Hydropsychid Caddisflies Research Articles

The Grand Caddis hatch of JASM 2022: Trichoptera natural history observations at the Joint Aquatic Sciences Meeting in Grand Rapids, Michigan ( USA )

In a stroke of good luck for aquatic scientists and insect enthusiasts, the May 2022 Joint Aquatic Sciences Meeting (JASM) in Grand Rapids, Michigan coincided with a spectacular hatch of hydropsychid caddisflies. To estimate density, we enumerated caddisflies on 12 polarized window panels on the western face of the DeVos Place, which faced the Grand River. We found an average of 57.8 caddisflies per 2.0 × 2.3 m window panel (density of 12.6 caddisflies m−2). We observed American robins, swallows, sparrows, and jumping spiders preying and scavenging during the hatch. We also describe here our observations of a novel precopulatory behavior in the species Hydropsyche morosa, which we describe as a “head-to-tail” position. We discuss our natural history observations and share thoughts on how conferences can be a springboard for networking and collaborative science, natural history-focused or otherwise.

Effects of Trace Metals and Municipal Wastewater on the Ephemeroptera, Plecoptera, and Trichoptera of a Stream Community.

Simple SummaryMayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera) (EPT) are aquatic insects that are well known to the general public and are commonly used as indicators of environmental quality in water management. Knowledge of how EPT communities react to human-induced gradients in real environments can be important, for example, during the assessment of the implications of newly planned or currently active human disturbances for natural or cultural landscapes. We sampled a stream ecosystem affected by mining and smelting industries and communal wastewaters with pronounced concentrations of cadmium, lead, and zinc, as well as high levels of pesticides, pharmaceuticals, illegal drugs, and sewage-derived organic matter. Changes in other environmental factors such as increases in temperature were also studied at the affected sites. The abundance and species richness of stoneflies fell rapidly at the study sites. The richness of mayfly families also declined, from four to one, even though overall mayfly abundance was not affected. Conversely, the abundances of caddisflies were higher at the affected sites, and their richness did not decrease. This study will provide feedback for ecotoxicologists who perform better controlled and manipulated tests in laboratories, although any such test results are limited by simple artificial environments.Abundances of EPT larvae sampled in a Central European locality affected by mining and smelting, as well as by the continual inflow of treated communal wastewaters (WWs), were recorded. High concentrations of trace metals in water (maximum 1200 µg·L–1 for zinc) and sediments (maximum 140,000 mg·kg–1 in dry weight for lead) were found at the most contaminated sites. The highest loads of pesticides, pharmaceuticals, and illegal drugs were found under the WW effluent. Other associated factors such as the physicochemical parameters of the water and alterations to microhabitats were also evaluated and taken into account. Although EPT richness was lower at affected sites, abundances did not fall. Stoneflies were dominant at unaffected sites, while caddisflies dominated at affected sites. Only baetid mayflies were detected at the sites contaminated by trace metals and WWs; ephemerellid, heptageniid, and leptophlebiid mayflies were absent from these sites. The site contaminated by trace metals was also inhabited by numerous limnephilid caddisflies, in which limb malformations were detected in up to 11.8% of all specimens of a single taxon. Downstream from the entrance of the WWs, the locality was dominated by hydropsychid caddisflies. The increasing prevalence of predator or passive filter-feeding strategies in these EPT communities was significantly related to increasing water conductivity and acute ecosystemic exposure to ‘poorly treated’ WWs.

Does stream current modify crayfish impacts on a benthic community?

