Benthic Invertebrate Community Structure Research Articles

Meiofaunal communities in a tropical seagrass bed and adjacent unvegetated sediments with note on sufficient sample size for determining local diversity indices.

Seagrass beds are highly diverse and productive marine habitats for many associated organisms in nearshore coastal waters. The differences in abundance, diversity, and community structure of benthic invertebrates between seagrass beds and adjacent unvegetated sediments have been stated, whereas most studies are primarily focused on macrofauna or based on a comparatively long distance, i.e., more than 10 m. The present study is designed to test if the community structures of meiofauna, especially the free-living nematodes, differ between seagrass beds and adjacent unvegetated sediments on a meter scale. There are 21 meiofaunal taxa and 63 nematode genera that have been identified from a tropical seagrass bedof Thalassia hemprichii inLudao, Taiwan. Although the compositions of higher meiofaunal taxa are undistinguished, according to correspondence analysis, the assemblages of nematode genera differ substantially between the seagrass bed and unvegetated sediments. Regarding the nematodes, approximately 50% of genera are restricted to the seagrass bed whereas 6% are restricted to unvegetated sediments, which indicate both habitats possessing distinct infaunas. The number of replicates for reasonable estimation of the local diversity index is calculated by the randomization technique. For local seagrass beds, only a single core is sufficient for reliably estimating meiofaunal diversity, but at least three cores or a sample size of 300 individuals is needed for the nematode community. Nematode assemblages provide more particular differences between seagrass and unvegetated habitats than meiofaunal communities on small spatial scales. Both seagrass beds and adjacent unvegetated sediments harbor specific meiofaunal communities, and hence, the conservation strategy for seagrass should also consider the peripheral bare area of seagrass beds.

环境因子对河流底栖无脊椎动物群落结构的影响

Benthic invertebrate refers to aquatic animals living at the bottom of water in the all or part of life history. As an important component in river ecosystem,it is also an indispensable connection link in energy flow and matter cycle. Benthic invertebrates are characterized by long life cycle,slow action,broad range of types and large body size,which are convenient for collection and observation. The distribution,abundance and diversity of benthic invertebrate can convey information of environmental pollution. Some groups display strong resistance against severe environment,while other groups are sensitive to changes in environmental conditions. The characteristics of benthic invertebrate reflect the health state of river ecosystem. Benthic invertebrate is one type of significant indicator organisms in river health assessment. At present,many scholars mainly focused on river health assessment and the effects of a few environmental factors on benthic invertebrate community structure. The effects of environment factors on community structure of benthic invertebrate are very complex: there are numerous environment factors and the effects of different environment factors on different benthic invertebrate groups are not completely the same. This article discusses the influences of environment factors including physical factors( bottom sediment,water temperature,water depth,water current,etc.),chemical factors( dissolvedoxygen,total phosphorous,total nitrogen, etc.), biological factors( aquatic plants, competition and predation),anthropogenic disturbance and other combined factors on community structure of benthic invertebrate. Different environment factors impose different impacts on benthic invertebrates. Bottom sediment is an essential condition for all life activities including growth,reproduction,etc. Any species has the strict living temperature range. Community structure of benthic invertebrate is directly influenced by the fluctuation of temperature. Water depth is one of major environment factors of community structure of benthic invertebrate. In general,the density and biomass of benthic invertebrate continuously vary with water depth. Water flow not only affects feed conditions of benthic invertebrate,rivers productivity,competition among species and within species,larval living places,but also has significant impacts on the community structure of river. Flow velocity determines the composition of benthic invertebrate community. Altitude determines the changes of temperature,light and other environment factors and indirectly affects the community structure of benthic invertebrate. Water chemical factors are closely related to community structure of benthic invertebrate. Aquatic plants provide excellent habitat fields for propagation,feeding and living for benthic invertebrate. Benthic invertebrates are affected by both competition and predation: excessive competition and predation often result in the reduction in species diversity,secondary productivity and feeding conditions as well as the changes in community structure of benthic invertebrate. Anthropogenic disturbance( such as power plant construction,thermal discharge and urbanization) is mainly response for the changes of the community structure of benthic invertebrate. The effects of water flow,water velocity,altitude and flood on community structure of benthic invertebrate are seldom reported. These environment factors should be perfected and investigated in the future.

