Shifts in the community composition of caddisflies (Insecta: Trichoptera) in a subtropical river over three decades

1. Trichoptera is an ecologically and taxonomically diverse order, and caddisfly species are under increasing pressure from anthropogenic threats to larval habitats, rivers, and streams. 2. This study evaluated long-term changes in caddisfly communities of the Ogeechee River, a subtropical blackwater river in the south-eastern U.S. Coastal Plain, to understand how changes manifest as a result of ongoing human impacts. Two datasets separated by more than 30 years were used, each representing a 2-year monthly quantitative sampling effort (1981–1983; 2015–2017). 3. Community structure of the Ogeechee River caddisflies significantly changed, though not in ways that were predicted. The average sensitivity values of the caddisfly community declined, contrary to the expectation that increasing human impacts on a river ecosystem would promote the survival of more pollution-tolerant taxa. 4. Generic richness increased in the 2010s from the 1980s, perhaps as a result of relaxed competition following declines of large, dominant taxa. The increases in various taxa have resulted in similar overall abundance metrics between time periods, although other studies of Ogeechee River invertebrates indicate that the biomass of the new taxa is far lower than that produced by the assemblages of the 1980s. Functional richness, evenness, and dispersion were higher in the 2010s, but divergence was not. 5. This suggests that more nuanced monitoring efforts, focused on the threats to ecological function and the role of caddisflies (and other sensitive freshwater organisms), will be required to evaluate the changes in community structure and determine which taxa are most adversely affected.     

Lipid Metabolism of Caddisfly Larvae at Low pH

The influence of low pH (5.0 and 4.0) on lipid metabolism of caddisfly larvae Hydropsyche contubernalis L. (Trichoptera) was studied in 48 h toxicity experiments. The results were correlated with lipid composition of caddisfly larvae directly isolated from natural water. Phospholipids, cholesterol, mono-, di-, triacylglycerols, and fatty acids were detected by thin-layer and liquid chromatography. Minimal environmental changes were shown to initiate the biochemical adaptation mechanisms strengthening the cellular membranes through their condensation due to additional phospholipid and cholesterol synthesis. In the natural medium the adaptation processes are more active than in the artificial medium. More serious changes, such as pH decrease to 4.0, suppress the adaptation processes in the first medium and terminate them in the second one.     

Longitudinal river zonation in the tropics: examples of fish and caddisflies from the endorheic Awash River,Ethiopia

Specific concepts of fluvial ecology are well studied in riverine ecosystems of the temperate zone but poorly investigated in the Afrotropical region. Hence, we examined the longitudinal zonation of fish and adult caddisfly (Trichoptera) assemblages in the endorheic Awash River (1,250 km in length), Ethiopia. We expected that species assemblages are structured along environmental gradients, reflecting the pattern of large-scale freshwater ecoregions. We applied multivariate statistical methods to test for differences in spatial species assemblage structure and identified characteristic taxa of the observed biocoenoses by indicator species analyses. Fish and caddisfly assemblages were clustered into highland and lowland communities, following the freshwater ecoregions, but separated by an ecotone with highest biodiversity. Moreover, the caddisfly results suggest separating the heterogeneous highlands into a forested and a deforested zone. Surprisingly, the Awash drainage is rather species-poor: only 11 fish (1 endemic, 2 introduced) and 28 caddisfly species (8 new records for Ethiopia) were recorded from the mainstem and its major tributaries. Nevertheless, specialized species characterize the highland forests, whereas the lowlands primarily host geographically widely distributed species. This study showed that a combined approach of fish and caddisflies is a suitable method for assessing regional characteristics of fluvial ecosystems in the tropics.

