Species composition,abundance and emergence phenology of midges (Deiptera: Chironomidae) in a brown-water stream of West-Central Alberta,Canada

Sixteen floating, box type emergence traps, each covering 0.1 m², were placed along 150 m of a third-order stretch of the Bigoray River, a slow-flowing, vegetation-choked, brown-water muskeg stream. Effects of trap design, trap shading, length of sampling interval, and stream velocity on the number of midges caught was examined. Of the 112 species of Chironomidae caught, 32 species made up 90% of the catch and their emergence phenology is described in detail. There were more rare species than expected from Preston's lognormal distribution. Percentage of Bigoray species belonging to Tanypodinae, Orthocladiinae, Chironomini and Tanytarsini was 18%, 43%, 20%, and 19%, and was compared with 27 other studies on lotic chironomids. During the 140-day emergence period an average of 19.3 × 10³ chironomids emerged per square meter of stream. Based on changes in male:female ratios throughout a species emergence period, it was postulated that 30% of the Bigoray chironomid species were univoltine, 50% were bivoltine, and 20% were trivoltine.     

A note on chironomids (diptera) of temporary pools in the National Park of Circeo,Central Italy

Preliminary observations on chironomid assemblages in 9 temporary pools of the National Park of Circeo (Central Italy) are reported. A total of 15 genera or species groups (6 Orthocladiinae, 3 Tanypodinae, 1 Tanytarsini and 5 Chironomini) were recorded during March and April, 1986.Psectrotanypus varius, Polypedilum nubeculosum gr.,Chironomus thummi gr. andC. plumosus gr. were the most abundant and frequent taxa in the nine pools. Almost all chironomids collected are eurytopic and widely distributed in Europe, including Italian waters. Only the finding ofGymnometriocnemus is reported in this paper as a new record for Central Italy. Similarity among pools and among taxa (coefficient of Jaccard) shows a major occurrence of aquatic Orthocladiinae in smaller pools and of Chironomini in larger pools. This relationship between chironomid assemblages and pool sizes can be partly related to the duration of the wet phase which affects chironomid species according to their survival strategies.     

Longitudinal zonation and food of larval chironomids (Insecta: Diptera) along the course of a river in temperate Canada

The chironomid larvae of the Rouge River, Ontario, Canada, showed a longitudinal zonation which may have been influenced by water temperature and substrate composition. Species of Orthocladiinae predominated in the cooler headwaters while species of Chironomini dominated the comparatively warmer water near the estuary. In the middle section the chironomid assemblage was of a more mixed nature.
Differences occurred in both food availability and feeding between sites along the river. Within genera, there were differences in the proportions of major food items between the larval guts and the available food material sampled from the same area. In most cases (e.g. Cryptochironomus, Polypedilum and Orthocladius ) larvae selected detritus over diatoms. Some genera (e.g. Microtendipes ) changed the proportions of food items ingested seasonally, while others (e.g. Psectrocladius ) exhibited a more stable diet throughout the year. Second instar larvae appeared to seasonally adjust their diet most often (e.g. Cricotopus. Tanytarsus and Eukiefferiella ), however these changes were not just in the types of food eaten, but also in the proportions of food types consumed. Larvae of all genera continued feeding throughout the cold water conditions (<5°C) of winter. Incidence of predation was very low, for example <10% in the Tanypodinae. In the laboratory, species of Chironomini ingested and assimulated, to varying degress, isolated populations of diatoms, detritus and bacteria.     

Drift dynamics of Chironomidae larvae: I. Preliminary results and discussion of importance of mesh size and level of taxonomic identification in resolving Chironomidae diel drift patterns

