Stream Invertebrate Communities Research Articles

Spatial and temporal effects of heat waves on the diversity of European stream invertebrate communities

The frequency and magnitude of extreme events, such as heat waves, are predicted to increase with climate change. However, assessments of the response of biological communities to heat waves are often inconclusive. We aimed to assess the responses in abundance, taxonomic and functional diversity indices of stream invertebrate communities to heat waves using long-term monitoring data collected across Europe. We quantified the heat waves' magnitude, analyzed the spatial (i.e., long-term mean) and temporal (anomaly around the long-term mean) components of variation in the magnitude of heat waves, and their interaction with anthropogenic stressors (ecological quality and land cover). For the spatial component of variation, we found a negative association of the community indices to the increasing magnitude of heat waves. Sites undergoing heat waves of higher magnitude showed fewer species and lower trait diversity compared with sites experiencing lower magnitude heat waves. However, we could not detect an immediate temporal response of the communities to heat waves (i.e., the temporal component). Furthermore, we found that the effects of heat waves interacted with the ecological quality of the streams and their surrounding land cover. Diversity declined with increasing heat waves' magnitude in streams with higher ecological quality or surrounded by forest, which may be due to a higher proportion of sensitive species in the community. Heat waves' impacts on diversity were also exacerbated by increasing urban cover. The interaction between heat waves' magnitude and anthropogenic stressors suggests that the effects of extreme events can compromise the recovery of communities. Further, the predicted increase in heat waves will likely have long-term effects on stream invertebrate communities that are currently undetected.

Correction to “Individual and combined impacts of carbon dioxide enrichment, heatwaves, flow velocity variability, and fine sediment deposition on stream invertebrate communities”

Correction to “Individual and combined impacts of carbon dioxide enrichment, heatwaves, flow velocity variability, and fine sediment deposition on stream invertebrate communities”

Microplastics and riverine macroinvertebrate communities in a multiple-stressor context: A mesocosm approach

Growing use of synthetic materials has increased the number of stressors that can degrade freshwater ecosystems. Many of these stressors are relatively new and poorly understood, such as microplastics which are now ubiquitous in freshwater systems. The effects of microplastics on freshwater biota must be investigated further in order to better manage and mitigate their impacts. Our experiment provides the first empirical evaluation of stream invertebrate community dynamics in response to microplastics of different concentrations and sizes, in combination with fine sediment, a pervasive known stressor in running waters. In a 7-week streamside experiment using 64 flow-through circular mesocosms, we investigated the effects of exposure to three simulated microplastic influxes (polyethylene microspheres at four levels between 0 and 28,800 items/event) and the addition of fine sediment (to simulate a polluted stream environment). Invertebrate drift was monitored for 48 h immediately after each microplastic influx, and benthic invertebrate communities were sampled after 28 days of microplastic and sediment manipulations. Microplastic concentration, size and fine sediment all had significant factor main effects on several invertebrate drift response metrics, whereas few microplastic main effects were seen in the benthic community. However, interactive stressor effects were common in different combinations between sediment, microplastic size and concentration, suggesting multiple-stressor relationships between microplastics and fine sediment. Microplastic ingestion was witnessed in four of 12 taxa analysed: Hydrobiosidae, Deleatidium spp., Potamopyrgus antipodarum and Archichauliodes diversus. Our findings provide insights into how microplastics affect drift and benthic community dynamics of stream invertebrates in a field-realistic experimental setting and highlight areas requiring further study. These include investigations of invertebrate drift dynamics in response to other types of microplastics, the role invertebrate size may play in determining their vulnerability to microplastic pollution, and framing more microplastic research in a field-realistic multiple-stressor context.

Effects of riparian forest and annual variation in stream environmental conditions on leaf litter breakdown and invertebrate communities in highland grassland streams

Effects of riparian forest and annual variation in stream environmental conditions on leaf litter breakdown and invertebrate communities in highland grassland streams

Long-term climate and hydrologic regimes shape stream invertebrate community responses to a hurricane disturbance.