Non-native crayfish can have impacts on stream communities that are highly variable. A possible explanation for this variability is that crayfish are responding in a context-dependent manner to variation in environmental factors. Among the most critical environmental factors in streams is current velocity. Moving water defines lotic ecosystems and many benthic organisms, including crayfish, respond to its influence. To examine how current velocity affected the impacts of non-native Orconectes rusticus crayfish on benthic communities, we conducted a cage-enclosure experiment in a Wisconsin stream. We hypothesized that current velocities > 50 cm s−1 would decrease the effects that O. rusticus had on community composition (macroinvertebrate richness and numbers) and physical structure (sediment accumulation). Three cage enclosure treatments (open, closed crayfish and closed control) were grouped into eight replicate blocks divided equally among streambed regions of slow (< 50 cm s−1) and fast (> 50 cm s−1) current. Open cages allowed resident crayfish access, closed crayfish cages contained one O. rusticus, and closed controls had no crayfish. After three weeks, crayfish cages had lower macroinvertebrate abundance and richness and less sediment accumulation. Current velocity showed a positive relationship to macroinvertebrates in general, and a negative relationship to sediment build-up. The most common macroinvertebrates were hydropsychid caddisflies that responded to O. rusticus in a context-dependent manner such that cages containing crayfish had decreased hydropsychid numbers in fast current, but not in slow. Open cage treatments showed a similar pattern, suggesting that natural crayfish densities in the stream were also sufficient for lowering hydropsychid numbers in fast current. Our study demonstrates that current velocity may provide an important context for understanding the effects that O. rusticus have on benthic communities, not just in terms of what these crayfish do, but how the benthic communities respond to their presence.

Evaluating potential effects of bigheaded carps on fatty acid profiles of multiple trophic levels in large rivers of the Midwest, USA

Recent work indicates that the establishment of bigheaded carps (Hypophthalmichthys spp.) in the United States has led to a reduction in condition of native planktivores and may detrimentally affect other trophic levels by altering the base of aquatic food webs. We used fatty acids to evaluate potential effects of bigheaded carps on taxa from multiple trophic levels in the Upper Mississippi, Illinois, and St. Croix rivers. Seston fatty acid concentrations were highest in the Illinois River lotic sites and connected backwaters and were positively associated with omega-3 highly unsaturated fatty acids, indicating that these locations had abundant, high-quality basal food resources despite hosting the greatest bigheaded carp densities. Fatty acid profiles of threeridge freshwater mussels tracked the fatty acid values in the seston and were not influenced by bigheaded carp abundances. Hydropsychid caddisflies and bluegill did not differ significantly in total fatty acids or percent lipid among spatial locations, indicating that omnivorous species may be relatively unaffected by bigheaded carps. Gizzard shad, however, exhibited the lowest fatty acid concentrations in the locations with the highest relative bigheaded carp densities, and multivariate models identified bigheaded carp densities as the predictive factor that explained the greatest amount of variability. Zooplankton abundance has been greatly reduced after bigheaded carps' establishment in the Illinois River, which may explain the disconnect between the gizzard shad fatty acids and the plentiful, high-quality phytoplankton in that river. Our data provide additional evidence that bigheaded carps are negatively affecting native planktivores such as gizzard shad.

Spatial and temporal variance in fatty acid and stable isotope signatures across trophic levels in large river systems

AbstractFatty acid and stable isotope signatures allow researchers, managers, and policy makers to better understand food webs, food sources, and trophic relationships. Research in marine and lentic systems has indicated that the variance of these biomarkers can exhibit substantial differences across spatial and temporal scales, but this type of analysis has not been completed for large river systems. Our objectives were (a) to evaluate variance structures for fatty acids and stable isotopes (i.e., δ13C and δ15N) of seston, threeridge mussels, hydropsychid caddisflies, gizzard shad, and bluegills across spatial scales (10s–100s of km) in large rivers of the Upper Mississippi River Basin, USA, that were sampled annually for 2 years and (b) to evaluate the implications of this variance on the design and interpretation of trophic studies. The greatest variance for both stable isotopes was present at the largest spatial scale for all taxa (except seston δ15N), indicating that these isotopic signatures are responding to factors at a larger geographic level rather than being influenced by local‐scale alterations. Conversely, the greatest variance for fatty acids was present at the smallest spatial scale (i.e., among individuals) for all taxa except caddisflies, indicating that the physiological and metabolic processes that influence fatty acid profiles can differ substantially between individuals at a given site. Our results highlight the need to consider the spatial partitioning of variance during sample design and analysis, as some taxa may not be suitable for use in assessing ecological questions at larger spatial scales.