Diel drift samples utilizing nets with mesh size less than 200 microns were taken in Linesville Creek, Pennsylvania, an eastern deciduous forest stream, and Inlet Run, Wyoming, an alpine snow melt stream. Identification of drifting Chironomidae larvae to lowest level taxonomic categories indicated 51 species or species group categories representing 51.95% of the total insect drift in Linesville Creek and 18 species or species group categories representing 70.47% of the total insect drift in Inlet Run. Orthocladiinae were the predominant larvae in the drift in Linesville Creek, with 19 species comprising 43.84% of the Chironomidae drift. In decreasing abundance were Chironomini (12 species, 40.36% of Chironomidae drift), Tanytarsini (10 species, 8.89%), and Tanypodinae (10 species, 6.91%). By contrast, Diamesinae were the predominant larvae in the drift in Inlet Run, (5 species, 71.43%) followed by Orthocladiinae (10 species, 27.25%), Tanytarsini (2 species, 1.20%), and Podonominae (1 species, 0.12%). Comparison of drift composition with substrate samples and/ or emergence data indicated a close relationship between relative abundance in drift and relative abundance in the benthos. Behavioral drift patterns with nocturnal peaks were seen for 3 species or species groups in Linesville Creek. Four species with diurnal drift peaks were present in Inlet Run. Analysis of the size distribution of drifting larvae indicates that a mesh size as small as 200 microns is required to resolve diel drift patterns. It is postulated that random factors greatly influence the apparent diel drift pattern of Chironomidae when nets with mesh size in excess of 400 microns are employed in drift studies. Conflicting literature reports of behavioral drift for Chironomidae may be due to differing species composition of drifting larvae and net mesh size related artifacts.     

Relationship between δ13C of chironomid remains and methane flux in Swedish lakes

1. Methanogenic carbon can be incorporated by methane‐oxidising bacteria, leading to a ¹³C‐depleted stable carbon isotopic composition (δ¹³C) of chironomids that feed on these microorganisms. This has been shown for the chironomid tribe Chironomini, but very little information is available about the δ¹³C of other abundant chironomid groups and the relationship between chironomid δ¹³C and methane production in lakes. 2. Methane flux was measured at the water surface of seven lakes in Sweden. Furthermore, fluxes from the sediments to the water column were measured in transects in two of the lakes. Methane fluxes were then compared with δ¹³C of chitinous chironomid remains isolated from the lake surface sediments. Several different chironomid groups were examined (Chironomini, Orthocladiinae, Tanypodinae and Tanytarsini). 3. Remains of Orthocladiinae in the seven study lakes had the highest δ¹³C values (?31.3 to ?27.0‰), most likely reflecting δ¹³C of algae and other plant‐derived organic matter. Remains of Chironomini and Tanypodinae had lower δ¹³C values (?33.2 to ?27.6‰ and ?33.6 to ?28.0‰, respectively). A significant negative correlation was observed between methane fluxes at the lake surface and δ¹³C of Chironomini (r = ?0.90, P = 0.006). Methane release from the sediments was also negatively correlated with δ¹³C of Chironomini (r = ?0.67, P = 0.025) in the transect samples obtained from two of the lakes. The remains of other chironomid taxa were only weakly or not correlated with methane fluxes measured in our study lakes (P > 0.05). 4. Selective incorporation of methane‐derived carbon can explain the observed correlations between methane fluxes and δ¹³C values of Chironomini. Remains of this group might therefore have the potential to provide information about past changes in methane availability in lakes using sediment records. However, differences in productivity, algal δ¹³C composition and the importance of allochthonous organic matter input between the studied lakes may also have influenced Chironomini δ¹³C. More detailed studies with a higher number of analysed samples and detailed measurement of δ¹³C of different ecosystem components (e.g. methane, dissolved inorganic carbon) will be necessary to further resolve the relative contribution of different carbon sources to δ¹³C of chironomid remains.     

Food and habitat of four Xenotilapia species (Teleostei, Cichlidae) in a sandy bay of northern Lake Tanganyika (Burundi)

The feeding ecology of four species of Xenotilapia (Teleostei, Cichlidae) from Lake Tanganyika was investigated by examining their intestine contents in three different habitats from two 24-h catch cycles. The fish were caught in a sandy bay 4 km north-west of Bujumbura (Burundi) during the dry season, from August until October 1993. Three different habitats were sampled: an area 600 m offshore at a depth of 15 m, a littoral zone near a reed bed (depth, 0–5 m), and an area near a sandy beach (depth, 5 m). The fish were most active in the early morning and at night, except for X. caudafasciata which was the most diurnal. X. ochrogenys was confined to the vicinity of the reeds, where few individuals of the other species were found, and prey comprised mainly ostracods, copepods and chironomid larvae (Tanytarsini). X. ornatipinnis and X. longispinis occurred in large numbers both at a depth of 15 m and near the sandy beach. X. ornatipinnis preyed mainly on copepods, oligochaetes, diatoms and chironomid larvae. X. longispinis had a wider range of temporal and spatial distribution compared with the other species and fed on copepods, ostracods and chironomid larvae (mainly Microchironomus spp.). X. caudafasciata (only caught at 15 m) fed mostly on profundal chironomid larvae (Tanypodinae and Microchironomus spp.). Trophic niche overlap between X. longispinis and X. caudafasciata appeared to be reduced through different activity patterns. Few intraspecific differences in food diet were found between sex and age groups.     

