Sericostoma Personatum Research Articles

Enlarging the Arsenal of Test Species for Sediment Quality Assessment

Since only a few standard benthic test species are available for sediment quality, our study aimed to employ multiple test species representing different sensitivity categories in the quality assessment of contaminated sediments. To this end three macroinvertebrate species, Sericostoma personatum (caddisfly, sensitivity category 10), Asellus aquaticus (isopod, category 3) and Chironomus riparius (chironomid, category 2), were exposed to sediments originating from various contamination sources in whole sediment bioassays using intact sediment cores. The agricultural sediment caused insect mortality, the agricultural and urban sediment caused isopod growth reduction and the urban and Wastewater Treatment Plant (WWTP) sediment affected chironomid emergence time. It is concluded that the arsenal of standard species can be successfully expanded by non-standard species, reducing over- or underestimation of the risks of contaminated sediments.

Aquatic Insect Bioconstructions Modify Fine‐Sediment Entrainment and Mobility

AbstractThe importance of two‐way interactions between animals and the physical hydraulic and sedimentological environment are increasingly recognized (e.g., zoogeomorphology). Caddisflies (Trichoptera) are a group of aquatic insects known for their bioconstructions, particularly cases built from fine sediment and silk. Caddisfly cases differ in size, shape and density from the incorporated sediment, and case construction may therefore affect the mobility of these sediments in rivers. However, although communities of caddisfly often use substantial quantities of sediment in case construction, the effect of these bioconstructions on sediment transport in rivers is unknown. We use a flume experiment to compare the bed shear stress required to transport (a) empty caddisfly cases and (b) individual sediment particles, following disaggregation from the case. The cases of three species were considered; two that construct different styles of tubular case (Potamophlax latipennis and Sericostoma personatum) and one that builds a domed case (Agapetus fuscipes). P. latipennis and S. personatum cases were easier to entrain than the sediment grains incorporated into them, whilst A. fuscipes cases were not. Despite their low mass, A. fuscipes cases required the most shear stress to transport them because their domed shape impeded rolling. These findings are important to understand how differences in case design between species, reflect different adaptation strategies to the turbulent hydraulic river habitat. Furthermore, the results suggest that un‐attached tubular caddisfly cases may be preferentially transported over other particles on the river bed and thus, where caddisfly occur in high abundance, they may increase fluvial entrainment of sand.

When barcoding fails: development of diagnostic nuclear markers for the sibling caddisfly species Sericostoma personatum (Spence in Kirby & Spence, 1826) and Sericostoma flavicorne Schneider, 1845.

The larval stages of the central European sibling caddisfly species Sericostoma personatum (Spence in Kirby and Spence, 1826) and S. flavicorne Schneider, 1845 are morphologically similar and can only be distinguished by differences in coloration in late larval instars. Identification using the mitochondrial barcoding gene, i.e., the Cytochrome c Oxidase 1, is impossible, as both species share the same highly differentiated haplotypes due to introgression. Nuclear gene markers obtained through double digest restriction site associate sequencing (ddRAD seq), however, can reliably distinguish both species, yet the method is expensive as well as time-consuming and therefore not practicable for species determination. To facilitate accurate species identification without sequencing genome-wide markers, we developed nine diagnostic nuclear RFLP markers based on ddRAD seq data. The markers were successfully tested on geographically distinct populations of the two Sericostoma species in western Germany, on known hybrids, and on another sericostomatid caddisfly species, Oecismus monedula (Hagen, 1859) that sometimes shares the habitat and can be morphologically confounded with Sericostoma. We describe a simple and fast protocol for reliable species identification of S. personatum and S. flavicorne independent of the life cycle stage of the specimens.

The complete mitochondrial genome of the long-horned caddisfly Triaenodes tardus (Insecta: Trichoptera: Leptoceridae)

The long-horned caddisfly Triaenodes tardus Milne, 1934 (Leptoceridae), is a widespread herbivorous North American caddisfly found in both lentic and lotic habitats. Whole genome Illumina sequencing allowed the assembly of a complete circular mitogenome of 14,963 bp from T. tardus consisting of 73.4% AT nucleotides, 22 tRNAs, 13 protein-coding genes, two rRNAs and a control region in the ancestral insect gene order. Triaenodes tardus COX1 features an atypical TTG start codon as in some lepdioptera and prokaryotes. Phylogenetic reconstruction places T. tardus as sister to Sericostoma personatum (Sericostomatidae) within a monophyletic Order Trichoptera, which is consistent with previous phylogenetic hypotheses.

