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Revision of Finnish Chaoboridae (Diptera, Culicomorpha)
Abstract
The 11 Finnish species of phantom midges (Chaoboridae) are revised. The study included nationwide field sampling, targeted investigations, DNA barcoding, examination of museum specimens and an extensive literature survey. The regional fauna now consists of all European taxa, with Mochlonyx triangularis Klink reported here for the first time from Fennoscandia. An illustrated key is provided to fourth instar larvae, pupae and adult males of all species. Chaoborus flavicans (Meigen) is noted as the only truly lake-dwelling species, whilst Ch. albipes (Johannsen) may also occasionally be present in ponds that contain fish populations, all other species are deemed inhabitants of fishless ponds. Among the pond-dwelling species, Ch. obscuripes (Van der Wulp) is dominant, both in terms of numbers of ponds and abundance. The number of chaoborid species in a given pond varies from one to six, with 1-2 taxa found universally. The number of Chaoborus species is most often from one to two and the presence of ≥3 Chaoborus species in a pond is quite rare. Reasons for the observed patterns are likely caused by niche differences, biotic interactions, depth and pond permanence. A total of 251 journal articles, reports or academic theses were found to include records on Finnish Chaoboridae. Chaoborus flavicans was the most often cited taxon (74 % of the studies), whilst the pond-dwelling species (20 %) were cited far more rarely.
... Phantom midges (Chaoboridae, Diptera) are flies that belong to a family of aquatic lower Diptera (Culicomorpha) which are closely related to mosquitoes (Culicidae) (Saether 1970, Borkent 2012, da Silva et al. 2020, Lorenz et al. 2021. Adults are highly similar to Culicidae in the wing venation, presence of scale-lake setae on the wing margin, and large plumose antennae in males, but phantom midges have smaller mouthparts and the females do not blood feed (Borkent 2012, Salmela et al. 2021. ...
... Larvae develop through four instars. The full-grown, last instar larvae are small (6-9 mm) to large (10-22 mm) (Saether 2002, Salmela et al. 2021 with strong mandibles and prehensile antennae that they use to grasp their prey, especially micro crustacean and Culicidae larvae (Lock et al. 2014, Kruppert et al. 2019. The presence of two or three pairs of air sacs serves to adjust larvae position in water according to their predatory behaviour (Teraguchi 1975). ...
... Only 53 species of Chaoboridae have been described globally (Salmela et al. 2021). According to the latest classification of Chaoboridae (Saether 2002 Soltész et al. (2016). ...
Genus Mochlonyx Loew, 1844 is reported for the first time from the Carpathians, with two species, Mochlonyx fuliginosus (Felt, 1905) and Mochlonyx velutinus (Ruthe 1831). Additionally, Chaoborus obscuripes (Wulp, 1859) is also newly recorded in Romania, marking new occurrences for all three species, and bringing the number of Chaoboridae species from the country from three to six. A total number of 525 larvae, pupae, and adults were morphologically analysed, and standard mtCOI DNA sequences were generated for 20 specimens in order to help species level identifications, and association of pupae and larvae with corresponding adults. DNA barcode data delimits well the six species identified from Romania in all life stages. The observed genetic distances are low, with an average p-distance of 0.9%, compared to the conspecific sequences that are available in public genetic databases. Specimens from Romania are grouped into seven different Barcode Index Number (BIN) System clusters. Only Ch. flavicans was represented by two different BINs from Romania, with a genetic distance of only 1.67%, while each of the specimens of the other five species undergoes genetic grouping into a single BIN. To the best of our knowledge, this is the first integrative study of Chaoboridae from Romania, and it contributes to a better understanding of the still largely overlooked aquatic Diptera biodiversity of the region.
... The larvae are predators, feeding mostly on other organisms, such as Daphnia (Crustacea) and culicid larvae . Some species may coexist with fish (Borkent 1981, 1993, Salmela et al. 2021a. ...
... Globally, 54 species in six genera in two subfamilies have been described (Borkent 2014, Salmela et al. 2021a). At least 43 of the currently described species belong to the genus Chaoborus Lichtenstein, and except for Mochlonyx Loew, the other four genera are monotypic (Saether 1970, Ogawa 2007, Borkent 2014. ...
Using reverse taxonomy and morphological analyses, this study describes a new species belonging to the C. flavicans species complex in the Korean Peninsula, Chaoborus pseudoflavicans Bang & Shin sp. nov. Descriptions of the new species from larvae to adults are provided, and the key to the C. flavicans species complex is updated accordingly. DNA barcodes (COI partial sequences) are shown to be sufficient for molecular identification in the C. flavicans species complex. Finally, the taxonomic accounts of all species in the C. flavicans complex are completely resolved for the first time.
... Immature stages (eggs, four larval instars and pupae) inhabit a wide array of freshwater ponds and lakes (e.g. Borkent 1979;Borkent 1981;Colless 1986;Salmela et al. 2021a), while adults are terrestrial. Among chaoborids, and other insects generally, the genus Chaoborus is the only group that is fully adapted to a planktonic lifestyle. ...
Chaoborus phantom midges have a cosmopolitan distribution and are often abundant inhabitants of lentic water bodies during their immature stages. Chaoborus punctipennis, a native species of lakes in the USA and Canada, is reported for the first time in the Palaearctic region in Ehime Prefecture, Japan, as invasive taxon. The species is easy to identify in the larval, pupal and adult stages using morphological keys, and has a distinct DNA barcoding (COI) profile. In order to monitor and manage the species in Japan, we recommend creating targeted inventories of lakes and ponds at Ehime and in neighboring prefectures.