Disturbances can produce a spectrum of short- and long-term ecological consequences that depend on complex interactions of the characteristics of the event, antecedent environmental conditions, and the intrinsic properties of resistance and resilience of the affected biological system. We used Hurricane Harvey's impact on coastal rivers of Texas to examine the roles of storm-related changes in hydrology and long-term precipitation regime on the response of stream invertebrate communities to hurricane disturbance. We detected declines in richness, diversity and total abundance following the storm, but responses were strongly tied to direct and indirect effects of long-term aridity and short-term changes in stream hydrology. The amount of rainfall a site received drove both flood duration and flood magnitude across sites, but lower annual rainfall amounts (i.e. aridity) increased flood magnitude and decreased flood duration. Across all sites, flood duration was positively related to the time it took for invertebrate communities to return to a long-term baseline and flood magnitude drove larger invertebrate community responses (i.e. changes in diversity and total abundance). However, invertebrate response per unit flood magnitude was lower in sub-humid sites, potentially because of differences in refuge availability or ecological-evolutionary interactions. Interestingly, sub-humid streams had temporary large peaks in invertebrate total abundance and diversity following recovery period that may be indicative of the larger organic matter pulses expected in these systems because of their comparatively well-developed riparian vegetation. Our findings show that hydrology and long-term precipitation regime predictably affected invertebrate community responses and, thus, our work underscores the important influence of local climate to ecosystem sensitivity to disturbances.

Individual and combined impacts of carbon dioxide enrichment, heatwaves, flow velocity variability, and fine sediment deposition on stream invertebrate communities.

Climate change and land-use change are widely altering freshwater ecosystem functioning and there is an urgent need to understand how these broad stressor categories may interact in future. While much research has focused on mean temperature increases, climate change also involves increasing variability of both water temperature and flow regimes and increasing concentrations of atmospheric CO2, all with potential to alter stream invertebrate communities. Deposited fine sediment is a pervasive land-use stressor with widespread impacts on stream invertebrates. Sedimentation may be managed at the catchment scale; thus, uncovering interactions with these three key climate stressors may assist mitigation of future threats. This is the first experiment to investigate the individual and combined effects of enriched CO2, heatwaves, flow velocity variability, and fine sediment on realistic stream invertebrate communities. Using 128 mesocosms simulating small stony-bottomed streams in a 7-week experiment, we manipulated dissolved CO2 (ambient; enriched), fine sediment (no sediment; 300 g dry sediment), temperature (ambient; two 7-day heatwaves), and flow velocity (constant; variable). All treatments changed community composition. CO2 enrichment reduced abundances of Orthocladiinae and Chironominae and increased Copepoda abundance. Variable flow velocity had only positive effects on invertebrate abundances (7 of 13 common taxa and total abundance), in contrast to previous experiments showing negative impacts of reduced velocity. CO2 was implicated in most stressor interactions found, with CO2 × sediment interactions being most common. Communities forming under enriched CO2 conditions in sediment-impacted mesocosms had ~20% fewer total invertebrates than those with either treatment alone. Copepoda abundances doubled in CO2-enriched mesocosms without sediment, whereas no CO2 effect occurred in mesocosms with sediment. Our findings provide new insights into potential future impacts of climate change and land use in running freshwaters, in particular highlighting the potential for elevated CO2 to interact with fine sediment deposition in unpredictable ways.

Multiple lines of evidence point to pesticides as stressors affecting invertebrate communities in small streams in five United States regions

Multistressor studies were performed in five regions of the United States to assess the role of pesticides as stressors affecting invertebrate communities in wadable streams. Pesticides and other chemical and physical stressors were measured in 75 to 99 streams per region for 4 weeks, after which invertebrate communities were surveyed (435 total sites). Pesticides were sampled weekly in filtered water, and once in bed sediment. The role of pesticides as a stressor to invertebrate communities was assessed by evaluating multiple lines of evidence: toxicity predictions based on measured pesticide concentrations, multivariate models and other statistical analyses, and previously published mesocosm experiments. Toxicity predictions using benchmarks and species sensitivity distributions and statistical correlations suggested that pesticides were present at high enough concentrations to adversely affect invertebrate communities at the regional scale. Two undirected techniques—boosted regression tree models and distance-based linear models—identified which pesticides were predictors of (respectively) invertebrate metrics and community composition. To put insecticides in context with known, influential covariates of invertebrate response, generalized additive models were used to identify which individual pesticide(s) were important predictors of invertebrate community condition in each region, after accounting for natural covariates. Four insecticides were identified as stressors to invertebrate communities at the regional scale: bifenthrin, chlordane, fipronil and its degradates, and imidacloprid. Fipronil was particularly important in the Southeast region, and imidacloprid, bifenthrin, and chlordane were important in multiple regions. For imidacloprid, bifenthrin, and fipronil, toxicity predictions were supported by mesocosm experiments that demonstrated adverse effects on naïve aquatic communities when dosed under controlled conditions. These multiple lines of evidence do not prove causality—which is challenging in the field under multistressor conditions—but they make a strong case for the role of insecticides as stressors adversely affecting invertebrate communities in streams within the five sampled regions.

