Nutrients and grazers both can regulate benthic algal structure and function in streams, but the relative strength of each factor depends on stream biotic and abiotic conditions. The abundance of stream organisms and nutrient availability can change rapidly after a flood. Thus, nutrient and grazer influences on algal development and how these drivers interact may vary temporally during recovery. We measured benthic structural and functional development for 35 d after a simulated flood in large outdoor mesocosms under a gradient of 6 nutrient loadings crossed with 6 densities of grazing fish (Southern redbelly dace, Phoxinus erythrogaster). Nutrients influenced algal development more than dace did and were better correlated with algal function (area-specific primary productivity and nutrient uptake) than with structure (biomass). Dace influenced all structural variables and biomass-specific gross primary productivity, but their influence was relatively weak and was observed only early in recovery. Dace influence weakened and nutrient influence strengthened during recovery. Understanding context-dependent relationships in postdisturbance community dynamics is essential for predicting ecosystem responses to future changes in nutrient inputs and biodiversity, particularly in systems, such as headwater streams, with frequent disturbance.

Low-flow disturbances are predicted to increase in frequency and intensity because of climate change and extensive human water withdrawal, but the effect of decreased flow on aquatic insect communities is not well understood. I explored the resistance of aquatic insects to reduced flow by creating an experimental low-flow disturbance that diverted ∼40 to 80% of the water in 3 replicate streams for 2 summers. I sampled the aquatic insect community in control and treatment reaches before and during the 3-mo water diversions. I used a trait-based approach to analyze the data because traits have the potential to increase mechanistic understanding and predictive capabilities. The analysis focused on 6 traits: desiccation resistance, maximum crawling rate, armoring, size at maturity, rheophily, and habit. Community trait composition underwent strong seasonal shifts, but few consistent responses to reduced flow were observed. The 2 trait states that did appear to confer increased resistance were high crawling rate and armoring. These trait states can provide protection from predators. Thus, biotic interactions might be important during low-flow disturbance.

We quantified macroinvertebrate production and organic matter standing stocks in riffle/run and pool habitats for 2 y in 2 reaches of Big Creek, a 3^rd-order stream in southern Illinois, USA. Habitat-weighted secondary production was 24.9 and 26.2 g ash-free dry mass (AFDM) m⁻² y⁻¹ in the upper and lower reaches, respectively, in year 1 of the study and 17.6 and 15.1 AFDM m⁻² y⁻¹ in year 2. Annual production to biomass (P/B) ratios of the macroinvertebrate assemblages ranged from 7 to 10. Collector-gatherers, which were dominated by nontanypodine Chironomidae and Oligochaeta, accounted for >60% of total habitat-weighted production in both reaches, and consumption estimates based on production efficiencies indicated they consumed high proportions of available organic matter resources ≤250 µm. Macroinvertebrate production in Big Creek was strongly correlated with organic matter standing stocks, and our subsequent analyses of production and organic matter resources across several low-order North American streams suggested standing stocks of small wood, a relatively refractory component of organic matter, are an important component of the relationship between macroinvertebrate production and organic matter. However, the apparent influence of small wood on production may be related to associated physical characteristics of these streams, such as pH and canopy cover. Secondary production estimates in our data set were a function of both adjusted total organic matter exclusive of wood and wood standing stocks. Although production–organic matter relationships may be obscured by other factors at the local level, our results indicate that patterns of macroinvertebrate production across large geographic scales may be driven largely by the availability of detrital resources.