     

Ecological and historical filters constraining spatial caddisfly distribution in Mediterranean rivers

1. Contemporary species distributions are determined by a mixture of ecological and historical filters acting on several spatial and temporal scales. Mediterranean climate areas are one of the world's biodiversity hotspots with a high level of endemicity, which is linked to complex ecological and historical factors. 2. This paper explores the ecological and historical factors constraining the distribution of caddisfly species on a large regional scale. A total of 69 taxa were collected from 140 sampling sites in 10 Iberian Mediterranean river basins. Approximately 74% of taxa can be considered rare, with the southern basins (the Baetic–Riffian region) having greater endemicity. The greatest richness, involving a mixture of northern and southern species, was found in the transitional area between the Baetic–Riffian region and the Hesperic Massif. 3. The historical processes occurring during the Tertiary (i.e. the junction of the Eurasian and African plates) explained 3.1% of species distribution, whereas ecological factors accounted for 20.7%. Only 0.3% was explained by the interaction of history and ecology. A set of multi‐scale ecological variables (i.e. basin, reach and bedform characteristics) defined five river types with specific caddisfly assemblages. The commonest caddisfly species accounted for the regional distribution pattern, while rare taxa contributed to the explanation of subtle patterns not shown by common species. 4. Despite the importance of historical factors for biogeography and the large scale used in our study, ecological variables better explained caddisfly distribution. This may be explained by the length of time since the historical process we are considering, the high dispersion and colonisation capacity of many caddisfly species, and the strong environmental gradient in the area. Because of the historical and environmental complexity of Mediterranean areas, rare taxa should be included in ecological studies so that the singularity of these ecosystems is not missed.     

Nonlinear effects of consumer density on multiple ecosystem processes

1.?In the face of human-induced declines in the abundance of common species, ecologists have become interested in quantifying how changes in density affect rates of biophysical processes, hence ecosystem function. We manipulated the density of a dominant detritivore (the cased caddisfly, Limnephilus externus) in subalpine ponds to measure effects on the release of detritus-bound nutrients and energy. 2.?Detritus decay rates (k, mass loss) increased threefold, and the loss of nitrogen (N) and phosphorus (P) from detrital substrates doubled across a range of historically observed caddisfly densities. Ammonium and total soluble phosphorus concentrations in the water column also increased with caddisfly density on some dates. Decay rates, nutrient release and the change in total detritivore biomass all exhibited threshold or declining responses at the highest densities. 3.?We attributed these threshold responses in biophysical processes to intraspecific competition for limiting resources manifested at the population level, as density-dependent per-capita consumption, growth, development and case : body size in caddisflies was observed. Moreover, caddisflies increasingly grazed on algae at high densities, presumably in response to limiting detrital resources. 4.?These results provide evidence that changes in population size of a common species will have nonlinear, threshold effects on the rates of biophysical processes at the ecosystem level. Given the ubiquity of negative density dependence in nature, nonlinear consumer density-ecosystem function relationships should be common across species and ecosystems.     

Current known range of the Platte River caddisfly, Ironoquia plattensis, and genetic variability among populations from three Nebraska Rivers

The Platte River caddisfly (Ironoquia plattensis Alexander and Whiles 2000) was recently described from a warm-water slough along the Platte River in central Nebraska and was considered abundant at the type locality. Surveys of 48 sites in 1999 and 2004 found eight additional sites with this species on the Platte River. The caddisfly was not found at the type locality in 2004 and one additional site in 2007, presumably because of drought conditions. Because of its apparent rarity and decline, the Platte River caddisfly is a Tier I species in Nebraska. For this project, surveys for the caddisfly were conducted at 113 new and original sites primarily along the Platte, Loup, and Elkhorn Rivers between 2009 and 2011. These surveys identified 30 new sites with the caddisfly. Larval densities were quantified at a subset of inhabited sites, and there was a large variation of densities observed. Seven sites on other Nebraska drainages were found to support morphologically similar caddisflies, presumably the Platte River caddisfly. Because of the discovery of populations outside the Platte River drainage, amplified fragment length polymorphism (AFLP) was used to determine the amount of genetic variability and breeding among sites on the Platte, Loup, and Elkhorn Rivers. Analysis of molecular variance (AMOVA) suggested moderate gene flow among the three river systems and that there was more genetic variation within populations than between populations. Differentiation, but not total divergence, was exhibited by the northernmost population from the Elkhorn River. Because it may be considered an indicator species and is vulnerable to ongoing habitat loss and degradation, all Platte River caddisfly populations should be conserved.     