Incorporating macroinvertebrate biological structures into gravel-bedded stream fluid dynamics using 3D CFD modelling

In gravel-bedded streams and rivers, silk nets of hydropsychid caddisfly larvae (Trichoptera:Hydropsychidae) can increase the critical shear stress, τ∗c, required for sediment particle motion, reduce bedload flux, and provide a low flow refuge for other organisms. However, there is still a limited understanding of the mechanisms that regulate how biological silk structures might influence near-bed fluid dynamics. Part of the challenge in identifying both the per capita and population level influences of caddisfly silk nets lies in the difficulty of modelling such fine-scale and detailed architecture of the structures. Here, we use a 3D computational fluid dynamics (CFD) model to evaluate the impact of silk nets on shear stress and pore space velocity by varying silk net aerial density within a modelled gravel bedded stream where the silk nets are simulated as small rigid bodies of realistic distribution, geometry, and orientation. The model revealed that silk net densities of 330 and 735 nets/m2 reduce the average shear stresses by an average 6.0% and 11.6%, respectively, over a range of inflow velocities. Silk nets also result in near-bed flows close to 0 m/s by reducing velocity by up to 60%. Our research sheds light on the important influence of small but numerous aquatic animals on water flow paths and highlights the significance of adding biological complexity into water flow models in lotic ecosystems to improve erosion models that may be used in river channel and riparian habitat design.

Environmental and spatial characterisation of an unknown fauna using DNA sequencing – an example with Himalayan Hydropsychidae (Insecta: Trichoptera)

Summary Ecological studies of freshwater biota in understudied regions are often obstructed by poor taxonomic knowledge. We posit that molecular tools can help alleviate this issue and present an example where we combined molecular tools, environmental data and ecological statistics to investigate the distribution and community ecology of an unknown fauna of hydropsychid caddisflies along altitudinal gradients in four Himalayan river systems of Central and Eastern Nepal. A total of 484 larval specimens from 34 tributaries were examined. Phylogenetic analysis of the mitochondrial cytochrome c oxidase I (COI) and the nuclear ribosomal RNA 28S were used to delineate molecular operational taxonomic units (MOTUs) applying three analytical methods: general mixed Yule‐coalescent (GMYC) model, Automatic Barcode Gap Discovery (ABGD) and Bayesian Phylogenetics and Phylogeography (BPP). Spatial distributional patterns and potential differences in ecological niches among MOTUs were statistically tested using regression and correlation approaches. Further, we examined the data for signs of non‐random structure in MOTU communities. MOTU diversity within the family of Hydropsychidae was generally high but varied across evaluated gene fragments and slightly among delineation methods. Yet, the subsequent evaluation of environmental and spatial drivers and resulting distributional patterns were highly consistent among the different MOTU estimates. Within each river system, we found community composition varied greatly along the altitudinal gradients, with many MOTUs associated with specific altitudinal ranges. Prevalent MOTU turnover at the river system scale indicated high β‐diversity in the hydropsychid community leading to high degrees of regional endemism. In the Langtang river system, we found fewer MOTU co‐occurrences than expected by chance. These results highlight the utility of DNA‐based approaches using variable genetic markers (mitochondrial or ribosomal nuclear) for primary biodiversity assessment of poorly studied groups or regions. Our study further shows that DNA‐based biodiversity measures are suitable for downstream applications, such as exploring fundamental questions in stream ecology.