Chaoborus flavicans (Meigen) is a widespread and much studied lacustrine phantom midge. As larvae, these insects are important aquatic predators. Based on the available type material, morphology of immature stages and adults, their aquatic
habitat, and DNA barcodes, C. flavicans is shown to be a composite of at least four species, with three of these named here. Chaoborus flavicans is primarily a lake-dwelling species with a Holarctic range. Chaoborus albipes (Johannsen,
1903 stat. rev.) and C. posio Salmela sp. n. are pond-dwelling Holarctic and north European species, respectively. The position of the larval subordinate mandibular tooth at the vertex of the second and fourth teeth is a synapomorphy of the Chaoborus flavicans species complex. We present an identification key to fourth instar larvae, pupae, and adult males. We also designate the lectotype and paralectotypes of Sayomyia rotundifolia Felt, 1904 (syn. nov. of C. albipes). We hypothesize that a fourth species of the species complex is present in Japan. Our revision indicates that Holarctic shallow ponds contain a hidden diversity of predators (C. albipes and C. posio sp. n.).
Filter feeding zooplankton are a crucial component of limnic food webs. Copepods and cladocerans are important prey organisms for first-level predators like the common and abundant larvae of phantom midges (Chaoborus sp.). The latter possess a complex catching basket built of head appendages specialized to capture small crustaceans. The predator-prey-relationship of Chaoborus (Diptera, Nematocera) and Daphnia (Crustacea, Cladocera) has been studied in particular detail owing to the daphniids’ ability to react upon the threat of predation with inducible defenses. Daphnia pulex expresses so-called ‘neckteeth’ in the presence of Chaoborus larvae that are discussed as a defensive trait that interferes with the larval head appendages and their effectiveness has been shown in several studies. Nonetheless, mode of function of these neckteeth is not understood and the hypothesis that they interfere with the predator’s head appendages still has to be confirmed. To clarify the role of neckteeth in Daphnia, an understanding of the Chaoborus capture apparatus is essential. Here, we present a detailed three-dimensional analysis of Chaoborus obscuripes’ larval head morphology as well as a kinematic analysis of the attack motion, which revealed an impressive strike velocity (14 ms to prey contact). The movement of the larvae’s head appendages is reconstructed in the three-dimensional space using a combination of high-speed videography, micro-computed tomography and computer animation. Furthermore, we provide predation trial data to distinguish between pre- and post-attack defensive effects in D. pulex. Our findings suggest a combination of pre- and post-attack defenses with an average effectiveness of 50% each. With this study, we quantitatively describe prey capture kinematics of C. obscuripes and take a further step to reveal the neckteeth’ mode of function in D. pulex.
Modern echosounders produce very accurate and versatile information on observed fish, but applicability of hydroacoustics in fish stock assessment is still largely determined by the behavior of aquatic animals. A valid assessment is possible only when the target species avoid the inaccessible zones of echo sounder: surface blind zone, bottom dead zone and shallow areas. In addition, it requires an applicable method for eliminating echoes from other targets, especially phantom midge (Chaoborus) larvae, which are abundant in clay-turbid lakes. In Fennoscandia, acoustics has been widely used in vendace (Coregonus albula (L.)) stock monitoring due to its high economic value but other species have been less frequently assessed.
In the present study, the applicability of hydroacoustics in fish stock assessment was investigated in two contrasting environments, in eutrophic, clay-turbid lakes dominated by smelt (Osmerus eperlanus (L.)) located in southern Finland and in oligotrophic, clear-water lakes dominated by whitefish (Coregonus lavaretus (L.)) located in northern Lapland. In both lake groups, the suitable diel periods and seasons for acoustic assessment were sought. In southern lakes, a new method was developed for eliminating the disturbance of Chaoborus. In northern lakes, the differences of the applicability of acoustics between whitefish populations were explored.
The developed method enabled valid smelt density estimation also in lakes with abundant Chaoborus population. Without the new method, the smelt density would have been seriously overestimated. In southern lakes, the pelagic occurrence of smelt favours acoustic assessment. Both day and night surveys can be used and the suitable seasonal sampling window lasts from late July to October. However, because young-of-the-year smelt may occasionally inhabit shallow areas, acoustics should be supplemented by trawling in these areas. In highly turbid lakes, the surface blind zone may be a considerable source of bias and acoustics should be supplemented by surface trawling. Hydroacoustics appeared to be a very useful method in smelt population monitoring and it enables versatile studies on pelagic food-web dynamics of eutrophic lakes.
In northern whitefish lakes, the diel period and season have dramatic effects on the applicability of acoustics. The only suitable conditions for an acoustic survey was occurred at night-time in autumn. In summer, under the midnight sun, and during the day in autumn, the pelagic fish density was very low as most whitefish remained in the bottom dead zone. The applicability of acoustics differed highly between the whitefish populations. In lakes with polymorphic whitefish, the applicability was good for densely-rakered (DR) whitefish due to its pelagic occurrence, but poor for large sparsely-rakered whitefish (LSR) inhabiting shallow areas and small sparsely-rakered (SSR) whitefish inhabiting a bottom dead zone. In lakes with monomorphic whitefish, the level of utilization of the pelagic habitat, and hence the applicability of acoustics differed highly between lakes. The duration of the autumnal sampling window remained unknown and more frequent surveys would be informative for determining the applicability of hydroacoustics in northern whitefish lakes. In addition, surveys revealed that very small-sized nine-spined stickleback (Pungitius pungitius (L.)) is abundant in some northern lakes. The composition of trawl catches indicated very low catchability of this species and their proportion was estimated from target strength (TS) distributions. The abundance of nine-spined stickleback suggests that its role in the pelagic food web of northern Fennoscandian lakes should be explored.
In conclusion, considerable differences exist in a suitable timing for a survey and in the most serious sources of bias between the lake groups. Northern whitefish lakes are more challenging subjects to hydroacoustic assessment and the applicability of acoustics may differ dramatically between whitefish populations. The results highlight that prior knowledge of the pelagic food-web is essential for successful hydroacoustic fish stock assessment.
