Biomass Of Benthic Macroinvertebrates Research Articles

Deterioration of the Littoral–Benthic Ecosystem Following Recent Expansion of Signal Crayfish (Pacifastacus leniusculus) in the World’s Clearest Large Lake

Some biological invasions can result in algae blooms in the nearshore of clear lakes. We studied if an invasive crayfish (Pacifastacus leniusculus) modified the biomass and community composition of benthic macroinvertebrates and therefore led to a trophic cascade resulting in increased periphyton biomass, elevated littoral primary productivity, and benthic algae bloom in a lake with remarkable transparency [Crater Lake, Oregon, USA]. After quantifying the changes in the spatial distribution of invasive crayfish over a 13-year period, we compared biomass and community composition of littoral–benthic macroinvertebrates, periphyton biovolume, community composition, nutrient limitation, and the development of benthic algae bloom in locations with high and low crayfish density. In addition, we determined if the alteration in community structure resulted in directional changes to gross primary production and ecosystem respiration. The extent of crayfish distribution along the shoreline of Crater Lake doubled over a 13-year period, leaving less than 20% of the shoreline free from crayfish. At high crayfish density sites, benthic macroinvertebrate biomass was 99% lower, and taxa richness was 50% lower than at low crayfish areas. High crayfish sites show tenfold greater periphyton biovolume, sixfold higher periphyton biomass (chlorophyll a), twofold higher metabolic productivity, and the presence of large filamentous algae (Cladophora sp.). The invasion of crayfish had negative consequences for a lake protected under the management of the USA National Park Service, with direct impacts on many levels of ecological organization.

Experimental warming and browning influence autumnal pelagic and benthic invertebrate biomass and community structure

Abstract Globally, lakes are warming and browning with ongoing climate change. These changes significantly impact a lake's biogeochemical properties and all organisms, including invertebrate consumers. The effects of these changes are essential to understand, especially during critical periods after and before the growing season, that is, autumn and spring, which can determine the composition of the invertebrate consumer community. In this study, we used a large‐scale experimental pond system to test the combined effect of warming (+3°C) and increased input of terrestrial and coloured dissolved organic carbon (gradient of 1.6–8.8 mg/L in the ambient and 1.6–9.3 mg/L in the warm)—which causes browning—on zooplankton and benthic macroinvertebrate biomass and composition during the autumn and the following spring. Total zooplankton biomass decreased with warming and increased with browning, while total zoobenthos did not respond to either treatment. Warming and browning throughout the autumn had no overall interactive effects on zooplankton or zoobenthos. Autumnal warming decreased total pelagic consumer biomass, caused by a decrease in both Rotifera and Copepoda. In contrast, there was no effect on overall benthic consumer biomass, with only Asellus sp. biomass showing a negative response to warming. An autumnal increase in dissolved organic carbon led to increased total pelagic consumer biomass, which was related to increases in Daphnia sp. biomass but did not affect zoobenthos biomass. While we expected zooplankton and zoobenthos biomass to follow responses in primary and bacterial production to treatments, we did not find any relationship between consumer groups and these estimates of resource production. Our results suggest that consumer responses to warming and browning during autumn may lead to less overarching general changes in consumer biomass, and responses are mostly taxon‐specific. This study gives novel insights into the effects of warming and browning on consumer biomass during autumn and spring and increases the understanding of the effects of climate change on invertebrate community biomass in the different habitats.

Does experimental seaweed cultivation affect benthic communities and shorebirds? Applications for extensive aquaculture.

Extensive seaweed aquaculture is a growing industry expected to expand globally due to its relatively low impact and benefits in the form of ecosystem services. However, seaweeds are ecosystem engineers that may alter coastal environments by creating complex habitats on previously bare mudflats. These changes may scale up to top-consumers, particularly migratory shorebirds, species of conservation concern that regulate trophic webs at these habitats. Understanding how habitats are transformed and how this affects different species is critical to direct ecological applications for commercial seaweed management. We experimentally assessed through a Before-After Control-Impact design the potential changes exerted by Gracilaria chilensis farming on bare mudflats on the abundance, biomass, and assemblage structure of benthic macroinvertebrates, and their scaled-up effects on shorebirds' habitat use and prey consumption. As predicted, experimental cultivation of G. chilensis significantly affects different components of biodiversity that scale-up from lower to upper trophic levels. The total biomass of benthic macroinvertebrates increased with seaweed cultivation and remained high for at least 2 months after harvest, boosted by an increase in the median size of polychaetes, particularly Nereids. Tactile-foraging shorebirds tracked these changes at the patch level increasing their abundance and spending more time foraging at seaweed cultivated plots. These results suggest that seaweed farming has the potential to impact shorebird populations by favoring tactile-foraging species which could lead to a competitive disadvantage to species that rely on visual cues. Therefore, the establishment of new seaweed farms in bare mudflats at key sites for shorebirds must be planned warranting habitat heterogeneity (i.e., cultivated and non-cultivated areas) at the landscape level and based on a previous experimental approach to account for local characteristics. Fostering properly designed extensive seaweed farming over other aquaculture industries with greater negative environmental impacts would provide benefits for human well-being and for ecosystem functions.