The larva of Schizopelex huettingeri Malicky 1974 (Trichoptera: Sericostomatidae), including a preliminary key to the Sericostomatidae larvae of the Hellenic western Balkan region

This paper presents a description of the hitherto unknown larva of Schizopelex huettingeri Malicky 1974 (Trichoptera: Sericostomatidae). We provide information on the morphology of the larva and figure the most important diagnostic features. Schizopelex huettingeri can be easily separated from Oecismus monedula (Hagen 1859), Sericostoma flavicorne Schneider 1845, and Sericostoma personatum (Kirby & Spence 1826) by the shape of the pronotum, the lack of a comma-like marking on the lateral protuberance, and by the number of setae on abdominal dorsum IX. With respect to distribution, S. huettingeri is an endemic of European Ecoregion 6 (= Hellenic western Balkan region), inhabiting the mountains of Central Greece. Ecological characteristics of the species are briefly discussed, and a preliminary key to the hitherto known Sericostomatidae larvae of European Ecoregion 6 is included.

The mitochondrial genomes of the caddisflies Sericostoma personatum and Thremma gallicum (Insecta: Trichoptera)

The mitochondrial genomes of the caddisfly species Sericostoma personatum and Thremma gallicum were sequenced on a 454 FLX and Illumina MiSeq platform, respectively. Reads were assembled de novo and remaining gaps in the S. personatum mitogenome closed by Sanger sequencing. The lengths of the assembled mitogenomes were 15,260 bp and 15,343 bp for S. personatum and T. gallicum, respectively. Both mitogenomes contained all 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes, and the control region. The mitochondrial gene order of both caddisflies is identical with the typical insect gene order. These are the third and fourth published mitogenomes of the order Trichoptera of two formerly unexplored families and thus will be useful in future phylogenetic analysis.

Fast reaction of macroinvertebrate communities to stagnation and drought in streams with contrasting nutrient availability

AbstractSmall, permanent streams are at risk of becoming stagnant or intermittent because of hydrological changes induced by climate change, which can be further intensified by anthropogenic disruptions, such as water abstraction. Macroinvertebrate communities are vulnerable to such changes because they depend on stream hydromorphological regime. We conducted a fully controlled field experiment in 1 impacted and 1 unimpacted Danish lowland stream with contrasting nutrient availability. We used dams and diversions to create short-term (2–10 wk) stagnant and drought conditions, and we installed pools in the drought area to test their value as refugia for benthic macroinvertebrates. After 2 wk, community composition had changed significantly in all treatments in both streams. The abundance of Chironomidae increased and the abundance of mayflies (Baetis rhodani), stoneflies (Amphinemura standfussi, Leuctra nigra), caddisflies (Silo pallipes, Sericostoma personatum), the amphipod Gammarus pulex, and some Dipte...

Temperature increase and respiratory performance of macroinvertebrates with different tolerances to organic pollution

Respiration rates (mg O 2 g −1 AFDW h −1 ) of Leuctra hippopus , Sericostoma personatum , Helodes minuta , Gammarus pulex and Asellus aquaticus were studied across an oxygen gradient at 2.8 and 6.3 °C, corresponding to an expected 3.5 °C increase in Danish winter stream temperature. Species were selected from the Danish Stream Fauna Index (DSFI), representing an expected hierarchy of tolerance towards water quality degradation. We expected that low-ranking, tolerant species (i.e. indicators of bad water quality) would have the capacity to regulate their oxygen uptake relatively independently of oxygen availability (oxy-regulators) and high-ranking, sensitive species (i.e. indicators of good water quality) would be less able to do so (oxy-conformers). For all species respiration rate was higher (although non-significantly) at 6.3 °C. The species’ oxy-regulatory capacity did not consistently reflect their DSFI ranking. As expected, and in accordance with its DSFI ranking, A. aquaticus had the highest oxy-regulatory capacity with the ability to regulate O 2 uptake until an oxygen saturation of only 20%, which did not change with increasing temperature, emphasizing the robustness of A. aquaticus towards changes in the environment. S. personatum , H. minuta and G. pulex revealed no oxy-regulatory capacity. In contrast, the plecopteran L. hippopus did display an unexpected oxy-regulatory capacity. Though an increase in temperature changed L. hippopus ’ capacity to oxy-regulate (the critical limit increased from 32.5 to 43.5% oxygen), respiration rates did not change significantly in spite of the temperature increase. This result contradicts the general belief that stoneflies, because of their affinity to well oxygenated habitats, are conformers. Our findings call for further studies on the respiratory conformer–regulator concept and its role as an eco-physiological trait for bio-assessment.