Patchiness is hierarchically structured in stream ecosystems and transcends multiple spatial and temporal scales. Regulation of streams through channelization and flow stabilization often homogenizes in-stream habitats, thereby reducing this patchiness. We conducted a patch-disturbance experiment with individual brick substrata in 2 reaches (open vs closed canopy) and 2 seasons (summer vs winter) in a eutrophic regulated stream. Although the stream was regulated, we expected coarse-scale attributes (canopy cover, season) to influence the effects of disturbance at the fine scale of individual bricks. Brick substrata had 3 degrees of structural complexity (low  =  smooth, intermediate  =  techno, high  =  hetero). Replicates of each brick type were physically disturbed at frequencies of every 5 and 10 d or were left undisturbed during each 30-d experimental period. At the end of each experiment, individual bricks were collected, periphyton biomass was estimated, and macroinvertebrates were identified and counted. Natural densities, taxon richness, and assemblage composition of macroinvertebrates differed significantly between sites and seasons. Periphyton biomass was higher in the open-canopy than in the closed-canopy site in both seasons, especially summer. Periphyton biomass differed among brick types at each site and season, but disturbance had no effect on periphyton biomass within a brick type. At the closed-canopy site, undisturbed hetero bricks had higher macroinvertebrate density, richness, and biomass than the other brick types and disturbance treatments in both seasons. At the open-canopy site, no effect of disturbance was found for any brick type in summer, whereas undisturbed and 10-d hetero bricks had higher macroinvertebrate density, richness, and biomass than the other brick types and disturbance treatments in winter. Besides the dominant role of site and season in this study, our results also suggest that substrate patch complexity can be significant in the response of macroinvertebrates to physical disturbance in regulated streams. As in natural systems, coarse-scale attributes of stream reaches, e.g., degree of canopy cover and season, also provide the spatiotemporal hierarchical context in which disturbance effects are realized in regulated streams, thus having major implications for resource managers.

Grass litter can be a dominant detritus type in many streams. However, use of this C source in stream food webs often is viewed as insignificant because of its relatively slow breakdown rates and low nutritional quality. We deployed leaf packs containing senesced bluejoint grass (Calamagrostis canadensis) across a natural nutrient gradient of 6 salmon-rearing headwater streams on the lower Kenai Peninsula, Alaska. We hypothesized that litter-colonizing microbes would use dissolved stream nutrients and enhance breakdown rates, litter nutrient concentrations, and densities of macroinvertebrates across streams. Leaf-pack mass and nutrient concentrations were measured on the material at 0 (predeployment), 2, 4, 6, and 8 wk in all streams. Breakdown rates were calculated from the mass measurements with an exponential decay model. Macroinvertebrate composition and abundance were measured at 8 wk in all streams and every 2 wk in 1 stream. Breakdown rates of bluejoint litter were relatively low (20–30% mass loss over 2 mo), but similar to rates found in previous studies of senesced grass litter. Weighted regressions showed that bluejoint breakdown rates in the 6 streams were significantly (p < 0.05) related to dissolved stream nutrient concentrations (r²  =  0.94 and 0.67 for dissolved inorganic N and PO₄-P, respectively), litter nutrient concentration (r²  =  0.72 and 0.96 for leaf % N and % P, respectively), total macroinvertebrates/g (r²  =  0.73), and nonmetric multidimensional scaling-axis-1 scores of macroinvertebrate community structure (r²  =  0.80). Litter nutrients changed after just 2 wk and were increasingly and significantly related to stream nutrient concentrations over time. NMS ordination showed that succession of macroinvertebrates on leaf packs from one stream followed a distinct direction over time, and a large shift in macroinvertebrate community structure occurred between weeks 6 and 8, a result potentially indicating a consumer response to microbial conditioning. The abundance and diversity of macroinvertebrate taxa using bluejoint litter provide evidence that it is an important habitat and energy pathway for consumers in headwater streams of the Kenai Peninsula. In addition, climate change has the potential to change terrestrial vegetation assemblages, which drive differences in stream nutrient concentrations in this region. If N-fixing shrubs become more abundant in the future, litter-decomposition rates will be positively affected by increases in both stream and leaf-litter nutrient concentrations.

