Riparian plant species loss alters trophic dynamics in detritus-based stream ecosystems

Riparian vegetation is closely connected to stream food webs through input of leaf detritus as a primary energy supply, and therefore, any alteration of plant diversity may influence aquatic ecosystem functioning. We measured leaf litter breakdown rate and associated biological parameters in mesh bags in eight headwater streams bordered either with mixed deciduous forest or with beech forest. The variety of leaf litter types in mixed forest results in higher food quality for large-particle invertebrate detritivores (‘shredders’) than in beech forest, which is dominated by a single leaf species of low quality. Breakdown rate of low quality (oak) leaf litter in coarse mesh bags was lower in beech forest streams than in mixed forest streams, a consequence of lower shredder biomass. In contrast, high quality (alder) leaf litter broke down at similar rates in both stream categories as a result of similar shredder biomass in coarse mesh bags. Microbial breakdown rate of oak and alder leaves, determined in fine mesh bags, did not differ between the stream categories. We found however aquatic hyphomycete species richness on leaf litter to positively co-vary with riparian plant species richness. Fungal species richness may enhance leaf litter breakdown rate through positive effects on resource quality for shredders. A feeding experiment established a positive relationship between fungal species richness per se and leaf litter consumption rate by an amphipod shredder (Gammarus fossarum). Our results show therefore that plant species richness may indirectly govern ecosystem functioning through complex trophic interactions. Integrating microbial diversity and trophic dynamics would considerably improve the prediction of the consequences of species loss.     

Fungal alteration of the elemental composition of leaf litter affects shredder feeding activity

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Leaf diversity influences in-stream litter decomposition through effects on shredders

1. The functioning of many aquatic ecosystems is controlled by surrounding terrestrial ecosystems. In a view of growing interest in linking biodiversity to ecosystem‐level processes, we examined whether and how leaf diversity influences litter decomposition and consumers in streams. 2. We tested experimentally the hypothesis that the effects of leaf diversity on decomposition are determined by the responses of leaf consumers to resource–habitat heterogeneity. Leaves from three common riparian trees, beech (Fagus sylvatica), hazel (Corylus avellana) and ash (Fraxinus excelsior), were exposed alone and in all possible mixtures of two and three species in a stream. We analysed individual leaf species for decomposition rate, microbial respiration and mycelial biomass, and we determined the species composition, abundance and biomass of shredders in leaf bags. 3. We found that the decomposition of the fastest decomposing leaves (hazel and ash) was substantially stimulated (up to twofold higher than single species leaf packs) in mixtures containing beech leaves, which are refractory. In contrast, the decomposition of beech leaves was not affected by leaf mixing. Such species‐specific behaviour of leaves in species mixtures has been overlooked in previous studies that examined the overall decomposition of litter mixtures. 4. The effects of leaf diversity on decomposition varied with the abundance and biomass of shredders but not with microbial parameters. Beech leaves alone were less attractive to shredders than leaf packs made of hazel, ash or any mixture of species. Moreover, the presence of beech leaves in mixtures led to higher shredder abundance and biomass than we had expected from data from single species exposed alone. Lastly, we found that early instars of the caddisfly Potamophylax (the dominant shredder in terms of biomass) almost exclusively used the toughest material (i.e. beech leaves) to construct their cases. 5. Leaf pack heterogeneity may have altered shredder‐mediated decomposition. Shredders colonising diverse leaf packs benefited from the stable substratum provided by beech leaves, whereas ash and hazel leaves were primarily used as food. Thus, our findings provide strong evidence for an intimate linkage between the diversity of riparian vegetation and aquatic communities.     

