Malacological assessment and natural infestation of Biomphalaria straminea (Dunker, 1848) by Schistosoma mansoni (Sambon, 1907) And Chaetogaster limnaei (K. Von Baer, 1827) in an urban eutrophic watershed.

The objective of this study was to perform a malacological assessment at the Ibirité reservoir watershed in the metropolitan region of Belo Horizonte (Minas Gerais) and to evaluate the natural infestation rate of Biomphalaria straminea (Gastropoda: Planorbidae) by Schistosoma mansoni (Platyhelminthes: Trematoda) and Chaetogaster limnaei (Oligochaeta: Naididae). The samples were collected from July to August 2002. The B. straminea individuals collected were kept in the laboratory; the natural infestation rate by S. mansoni and C. limnaei was assessed weekly. The malacological assessment identified five mollusk species present in the Ibirité reservoir watershed: B. straminea, Physa marmorata, Lymnea sp., Melanoides tuberculatus, and Pomacea austrum. Laboratory observations showed that the B. straminea individuals were infected by C. limnaei rather than S. mansoni. Although there was no infection of B. straminea by S. mansoni, presence of B. straminea in itself merits close attention due to possible risk of human schistosomiasis by the local population.     

Environmental gradients determining the distribution of benthic macroinvertebrates in Lake Takkobu, Kushiro wetland, northern Japan

Effects of environmental variables on the distribution of benthic macroinvertebrates inhabiting sediments were studied at 25 sites along the shoreline of Lake Takkobu in the Kushiro wetland of northern Japan in summer 2003. During the last decade, the lake’s status has undergone a drastic shift from clear water dominated by submerged macrophytes to turbid water dominated by phytoplankton. The canonical correspondence analysis showed that four environmental variables explained the significant variation in the macroinvertebrate species composition: submerged plant biomass, bottom sediment organic matter content (OMC), distance from the mouth of the Takkobu River, and bottom-layer pH. Five species of Chironomidae [Chironomus sp. (except plumosus group), Psectrocladius sp., Corynoneura sp., Parachironomus sp. arcuatus group, and Zavreliella sp.] occurred in sites with relatively lower pH and a high submerged plant biomass, whereas three species of Tubificidae (Tubifex tubifex, Aulodrilus limnobius and Aulodrilus sp.) and two of Chironomidae (Nanocladius sp. and Monodiamesa sp.) occurred in sites with high pH and little vegetation. The three Tubificidae species also preferred organic-rich sediments. Irrespective of aquatic vegetation, Sphaerium sp. (Bivalvia) and Monodiamesa sp. (Chironomidae) occurred in low-OMC sites, whereas Tanypus sp. (Chironomidae) preferred high-OMC sites. The number of macroinvertebrate taxa showed the highest correlation with the number of submerged plants, suggesting that macroinvertebrate species richness was related mostly to submerged plant species diversity in this lake. The quantity and species richness of submerged plants and OMC are thus important determinants of the community structure of macroinvertebrates inhabiting sediments in Lake Takkobu.     

Invasive bivalves increase benthic communities complexity in neotropical reservoirs

Invasive bivalves often act as ecosystem engineers, generally causing physical alterations in the ecosystems in which they establish themselves. However, the effects of these physical alterations over benthic macroinvertebrate communities’ structure are less clear. The objective of this study was to characterize the ecological effects of the invasive bivalves Corbicula fluminea and Limnoperna fortunei on the structure of benthic macroinvertebrate communities in neo-tropical reservoirs. Three hypotheses were tested: (1) invasive bivalves act as facilitator species to other benthic macroinvertebrates, resulting in communities with higher number of species, abundance and diversity; (2) invasive bivalves change the taxonomic composition of benthic macroinvertebrate communities; (3) invasive bivalves increase the complexity of benthic macroinvertebrate communities. For that it was used data from 160 sampling sites from four reservoirs. We sampled sites once in each area, during the dry season from 2009 to 2012. The first hypothesis was rejected, as the presence of invasive bivalves significantly decreased the host benthic communities’ number of species and abundance. The second hypothesis was corroborated, as the composition of other benthic macroinvertebrates was shown to be significantly different between sites with and without invasive bivalves. We observed a shift from communities dominated by common soft substrate taxa, such as Chironomidae and Oligochaeta, to communities dominated by the invasive Gastropoda Melanoides tuberculata. The biomass data corroborated that, showing significantly higher biomass of M. tuberculata in sites with invasive bivalves, but significantly lower biomass of native species. Benthic macroinvertebrate communities presenting invasive bivalves showed significantly higher eco-exergy and specific eco-exergy, which corroborate the third hypothesis. These results suggest that while the presence of invasive bivalves limits the abundance of soft bottom taxa such as Chironomidae and Oligochaeta, it enhances benthic communities’ complexity and provide new energetic pathways to benthic communities in reservoirs. This study also suggests a scenario of invasion meltdown, as M. tuberculata was facilitated by the invasive bivalves.     