Perch was the only fish species caught from most of the very acid (pH<5) and moderately acid (pH 5-6) lakes. Mean weights of the perch were higher and numbers/catch smaller in very acid than in other lakes. Perch grew faster in very acid lakes, probably because of increased availability of food due to thinning of the perch populations as a consequence of acid-induced reproduction failures. An exception was Lake Hauklampi (pH 4.8), possibly due to the stress attributable to a high total aluminium content in the water (400μg/l). -from Authors
The effects of water turbulence on rotifer communities were experimentally studied under different predation pressures. When the larvae of the phantom midge (Chaoborus flavicans) were present in turbulent water, the abundance of most rotifer taxa was enhanced. Especially the genera Chromogaster, Keratella, Polyarthra, and Trichocerca, increased in abundance. In calm water, chaoborids did not affect the rotifer community. In turbulent water predation by chaoborids was targeted more towards cladocerans (Bosmina sp.) and predation pressure on rotifers was relaxed. Additionally, reduced competition with cladocerans probably contributed to the increase of rotifer abundance. Turbulence alone had no significant effect on rotifer abundance because their individual size was small compared with the diameter of the turbulent eddies. The study suggested that the effects of turbulence on rotifers is not direct but takes place through changed predator–prey relations, i.e., the effect depends on the abundance of invertebrate predators. In aquatic ecosystems with a high density of chaoborids, increasing turbulence can considerably increase the abundance of rotifers.
Differences in diet can explain resource partitioning in apparently similar, sympatric
species. Here, we analyzed 1,252 fecal droppings from five species (Eptesicus nilsso‐
nii, Myotis brandtii, M. daubentonii, M. mystacinus, and Plecotus auritus) to reveal their
dietary niches using fecal DNA metabarcoding. We identified nearly 550 prey spe‐
cies in 13 arthropod orders. Two main orders (Diptera and Lepidoptera) formed the
majority of the diet for all species, constituting roughly 80%–90% of the diet. All five
species had different dietary assemblages. We also found significant differences in
the size of prey species between the bat species. Our results on diet composition
remain mostly unchanged when using either read counts as a proxy for quantitative
diet or presence–absence data, indicating a strong biological pattern. We conclude
that although bats share major components in their ecology (nocturnal life style, in‐
sectivory, and echolocation), species differ in feeding behavior, suggesting bats may
have distinctive evolutionary strategies. Diet analysis helps illuminate life history
traits of various species, adding to sparse ecological knowledge, which can be utilized
in conservation planning.
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.
We examined a sediment record from Lake Hiidenvesi in southern Finland using paleolimnological methods to trace its limnoecological history. In our record, beginning from the 1940s, chironomid (Diptera) assemblages shifted from typical boreal taxa towards mesotrophic community assemblages at ~ 1960–1980 CE being finally replaced by eutrophic taxa from the 1990s onward. The diatom (Bacillariophyceae) assemblages reflected relatively nutrient rich conditions throughout the record showing a further increase in eutrophic taxa from the 1970s onward. A chironomid-based reconstruction of late-winter hypolimnetic dissolved oxygen (DO) conditions suggested anoxic conditions already in the 1950s, probably reflecting increased inlake production due to allochthonous nutrient inputs and related increase in biological oxygen consumption. However, the reconstruction also indicated large variability in long-term oxygen conditions that appear typical for the basin. With regard to nutrient status, chironomid- and diatom-based reconstructions of total phosphorus (TP) showed a similar trend throughout the record, although, chironomids indicated a more straightforward eutrophication process in the benthic habitat and seemed to reflect the intensified human activities in the catchment more strongly than diatoms. The DO and TP reconstructions were mostly similar in trends compared to the measured data available since the 1970s/1980s. However, the increase in TP during the most recent years in both reconstructions was not visible in the monitored data. The results of our multiproxy study emphasize the significance of including both epilimnetic and hypolimnetic systems in water quality assessments and provide important long-term limnoecological information that will be useful in the future when setting targets for restoration.
In order to simulate food web responses of small boreal lakes to changes in thermal stratification due to global warming, a 4 year whole-lake manipulation experiment was performed. Within that time, period lake mixing was intensified artificially during two successive summers. Complementary data from a nearby lake of similar size and basic water chemistry were used as a reference. Phytoplankton biomass and chlorophyll a did not respond to the greater mixing depth but an increase was observed in the proportional abundance of diatoms, and the proportional abundance of cryptophytes also increased immediately after the onset of mixing. Obligate anoxic green sulphur bacteria vanished at the onset of mixing but gradually recovered after re-establishment of hypolimnetic anoxic conditions. No major effect on crustacean zooplankton was found, but their diversity increased in the metalimnion. During the mixing, the density of rotifers declined but protozoan density increased in the hypolimnion. Littoral benthic invertebrate density increased during the mixing due to Ephemeroptera, Asellus aquaticus and Chironomidae, whereas the density of Chaoborus larvae declined during mixing and lower densities were still recorded one year after the treatment. No structural changes in fish community were found although gillnet catches increased after the onset of the study. The early growth of perch (Perca fluviatilis) increased compared to the years before the mixing and in comparison to the reference lake, suggesting improved food availability in the experimental lake. Although several food web responses to the greater mixing depth were found, their persistence and ecological significance were strongly dependent on the extent of the disturbance. To better understand the impacts of wind stress on small lakes, long term whole-lake experiments are needed.