Direct and indirect effects of amphidromous shrimps on nutrient mineralization in streams in Japan.

Animals affect element cycling in ecosystems by consumption and excretion. Amphidromous shrimps frequently dominate low-mid altitude streams, where downstream connectivity to oceans is sustained. Although shrimps' direct influence on benthic communities has been studied, little is known about their influences on nutrient cycling. Here, we hypothesized that the dominance of shrimps alters nutrient mineralization by benthic macroinvertebrates in streams due to the difference in the quality and quantity of excretion between shrimps and aquatic insects. We tested this hypothesis through a field manipulative experiment, excretion measurements of animals, and field surveys. In the field manipulative experiment, the presence of shrimps slightly decreased the biomass of aquatic insects but tripled total benthic macroinvertebrate biomass directly through their own biomass. The mass-specific NH4+ excretion rate by shrimps was similar to aquatic insects, and the areal NH4+ excretion by benthic macroinvertebrates was increased by 2.5 times in the presence of shrimps. In contrast, shrimps excreted significantly less soluble reactive phosphorus (SRP) than aquatic insects, and the presence of shrimps did not affect areal SRP excretion by benthic macroinvertebrates. The field survey showed a positive correlation of NO3- concentration with the shrimp density, inferring the excess NH4+ was nitrified. Although the nutrient concentration of stream water is frequently attributed to watershed conditions, the results of this study indicate that downstream connectivity to oceans may also influence nutrient dynamics of the stream through the density of amphidromous shrimps.

Variability of benthic macroinvertebrate biomass in two contrasting streams in southern Chile

Variability of benthic macroinvertebrate biomass in two contrasting streams in southern Chile

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.

Predictors of Biofilm Biomass in Oligotrophic Headwater Streams

Biofilm forms the base of food webs as an autochthonous resource in nutrient-poor, heavily shaded headwater streams. However, we know little about the influence of bottom-up and top-down controls on the standing stock of biofilm biomass in headwater streams. We used spatially extensive stream surveys and pre-existing stream chemistry data to assess the influence of potential bottom-up and top-down controls of biofilm biomass in the oligotrophic headwater streams of the Hubbard Brook Experimental Forest (HBEF), NH. The potential bottom-up controls we considered were canopy cover and aspect (determinants of available radiation at the stream surface), available nutrients (e.g., nitrogen, phosphorus), physical habitat characteristics (e.g., stream width, substrate), and physicochemical properties of water (e.g., water conductivity, pH). The potential top-down controls we examined were benthic macroinvertebrate biomass and stream salamander occurrence. Salamanders may affect biofilm biomass indirectly by preying on benthic macroinvertebrate consumers. We used stepwise multiple linear regression to assess the relative importance of these variables in predicting biofilm biomass and found that biofilm increased with light availability (as indicated by canopy cover and aspect), nutrient availability, and lower acidity, suggesting that the autotrophic components of biofilm may be particularly important. Our top-down control indices were unrelated to biofilm biomass; however, more intensive studies on top-down controls are needed in these systems.

Trophic status index and natural fisheries potential of some Iranian reservoirs.

