into two groups: cold stenotherms and medium-sized filtrators, such as Bosmina longirostris. A specific analysis of vertical profiles generated five variants of diel vertical migrations. When time–space distributions of the plankters were analysed the highest numbers of different species were usually in different times and depths. The epilimnion was inhabited by small fishes and was dominated by rotifers but was free from C. flavicans which inhabited the cold hypolimnion, together with the remaining invertebrate predators (copepods and Asplanchna).Chaoborus and the other invertebrate predators participated more evenly in the contributions of species to the total density. In the presence of invertebrate predators the structure of the rotifer population shifted from soft-bodied species to spined or fast-moving species. When the predation pressure was too strong, as in the hypolimnion, the soft-bodied species were, in practice, absent. When the pit was in an oligotrophic state the hypolimnion population was composed of up to 60–90% rotifers. When the trophic state shifted to mesotrophy, the proportion of cladocerans increased.

Effects of pH and predation by Chaoborus larvae on the plankton of a shallow and acidic forest lake

Summary1. Eutrophic acid lakes are not common. Delamere Lake in Cheshire, U.K. is shallow and acid (mean pH 4.5) with a very high phytoplankton crop (mean 290 μg chlorophyll a L−1), dominated by Dictyosphaerium pulchellum. Rotifers were dominant in the pelagic waters but small cladocerans (Alona guttata, Chydorus sphaericus and Scapholeberis mucronata) were occasional in the littoral waters. Chaoborus flavicans larvae were the top predators in this fishless lake. Two mesocosm experiments were carried out in which pH and Chaoborus populations were manipulated.2. Progressively higher concentrations of D. pulchellum were maintained in the elevated pH treatments (pH 6 and 8; P &lt; 0.001) with increased amounts of a Chlamydomonas species at the end of the experiment. Highest species richness was seen at ambient pH. Thus the low pH of Delamere Lake alone did not control the structure of the phytoplankton community. Keratella quadrata showed significantly higher abundance at pH 6 than in other pH treatments (P &lt; 0.001). Species richness of rotifers was unaffected by pH.3. Most Cladocera were C. sphaericus. Although never seen in the open lake, Daphnia pulex appeared in all the pH treatments. Low pH did not control small Cladocera abundance in Delamere Lake, but probably hampered reproduction in Daphnia. Negative correlations between chlorophyll a concentrations and Daphnia in the mesocosms (r2 = 0.215, P &lt; 0.05), however, indicated the potential of large‐bodied daphniids in controlling phytoplankton.4. Neither different combinations of Chaoborus instars (none, instars 1 and 2 and instars 3–5) nor different densities of instars 3–5 (0.15, 0.5 and 1.0 L−1) had a negative impact on Cladocera. Daphnia pulex remained unaffected in the experiment, perhaps because of its large size, and C. sphaericus because of its high reproductive rate compensating predatory losses.5. Very low pH in Delamere Lake might suppress Daphnia by hampering its reproduction. Consequently, Daphnia may be vulnerable to invertebrate predation even at low predator density in the lake.

Diel distribution and migration ofChaoborus flavicans: a field anaysis using broadband Acoustic Doppler Current Profiler (ADCP) techniques

Diel distribution and migration of<i>Chaoborus flavicans</i>: a field anaysis using broadband Acoustic Doppler Current Profiler (ADCP) techniques

Limnology of an Unusual Eutrophic Acid Forest Lake

ABSTRACT Delamere Lake is a small (< 2 ha), shallow (mean depth 1.7 m), acidic (pH 4.5) lake amid coniferous forest in Cheshire, England. It showed high total nutrient concentrations (200 ± SEM 14 μg L−1 total phosphorus, 2.2 ± 0.1 mg L−1 total nitrogen), very high phytoplankton biomass (290 ± 30 μg L−1 chlorophyll a), and monospecific green algal dominance (Dictyosphaerium pulchellum, maximum biovolume 33.8 mm3 L−1, < 99% of total phytoplankton biovolume). Zooplankton was dominated by rotifers (mainly Keratella quadrata and Brachionus urceolaris), with a few cladoceran species (Alona guttata, Chydorus sphaericus, and Scapholeberis mucronum). Abundant Chaoborus flavicans larvae were the top predators in this fishless lake.

