Benthic Macroinvertebrate Density Research Articles

Spatiotemporal Changes and Recovery of Benthic Macroinvertebrate Communities after the Hebei Spirit Oil Spill in the Subtidal Area around the Taean Peninsula in South Korea

Marine oil pollution is a significant environmental issue that significantly threatens ocean ecosystems. It occurs frequently and has devastating consequences for marine life, coastal habitats, and human communities. We examined the recovery of benthic macroinvertebrate communities in shallow subtidal areas following the Hebei Spirit oil spill around the Taean Peninsula, South Korea, in 2007. Benthic macroinvertebrates were collected seasonally from 15 survey sites between 2008 and 2015. Immediately after the spill in 2008, species richness and density of benthic macroinvertebrates decreased by 66.7% and 37.0%, respectively, compared to before the oil spill in 2007. Cluster analysis based on benthic macroinvertebrate communities delineated the communities from 2008 to 2009 as a distinct cluster characterized by markedly low species richness. Communities from other periods exhibited spatiotemporal variability based on the sampling location and sediment characteristics. By 2011, species richness and density had recovered to levels similar to those in 2007, which was particularly pronounced regarding the resurgence of arthropods and mollusks. Notably, populations of amphipods that are particularly sensitive to oil, such as Urothoe sp. and Byblis spp., showed signs of recovery in 2011; however, recovery of the benthic community at the site nearest to the oil spill area, was not evident until July 2013, as indicated by the benthic opportunistic polychaete amphipod index. This underscores that prolonged time periods are required for communities to fully recuperate after oil spills.

Nature-based bank protection measures improve benthic macroinvertebrates in a stream draining an agriculturally dominated watershed

Increased bank erosion is one of the most significant threats to agricultural stream ecosystems. However, it is challenging to ascertain whether bank restoration measures positively affect in-stream habitats and aquatic communities. This study evaluated three nature-based bank protection measures' short-term (2-year) effects on aquatic physical habitat quality and benthic macroinvertebrate communities in a headwater stream in agricultural areas. The results demonstrate that nature-based bank protection measures can significantly improve the quality of aquatic physical habitat in streams. The TPRW (timber piles + riprap + willow cuttings) and WTRW (waste tires + riprap + willow cuttings) measures exhibited the most pronounced improvement in the quality of aquatic physical habitat in streams. The diversity of benthic macroinvertebrates was the highest in the TPRW reach, and the seasons significantly affected the density of benthic macroinvertebrates. The Shannon-Wiener diversity index and Margalef's richness index were the most consistent with the changing trend of physical habitat quality and are effective indicators of the ecological effects of stream restoration measures in our study area. In this study area, TPRW is the preferred measure for streambank restoration of agricultural streams, and WTRW is the alternative measure. However, the ecological effects of WTRW need to be monitored over a more extended period to identify whether there is potential ecotoxicity in the process of weathering and decomposition.

Density data for Lake Erie benthic invertebrate assemblages from 1930 to 2019.

Benthic invertebrates are important trophic links in food webs and useful bioindicators of environmental conditions, but long-term benthic organism abundance data across broad geographic areas are rare and historic datasets are often not readily accessible. This dataset provides densities of benthic macroinvertebrates collected from 1930 to 2019 during surveys in Lake Erie, a Laurentian Great Lake. The surveys were funded by the governments of the United States and Canada to investigate the status and changes in the benthic community. From the total of 21 lake-wide and basin-wide benthic surveys conducted in Lake Erie from 1929 to 2019, we were able to acquire data for 17 surveys, including species-level data for 10 surveys and data by higher taxonomic groups for seven surveys. Our amassed Lake Erie dataset includes data from 11 surveys (including five with species-level data) conducted in the western basin in 1930-2019, seven surveys (six with species-level data) in the central basin, and eight surveys (seven with species-level data) in the eastern basin (1973-2019). This Lake Erie dataset represents the most extensive temporal dataset of benthic invertebrates available for any of the Laurentian Great Lakes. Benthic samples were collected using Ponar or Shipek bottom dredges and taxa densities were calculated as individuals per square meter using the area of the dredge. Density data are provided for taxa in the Annelida, Arthropoda, Mollusca, Cnidaria, Nemertea, and Platyhelminthes phyla. Current taxonomy was used for most groups but, in a few cases, older taxonomic names were used for consistency with historical data. Analysis of this dataset indicates that eutrophication, water quality improvement, and dreissenid introduction were the major drivers of changes in the benthic community in the western basin, while hypoxia was a major factor in the central basin, and dreissenid introduction was the most important driver in the eastern basin. Considering the rarity of high taxonomic resolution long-term benthic data for lake ecosystems, this dataset could be useful to explore broader aspects of ecological theory, including effects of eutrophication, hypoxia, invasive species, and other factors on community organization, phylogenetic and functional diversity, and spatial and temporal scales of variation in community structure. In addition, the dataset could be useful for studies on individual species, including abundance and distribution, species co-occurrence, and how the patterns of dominance and rarity change over space and time. Use of this dataset for academic or educational purposes is encouraged as long as this data paper is properly cited.