The drift of some chironomid egg masses (Diptera: Chironomidae)

SUMMARY. The drift of chironomid egg masses was investigated in the River Mole (Devon) and the River Wye (Powys) in 1981. Large numbers of egg masses were found in the drift just after dusk; on one occasion an estimated 50,000 egg masses passed a sampling point in 5 h. Oviposition of free-floating egg masses appeared to be initiated and synchronized by the onset of darkness. Egg masses of some Pentaneurini (Tanypodinae), Tanytarsini and Chironomini (Chironominae) were found in the drift and adhering to submerged stones.
Flotation by means of a gas vacuole within the egg mass was observed in the Polypedilum 'convictum' group. The gas vacuole decreased in size over 8–11 h and the egg masses sank after 2–3h.
Some chironomid egg masses are capable of drifting large distances after oviposition. The implications of sueh drift are briefly discussed in relation to the distribution of chironomid larvae.     

Diversity of chironomid larvae in palustrine wetlands of the coastal plain in the south of Brazil

The Chironomidae of tropical South America are a very rich species, but are scarcely known. The range of environmental conditions under which chironomids are found is more extensive than that of any other group of aquatic insects. The objectives of this study were to carry out a diversity survey of chironomid larvae in wetland systems of the coastal plain in the south of Brazil and to analyze the effects of area, altitude, water conductivity, nitrate and phosphorus concentrations, and the life form of the dominant plant species on chironomid richness and composition. Collections were carried out from March to April in 2002. A total of 30 taxa (23 morphospecies and 7 species) distributed along 23 genera were found, and the Chironominae showed the greatest richness, followed by Tanypodinae and Orthocladiinae. The chironomid richness was higher in the emergent than in the multistratified wetland class. The wetland area, altitude, nitrate and phosphorus concentrations, and water conductivity did not influence the richness of Chironomidae. The Chironomidae genera and species were present in both the wetland classes (emergent and aquatic bed vegetation). However, while Chironominae were more frequent in the emergent than in the aquatic bed wetlands, no difference was observed for Tanypodinae. The aquatic vegetation was an important environmental predictor for chironomid larvae richness in the studied wetlands in the south of Brazil.     

Food preferences of tanypodinae larvae (Diptera: Chironomidae)

Analyses of the gut contents of larvae of three species of Tanypodinae, collected from four sites in north-east England and Scotland, invariably showed small particles (1–10 µm²), predominantly of detritus, to be more abundant than large particles (10–100 µm²), mostly algae and diatoms. No animal remains, such as carapaces, head capsules and chaetae, or vascular plant fragments were found in any of the intestines. In contrast, food-choice and growth experiments suggested that animal food (particularly Tubificidae and Chironominae larvae) was important in the tanypod diet. In the food-choice experiments, six different foods offered to small (4–7 mm long) and to large (8–12 mm long) larvae of Procladius choreus Meigen, were chosen in the following order: live Tubificidae spp.; detritus; live Chironominae larvae; a mixture of algae and diatoms; live Ostracoda spp.; and live Cladocera spp. However, when the results of the individual choices were examined, it was clear that the small larvae had consumed greater amounts of the small types of food (i.e. detritus, algae and diatoms) in comparison to the large larvae. In the growth experiment, those larvae of P. choreus reared solely on Tubificidae, detritus or Chironominae larvae thrived, while those fed on algae and diatoms, ostracods or cladocerans grew more slowly and fewer survived the experimental period.It was concluded that although Tanypodinae larvae are primarily predators with definite food preferences in ideal foraging conditions, in adverse conditions they will utilize a range of available stand-by foods, the most important of which appears to be detritus.     