Clay‐Turbid Interactions May Not Cascade—A Reminder for Lake Managers

Abstract Food web management is a frequently used lake restoration method, which aims to reduce phytoplankton biomass by strengthening herbivorous zooplankton through reduction of planktivorous fish. However, in clay‐turbid lakes several factors may reduce the effectivity of food web management. Increasing turbidity reduces the effectivity of fish predation and weakens the link between zooplankton and phytoplankton. Therefore, the effects of fish stock manipulations may not cascade to lower trophic levels as expected. Additionally, in clay‐turbid conditions invertebrate predators may coexist in high densities with planktivorous fish and negate the effects of fish reductions. For instance, in the stratifying regions of the clay‐turbid Lake Hiidenvesi, Chaoborus flavicans is the main regulator of cladocerans and occupies the water column throughout the day, although planktivorous Osmerus eperlanus is very abundant. The coexistence of chaoborids and fish is facilitated by a metalimnetic turbidity peak, which prevents efficient predation by fish. In the shallow parts of the lake, chaoborids are absent despite high water turbidity. We suggest that, generally, the importance of invertebrate predators in relation to vertebrate predators may change along turbidity and depth gradients. The importance of fish predation is highest in shallow waters with low turbidity. When water depth increases, the importance of fish in the top‐down regulation of zooplankton declines, whereas that of chaoborids increases, the change along the depth gradient being moderate in clear‐water lakes and steep in highly turbid lakes. Thus, especially deep clay‐turbid lakes may be problematic for implementing food web management as a restoration tool.

Hydroacoustic fish stock assessment in the presence of dense aggregations of Chaoborus larvae

A new method for eliminating reverberation due to Chaoborus larvae from hydroacoustic recordings is presented based on an assumption of a constant dependence between the area backscattering strength (sa) with a high-volume backscattering threshold (sv) and sa with a low sv threshold for fish. The idea was to analyze data with a threshold high enough to eliminate reverberation and then convert the estimate to coincide with the result that would have been achieved with a low threshold containing all backscattering from fish. The approach was validated with a secondary dataset, and the magnitude of overestimation of fish density by reverberation was evaluated using data from four surveys conducted in a clay-turbid lake, where small planktivorous fish, smelt (Osmerus eperlanus), and larvae of Chaoborus flavicans coexist in the water column. With the presented method, estimation of smelt density was possible even when Chaoborus density was &gt;200 individuals·m–3. The analyses revealed that the overestimation of fish density could be as high as 50% if the reverberation is not taken into account. The presented method might also be applicable for eliminating reverberation due to other unwanted targets, because it is based on the acoustic properties of fish rather than those of unwanted targets.

Effects of clay turbidity and light on the predator–prey interaction between smelts and chaoborids

The effects of clay turbidity and light on the predator–prey interaction between planktivorous smelts (Osmerus eperlanus) and phantom midge (Chaoborus flavicans) larvae were studied by means of laboratory experiments. Irrespective of light intensity, fish-mediated mortality of chaoborid larvae was highest at intermediate turbidity (20 nephelometric turbidity units (NTU)). Increases in light intensity enhanced the feeding rate of smelts at very low light intensities. A regression model describing the dependence of smelt-mediated mortality of chaoborids on light intensity and turbidity was fitted to the data. The model suggested that turbidity exceeding 30 NTU combined with light intensity below 0.1 µE·m–2·s–1provides an efficient daytime refuge for chaoborids even in the presence of planktivorous smelts. In the field studies, the depth distribution of chaoborids followed the predictions of the model. The depth at which chaoborid density was highest depended on the existence and location of the thermocline, the densest swarms occurring beneath the turbidity maximum in the metalimnion. The smelts occupied water layers above the chaoborids, suggesting that the chaoborids used the steep turbidity gradient in the thermocline as a shelter against predation.