Assessing stream dwelling caddisfly assemblages (Insecta: Trichoptera) collected by light traps in Hungary

In the present study the conservation status of light trap-collected stream dwelling caddisfly assemblages was evaluated on the basis of original data and also from the literature representing different regions in Hungary. Altogether the catches of eight complete seasons were compared. Species richness, diversity and endangerment indices as well as a newly introduced rarity index (RI) expressing the average rarity of the collected species in Hungary were calculated to evaluate the conservation status of the streams in the Bakony, Börzsöny and Bükk Mountains and in the Zala Hills. The results highlight the importance of streams in maintaining endangered species of caddisfly in Hungary and bring to attention the fact that species richness or diversity are not necessarily the best indicators of conservation status of caddisfly assemblages. Indicators, for instance RI, which take into consideration the general rarity of the species seem to reflect more sharply conservation status and thus are more appropriate for the assessment of caddisfly assemblages.     

Environmental variables interact across spatial scales to structure trichopteran assemblages in Ouachita Mountain rivers

An important goal in aquatic ecology is to determine the interacting variables that regulate community structure; however, complex biotic and abiotic interactions coupled with the significance of scale have confounded the interpretation of community data. We evaluated stream and riparian habitat features in southeastern Oklahoma, USA at a range of spatial scales from local, in-stream variables to large-scale, regional characteristics to address the following questions: (1) How much variation in trichopteran community composition can be attributed to local, regional, and spatial variables? and (2) What environmental variables are most important in determining trichopteran community structure? We collected data on caddisfly community structure, local and regional environmental variables, and spatial location on the landscape from 25 sites in four rivers. We analyzed these data using canonical correspondence analysis (CCA) and variation partitioning. Our analysis explained approximately 60% of the variation in caddisfly community composition. We found that local and regional environmental variables were near equal in importance in governing caddisfly communities, with each accounting for approximately a quarter of the explained variation. Although pure spatial variables were less important, the amount of variation shared among spatial variables and local and regional variables was substantial, indicating that biogeographic history is also key to understanding caddisfly distributions. We also found a strong influence of human landuse (i.e., percent of land in agriculture, distance to roads) on caddisfly community composition. Our study indicated that communities are influenced by factors across scales, and that bioassessments should focus on not only local habitat conditions, but also incorporate larger-scale factors.     

Spatial and Temporal Pattern of Caddisfly Distribution at a Mesohabitat Scale in two Patagonian Mountain Streams Subjected to Pastoral Use

Substrate, flow type, nutrients, aquatic vegetation, organic matter, and caddisfly community structure were studied at two low order streams (Glyn and Nant y Fall) subjected to pastoral use in the Patagonian mountains. At both sites, we examined the effect of habitat type (boulder‐pebble with and without filamentous algae, cobble‐pebble, gravel‐sand, leaf‐pack, the submerged macrophytes Myriophyllum quitense and Isoetes savatieri) and season (high and low water period) on caddisfly assemblages. Benthic particulate organic matter (BPOM) ranged between 4.6 and 472 g m^–2, all allochtonous detrital fractions were significantly higher at leaf‐packs at Glyn, whereas M. quitense habitats supported more BPOM and macrophytes biomass at Nant y Fall. As expected, boulder‐pebble sustained higher Trichoptera richness than M. quitense and gravel‐sand, moreover all habitats showed higher density than M. quitense at Nant y Fall. According to our results at least nine caddisfly species exhibited some habitat preference with boulder‐pebble and cobble‐pebble the most selected habitat. These particular habitats sustained more than 68% of the total caddisfly species. Multidimensional scaling ordination highlighted differences in composition per habitat for both sites showing a clear distinction among depositional and erosional habitats. Substrate, flow type, detritus biomass were important predictors defining assemblages. Based upon our findings, those anthropogenic actions or stressors that change hydraulic as well substrate attributes in mountain streams such as stock trampling, dredging, clearing of riparian areas, will reduce caddisfly richness. These results are relevant for outline management and conservation biomonitoring and schemes in headwater Patagonian streams as well as other similar environments worldwide (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spatial Distribution and Coexistence Patterns of Caddisfly Larvae (Trichoptera) in a Hungarian Stream