The biostratigraphical history of a small lake Otalampi in southern Finland has been studied. The remains of subfossil Bosmina have been analysed and the biostratigraphy of the larvae of lacustrine Diptera has now been applied in Finnish palaeolimnology. It has been shown in this paper that the phantom midge larva (Chaoborus) with the midge groups Tanytarsarie and Chironomarie predominate in the early history of the lake. After the stratigraphical transition from fine to coarse detritus gyttja Orthocladiinae occur in abundance and are associated with Tanytarsarie and Chironomarie. In pollen zone IX Chironomarie clearly increase and with Tanytarsarie they form the predominating species in the midge community. The occurrence of Chaoborus at the bottom part of the core is believed by authors that the lake initially had a more or less reduced hypolimnion and that the lake was more eutrophic in character. Oithocladiinae, Tanytarsarie and probably Chironomarie in the upper part of the biostratigraphy might indicate that Lake Otalampi was more oligotrophic with a well-oxygenated hypolimnion. Lake Otalampi is now eutrophic.
Small humic forest lakes often have high contributions of methane-derived carbon in their food webs but little is known about the temporal stability of this carbon pathway and how it responds to environmental changes on longer time scales. We reconstructed past variations in the contribution of methanogenic carbon in the pelagic food web of a small boreal lake in Finland by analyzing the stable carbon isotopic composition (δ13C values) of chitinous fossils of planktivorous invertebrates in sediments from the lake. The δ13C values of zooplankton remains show several marked shifts (approx. 10 ‰), consistent with changes in the proportional contribution of carbon from methane-oxidizing bacteria in zooplankton diets. The results indicate that the lake only recently (1950s) obtained its present state with a high contribution of methanogenic carbon to the pelagic food web. A comparison with historical and palaeobotanical evidence indicates that this most recent shift coincided with agricultural land-use changes and forestation of the lake catchment and implies that earlier shifts may also have been related to changes in forest and land use. Our study demonstrates the sensitivity of the carbon cycle in small forest lakes to external forcing and that the effects of past changes in local land use on lacustrine carbon cycling have to be taken into account when defining environmental and ecological reference conditions in boreal headwater lakes.
We examined functional climate responses of two small taiga lakes in eastern Scandinavia with the aim to compare biogeochemical shifts in the hydrologically different basins over the past 3500 years. Sediment cores from one seepage and one drainage lake were studied for C and N elemental and stable isotopic composition to track organic matter origin, elemental cycles, and trophic structure. Fossil Cladocera assemblages and functional grouping of Chironomidae were determined to understand food web structure, biotic interactions, and habitat quality. In the seepage lake, the warm Medieval Climate Anomaly (MCA, ~1400 to 1000 cal BP) induced thermal stratification, hypolimnetic anoxia, and increased in-lake production, similar to the 20th century development. The Neoglacial cooling, with a high precipitation period at ~2200 to 2000 cal BP, and the cold Little Ice Age (LIA, ~700 to 300 cal BP) increased terrestrial carbon inputs and reduced productivity. The drainage lake was shallow, productive, and humic during the warm and dry period at ~4000 to 3000 cal BP but cooler and moister climate induced higher lake level with stratification and hypolimnetic anoxia around 2500 cal BP. The MCA was characterized by increased in-lake production and altered food web structure, as the keystone zooplankton taxon Daphnia was extirpated, and LIA by intensified anoxia and reduced planktonic production due to longer ice-cover period. Coherent responses to climate warming included increased planktonic production, stronger stratification, and hypolimnetic anoxia with anaerobic processes in both lakes, but responses to moisture were site-specific and dependent on basin hydromorphology.
Effects of fish introductions on lake ecosystems have long been debated. It has been hypothesized that such effects should be strongest in oligotrophic lakes, where fish were not originally present. We investigated two lakes (one naturally fishless, one fish-stocked in 1980) in northern Fennoscandia, selected because of the absence of other anthropogenic stressors and a well-known stocking history. The diet of the introduced brown trout (Salmo trutta L.) was analysed to estimate the effect of their predation on the pelagic invertebrate communities. Quantitative and qualitative samples were taken to assess the current abundances of pelagic macro- and micro-invertebrates in different habitats of both lakes, to infer the impact of brown trout presence. Past abundances of Cladocera, Chironomidae, Gammarus
lacustris and Daphnia longispina were also estimated based on subfossil remains in the sediment, and used to assess how brown trout introduction affected macro- and micro-invertebrates living in different habitats. Relative abundance and species richness of Cladocera were evaluated in sediment cores from both lakes, to assess whether changes were caused by fish-introduction-induced trophic cascades or climate change. Also, planktonic Cladocera (Eubosmina) body sizes were measured to evaluate their response to the release of macro-invertebrate predation pressure. Brown trout introduction displaced macro-invertebrates, i.e. G. lacustris, from the pelagic area, and caused a trophic cascade effect that slightly increased the species richness of Cladocera, but markedly increased their abundance, as shown in the sediment record. Introduced brown trout did not, however, cause a decline in Chironomidae, G. lacustris or D. longispina abundances. On the contrary, it resulted in an approximately five-fold increase in Chironomidae accumulation rates in the sediment. The release of macro-invertebrate predation pressure did not lead to changes in the body shapes of Eubosmina, which could be a consequence of the composition of the original macro-invertebrate species assemblage.
In order to examine the effects of acidity on abundance and community structure of the benthic invertebrates in forest lakes and to evaluate the applicability of certain benthic animals as early warning indicators of lake acidification, 140 lakes, situated mainly in southern Finland, were studied by quantitative and qualitative sampling methods.
The biomass and number of animals showed no significant correlation with lake acidity, although the number of species decreased markedly with increasing acidity in the littoral zone of the lakes. The fauna in the deeper zones was often reduced as a result of poor oxygen conditions, and it was not possible here to separate the effects possibly attributable to acidity from those of other factors.