Responses of benthic invertebrate communities to shoreline retrogressive thaw slumps in Arctic upland lakes

Permafrost disturbance (shoreline retrogressive thaw slumping [SRTS]) causes solute-rich terrestrial inputs to Arctic tundra lakes. Eight upland tundra lakes (3 undisturbed [U], 5 disturbed [D]) in the Inuvik region of the Northwest Territories, Canada, were sampled to assess the effects of SRTS on benthic invertebrate community structure, abundance, and whether localized SRTS effects in D lakes could be discriminated by comparing samples taken adjacent to (Da) or further from (Do) the disturbance. Community composition and abundance differed between U and D lakes. Macroinvertebrates were more abundant in areas adjacent to SRTS (Da) than in areas away from SRTS (Do), but community composition did not differ between Da and Do areas. Abundance was >2× greater in D than in U lakes. Ostracoda abundance was 4× greater in D than U lakes and 2× higher in Da than Do areas. Nematoda abundance was ∼10× higher in D than U lakes, whereas Chironomidae abundance was lower in D than U lakes. Bivalvia and Oligochaeta had similar abundance in D and U lakes, and both groups were more abundant in Da than Do areas. Differences in abundance and community composition were related primarily to higher concentrations of Ca2+ in D than U sediments and to higher organic C and N in U than D sediments. Sediment organic C and Mg concentrations, macrophyte biomass, and dissolved organic C concentrations best explained differences in community composition among lake types and areas. Our study adds to our understanding of cascading changes in the foodweb structure and ecological states of freshwater ecosystems caused by climate change in the Arctic.

Environmental effects monitoring at the Terra Nova offshore oil development (Newfoundland, Canada): Program design and overview

An environmental effects monitoring (EEM) program was developed by Suncor (formerly Petro-Canada) in 1997/98 to assess effects of the Terra Nova offshore oil and gas development on the receiving environment. The Terra Nova Field is located on the Grand Banks approximately 350km southeast of Newfoundland (Canada), at approximately 100m water depth. The EEM program was developed with guidance from experts in government, academia and elsewhere, and with input from the public. The EEM program proposed by Suncor was accepted by Canadian regulatory agencies and the program was implemented in 2000, 2001, 2002, 2004, 2006, 2008 and 2010, with pre-development sampling in 1997. The program continues to be implemented every two years. EEM includes an assessment of alterations in sediment quality through examination of changes in sediment chemistry, particle size, toxicity and benthic invertebrate community structure. A second component of the program examines potential effects on two species of commercial fishing interest: Iceland scallop (Chlamys islandica) and American plaice (Hippoglossoides platessoides). Chemical body burden for these two species is examined and taste tests are performed to assess the presence of taint in edible tissues. Effects on American plaice bioindicators are also examined. A final component of the program assesses potential effects of the Terra Nova development on water quality and examines water column chemistry, chlorophyll concentration and physical properties. The papers presented in this collection focus on effects of drill cuttings and drilling muds on the seafloor environment and, as such, report results on sediment quality and bioaccumulation of drilling mud components in Iceland scallop and American plaice. This paper provides information on drilling discharges, an overview of the physical oceanography at the Terra Nova Field, and an overview of the field program designed to assess environmental effects of drilling at Terra Nova.

Effects of hypoxia on biofilms and subsequently larval settlement of benthic invertebrates

Biofilms on submerged surfaces are important in determining larval settlement of most marine benthic invertebrates. We investigated if exposure of biofilms to hypoxia would alter the larval settlement pattern and result in a shift in benthic invertebrate community structure in the field. Biofilms were first exposed to hypoxia or normoxia in laboratory microcosms for 7days, and then deployed in the field for another 7days to allow for larval settlement and recruitment to occur. Using terminal-restriction fragment length polymorphism of the 16S rRNA gene, this study showed that hypoxia altered the biofilm bacterial community composition, and the difference between the hypoxic and normoxic treatments increased with the time of exposure period. This study also demonstrated significantly different benthic invertebrate community structures as a result of biofilm exposure to hypoxia and that the hypoxic and normoxic treatments were dominated by Hydroides sp. and Folliculina sp., respectively.