Leaf litter degradation in the wave impact zone of a pre-alpine lake

Contrary to streams, decomposition processes of terrestrial leaf litter are still poorly understood in lakes. Here, we examined the decomposition of two leaf species, beech (Fagus sylvatica) and poplar (Populus nigra ‘italica’) in the littoral zone of a large pre-alpine lake at a wave exposed site. We focussed on the shredding impact of benthic invertebrates in a field experiment and on the effects of wave-induced disturbances under field and mesocosm conditions. In contrast to our expectations, benthic shredders did not reveal an important role in leaf processing under the conditions of the field experiment (early spring time, wave impact zone). Strong wave turbulence during storm events significantly reduced leaf mass, FPOM and invertebrate densities at field conditions. Several reasons can explain the low importance of shredders in our field study: (a) phenology of the shredder species, (b) feeding preferences and alternative food sources for gammarids, (c) generally low abundance of the native gammarid species due to the recent occurrence of an invasive predator, (d) disturbance of shredder activity due to high wave impact and (e) relatively low food value of the offered leaves. We suggest that leaf litter decomposition in lakes occurs in specific process domains, which largely depend on the hydraulic characteristics and on water-level fluctuations.     

Onshore–offshore variations of copepod community in northern South China Sea

Previous studies which have tested the feeding preferences of shredders for fungal species and the food quality of fungi used detritus uniformly colonized by a fungus, which is not the case for decaying leaves in streams. It is not known whether shredders in different development stages exhibit variations in feeding preference and larval performance. This study examined the feeding preferences and the growth of the third and the fifth instars of Pycnopsyche gentilis larvae using fungal-colonized patches and whole leaves, respectively, having different fungal species compositions (Alatospora acuminata, Anguillospora filiformis, Articulospora tetracladia, Tetrachaetum elegans, and all species combined). The aquatic hyphomycetes used were co-dominant on leaves in the stream inhabited by the caddisfly. During 14 d of feeding, the larvae of both instars did not show significant differences in feeding preferences for the patches growing on oak leaves, although the third instar larvae were slightly more selective than the fifth instar larvae. When fed with maple leaves for 18 d, larval growth rates, gross growth efficiencies, and survivorship were not significantly different among the fungal treatments. However, the larval growth of both instars fed with fungal-colonized leaves was always significantly greater than the growth of larvae fed with diets of uncolonized leaves. The third instar larvae grew faster than the fifth instar larvae, but the growth efficiencies of the two instars were similar. These results suggest that P. gentilis larvae exhibit less selectivity in their feeding than other caddisfly shredders that have been examined and that the dominant fungi colonizing leaves in their habitat are similar in palatability and food quality for this shredder. Handling editor: B. Oertli     

Food preference of the trichopteran larva Anabolia nervosa from two streams with different food availability

The food preference of the trichopteran shredder Anabolia nervosa from two streams with different food availability was studied in laboratory preference experiments. One stream was unshaded and had abundant growth of the submerged macrophyte Potamogeton perfoliatus. The other was shaded by trees (Alnus glutinosa) and had very sparse growth of submerged macrophytes. To test the food preference of Anabolia nervosa for terrestrial leaf litter and submerged plants we offered leaves of: conditioned Alnus glutinosa, fresh green Alnus, conditioned Fagus sylvatica, fresh green Fagus, and fresh submerged Potamogeton perfoliatus. For both larval populations conditioned Alnus was the most consumed food item, followed by Potamogeton. Larvae from the Alnus-shaded stream preferred conditioned Alnus over all other food items, while larvae from the macrophyte stream did not clearly discriminate between conditioned Alnus and Potamogeton. The three remaining food items were largely rejected. Food items were analyzed for dry matter, organic matter, fibre, nitrogen, phosphorus and toughness. Preference was not correlated to any of these food characteristics, but we suggest that they may still be important and influence food choice in a complex manner. The study indicates that the preference pattern of Anabolia nervosa is not clearly related to previous feeding habituation. The ability to feed on fresh Potamogeton is, therefore, not acquired by certain populations of larvae through long exposure to this resource in the field. The high preference for fresh Potamogeton suggests that Anabolia nervosa may actively select Potamogeton as food even when alternative food sources such as terrestrial leaf litter are abundant in the field.     