Effects of flow reduction and artificial light at night (ALAN) on litter decomposition and invertebrate communities in streams: A flume experiment

River ecosystems are heavily impacted by multiple stressors, where effects can cascade downstream of point sources. However, a spatial approach to assess the effects of multiple stressors is missing. We assessed the local and downstream effects on litter decomposition, and associated invertebrate communities of two stressors: flow reduction and artificial light at night (ALAN). We used an 18-flow-through mesocosm system consisting of two tributaries, where we applied the stressors, merging in a downstream section. We assessed the changes in decomposition rate and invertebrate community structure in leaf bags. We found no effect of ALAN or its interaction with flow reduction on the litter decomposition or the invertebrate community in the tributaries. Flow reduction alone led to a 14.8 % reduction in decomposition rate in the tributaries. We recorded no effect of flow reduction on the macroinvertebrates community composition in the litter bags. We also observed no effects of the spatial arrangement of the stressors on the litter decomposition and macroinvertebrate community structure downstream. Overall, our results suggest the impact of stressors on litter decomposition and macroinvertebrate communities remained local in our experiment. Our work thus calls for further studies to identify the mechanisms and the conditions under which spatial effects dominate over local processes.

Slow recovery of stream invertebrates on subantarctic Macquarie Island after eradication of introduced rabbits and regrowth of vegetation

Context Streams on subantarctic Macquarie Island were first sampled for freshwater invertebrates in 1992 when rabbit numbers were low. Then an average 11.6 taxa per site were recorded. Between 2000 and 2011, vegetation was overgrazed as rabbit numbers increased. In 2008 and 2010, 7.4–8.4 taxa per site were recorded, abundance of most taxa had decreased and greatest compositional changes occurred at sites exposed to moderate or severe vegetation damage. Rabbits were eradicated in 2011 and substantial regrowth of vegetation was evident by 2016. Aims Sites were resampled in 2016 to determine the extent to which the invertebrate communities had changed after rabbit removal. Methods In all, 13 of the original 15 sites sampled in 1992 were resampled. Five kick samples were taken at each site. Key results Mean taxon richness (8.2 taxa per site) and community composition at individual sites remained, in 2016, very similar to that recorded in 2008 and 2010 when the island was heavily grazed. Conclusions Recovery of stream invertebrate communities appeared to be slow, possibly because few refuges were available. Minor changes in climate and water quality did not influence recovery. Implications Stream invertebrate communities could take a decade or more to recover.

Facilitation strength across environmental and beneficiary trait gradients in stream communities.

Ecosystem engineers modify habitats in ways that facilitate other community members by ameliorating harsh conditions. The strength of such facilitation is predicted to be influenced by both beneficiary traits and abiotic context. One key trait of animals that could control the strength of facilitation is beneficiary body size because it should determine how beneficiaries fit within and exploit stress ameliorating habitat modifications. However, few studies have measured how beneficiary body size relates to facilitation strength along environmental gradients. We examined how the strength of facilitation by net-spinning caddisflies on invertebrate communities in streams varied along an elevation gradient and based on traits of the invertebrate beneficiaries. We measured whether use of silk retreats as habitat concentrated invertebrate density and biomass compared to surrounding rock surface habitat and whether the use of retreat habitat varied across body sizes of community members along the gradient. We found that retreats substantially concentrated the densities of a diversity of taxa including eight different Orders, and this effect was greatest at high elevations. Caddisfly retreats also concentrated invertebrate biomass more as elevation increased. Body size of invertebrates inhabiting retreats was lower than that of surrounding rock habitats at low elevation sites, however, body size between retreats and rocks converged at higher elevation sites. Additionally, the body size of invertebrates found in retreats varied within and across taxa. Specifically, caddisfly retreats functioned as a potential nursery for taxa with large maximal body sizes. However, the patterns of this taxon-specific nursery effect were not influenced by elevation unlike the patterns observed based on community-level body size. Collectively, our results indicate that invertebrates use retreats in earlier life stages or when they are smaller in body size independent of life stage. Furthermore, our analysis suggests that facilitation strength intensifies as elevation increases within stream invertebrate communities. Further consideration of how trait variation and environmental gradients interact to determine the strength and direction of biotic interactions will be important as species ranges and environmental conditions continue to shift.