Large-scale surface mining in southern West Virginia significantly alters headwater stream networks. The extent to which mining interacts with other stressors to determine physical, chemical, and biological conditions in aquatic systems downstream is unclear. We conducted a watershed-scale assessment of Pigeon Creek, an intensively mined watershed of the Tug Fork drainage in Mingo County, West Virginia. Our objectives were to: 1) develop landscape-based indicators of mining and residential development, 2) quantify the interactive effects of mining and residential development on in-stream conditions, and 3) identify landscape-based thresholds above which biological impairment occurs in this watershed. Macroinvertebrate community structure was negatively correlated with intensity of mining and residential development. Correlation analysis and partial Mantel tests indicated that mining (% of total subwatershed area) caused acute changes in water chemistry (r = 0.55–0.91), whereas residential development (parcel density) strongly affected both physical habitat (r = 0.59–0.81) and macroinvertebrate community structure (r = 0.59–0.93). The combined effects of mining and development on in-stream biotic conditions were additive. Sites affected by equivalent levels of both stressors had lower Ephemeroptera, Plecoptera, Trichoptera richness than sites affected by either stressor alone. Biological impairment thresholds occurred at ~25% total mining (equivalent to a specific conductance of ~250 µS/cm) and at parcel densities of ~5 and 14 parcels/km². Our results provide a tool that can be used to predict downstream ecological response to proposed mining given pre-existing watershed conditions. Our study suggests that effective management of impacts from new mine development must address nonmining-related impacts in this region.

The biological effect of water abstraction from unregulated streams in New South Wales, Australia, was assessed with data on macroinvertebrate assemblages in riffles (445 samples) and pool edges (718 samples) obtained from a national assessment of river condition in 1995 to 2000. We used limiting environmental difference (LED) modeling to predict the macroinvertebrate assemblage expected for each sample in the absence of water abstraction and estimated effect by comparing predicted and observed assemblages for sites with upstream abstraction. We found a high likelihood of effect on macroinvertebrates in 30% of riffles with upstream abstraction and 22% of edges. Complex combinations of biological traits appeared to determine the sensitivities and tolerances of individual taxa to water abstraction. For example, rheophilous families generally were rarer than predicted in apparently affected riffles, where thermophilic families seemed tolerant of the effects of water abstraction, and free-swimming families were less common than predicted in apparently affected edges, where families with tegument respiration appeared unaffected by water withdrawals. The trait response was clearer for the riffle fauna than for the edge fauna, perhaps because the physical and chemical effects of abstraction are more consistent for riffles than for edges. Our approach can support management planning by identifying taxa that are most at risk from water abstraction and sites where apparent effects are most evident.

We examined seasonal patterns of abundance of mussel larvae (glochidia) in stream drift in a diverse, large-stream mussel assemblage in the Sipsey River, Alabama, across 1 y. We used recently developed techniques for glochidial identification combined with information about mussel fecundity and benthic assemblages to evaluate how well observed glochidial abundance corresponded to expected abundance based on glochidial production. Glochidia from short-term brooding species (Amblema plicata, Elliptio arca, Fusconaia cerina, Pleurobema decisum, Obliquaria reflexa, and Quadrula asperata) were abundant from May to August but did not occur in drift between November and the end of April. Long-term brooders (Lampsilis spp., Medionidus acutissimus, Obovaria unicolor, and Villosa spp.) occurred in several short peaks in spring, summer, and autumn, but generally were less abundant than short-term brooders. We estimated that the benthic assemblage at our study site produced >500,000 glochidia/m² annually and production varied widely among species. Abundance of species in the drift was positively related to benthic abundance but was only weakly related to glochidial production. The poor relationship between glochidial production and abundance in the drift suggests that release and transport of glochidia are influenced by a wide variety of abiotic and biotic factors.