Leaf litter quality drives the feeding by invertebrate shredders in tropical streams

Amazon and Cerrado‐forested streams show natural fluctuations in leaf litter quantity along the time and space, suggesting a change on litter quality input. These natural fluctuations of leaf litter have repercussion on the organic matter cycling and consequently effects on leaf decomposition in forested streams. The effects of the quantity of leaf litter with contrasting traits on consumption by larvae of shredder insects from biomes with different organic matter dynamics have still been an understudied question. The Trichoptera Phylloicus spp. is a typical shredder in tropical headwater streams and keep an important role in leaf litter decomposition. Here, we assessed the consumption by shredder Phylloicus spp., from Amazonia and Cerrado biomes, on higher (Maprounea guianensis) and lower quality leaves (Inga laurina) in different proportions and quantities. Experiments were performed concomitantly in microcosms approaches, simulating Cerrado and Amazonian streams. Higher leaf consumption occurred in Cerrado microcosms. Litter quantity influenced negatively leaf consumption by shredders in Cerrado, in opposition to Amazonia, where consumption was not affected by leaf quantity. In both sites, we observed higher consumption by shredders in treatment with only M. guianensis and no difference between other treatments with mixture of leaves. In treatment with litter of I. laurina, we noted the use of substrate for case building (due to the higher leaf toughness), affecting the fragmentation process. Therefore, our results indicate that leaf litter quality drives the preference of consumption by Phylloicus larvae in Cerrado and Amazonia streams.     

Food quality, feeding preferences, survival and growth of shredders from temperate and tropical streams

1. The importance of leaf quality to the nutritional ecology of lotic shredders is well established for temperate species but virtually unknown for tropical taxa. In the present study, we compared the feeding behaviour and performance of two tropical and two temperate shredders in a series of pair‐wise experiments. 2. Specifically, we tested whether leaf conditioning status (stream‐conditioned versus unconditioned leaves) and geographical origin (temperate Alnus glutinosa versus tropical Hura crepitans leaves) affect the food preference, survivorship, and growth of selected shredders from low and high latitudes in a consistent manner. The animals used in experiments were the caddis‐flies Nectopsyche argentata and Phylloicus priapulus from Venezuela, Sericostoma vittatum from Central Portugal, and the amphipod Gammarus pulex from Northern Germany. 3. In general, all shredders exhibited the same high preference for conditioned over unconditioned leaves, irrespective of the geographical origin of the leaf or shredder species. 4. A corresponding tendency for higher growth was found for sets of animals offered conditioned leaves, with the differences in growth being clearer in the two tropical shredders. Survivorship of the two temperate species was consistently high (> 83%) regardless of the diet offered, whereas the tropical shredders survived better on conditioned (77–90%) as compared with unconditioned (54–87%) leaves, although not significantly so. 5. With the exception of the temperate S. vittatum, shredders did not select or perform better on leaves to which they had previously been exposed, indicating a potential adaptation to native leaf species is over‐ridden by intrinsic leaf properties. 6. Taken together, the results of this study suggest that tropical shredders may exhibit the same basic patterns of food exploitation as their temperate counterparts. Consequently, current concepts relating to the role of shredders in stream detritus dynamics may well be applicable to tropical streams, although essentially derived from temperate systems.     

Palatability of Leaves Conditioned in Streams Affected by Mine Drainage: A Feeding Experiment with Gammarus Pulex (L.)

Both the absence of leaf shredding macroinvertebrates and low microbial activity are of major importance in determining slow and incomplete leaf decay in extremely acidic (pH<3.5) mining streams. These streams are affected by a heavy ochre deposition causing the formation of massive iron plaques on leaf surfaces that hinder microbial exploitation. An investigation was carried out to determine whether iron plaques and leaf conditioning status (acid conditioned with and without iron plaques, neutral conditioned, unconditioned) affect the feeding preference of the shredder Gammarus pulex (L.). Leaf respiration rates and fungal biomass (ergosterol contents) were measured to determine microbial colonization. Neutral conditioned leaves had significantly higher microbial colonization than acid conditioned leaves with iron plaques. Notwithstanding, leaves of both conditioning types were consumed at high rates by G. pulex. The microbial colonization had no influence on feeding preference in the experiment. It is presumed that iron adsorbed organic material caused the high palatability of leaves with iron plaques. The results indicate that the large deposits of leaves coated with iron plaques will be available to the stream food web when water quality will be restored to neutral as planed in scenarios for the future development of mining streams.     