Secondary production of chironomid communities in insecticide-treated and untreated headwater streams

SUMMARY.

• 1 Production of chironomid communities of three first order, Appalachian Mountain streams was estimated and the effects of an insecticide-induced disturbance on chironomid production was examined.
• 2 Annual production of non-Tanypodinae chironomids in the streams during the first study year (no treatment) ranged from 1366 to 3636 mg m^?2, while production of Tanypodinae chironomids ranged from 48 to 116 mg m ^?2. Production/biomass ratios ranged between 19 and 23 for non-Tanypodinae and from 6 to 7 for Tanypodinae chironomids.
• 3 Insecticide applications resulted in significantly lower chironomid densities and biomass in the treated stream relative to the pretreatment year and reference stream. Annual production of non-Tanypodinae (703 mg m^?2) and Tanypodinae (32 mg m ^?2) chironomids in the treated stream decreased by 64% and 67%, respectively, compared with the pretreatment year. In contrast, production of non-Tanypodinae (2084 mg m^?2) increased by 34% and production of Tanypodinae (96 mg m^?2) by 57% in the reference stream.

     

Diel emergence patterns of drifting chironomid (Diptera) pupal exuviae in the Aude River (Eastern Pyrenees,France)

Two diel emergence patterns (April and October 1990) of chironomids from a hyporhithral site (4th–5th order) in the Aude River are described. In April, 62 species were collected with a mean hourly richness of 31 (±4). The Orthocladiinae (91%) largely dominated the emergence. The total number of exuviae captured by one drift-net varied from 1300 to 11600 per one hour period. There was a clear bimodal pattern with peaks post dawn (07.00–09.00 hrs) and around sunset (18.00 hrs).In October, the total number of exuviae captured was much lower and varied from 150 to 540 per one hour period with post dawn (06.00–08.00 hrs) and post sunset (18.00 hrs) peaks. Nevertheless, the total species richness (65) was higher as was the mean hourly richness (37±4). The Orthocladiinae (68%) dominated less because of increases in the Tanytarsini (15%) and Chiromini (14%). A diel rhythm appeared in autumn emergence. Most of the Orthocladiinae exuviae were collected during daylight hours, whereas most of the Chironomini and Tanytarsini were sampled during darkness. A majority of the exuviae with a length below 3 mm emerged during daylight, but most of the exuviae above 5 mm length emerged during darkness. The exuviae with an intermediate length (3–5 mm) had an amodal diel emergence pattern. In spring and autumn, the majority of species had a bimodal emergence pattern either by day (Orthocladiinae) or by night (Chironominae). But the smallest species had either an unimodal (Thiennemaniella vittata) or bimodal (Neozavrelia fuldensis) daytime emergence. The diel emergence patterns of 10 of the most frequently recorded species are presented.     

Methane-Derived Carbon in the Benthic Food Web in Stream Impoundments

Methane gas (CH₄) has been identified as an important alternative source of carbon and energy in some freshwater food webs. CH₄ is oxidized by methane oxidizing bacteria (MOB), and subsequently utilized by chironomid larvae, which may exhibit low δ¹³C values. This has been shown for chironomid larvae collected from lakes, streams and backwater pools. However, the relationship between CH₄ concentrations and δ¹³C values of chironomid larvae for in-stream impoundments is unknown. CH₄ concentrations were measured in eleven in-stream impoundments located in the Queich River catchment area, South-western Germany. Furthermore, the δ¹³C values of two subfamilies of chironomid larvae (i.e. Chironomini and Tanypodinae) were determined and correlated with CH₄ concentrations. Chironomini larvae had lower mean δ¹³C values (−29.2 to −25.5 ‰), than Tanypodinae larvae (−26.9 to −25.3 ‰). No significant relationships were established between CH₄ concentrations and δ¹³C values of chironomids (p>0.05). Mean δ¹³C values of chironomid larvae (mean: −26.8‰, range: −29.2‰ to −25.3‰) were similar to those of sedimentary organic matter (SOM) (mean: −28.4‰, range: −29.3‰ to −27.1‰) and tree leaf litter (mean: −29.8 ‰, range: −30.5‰ to −29.1‰). We suggest that CH₄ concentration has limited influence on the benthic food web in stream impoundments.     