Disproportional vulnerability of mountain aquatic invertebrates to climate change effects

ABSTRACT Mountain freshwater communities are generally considered sensible to accelerated climatic changes, though their vulnerabilities have not been well evaluated. Individual species or species groups are expected to respond differently depending on their adaptations, traits, or distributions, but this has not yet been distinguished. This work used available climate change vulnerability scores (ccvs) of European Ephemeroptera, Plecoptera, and Trichoptera (EPT) species (n = 1,402) to (1) compare the vulnerability between species pools of different ecoregions including alpine species and alpine endemics, (2) contrast the vulnerability between the different insect orders, and (3) assess the altitude–vulnerability relationship within the European Alps. We revealed fifty alpine Plecoptera and Trichoptera species that are categorized highly vulnerable to climate change effects (= 31 percent of all highly vulnerable European species) with the highest proportions in species inventories of alpine endemics and high-altitude waters (51 percent of high-altitude species are classified as highly vulnerable). The ccvs analysis specifically for mountain waters shows that a disproportionately high number of alpine species, and particularly alpine endemics, will be affected by climate change and suggests that Ephemeroptera may be better prepared than Plecoptera and Trichoptera. Thus, this trait-based evaluation suggests that mountain stream invertebrate communities are undergoing disproportionate restructurings in response to climate change effects more than lowland communities are.

On the delay between water temperature and invertebrate community response to warming climate.

We evaluated the effect of global warming on invertebrate communities at high altitudes using data from the Careser system. We procured data on air temperature, which was obtained over 50 years at altitudes above 2600 m a.s.l., and data on water temperature, which was available for approximately 30 years. We sampled thrice in the past 20 years (2001, 2014, 2018) at three sampling sites (CR0-metakryal, CR1-hypokryal, CR2-glacio-rhithral) of the Careser glacier-fed stream and its main non-glacial tributary (CR1bis-krenal). Warmer climates were observed in the last decade compared to the 1980s, with a mean maximum summer air temperature (mTmax) increase of 1.7 °C at 2642 m a.s.l. and 1.8 °C at 2858 m a.s.l. Compared to air temperatures, the rise in water temperature was delayed by approximately 20 years; water mTmax started to increase in 2003, reaching 8.1 °C at 2642 m a.s.l. and 2.4 °C at 2858 m a.s.l in the year 2020. The invertebrate community exhibited a delayed response approximately 13 years from the water warming; there was a sequential increase in the number of taxa, Shannon diversity, and after 17 years, functional diversity. In the kryal sites, taxonomical and functional diversity changed more consistently than in the glacio-rhithral site in the same period, due to the arrival of taxa that were previously absent upstream and bearers of entirely new traits. Progressive taxonomical homogenisation was evident with decreasing glacial influence, mainly between glacio-rhithral and krenal sites. The numbers of Diamesa steinboecki, an insect that was adapted to the cold, declined in summer (water mTmax >6 °C and air mTmax >12 °C). This study highlights the mode and time of response of stream invertebrate communities to global warming in alpine streams and provides guidelines for analysing changes in the stream invertebrate communities of other glacial systems in alpine regions.