Community Structure and Water Quality Assessment of Benthic Macroinvertebrates in Hongze Lake.

This study investigated the species, density, biomass and physicochemical factors of benthic macroinvertebrates in Hongze Lake from 2016 to 2020. Redundancy analysis (RDA) was used to analyze the relationship between physicochemical parameters and the community structure of macroinvertebrates. Macroinvertebrate-based indices were used to evaluate the water quality conditions in Hongze Lake. The results showed that a total of 50 benthic species (10 annelids, 21 arthropods and 19 mollusks) were collected. The community structure of benthic macroinvertebrates varied in time and space. The dominant species were Limnodrilus hoffmeisteri (L.hoffmeisteri), Corbicula fluminea (C.fluminea), Nephtys oligobranchia (N.oligobranchia). In 2016, arthropods such as Grandidierella sp. were the dominant species of benthos in Hongze Lake while annelids and mollusks dominated from 2017 to 2020, such as L.hoffmeisteri, N.oligobranchia, C.fluminea. The benthic fauna of Chengzi Lake and Lihewa District were relatively abundant and showed slight variation, while the benthic macroinvertebrates of the Crossing the water area were few and varied greatly. RDA showed that changes in benthic macroinvertebrate structure were significantly correlated with dissolved oxygen (DO), Pondus Hydrogenii (pH) and transparency (SD). The Shannon Wiener, Pielou, and Margalef indices indicate that Hongze Lake is currently in a moderately polluted state. Future studies should focus on the combined effects of various physicochemical indicators and other environmental factors on benthic communities.

The impacts of non-native watercress in Oklahoma spring ecosystems

Watercress (Nasturtium officinale) has spread widely from Europe and commonly occurs in Oklahoma (USA) springs. Watercress is usually an emergent plant and affects water flow patterns and may provide habitat for biota. Although watercress is not considered an invasive species, its impacts in springs have not been reported. With a goal to describe possible impacts of watercress in springs, 14 karst-associated springs (12 with watercress) were surveyed for sediment characteristics, macroinvertebrates, and diatoms in July 2021. The effects of watercress were evident. Sediment particle size was unaffected by the presence of watercress but sediment organic matter was higher under watercress beds than outside of beds. Although there was no difference in total benthic macroinvertebrate density or richness, higher organic matter was associated with slightly higher abundances of detritivorous and predatory macroinvertebrates (SIMPER). Submerged portions of watercress had significantly much lower diatom density than other spring substrates, with diatom composition similar to other plants but different from that of rocks. Self-shading or possible allelopathy may cause the low diatom density. The significantly lower macroinvertebrate density within watercress mats relative to that of other plants may result from a reduced food source because the plant’s low diatom density. Only predatory damselflies were more common in watercress than in other plants, which had more abundant grazers. Although watercress can increase heterogeneity in sediments and is sometimes valued as an edible plant, watercress supports low algal and macroinvertebrate densities, such that extensive growth of watercress can have an overall negative impact on spring ecosystems.