Interactions ofMonoporeia affinis (Lindström) (Amphipoda) with sedentary Chironomidae

Interannual population oscillations ofMonoporeia affinis and sedentary chironomids are negatively correlated in Lake Mälaren. Sedentary chironomid abundance regressed againstM. affinis density was highly significant at a lag response of one year (adj. R²=0.54, P=0.0001). The inverse correlation between Tanytarsini (Micropsectra sp. andTanytarsus sp.) andM. affinis densities supports a recruitment limitation hypothesis,viz. that the growth or survival of early instar chironomids is low at high amphipod densities. Microcosm studies showed density-dependent effects on the growth and survival of second instarCh. riparius larvae across an amphipod density gradient. No significant effects were found on growth or survival of third instars. These findings support the chironomid recruitment limitation hypothesis. Amphipod predation on early instar chironomid larvae is suggested as a population controlling mechanism.     

Patterns of macroinvertebrate abundance in inland saline wetlands: a trophic analysis

We used stable isotopes and gut-content analysis to compare trophic relations of macroinvertebrates between two types of saline wetlands in the Laramie Basin, Wyoming, USA. Amphipods (Hyallela azteca), chironomid larvae, and predatory insects (mainly Zygopteran larvae) occurred in both wetland types. However, in oligosaline wetlands (0.5–5‰ total dissolved solids) amphipods were dominant, whereas in mesosaline wetlands (5–18‰) amphipods were scarce and chironomid larvae and predatory insects were much more abundant. Salinity alone seemed inadequate to explain these differences, so we examined trophic interactions to address three main questions: (1) why are predatory insects more abundant in mesosaline wetlands, (2) why are chironomid larvae less abundant in oligosaline wetlands, and (3) why are amphipods uncommon in mesosaline wetlands? Zygopteran larvae ate mainly chironomid larvae and zooplankton, and did not eat amphipods; chironomid larvae were an average 93 dry mass of zygopteran intake. Guts of amphipods contained no animal parts and little vascular plant tissue, but rather mainly amorphous detritus. Chironomid larvae ate amorphous detritus as well as diatoms. There is potential for competition between amphipods and chironomids, but the nature of amorphous detritus in these wetlands needs further study. Because amphipods appear unavailable as prey for predatory insects, top-down impacts on chironomid larvae may be greater in oligosaline than in mesosaline wetlands. Our results suggest that (1) predatory zygopteran larvae and hemipterans are more abundant in mesosaline wetlands due to more abundant chironomid prey, (2) chironomids are less common in oligosaline wetlands because of both competition with amphipods and greater per capita consumption by predatory insects, and (3) amphipods are scarce in mesosaline wetlands because, lacking a resting stage and mode of direct dispersal, they do not cope well with extremes created by hydrologic instability in mesosaline wetlands. These mechanisms may apply to wetlands in other regions where similar patterns of invertebrate community structure have been reported.     