It is well known that stream macroinvertebrates usually show aggregated spatial distributions caused by extrinsic factors and interactions among species and individuals. In the present study, the spatial distribution of caddisfly assemblages and coexistence patterns of larval caddisfly species (Insecta: Trichoptera) were measured in a Hungarian stream reach at three different spatial scales. Caddisfly assemblages showed aggregated, random and regular distributions as measured by the variance‐mean relationship of species richness as sampling area increased from 0.0225 m² to 0.2025 m². The observed coexistence patterns indicated interactions (lower diversity of unique species combinations than expected by chance) among species for aggregated distributions. These interactions among species proved to be positive associations particularly among species belonging to the same functional feeding group. The positive associations and the aggregated distribution of caddisflies supported the hypothesis that microhabitat patches (patchy microhabitat‐macroinvertebrate model) and/or positive biological interactions among species using the same resource (hypothesis of facilitation) have a deterministic effect on the spatial distribution of caddisfly assemblages. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Water temperature determines strength of top-down control in a stream food web

1. We examined effects of water temperature on the community structure of a three trophic level food chain (predatory fish, herbivorous caddisfly larvae and periphyton) in boreal streams. We used laboratory experiments to examine (i) the effects of water temperature on feeding activities of fish and caddisfly larvae and on periphyton productivity, to evaluate the thermal effects on each trophic level (species‐level experiment), and (ii) the effects of water temperature on predation pressure of fish on abundance of the lower trophic levels, to evaluate how temperature affects top‐down control by fish (community‐level experiment). 2. In the species‐level experiment, feeding activity of fish was high at 12 °C, which coincides with the mean summer temperature in forested streams of Hokkaido, Japan, but was depressed at 3 °C, which coincides with the mean winter temperature, and also above 18 °C, which coincides with the near maximum summer temperatures. Periphyton productivity increased over the range of water temperatures. 3. In the community‐level experiments, a top‐down effect of fish on the abundance of caddisfly larvae and periphyton was clear at 12 °C. This effect was not observed at 3 and 21 °C because of low predation pressure of fish at these temperatures. 4. These experiments revealed that trophic cascading effects may vary with temperature even in the presence of abundant predators. Physiological depression of predators because of thermal stress can alter top‐down control and lead to changes in community structure. 5. We suggest that thermal habitat alteration can change food web structure via combinations of direct and indirect trophic interactions.     

Implications of anthropogenic disturbance factors on the Trichoptera assemblage in a Mediterranean fluvial system: Are Trichoptera useful for identifying land-use alterations?

From autumn 2005 to spring 2008, a study focusing on the collection of Trichoptera larvae was conducted in the catchment of the Guadiamar River (SW Spain). The distribution of caddisfly species in relation with environmental factors was examined. Four groups of species were recognised according to the environmental gradient. A direct ordination analysis (CCA) used to describe assemblage changes among sites corroborated that conductivity, land-use, geomorphological gradient, and temporality were the variables that best explain the Trichoptera distribution, but to establish the relative influence of the land-use variables was difficult. On the other hand, mining pollution appeared to be the main factor explaining Trichoptera community structure. In April 1998 this river system underwent an accidental release of a large mass of toxic mine waste, which exterminated macroinvertebrates in the middle and lower parts and floodplain. Several years later, caddisfly communities in these areas were different from those of unaffected upper reaches. The species assemblage was especially poor in lower river reaches that underwent the permanent, diffuse urban and agricultural pollution. These conditions were tolerated only by Hydropsyche exocellata Duföur.     