Short‐term effects of wildfire on high elevation stream‐riparian food webs

Understanding how wildfires affect food web structure and function remains an important challenge, especially at high elevations that historically have burned infrequently. In particular, fires may alter the magnitude of reciprocal cross‐ecosystem subsidies, leading to indirect effects on aquatic and terrestrial consumers. We quantified characteristics of high‐elevation (2500–3000 m) stream‐riparian food webs at 10 locations in the southern Rocky Mountains less than one year following high‐intensity, stand‐replacing wildfires. Using a paired ‘burned−unburned' stream survey design, we assessed benthic periphyton, aquatic macroinvertebrate community structure, trout population characteristics, trout stomach contents, inputs and emergence of insects to and from streams, and abundance of predatory riparian spiders that consume aquatic insects. Benthic macroinvertebrate density, flux of emerging aquatic insects, and riparian spider abundances were lower at burned sites. Fluxes of insect inputs entering the stream did not differ with burn status, despite the loss of riparian vegetation due to fire. Trout were somewhat less abundant, but larger on average at burned sites and did not differ in body condition. These results suggest mortality of smaller trout from fire disturbance and/or recolonization of burned sites by larger individuals. Trout showed subtle changes in diet composition with burn status, but no change in biomass or number of prey consumed. In general, burned sites showed greater variation in community characteristics than unburned sites, which may reflect differences in the timing and magnitude of post‐fire flooding, erosion, and scouring of the stream bed. Taken together, our results suggest that short‐term effects of fire disturbance strongly altered some food web responses, but others appeared relatively resilient, which is notable given the high severity of the wildfires in the study area.

The Effects of Channelization with Low In-Stream Barriers on Macroinvertebrate Communities of Mountain Rivers

The effects of channelization with low in-stream barriers in mountain rivers on macroinvertebrate communities are still weakly recognised. We aimed to assess the differences in structure and density of benthic macroinvertebrates between two north Carpathian mountain rivers: one channelized with a cascade of concrete sills and the other one with block ramps. Water was collected five times for physicochemical analysis. Macroinvertebrate fauna and fine bottom sediments were collected three times (spring, summer, autumn) from different habitat types: glides, runs, pools and riffles of the estimated channel surface. The in-stream barriers altered the channel gradient and flow velocity, reducing the area of pools and riffles as well as extending the area of glides with slow current velocities, associated with the highest rate of fine sediment deposition. Channel modifications induced a general shift of investigated fluvial systems toward lentic habitat conditions. Macroinvertebrate communities characteristic of slow-flowing rivers and pools became dominant, while those characteristic for the riffles of mountain rivers were confined to only small areas. The studied section of the Porębianka River channelized with block ramps exhibited greater diversity in the macroinvertebrate community between habitats and significantly higher macroinvertebrate density than the Mszanka River which was channelized with concrete sills.

Habitat formed by the invasive macroalga Caulerpa filiformis (Suhr) Hering (Caulerpales, Chlorophyta) alters benthic macroinvertebrate assemblages in Peru

The green macroalga Caulerpa filiformis has been spreading on shallow soft sediment habitats along the Peruvian coast, colonizing previously unvegetated sediments to create monospecific meadows. We examined the nature of the impact of C. filiformis meadows on the density, taxonomic richness and assemblage structure of epifaunal and infaunal benthic macroinvertebrates. Specifically, we tested whether the spread of C. filiformis has resulted in different macroinvertebrate assemblages than those formed by the dominant native macroalgae (i.e., Rhodymenia spp.) and unvegetated sediments. Surveys were undertaken in two bays in each of two locations, in central and southern Peru, during winter 2017 and summer 2018. In general, our results show that macroinvertebrate assemblages were similar across all three habitats, although there were some differences, related to location and time, but with no clear patterns observed. Taxonomic richness and density was generally higher in the vegetated habitats than the unvegetated habitat, and where there were differences between the two vegetated habitats there was no consistent pattern of which habitat supported the highest richness or density. Given invading C. filiformis is primarily colonizing unvegetated habitats it would appear that this species is creating a new niche which supports similar assemblages, but higher taxonomic richness and density than unvegetated habitats. While our study suggests that C. filiformis is having a limited ecological impact we recommend that actions be put in place to limit the spread of this invasive species at the same time as increasing monitoring of the ecological impacts of this species as lags in the ecological impacts of invasive species are common.