The Iran Water Resources Management Company constructs many dams to control surface water that provide a new potential for aquaculture activities. Trophic status index and natural potential for fish production were investigated in nine small dam reservoirs from northwest of Iran. Prediction of fish productivity was calculated based on phytoplankton biomass (using chlorophyll a concentration in water; p Chl-a) and benthic macro invertebrate biomass (p BMI). Average p Chl-a and p BMI of reservoirs were estimated as 233.9±479.4 kg ha-1yr-1 and 14.76±19.18 kg ha-1yr-1 respectively. Concentrations of total phosphorus and total nitrogen varied between 0.023-0.345 and 0.42-3.58 mgl-1, respectively. According to Carlson's transformed model (TSIPN) the mesotrophic status was dominant in reservoirs in which TSIPN varied between 38.7 and 51.2. The eutrophication trend seems to be very fast in these reservoirs because of high nutrient input by aquacultures activities. The usage of fertilizers and amounts of food for aquaculture proposes and expansions of exotic species decline the natural fisheries potential of these reservoirs. Maintenance of water quality and investigation of native species should be planned to preserve sustainable fisheries activities in these reservoirs.

A small omnivorous bitterling fish (Acheilognathus macropterus) facilitates dominance of cyanobacteria, rotifers and Limnodrilus in an outdoor mesocosm experiment.

Small omnivorous fish often dominate in subtropical shallow lakes, and they may affect the community structure of aquatic organisms on at least two trophic levels. However, in the study of aquatic food webs in subtropical lakes, most ecologists have focused on the effects of large-sized omnivorous species (e.g. common carp), studies of small-sized species being scarce. We conducted a mesocosm experiment with two treatments (fish presence and absence) to examine the effects of a small-sized omnivore, bitterling (Acheilognathus macropterus), on phytoplankton, zooplankton and benthic macroinvertebrates. Our results showed that bitterling presence significantly increased the chlorophyll a concentration and biomass of phytoplankton, which became dominated by cyanobacteria (mainly Aphanizomenon spp.) that accounted for >99% of both total phytoplankton abundance and biomass. Both the abundance and biomass of zooplankton were also higher in the fish-present treatment, but small rotifers became dominant, and the zooplankton:phytoplankton biomass ratio decreased, indicating less grazing on phytoplankton. Moreover, both the abundance and biomass of benthic macroinvertebrates (tubificids) were higher in the bitterling-present treatment than in the controls, which is opposite to the situation found when omni-benthivorous fish (e.g. crucian carp) dominate. Higher biomass of tubificids may, in turn, result in higher sediment nutrient release. Our study suggests that A. macropterus, and maybe also other bitterling species, can alter both pelagic and benthic assemblages via both top-down and bottom-up control effects and lead to more turbid water in eutrophic lakes. Thus, more attention should be paid to these small omnivorous species in the restoration and management of shallow subtropical lakes.

Threatened habitat at Great Salt Lake: Importance of shallow-water and brackish habitats to Wilson’s and Red-necked phalaropes

Abstract Great Salt Lake (GSL) is the largest hypersaline lake in North America and is the fall staging area for a high proportion of North America’s Wilson’s Phalaropes (Phalaropus tricolor) and Red-necked Phalaropes (Phalaropus lobatus). Unfortunately, diversion of freshwater for agriculture and development has decreased the size of GSL by 48%. To assess the potential impact of a smaller GSL on phalaropes, we collected data from 2013 to 2015 from sites where large, dense flocks of phalaropes congregated and sites where there were no phalaropes. At each site, we measured the densities of invertebrates that were preyed upon by phalaropes, including larval and adult brine flies (Ephydridae), adult brine shrimp (Artemia franciscana), chironomid larvae (Chironomidae), and corixid adults (Corixidae). Abiotic characteristics measured included water depth, water salinity, water temperature, wind speed, and benthic substrate. We analyzed high-salinity sites separately from low-salinity sites because they contained different invertebrates. High-salinity sites were in Carrington and Gilbert bays and were relatively deep (mostly <2 m). At the high-salinity sites, phalaropes exhibited a preference for sites with an abundance of adult brine flies and for microbialite substrates. The low-salinity sites were in Ogden and Farmington bays and were shallow (<1 m). At low-salinity sites, large phalarope flocks were more likely to occur at sites that were shallower, less saline, and had a high biomass of benthic macroinvertebrates. Our results indicate that physical features and prey availability are both important in determining phalarope habitat use at GSL. Phalaropes prefer to use shallower parts of GSL and brackish waters. These areas will be especially impacted by decreased freshwater inflow into GSL.