Predator defense along a permanence gradient: roles of case structure, behavior, and developmental phenology in caddisflies

Species replacements along freshwater permanence gradients are well documented, but underlying mechanisms are poorly understood for most taxa. In subalpine wetlands in Colorado, the relative abundance of caddisfly larvae shifts from temporary to permanent basins. Predators on caddisflies also shift along this gradient; salamanders (Ambystoma tigrinum nebulosum) in permanent ponds are replaced by predaceous diving beetles (Dytiscus dauricus) in temporary habitats. We conducted laboratory and field experiments to determine the effectiveness of caddisfly cases in reducing vulnerability to these predators. We found that larvae of a temporary-habitat caddisfly (Asynarchus nigriculus) were the most vulnerable to salamanders. Two relatively invulnerable species (Limnephilus externus, L. picturatus) exhibited behaviors that reduced the likelihood of detection and attack, whereas the least vulnerable species (Agrypnia deflata) was frequently detected and attacked, but rarely captured because cases provided an effective refuge. Vulnerability to beetle predation was also affected by cases. The stout cases of L. externus larvae frequently deterred beetle larvae, whereas the tubular cases of the other species were relatively ineffective. Two of these vulnerable species (A. nigriculus and L. picturatus) often co-occur with beetles; thus, case construction alone is insufficient to explain patterns of caddisfly coexistence along the permanence gradient. One explanation for the coexistence of these two species with beetles is that they develop rapidly during early summer and pupate before beetle larvae become abundant. One species (L. picturatus) pupates by burying into soft substrates that serve as a refuge. The other (A. nigriculus) builds stone pupal cases, which in field experiments, more than doubles survival compared to organic pupal cases. The combined results of these experiments suggest that caddisfly distributions along permanence gradients depend on a suite of primary and secondary predator defenses that include larval and pupal case structure, predator-specific escape behaviors, and the phenology of larval development.     

Spatial structure of the caddisfly (Insecta,Trichoptera) communities in a river basin in NW Spain affected by coal mining

The changes in caddisfly community structure and composition in the Sil River basin (NW Spain), associated with a gradient in natural conditions and a succession of alterations induced by human activity (mainly urban wastes and coal mining), were studied. Twenty-nine Trichoptera taxa belonging to 11 families were collected. The community diversity analysis showed important spatial differences from source to mouth. Towns and, above all, coal mines produced an increase in sulphate and chloride concentrations and conductivity, which adversely affected the trichopteran assemblages. A stepwise regression model, which introduced sulphate and chloride as variables, explained the changes in diversity produced in the basin (r=0.837, p< 0.01). The lowest diversity and richness values were recorded in the rivers suffering the greatest impact from coal mining or urban wastes. The heterogeneity values of the communities for the main rivers were clearly different. The greatest community heterogeneity corresponded to the main axis of the basin and was explained by spatial variability in water chemical composition. No relation was detected between structural changes at spatial level and geographical distance, such that pollution processes basically controlled the dynamics of the Trichoptera communities. Partial-CCA using distance from the source as a covariable revealed alkalinity and urban and mining-derived pollution as the main factors influencing caddisfly distribution. However, an ordination of sites in relation to the corresponding vectors did not fully agree with the chemical characteristics of the water. The species composition of the Trichoptera communities, therefore, did not seem to be good indicators of the chemical features of the rivers. The structure of the community (as expressed by richness and the Shannon index) appeared to be the better indicator of pollution.     