Acoustic observations of zooplankton in lakes using a Doppler current profiler

Summary1. In this paper we test the usefulness of acoustic backscatter measurements from a 614 kHz Acoustic Doppler Current Profiler (ADCP) for the qualitative and quantitative characterisation of zooplankton distributions in lakes. ADCP‐based backscatter estimates were compared with frequent net hauls obtained during a calibration experiment in which the acoustic backscatter was strongly dominated by vertical migrating Chaoborus flavicans larvae.2. The correlation between backscatter estimates and the C. flavicans concentration was very good. Vertical swimming speed of larvae, measured directly by the ADCP, was up to a maximum of 5 mm s−1 and agreed very well with the observed vertical movement of the backscatter contour lines. Although the strong backscatter from C. flavicans overwhelmed the signal from the remaining zooplankton, a good correlation between backscatter strength and the total remaining zooplankton concentration, dominated by Cyclops spp., was found for the depth and time intervals where no C. flavicans were present.3. In addition to the calibration experiment, longer‐term ADCP measurements from different lakes revealed a strong temporal correlation between the onset of the up‐ and downward migration of zooplankton and the local sunset and sunrise.4. We conclude that ADCPs can be used to monitor plankton distributions both temporally and spatially. It also seems possible to estimate plankton densities after appropriate calibration.

INDUCIBLE DEFENSES IN MULTIPREDATOR ENVIRONMENTS: CYCLOMORPHOSIS IN DAPHNIA CUCULLATA

Phenotypically plastic defenses are strategies to reduce predation risk in variable environments. Predator-induced formations of protective devices in cladocerans are prominent examples of phenotypically plastic defenses. To understand the adaptive value of a defense, it is better to investigate its effects in a multipredator context, instead of merely concentrating on a two-species interaction. Small cladocerans such as Daphnia cucullata are prey items for many aquatic invertebrate predators and thus comprise a useful model system to investigate defenses and their effects. In this study, we tested the hypothesis that the helmets of Daphnia cucullataare inducible with chemical cues from different kinds of predators and that they act as a generalized defense offering protection against several predators, each using a different hunting strategy. Results from our induction experiment show that chemical cues released from Chaoborus flavicans, Leptodora kindtii, and Cyclops sp. induce significantly longer helmets and tail spines and thus act as proximate factors for cyclomorphosis in Daphnia cucullata. Our predation experiments revealed that the induced morphological changes offered protection against each of the predators tested. Interestingly, the protective mechanisms and the prey size classes which were protected differed between predator systems. Our results suggest that phenotypic plasticity in Daphnia cucullata evolved as a ''dif- fuse'' coevolution against different invertebrate predators which selectively feed on small prey items. The additive benefits may increase the adaptive value and thus facilitate the evolution and persistence of this generalized defense.

Seasonal bottlenecks in diet shifts and growth of smelt in a large eutrophic lake

Seasonal growth of smelt Osmerus eperlanus was studied in the Kiihkelyksenselkä basin in the eutrophic Lake Hiidenvesi, southern Finland. The growth of age 1+ and 2+ year smelts was very low probably due to the discontinuous supply of large invertebrates Chaoborus flavicans and Mysis relicta. Diet shift back to zooplankton in autumn, suggested the existence of a bottleneck in the growth of these age groups. Slow growth rate was further intensified by the onset of maturity at age 2 years, combined with the high diet and habitat overlaps between similar‐sized 1+ and 2+ year smelts. Older 3+ and 4+ year smelts shifted to piscivory, i.e. cannibalism, during the growing season, which was seen as rapid increases in their growth rates.

Burrowing behavior ofChaoborus flavicanslarvae and its ecological significance

The form and extent of the galleries created by burrowing invertebrates influence sediment structure, bioturbation, and the fluxes of nutrients and contaminants between the sediment and the water column. An important burrowing insect in soft sediments is the phantom midge Chaoborus flavicans. Larvae of this dipteran migrate between the water column, where they feed at night on zooplankton, and the sediment, where they find refuge from predatory fish during the day. The extent to which these larvae disturb sediment during their daily migrations and the depth to which they burrow are poorly known in large part because of a lack of adequate techniques for studying animal behavior near and below the sediment–water interface. We used 2 techniques to record larval behavior in the laboratory, that is, infrared videos to determine how larvae burrow into sediment and X-ray images of burrowed larvae to determine whether they burrow into deeper anoxic sediment and whether they maintain a tube connected to the overlying water. Our observations indicate that larval burrowing visibly disturbs surface sediments thereby contributing to bioturbation. Once buried, larvae do not remain in the thin surface oxic layer but burrow into anoxic sediment. In anoxic sediment, larvae assume a vertical, anterior-end up, S-shaped posture and do not create a tube connected to the overlying water through which they could pump oxygenated water. Thus, larvae are likely exposed to toxic hydrogen sulfide and contaminants in interstitial water, to which they are likely tolerant.