The salinity tolerance of freshwater macroinvertebrate eggs and hatchlings in comparison to their older life-stages: a diversity of responses

The tolerance to high salinity of older life stage macroinvertebrates could underestimate the effects of increasing salinity on freshwater macroinvertebrates. The salinity tolerance of the eggs and/or hatchlings of Glyptophysa gibbosa (Planorbidae), Glyptophysa aliciae, Glacidorbis sp. (Glacidorbidae), a Glossiponiidae, Piona cumberlandis (Pionidae), and Chironomus sp. (Chironomidae) were determined. The salinity tolerances of younger life-stages of species studied here and elsewhere were then compared to salinity tolerances of their mature aquatic or dominant life-stage. A diversity of responses have been observed with some species having similar salinity tolerances in all life-stages examined, whilst the eggs or hatchlings of other species had salinity tolerances ranging from 4% to 88% of their older life stages. On present knowledge, this diversity of responses presents some difficulties for simple rules of thumb to approximate sensitivity of young life-stages of freshwater macroinvertebrates inferred from their dominant stage’s tolerance.     

Colonization and succession of benthic macroinvertebrates in Arcadia Lake,a South-Central USA reservoir

Colonization and succession of benthic macroinvertebrates in Arcadia Lake, an urban reservoir, were studied for four years. Physicochemical conditions including water temperature, dissolved oxygen concentrations, pH, specific conductance, and Secchi disc depth were also recorded. Colonization of the reservoir occured fairly rapidly through a sequence of three invasions. The first, and most significant, colonists were primarily facultative species already present in streams and ponds that were inundated by the impoundment. Later arrivals tended to be limnophilic species that probably came from other bodies of water. Of 30 species encountered in a pre-impoundment collection, only six were still present three years following impoundment. Thirty-three additional benthic macroinvertebrates species invaded the area following impoundment. Dominant taxa in the reservoir included Dero nivea, Limnodrilus sp., Chaoborus punctipennis, Chironomus sp., and Procladius sp. Pollutants accumulating in this urban reservoir, including metals and pesticides, and siltation probably have kept benthic populations relatively low and possibly reduced potential species diversity.     

Benthic macroinvertebrates associated with four species of macrophytes

Benthic macroinvertebrates associated with four species of macrophytes (Nymphoides peltata, Ceratophyllum demersum, Polygonum amphibium and Carex sp.) were investigated during two growing seasons (2001 and 2002) in the slow-flowing Čonakut Channel in the Kopački rit Nature Park in Croatia. A total of 31 macroinvertebrate taxa were found. C. demersum, a submerged plant with dissected leaves, supported the highest macroinvertebrate abundance, almost seven times more than N. peltata, a floating plant with undissected leaves, which harboured the lowest abundance during the research period. Chironomidae larvae (50–83%) and Oligochaeta (14–46%) were the most abundant groups recorded on all macrophyte species. Water-level fluctuation, because of its influence on the appearance and growth of aquatic vegetation, and the trophic state of water within the macrophyte stands seemed to be the main factors which affected the taxonomic composition and abundance of macroinvertebrates.     

Analysis of environmental factors in sediment based on benthic macroinvertebrates in streams,Korea

This research summarizes the data on benthic macroinvertebrates collected in the 15 streams during spring (June) and fall (September–October) of 2022. The objectives of this study were (i) to evaluate the quality of surface waters, sediments, and benthic macroinvertebrates ; and (ii) to compare the relationship with the environmental variables in water, sediments and benthic macroinvertebrates that inhabit 15 streams. A total of 114 taxa were collected. The assemblages from the 15 sites were dominated by Chironomidae and Tubificidae, especially Chironomidae constituted 45.0% density occurrence. The low grades of Benthic Macroinvertebrate Index (BMI) were calculated in 10 sites with disturbed (“poor” or “very poor”). Low BMI sites mostly showed Tubificidae or Chironomidae dominant characteristics. The biological indices, BMI, % Tubificidae, and % Chironomidae, were significantly correlated with DO and conductivity. DO was also significantly correlated with all the benthic macroinvertebrate factors and diversity except percent Tubificidae. The heavy metal parameters were correlated mostly with species number, BMI, and diversity index. The objectives of this study examine the diversity of benthic macroinvertebrate in the 15 streams and investigate the relative importance of environmental quality for benthic macroinvertebrate distribution.     