Seston capture by Hydropsyche siltalai and the accuracy of capture efficiency estimates

1. Suspension feeding by caseless caddisfly larvae (Trichoptera) constitutes a major pathway for energy flow, and strongly influences productivity, in streams and rivers. 2. Consideration of the impact of these animals on lotic ecosystems has been strongly influenced by a single study investigating the efficiency of particle capture of nets built by one species of hydropsychid caddisfly. 3. Using water sampling techniques at appropriate spatial scales, and taking greater consideration of local hydrodynamics than previously, we examined the size‐frequency distribution of particles captured by the nets of Hydropsyche siltalai. Our results confirm that capture nets are selective in terms of particle size, and in addition suggest that this selectivity is for particles likely to provide the most energy. 4. By incorporating estimates of flow diversion around the nets of caseless caddisfly larvae, we show that capture efficiency (CE) is considerably higher than previously estimated, and conclude that more consideration of local hydrodynamics is needed to evaluate the efficiency of particle capture. 5. We use our results to postulate a mechanistic explanation for a recent example of interspecific facilitation, whereby a reduction of near‐bed velocities seen in single species monocultures leads to increased capture rates and local depletion of seston within the region of reduced velocity.     

Tufa Barriers from a Caddisfly's Point of View: Streams or Lake Outlets?

The caddisfly community composition in different microhabitats at tufa barriers was studied in the Plitvice Lakes NP, Croatia. Three tufa barriers were investigated and six emergence traps were installed at each site covering various microhabitats. Sampling was conducted monthly during the year 2008. Tufa barriers are lake outlet habitats, but they feature a variety of microhabitats similar to streams, which is reflected in the composition of caddisfly communities regarding longitudinal distribution preferences. The caddisfly communities at all three sites were dominated by species typical for the rhithral zone, but there was a shift in species composition along a longitudinal gradient, from the epirhithral to the metarhithral zone. Analysis of functional feeding guilds showed considerable differences between the caddisfly community at the Labudovac barrier and both downstream barriers, shifting from one with a quite diverse composition, to one completely dominated by passive filter‐feeders. Passive filter feeders were not represented by the same taxa at up‐ and downstream barriers (i.e., by Hydropsyche species and Wormaldia species, at the Labudovac barrier and at both downstream barriers, respectively). Due to high complexity and habitat diversity, the highest diversity and equitability of caddisfly communities were recorded at microhabitats with particulate tufa and medium current velocity (10–20 cm/s). The lowest diversity and species richness were recorded for silt with low current velocity (0–10 cm/s). Abundance of caddisflies was positively correlated with current velocity due to a very high proportion of rheophilic passive filter feeders in the communities. However, community composition and structure is only to some degree influenced by microhabitat characteristics, but rather by their general position within the barrage‐lake system, i.e., longitudinal distribution and thereby availability of different food resources. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The consumption of eggs of the perch, Perca fluviatilis L., by macroinvertebrates in the field

SUMMARY. 1. Perch egg masses, in a late stage of development, were collected from a small stillwater and the composition of the egg masses and the number of invertebrates which colonized them was recorded.
2. All of the invertebrates that colonized the egg masses were tested serologically for the presence of perch eggs and the ability of some invertebrates to eat live and dead perch eggs in the laboratory was determined.
3. Of the nineteen taxa that colonized the egg masses, only two species of flatworm and three species of caddisfly larva ate perch eggs in the field and, of these, only one genus of caddisfly larva ate live eggs in the laboratory.
4. It is concluded that the invertebrates present were not important predators of perch eggs.     