Structure and functional composition of macroinvertebrate communities in coastal plain streams across a precipitation gradient

Abstract Climate change is expected to alter rainfall and temperature regimes across the world. The hydrology and riparian zone vegetation of lotic ecosystems are tightly linked to rainfall and a mechanistic understanding of the effects of rainfall on lotic ecosystems is needed to forecast the ecological impacts of climate change. However, it is difficult to isolate rainfall effects from other environmental variables that covary across climates. To address this, we leveraged a unique steep rainfall gradient with few covarying changes in elevation, temperature, and geology to evaluate the effects of rainfall on stream invertebrate communities. We surveyed nine streams in the Texas Gulf Coast Prairie distributed along a 550–1,350 mm/year rainfall gradient. Four sites were classified as drier semi‐arid streams (<750 mm annual rainfall) and five sites were classified as wetter sub‐humid streams (>750 mm annual rainfall). A suite of characteristics including benthic invertebrate community metrics, flow conditions, and water quality variables were assessed monthly for 14 months at each site to relate precipitation regime to stream structure and function. Precipitation regime was observed to be a master explanatory variable. As annual rainfall increased, the flow environment became more stable within seasons and predictable across seasons, influencing spatial structure and temporal variability of invertebrate community composition. Wetter streams were dominated by slower growing taxa without adaptions for desiccation resistance and strong dispersal. Wetter sites displayed seasonal variation in community composition and species richness, whereas temporal variation in communities in drier streams was controlled by stochastic variation in flow conditions. These observations show that differences in local annual rainfall correlated with major changes to community structure and functional composition. We hypothesise that this association is related to the connection of rainfall to hydrological stability, particularly the frequency of low flow disturbances, and the subsequent effects on riparian vegetation and temporally available niches to stream invertebrates. Our work adds to evidence that alterations in precipitation patterns associated with climate change have sweeping impacts on lotic fauna.

Rethinking biodiversity patterns and processes in stream ecosystems

AbstractA major goal of community ecology is understanding the processes responsible for generating biodiversity patterns along spatial and environmental gradients. In stream ecosystems, system‐specific conceptual frameworks have dominated research describing biodiversity change along longitudinal gradients of river networks. However, support for these conceptual frameworks has been mixed, mainly applicable to specific stream ecosystems and biomes, and these frameworks have placed less emphasis on general mechanisms driving biodiversity patterns. Rethinking biodiversity patterns and processes in stream ecosystems with a focus on the overarching mechanisms common across ecosystems will provide a more holistic understanding of why biodiversity patterns vary along river networks. In this study, we apply the theory of ecological communities (TEC) conceptual framework to stream ecosystems to focus explicitly on the core ecological processes structuring communities: dispersal, speciation, niche selection, and ecological drift. Using a unique case study from high‐elevation networks of connected lakes and streams, we sampled stream invertebrate communities in the Sierra Nevada, California, USA to test established stream ecology frameworks and compared them with the TEC framework. Local diversity increased and β‐diversity decreased moving downstream from the headwaters, consistent with the river continuum concept and the small but mighty framework of mountain stream biodiversity. Local diversity was also structured by distance below upstream lakes, where diversity increased with distance below upstream lakes, in support of the serial discontinuity concept. Despite some support for the biodiversity patterns predicted from the stream ecology frameworks, no single framework was fully supported, suggesting “context dependence.” By framing our results under the TEC, we found that species diversity was structured by niche selection, where local diversity was highest in environmentally favorable sites. Local diversity was also highest in sites with small community sizes, countering the predicted effects of ecological drift. Moreover, higher β‐diversity in the headwaters was influenced by dispersal and niche selection, where environmentally harsh and spatially isolated sites exhibit higher community variation. Taken together our results suggest that combining system‐specific ecological frameworks with the TEC provides a powerful approach for inferring the mechanisms driving biodiversity patterns and provides a path toward generalization of biodiversity research across ecosystems.

Impacts of urbanization on chloride and stream invertebrates: A 10-year citizen science field study of road salt in stormwater runoff.