Five‐year legacy of wildfire and salvage logging impacts on nutrient runoff and aquatic plant, invertebrate, and fish productivity

ABSTRACTEcohydrological linkages between phosphorus (P) production, stream algae, benthic invertebrate, and fish communities were studied for 4 years after severe wildfire in the Rocky Mountains (Alberta, Canada). Mean concentrations of all forms of P (soluble reactive, total dissolved, particulate, and total) were 2 to 13 times greater in burned and post‐fire salvage‐logged streams than in unburned streams (p < 0.001). Post‐disturbance recovery of P was slow with differences in P‐discharge relationships still evident 5 years after the fire (p < 0.001). Coupled P and sediment interactions were likely responsible for slow recovery of P regimes in fire‐disturbed watersheds. P loading was associated with strong ecological responses in stream biota. Annual algal productivity was 5 to 71 times greater in streams within burned watersheds than in reference watersheds and persisted for 5 years after the fire (p < 0.001). Elevated algal production was associated with strong differences in benthic invertebrate community structure, including greater invertebrate densities, biomass, species diversity, and shifts in species composition. Monotonic shifts in invertebrate stable carbon and nitrogen isotope ratios indicated increased consumption of autochthonous food sources and effects on energy pathways for invertebrates from fire‐affected streams. Wildfire‐related changes at lower trophic lead to increases in size (weight and length) and growth rate (weight : age ratios) of cutthroat trout (Oncorhynchus clarki). This cascading series of effects of wildfire on stream productivity (primary production, secondary invertebrate consumers, and fish) may be long‐lived legacies of wildfire because of the slow recovery of P regimes. Copyright © 2014 John Wiley & Sons, Ltd.

Niche differentiation among invasive crayfish and their impacts on ecosystem structure and functioning

Summary Many aquatic ecosystems sustain multiple invasive species and interactions among them have important implications for ecosystem structure and functioning. Here, we examine interactions among two pairs of invasive crayfish species because of their close proximity and thus chance of sympatric populations in the near future within the Thames catchment, U.K. (signal, Pacifastacus leniusculus and virile crayfish, Orconectes virilis within a river system; red swamp, Procambarus clarkii and Turkish crayfish, Astacus leptodactylus found within a suite of ponds). We address two questions: do sympatric invasive crayfish occupy a smaller niche than their allopatric counterparts due to potential resource competition? and do interactions among invasive species amplify or mitigate one another's impacts on the ecosystem? Two fully factorial mesocosm experiments (one for each crayfish pair) were used to investigate crayfish diet and their impact on benthic invertebrate community structure, benthic algal standing stock and leaf litter decomposition rates in allopatric and sympatric populations, compared with a crayfish‐free control. We used stable isotope analysis to examine crayfish diet in the mesocosms and in allopatric populations of each species in the Thames catchment. Isotopic niche width did not vary significantly between allopatric and sympatric populations of crayfish in the mesocosm experiments, and isotopic niche partitioning in all the wild populations suggests the invaders can coexist. All four species altered benthic invertebrate community structure but with differing functional effects, often mediated via trophic cascades. Red swamp crayfish predation upon snails evidently promoted benthic algal standing stock via reduction in grazing pressure. However, a trophic cascade whereby the crayfish consumed native invertebrate shredders, causing a reduction in net leaf litter decomposition, was decoupled by red swamp and signal crayfish since they consumed leaf litter directly and thus moderated the cascade to a trickle when in sympatry with Turkish or virile crayfish, respectively. Benthic invertebrate predator abundance was significantly reduced by sympatric red swamp and Turkish crayfish but not independently when in allopatry, indicating an amplified effect overall when in sympatry. Our results suggest that the combined effect of multiple invasions on the ecosystem can reflect either an additive effect of their independent impacts or an amplified effect, which is greater than the sum of their independent impacts. A lack of general pattern in their effects makes any potential management strategy more complex.