There are certain acid-sensitive species, especially among the snails, mayflies and small mussels, by means of which it would be possible to evaluate the stage of acidification of a lake. The presence of these key species is closely related to minimum pH, the acid peak in a lake usually occurring as the snow is melting. This means that the acid periods can be detected also afterwards, which is a considerable advance compared with physico-chemical monitoring of water quality. The comparison of the sampling methods indicated that the qualitative hand net offers a superior method for sampling the littoral invertebrates, making it much easier to obtain samples containing a high number of individuals and species than with the Ekman grab.
Population dynamics and growth of perch (Perca fluviatilis) were studied over a 20-year period in a small, humic, boreal lake (Valkea-Kotinen). The annual estimated total population size of perch (> 8 cm, total length) varied from 2700-13 400 and the biomass from 16.1-44.2 kg ha-1. Strong year-classes were born at four-year intervals between 1991 and 2003. A decreasing trend was recorded in the growth of 1- and 2-year-old perch, whereas a slight increase appeared in the yearly growth of 4- and 5-year-old fish. Our view is that the decrease in the early growth was caused by negative effects of increased organic carbon loads on water colour and hence on light conditions and the general productivity of the plankton community. These changes outweighed the expected positive effect of increasing temperature for young perch but not for the older fish.
The artificial lakes of Kalajärvi, Kyrkösjärvi, Liikapuro and Pitkämö are situated within the catchment of the River Kyrönjoki and their permission holder is West Finland Regional Environment Centre. The main purpose of the reservoirs has been flood protection and regulation of water flow. Now the reservoirs have an average age of 30 years. The characteristics of the artificial lakes affect their biology and water quality. The composition of the benthic fauna is affected by e.g. low oxygen content, which often is caused by regulation and long retention time. The dark colour of the water and the regulation together have a limiting effect on the occurrence of vegetation in the reservoirs. The status of the artificial lakes has changed since the beginning of the 1990’s. The water
quality has improved as for the oxygen situation and the phosphorous content, whereas
the chlorophyll content has increased. Changes have been noted also in the benthic fauna
and the fish stock. The fish mercury content of the artificial lakes has decreased since the
record figures of the 1970’s and 1980’s, but the limiting values of the Ministry of Agriculture
and Forestry are exceeded in some occasions. During the last 20 years, the artificial lakes in the River Kyrönjoki catchment are have, at least to some extent, becom more like natural eutrophic lakes. Changes in the variation of the water quality have decreased. Also the benthic fauna in some of the lakes resembled, more than before, the fauna typically found in eutrophic and polyhumic lakes.
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.
Partly anoxic stratified humic lakes are important sources of methane (CH4) and carbon dioxide (CO2) to the atmosphere. We followed the fate of CH4 and CO2 in a small boreal stratified lake, Alinen Mustajärvi, during 2007–2009. In 2008 and 2009 the lake received additions of dissolved organic carbon (DOC) with stable carbon isotope ratio (δ13C) around 16‰ higher than that of local allochthonous DOC. Carbon transformations in the water column were studied by measurements of δ13C of CH4 and of the dissolved inorganic carbon (DIC). Furthermore, CH4 and CO2 production, consumption and emissions were estimated. Methane oxidation was estimated by a diffusion gradient method. The amount, location and δ13C of CH4-derived biomass and CO2 in the water column were estimated from the CH4 oxidation pattern and from measured δ13C of CH4. Release of CH4 and CO2 to the atmosphere increased during the study. Methane production and almost total consumption of CH4 mostly in the anoxic water layers, was equivalent to the input from primary production (PP). δ13C of CH4 and DIC showed that hydrogenotrophic methanogenesis was the main source of CH4 to the water column, and methanogenic processes in general were the reasons for the 13C-enriched DIC at the lake bottom. CH4 and DIC became further 13C-enriched in the anoxic layer of the water column during the years of DOC addition. Even gradient diffusion measurements showed active CH4 oxidation in the anoxic portion of the water column; there was no clear 13C-enrichment of CH4 as generally used to estimate CH4 oxidation strength. Increase in δ13C-CH4 was clear between the metalimnion and epilimnion where the concentration of dissolved CH4 and the oxidation of CH4 were small. Thus, 13C-enrichment of CH4 does not reveal the main location of methanotrophy in a lake having simultaneous anaerobic and aerobic oxidation of CH4. Overall the results show that organic carbon is processed efficiently to CH4 and CO2 and recycled in the anoxic layer of stratified boreal lakes by CH4 oxidation. In spite of this, increased DOC input led to increased greenhouse gas release, mainly as CO2 but also as CH4. Due to the predominantly anaerobic CH4 oxidation, a relatively small amount of CH4-derived biomass was produced, while a large amount of CH4-derived CO2 was produced in the anoxic bottom zone of the lake.
Lakes are important habitats for biogeochemical cycling of carbon. The organization and structure of aquatic communities influences the biogeochemical interactions between lakes and the atmosphere. Understanding how trophic structure regulates ecosystem functions and influences greenhouse gas efflux from lakes is critical to understanding global carbon cycling and climate change. With a whole-lake experiment in which a previously fishless lake was divided into two treatment basins where fish abundance was manipulated, we show how a trophic cascade from fish to microbes affects methane efflux to the atmosphere. Fish exerted high grazing pressure and removed nearly all zooplankton. This reduction in zooplankton density resulted in increases in the abundance of methanotrophic bacteria, which in turn reduced CH4 efflux rates by one quarter. Given that globally there are millions of lakes emitting methane, an important greenhouse gas, our findings that aquatic trophic interactions significantly influence the biogeochemical cycle of methane has important implications.