DNA barcoding supports reclassification of Japanese Chironomus species (Diptera: Chironomidae)

Non‐biting midges (Diptera: Chironomidae) adapt to species‐specific environmental conditions and hence are promising bioindicators for aquatic and ecotoxicological monitoring. Although their utility for these purposes was historically limited by difficulties in their morphological identification, DNA barcoding offers a possible solution. Here, eight Japanese species of the genus Chironomus, which is characterized by its worldwide distribution and abundance among Chironomidae, were subjected to DNA barcoding using cytochromec oxidase subunit I (COI). To examine whether this DNA barcode is a useful indicator for Japanese species of Chironomus, we calculated genetic distances within and between the COI sequences of Chironomus species both from this study and worldwide and constructed phylogenetic trees. Based on 415 bp COI sequences and the Kimura two‐parameter model, the average genetic distances within 37 species and between 72 species were 2.6% and 17.2%, respectively. Although the ranges of genetic distances within and between species overlapped from 0.8% to 17.3%, 99.7% of average genetic distances between species were >3.0%. Some of this overlap is attributable to distances within species that were “too large” as well as those between species that were “too small”. Of eight Japanese species examined, two showed genetic distances between species that were below a 3.0% threshold, and four had distances within species that were greater than 3.0%. These results suggest a possible reclassification of these species and the need for further sampling to unveil biogeographic variations among different countries and regions.     

Factors affecting the distribution of stream macroinvertebrates in geothermal areas: Taupo Volcanic Zone,New Zealand

The distribution of macroinvertebrates was investigated among sites within five geothermally influenced and two non- or minimally-influenced streams in the Taupo Volcanic Zone, New Zealand, to examine the responses of communities to broad environmental gradients within and among habitats. To date, examination of geothermal stream macroinvertebrates has typically been from single habitats, and has not been examined over a regional scale. Sites within and among streams represented a range of sizes, depths, water velocities and substrate types. Sites with little or no geothermal influence typically had temperatures less than 15°C and pH between 5 and 8. Four of the geothermally influenced streams had temperatures greater than 25°C, and ranged from alkaline (pH 9.1) to highly acidic (pH 3.0). Most taxa recorded were typical inhabitants of non-geothermal streams that are tolerant to elevated temperatures, extreme pH conditions and/or high toxicant levels. Diptera, Coleoptera and Mollusca dominated geothermal sites, and Ephemeroptera, Plecoptera and Trichoptera were absent. In addition, an obligate dweller of geothermal habitats, Ephydrella thermarum, and a nonindigenous tropical gastropod, Melanoides tuberculata, were recorded. Canonical correspondence analysis implicated multiple factors in determining the distribution of invertebrates over the region. Overall, distribution was most strongly associated with temperature gradients, particularly longitudinally within streams. This distribution was likely directly related to species temperature tolerances, but also temperature effects on algal abundance and composition, its differential effects on species’ potential competitors and predators, and its effects on toxicant availability. Differences in invertebrate composition among streams were associated with major differences in pH and substrate. Increased acidity was associated with a significant decrease in invertebrate taxa richness, with acidic sites having a limited fauna dominated by dipterans (e.g., Naonella sp., Polypedilum sp.). Stability of flow and environmental conditions may enhance competitive interactions among taxa, enhancing the importance of substrate type in these systems. The presence of non-indigenous species (e.g., M. tuberculata, Poecilia reticulata), currently limited in distribution, also affected species composition. Overall, communities become less speciose, although more unusual in composition, with increased geothermal influence. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: K. Martens     

Macrobenthic distribution and community structure in the upper navigation pools of the Upper Mississippi River