Contribution of alien peracarid crustaceans to the biocontamination of benthic macroinvertebrate assemblages in Croatian large rivers

Peracarid crustaceans (orders Amphipoda, Isopoda and Mysida) are one of the most important groups of invaders in fresh and brackish waters. Although large rivers in Croatia have been heavily invaded by peracarid crustaceans, little is known about their impact on local benthic macroinvertebrate assemblages. The main aim of this study was to investigate the contribution of alien Peracarida to the biocontamination of macroinvertebrate assemblages in Croatian large rivers as a proxy measure of their impact. Quantitative sampling was conducted twice (2015 and 2016/2017), at 48 sites on four large rivers (Danube-4, Sava-21, Drava-20, Mura-3). Physicochemical parameters were measured eight times during 2015 and 2016. In total, 16 species were recorded, five native and 11 alien species. The highest number (10 alien species, most from genus Dikerogammarus and Chelicorophium) were found in the Danube River, while subsets of alien species were found in the Sava (5 spp.) and Drava Rivers (6 spp.), and no alien species were found in the Mura River. The most upstream reaches of the Mura, Drava, and Sava Rivers in Croatia have not yet been colonized by invasive peracarids and the native peracarids are still abundant there. In the Drava River, alien Peracarida had the highest densities. Significant negative correlations were established between the number of native taxa and alien Peracarida species. Proportions of alien peracarids in the total density of benthic macroinvertebrates were spatially variable, the highest average values in the Drava River (24.4 %), and lower in the Danube (20 %) and the Sava (17.7 %) Rivers. Alien Peracarida had the most important contribution to the richness and abundance contamination of macro¬invertebrate assemblages. The upstream spread of invasive peracarids will increase biocontamination and could cause a decline of native species richness and abundance in the most upstream reaches of the Sava and Drava Rivers. To prevent further up¬stream spread of alien Peracarida, “check, clean and dry” protocols should be included in the national regulations.

The Impact of Pollution on Diversity and Density of Benthic Macroinvertebrates in Mountain and Upland Rivers

This article summarizes the studies concerning the impact of pollutants on benthic macroinvertebrate communities in the mountain and upland rivers of southern Poland. The Carpathian Raba River, which in the 1960s retained its natural character and had good water quality, was considered as a reference in terms of benthic macroinvertebrate communities. The other two analyzed rivers were polluted to different degrees. The Carpathian Dunajec River was contaminated mainly by sewage from small towns and treatment plant, while the upland Vistula River mainly by sewage from the Upper Silesian Industrial Region and saline waters from coal mines. In studied ecosystems in response to pollutions, a rapid increase in density of fauna caused mainly by the massive development of Oligochaeta was found. In the mountain river, the impact of contamination on macroinvertebrate diversity was negligible. There, taxa considered as indicators of clean water (Ephemeroptera, Plecoptera, and Trichoptera) were abundant and their diversity was similar to that of an uncontaminated river. In the heavily polluted upland Vistula River, the sites with a muddy bottom were dominated by Oligochaeta (99.4–99.9%), while at sites with stony bottoms, apart from Oligochaeta, there were also Chironomidae, Gastropoda, and Hirudinea. In comparison to the 1950s, all Ephemeroptera, Plecoptera, Odonata, Trichoptera, and Megaloptera were extinct.

Long-lasting effects of experimental flow intermittency on alpine stream macroinvertebrates (Val Roseg, Switzerland)

Changing weather patterns and receding glaciers are predicted to increase flow intermittency in alpine streams. If aquatic macroinvertebrate communities largely comprise taxa adapted to perennial flows, an increase in flow intermittency substantially reduces biodiversity and affects functional processes. We conducted a before-after-control-impact field experiment to examine how macroinvertebrate communities in an alpine headwater stream responded to and recovered from a repeated experimental increase in flow intermittency. Flow in one channel was manipulated to simulate increased summer intermittency (June–September) over two consecutive years, whilst an adjacent channel served as a control. We monitored the density of benthic macroinvertebrates, periphyton and organic matter at approximately monthly intervals over three years during the snow-free period. Before manipulation, both channels had similar ecological properties. The flow manipulation reduced the overall macroinvertebrate density, and especially the proportional rheophile density, across both years. Recovery of the macroinvertebrate community following experimental flow intermittency took more than a year, and longer than our study period. This could be due to long aquatic life stages, dispersal limitation and biotic interactions. We conclude that climate-induced changes in alpine stream flow regimes can lead to a fundamental shift in macroinvertebrate assemblages through local extinctions, mostly of rheophilic species.