Leaf traits induce the feeding preference of a shredder of the genus Triplectides Kolenati, 1859 (Trichoptera) in an Atlantic Forest stream,Brazil: a test with native and exotic leaves

This study assessed the feeding preference of larvae of Triplectides sp. (Trichoptera, Leptoceridae) exposed to leaves of native (Hoffmannia dusenii Standley, 1931) and exotic (Eucalyptus globulus Labillardiere, 1799) trees. We hypothesized that, regardless of the origin of the leaves, larval preference is determined mainly by leaf anatomy and quality. Leaves from both species were conditioned with and without nutrient enrichment (NPK), and the four food items were offered in paired combinations to 162 larvae. Larval preference varied according to leaf combinations. In treatments containing both species, larvae preferred to feed on H. dusenii because of softer tissues and anatomical structure. The only exception was the treatment containing discs of enriched E. globulus and non-enriched H. dusenii where enhanced microbial activity on enriched leaves provided a softer resource to shredders. Our results corroborate the initial hypothesis and suggest that introduction of exotic leaves and changes in nutrient availability may affect shredder activity in streams and, consequently, organic-matter processing and ecosystem functioning.     

Leaf Quality of Some Tropical and Temperate Tree Species as Food Resource for Stream Shredders

We tested the hypotheses that (1) plant defenses against consumers increase in the tropics, and that these differences in quality are perceived by detritivores; and (2) microbial conditioning of leaf litter is important for the feeding ecology of shredders from both geographical regions. We compared quality parameters of 8 tree species from Portugal and 8 from Venezuela. The tropical leaves were tougher, but did not differ from temperate leaves in terms of N, C: N, and polyphenols. In multiple‐choice experiments, shredders from Portugal (Sericostoma vittatum and Chaetopteryx lusitanica) and from Venezuela (Nectopsyche argentata and Phylloicus priapulus) discriminated among conditioned leaves, preferentially consuming softer leaves. In another set of experiments, all shredders preferentially fed on conditioned rather than unconditioned leaves, grew faster when fed conditioned than unconditioned leaves and fed more on temperate than tropical leaves. We conclude that leaf litter from the tropics is a low‐quality resource compared to leaves in temperate systems, because of differences in toughness, and that tropical shredders benefit from microbial colonization, as previously demonstrated for temperate systems. We suggest that leaf toughness could be one explanation for the reported paucity of shredders in some tropical streams. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

Grass,mosses, algae,or leaves? Food preference among shredders from open-canopy streams

Shredder feeding is a vital process in making decomposition products available to biota in streams. To investigate which food sources shredders in open-canopy streams exploit, we conducted a feeding preference experiment with the invertebrate detritivores Limnephilus bipunctatus and Nemoura sp., which are commonly found in open-canopy streams on the Swedish island of Öland in the southern Baltic Sea. Leaves of birch, Swedish whitebeam, and shrubby cinquefoil; dead and fresh grass; water moss; and algae were offered to the shredders in multi- and single treatments. We hypothesized that food with high nutritional value would be preferred. Both taxa preferred leaves of shrubby cinquefoil, a bush common in the riparian zone of Öland streams; additionally Nemoura sp. also chose algae. Dead grass, the most abundant food source in the streams during the whole year, was the least consumed food type. The fresh food types had highest nutritional value, measured as carbon to nitrogen content. Therefore, food quality could not alone explain the preference of shrubby cinquefoil. However, among the detritus type offered, shrubby cinquefoil had the highest nutritional value. Shrubby cinquefoil may constitute one important energy source to these open-canopy stream ecosystems and may be essential in maintaining an abundant shredder community in these streams. Thus, the results of this study indicate that detrital resources are indeed important in open-canopy stream systems.     