Occurrence of Sediment-Bound Pyrethroids in Danish Streams and their Impact on Ecosystem Function

In a total of 189 water samples collected from Danish streams no traces of the pyrethroid esfenvalerate were detected. However, pyrethroids have previously been found in sediments in 9 out of 30 streams investigated. We found that the shredding activity of the Trichopteran Sericostoma personatum and the amphipod Gammarus pulex was significantly reduced with increased concentration of the pyrethroid lambda-cyhalohtrin adsorbed to the leaves on which they fed. Predation rate on the Plecopteran Leuctra nigra by the leech Erpobdella octoculata increased significantly with increasing concentration of lambda-cyhalothrin on the leaves on which L. nigra was fed. Our results clearly indicate that the ongoing monitoring of pesticides is likely to underestimate pyrethroid occurrence and that sediment-bound pyrethroids have a potential negative impact on ecosystem function and biotic interactions in streams.

Using aquatic macroinvertebrate species traits to build test batteries for sediment toxicity assessment: Accounting for the diversity of potential biological responses to toxicants

An original species-selection method for the building of test batteries is presented. This method is based on the statistical analysis of the biological and ecological trait patterns of species. It has been applied to build a macroinvertebrate test battery for the assessment of sediment toxicity, which efficiently describes the diversity of benthic macroinvertebrate biological responses to toxicants in a large European lowland river. First, 109 potential representatives of benthic communities of European lowland rivers were selected from a list of 479 taxa, considering 11 biological traits accounting for the main routes of exposure to a sediment-bound toxicant and eight ecological traits providing an adequate description of habitat characteristics used by the taxa. Second, their biological and ecological trait patterns were compared using coinertia analysis. This comparison allowed the clustering of taxa into groups of organisms that exhibited similar life-history characteristics, physiological and behavioral features, and similar habitat use. Groups exhibited various sizes (7-35 taxa), taxonomic compositions, and biological and ecological features. Main differences among group characteristics concerned morphology, substrate preferendum and habitat utilization, nutritional features, maximal size, and life-history strategy. Third, the best representatives of the mean biological and ecological characteristics of each group were included in the test battery. The final selection was composed of Chironomus riparius (Insecta: Diptera), Branchiura sowerbyi (Oligochaeta: Tubificidae), Lumbriculus variegatus (Oligochaeta: Lumbriculidae), Valvata piscinalis (Gastropoda: Valvatidae), and Sericostoma personatum (Trichoptera: Sericostomatidae). This approach permitted the biological and ecological variety of the battery to be maximized. Because biological and ecological traits of taxa determine species sensitivity, such maximization should permit the battery to better account for the sensitivity range within a community.

The influence of stream water temperature on size and weight of caddisflies (Insecta, Trichoptera) along the Breitenbach 1983-1991