Effects of short-term hydrological processes on benthic macroinvertebrates in salt marshes: A case study in Yangtze Estuary, China

Understanding the effects of hydrological processes on the benthic macroinvertebrates in salt marshes can provide theoretical basis for species diversity restoration, coastal environment protection, and comprehensive exploitation and utilization of salt marsh ecosystems. In this study, 4 fixed-point sampling sites were set up in the salt marsh of the East Nanhui tidal flat in the Yangtze Estuary for benthic macroinvertebrate survey, hydrological monitoring and sedimentary parameter collection over two short-time scales (semidiurnal and fortnightly cycles). Based on the results of these surveys, we analyzed the effects of hydrological processes on the benthic macroinvertebrates over different timescales. The results showed that benthic macroinvertebrates assemblages varied significantly over the semidiurnal and fortnightly tide periods but not between sites. The number of species and the abundance of the benthic macroinvertebrates during spring tide period were significantly lower than that during neap tide period, although the biomass during both tidal periods were not significantly different. There was no significant variation in the number of species, abundance, and biomass of benthic macroinvertebrates over the semidiurnal tidal scale in general with few exceptions. However, there were significant differences in most of the hydrological and sedimentary parameters between the spring and neap tide periods, as well as between semidiurnal tides in these two periods. Two principal components, the intensity of hydrological processes (PC1) and the physicochemical properties of water and sediment (PC2), were derived from principal component analysis on hydrological factors and sedimentary physicochemical parameters. The results show that PC1 had a significant effect on abundance of benthic macroinvertebrate community; while PC2 had a significant effect on biomass. The best combined environmental factors, which exhibited significant correlations with the characteristics of the benthic macroinvertebrates and also their taxonomic classes, varied across the sampling periods. This study indicates that short-term hydrological processes can not only directly affect the benthic macroinvertebrates, but also indirectly affect the communities by altering sedimentary physicochemical factors. There were significant differences in the effects of the hydrological processes on the benthic macroinvertebrate community over the semidiurnal and fortnightly tidal scales, and it could be inferred that the scale effect still exists in the short-time scale.

Fishing-induced changes in predation pressure by perch (Perca fluviatilis) regulate littoral benthic macroinvertebrate biomass, density, and community structure

We aimed to study whether the varying changes in predation pressure by perch (Perca fluviatilis) reflect the biomass, density, and community structure of the benthic macroinvertebrates. Prey preference is size-dependent, and overall predation pressure is density dependent, and thus the size structure of the P. fluviatilis population should affect the structure of the macroinvertebrate community, and the population density of P. fluviatilis should reflect the overall density of benthic macroinvertebrates. We sampled the littoral benthic community in a boreal lake that had been divided into two parts that were subjected to two different fishing procedures during 2007–2012 period and analyzed the macroinvertebrate diet of fish. The benthic macroinvertebrate community reflected the predation pressure. Total macroinvertebrate biomass increased during the study period in the lake division with a non-size-selective fishing procedure (NSF), i.e., all invertivorous perch size-classes targeted, but decreased in the section with negatively size-selective fishing procedure (SSF), i.e., large invertivorous individuals ≥ 16 cm were not targeted. This difference was a result of the increase in large-sized species, such as Odonata, for the NSF procedure and decrease in the SSF procedure. In contrast to total biomass, total macroinvertebrate density did not show a response to predator size structure but rather total macroinvertebrate density decreased with increasing fish density. The study demonstrates the effect of predation pressure of P. fluviatilis on benthic communities, thus highlighting the keystone predator role of the species in boreal lakes and gives more insight on the multiple effects of fish predation on littoral benthic communities.

Distribution of heavy metals and benthic macroinvertebrates: Impacts from typical inflow river sediments in the Taihu Basin, China