Ecological factors influencing macroinvertebrate standing crop distribution

Influence of substrate, macrophyte growth and detritus on macroinvertebrate standing crop (numbers and biomass) as well as seasonal variations in standing crop were investigated in a trout stream.Ephemeropterans showed no consistent relationship to substrate type, either in numbers or biomass. Numbers of dipteran larvae (primarily chironomids and simuliids) did not show a definite relationship to substrate size. But a larger biomass was associated with larger substrates. Higher numbers and biomass of trichopterans (including Helicopsyche borealis) were associated with larger substrates. Numbers of coleopteran larvae showed no relation to substrate size, but biomass was greater in large substrates. Biomass and numbers of water mites were generally associated with larger substrates, whereas no relationship was observed in plectopterans.Larger numbers and biomass of ephemeropterans, dipterans (chironomids and simuliids but no other dipterans) and trichopterans are associated with macrophyte beds; this is attributed to drifting species and those that have summer generations. Macrophyte growth reduced numbers and biomass of H. borealis, but no differences were observed in coleopterans or plecopterans.A substrate/detritus substitution study was done under natural stream conditions. An area of relatively constant current and depth was selected from which eighteen sites were randomly selected. Gravel and detritus were removed and replaced with two distinct sizes of substrate and three different levels of detritus. This was a 2 × 3 factorial analysis design. Ephemeropteran numbers were significantly related to substrate type and detritus level, whereas biomass was only related significantly to substrate. Numbers of chironomids and other dipterans responded significantly to substrate manipulation. Biomass of dipterans other than chironomids was significantly related to substrate type but not detritus level and chironomid biomass did not respond to either manipulations.Trichopteran numbers responded significantly to substrate and detritus manipulations, whereas biomass was significantly related only to substrate type. Analysis of variance showed that coleopteran numbers did not respond significantly to either manipulation; however, orthogonal contrasts showed that, within large substrate, medium detritus level was significantly different from high detritus level. Oligochaetes did not respond to either substrate or detritus manipulation. The responses of the organisms to manipulations are explained in relation to interstitial spaces and oxygen as well as the interaction between substrate type and amount of detritus.Michigan Agricultural Experiment Station Journal Article No. 5734.     

Two unusual Chironomini (Diptera: Chironomidae) from Australian rainforest streams: One new genus and a neotropical genus new for the region

Two genera of chironomine Chironomidae are reported: Anuncotendipes , gen. n., type species Anuncotendipes australotropicus sp. n. and included Anuncotendipes kakadu sp. n., and Nandeva Wiedenbrug, Reiss and Fittkau as new to Australia for the species Nandeva fittkaui sp. n. The pupa and adults are known for each genus, but the larvae only for Anuncotendipes . The female of Nandeva is described for the first time. Pupal exuviae of both genera occur in smaller streams in the wet tropics of Far North Queensland, and A. kakadu is lotic in the Northern Territory. Phylogenetic analysis of the subfamily Chironominae at generic level suggests that Anuncotendipes is a sister genus to Rheomus in the Harnischia -complex of genera. Nandeva shows convergent resemblance to the tribe Tanytarsini, but more likely belongs to an austral radiation of Chironomini including Nilodosis Keiffer, Fissimentum Cranston and Nolte and Imparipecten Freeman. These genera show tropical Gondwanan tracks linking Australia with the Afrotropics and Neotropics.     

Laboratory investigation on community composition, emergence patterns and biomass of wood-inhabiting Chironomidae (Diptera) from a sandy lowland stream in Central Europe (Germany)

Wood-inhabiting chironomid communities were investigated from June 1998 to July 1999 by laboratory rearing of randomly collected submerged branches from a headwater and mid-reach site of a sandy lowland stream, separated by an impoundment used for fishery purposes. Total annual emergence (males and females) from headwater samples was higher (2551 ind m^–2 y^–1) compared to the mid-reach (1576 ind m^–2 y^–1), which could be due to disturbances caused by frequent impoundment openings resulting in high discharge events. Chironomid community from branches comprised three subfamilies, with Orthocladiinae (18 species, 2189 ind m^–2 y^–1) clearly predominating at the headwater (total of 36 species). Mid-reach samples (total of 48 species) showed similar emergent numbers of Orthocladiinae (19 species, 786 ind m^–2 y^–1) and Chironominae (26 species, 764 ind m^–2 y^–1). Tanypodinae were caught very rarely in the laboratory emergence (12 ind m^–2 y^–1 at both sites). Shannon-Wiener diversity index for the mid-reach chironomid community was higher (2.52) than for the headwater community (1.68). Chironomid species composition on woody debris was similar between stream sites, with a Sørensen index of 0.75, but showed different dominance structures indicated by a Wainstein index of 0.26. Total adult biomass (in the manner of dry mass) during the study period was higher for wood-dwelling chironomids from the headwater (158.2 mg m^–2 y^–1) compared to the mid-reach (123.8 mg m^–2 y^–1), but individual biomass was higher for mid-reach chironomids (0.079 mg ind^–1 vs. 0.062 mg ind^–1 at the headwater), indicating the predominance of larger species. Total biomass of wood-inhabiting chironomids in the investigated lowland stream was low compared to other field emergence studies, which could be attributed to the laboratory approach for investigating the emergence from a single substrate type (submerged wood) instead of the integrative field surveys where chironomids from all habitats were caught. Main reason for the lack of chironomid species closely associated to wood in this sandy lowland stream could be infrequent but episodic disurbances caused by the anthropogenic induced highly fluctuating discharge regime of the downstream study site.     