Response of the benthic food web to short- and long-term nutrient enrichment in saltmarsh mudflats

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 474:27-41 (2013) - DOI: https://doi.org/10.3354/meps10090 Response of the benthic food web to short- and long-term nutrient enrichment in saltmarsh mudflats Pierre-Yves Pascal1,2,*, John W. Fleeger2, Henricus T. S. Boschker3, Hanan M. Mitwally4, David S. Johnson5 1UMR 7138, Equipe Biologie de la Mangrove, Laboratoire de Biologie Marine, Université des Antilles et de la Guyane, 97159 Pointe-à-Pitre, Guadeloupe, France 2Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, USA 3Center for Estuarine and Coastal Ecology, Netherlands Institute of Ecology, 4400 AC Yerseke, The Netherlands 4Oceanography Department, Faculty of Science, Alexandria University, 21511 Alexandria, Egypt 5The Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA *Email: pypascal@univ-ag.fr ABSTRACT: We examined the responses of biota at or near the base of the benthic food web to nutrient enrichment in salt marsh mudflats in Plum Island estuary (Massachusetts, USA). To simulate eutrophication, nitrate and phosphate loading rates were increased 10- to 15-fold in creeks fertilized for 2 mo (i.e. short-term enrichment) or 6 yr (chronic enrichment). We found that benthic invertebrate community structure was not altered by nutrient enrichment, although the abundance of epifaunal, but not infaunal, grazers increased. Short-term enrichment had no effect on the food web, but significant changes were detected with chronic enrichment. Grazing experiments with 15N-enriched bacteria and 13C-enriched benthic algae revealed higher per capita ingestion rates of benthic microalgae by nematodes, copepods and hydrobiid snails in the creek with chronic nutrient enrichment where isotope composition also indicated that algae increased in dietary importance. The fraction of bacterial biomass grazed was not affected by nutrient enrichment; however, the fraction of benthic algal biomass grazed increased by 235% with chronic enrichment. This higher grazing pressure was partly the result of dietary changes (increases in per capita feeding rate or a change in selection) but was mostly due to an increased abundance of the grazing consumer with the highest biomass, the snail Nassarius obsoletus. This increased top-down control partially masked the bottom-up effects of nutrient enrichment on algal biomass and helps explain the slow and inconsistent response of microalgal biomass to chronic nutrient enrichment previously observed in this estuary. Our research shows that eutrophication may subtly affect benthic food webs before large, sustained increases in algal biomass are observed. KEY WORDS: Nutrient enrichment · Benthic food web · Bacteria · Benthic microalgae · Meiofauna · Nassarius obsoletus · Grazing rates Full text in pdf format PreviousNextCite this article as: Pascal PY, Fleeger JW, Boschker HTS, Mitwally HM, Johnson DS (2013) Response of the benthic food web to short- and long-term nutrient enrichment in saltmarsh mudflats. Mar Ecol Prog Ser 474:27-41. https://doi.org/10.3354/meps10090 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 474. Online publication date: January 31, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Changes in the benthic communities of Muskegon Lake, a Great Lakes Area of Concern

Sediment contamination resulting from the direct discharge of industrial and municipal wastes contributed to the designation of Muskegon Lake (Michigan) as a Great Lakes Area of Concern. To assess the changes occurring in the sedient-dwelling invertebrate communities since wastewater diversion began in 1973, benthic samples were collected three times per year (spring, summer, fall) between 2004 and 2010 from six sites and compared to historic samples. The density and diversity of invertebrate populations were analyzed to: 1) identify spatial and temporal patterns in the community structure; 2) determine if community structure patterns were related to environmental variables; and 3) assess the recovery of Muskegon Lake's benthic community following wastewater diversion. Our results revealed that invertebrate community structure changed on both annual and spatial scales, while seasonal differences were shown to be modest between 2004 and 2010. The environmental variables with the greatest explanatory power included dissolved oxygen, pH, and depth. Overall, recovery of benthic invertebrate community structure was evident based on multiple lines of evidence, including increased densities of all major taxonomic groups and species diversity since wastewater diversion, decreases in both the oligochaete–chironomid ratio (0.92 in 1972; 0.69 in 2010) and the proportion of oligochaetes, and declining sediment metal concentration over time. However, comparisons of present-day and historic sampling sites must be viewed with caution because sampling locations and protocols varied among years. Significant changes in benthic invertebrate composition and water quality metrics since 1972 suggest improved environmental conditions and the continued recovery of Muskegon Lake from historic pollution.