The use of deicing agents during the winter months is one of many stressors that impact stream ecosystems in urban and urbanizing watersheds. In this study, a long-term data set collected by citizen scientists with the Missouri Stream Team was used to evaluate the relationships between watershed urbanization metrics and chloride metrics. Further, these data were used to explore the effects of elevated chloride concentrations on stream invertebrate communities using quantile regression. While the amount of road surface in a watershed was a dominant factor in predicting the maximum chloride measurement, the median chloride concentration was also strongly related to the amount of medium-to-high density development in the watershed, suggesting that nonmunicipal salt use is an important contributor to increases in base flow chloride concentrations. Additionally, chloride concentration appears to be one of the many factors that impact invertebrate density and diversity measurements, with decreases in invertebrate diversity corresponding with the US Environmental Protection Agency water quality criteria. Our findings suggest that the use of chloride-based road salt on municipal roads as well as on nonmunicipal settings is contributing to a loss of diversity and density of aquatic invertebrate communities in urban regions. Integr Environ Assess Manag 2022;18:1667-1677. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Macroinvertebrate responses to differing riparian treatments following forest harvest in the headwaters of Trask River watershed

Although it is well-established that macroinvertebrates are an integral part of a healthy stream ecosystem, studies designed to inform forest harvest best management practices for sustainability of macroinvertebrate communities in small streams have been limited. Current riparian management practices for headwater streams generally focus on providing adequate wood supply, reducing debris flows and transport of sediment, and maintaining water quality in larger streams that contain fish. Here we studied the effects of contemporary forest harvest practices on benthic macroinvertebrate density and community composition in 12 small headwater streams as part of the Trask River Watershed Study. To account for seasonal and year-to-year variability in macroinvertebrate densities, we sampled each site at the same time of year for six years before and four years after harvest. Three watersheds were clearcut with variable riparian buffers, three were clearcut with 12 m riparian buffers, and one was thinned with 15 m buffers. Five adjacent watersheds were not treated and were studied as reference sites. All sites had approximately 50 yr old conifer and alder forests, which had revegetated following fires and harvest in prior decades.In these steep mountain streams, benthic macroinvertebrate density and community composition were generally similar across watersheds prior to harvest. Collectors were the most abundant functional feeding group, followed by shredders; scrapers were the least abundant. After harvest, in two of the three clearcut watersheds with variable buffers, the total benthic density and percentage of collectors increased, primarily due to greater numbers of Chironomidae. We also observed more abundant emergence post-harvest at these two watersheds. In the third clearcut watershed with a variable buffer and in the three clearcut watersheds with uniform 12 m riparian buffers, we did not see changes in density or functional feeding groups after harvest. We explored the spatial and temporal aspects of the data using both non-parametric and parametric statistical methods. High variability swamped the treatment effect when watersheds were grouped by riparian treatment for the repeated measure analyses, while NMDS showed a significant shift post-harvest for the watersheds with variable buffers. In the clearcut watersheds with uniform buffers, macroinvertebrates densities and community composition did not shift. At two of the clearcut watersheds with variable buffers, we observed increased density for the first two years after harvest, and chironomids comprised up to 80% of the abundance in samples. In the subsequent years, we documented mixed responses for two watersheds. It was invaluable to have multiple pre- and post-harvest sampling periods in both harvested and reference watersheds in order to better identify site specific responses to treatment and to separate background variability from responses to harvest. We show that retention of riparian vegetation on headwater streams during clearcut harvesting minimized changes in total macroinvertebrate densities and community composition. Small buffers may be key to maintenance of diverse stream invertebrate communities in headwaters.

Explorando o impacto da presença de detritos exóticos na comunidade de invertebrados aquáticos e no processo de decomposição foliar em um riacho na Mata Atlântica

Abstract: Aim In this study, we examined the effects of non-native leaf litter on the functioning of an Atlantic Forest stream ecosystem. Methods Were tested two predictions: (i) Leaf litter from the native trees with high nutritional quality will have higher decomposer’s activity and faster litter decomposition; (ii) Given the presence of anti-grazing defenses, we also hypothesized that non-native leaf litter would be colonized by fewer invertebrates and that native species would be more species-rich. For this, in a forest stream (Florianópolis, SC, Brazil) we conduct the experiment to understand the decomposition and biological colonization of leaf litter among two non-native (Eucalyptus sp. and Pinus radiata D. Don) and two native trees (Ficus eximia Schott and Alchornea triplinervia (Spreng) Mull. Arg). Results Our predictions were partially corroborated. The percentage of dry mass remaining was lower for the native leaf litter. The invertebrate abundance and richness, and functional feeding groups vary between native and non-native leaf litter. Invertebrate abundance was higher in non-native Eucalyptus detritus, largely due to the high larval abundance of Chironomidae (Diptera). Conclusions Our results indicate that the presence of non-native riparian species can modify leaf decomposition and aquatic invertebrate communities in subtropical streams, with potential consequences for ecosystem functioning.