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.

Local and sub-basin effects of timber harvests on stream macroinvertebrates in Hinkle Creek watershed

We studied the impacts of clear cut timber harvest over six-years, focusing on aquatic macroinvertebrate response using a BACI design. Data were collected before and after logging throughout a stream network to examine both local and downstream effects of upstream treatments. Sites were located in fishless headwater tributaries, fish-bearing tributaries and main stems in Hinkle Creek’s north fork (reference) and south fork (sequentially harvested) where benthic macroinvertebrates (from 2004 to 2009) and emergent insects (in 2005–2007 and 2009) were sampled. Pre-harvest (2004–2005) benthic macroinvertebrate composition was similar across sub-basins, with distinct longitudinal differences from tributaries to the main stems. At clear cut sites in fishless tributaries, benthic macroinvertebrate densities and percent Chironomidae increased, while taxa richness decreased, and these effects remained consistent for four years after the first harvest; aquatic insect emergence rates were also significantly higher in harvested v. reference fishless tributaries. No downstream macroinvertebrate responses were detected after the first harvest event. Following main stem harvest, confounded by a dam-break flood in December 2008, responses at main stem harvested sites were consistent with the localized responses observed in fishless tributaries, except benthic densities did not increase. While strong differences persisted among macroinvertebrates along the longitudinal gradient in the reference sub-basin, localized decreases in taxa richness and increased proportional contributions of generally disturbance tolerant chironomid midges among harvested sites resulted in altering the structure of invertebrate communities along the stream continuum. We conclude that additive effects of localized changes to instream resources along the stream continuum following successive harvest activities should be considered in plans for basin-wide timber harvests.

Density data for Lake Ontario benthic invertebrate assemblages from 1964 to 2018.

Benthic invertebrates are important trophic links in aquatic food webs and serve as useful bioindicators of environmental conditions because their responses integrate the effects of both water and sediment qualities. However, long-term data sets for benthic invertebrate assemblages across broad geographic areas are rare and, even if collected, historic data sets are often not readily accessible. This data set provides densities of benthic macroinvertebrates for all taxa collected during lake-wide surveys in Lake Ontario, a Laurentian Great Lake, from 1964 to 2018. This information resulted from surveys funded by the governments of the United States and Canada to investigate the status and changes of Lake Ontario benthic community. Of the 13 lake-wide benthic surveys conducted in Lake Ontario over the course of 54 yr, we were able to acquire taxonomic data to the species level for 11 of the surveys and data to the group level for the other two surveys. Density data are provided for taxa representing the Annelida, Arthropoda, Mollusca, Cnidaria, Nemertea, and Platyhelminthes phyla. Univariate and multivariate analyses revealed that the compositional structure of Lake Ontario invertebrate assemblages differed markedly by depth and were also significantly altered by the Dreissena spp. invasion in early 1990s. The introduction of invasive dreissenids has changed the community historically dominated by Diporeia, Oligochaeta, and Sphaeriidae, to a community dominated by quagga mussels and Oligochaeta. Considering the rarity of long-term benthic data of high taxonomic resolution in lake ecosystems, this data set could be useful to explore broader aspects of ecological theory, including effects of different environmental factors and invasive species on community organization, functional and phylogenetic diversity, and spatial scale of variation in community structure. The data set could also be useful for studies on individual species including abundance and distribution, species co-occurrence, and how the patterns of dominance and rarity change over space and time. Use of this data set for academic or educational purposes is encouraged as long as the data source is properly cited using the title of this Data Paper, the names of the authors, the year of publication, the journal name, and the article number.