Aquatic insects in an estuarine environment: densities, distribution and salinity tolerance

1. Aquatic insects were quantitatively surveyed at five sites along the tidally influenced section of a river-dominated estuary in North Wales. Site 1 was the furthest upstream and was established as a reference site as it was never inundated by salt water. Site 5 was the furthest downstream and was inundated by all incoming tides. Numerically, insects made up 32% of the estuarine invertebrate fauna. 2. Although the densities of most insect taxa decreased towards the estuary mouth, there were significant numbers present downstream for much of the year; for example, in April at site 4 (which was inundated by 81% of all high tides), a mean of 3514 chironomid larvae were recorded per m² of estuary bed. Even at site 5, which was inundated twice daily, there were 747 larvae per m². Among the larger aquatic insects, caddisfly and elmid beetle larvae, together with stonefly nymphs, were consistently taken at site 4 (e.g. maxima of forty-eight caddisfly larvae m^–2 in December and seventy elmids m^–2 in April), although their densities were lower than upstream. 3. There were seasonal shifts in the longitudinal distribution of several taxa, most notably the extension of chironomids down the estuary in April and July, and the concentration of simuliid larvae and mayfly nymphs at site 2 in July. The total freshwater benthos showed a downstream shift between September and December, which was maintained through April and into the summer. The latter was despite peak saltwater inundation (highest tides) in October, November and April. In June and July, when saltwater intrusion was lowest, the ranges of many aquatic insects had contracted to sites 1 and 2. 4. Laboratory experiments showed that virtually all individuals of nineteen species of insects collected from site 1 (freshwater) survived a 4-h immersion in 8.75‰ saltwater (25% strength seawater). Immersion in progressively more saline solutions reduced the survivorship of first the mayflies, followed by the caddisflies Glossosoma conformis and Hydropsyche instabilis. After 4 h in full strength seawater, all specimens of the stonefly Dinocras cephalotes, over half of the Perla bipunctata, and some individuals of nine species of caddisfly were alive. Four species of caddisfly (Sericostoma personatum, Odontocerum albicorne, Potamophylax cingulatus and Adicella reducta) survived a 24-h simulated tidal cycle of immersion. With the exception of P. cingulatus, a few individuals of these caddisfly species survived immersion in full-strength seawater for 24 h. For some individual species there was good agreement between their observed longitudinal distribution in the estuary and laboratory-measured salinity tolerance; however, there was no significant correlation, overall, for the fauna.     

The effect of drought on benthic invertebrate communities in a lowland river

Benthic macroinvertebrates were sampled at regular intervals from rural and urban sections of the River Roding, Essex, England, in 1975 and 1976. During the latter year a severe drought led to a marked decline in flows and to desiccation of parts of the river bed. In general, drought conditions resulted in an increase in invertebrate populations and possible reasons for this are presented. A considerable number of individuals of certain groups such as cased caddisfly larvae and prosobranch molluscs were, however, eliminated from the river at this time, mainly as a result of stranding and chemical changes in the environment. The effect of reduced flows on river faunas is briefly discussed.     

Caddisflies (Trichoptera) as good indicators of environmental stress in mountain lotic ecosystems

We analysed the influence of environmental stress (mainly deforestation of catchment due to windstorm) on taxonomic structure as well as composition of functional groups (FG) based on zonation preferences and feeding types of caddisfly species in 11 streams (12 sites) with various environmental conditions situated in the High Tatra Mts, Slovakia. Using Spearman correlation, we confirmed an expected positive association between taxonomic and functional groups richness (Ri), diversity (Shannon — Wiener Index) (Di) and equitability (Eq), but not with habitat diversity (HQA indices). By testing measured physiographical, physico-chemical and hydromorphological factors using CCA analysis we found that stream order and temperature best explained the functional and taxonomic structure of caddisfly assemblages. The occurrence of Rhyacophila glareosa decreased with increasing daily mean water temperature positively correlated with deforestation, whereas R. tristis (dominating at sites most affected by erosion) showed the opposite pattern. Composition of functional groups based on zonation preferences and feeding types distinguished well near natural sites from impacted ones, dominated by crenal/rhithral predators, and explained more of the overall variance of the species-environment relationships than taxonomic composition of caddisfly assemblages.