The Finnish Lake Survey, conducted in 1987, was designed to quantify the present extent of lake acidification in Finland. The surveyed lakes were selected statistically (n = 987), allowing estimation of lake frequencies, as well as corresponding variances, for any predetermined criteria. The median pH of the lakes was 6.3, median acid neutralizing capacity (ANC) 75 μeq l −1 and median sulphate concentration 71 μeq l−1. The organic anion was estimated to be the most significant anion in Finnish lakes (median 89μeq l−1). Sulphate concentrations in lakes corresponded to the pattern of acidic deposition, being highest in southern Finland. The acidity of Finnish lakes reflects the interaction of the atmospheric loading of sulphate, the catchment sensitivity, and the amount of organic anions present. The estimated proportion of acidic lakes (ANC ≤ 0 μeq l−1) in Finland was 12%, representing 4900 lakes. The proportion of the acidic lakes with pH < 5.3 estimated to be naturally acidic (original pH < 5.3), was 56–81%.
The pupae of each of the families of the Culicomorpha are described and, for the first time, their structures homologized.A glossary provides a standard set of terms to be applied to each structure, including a common chaetotaxy. A cladisticanalysis incorporates information from each life stage, including a number of new features discovered from the pupalstage, to provide a new phylogenetic hypothesis, as well as indicating autapomorphies for each family. Analysisincluded states for one egg, 21 larval, 33 pupal, and 37 adult characters. The Chironomidae is the sister group of allremaining Culicomorpha, the Ceratopogonidae is the sister group of Thaumaleidae + Simuliidae and these three arenewly recognized as members of the re-defined superfamily Simulioidea. The superfamily Culicoidea are the sistergroup of the Simulioidea and include, as previous work has already demonstrated, the Dixidae as the sister group ofCorethrellidae + Chaoboridae + Culicidae. Corethrellidae is the sister group of Chaoboridae + Culicidae. Thesuperfamily Chironomoidea now includes only Chironomidae.Analysis of the fossil record shows that the Chironomidae (and the Culicomorpha) originated in the Triassic andboth Simulioidea and Culicoidea were present by 176 million years ago in the Jurassic. Phylogenetic patterns are used tointerpret bionomic features such as differences in the nature of blood-feeding by adult females, daytime or nighttimefeeding by adult females, and occurrence of immature stages in aquatic habitats. Chironomidae do not feed on blood asadults and have likely diversified by invading virtually all aquatic habitats as larvae. Its sister group is more than twiceas diverse and feeding on vertebrate blood is strongly correlated with high diversification within the Simulioidea +Culicoidea (likely because a reliable source of protein was available to dispersing females since the Triassic fromterrestrial vertebrates). Families with blood-feeding females have larger numbers of species than do those without thisbehaviour. Each family in the Simulioidea + Culicoidea have specialized larval habitats or specialized habits, largely inaquatic habitats where Chironomidae are either not, or are marginally present, suggesting a level of competitive exclusion by the Chironomidae.
Understanding phylogenetic relationships within the family Culicidae informs mosquito evolution and may have public health implications as this family includes numerous species of medical and veterinary importance. We investigated the mitochondrial genomes of 102 mosquitoes, including six newly sequenced species, representing 21 genera with an emphasis on the Neotropical region. We estimated divergence times based on sequence data and three fossil calibration points, using Bayesian relaxed clock methods. Bayesian and maximum‐likelihood phylogenetic analyses based on the DNA sequences of 13 PCGs of the 102 species provided robust support for the monophyly of the subfamily Anophelinae and the tribes Aedini, Culicini, Mansoniini and Sabethini. Despite the current genera of Anophelinae being consistently recovered as monophyletic, relationships among them proved to be quite variable depending on the method used (concatenated or partitioned) and the number of taxa sampled. Molecular divergence time estimates revealed that the two mosquito subfamilies, Anophelinae and Culicinae, diverged in the early Jurassic (approximately 197.5 Mya). However, most major lineages of these groups arose after the Cretaceous, coincident with the emergence of angiosperms and the expansion of mammals and birds. The diversification and worldwide distribution of Culicidae may also be determined in part by geographic isolation as a result of continental drift during the Cretaceous.
Chitinous aquatic invertebrate remains are abundant in late Quaternary lake sediment sequences. However, for standard analysis of invertebrate indicator groups usually only the remains of one particular invertebrate group (e.g. water fleas, midges) are systematically isolated from the sediments and analysed numerically. In a calibration study focusing on surface sediment samples from 36 small Swiss lakes, we show that the abundances of other chitinous aquatic invertebrate remains in samples prepared for chironomid analysis provide important information on in-lake oxygen conditions when assessed relative to and together with the overall number of chironomid remains. Our results show that particularly high abundances of chironomid and chaoborid remains are indicative for lakes with high and low deepwater oxygen concentrations, respectively, but that also the remains of other invertebrate groups such as Ceriodaphnia ephippia and Plumatella statoblasts tend to be more abundant in warm, stably stratified and anoxic lakes. Direct gradient analyses of the isolated invertebrate assemblages indicate that deepwater oxygen concentration during late summer is the strongest predictor for assemblage changes in our dataset, followed by variables representing temperature conditions (summer surface water temperature, altitude), summer stratification stability (temperature difference between surface and deepwater layers), water depth and the relative volume of the late summer hypoxic water layer. We show, based on invertebrate assemblages in a Lateglacial sediment sequence from Rotsee, Switzerland, that our new calibration data can provide information on past changes in deepwater oxygen availability from late Quaternary lake sediment sequences, when fossil invertebrate assemblages are added as passive samples to ordinations of the surface sediment calibration data. This provides a new approach for developing assessments of past changes in deepwater oxygen concentrations from late Quaternary sediment samples prepared for chironomid analysis. Such assessments can provide important supplementary information for e.g. interpreting palaeotemperature reconstructions based on chironomid remains.