Competing hypotheses that try to relate population size, individual weight, and water temperature in running waters were tested. Female and male dry weight and specimen numbers of eleven caddisfly species (Trichoptera) collected from 1983 to 1991 in four emergence traps along the Breitenbach (Germany) were related to site specific water temperatures. Water temperature along the stream showed the classical pattern, almost constant near the source and increasing annual variability downstream. Temperature sum (dd = degree days) increased downstream; sums of the last three, six and nine months had a clear seasonality, twelve months sums were almost constant. Greatest upstream-downstream differences occurred in autumn and winter. Comparison of Trichoptera was based on yearly abundance and weight data. Females were heavier in all species but Potamophylax cingulatus. Among sites, weight differences were not detected for Apatania fimbriata. Silo pallipes, Tinodes rostocki, Plectrocne-mia conspersa and for P. cingulatus (♂) and Rhyacophila fasciata (♂) at least in stream sections where they occurred regularly and abundantly. Weight differences were usually significant only between the uppermost or the lowermost, and the remaining sites along the stream. Sericostoma personatum exhibited an almost site by site weight increase downstream. Drusus annulatus (♂, ♀), R. fasciata (9) and P. cingulatus (♀) were lightest at the downstream site, where only R. fasciata occurred regularly. C. villosa (♂, ♀). Potamophylax luctuosus (♂), S. personatum (♂) and Agapetus fuscipes (♂) were lightest at the uppermost site. No single hypothesis explained all results. High individual and population success (high weight or abundance) as predicted by the 'Thermal Equilibrium Hypothesis' occurred in D. annulatus, P. cingulatus and P. luctuosus. In contrast, high abundance and low weight occurred in C. villosa and S. personatum. Individual success seems to depend on a specific fit of genetic pre-adaptations, appropriate physiographical and ecological conditions, and competitive ability; it is not necessarily connected with population success.

Shredder guilds in three Danish forest streams contrasting in forest type

We investigated the impact of riparian vegetation type on shredder guilds in three similarly sized Danish forest streams during the period 1992-1994. One stream drained beech forest (Fagus sylvatica L.), one drained mixed, mainly deciduous forest, and one drained conifer plantations. Temperature was lowest in the conifer stream reflecting the high degree of shading during winter. The standing stock of coarse particulate organic matter (CPOM) differed only slightly among streams, although CPOM quality differed more markedly. Leaf litter respiration rates differed significantly among streams, being lowest in the conifer stream. The shredder guild was comprised of 9 species, of which only Nemoura flexuosa AUBERT. was present in all 3 streams. In terms of biomass, the dominant shredders were the amphipod Gammarus pulex L. and the trichopteran Sericostoma personatum SP. in the deciduous streams, and the plecopteran Nemurella picteti KLP. in the conifer stream. Shredder biomass was significantly higher in the two deciduous streams than in the conifer stream. The condition index expressed as mass: head width ratio was significantly lower for Leuctra nigra (OLV.) and N. flexuosa in the conifer stream than in the deciduous streams. Total shredder guild production was 5982 mg m -2 yr -1 in the beech stream, 4681 mg m -2 yr -1 in the mixed deciduous stream and 1310 mg m -2 yr -1 in the conifer stream. Our results thus suggest that forest stream shredder guilds are influenced by forest type, and apparently attributable to a combination of factors including water temperature and chemistry, and the quality of the available food resource. If low secondary production of the shredder guild is a general feature of streams draining conifer plantation forest, it could have important implications for higher trophic levels and ecosystem functioning.

Influence of shredders in mediating breakdown rates of beech leaves in circumneutral and acidic forest streams

From December 1997 to July 1998, the breakdown of beech leaves (Fagus sylvatica) and associated macroinvertebrate assemblages was investigated in seven headwater forested streams that differed in mean pH (4.64 to 7.20) due to acidification. Comparisons were made between leaves held in 0.3 mm, and 5 mm mesh bags in order to assess the contribution of macroinvertebrate shredders in litter breakdown. In addition, shredding efficiencies of five acid-tolerant and acid-sensitive invertebrate taxa (Protonemura sp., Leuctra sp., Sericostoma personatum, Potamophylax cingulatus, Gammarus fossarum) were investigated under laboratory conditions. Results showed that breakdown of leaves enclosed in fine-mesh bags was very low in all the streams, indicating that direct microbial contribution to the mass loss of beech leaves was small. On the contrary, breakdown of leaves enclosed in coarse-mesh bags was drastically reduced under acidic conditions (mass loss = 15 to 23 % after 270 days) when compared to circumneutral conditions (mass loss = 91.7 to 97.7 % after 270 days). Shredder assemblages associated with bags in acidic streams were dominated by Nemouroidea stonefly larvae, which showed low shredding efficiencies in laboratory experiments, particularly the early-instar larvae. Beech leaf breakdown rates rapidly increased at a mean stream pH>5.5, apparently due to the increasing abundance of the acid-sensitive shredders, S. personatum and G. fossarum, which shredded beech leaves more efficiently in laboratory feeding trials (even the first instars in the case of G. fossarum). The results of this study suggest that invertebrate shredders play an important role in controlling rates of beech leaf breakdown in forested Vosgian streams that differ in levels of anthropogenic acidification.