Green leaves enhance the growth and development of a stream macroinvertebrate shredder when senescent leaves are available

1. Freshly fallen green leaves and flowers of terrestrial plants enter temperate streams in spring and summer, when senescent leaf litter is often scarce. These resources appear to provide good supplementary food for macroinvertebrate shredders, but have some potential shortcomings as food or case material for caddisflies. 2. To compare suitability of green leaves or flowers and senescent leaves for the growth and development of stream shredders, we reared the caddisfly Lepidostoma complicatum in the laboratory with treatments that provided larvae with senescent (oak) and green (oak or maple) leaves separately, and also together, in case the combined use of both types of leaf may benefit the shredder. 3. Larvae supplied with green leaves alone grew at 65% of the rate of those provided with senescent leaves alone, due to their lower consumption rate. No individuals given green leaves alone developed into adults, whereas 70% of the individuals given senescent leaves alone did. Green leaves may inhibit larval consumption due to their high phenol content, or they may be unsuitable for case material because they are less tough than senescent leaves. 4. Larvae supplied with both senescent and green leaves (or flowers) had a higher growth rate and developed faster, than those given senescent leaves alone, whereas the proportions of successfully emerged individuals did not differ. Lepidostoma probably benefits from the higher nitrogen content of the green leaves when used together with senescent leaves. 5. These results suggest that green leaves (or flowers) cannot serve as an alternative food resource to senescent leaves, but that they can enhance the growth and development of a Lepidostoma stream shredder if senescent leaves are also available.     

The effect of sunlight on leaf litter quality reduces growth of the shredder Klapopteryx kuscheli

• 1 The direct effect of sunlight on the conditioning, breakdown and incorporation of leaf litter in stream food webs has not yet been considered. The aim here was to evaluate the effects of light intensity on the colonization of leaf litter by microorganisms and its resulting quality as food for the stonefly shredder Klapopteryx kuscheli.
• 2 Leaf litter was conditioned for 2 months in an open reach of a second‐order stream in litter bags either exposed to or shaded from direct sunlight. Subsequently, we performed laboratory experiments to test larval consumption, growth, growth efficiency and feeding preference fed on both leaf litter treatments.
• 3 Leaf litter in the unshaded treatment had three times more chlorophyll‐a (Chl‐a) than that in the shaded treatment, 50% lower fungal biomass and similar bacterial abundance. Although larvae did not prefer either food and fed at the same rate on both leaf litter treatments, they grew twice as fast on the shade‐conditioned leaves and attained a two‐fold higher growth efficiency.
• 4 Sunlight can have significant effects on detritus‐based food webs. Riparian modification induced by human activities in forested catchments increases the potential for sunlight to influence detritus dynamics.

     

Factors affecting litter processing by Anisocentropus kirramus (Trichoptera: Calamoceratidae) from an Australian tropical rainforest stream

• 1 Larvae of the caddisfly Anisocentropus kirramus are common leaf shredders in rainforest streams in tropical Queensland. Laboratory experiments were undertaken to examine the effects of (a) differences in leaf species, age and degree of conditioning, (b) leaf preferences, (c) temperature and (d) larval stage on processing of leaf litter by A. kirramus.
• 2 Leaf species (five tested), age (fresh v senescent) and condition (conditioned in stream v unconditioned) each had a significant effect on the amount of leaf material that was processed. For most species, conditioned leaves were processed faster but for one species unconditioned leaves were processed faster. Senescent leaves were processed more rapidly than green leaves in three species but not in the other two. Given a choice of leaf types A. kirramus actively selected leaves that were processed faster; no preference was shown between two different ‘fast’ leaves.
• 3 Processing occurred at all temperatures tested (10, 18 and 25°C), with the processing rate increasing with temperature. Younger instar larvae processed leaves at a greater rate per unit body weight (up to 343% day^?1) than older instars. Final instar (5) larvae were capable of processing some tough leaves that younger instars did not process.
• 4 In rainforest streams, processing of leaves by A. kirramus takes place throughout the year. Its ability to process green leaves is important because of the high input of fresh green leaves into tropical streams, and because of the severe depletion of the supply of conditioned leaves and fine detritus after floods.