Surveys of freshwater mussel populations are used frequently to inform conservation decisions by providing information about the status and distribution of species. It is generally accepted that not all mussels or species are collected during surveys, and incomplete detection of individuals and species can bias data and can affect inferences. However, considerably less attention has been given to the potential effects of species misidentification. To evaluate the prevalence of and potential reasons for species misidentification, we conducted a laboratory-based identification exercise and quantified the relationships between mussel species characteristics, observer experience, and misidentification rate. We estimated that misidentification was fairly common, with rates averaging 27% across all species and ranging from 0 to 56%, and was related to mussel shell characteristics and observer experience. Most notably, species with shell texturing were 6.09× less likely than smooth-shelled species to be misidentified. Misidentification rates declined with observer experience, but for many species the risk of misidentification averaged >10% even for observers with moderate levels of experience (5–6 y). In addition, misidentification rates among observers showed substantial variability after controlling for experience. Our results suggest that species misidentification may be common in field surveys of freshwater mussels and could potentially bias estimates of population status and trends. Misidentification rates possibly could be reduced through use of regional workshops, testing and certification programs, and the availability of archived specimens and tissue samples in museum collections.

Understanding the broad-scale factors that influence biological communities has long been a goal of community ecology. We used benthic macroinvertebrate data to identify broad geographical patterns in macroinvertebrate community composition and specifically to examine the influence of the Precambrian Shield on stream abiotic and biotic conditions. The Precambrian Shield is a geological feature that encompasses most of northern North America. Geology differs between Shield and off-Shield areas, creating distinctly different physical and chemical conditions in aquatic systems. We focused our regional-scale study on south-central Ontario, where both Shield and off-Shield conditions are found in adjacent areas. We used constrained and unconstrained multivariate analyses to examine patterns in biotic, abiotic, and spatial variables. Our results showed that, in low-order lotic systems, macroinvertebrate communities differ between Shield and off-Shield streams. Shield streams have higher dissolved O₂, velocity, and discharge, larger amounts of woody debris, and greater canopy cover than off-Shield streams. In contrast, off-Shield streams have higher conductivity, alkalinity, pH, turbidity, and water temperature, and frequently are surrounded by meadow, cultivated, or pastured land. In general, macroinvertebrate communities at off-Shield sites had a greater proportion of taxa preferring pool or depositional habitats, whereas macroinvertebrate communities at Shield sites contained taxa typically associated with riffles or erosional habitats. Analysis of spatial location indicated that the Shield/off-Shield distinction probably is the result of a combination of intertwined abiotic and spatial factors.

In this experimental study, conducted in coastal Oregon USA, we examined how small increases in summer water temperatures affected aquatic insect growth and autumn emergence. We maintained naturally fluctuating temperatures from 2 nearby streams and a 3^rd regime, naturally fluctuating temperatures warmed by 3–5°C, in flow-through troughs from mid-summer until autumn. We added selected abundant Ephemeroptera, Plecoptera, and Trichoptera species to the 3 treatments in late July and observed emergence until early December. We described the taxon-specific responses of the caddisfly Psychoglypha bella and the mayfly Paraleptophlebia bicornuta, both of which survived well in the troughs (67–86%), and the stonefly Mesocapnia projecta, which we did not collect in mid-summer but had colonized all experimental troughs by October. We observed primarily phenological rather than morphological responses to higher water temperatures. The most synchronous emergence of male and female P. bella and P. bicornuta occurred in the trough with the coolest temperatures. Only P. bella emerged asynchronously from the trough with the warmest temperatures. The decreases in synchrony were largely the result of earlier emergence of males. Paraleptophlebia bicornuta were larger and tended towards asynchrony in the trough with water (and temperatures) from their natal stream. Individuals in the trough with the warmest temperature were smaller than individuals in other troughs, but did not emerge earlier. Mesocapnia projecta showed greater synchrony in emergence, which occurred over a shorter interval, than the other species. When exposed to increased water temperatures, autumn-emergent taxa may be most vulnerable to trade-offs between asynchronous emergence and the probabilities for finding mates in unpredictable weather conditions.