Variation in growth of the detritivore‐shredder Sericostoma personatum (Trichoptera)

1. We investigated the growth of the detritivore‐shredder Sericostoma personatum by feeding groups of larvae on a fresh macrophyte, Potamogeton perfoliatus, conditioned sitka spruce needles, Picea sitchensis, conditioned alder leaves, Alnus glutinosa, conditioned ash leaves, Fraxinus excelsior, and a fresh filamentous green alga, Microspora sp. A sixth treatment group of larvae was fasted.2. The nitrogen content of the food items ranged from 1.4% dry weight (DW) for Picea needles to 4.4% DW for Microspora filaments. Consumption of the various food items by Sericostoma differed significantly, being highest for Picea, and lowest for Potamogeton and Microspora.3. The instantaneous growth rate ranged from −1.3% DW day−1 in the fasting group to 0.75% DW day−1 in the Alnus group. The growth rate of larvae fed on Alnus, Fraxinus and Microspora was similar, and significantly higher than that of the other three groups. An increase in the size of larval cases followed the same pattern as larval growth, although with less variation between food items.4. Larvae fed on Microspora exhibited the greatest increase in fat content, while that of the larvae fed on Picea and those in the fasting group decreased. The gross growth efficiency (G/I%) of Sericostoma (larva + case) ranged from 2% when fed on Picea to 34% when fed on Microspora. Consumption was significantly correlated with the nutrient content of food items, whereas G/I% and growth rate were only weakly related to food quality.5. The growth of Sericostoma varies with diet and the food items sustaining highest growth rate are not necessarily the ‘typical’ shredder food resources.

Life history patterns of stream-dwelling caddis

Full life histories of fourteen coexisting species of caddis in an Irish stream are described. The study is based on growth patterns and distribution of larval head-capsule width through time. It also notes adult flight periods. Most species had simple life histories and were univoltine (Agapetus fuscipes, Hydropsyche siltalai, H. instabilis, Philopotamus montanus, Ecclisopteryx guttulata, Glossosoma conformis, Drusus annulatus, Potamophylax cingulatus and Halesus radiatus). In the latter four species the occurrence of instar-1 larvae indicated that egg hatching was delayed or prolonged over several months. Complex univoltine life histories were found in three species (Sericostoma personatum, Plectrocnemia conspersa and Silo pallipes) where, generally, a one-year life cycle occurred, although some individuals required more than one year to emerge. Data for two species (Rhyacophila dorsalis, Odontocerum albicorne) suggested the possibility of bivoltine life histories. Both types of complex life history led to overlapping generations. This is the most comprehensive information to date on the life histories of most of the species. Intraspecific variation in development rates, the wide range of size classes present at one time, the ability to overwinter in different larval stages and the asynchronous extended flight periods may be evidence of a spreading of risk within life histories. Without knowledge of whether the variations in development rates are genetically determined, it is difficult to advance a hypothesis based on an adaptive strategy to explain such variation as opposed to attribution to environmentally-controlled variation in growth, influenced by such factors as temperature and food.

Der Einfluß des Bibers ( Castor fiber albicus) auf die Fauna (Odonata, Mollusca, Trichoptera, Ephemeroptera, Diptera) von Mittelgebirgsbächen in Hessen (Deutschland)

Due to the return of the beaver an increasing number of brooks become restored to a natural condition. It is characterized by an alternation of flowing and standing sectors. In the summer of 1995, different groups of organisms (Odonata, Mollusca, Trichoptera, Ephemeroptera, Diptera) of two brooks in the Spessart mountains (Hesse, Germany) were studied to compare the composition of invertebrates in beaver homeranges and in the non-influenced sectors above. The new living conditions resulted in the disappearance of some species ( Drusus anulatus, Trich., Sericostoma personatum, Trich., Radix peregra, Gastr.). Nevertheless the beaver homeranges accommodate a significant higher number of species of dragon flies and damsel flies, molluscs and caddis flies than the brooks above the homeranges. The heterogeneity of natural river systems make a coexistence of running water and silent water organisms possible. The examinations result in a significant higher group dominance of ephemeras (i.p. Cloeon dipterum) in a beaver pond than in lenitic sectors conditioned by the gradient without beaver influence. Here the dominance of chironomids was much higher. High current sectors with their characteristic organisms are also present in the beaver homeranges. The higher number of insects is the basis of nourishment for predatory insects and fishes. The potential effects of beaver ponds on fishes are discussed.