Notes on the ecological roles of Podostemum ceratophyllum Michx., 1803 and Cladophora glomerata (L.) Kütz., 1843 in the habitat and diet of riverine hydropsychid caddisflies (Trichoptera)

ABSTRACTLarvae of net-spinning Hydropsychidae caddisflies (Trichoptera) are common inhabitants of lotic systems and are typically categorised as filtering-collectors, but feeding habits vary in response to the availability of food resources. This study addressed two questions. First, are Hydropsyche simulans Ross, 1938 and Cheumatopsyche Wallengren, 1891 found in higher densities in patches of the macrophyte Podostemum ceratophyllum Michx., 1803? Second, do H. simulans and Cheumatopsyche spp. assimilate the filamentous alga Cladophora glomerata (L.) Kütz., 1843 during a late summer bloom? Cladophora glomerata standing stocks increased during summer, coincident with increasing water temperatures and decreasing flow. Densities of both hydropsychid taxa were significantly greater in high (> 75% cover) P. ceratophyllum habitat. A multisource mixing model (IsoSource) using carbon and nitrogen stable isotope data showed that C. glomerata was the prominent assimilated dietary item during August and September. Overall, hydropsychid caddisfly larvae showed a clear habitat association with P. ceratophyllum and the capacity to assimilate C. glomerata when this resource is abundant during summer base-flow conditions.

Resilience of aquatic net‐spinning caddisfly silk structures to common global stressors

SummaryTwo of the most common consequences resulting from land use and climate change are increased fine sediment loads and shifts in hydrological regimes in freshwater ecosystems.Although a growing number of studies indicate that these stressors are likely to directly affect community composition and organism physiology, little is known about how biological structures produced by aquatic organisms might respond. For example, hydropsychid caddisflies (Trichoptera) are a group of globally distributed aquatic insects that spin silk mesh nets that they use to filter feed. These silk mesh nets are important ecosystem engineering structures in flowing waters that can regulate sediment erosion, food particle delivery by altering near‐bed current velocities, and enhance habitat availability for other macroinvertebrates.We conducted two experiments in laboratory mesocosms to assess the effects of increased fine sediment and drought on hydropsychid caddisfly silk. We compared silk thread diameter, thread count, mesh pore area, and thread tensile strength across treatments in which the silk nets were exposed to high levels of total suspended solids or to stream drying over 2 weeks.We found that caddisfly silk was resilient to both forms of stress and maintained its overall structure and tensile strength.Our findings indicate that biological silk structures may be viable ecosystem engineering tools following short‐lived disturbances associated with increased sediment loads and drying events. Caddisfly silk may be resilient to various forms of environmental change, with important consequences for recovery of aquatic communities.

Stream macroinvertebrate communities across a gradient of natural gas development in the Fayetteville Shale

Oil and gas extraction in shale plays expanded rapidly in the U.S. and is projected to expand globally in the coming decades. Arkansas has doubled the number of gas wells in the state since 2005 mostly by extracting gas from the Fayetteville Shale with activity concentrated in mixed pasture-deciduous forests. Concentrated well pads in close proximity to streams could have adverse effects on stream water quality and biota if sedimentation associated with developing infrastructure or contamination from fracturing fluid and waste occurs. Cumulative effects of gas activity and local habitat conditions on macroinvertebrate communities were investigated across a gradient of gas well activity (0.2–3.6wells per km2) in ten stream catchments in spring 2010 and 2011. In 2010, macroinvertebrate density was positively related to well pad inverse flowpath distance from streams (r=0.84, p<0.001). Relatively tolerant mayflies Baetis and Caenis (r=0.64, p=0.04), filtering hydropsychid caddisflies (r=0.73, p=0.01), and chironomid midge densities (r=0.79, p=0.008) also increased in streams where more well pads were closer to stream channels. Macroinvertebrate trophic structure reflected environmental conditions with greater sediment and primary production in streams with more gas activity close to streams. However, stream water turbidity (r=0.69, p=0.02) and chlorophyll a (r=0.89, p<0.001) were the only in-stream variables correlated with gas well activities. In 2011, a year with record spring flooding, a different pattern emerged where mayfly density (p=0.74, p=0.01) and mayfly, stonefly, and caddisfly richness (r=0.78, p=0.008) increased in streams with greater well density and less silt cover. Hydrology and well pad placement in a catchment may interact to result in different relationships between biota and catchment activity between the two sample years. Our data show evidence of different macroinvertebrate communities expressed in catchments with different levels of gas activity that reinforce the need for more quantitative analyses of cumulative freshwater-effects from oil and gas development.