Decadal changes in benthic invertebrate biomass and community structure in Lake Simcoe

Total benthic invertebrate biomass in shallow offshore waters (depths 10–15 m) increased 17-fold on average following the invasion of dreissenid mussels and implementation of P controls in Lake Simcoe, Ontario, despite a 50% overall decrease in total invertebrate density during the same time period. The increase in total invertebrate biomass at 10- and 15-m depths was primarily dreissenid biomass. Patterns of biomass with depth and dreissenid invasion for individual taxa were typically similar to those for density. Biomass of chironomid and nondreissenid bivalves declined at shallow (10–15 m) sites but increased at the deepest (20–30 m) sites, whereas biomass of oligochaetes declined at all sites. Density and biomass of Amphipoda, Isopoda, and Gastropoda increased at depths ≥10 m, and these taxa were found more frequently in deeper sites after dreissenid invasion than before. Increased habitation of deeper sites by these taxa may be mediated by increased habitat complexity caused by deposition of dreissenid shells, nutrient enrichment of substrate occupied by dreissenids, and improvements in hypolimnetic dissolved O2 and water clarity observed during dreissenid invasion. Increased length and biomass of profundal chironomids after dreissenid invasion may be the result of taxonomic changes in the chironomid community, which in turn appear to be closely associated with improvements in deep-water O2 concentrations. Changes in the benthic community described here probably have important consequences for the degree of coupling between nearshore and offshore habitats in Lake Simcoe.

Utility of a spatial habitat classification system as a surrogate of marine benthic community structure for the Australian margin

Abstract Przeslawski, R., Currie, D. R., Sorokin, S. J., Ward. T. M., Althaus, F., and Williams, A. 2011. Utility of a spatial habitat classification system as a surrogate of marine benthic community structure for the Australian margin. – ICES Journal of Marine Science, 68: 1954–1962. This study tests whether a continental-scale classification of Australian benthic habitats (termed “seascapes”) and the interpolated environmental data from which they are derived are useful as abiotic surrogates of biodiversity at a local [tens of kilometres, Great Australian Bight (GAB)] and regional scale [hundreds of kilometres, Western Australian (WA) margin]. Benthic invertebrate community structure is moderately associated with specific seascapes in both the GAB (R = 0.418) and WA margin (excluding hard substrata, R = 0.375; all substrata, R = 0.313). Mud content, seafloor slope, and seafloor temperature are significantly correlated with invertebrate communities at both scales, with disturbance and primary production correlated with GAB communities. Seascapes are not consistently useful surrogates because the strength and significance of relationships between seascapes and community structure differs among seascapes, regions, and spatial scales. Nevertheless, a national system of seascapes is an appropriate surrogate for broad-scale benthic invertebrate community patterns when biological data are limited, provided the uncertainty is acknowledged and, where possible, an assessment made of each seascape's ability to differentiate biological communities. Further refinement of seascape derivations may include updated and additional environmental data (particularly for hard vs. soft substrata) and validation among biological datasets from a range of habitats and scales.

Linking the Structure of Benthic Invertebrate Communities and the Diet of Native and Invasive Fish Species in a Brackish Water Ecosystem

To date the studies that link community structure of benthic invertebrates with fish feeding are rare as well as factors that are behind this feeding selectivity are poorly known. In this study, we related invertebrate species composition, their dominance structure and fish biological characteristics to the feeding selectivity and overlap of the native flounder, perch and the invasive round goby in Muuga Bay, the Baltic Sea. Species composition and proportion of benthic invertebrates in the diet of fishes differed from what was available in the field. Except for the round goby, the studied fishes preferred small and mobile invertebrates over large bivalves. However, diet of the studied species, namely the round goby and flounder overlapped. Besides, perch preyed on young stages of the round goby indicating that the introduction of round goby may negatively affect flounder but positively perch.