The northern section of the Upper Mississippi River supports a diverse macrobenthic assemblage. Distribution of this benthic fauna, benthic community structure, and factors which influences which influence both of these phenomena in these upper pools are reviewed. Dumping of heavy loads of municipal and industrial wastes from the Minneapolis-St. Paul metropolitan area has severely stressed the benthic community. Once abundant, pollution-sensitive mayflies, Hexagenia bilineata and H. limbata, are noticeably absent, replaced by pollution-tolerant oligochaetes and midges (notably Chironomus). Harmful effects of this pollution are not restricted to the area immediately downstream from the Twin Cities. In Lake Pepin, the Hexagenia population has suffered a drastic decline. The benthic community is characterized by low species diversity and a dominant, pollution-tolerant Chironomus plumosus — Oligochaeta — Sphaeriidae — Hirudinea community complex. Farther south, effects of the high organic load which originates approximately 226 km upstream are ameliorated. Inundation of large, diverse land areas contributes to the great ecological diversity in Pools No. 7 and No. 8. In Navigation Pool No. 7, benthic standing crops in the backwater pool areas (biomass range: 2.08–26.96 g m^–2) exceed those in the main channel (biomass range: 0.05–1.02 g m^–2). Greater numbers of burrowing mayflies and mollusks were found in the pool areas. Of 131 taxa collected from 1976–1977 in Lake Onalaska, which occupies most of Pool No. 7, eight dominant groups — Oligochaeta, Hirudinea, Isopoda, Amphipoda, Lepidoptera, Diptera, Gastropoda, and Pelecypoda — accounted for 90–93% of the macroinvertebrates. In Pool No. 8, over half of the 144 benthic taxa collected during the summer of 1975 were insect nymphs and larvae. Oligochaetes were by far the most ubiquitous and dominant macroinvertebrates. Habitat preferences of particular benthic forms reflected distributional relationships between macroinvertebrates and physical-chemical conditions. Benthic production, in terms of total wet weight m^–2 and macroinvertebrate density in each study area, was generally greater in the more eutrophic areas. However, fewer taxa were supported in these areas. These taxa were generally pollution-tolerant organisms, such as oligochaetes and certain chironomids, which were capable of burrowing into depositional-type substrates. More taxa and greater numbers of gill breathers and filter feeders, such as caddisflies, mayflies, stoneflies, and dipterans, were collected from less eutrophic areas.     

Spatial and temporal distribution of the zoobenthos community in a woodland pond (Switzerland)

Spatial and temporal changes of zoobenthos composition and density were assessed in a woodland pond, near Geneva (Switzerland), by monthly sampling (during 15 months), on the three main substrates: a submerged macrophyte (Chara sp.), an emergent macrophyte (Typha latifolia stems) and allochthonous detritus (oak leaves).Many taxa showed preferences for one or two of the substrates, as expressed by differences in densities, but few taxa presented an exclusivity for one substrate. Zoobenthos densities (per m² of pond bottom) were largely dominated on all substrates and seasons by Chironomidae and Oligochaeta. Other dense macroinvertebrates included Ostracoda (on Chara and Typha stems), Gastropoda (on Typha stems), Ephemeroptera (all substrates), and Ceratopogonidae (on Typha stems).The magnitude of temporal differences in densities was expressed by the ratio of maximal to minimal monthly densities and reached values between 2.8 to 11.8. On all substrates the highest monthly densities were observed in summer or beginning of autumn. The temporal changes in densities were strongly influenced by the life cycles of the invertebrates: presence of numerous young individuals in summer (for example Cypridopsis vidua, Cloeon dipterum, Caenis horaria, Ferrissia wautieri), and emergence (for example Chironomidae in April). Fluctuations in densities, especially on Chara and leaves, were also attributed to modification of substrate condition (surface availability, stage in the decomposition or senescence process). Temporal fluctuations of densities were compared with other lentic water bodies: highest densities showed a common trend, occurring between end of spring and beginning of autumn.     

Northern pike (<Emphasis Type="Italic">Esox lucius</Emphasis>) in a warming lake: changes in population size and individual condition in relation to prey abundance