Chironomids as water quality indicators in the River Mignone (Central Italy)

Chironomids of the River Mignone (Central Italy) were studied in order to examine their community structure and their relationship to some common biological indices (Biotic Score, Extended Biotic Index, Indice Biotique de Qualité Générale) utilizing the total macroinvertebrate fauna (chironomids generally at family level) for water quality assessment in rivers.A total of 36 taxa belonging to Tanypodinae (2 taxa), Orthocladiinae (22 taxa) and Chironominae (12 taxa) was collected at seven stations four times during a year. The results support the importance of the chironomid identification in water quality assessment studies in rivers, and demonstrate the usefulness of the factorial correspondence analysis as ordination technique based on both qualitative and quantitative chironomid data to determine environmental quality gradients.The value as bioindicator of some taxa was discussed, and chironomid assemblages were related to biological water quality of the river according to functional feeding groups.This study forms part of a larger Research project supported by MPI and CNR grants and is aimed at the biological water quality assessment of the river and at the analysis of the total macrobenthic community.     

Structure and function of a benthic invertebrate stream community as influenced by beaver (Castor canadensis)

Summary Beaver (Castor canadensis) affect the benthic invertebrate community of small woodland streams in Quebec through habitat modifications. Their activities influence community structure through the replacement of lotic taxa by lentic forms and community function by increasing the absolute importance of collectors and predators while decreasing the relative importance of shredders and scrapers in impounded sites. At our study site during the 1983 ice-free season, standing stocks of coarse particulate organic matter (>1 mm) were 2–5 times greater (P<0.05) in impounded sites than riffle sites in spring and summer. Fine (212 m–1 mm) and very fine (0.5 m–212 m) particulate organic matter were 3–10 times greater (P<0.05) in impounded sites in all seasons. Chlorophyll a standing stocks did not differ statistically among sites. Total density and biomass of invertebrates in impoundments were 2–5 times greater (P<0.05) than riffle sites in spring and summer, but statistically similar in autumn. Generic diversity (H) was greater (P<0.05) in unaltered sites in autumn. Non-impounded sites were dominated by Simuliidae, Tanytarsini chironomids, scraping mayflies and net spinning caddisflies while impounded sites were characterized by Tanypodinae and Chironomini chironomids, predacious odonates, Tubificidae, and filtering pelycopods. Our results suggest that current paradigms applied to lotic ecosystems need to be reevaluated to incorporate the influence of beaver upon invertebrate communities.     

仙居国家公园溪流摇蚊幼虫群落结构及其对水质的指示作用

为了解浙江仙居国家公园内溪流中摇蚊幼虫的群落结构及其对水质的指示作用,于2016年8月对仙居国家公园内13条溪流59个点位进行了调查,运用Hilsenhoff生物指数对溪流水质进行评价.结果表明: 59个点位中有37个点处于清洁状态,19个点处于轻污染状态,3个点处于中污染状态.此次调查共获得摇蚊幼虫86种,隶属于4亚科51属.其中,摇蚊亚科种类数最多,有19属37种;直突摇蚊亚科次之,有21属35种;长足摇蚊亚科有9属12种;寡角摇蚊亚科最少,为2属2种.摇蚊亚科密度比重最大,为40.3%;长足摇蚊亚科与直突摇蚊亚科所占比重差异不大,分别为30%与29.4%;寡角摇蚊亚科比重最小,仅为0.3%.壳粗腹摇蚊为仙居国家公园溪流摇蚊幼虫绝对优势种;黄色多足摇蚊、流环足摇蚊、平滑环足摇蚊、纽流长跗摇蚊和小型棒脉摇蚊为优势种.仙居国家公园溪流中摇蚊幼虫指示种分析结果显示,平滑环足摇蚊、双色矮突摇蚊、台湾长跗摇蚊和渐变长跗摇蚊可作为污染水体指示种,流环足摇蚊可作为清洁水体指示种.