Bioaccumulation of arsenic and silver by the caddisfly larvae Hydropsyche siltalai and H. pellucidula: A biodynamic modeling approach

Biodynamic modeling was used to investigate the uptake and bioaccumulation of arsenic and silver from water and food by two Hydropsychid caddisfly larvae: Hydropsyche siltalai and Hydropsyche pellucidula. Radiotracer techniques determined the uptake rate constants of arsenic and silver from water, and assimilation efficiencies from food, and their subsequent loss rate constants after accumulation from either route. The uptake rate constants (±SE) of As and Ag from solution were 0.021±0.005 and 0.350±0.049Lg−1day−1, respectively, for H. siltalai, and 0.435±0.054 and 0.277±0.021Lg−1day−1, respectively, for H. pellucidula in moderately hard synthetic water at 10°C. The assimilation efficiencies (±SE) of As and Ag from radiolabeled ingested food were 46.0±7.7% and 75.7±3.6%, respectively, for H. siltalai, and 61.0±4.2% and 52.6±8.6%, respectively, for H. pellucidula. Ag, but not As, AEs were significantly different between species. The AE of Ag differed from the AE of As in H. siltalai, but not in H. pellucidula. Mean efflux rate constants after accumulation of metals from solution or food ranged from 0.039 to 0.190day−1. The efflux rate constants of As and Ag accumulated from solution were significantly lower than those of As and Ag assimilated from ingested food in both species. Experimentally derived ku and ke values were then used to predict As and Ag tissue concentrations in hydropsychids collected from 13 UK sites, including metal-contaminated streams in Cornwall. Arsenic and silver concentrations in environmental water and food (suspended particles) samples were measured. Biodynamic models successfully predicted accumulated As and Ag concentrations in resident H. siltalai and H. pellucidula at each site. The models also showed that more than 95% of accumulated As and almost 100% of accumulated Ag in H. siltalai and H. pellucidula are derived from ingested food rather than from water.

High secondary production in a Coastal Plain river is dominated by snag invertebrates and fuelled mainly by amorphous detritus

Summary The 2‐years production dynamics of major taxa (family/order) and functional feeding groups was synthesised from detailed production analyses previously published for all major invertebrate species/genera (retained by a 100 μm sieve) found on snags (submerged wood) in a sixth‐order south‐eastern U.S. Coastal Plain river. The trophic basis of this production and annual consumption of six food types were quantified. Invertebrate production (148 and 203 g dry mass m−2 year−1 of snag surfaces for the 2 years) was among the highest ever measured for a specific habitat in non‐polluted or unregulated rivers and was still relatively high when converted to overall area of the river bed (48 and 70 g m−2 year−1). Snag production constituted 73% of total main‐channel production (production from snag and river bed combined). Chironomidae (40–44% over the 2 years), Ephemeroptera (14–21%) and Trichoptera (25–31%) together represented the majority (88–93%) of the putative production of primary consumers on snags. Functional group analysis showed that fine filterers (26–36% over the 2 years), gatherers (36–44%) and macro‐filterers (21–25%) represented the majority of total invertebrate production. Production of predaceous insects (mostly Plecoptera, Odonata and Megaloptera) represented only 5–7% of the total. Production of the three major taxa and three major functional groups was remarkably consistent over 2 years of monthly sampling, despite strong seasonal variation in discharge/light/temperature and production of individual genera and families. Seventy‐nine per cent of production by primary consumers was supported by microbially enriched amorphous detritus, the major component of seston originating primarily from floodplain forests. Invertebrates consumed ˜357 g AFDM m−2 (river bed) year−1 of seston, 325 g m−2 year−1 of amorphous detritus and 20 g m−2 year−1 of diatoms. Dividing seston consumption by seston transport indicated that ˜67% of seston was consumed over 100 km of river length. Consumption was higher than autochthonous net primary production, supporting other evidence that terrestrially derived dissolved organic matter, incorporated via the microbial loop, is the main trophic basis of this riverine food web. Macro‐filtering hydropsychid caddisflies were omnivorous with &gt; half their production from carnivory. Snag predators, including hydropsychids, consumed ˜60% (29 g m−2 year−1 of river bed) of invertebrate production (assumed to be from snags), leaving the remainder for emergence, downstream transport and consumption by fish.