Baseline Ecological Risk Assessment of the Calcasieu Estuary, Louisiana: Part 3. An Evaluation of the Risks to Benthic Invertebrates Associated With Exposure to Contaminated Sediments

The sediments in the Calcasieu Estuary are contaminated with a wide variety of chemicals of potential concern (COPCs), including heavy metals, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, phthalates, chlorinated benzenes, and polychlorinated dibenzo-p-dioxins and dibenzofurans. The sources of these COPCs include both point and non-point source discharges. As part of a baseline ecological risk assessment, the risks to benthic invertebrates posed by exposure to sediment-associated COPCs were assessed using five lines of evidence, including whole-sediment chemistry, pore-water chemistry, whole-sediment toxicity, pore-water toxicity, and benthic invertebrate community structure. The results of this assessment indicated that exposure to whole sediments and/or pore water from the Calcasieu Estuary generally posed low risks to benthic invertebrate communities (i.e., risks were classified as low for 68% of the sampling locations investigated). However, incremental risks to benthic invertebrates (i.e., compared with those associated with exposure to conditions in reference areas) were indicated for 32% of the sampling locations within the estuary. Of the three areas of concern (AOCs) investigated, the risks to benthic invertebrates were highest in the Bayou d'Inde AOC; risks were generally lower in the Upper Calcasieu River AOC and Middle Calcasieu River AOC. The areas showing the highest risks to sediment-dwelling organisms were generally located in the vicinity of point source discharges of COPCs. These results provided risk managers with the information required to make decisions regarding the need for remedial actions at the site.

Food selection of Coregonus lavaretus in a brackish water ecosystem

This study examined how variability in the abundance and biomass structure of benthic invertebrates affected the feeding choice of the whitefish Coregonus lavaretus on a hard bottom habitat of the brackish Baltic Sea. In general, crustaceans such as Idotea balthica and Gammarus spp. were preferred over molluscs. Although being the most numerous taxon in the invertebrate samples, Mytilus trossulus was the lowest ranking in C. lavaretus food preference. The availability of benthic invertebrate prey set the dietary range of fish but the selectivity largely described fish feeding within this range. There was no clear link between fish predation and the dominance structure of benthic invertebrate communities, suggesting that species composition, abundance and biomass of invertebrate species had no impact on the feeding selectivity of the fish. Thus, while fish predation may not affect the dominant species within a benthic community, due to strong selectivity fish may impose strong pressure on some rarer but highly preferred invertebrate prey species.

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

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

Aquatic invertebrate community structure along an intermittence gradient: Selwyn River, New Zealand

Changes in community structure and life-history traits of benthic invertebrates were examined along a longitudinal intermittence gradient in an alluvial river. The gradient was characterized with modeled and measured hydrologic, chemical, and physical environmental variables. The invertebrates were collected in the Selwyn River, southeastern New Zealand, at multiple sites in each of 4 river sections with distinct hydrological conditions (perennial-losing, ephemeral, intermittent, perennial-gaining). Values of hydrological metrics for each site were generated with an empirical model developed for the Selwyn River. The metrics included 4 that characterized intermittent flow (flow permanence, flow duration, drying frequency, distance to nearest perennial site). Most invertebrate richness and density metrics were significantly higher in the perennial-losing and perennial-gaining sections than in the ephemeral and intermittent sections. A principle components analysis (PCA) separated invertebrate samples from the 4 sections along 2 primary factors. Nine of 13 hydrological metrics, including the 4 intermittence metrics, were correlated with the PCA site scores. Linear regressions indicated that most taxon-richness metrics and some density metrics were related to flow permanence, flow duration, or both. Based on the regression analysis, we predicted that 1.9 taxa/m2 are added with each 10% increase in flow permanence, and 0.5 taxa/m2 are added with each 10-d increase in flow duration. Results from a nestedness analysis indicated that communities at ephemeral and intermittent sites were nested subsets of the communities at perennial sites, and the nesting order of sites was related to both flow permanence and flow duration. Assemblages of taxa with particular life-history traits (life span, fecundity, maximum size, and voltinism) varied linearly with flow permanence and flow duration. The variation in invertebrate communities along the Selwyn River was primarily the result of progressive removal of desiccation-sensitive taxa with increasing intermittence, not to selection for desiccation-resistant specialists. Quantitative intermittence–ecology relationships are needed to predict the consequences of future changes in flow intermittence, but such relationships are rare. The univariate relationships reported in our study contribute to a small but growing array of intermittence–ecology relationships.