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.

Longitudinal zonation and life cycles of macrozoobenthos in the Mauerbach near Vienna, Austria

AbstractA total of 12277 benthic invertebrates were caught from November 1990 to October 1991 at the Mauerbach, a first to fourth order forest brook near Vienna, Austria, using a Surber sampler and a hand net. Five taxa comprised 96.6% of the catch: Diptera larvae (45.6%), Amphipoda (37.6%) and larvae of Ephemeroptera (6.4%), Plecoptera (5.3%) and Trichoptera (1.7%).Mean values of macrozoobenthos density ranged from 39514 specimens m−2 at upstream sampling site 5 in December to only 286 specimens m−2 at sampling site 3 in May, shortly after a severe flood.Based on benthic invertebrate population structure, sites 5 and 6 (situated near the source) were clearly separated from the downstream sites 1 to 4. At upstream sites, shredders comprised up to 71.7% of the total, whereas at downstream sites collectors were most abundant. In addition, the proportion of eucrenal species decreased from 12% at site 6 near the source to only 2% at site 1 near the mouth.Among the insect species studied in detail, most were univoltine except Ephemera danica (Ephemeroptera) and Sericostoma personatum (Trichoptera), which had a two‐year life cycle.

Feeding plasticity of two detritivore‐shredders

SUMMARY1. The feeding preferences of the trichopteran shredder Sericostoma personatum Spence and the amphipod shredder Gammarus pulex L. were studied using specimens collected in a springbrook where the major food source was beech litter (Fagus sylvatica L.). Six food items were tested: conditioned beech leaves, conditioned alder leaves (Alnus glutinosa L.), conditioned Sitka spruce needles [Picea sitchensis (Bong.) Carr], fresh beech leaves, a fresh macrophyte (Potamogeton perfoliatus L.) and a fresh filamentous green alga (Microspora sp.).2. The overall preference pattern shown by the two shredders was the same: both preferred conditioned Alnus most, followed by fresh Microspora. The least preferred food items were conditioned Fagus leaves and Picea needles.3. The feeding preference of the two shredders proved to be unrelated to food source fibre content, toughness, total phosphorus, C:N ratio and total nitrogen (P>0.05).4. Despite the overall similarity in their feeding preferences, Gammarus was more selective than Sericostoma. The reason for this difference is discussed.5. We interpret our findings as indicating that detritivore‐shredders do not per se prefer leaf litter, but in fact actively select other food items such as filamentous green algae or macrophytes, even when terrestrial leaf litter is abundant. Most shredders in Danish forest streams thus seem to live on a growth‐limiting food resource that they do not prefer. This may have important implications for secondary production in such streams.

The influence of the diel activity pattern of the larvae of Sericostoma personatum (Kirby & Spence) (Trichoptera) on organic matter distribution in stream-bed sediments ? a laboratory study

Diel patterns in mobility and feeding behaviour of the larvae of the stream-dwelling trichopteran Sericostoma personatum larvae were investigated. Larvae fed at night on coarse particulate organic matter (CPOM) at the sediment surface. In the daytime they rested a few cm below the sediment surface, during which time their defaecation activity effected a release of fine particulate organic matter (FPOM) into the sediment. The amount of faeces (mean particle size = 0.1 ± 0.044 mm, x ± SD, n = 500) introduced into the sediment by the larvae, evaluated in two experiments, was 0.4–0.56 mg day−1. This amount did not differ significantly from the organic input resulting from bacterial activity (0.36–0.64 mg day−1). The presence of S. personatum larvae increased the sediment organic content by 42.9 mg (75.8 %) and 59.8 mg (185.6%) AFDW per 16 cm3 sediment over a 90-day period, as compared with control systems containing no larvae.