To characterize the distribution of heavy metals and benthic macroinvertebrates and to evaluate the relationship between metal pollution and benthic community structure, we collected samples of typical inflow river sediments from nineteen sites in the Taihu Basin in December 2012 and April and September 2013. The results showed that the mean concentration of heavy metals in the river sediments followed the order of Zn>Cr>Cu>Pb>Ni>As>Cd>Hg, and these metals may present moderate ecological risks. Compared to the background concentrations, it is likely that Cd and Cu pose much higher pollution than the other metals and should receive more attention. In terms of the distribution of the heavy metals, higher concentrations were found at the S1 and S2 sampling sites, while the other sampling sites exhibited relatively lower concentrations because of industrial wastewater containing heavy metals. The structure of the benthic macroinvertebrate community was also investigated, and the correlations between the heavy metals and the benthic communities were analyzed. The mean abundance and biomass of benthic macroinvertebrates in the study area were 49.22–117.23ind./m2 and 42.70–55.70g/m2, respectively, and 4 phyla and 8 classes were represented. The dominant groups were mollusks and arthropods. The FBI, BPI, GI values were low with means of 0.51, 0.41 and 0.16, respectively, and based on the GI and BPI values, most of the sampling sites were clean or slightly polluted with a minimal amount of the study area being moderately polluted. However, the FBI results indicated that all sampling sites were clean, but this may not be consistent with the pattern of pollution in the study area. The results of the correlation relationship analysis between the benthic community metrics and the heavy metal risk indices indicated that the abundance and biomass of Oligochaeta is the most sensitive to heavy metal contamination followed by Hirudinea, Gastropoda, Insecta, and the Goodnight–Whitley index because of significant correlation. And within a certain range, the Goodnight–Whitley index showed an increasing trend when pollution become more serious. However, some metals, such as Eri of Ni, Eri of Cd, Eri of Hg, Eri of Cu, Eri of As, and the RI significantly correlated with the benthic community metrics. Heavy metals in sediments may adversely impact the benthic community, and As and Cu have the greatest effect. Thus, the key influencing environmental factors may be As and Cu, and our results suggest that the benthic community, especially the abundance and biomass of Oligochaeta could be used in biomonitoring for heavy metal ecological risk from the studied area in the Taihu Basin, China.

Diet composition of two larval headwater stream salamanders and spatial distribution of prey

Summary Interspecific overlap in resource use can determine the degree to which different presumed guild members have distinct or similar effects on ecosystem processes or responses to environmental change. Many headwater streams of North America support multiple species of larval salamanders commonly defined as a single guild that can influence macroinvertebrate communities and nutrient dynamics and are sensitive to stream alteration. We explored macroinvertebrate distributions in conjunction with stable isotope and gut content analyses of salamanders to examine similarities in diet between two sympatric larval salamander species (Desmognathus quadramaculatus and Eurycea cirrigera) in four headwater streams. We determined the degree to which larval salamanders used similar prey functional feeding groups (FFGs) and taxa and determined the primary source habitat (pools versus riffles) of prey. Stable isotopes of carbon (δ13C) and nitrogen (δ15N) suggest the two salamander species occupied similar trophic positions and individual‐based stable isotope mixing models indicated similar use of macroinvertebrate predators and filterers by both species. Diet analyses were generally consistent with stable isotope results in identifying prey FFGs that composed the largest biomass of salamander diets. However, despite similarities in diet at the resolution of FFGs, there was little overlap in the specific taxa consumed by the two salamander species: 52 prey taxa were consumed over all samples, with only 16 taxa in common. Further, only five prey taxa were common in dominating diet biomass of both species; there was more overlap in taxa in terms of diet abundance. We assessed patterns in benthic macroinvertebrate biomass and compared the biomass of taxa that were in pools versus riffles to the biomass and abundance of taxa in salamander diets. Total macroinvertebrate biomass was generally higher in pools; however, the majority of salamander prey biomass was from riffle habitats, a trend that was stronger for D. quadramaculatus than for E. cirrigera. There was greater similarity in taxa comprising diet by abundance with the majority of prey items originating from pools. The larval salamander species used similar prey FFGs but differed significantly in specific prey taxa. We hypothesise that species differences in diets were most likely a function of differences in larval size and microhabitat use. Consequently, the treatment of larval salamanders as a guild is probably inadequate for predicting the effect of larval salamander diversity on some stream processes, and species may differ in how they respond to factors affecting prey assemblages.

Evaluating habitat suitability curves for predicting variation in macroinvertebrate biomass with weighted usable area in braided rivers in New Zealand

We investigated changes in seasonal biomass of benthic macroinvertebrates over whole floodplain transects upstream and downstream of existing flow diversions in the Wilberforce and South Ashburton Rivers, Canterbury, New Zealand. We tested the predictive performance of a 1-dimensional hydraulic-habitat model informed with existing general habitat suitability curves (HSC), as well as river- and channel-specific HSC developed from the studied rivers. Diversions resulted in significant declines in wetted width, habitat complexity, and resulting declines in benthic biomass, but community composition was unchanged. Weighted usable area (WUA) predictions based on general HSC were often poorly correlated with cross-sectional macroinvertebrate biomass. River- and channel-type-specific HSC greatly improved the accuracy of predictions; however, all HSC generally under-predicted the total proportional change in cross-sectional macroinvertebrate biomass associated with flow change. We conclude that WUA was an insensitive indicator of flow-related macroinvertebrate biomass change. We encourage development of HSC categorised by river hydrology, size and channel form.