The spring-fed Comal River in Texas, USA, has been impounded and channelized resulting mainly in a lentic environment with four headwater spring runs. We sampled two spring runs (lotic sites) and two lentic sites seasonally from April 2001 through April 2002 to assess (1) co-occurrence of native and exotic snail species (as determined by interspecific association), (2) the importance of habitat conditions in structuring relationships among these species, and (3) the distribution of snails infected with exotic trematode parasites. Three exotic and four endemic species of aquatic snails were collected, but only Elimia comalensis (Prosobranchia: Pleuroceridae, native), Melanoides tuberculatus, and Tarebia granifera (Prosobranchia: Thiaridae, exotic) were in sufficient densities for further analyses. Tarebia granifera was positively associated with both M. tuberculatus (χ² = 18.5, P < 0.001) and E. comalensis (χ² = 7.3, P < 0.01), although the co-occurrence between the two exotics was much stronger. Melanoides tuberculatus and E. comalensis exhibited a strong, negative association (χ² = 10.9, P < 0.001). The weaker co-occurrence between E. comalensis with the thiarids appeared to be driven by differences in habitat use by the thiarids and native E. comalensis. In lentic habitats, densities of M. tuberculatus and T. granifera were similar but differed significantly from E. comalensis whose densities were 200 times less than the exotic snails. In lotic spring runs, densities of T. granifera and E. comalensis were similar, but differed significantly from M. tuberculatus whose densities were 10 times fewer. Lower densities of M. tuberculatus and T. granifera in habitat conditions common to the spring runs may explain why exotic snail interactions were less with the native E. comalensis than with each other. The native snail, E. comalensis, was not infected with any trematodes, while 6.1% of M. tuberculatus and 4.8% of T. granifera were infected with exotic trematodes. Distributions of infected snails were aggregated; such that most infected snails were found in lentic habitats with silt substrates and moderate to high levels of detritus. Continued declines in spring-flows due to aquifer withdrawals and droughts will increase lentic habitats that may lead to increased densities of T. granifera and M. tuberculatus and their concomitant parasites. Handling editor: K. Martens     

长江中下游湖群大型底栖动物群落结构及影响因素

长江中下游地区是我国淡水湖泊分布最为密集的区域,其中面积大于10 km²的湖泊总面积占相同级别中国淡水湖泊总面积的51.3%。目前对本地区湖泊大型底栖动物研究主要是关于单个湖泊或几个湖泊之间的比较,将区域内湖泊作为一个整体来分析的研究较少。为揭示现阶段长江中下游浅水湖泊底栖动物群落现状及其主要影响因素,于2008年和2009年夏季对本地区5个湖群69个湖泊大型底栖动物和水化学进行了调查,并分析区域过程和局域环境条件在决定该地区底栖群落结构中的相对重要性。结果表明水体矿化度、电导率及氮磷指标在不同湖群间具有显著差异,而高锰酸盐指数、叶绿素a及营养状态指数无显著差异。密度方面,以寡毛类和摇蚊幼虫为优势类群的湖泊共46个,占总数量的66.7%,以螺类为优势类群之一的湖泊16个,占总数量的23.2%;生物量方面,以螺类为优势的湖泊数量最多(33个),占总数量的46.4%,但以寡毛类和摇蚊幼虫占优势的湖泊亦有27个,占总数量的39.1%,双壳类仅在9个湖泊占据优势。典范对应分析结果表明该地区底栖动物群落结构是局域环境条件和区域过程共同作用的结果,两类因子共解释了33.9%的底栖动物群落变异,其中局域环境因子占被解释量的48.1%,空间变量占35.4%。空间变量较高的解释量表明对整个长江中下游地区湖泊而言,区域过程对底栖动物的分布也起着非常重要的作用。     

The benthic macrofauna community of Kenyan waters of Lake Victoria

The benthic macroinvertebrates in the Kenya waters of Lake Victoria (ca. 1400 km²) were surveyed during four 10 day sampling periods in February, April, August and November 1984. Fourty three taxonomic groups were recorded. Oligochaetes, molluscs and dipteran larvae were the most abundant and widely distributed groups. The dominant oligochaetes were Branchiura sowerbyii Beddard and the swamp worm Alma emini Michaelsen, which were abundant in all silty and soft mud areas in both littoral and open water zones. Melanoides tuberculata Müller, Bellamya unicolor Olivier and Caelatura spp. were the most abundant molluscs. Different patterns were observed between near-littoral stations (<8 m deep) and deep water stations (8–40 m deep). After 10 years (1994), the macroinvertebrates of Lake Victoria were examined again. No evidence was found of seasonal changes in the composition or benthos density, although local changes occurred in some species which were attributed to swarming behaviour or larval settlement patterns. The spatial distribution of the fauna may be influenced primarily by oxygen availability and industrial effluent discharged from paper mill and agro-based industries in the catchment of the lake. There has been a shift in abundance, from an Oligochaeta and Insecta dominated community in 1984, to the present community dominated by Mollusca and Oligochaeta. The ecological role of the benthic community and its recent changes to fisheries production in the lake is discussed.     