The Talvivaara/Terrafame multi-metal mining company is Europe's largest nickel open cast mine, it is also known for the largest wastewater leakage in the Finnish mining history and a series of other accidents. In this paleolimnological study, influences of a recently constructed treated waste water discharge pipeline into Lake Nuasjärvi were investigated by analyzing past (pre-disturbance) and present community compositions of key aquatic organism groups, including diatoms, Cladocera and Chironomidae, along spatial (distance, water depth) gradients. In addition to defining ecological changes and impacts of saline mine waters in the lake, chironomids were used to quantitatively reconstruct bottom water oxygen conditions before and after the pipe installation (in 2015). The diatom and cladoceran communities, which reflect more the open-water habitat, showed only relatively minor changes throughout the lake, but a general decrease in diversity was observed within both groups. Chironomids, which live on substrates, showed more significant changes, including complete faunal turnovers and deteriorated benthic quality, especially at the sites close to the pipe outlet, where also chironomid diversity was almost completely lost. Furthermore, the reconstructed hypolimnetic oxygen values indicated a major oxygen decline and even anoxia at the sites near the pipe outlet. The limnoecological influence of the pipe decreased at sites located counter-flow or behind underwater barriers suggesting that the waste waters currently have location-specific impacts. Our study clearly demonstrates that whereas the upper water layers appear to have generally maintained their previous state, the deep-water layers close to the pipe outlet have lost their ecological integrity. Furthermore, the current hypolimnetic anoxia close to the pipe indicates enhanced lake stratification caused by the salinated mine waters. This study clearly exhibits the need to investigate different water bodies at several trophic levels in a spatiotemporal context to be able to reliably assess limnoecological impacts of mining.
To clarify the effect of brownification on the functioning of lake ecosystems, the utilization of daytime refuges by chaoborids was examined in two lakes having different water colour. It was hypothesized that with high water colour, oxygen concentration plays a smaller role for the behavior of chaoborids than with lower water colour. It was also expected that the depth distribution of chaoborids is associated with light intensity at 680–700 nm. This could decrease their visibility to predators. In Lake Iso Valkjärvi with 50 mg L−1 Pt water colour, chaoborids occurred below 5 m depth, where the oxygen concentration was 0.4 mg L−1. Supporting the first hypothesis, in Lake Majajärvi with 200 mg L‐ 1 Pt colour, the leading edge of the population was at 3 m with 3.5 mg L−1 oxygen concentration. In Majajärvi, chaoborids remained in a layer where planktivorous fish could feed, explained by the low light intensity that decreased the potential predation pressure of fish. In Iso Valkjärvi with higher light intensity, chaoborids inhabited only the layers where oxygen concentration was too low for fish. Supporting the second hypothesis, the intensity of 693 nm light in the two lakes was similar at the depth of the leading edge of the chaoborid population. This wavelength represents the wavelengths that chaoborids reflect most effectively and is beyond the sensitivity peak of their main predator perch. The results suggested that combined effects of oxygen and water colour are potential explanatory mechanisms of the observed patterns in the behavior of chaoborids. The results thus suggested that along the worldwide brownification of lakes, the role of oxygen as a regulator of invertebrate predators may change. Because invertebrate predators are important components of lake food webs, such effects may be reflected to the whole ecosystem and further studies on the subject are encouraged.
Lake Karhujarvi has a perch population of 200 individuals. The growth and the composition of the diet resemble those in other, less acid lakes in the same area. Reproduction of the perch failed in the springs of 1980-1982 as a result of high mortality of roe caused by low pH. The fertilization of most eggs may have been inhibited by decreased activity of the sperm cells, but even fertilized eggs showed high mortality. In spring 1981, many adult fish died, probably due to the low pH and high Al concentration of the water. -Author
The biomass and the species richness of the zooplankton communities were reduced in the most polluted parts of the watercourse below a sulfite pulp mill in central Finland. Only occasional cladocers and copepods were found in the vicinity of the mill, whereas the rotifers Keratella cochlearis, K. ticinensis, Kellicottia longispina, Polyarthra remala and P. vulgaris occurred more frequently. Ciliates were characteristic inhabitants of these areas. Dominant crustacean species were Daphnia cristata, Diaphanosoma brachyurum, Eudiaptomus gracilis and Mesocyclops leuckarti. Many zooplankton species probably avoided the polluted areas because of the scarcity of suitable food. The zooplankton biomass and species richness showed zonation similar to that of the phytoplankton biomass, and the zooplankton biomass maxima were found in the same areas as the phytoplankton maxima. The zooplankton biomass was rather small in the hypolimnic waters because of the oxygen depletion up to 35 km from the mills.
Long-term changes in the macrozoobenthos of Vanajavesi are described over 50 years from 1926, when the first benthic survey was made. This lake was then rather oligotrophic, but has become eutrophicated and polluted during the last two or three decades. Monitoring was started in 1965. The survey was repeated in 1971 and 1977 using identical methods. Some benthic stations were checked in 1966-1967 and 1974. Between 1926 and 1965 the Monodiamesa-Pontoporeia community was replaced by a Chironomus anthracinus community in the profundal of the central basin of Vanajavesi. Regressive species were still present, especially in the sublittoral. Between 1965 and 1977 succession towards a Chironomus plumosus community was detected. Pontoporeia and Monodiamesa almost totally vanished. C. plumosus and oligochaetes became more abundant. Changes in the macrozoobenthos of the other basins, which are heavily polluted by industrial or municipal effluents, were rather small during the period 1965-1977. A slight improvement was detected in 1977. This was indicated by a change in the bathymetric distribution of benthos. The profundal areas near the pollution outfall, which were totally desolate, were colonized by C. plumosus in 1977. In general, the bottom faunal lake type system proposed by Brundin seems to be applicable in the large polluted lakes of the Finnish lake district. Besides the chironomid fauna Pontoporeia affinis, in particular, is one of the most used organisms for analysing the degree of pollution in the lakes studied.