Non-additive increases in sediment stability are generated by macroinvertebrate species interactions in laboratory streams.

Previous studies have shown that biological structures such as plant roots can have large impacts on landscape morphodynamics, and that physical models that do not incorporate biology can generate qualitatively incorrect predictions of sediment transport. However, work to date has focused almost entirely on the impacts of single, usually dominant, species. Here we ask whether multiple, coexisting species of hydropsychid caddisfly larvae have different impacts on sediment mobility compared to single-species systems due to competitive interactions and niche differences. We manipulated the presence of two common species of net-spinning caddisfly (Ceratopsyche oslari, Arctopsyche californica) in laboratory mesocosms and measured how their silk filtration nets influence the critical shear stress required to initiate sediment grain motion when they were in monoculture versus polyculture. We found that critical shear stress increases non-additively in polycultures where species were allowed to interact. Critical shear stress was 26% higher in multi-species assemblages compared to the average single-species monoculture, and 21% greater than levels of stability achieved by the species having the largest impact on sediment motion in monoculture. Supplementary behavioral experiments suggest the non-additive increase in critical shear stress may have occurred as competition among species led to shifts in the spatial distribution of the two populations and complementary habitat use. To explore the implications of these results for field conditions, we used results from the laboratory study to parameterize a common model of sediment transport. We then used this model to estimate potential bed movement in a natural stream for which we had measurements of channel geometry, grain size, and daily discharge. Although this extrapolation is speculative, it illustrates that multi-species impacts could be sufficiently large to reduce bedload sediment flux over annual time scales in streams where multiple species of caddisfly are present.

Differences between kick sampling techniques and short-term Hester-Dendy sampling for stream macroinvertebrates

Abstract. Differences among sampling techniques are of crucial importance when interpreting the results of aquatic biomonitoring studies. We compared two commonly used variations of the kick sampling technique with the Hester-Dendy (multi-plate substrate) technique in an urban impacted stream. The effect of sample pooling on data interpretation was also examined. Hand scrubbing and disrupting substrates yielded more hydropsychid caddisflies than either kick sampling or Hester-Dendy samples. Total macroinvertebrate abundance, species richness, and Shannon's diversity (H') were all lower in Hester-Dendy samples than in samples taken by kick sample or by hand scrubbing substrates. Species richness pooled within sampling technique was highest in kick samples and lowest in Hester-Dendy samples. Richness of Ephemeroptera, Plecoptera, and Trichoptera (EPT) pooled among sampling techniques was higher in Hester-Dendy samples than in either kick samples or substrate-scrubbed samples. Relatively subtle differences a...

Influence of Dissolved Organic Carbon on Methylmercury Bioavailability across Minnesota Stream Ecosystems

Stream ecosystems are widely contaminated by mercury (Hg) via atmospheric transport and deposition in watersheds. Dissolved organic carbon (DOC) is well-known to be the dominant ligand for aqueous methylmercury (MeHg), the bioaccumulative form of Hg in aquatic food webs. However, it is less clear if and how the concentration and character (e.g., aromaticity) of DOC influences the availability of dissolved MeHg to stream food webs. In this work, we analyzed total-Hg and/or MeHg concentrations in water, seston, and macroinvertebrates (filter-feeding hydropsychid caddisflies), and other physiochemical properties in 30 streams along a south-north geographic gradient in eastern Minnesota that corresponds to substantial changes in dominant land cover (i.e., agriculture, urban, wetland, and forest). In general, MeHg concentrations in seston and hydropsychids were higher in watersheds with more forest and wetland coverage, and increased with dissolved MeHg concentration. However, we found that the efficiency of MeHg incorporation into the stream food webs (i.e., bioconcentration factors of MeHg in both seston and hydropsychids, BCF(MeHg) = solid MeHg ÷ dissolved MeHg) decreased significantly with DOC concentration and aromaticity, suggesting that MeHg bioavailability to the base of food webs was attenuated at higher levels of terrestrial DOC. Therefore, our findings suggest that there is a dual role of DOC on MeHg cycling in streams: terrestrial DOC acts as the primary carrier ligand of dissolved MeHg for transport into surface waters, yet this aromatic DOC also attenuates dissolved MeHg uptake by aquatic food webs. Thus, consideration of MeHg bioavailability and its environmental regulation could help improve predictive models of MeHg bioaccumulation in stream ecosystems.