Recovery of a mining-damaged stream ecosystem

AbstractThis paper presents a 30+ year record of changes in benthic macroinvertebrate communities and fish populations associated with improving water quality in mining-influenced streams. Panther Creek, a tributary to the Salmon River in central Idaho, USA suffered intensive damage from mining and milling operations at the Blackbird Mine that released copper (Cu), arsenic (As), and cobalt (Co) into tributaries. From the 1960s through the 1980s, no fish and few aquatic invertebrates could be found in 40 km of mine-affected reaches of Panther Creek downstream of the metals contaminated tributaries, Blackbird and Big Deer Creeks.Efforts to restore water quality began in 1995, and by 2002 Cu levels had been reduced by about 90%, with incremental declines since. Rainbow Trout (Oncorhynchus mykiss) were early colonizers, quickly expanding their range as areas became habitable when Cu concentrations dropped below about 3X the U.S. Environmental Protection Agency’s biotic ligand model (BLM) based chronic aquatic life criterion. Anadromous Chinook Salmon (O. tshawytscha) and steelhead (O. mykiss) have also reoccupied Panther Creek. Full recovery of salmonid populations occurred within about 12-years after the onset of restoration efforts and about 4-years after the Cu chronic criteria had mostly been met, with recovery interpreted as similarity in densities, biomass, year class strength, and condition factors between reference sites and mining-influenced sites. Shorthead Sculpin (Cottus confusus) were slower than salmonids to disperse and colonize. While benthic macroinvertebrate biomass has increased, species richness has plateaued at about 70 to 90% of reference despite the Cu criterion having been met for several years. Different invertebrate taxa had distinctly different recovery trajectories. Among the slowest taxa to recover were Ephemerella, Cinygmula and Rhithrogena mayflies, Enchytraeidae oligochaetes, and Heterlimnius aquatic beetles. Potential reasons for the failure of some invertebrate taxa to recover include competition, and high sensitivity to Co and Cu.

Chlorophyll-aconcentrations and macroinvertebrate declines coincide with the collapse of overwintering diving duck populations in a large eutrophic lake

SUMMARY 1. Lough Neagh is one of the most important non-estuarine sites in the British Isles for overwintering wildfowl. A change in the waterbird assemblage following the winter of 2000/2001 was driven mainly by a rapid decline in the population of overwintering diving ducks. Sudden and discrete changes in resident as well as migratory waterbirds may suggest an intrinsic cause. 2. We compared the density and biomass of benthic macroinvertebrates, the food of overwintering diving ducks, in 2010 (following the diving duck population decline) with values from a baseline survey conducted in 1997/1998 (before the decline in diving ducks). 3. The mean total density of macroinvertebrates declined significantly by c. 65% from 15 300 m 2 in 1997/1998 to 5136 m 2 in 2010. There was a concomitant c. 70% decline in mean macroinvertebrate biomass from 15 667 mg m 2 to 5112 mg m 2 . In terms of taxonomic composition, the relative contribution of Tanypodinae, Glyptotendipes spp. and Tanytarsini declined, while the relative contribution of Chironomus spp. increased. 4. We describe a shift in chlorophyll-a concentration, a proxy of phytoplankton biomass, in the largest freshwater lake in the British Isles coincident with a significant reduction in macroinvertebrate density and biomass, with potential implications for ecosystem processes and ecologically and economically important consumer populations, including waterbirds and fishes.

Habitat values for artificial oyster (Crassostrea ariakensis) reefs compared with natural shallow-water habitats in Changjiang River estuary

Oyster reefs have an equivalent, complex 3-dimensional structure to vegetated habitats and may provide similar functions in estuarine environments. Nevertheless, few studies have compared oyster reefs with adjacent natural shallow-water habitats. Here the resident benthic macroinvertebrate communities in an artificial oyster (Crassostrea ariakensis) reef and in adjacent natural estuarine shallow-water habitats (salt marsh, intertidal mudflat, and subtidal soft bottom) in the Changjiang (Yangtze) River estuary were described. The mean total densities and biomass, Margalef’s species richness, Pielou’s evenness and Shannon-Weaver biodiversity indices of the resident benthic macroinvertebrate communities differed significantly among the habitats. Significantly higher densities and biomass of benthic macroinvertebrates occurred in the oyster reef compared with the other three habitats. Ordination plots showed a clear separation in benthic macroinvertebrate communities among the four habitat types. The results demonstrated that the artificial oyster reef supported distinct and unique benthic communities, playing an important role in the complex estuarine habitat by supplying prey resources and contributing to biodiversity. In addition, the results suggested that the oyster reef had been restored successfully.