Is <Emphasis Type="Italic">Nuphar lutea</Emphasis> (L.) Sm. a structuring factor for macrozoobenthos and selected abiotic parameters of water and bottom sediments throughout the year?

Studies on the role of nymphaeids in water bodies are uncommon, despite the fact that they often dominate in eutrophic lakes. Therefore, we decided to evaluate the effect of a nymphaeid Nuphar lutea on its environment. We hypothesised that its presence can increase the diversity and abundance of zoobenthos, as well as modify selected abiotic parameters, both during the growing season (in the presence of leaves) and outside it (with underground structures only). Three pairs of stations (within and outside Nuphar stands) were established in two shallow, eutrophic lakes and sampled monthly during an entire year. Zoobenthos taxon richness, biodiversity and total density were higher among nymphaeids throughout the year. On the other hand, total zoobenthos biomass was not affected by the presence of plants. Most macroinvertebrates reached higher densities within Nuphar stands, the most abundant being Polypedilum nubeculosum, Potamothrix bavaricus, Ephemeroptera and Ceratopogonidae. In turn, Potamothrix hammoniensis, Chaoborus sp. and Tanypus sp. were more abundant outside the stands. Other taxa, including the dominants (Chironomus sp., Procladius spp., Einfeldia dissidens, Valvata piscinalis), were not affected by the presence of Nuphar. Nuphar did not influence water temperature, oxygen concentration, and conductivity, though sediments within the stands exhibited lower water content and higher proportion of large organic particles. Thus, Nuphar effect on macroinvertebrates was probably direct, through increased habitat heterogeneity, physical stability of substratum and food availability. Our study has shown that nymphaeids, despite their structural distinctness, can affect positively bottom fauna similarly to other morphological groups of plants.     

Benthic invertebrates of Rutland Water

The colonisation of Rutland Water by benthic invertebrates has been monitored from 1976 when the reservoir was first filled. A modified Ekman grab was used to sample populations quantitatively while false substrates and dredge samples were used to obtain supplementary data. Hand net and hand-sorting were used to study the littoral zone.The dominant taxa in the reservoir are Asellus aquaticus, A. meridianus, Gammarus pulex, Crangonyx pseudogracilis, Helobdella stagnalis, Erpobdella octoculata, Polycelis tenuis, larval Chironomidae and Oligochaeta. Other species which appeared abundantly, such as Limnaea pereger and Planorbis albus, have now disappeared and it is suggested that the generally low levels of gastropods might account for the poor performance of species such as Dugesia lugubris and Glossiphonia complanata.Other aspects of abundance are discussed, as are the effects of maturation of the system.     

Development of the macro-invertebrate fauna of Cow Green reservoir (Upper Teesdale) in the first five years of its existence

SUMMARY. The development of marginal (shore-line), sub-littoral (3–6 m) and profundal (15–18 m) fauna was followed using timed collections in shallow water and artificial substrata in deeper regions. The reservoir started filling in July 1970 and was close to top water level in the autumn of that year. Samples in the marginal zone contained drowned terrestrial organisms and some Cladocera (Chydoridae) in February 1971 but by October, Chironomidae and Oligochaeta became abundant and micro-crustaceans (copepods and cladocerans) formed about 98% of the total catch. Peak densities of micro-crustaceans in the marginal zone were reached in the summer of 1971, but chironomids and oligochaetes were most abundant in the second year after filling. The numbers of marginal zone animals were greatest at the most sheltered site, and lowest at a site on the windward shore. At a stream mouth the rheophilic fauna present in April 1971 was replaced with limnophilic organisms (Chironomidae and Tubificidae) by September 1971. In the sub-littoral, Hydra, Enchytraeidae, Orthocladiinae Tanytarsini and oribatoid mites were the most abundant taxa, whereas Naididae, Hirudinea, Ostracoda, Gammarus pulex, Chironomini and Pisidium spp. were numerous in the profundal zone. Total faunal numbers and biomass were greatest in the profundal zone in all years. The highest annual mean estimate of biomass in the sub-littoral was 3.07 g (wet wt)m^?2 in the second year after filling, thereafter both numbers and biomass fell. In the profundal the maximum biomass (about 29 gm^?2) was observed in the third and fourth years after filling. An estimate of total standing crop of benthic organisms below the drawdown limit, made in July 1974, gave a figure of about 43 tonnes, wet weight. Biomass estimates at Cow Green were compared with those in eighteen other reservoirs and were found to be high especially in relation to those from other upland areas.     