The supremacy of invertebrate predators over fish - factors behind the unconventional seasonal dynamics of cladocerans in Lake Hiidenvesi

In the eutrophic Lake Hiidenvesi (30.3 km 2 ), the early summer biomass maximum of cladoceran zooplankton is missing and the highest biomass is found unusually in mid summer. The contribution of the phantom midge Chaoborus flavicans to the unconventional seasonal dynamics of cladocerans was studied. The seasonal development of the C. flavicans population and the zooplankton community was studied together with food consumption by chaoborids and the most common vertebrate predator, smelt. The population density of Chaoborus peaked in June and collapsed in mid summer. Thereafter, another peak occurred at the end of August. The maximum density of chaoborids in the water column varied between 5,500 and 8.700 inc./m 2 . In early summer, the most common food items of Chaoborus were bosminids while later in summer the share of daphnids increased. Food consumption by the Chaoborus population peaked at 26-46 μg Cl -1 d -1 in June and clearly exceeded the production rate of cladocerans. Cladoceran consumption by smelt population reached its maximum, 1.13 μg Cl -1 d -1 , in early July. Cladocerans showed a 20-40 μg C/l biomass peak in July-August, coincidently with the minimum density of chaoborids. When predation pressure decreased, the mean size of cladocerans increased at 10-15 m, the depth occupied by chaoborids during daytime. The results suggest that in early summer the high predation pressure prevents cladocerans from reaching a sufficient body length to defend them against Chaoborus and that the timing of the cladoceran biomass peak is determined by the relaxation of chaoborid predation.

Unusual allometry between respiration rate and body size in Chaoborus species

The respiration rates of all four instars of Chaoborus flavicans were measured with a flow-through respirometer at an experimental temperature of 20°C. The respiration rates (μg O2 larva -1 h -1 ) increased parallel to the larval stages according to R = 0.027 X W 0.416 (W = μg dry weight), reaching a respiration rate eight times higher for instar IV than for instar I. The slope of the increase with body weight was as low as in two tropical Chaoborus species and was considerably lower than usually found for other aquatic animals. Instar IV larvae collected in the spring showed a significantly higher respiration rate than those collected in the fall. The respiration rate of the fourth instar approximately doubled with a Q 10 of 2. 1 when the experimental temperature was increased from 10 to 20°C.

Adatok a Látrányi Puszta Természetvédelmi Terület kétszárnyú (Diptera) faunájához

In the years of 2000, 2001, and 2002, the author carried out a basic faunistical researches on the Diptera fauna of the area announced to be protected in 1992. During the survey, the occurrence of 305 taxa of 25 Diptera families was reported. Among the relatively interesting species, the following ones are worth mentioning: Nephrotoma scurra (Mcigen, 1818), Ptychoptera albimana (Fabricius, 1787), Chaoborus flavicans (Mcigen, 1830), Systoechus gradatus (Wiedemann, 1820), Villa humilis (Ruthe, 1831), Callicera aenea (Fabricius, 1781), Pelecocera tricincta Mcigen, 1822, Merodon clavipes (Fabricius, 1781), Eristalis abusiva Collin, 1931. Upon the results of these researches, it can be ascertained that in the Diptera fauna of the area, elements which are typical to the sandy steppes of the Transdanubian and Great Plain regions occur in abundance.