Most caddisfly larvae build cases of silk and a variety of collected materials. Multiple functions, including protection from predators, resistance to entrainment by high flows, and improved respiration, have been suggested for caddisfly cases. We investigated the functional role of cases built by Dicosmoecus gilvipes, a limnephilid caddisfly. In this species, the 1^st- through 4^th-instar larvae build cases with plant material and attach Douglas-fir needles as lateral extensions that resemble vanes on an arrow. We tested whether the lateral extensions and entire case deterred predators by manipulating lateral extensions and case presence for larvae exposed to large steelhead trout. No larva with a case (with or without lateral extensions) was consumed during the experiment, whereas all larvae without a case were consumed. We tested whether lateral extensions provided stability against overturning and entrainment by manipulating presence of lateral extensions and subjecting larvae to turbulent flow conditions. Once dislodged, larvae with lateral extensions experienced fewer revolutions and regained their footing faster than those without extensions. Our results suggest lateral extensions provide stability against overturning in fast flow and may improve the ability of larvae to forage efficiently in turbulent flow conditions. Other caddisfly species build lateral extensions on their case, and the extensions may provide similar benefits for these taxa.

The stream-dwelling larvae of the caddisfly Glossosoma spp. are dominant grazers in lotic food webs and are capable of suppressing stream periphyton. We explored a method for developing a scaling relationship between macroinvertebrate density and local hydraulic variables. As an example of this method, we quantified habitat for larval stone-cased caddisflies, Glossosoma califica and Glossosoma penitum, in 3 coastal mountain streams in northern California over 2 y. We applied dimensional analysis to develop a functional relationship from a power law based on dimensionless local hydraulic and larval density variables that was applicable to areas where Glossosoma are present. Glossosoma densities were negatively correlated with streambed relative roughness and positively correlated with the ratio of inertial to gravitational forces in the stream. The proposed functional relationship described 41% of the variance in the spatial distribution of glossosomatid larvae. This expression could predict how density and constraints on effects of these important grazers would change under variable hydraulic conditions. Variogram analysis of Glossosoma spatial density and relative roughness revealed overlap in the variogram range, the separation distance above which point measurements were statistically independent. The analysis resulted in an average variogram range of 0.39 m for Glossosoma density and 0.26 m for roughness height. Abiotic variables are increasingly available from laser altimetry, so even where field sampling is limited the proposed scaling relationship facilitates prediction of larval biomass over a range of scales in lotic ecosystems.

The decline of freshwater mussels in the southeastern US emphasizes the need to evaluate the current status of mussel populations. We used the Robust Design, which is a capture–recapture sampling design, to estimate demographic parameters (apparent survival and temporary emigration) and capture probabilities of Alasmidonta arcula, Lampsilis dolabraeformis, Lampsilis splendida, and Pyganodon gibbosa in a large lowland river in Georgia. Mussels were sampled in individual habitat units using line-transect methods at ∼6-wk intervals from summer 2006–2007. We used an information-theoretic approach to evaluate the relative importance of maximum river discharge, habitat characteristics, mussel species, and season on temporary emigration (i.e., proportion of mussels not at the surface), apparent survival, and capture probability. The best-supported models indicated that apparent survival and capture probability varied positively with mussel shell length and among habitat types. Apparent survival (6-wk interval) ranged from 94 to 99% and was greatest in slackwater and lowest in swiftwater habitat. Capture probability ranged from 8 to 20% and was greatest in slackwater and lowest in swiftwater habitat. Temporary emigration also varied among species and season and appeared to be related to reproductive behavior, with the largest proportion of mussels occurring at the surface when mussels appeared to be reproductively active. A comparison of catch-per-unit-effort indices to population estimates suggested that the reliability of catch-per-unit-effort indices was influenced by vertical migration behavior and other factors affecting mussel capture probability.