Effects of urban demand for food and water on physicochemicals and biotic structure of riverine wetlands in the Pampean plain

ABSTRACT Riparian areas of riverine plains develop extensive floodable areas named riverine wetlands, which are essential to the water cycle balance and ecosystem dynamics. In this study, we contrasted the hydrological and physicochemical variables of riverine wetlands of both peri-urban areas impacted by intensive farming and those of rural areas with the indicators of the biotic structure (taxonomic richness, Shannon diversity and total density) of benthic diatoms, phytoplankton, zooplankton, macroinvertebrates, chironomids, fishes, turtles, and birds. The study was performed on riverine waters of the Pampean plain, Argentina, with four seasonal samplings conducted in 2017–2018. Our results showed that the significant deepening of the groundwater level caused by aquifer overexploitation in peri-urban areas, as well as the declining surface water quality with higher phosphorus and total nitrogen concentrations, affected the taxonomic richness, diversity, and total density of the biotic assemblages of riverine wetlands. The taxonomic richness of birds, turtles, phytoplankton, chironomids, and fishes was the most sensitive to land use. Phytoplankton, chironomid, and fish diversity showed the greatest differences between rural and peri-urban riverine waters, while the total density of chironomids and birds showed the greatest differences according to land use. The results suggest that the socioeconomic development in those riverine wetlands that still maintain conditions close to the natural ones needs to be subject to guidelines derived from integrated basin management and sustainable urban planning.

Benthic macroinvertebrate communities of three tropical, warm monomictic Mexican lakes

Most studies of benthic macroinvertebrate communities are from shallow lakes or restricted to the littoral zone of deep, temperate lakes, with just a few dealing with the deep benthos. Furthermore, the deep benthic macroinvertebrate communities of tropical lakes are almost unknown. The present work describes the benthic macroinvertebrate communities of three tropical, warm monomictic lakes in “Lagunas de Montebello” National Park, Mexico, by describing the differences along the bathymetric profile, from the littoral down to the profound benthos. We studied the benthic macroinvertebrate communities in the two contrasting hydrodynamic periods of the warm monomictic lakes: a) stratification, when the hypolimnion becomes anoxic, and b) mixing, when the water column becomes oxygenated. We expected: 1) a reduction in the benthic macroinvertebrate taxonomic richness, density, and biomass from the littoral to the deep zone, 2) an impoverished benthic macroinvertebrate community while stratified (anoxia) compared to mixing (oxygenated), and 3) depletion in the taxonomic richness, density, and biomass of the profundal benthic macroinvertebrates in the tropical compared to temperate lakes. We found: 1) a decreasing trend in taxonomic richness (6 ± 2–3 ± 1 taxa), density (1868.7 ± 1069.7–349.1 ± 601.8 in. m−2) and biomass (277.8 ± 188.9–85.1 ± 95.6 mg C m−2) from the littoral to the deep zone; chironomids dominated the littoral zone, while oligochaetes dominated the deep zone. 2) Lower density and biomass but not taxonomic richness while stratified (4 ± 3 taxa; 586.2 ± 527.6 in. m−2; 81.6 ± 164.3 mg C m−2) compared to mixing (4 ± 3 taxa; 877.5 ± 1051.4 in. m−2; 190.1 ± 131.1 mg C m−2). 3) lower taxonomic richness and density but not biomass in tropical Montebello oligotrophic lakes (3 ± 3 taxa; 349.1 ± 601.8 in. m−2; 85.1 ± 195.6 mg C m−2) compared to temperate analogous (2–48 taxa; 492−83,189 8 in. m−2; 0.13−201.5 mg m−2). We conclude the early onset and long-lasting hypolimnetic anoxia restrict the benthic macroinvertebrate community radiation and diversification in tropical, oligotrophic, warm monomictic lakes.

Top-Down Effects of Salamanders on Macroinvertebrates in Fishless Headwater Streams

Salamanders are the top predators in many fishless headwater streams, and intraguild interactions among stream salamanders are well documented. However, little is known about the top-down effects of salamanders on stream food webs or how intraguild interactions mediate these effects. To investigate the effects of salamanders on macroinvertebrate communities of headwater streams, we conducted an experiment in stream mesocosms to test for effects of two stream salamander species, namely, Eurycea bislineata and Gyrinophilus porphyriticus, alone or in combination, on benthic and emerging macroinvertebrate density, biomass, and community composition. We also assessed intraguild interactions between these salamander species by comparing Eurycea bislineata survival and G. porphyriticus growth in single-species versus two-species treatments. Gyrinophilus porphyriticus reduced benthic macroinvertebrate densities when alone but not when co-occurring with E. bislineata. There were no effects of salamanders on benthic macroinvertebrate biomass or community composition and no effects on emerging macroinvertebrate density, biomass, or community composition. Eurycea bislineata survival decreased and G. porphyriticus weight increased in two-species treatments, suggesting that intraguild predation was occurring. Overall, although some of our findings are equivocal, these results suggest that salamanders can exert top-down control on macroinvertebrate communities in fishless headwater streams, decreasing benthic macroinvertebrate density. But this effect is dependent on the salamander species present, and can be removed by intraguild interactions between salamander species.