신불산 고산습지의 저서성 대형무척추동물 군집구조의 특성

The distribution of benthic macroinvertebrates of Shinbulsan wetland was investigated. This study was focused on the degree of recovery of habitat by comparing the community structure of benthic macro invertebrates of zone D to that of zone A, intact habitat. The zone D was destructed due to the construction of a golf club and the survey was performed in zone A and zone D of Shinbulsan wetland. The seasonal survey was performed in April, July and September from 2006 to 2007. From the sampling, 2 phyla, 3 classes, 9 orders, 31 families, 69 species and 1155 individuals of benthic macroinvertebrates were collected. From zone A, 2 phyla, 3 classes, 9 orders, 23 families, 54 species and 678 individuals were identified. From zone D, 2 phyla, 3 classes, 9 orders, 23 families, 43 species and 477 individuals were identified. Species diversity and species richness were higher in zone A than in zone D. The recovery of zone D was inefficient as humidity of soil was not enough to live macroinvertebrates. Also, an endangered species of macroinvertebrates, Nannophya pygmaea was found during this investigation.

Do agricultural pollutants affect competition between filter‐feeding caddis fly larvae? Results of laboratory microcosm experiments

Summary1. Predictable changes in the composition of macroinvertebrate communities in response to non‐point source pollution are the basis of macroinvertebrate community indices. However, other factors, such as biotic interactions, also affect the composition of macroinvertebrate communities and may complicate the interpretation of such indices by interacting with abiotic stressors.2. The effect of agricultural pollutants on competition between two filter‐feeding caddisflies, Brachycentrus appalachia and Hydropsyche spp. was studied in the laboratory using recirculating flow tanks.3. Experiments were conducted at two densities of Hydropsyche: high (300 per tank) and low (80 per tank). Brachycentrus density was kept constant at 40 per tank in all experiments. Experiments assessed the effect of an agricultural pollutant mix (sand, cow‐manure compost mix) and the presence of the competitor on both taxa.4. The only negative response to pollutants was a larger number of Hydropsyche drifting in high‐density tanks. In fact, at high densities, mortality of Hydropsyche was higher in controls than in tanks receiving pollutants.5. Hydropsyche and B. appalachia competed for resources and the presence of pollution did not affect the outcome of this competition. The presence of high densities of Hydropsyche resulted in higher drift and lower condition of B. appalachia. At low densities of Hydropsyche, B. appalachia larvae suffered greater mortality and tended to be in poorer condition. Brachycentrus appalachia may be less successful at even moderate densities of Hydropsyche due to competition between these taxa, most likely for prime feeding positions.6. Streams receiving non‐point source pollution from agriculture may be able to support higher densities of Hydropsyche, which may further reduce the suitability of these habitats for B. appalachia.7. This experimental study suggests that competition may complicate interpretation of biotic indices, as changes in benthic invertebrate community structure normally ascribed to pollution may arise from intra‐specific competition.

千曲川流域の水田における底生動物の群集構造に及ぼす捕食者と除草剤の影響

千曲川流域の水田における底生動物の群集構造に及ぼす捕食者と除草剤の影響

Variabilité structurelle des peuplements de macro-invertébrés benthiques dans le bassin versant de la Soummam (Algérie, Afrique du Nord)

Summary. — Structural variability of benthic macro-invertebrate communities in the watershed of the Soummam (Algeria, North Africa). — The spatio-temporal distribution and structure of benthic invertebrate communities has been studied in a catchment area of northern Algeria (the watershed of Soummam). The samples were collected over two seasons (spring and summer) in 2005 and 2006 with some additional ones in 2007. They were obtained in 34 stations located at elevations between 20 m and 1100 m a. s. l. Community variability was analysed in terms of space (taxonomic variability in the three parts of the Soummam catchment area) and time (seasonal variation between spring and summer). In the Soummam catchment area, two types of large-scale factors (altitude and slope) govern the distribution of benthic macro-invertebrates by acting on the flow velocity and nature of the substrate. Changes in current speed affect the nature of the substrate which in turn affects the structure of the benthic macro-invertebrate fauna. Five groups of taxa were determined by their density : 56.4 % of taxa have a number of individuals less than 50 per m2, 25.5 % between 50 and 500 per m2, 14.1 % between 500 and 2500 per m2, 2.4 % between 2500 and 5000 per m2, and 1.8 % of taxa with numbers higher than 5000 per m2. This structure shows slight differences between the three parts of Soummam catchment area.