Nutrient limitation plays an important role in shaping community structure and ecosystem processes in aquatic environments. Many types of nutrient diffusing substrata (NDS) have been used to estimate nutrient limitation in lotic systems. However, whether these various NDS methods produce comparable results is unknown. We evaluated the 3 most commonly used NDS methods—clay pots, plastic cups, and periphytometers—in a single stream to determine if they gave qualitatively similar results. We also examined the effects of initial nutrient ratios on diffusion rates in all 3 types of NDS and periphyton stoichiometry on clay pots. The largest response in chlorophyll a biomass consistently occurred on substrata that simultaneously diffused both inorganic N and P. However, each NDS method produced a significantly different picture of limitation. Clay pots showed that primary producers were colimited by N and P, plastic cups showed primary limitation by N and secondary limitation by P, and periphytometers showed primary limitation by P and secondary limitation by N. Nutrient diffusion rates were very different among methods. Effects of different N∶P ratios were only seen in clay pots. When N∶P was 16∶1, chlorophyll a biomass was low. When N∶P was 1∶1, periphyton had greater %C and %P and low C∶P and N∶P. Our results indicate that further research is required to clarify methodological differences between the types of NDS. Until such discrepancies are addressed, the results obtained with NDS methods should be interpreted with caution.

Urban land use has increased dramatically over the past few decades. Urban streams are distinguished from forested or agricultural streams, in particular, by their more variable and unpredictable hydrologic pattern. The resulting high variability in nutrient loading is likely to alter the elemental composition of primary producers and, ultimately, to change the elemental composition of other foodweb components. Ecological stoichiometry is a useful framework for improving our understanding of the mass balance of multiple key elements in ecosystems. To this end, the C∶N∶P of key foodweb components were measured in Oxley Creek, an urban catchment in southeastern Queensland, Australia. Ten stream reaches were sampled to explore the spatial variation of C∶N∶P of abundant taxonomic groups across the catchment. Four of these sites were sampled weekly (for 8 wk) to examine temporal variation in elemental composition. Our results suggested that spatial and temporal variation in elemental composition of primary producers and some animal taxa were highly dependent on local (i.e., site) conditions. This local dependence makes determination of catchment-wide drivers of stoichiometric variability difficult, but our results do suggest that site-based influences in urban streams can generate substantial variability in the C∶N∶P content of in-stream biota. In the context of other studies that have been undertaken principally in forested streams, this application of ecological stoichiometry promises to further our understanding of the effects of urbanization on stream food webs and the stability of elemental flow.

Great Plains rivers are characterized by unpredictable, thunderstorm-generated flow events that can abruptly restructure their physical complexity. These morphodynamic disturbances force river organisms to overcome hydrologic challenges. Some organisms surmount these challenges by using refugia, which play a key role in the ecological processes that govern lotic systems. The physical complexity of rivers can determine the availability and diversity of refugia both within and among rivers. However, physical complexity often changes with the hydrologic cycle and position along the river. We determined how the benthic community was affected by changes in the structure and abundance of in-channel refugia created by hydrologic fluctuations. We worked on and around sandbars in the Kansas River (Kaw), a multithread, sand-bed river. The composition of the zoobenthic community was directly related to the complexity of river morphology and flow rates. The community of 1 side channel consistently shifted over time between 2 distinct assemblages depending on whether the side channel was flowing or a disconnected slackwater. The benthic invertebrate community exploits many strategies to survive in the abrasive and continually fluctuating Kaw, including using sandbars as refugia and places for recolonization. The refuge provided by these sandbars will become increasingly important in the future if precipitation regimes become more variable as predicted by climate-change scenarios for the region. However, increased levee and dam construction threaten the persistence of the sandbars and vital habitats that they create.