Hypolimnetic anoxia hampers top–down food‐web manipulation in a eutrophic lake

SUMMARY 1. A biomanipulation experiment was carried out in a small (10 ha), but relatively deep (17 m) and highly eutrophic lake in northern Poland. The lake had been stocked in 1996, 1997 and 1998 with a variety of piscivorous fish (pike, catfish, trout and pikeperch), in order to reduce numbers of cyprinid planktivores.2. Piscivore stocking was associated with a threefold decrease in the offshore fish density (night echosounding). Despite this reduction, the large planktonic cladoceran, Daphnia hyalina, remained scarce, whereas the density of small‐sized zooplankton increased greatly.3. The lack of demographic response in D. hyalina was probably due to the anoxia in the hypolimnetic refuge of this vertically migrating species. The anoxic hypolimnion, below 3–4 m depth, was inhabited day and night by numerous Chaoborus flavicans larvae.4. Changes in zooplankton were associated with shifts in the taxonomic composition (from single‐cell green algae to filamentous cyanobacteria), size structure (from nano‐ to net phytoplankton) and seasonal dynamics of phytoplankton, but not in the average biomass of planktonic algae. A clear‐water phase, which was absent in the prestocking years, developed in spring, with Secchi depth reaching 2.5 m, a value which had never been recorded in the 20 years preceding the biomanipulation. In general, the lake's status was switched from hypertrophic to eutrophic.5. Deteriorating food conditions, resulting from qualitative changes in the phytoplankton community, combined with predation pressure by the remaining fish and Chaoborus larvae were associated with the ultimate elimination of D. hyalina from the lake.

Predator evasion in Daphnia: the adaptive value of aggregation associated with attack abatement.

To evaluate the adaptive value of daphnian aggregation associated with attack abatement, a combined laboratory and field experiment was performed. As the lake investigated does not contain planktivorous fish, only invertebrate predation is important. In the laboratory, newly collected Chaoborus flavicans, among the most important predators to exploit the Daphnia population in the lake, were individually placed in a spherical flask containing different densities of juvenile Daphnia prey. The number of successful attacks of Chaoborus was independent of prey abundance. Thus, in a given density regime, each individual prey gained protection from a dilution effect. In the field, dense aggregates of Daphnia were created by continuously adding food at a localized point in the littoral. Even though the food input produced aggregates of Daphnia which were maintained for 3h, the number of invertebrate predators did not increase in the input area. It is concluded that each Daphnia in a group reduces the probability of predation through an effect of attack abatement which is approximately proportional to the number of prey in the group. However, when considering the high median density of Daphnia, together with their strong response to food input, it seems more plausible that natural aggregates are driven by a patchy food distribution, whereas attack abatement is only a secondary effect of aggregation.

The seasonal dynamics and distribution of Chaoborus flavicans larvae in adjacent lake basins of different morphometry and degree of eutrophication

1. Seasonal dynamics, spatial distribution and population size of the phantom midge Chaoborus flavicans in different parts of the eutrophic Lake Hiidenvesi (30.3 km2) were studied.2. Density of larvae was low in the shallow, most eutrophic parts of the lake, while the deep Kiihkelyksenselkä basin was inhabited by a dense population. In the deepest part of Kiihkelyksenselkä (33 m) density was 13 989 ± 3542 m–2 in May, declined to 1102 ± 274 m–2 in July and recovered to 7225 ± 1314 m–2 by October. In spring and autumn the majority of larvae were benthic while, during high summer, few larvae were found in the sediment.3. Horizontal distribution fluctuated seasonally. On 3 June &lt; 5% of the population inhabited areas shallower than 10 m. On 6 July the limnetic fraction was still restricted to regions deeper than 10 m, but 43% of benthic larvae were found between 6 and 10 m depths. In October both limnetic and benthic larvae were concentrated in areas deeper than 20 m.4. Within the lake, distribution was mainly regulated by stratification characteristics, degree of eutrophy being less important. The seasonal horizontal movements were probably induced by food shortage. Larvae could not meet their energetic demands in stratified areas and dispersed to shallower water, reducing predation risk by use of the benthic habitat.

Chaoborus flavicans (Díptera) is an oxy-regulator

The respiration rates of Chaoborus flavicans instar IV were measured in a flow-through respirometer at oxygen concentrations between 5 % and 100 % saturation at an experimental temperature of 20 °C. The respiration rate of the instar IV followed a hyperbolic function with the critical point at an oxygen saturation of 15 %. Thus, C. flavicans instar IV appeared to be an oxy-regulator and maintained the aerobic pathway even under low oxygen saturations. On their diel vertical migration in stratified lakes, the larvae should be able to use even small amounts of oxygen.