Feeding ecology and habitat preferences of the catfish genus Trichomycterus in low‐order streams of the Colombian Andes

Six lower order streams in the south‐west of Colombia were sampled on a monthly basis in order to determine the status of Trichomycterus species in relation to their food supply (macroinvertebrates), and physico‐chemical habitat. Fishes were sampled by electrofishing and samples taken for dietary analysis. Macroinvertebrates were collected using a Surber sampler. Trichomycterus spp. populations were present in all streams in habitats ranging from soft to hard substrata and from relatively stagnant waters to fast flowing streams. The average density of the fishes ranged from 0·06 to 1·14 individuals m⁻² with peaks in population corresponding to recruitment of individuals of <1 g. Trichomycterus spp. were found to be benthic carnivores with a diet mostly of aquatic insects. The index of relative importance for the dietary items was 35·0, 10·5, 1·9 and 7·8% for Chironomidae, Trichoptera, Ephemeroptera and Oligochaeta respectively. Combined with physical habitat data, ordinations of fishes and macroinvertebrate data suggested that differences in abundance among sites were driven by stream size and flow regime, indicating dominance of the physical habitat, although a high correlation between Trichomycterus spp. and Chironomidae abundances ( r  = 0·81, P  = 0·049) was also recorded.     

Distribution of Chironomidae in a Semiarid Intermittent River of Brazil

The effects of the intermittency of water flow on habitat structure and substrate composition have been reported to create a patch dynamics for the aquatic fauna, mostly for that associated with the substrate. This study aims to describe the spatial distribution of Chironomidae in an intermittent river of semiarid Brazil and to associate assemblage composition with environmental variables. Benthic invertebrates were sampled during the wet and dry seasons using a D-shaped net (40?cm wide and 250???m mesh), and the Chironomidae were identified to genus level. The most abundant genera were Tanytarsus, Polypedilum, and Saetheria with important contributions of the genera Procladius, Aedokritus, and Dicrotendipes. Richness and density were not significantly different between the study sites, and multiple regression showed that the variation in richness and density explained by the environmental variables was significant only for substrate composition. The composition of genera showed significant spatial segregation across the study sites. Canonical Correspondence Analysis showed significant correspondence between Chironomidae composition and the environmental variables, with submerged vegetation, elevation, and leaf litter being important predictors of the Chironomidae fauna. This study showed that Chironomidae presented important spatial variation along the river and that this variation was substantially explained by environmental variables associated with the habitat structure and river hierarchy. We suggest that the observed spatial segregation in the fauna results in the high diversity of this group of organisms in intermittent streams.     

The stabilizing effect of resting egg banks of the <Emphasis Type="Italic">Daphnia longispina</Emphasis> species complex for longitudinal taxon heterogeneity in long and narrow reservoirs

The aim of this study was to determine the effect of monsoonal spates and land uses on abundance, richness, diversity, and evenness of benthic macroinvertebrates in streams, and whether these factors interacted with each other to influence community structure. Two groups of streams with different underlying disturbance profiles were studied. One group was in a native forest (non-degraded area) and experienced only spate, and the other group drained an area degraded by agriculture and cattle grazing, and so was subject to two types of disturbances. Spates produced a strong decline in invertebrate abundance and an increase in evenness, whereas changes in land uses caused an increase in abundance of tolerant taxa and a significant decline in richness, diversity, and evenness. Differences in richness and Oligochaeta abundance between land uses were mostly evident in the pre-spate period due to low water levels magnifying some physicochemical changes caused by ecosystem degradation. Canonical correspondence analysis indicated that degraded sites had the highest conductivity, nitrate, pH, and water temperature. Upstream non-degraded streams generally exhibited higher dissolved oxygen values. Taxa such as Psychodidae and Tipulidae, Camelobaetidius penai, Austrelmis spp. (adult), Macrelmis spp. (adult), and Marilia spp. dominated in non-degraded sites, while Tricorythodes popayanicus, Caenis ludicra, Dodecabates dodecaporus, Atractides sp., and Torrenticola columbiana were abundant in downstream degraded streams. These two groups of taxa may be useful biological indicators of water quality in streams of northwestern Argentina.