Stream ecosystems receive and transport nutrients from terrestrial ecosystems and are important sites of N retention and removal in catchments. Many streams experience high anthropogenic N loading, which can overwhelm N retention and removal mechanisms and cause large downstream fluxes. Small, headwater streams are important sites of N retention, but the role of streams in larger catchments or as discharge increases is less clear. We evaluated how NO₃⁻ uptake dynamics responded to chronic N loading at different sites in a river draining a large desert catchment (∼7600 km²). Based on nutrient saturation theory, we predicted that chronic N loading would result in decreased uptake efficiency. Previous research suggested that increasing stream discharge also is associated with decreasing N-uptake efficiency. We addressed these relationships for a desert river by examining NO₃⁻ uptake dynamics over variable stream discharge encompassing its long-term range in base flow. We used short-term nutrient-addition studies to estimate uptake parameters for NO₃⁻ in a reference reach and a reach subject to chronic NO₃⁻ input. NO₃⁻ uptake efficiency was lower in the N-enriched reach than in the reference reach. However, within a reach, temporal changes in discharge and N concentration did not always affect uptake efficiency as predicted; e.g., pulses of high N flux following monsoon-season flooding did not result in reduced uptake efficiency. Estimates of denitrification rates indicated that this N-removal process was only a small fraction of N uptake, a result suggesting that most N is temporarily retained and eventually is exported downstream. N concentration exerted the primary influence on NO₃⁻ uptake efficiency in this large desert stream. However, within reaches, other factors that influence N retention, including floods, biota, and variable flow paths, probably contributed to observed temporal variation.

We evaluated the potential of habitat restoration to improve stream and riparian habitat and to minimize the prevalence of whirling disease in a population of native cutthroat trout in northern Utah. We fenced 67 ha of riparian habitat to exclude livestock and measured key response variables at impact and control sites before and after the completion of the exclosure. Total N concentrations decreased in response to the exclusion. Over this short time period (1–2 y postrestoration), the combination of natural variability and exclusion of livestock grazing appeared to alter the vegetation and riparian conditions through increased bank stability and decreased % cover of exotic plant species. The effect of the exclosure on whirling disease was confounded by climatic variation. However, restoration appeared to reduce the prevalence of whirling disease during a nondrought year, but not during a drought year. Therefore, in the short term, these beneficial effects of restoration on trout appeared to hinge on favorable climatic conditions. We expect the longer-term restoration response to be affected less than the short-term response by climatic conditions. The results of our study indicate that passive stream restoration is an effective management approach for restoring stream habitat and has the potential to minimize interactive effects of disease and habitat degradation, especially when other options for disease management are not possible or practical.

A systematic investigation of macrozoobenthos was conducted in Yangtze floodplain waters to reveal patterns of density, biomass, and production in relation to river connectivity. In the Yangtze-connected lakes, 78 taxa belonging to 33 families and 62 genera were identified. Macrozoobenthos density was 327 individuals/m², biomass was 1.40 g dry mass/m², and production was 3.23 g dry mass m⁻² y⁻¹. The assemblages were characterized by high diversity, high production, and high bivalve-filterer abundance. The key factor determining the macrozoobenthic assemblages was river connectivity. As river connectivity increased, 3 types of response patterns were observed: 1) density, biomass, and production of collector-filterers (mainly Bivalvia), shredders (e.g., Stictochironomus), and predators (e.g., Dytiscidae) showed unimodal changes, i.e., first increased and then decreased; 2) density, biomass, and production of collector-gatherers (mainly Tubificidae and Chironomidae) decreased continuously; and 3) density of scrapers (mainly Gastropoda) decreased, whereas their biomass and production changed unimodally. At an intermediate level of river connectivity, biomass and production of total macrozoobenthos reached maxima, whereas density decreased with increasing river connectivity. Previous research showed that α diversity of zoobenthos also peaks at moderate connectivity with rivers. Therefore, to maintain high productivity as well as high biodiversity in the Yangtze floodplain, protecting the remnants of river-connected lakes and linking disconnected lakes freely with the mainstream are crucial.