In 2 small forest lakes total fish biomass was 73kg/ha and 32kg/ha, and fish production 30 and 15kg/ha, respectively. The fish of the 1st lake were perch Perca fluviatilis, pike Esox lucius and introduced whitefish Coregonus muksun, of the 2nd perch and whitefish. The main reasons for the differences in fish biomass and production were probably light and oxygen conditions. The diet segragation between perch and whitefish, which reduced interspecific competition, and predation by pike on perch, which reduced intraspecific competition for food among perch, also resulted in improved fish producton in the 1st lake.-Authors
In order to improve the reliability of climate models in their projections for the future, spatially and temporally detailed paleoclimate proxy data are needed. In this study, we examined annually laminated sediments from Lake Nurmijärvi (Finland) for their fossil Chironomidae assemblages over a time period with available meteorological observational data (since 1830s). In doing so, we correlated chironomid-based inferences of summer air temperatures against instrumentally measured values using two different reconstruction approaches, namely, calibration-in-space (CiS, multilake training set) and calibration-in-time (CiT, calibration of time series data against meteorological data). The results showed that the principal variability in fossil chironomid assemblages in the sediment core corresponded to the measured air temperatures. In addition, the temperatures reconstructed using CiS (R = 0.38, p = 0.014) and CiT (R = 0.51, p = 0.001) correlated significantly with the meteorological data; however, the CiS approach showed higher variability and larger differences against the instrumentally measured values. A significant lag of on average 4–8 years was also found in the chironomid response to observed temperature change that is, nevertheless, much shorter time span than with some other paleoclimate proxies. The results verify the usability and sensitivity of chironomids as a paleoclimate proxy in the Nurmijärvi varved sediment record with the potential value of an exceptionally well-resolved downcore record of the Holocene climate change in the future. The CiT approach can potentially provide accurate paleotemperature estimates at the late-Holocene scale, but the CiS approach may be more useful at longer timescales if the community compositions change significantly from those occurring during the calibration period of the CiT.
Land uplift isolated the basins in individual lakes in different phases of the Baltic Sea, and, because the land uplift was uneven, the drainage basins tilted causing transgression or regression in lake basins and many shifts of outlet channels, particularly in the Finnish lake district. Nearly 3000 lakes have been entirely or partially drained by man, and about 30 reservoirs with a total area 800km 2 have been made by damming. More than 30% of the watercourses are under regulation today. The usability of waters in about 78% of the lake area is excellent or good, and in only 4% it is passable or poor. Water pollution problems caused primarily by industrial and municipal waste waters do exist in rivers and lakes, but most of them are local in nature. -from English summary
Precambrian crystalline bedrock determines the major features of the present relief of Finland while the influence of overlying glacial and postglacial deposits is much less marked. Weathering and erosion processes have worn down originally mountainous landscape to a low-lying peneplain. About 80% of Finland may be classified as lowland, lying below 200 metres, and the highest point in the country is Halti, at 1328 m a.s.l. Structurally controlled valleys, fault-line scarps, quartzite monadnocks, rounded horsts and roches moutonnees are typical bedrock forms in the country. Six circular remnants of old meteorite impact craters have also been found in the ancient bedrock. The eroded bedrock surface is usually covered by till deposits, most commonly 3-4 m in thickness, and there are numerous large drumlin and moraine fields in different part of the country. Glaciofluvial eskers, deltas and kame fields are also basic elements of the relief, but the large end formations, such as the Salpausselkas and Central Finland ice marginal formation, are the most famous glacial accumulation forms in Finland. After deglaciation, clay plains with river valleys, beach and dune formations and peat bogs have developed during different phases of the postglacial era. The human role in creating landforms and modifying the operation of geomorphological processes is included as a matter of increasing importance. -from English summary
The qualitative and quantitative changes in the meiozoobenthos are described along a pollution gradient downstream from the Valkeakoski industrial area. Material was collected in late summer. The response of the meiozoobenthos to the industrial waste water load is compared with that of the macrozoobenthos. Reference material was also collected from an area loaded with municipal effluents and from the least polluted part of Vanajavesi. The response of the meizoobenthos to heavy pollution was in principle similar to that of the macrozoobenthos. The zoobenthos is either scarce or even totally eliminated below the pollution outfall. Cyclopoida is the only group which thrives on these anoxic bottoms. The most tolerant sedentary meiofaunal species were some nematods and Rotaria neptunia, which were found in low numbers at a station where the conditions were too extreme for the most tolerant macrofaunal species Chironomus plumosus. The diversity of both meiofauna and macrofauna increased downstream, where the oxygen conditions improved. The total abundance of both meiofauna and macrofauna reached a huge maximum in a zone where the oxygen concentration was 0-4 mg/l. Downstream from this point the abundance again decreased to a normal level. The industrial effluents (mainly from the wood-processing industry) and the municipal waste waters caused similar changes in the meiozoobenthos. Potentially toxic effects are not easy to detect, because the oxygen depletion is the main limiting factor. There are, however specific changes in the composition of the meizoobenthos which may be valuable in the biological assessment of the pollution, such as the composition of the macrofauna.
A mesocosm experiment with enclosures was constructed to examine the influence of an invertebrate predator, Chaoborus flavicans, on cladoceran seasonal succession in Lake Hiidenvesi. One of the treatments had no Chaoborus or fish, one contained no fish, but did have naturally dense population of Chaoborus and one had both Chaoborus and fish at natural densities. The cladocerans showed a biomass spring peak when both Chaoborus and fish were absent, but not when only fish were eliminated. After the emergence of Chaoborus, the cladoceran biomass increased in the enclosure with no fish but with Chaoborus. The average individual size of the cladocerans was higher in the enclosure with no Chaoborus or fish. In the other treatments, the size of the cladocerans did not differ. The results confirmed earlier conclusions that Chaoborus flavicans is the main predator of the cladoceran community in the deep area of Lake Hiidenvesi.