     

Stronger effects of litter origin on the processing of conifer than broadleaf leaves: A test of home‐field advantage of stream litter breakdown

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Consequences of the colonisation of leaves by fungi and oomycetes for leaf consumption by a gammarid shredder

1. Leaf litter breakdown by shredders in the field is affected by leaf toughness, nutritional value and the presence of secondary compounds such as polyphenols. However, experiments involving the use of single fungal strains have not supported the assumption that leaf parameters determine food selection by shredders perhaps because of a failure to test for high consumption prior to isolation of fungal strains, overrepresentation of hyphomycetes or the potential effects of accompanying bacteria. In this study, we used bacteria‐free, actively growing fungi and oomycetes isolated from conditioned leaf litter for which a shredder had already shown high consumption rates. 2. Black alder (Alnus glutinosa) leaf litter was exposed to the littoral zone of Lake Constance in autumn, and subsamples were analysed for leaf parameters and consumption by Gammarus roeselii under standard conditions at regular intervals. On dates with a high consumption rate of the exposed leaves, 14 single strains of fungi and oomycetes were isolated, freed of bacteria and grown on autoclaved leaves. 3. Six of eight measured leaf parameters of exposed leaves were significantly correlated with Gammarus consumption rates, with high colinearity among leaf parameters hampering the identification of causal relations between leaf parameters and feeding activity. 4. When single strains of fungi and oomycetes were grown on autoclaved leaf litter, toughness of colonised leaves was always lower than in the control and the content of protein, N and P were increased. There were pronounced strain‐specific effects on leaf parameters. Consumption rates also differed significantly, with nine of fourteen isolates consumed at higher rates than controls and none proving to be a deterrent. Protein and polyphenol content were significantly correlated with consumption rates. Oomycete‐colonised leaves were consumed at similar rates but were of lower food quality than fungi‐colonised leaves. 5. We argue that direct strain‐specific attractant or repellent effects of fungi and oomycetes on consumption by G. roeselii are not important. However, we found indirect strain‐specific role operating via effects on leaf parameters.     

Understanding of colonization and breakdown of leaves by invertebrates in a tropical stream is enhanced by using biomass as well as count data

We hypothesized that (i) the importance of shredders for leaf breakdown is more evident in terms of their biomass than their abundance, due to the large bodies and high-feeding efficiencies of some typical shredders; (ii) non-shredder invertebrates select more refractory leaves because these are a more stable substrate for colonization or to obtain other forms of food. To test these hypotheses, we performed a decomposition experiment with leaves of contrasting chemical composition in a tropical stream, and determined the changes in the ash-free dry mass (AFDM) of the litter, and the invertebrate abundance and biomass during a 44-day period. The biomass of shredders showed a positive relationship with AFDM remaining, whereas their abundance was unrelated to AFDM. While shredder abundance represented only 4–12% of total invertebrate abundance, shredder biomass constituted 19–36% of total invertebrate biomass. We conclude that (i) shredder biomass expresses better than abundance the role of this guild in the decomposition of leaf detritus, demonstrating that they are important for the functioning of tropical streams; (ii) incubation time rather than stability of leaf litter as a substrate influences colonization by non-shredder invertebrates.     

The shredding activity of gammarids facilitates the processing of organic matter by the subterranean amphipod Niphargus rhenorhodanensis

1. The functional feeding group approach has been widely used to describe the community structure of benthic invertebrates in relation to organic matter resources. Based on this functional framework, positive interactions between feeding groups (especially shredders and collector‐gatherers) were postulated in the River Continuum Concept. However, relationships with organic matter have been poorly documented for invertebrates living in the hyporheic zone. 2. We hypothesised that the common subterranean amphipod Niphargus rhenorhodanensis would feed on fine particulate organic matter (FPOM), which is more abundant than coarse particulate organic matter (CPOM) in hyporheic habitats, and should be favoured by the occurrence of shredders that produce FPOM from CPOM. 3. We used laboratory experiments to quantify leaf litter processing by N. rhenorhodanensis and a common shredder, the surface amphipod Gammarus roeselii. We estimated rates of feeding and assimilation (using nitrogen stable isotopes) of the two species separately and together to reveal any potential shredder–collector facilitation between them. 4. Measured leaf litter mass loss showed that N. rhenorhodanensis did not act as a shredder, unlike G. roeselii. Organic matter dynamics and ¹⁵N/¹⁴N ratios in tissues of niphargids indicated that N. rhenorhodanensis was a collector‐gatherer feeding preferentially on FPOM. We also found a positive influence of the gammarid shredders on the assimilation rate of N. rhenorhodanensis, which fed on FPOM produced by the shredders, supporting the hypothesis of a positive interaction between surface shredders and hyporheic collector‐gatherers.