Riparian plant species offer a range of organic resources to stream invertebrate communities through varied leaf breakdown rates

ABSTRACT Riparian plants provide an important source of energy for freshwater food webs through inputs of leaf litter. Planting riparian buffers with mixed species could enhance the detrital resource supply for invertebrates through varied leaf breakdown rates. To quantify leaf breakdown rates and invertebrate colonisation, we used leaves from eleven grass, shrub and tree species common along agricultural waterways in New Zealand. Breakdown of leaves immersed in a spring-fed stream differed significantly among species, being fastest for pasture grass (k = 0.0458 day−1) followed by broadleaf, pittosporum, willow, toetoe, poplar, gorse, Carex, eucalyptus, flax, and slowest for cabbage tree leaves (k = 0.0099 day−1). Invertebrate community composition did not differ between leaf species, but consumers were extremely abundant on some leaves (e.g. 51–83 Potamopyrgus snails g−1 pasture grass), indicating coarse detrital resources were in high demand for food or habitat. These breakdown rates could inform selection of riparian plant combinations that will enhance food availability for stream communities, especially continuity of supply, thereby contributing to waterway restoration.

Fresh insights into Mediterranean biodiversity: environmental DNA reveals spatio-temporal patterns of stream invertebrate communities on Sicily

The Mediterranean region with its islands is among the top biodiversity hotspots. It houses numerous freshwater taxa with a high rate of endemism, but is heavily impacted by anthropogenic pressures and global climate change. To conserve biodiversity, reliable data on species and genetic diversity are needed especially for the scarcely known insular freshwater ecosystems. Environmental DNA (eDNA) metabarcoding provides a straight-forward opportunity to assess aquatic biodiversity. Therefore, we conducted the first eDNA metabarcoding study in one stream catchment on Sicily. Specifically, we aimed to (i) investigate spatial diversity patterns of macroinvertebrate communities, (ii) assess seasonal changes (autumn and winter), and (iii) check if dispersal barriers can be identified. Water samples were taken at 27 different sites in two seasons and eDNA metabarcoding was performed using a fragment of the mitochondrial cytochrome c oxidase subunit I gene as a marker. In total, we detected 98 macroinvertebrate species, including 28 taxa potentially new to Sicily. Exact sequence variant and species composition data showed that diversity differed between seasons with less taxa detected in winter. We also detected a dispersal barrier, which had a stronger effect in autumn. Our findings show that eDNA metabarcoding provides valuable information on Sicilian freshwater biodiversity. We therefore encourage its application for understudied regions to better understand the state and dynamics of freshwater biodiversity.

Energy pathways modulate the resilience of stream invertebrate communities to drought

While climate change is altering ecosystems on a global scale, not all ecosystems are responding in the same way. The resilience of ecological communities may depend on whether food webs are producer- or detritus-based (i.e. 'green' or 'brown' food webs, respectively), or both (i.e. 'multi-channel' food web). Food web theory suggests that the presence of multiple energy pathways can enhance community stability and resilience and may modulate the responses of ecological communities to disturbances such as climate change. Despite important advances in food web theory, few studies have empirically investigated the resilience of ecological communities to climate change stressors in ecosystems with different primary energy channels. We conducted a factorial experiment using outdoor stream mesocosms to investigate the independent and interactive effects of warming and drought on invertebrate communities in food webs with different energy channel configurations. Warming had little effect on invertebrates, but stream drying negatively impacted total invertebrate abundance, biomass, richness and diversity. Although resistance to drying did not differ among energy channel treatments, recovery and overall resilience were higher in green mesocosms than in mixed and brown mesocosms. Resilience to drying also varied widely among taxa, with larger predatory taxa exhibiting lower resilience. Our results suggest that the effects of drought on stream communities may vary regionally and depend on whether food webs are fuelled by autochthonous or allochthonous basal resources. Communities inhabiting streams with large amounts of organic matter and more complex substrates that provide refugia may be more resilient to the loss of surface water than communities inhabiting streams with simpler, more homogeneous substrates.