Long-Term Benthic Macroinvertebrate Community Monitoring to Assess Pollution Abatement Effectiveness

The benthic macroinvertebrate community of East Fork Poplar Creek (EFPC) in East Tennessee was monitored for 18 years to evaluate the effectiveness of a water pollution control program implemented at a major United States (U.S.) Department of Energy facility. Several actions were implemented to reduce and control releases of pollutants into the headwaters of the stream. Four of the most significant actions were implemented during different time periods, which allowed assessment of each action. Macroinvertebrate samples were collected annually in April from three locations in EFPC (EFK24, EFK23, and EFK14) and two nearby reference streams from 1986 through 2003. Significant improvements occurred in the macroinvertebrate community at the headwater sites (EFK24 and EFK23) after implementation of each action, while changes detected 9 km further downstream (EFK14) could not be clearly attributed to any of the actions. Because the stream was impacted at its origin, invertebrate recolonization was primarily limited to aerial immigration, thus, recovery has been slow. As recovery progressed, abundances of small pollution-tolerant taxa (e.g., Orthocladiinae chironomids) decreased and longer lived taxa colonized (e.g., hydropsychid caddisflies, riffle beetles, Baetis). While assessments lasting three to four years may be long enough to detect a response to new pollution controls at highly impacted locations, more time may be needed to understand the full effects. Studies on the effectiveness of pollution controls can be improved if impacted and reference sites are selected to maximize spatial and temporal trending, and if a multidisciplinary approach is used to broadly assess environmental responses (e.g., water quality trends, invertebrate and fish community assessments, toxicity testing, etc.).

Environmental flow allocations in monsoonal Hong Kong

1. Hong Kong streams are subject to aggressive water extractions but the downstream water needs of ecosystems – i.e. environmental flow (e-flow) requirements – have not yet been addressed. This study investigated hydro-ecological relationships that could be used to establish e-flow allocations for streams in monsoonal Hong Kong. 2. Data were collected during the wet and dry seasons from 10 unpolluted streams experiencing a gradient of flow reductions (c. 0–98%). Relationships between flow conditions (percentage discharge reduction and absolute discharge volume) and responses of macroinvertebrate composition and periphyton condition were established for each season. 3. Declines in richness of Ephemeroptera and abundance of hydropsychid caddisflies, as well as increases in the proportion of predators, were linearly related to percentage discharge reduction during both seasons. Relationships were also recorded for eight other macroinvertebrate richness or compositional metrics during the dry season only. Relationships between macroinvertebrate assemblage attributes and absolute discharge volume across downstream reaches were also evident. Periphyton was relatively insensitive to flow reductions and did not provide useful hydro-ecological relationships, although declines in autotrophic index were related to percentage discharge reduction during the dry season. 4. Using hydro-ecological relationships established for macroinvertebrates, two levels of e-flow were proposed: a ‘threshold’ intended to maintain near-natural conditions and a ‘degradation limit’ that allowed no more than 25% of the maximum indicator response to flow reduction. Calculated threshold e-flows required downstream allocation of ≥74% of natural flows; degradation limit e-flows were ≥12% (wet) and ≥27% (dry). The discharge needed to maintain threshold conditions was 30–105 L s−1 (wet) and 5–14 L s−1 (dry), with degradation limit e-flows of 19–57 L s−1 (wet) and 3–6 L s−1 (dry), relative to natural mean discharges of 77–303 L s−1 (wet) and 3–18 L s−1 (dry). 5. The proposed e-flow allocations are indicative only, and significant obstacles to implementation have yet to be surmounted. Any such implementation requires monitoring of outcomes in order to refine the allocations and inform adaptive flow management for Hong Kong streams.