Fish vs. Aliens: predatory fish regulate populations of Limnoperna fortunei mitigating impacts on native macroinvertebrate communities

Limnoperna fortunei, an invasive mussel altering the structure of benthic communities, is preyed upon by several fish species in South America. To investigate the impact of predatory fish on populations of this mussel, and the effects of this top-down interaction on native macroinvertebrates, we performed an in situ experiment in the Uruguay River. By comparing benthic communities of artificial substrates colonised in treatments allowing or excluding fish access, it was demonstrated that fish significantly reduce colonisation by L. fortunei (i.e. its density, biomass and body size). In the absence of mussels (before settlement), fish preyed upon the native macroinvertebrate community inhabiting artificial substrates, reducing their densities compared to the fish exclusion treatment. However, it was found that in the presence of golden mussel (after settlement), the total density of benthic macroinvertebrates, densities of scrapers, and densities of dipterans and gastropods strongly decreased in fish exclusion treatments, suggesting a strong effect of L. fortunei in reducing the native fauna. By preying on L. fortunei, fish favoured the persistence of native macroinvertebrates. Further studies focused on predatory fish species and their efficiency in removing L. fortunei may contribute to advancing towards using native fish as mitigating agents.

Limited evidence of zebra mussel (Dreissena polymorpha) consumption by freshwater drum (Aplodinotus grunniens) in Lake Winnipeg

Freshwater drum (Aplodinotus grunniens) may be a predator of the invasive zebra mussel (Dreissena polymorpha), which established in Lake Winnipeg in 2013. In this study, the diets, trophic position, and growth of 51 freshwater drum collected in 2019 (six years post-zebra mussel invasion) were compared to 64 freshwater drum sampled in 2000. Benthic insect larvae were the dominant food items in both years. Although mollusks occur in high densities in Lake Winnipeg, they were only consumed by a few freshwater drum in either sample year. Zebra mussels were not a frequent prey item in 2019 as they were only consumed by four of the sampled freshwater drum. Stable isotope analysis of white muscle tissue yielded similar δ13C and δ15N values in both years and were consistent with a benthic, insectivorous diet. Length-at-age data derived from otoliths revealed that the 2019 population had at least an equal growth rate to the 2000 population. Weight-at-length data suggested that fish condition was greater in 2019 than in 2000, which coincided with increased benthic macroinvertebrate density in Lake Winnipeg. Based on these findings, Lake Winnipeg freshwater drum continue to feed predominantly on insect larvae and not zebra mussels.

Longitudinal Distribution of Benthic Macroinvertebrates Affected by a Hydropower Plant Cascade in the Mudan River

Hydropower plant operation changes river habitats in various aspects, and thus affects the community composition of the river ecosystem. As a result, the river health is adversely affected. The influence of a hydropower plant cascade on river continuity is even more pronounced. In this study, benthic macroinvertebrates and environmental factors were sampled from the Jingbohu Hydropower Plant to the Shiyan Hydropower Plant, along the Mudan River, and the influence of a hydropower plant cascade on the longitudinal distribution of benthic macroinvertebrates was analyzed. The results demonstrate that the hydropower plant cascade affected several environmental variables and led to changes in the community composition of benthic macroinvertebrates in the Mudan River. Significant differences were observed between sites upstream and downstream of the hydropower plants, with more sensitive species downstream of the hydropower plants. "Run-of-river" hydropower plants exert less adverse influence on benthic macroinvertebrates than dam-type plants. The influence of hydropower plants decreases along the longitudinal direction of the river, with the density and richness of benthic macroinvertebrates increasing.