Effects of indomethacin and propranolol on Chironomus riparius and Physella (Costatella) acuta

New analytical methods are available for detecting novel xenobiotic compounds in freshwater systems. Pharmaceuticals are suspected of having effects on freshwater biota at very low concentrations, although the nature of these effects remains unclear. Previous data from the Llobregat River revealed a positive statistical relationship between the biomass of benthic macroinvertebrates and the presence of certain non-steroidal anti-inflammatory drugs (NSAIDs) and beta-blockers. Here, experiments were conducted with the midge Chironomus riparius and the freshwater snail Physella (Costatella) acuta in sediments and water, respectively. The sediments and water were treated with the pharmaceuticals propranolol and indomethacin, with the aims of assaying the effects of these compounds on the organisms and testing the statistical relationships observed in field. The variables measured were survival; C. riparius biomass; and the carbon/nitrogen ratio, lipid content and fertility of freshwater snails. Indomethacin in treated sediments induced an increase in C. riparius biomass, whereas propranolol inhibited growth, albeit at marginal statistical significance. By contrast, indomethacin in water had no effect on any of the parameters measured in P. acuta.

Community structure of benthic macroinvertebrates in Lake Ulungur in Xinjiang

乌伦古湖是我国十大内陆淡水湖之一, 同时也是新疆维吾尔自治区的第二大湖泊和主要渔业基地.近年来, 随着气候变化和人为因素的影响, 湖区水体营养状况、生物群落组成等均发生了较大变化.为揭示该湖大型底栖无脊椎动物的群落结构特征及其对生态系统变化的响应, 2006年11月至2008年7月设28个采样点对大型无脊椎底栖动物的群落结构特征进行了季节性调查分析.共采集到底栖动物87种, 其中水生昆虫61种, 占种类总数的70.1%, 寡毛类14种, 占总种数16.2%, 软体动物7种, 占总种数的8.0%, 其它类5种, 占总种数的5.7%.大型底栖无脊椎动物年平均密度为1015.01 ind./m², 年平均生物量为9.83g/m².各季度大型底栖动物的密度表现为冬季(1234.96 ind./m²) >春季(1044.47 ind./m²) >秋季(931.16 ind./m²) >夏季(849.44 ind./m²), 生物量同样表现为冬季(13.54g/m²)>春季(12.01g/m²)>秋季(8.37g/m²)>夏季(5.02g/m²).Shannon-Wiener多样性指数年均值为2.19, Margalef丰富度指数年均值为1.34.相关分析表明, 水深是影响大型底栖无脊椎动物密度和生物量分布的关键因子。;Lake Ulungur is the second largest lake of Xinjiang Uigur Autonomous Region and one of the ten largest freshwater lakes in China.With the impact of human activities and climate variation, nutrients and biotic communities in the lake have been changed obviously.To understand the community of benthic macroinvertebrates and its response to the changes in their environ-ment, we surveyed the benthic macroinvertebrates community in Lake Ulungur seasonally from Nov.2006 to July 2008.In total, 87 taxa were recorded, including 61 Insecta (70.1%), 14 Oligochaeta (16.2%), 7 Mollusca (8.0%) and other 5 taxa (5.7%).The annual density and biomass averaged 1015.01 ind./m² and 9.83 g/m², respectively.The density was highest in winter(1234.96 ind./m²), followed by spring (1044.47 ind./m²) and autumn(931.16 ind./m²), and lowest in summer (849.44 ind./m²).The biomass of benthic macroinvertebrates was highest in winter(13.54 g/m²), followed by spring(12.01 g/m²) and autumn(8.37 g/m²), and lowest in summer(5.02 g/m²).The annual average value of Shannon-Wiener diversity index and Margalef diversity index was 2.19 and 1.34, respectively.Correlation analyses indicated that water depth was the key factor influ-encing the standing crops of the benthic macroinvertebrates in this lake.