Physical properties and structure of aquatic silk fiber from Stenopsyche marmorata

To study the properties and structure of aquatic silk, nest-spinning hydropsychid caddisfly ( Stenopsyche marmorata) larva were collected from a Japanese river and the silk glands were removed from the larva by dissecting and dried on the glass plate at room temperature. The silk fibers were obtained by removing fibrous materials, which the aquatic insects spun at the bottom of glass container and the microstructure and physical properties of aquatic silk protein fibres and their solid silk protein gland were evaluated. Silk fiber produced by the caddisfly larvae is composed of two filament embedded in a layer of glue. The results of Fourier transform infrared spectroscopy and X-ray diffraction measurements suggested the existence of binary structure containing random coil conformation and additional minor β-molecular structure. Differential scanning calorimetry results are characterized by two broad endothermic transitions, at 230 °C and 320 °C, which corresponds to the decomposition of silk glue and silk fiber from caddis fly, respectively. The storage modulus ( E′) remained almost unchanged and nearly constant at above 60 °C until about 214 °C, where it began to show a sharp drop. A prominent relaxation peak appeared in the imaginary part of the modulus (loss peak at 230 °C), in response to the strong motional transitions exhibited by the silk fiber at this temperature. There was significant difference of tensile strength of single solid silk protein gland in dry and wet state. The results obtained are quite promising as a basis for possible future biotechnological and adhesive applications of aquatic silk.

Monitoring the health of large rivers with macroinvertebrates: Do dominant taxa help or hinder the assessment?

AbstractMacroinvertebrate communities in the Mississippi River are often dominated by a few taxa (e.g. oligochaetes in the fine sediments and hydropsychid caddisflies on rocks) that exploit the natural abundance of fine organic particles. These taxa are moderately to highly tolerant of pollution, and the combination of high abundance and high pollution tolerance could result in the river being assessed as highly polluted. We examined how the presence or absence of dominant oligochaetes or hydropsychid caddisflies affected biometric values and responses used to monitor environmental stress in large rivers. Responsiveness was assessed across five simulated impairments created by removing different subsets of sensitive taxa from the original data for macroinvertebrates in the Upper Mississippi River near Cape Girardeau, MO. For many metrics, removal of the dominant taxa changed values, and increased the difference between existing conditions and simulated impairments. For macroinvertebrate data from fine‐sediment habitat, 8–9 of 12 metrics responded to the two most severe impairments simulated with or without dominant oligochaetes, but none changed for less severe impairments. For rock habitat, more metrics responded to moderate or severe impairments simulated when dominant hydropsychids were excluded. Few metrics performed better with dominant taxa. Overall, removal of dominant macroinvertebrate taxa improved both the accuracy and interpretability of several metrics commonly used to monitor effects of water pollution on large‐river faunas dominated by a few taxa. Removing them also makes observed responses more comparable to those frequently quantified for wadeable streams and rivers. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Coping with Saltwater: The Condition of Aquatic Insects in Estuaries as Determined by Gut Content Analysis

The immature stages of freshwater insects can sometimes be found in densities of up to 25,000 m -2 in saltwater- inundated regions of estuaries, however little is known of their condition there. The gut fullness and contents of larvae of two species of hydropsychid caddisfly (Hydropsyche siltalai and H. instabilis) from freshwater and saltwater-inundated sites on the Aber Estuary, Wales were compared in an attempt to assess if the insects were functioning normally, or were in a degraded state after having been displaced downstream by the current. The findings suggest that the downstream lar- vae were in some ways functioning normally (i.e., attaching to rocks, spinning catch-nets, ingesting locally available food), although the lesser amounts of food contained in their guts (half-full or less) likely indicate that these downstream populations were existing in suboptimal conditions. Further data, for example, on growth rates and success at pupation and adult emergence, will be required to determine if such saltwater inundated populations are truly viable.