Composition Of Invertebrate Assemblages Research Articles

Predicting invertebrate assemblage composition from harvesting pressure and environmental characteristics on tropical reef flats

Invertebrates represent an essential component of coral reef ecosystems; they are ecologically important and a major resource, but their assemblages remain largely unknown, particularly on Pacific islands. Understanding their distribution and building predictive models of community composition as a function of environmental variables therefore constitutes a key issue for resource management. The goal of this study was to define and classify the main environmental factors influencing tropical invertebrate distributions in New Caledonian reef flats and to test the resulting predictive model. Invertebrate assemblages were sampled by visual counting during 2 years and 2 seasons, then coupled to different environmental conditions (habitat composition, hydrodynamics and sediment characteristics) and harvesting status (MPA vs. non-MPA and islets vs. coastal flats). Environmental conditions were described by a principal component analysis (PCA), and contributing variables were selected. Permutational analysis of variance (PERMANOVA) was used to test the effects of different factors (status, flat, year and season) on the invertebrate assemblage composition. Multivariate regression trees (MRT) were then used to hierarchically classify the effects of environmental and harvesting variables. MRT model explained at least 60% of the variation in structure of invertebrate communities. Results highlighted the influence of status (MPA vs. non-MPA) and location (islet vs. coastal flat), followed by habitat composition, organic matter content, hydrodynamics and sampling year. Predicted assemblages defined by indicator families were very different for each environment-exploitation scenario and correctly matched a calibration data matrix. Predictions from MRT including both environmental variables and harvesting pressure can be useful for management of invertebrates in coral reef environments.

Drought refuges, spatial scale and recolonisation by invertebrates in non-perennial streams

Summary 1. If resistance traits drive recolonisation after drought, then drought refuges should contribute strongly to assemblage composition within streams. If resilience traits drive recolonisation, macroinvertebrates emerging from refuges may disperse widely, colonising many streams. To determine whether the contribution of drought refuges to macroinvertebrate recolonisation in non-perennial streams was mostly local (within stream) or broader scale (across streams), we measured the association between the composition of invertebrate assemblages in different types of in-stream drought refuge and the assemblage composition of streams when flow resumed. 2. We sampled 16 streams of varying hydrological regime on the western side of the Victoria Range in the Grampians National Park, Victoria, Australia. Drought refuges (perennial pools, dry sediment, damp sediment, seeps, patches of leaf litter, beneath stones) were identified and sampled during autumn. Most taxa were found in perennial pools; few taxa were found aestivating beneath stones or having desiccation-resistant stages in dry sediment. Perennial pools and perennially flowing reaches were the refuges that harboured the greatest diversity of macroinvertebrate taxa. 3. Streams were sampled again during spring. Assemblage composition of non-perennial reaches in spring was unrelated to composition in nearby refuges in the previous autumn. In contrast, assemblage composition in perennial reaches during spring was strongly correlated with composition during autumn. Therefore, drought refuges did not directly influence assemblage composition locally within non-perennial streams. Rather, both perennially flowing reaches and perennial pools acted as drought refuges across the broader landscape. Resilience traits are likely to drive recolonisation in these streams. 4. Monitoring of drought refuges in a particular stream will therefore not predict species composition when flow resumes. Drought refuges are likely to sustain biodiversity over larger spatial scales such as groups of streams or whole drainage networks. Consequently, stream networks will need to be managed as entities rather than as single waterways and the focus of drought refuge protection should be on perennial pools and reaches.

Natural flow regime, temperature and the composition and richness of invertebrate assemblages in streams of the western United States

Natural flow regime, temperature and the composition and richness of invertebrate assemblages in streams of the western United States

Experimental effects of sediment deposition on the structure and function of macroinvertebrate assemblages in temperate streams

AbstractFine sediment in streams and rivers is one of the most globally widespread of all freshwater pollutants. However, the ecological implications are still poorly quantified, and field experiments to assess likely functional and structural effects are scarce.We assessed the response of stream invertebrates to fine sediment (i.e. inert sand) added to trays (n = 65) containing otherwise natural substrata over a three‐week period in three replicate streams in the Usk catchment, Wales.Sediment addition to 0.6–18 kg m−2 affected both the structure and functional composition of invertebrate assemblages while also reducing overall abundance and in some common species (Baetis rhodani, Ecdyonurus sp. and Leuctra geniculata).Sediment also reduced richness and overall trait diversity (TD), while different life‐history traits were either favoured (polivoltinism, tegumental respiration and burrowing behaviour) or disfavoured (swimmers, attached taxa, gill respiration). Moreover, sediments appeared to promote a nested subset pattern in species composition, with generalists favoured at the expense of specialists either through exclusion or impaired colonization. Effects were due largely to the loss of five taxa that contributed to the significant nestedness across the sand gradient: B. rhodani, Ecdyonurus sp., Leuctra geniculata, Simuliidae and Ephemerella ignita.This short‐term experiment supports recent surveys in indicating how sedimentation can change the structural and functional composition of stream invertebrate assemblages even at low to moderate rates of deposition. In revealing direct effects on trait adversity, trait representation and nestedness, the data are also consistent with survey data in indicating that sediments have potentially important ramifications for conservation by removing organisms systematically according to life‐history features. Copyright © 2010 John Wiley & Sons, Ltd.

Forestcheck: the response of macro-invertebrates to silviculture in jarrah (Eucalyptus marginata) forest

Summary The response of invertebrates to silvicultural treatments (including timber harvesting and post-harvest burning) was examined as part of the FORESTCHECK monitoring project in the jarrah (Eucalyptus marginata) forest of south-west Western Australia. Invertebrates were collected twice yearly (spring and autumn) at 48 sample grids in four jarrah forest ecosystems, which included two different vegetation complexes within the same ecosystem. Grids represented examples of unharvested forest (reference) and forest subject to gap release and shelterwood/selective cut treatments. Collection methods included light trapping, pitfall trapping and hand sampling. A total of 56 705 invertebrate specimens comprising 1497 morphospecies were collected. Within each forest ecosystem, species richness did not differ significantly between gap release, shelterwood/selective cut and reference forest. Estimated total richness of macro-invertebrates varied with silvicultural treatment and collection method: 630 species for pitfall trapping and 1095 for light trapping. Estimated richness from light trapping of grids in unharvested forest was 892 species, compared with 780 species in shelterwood/selective cut and 665 species in gap release treatments. Collection method influenced the direction and magnitude of changes in estimated richness following timber harvesting and post-harvest burning, indicating that multiple collection methods are needed to assess invertebrate response to disturbance. Based on combined capture methods, estimated whole bioregional richness of macro-invertebrate morphospecies was highest in reference forest (1783), intermediate in forest subject to shelterwood/selective cut treatment (1652) and lowest in forest subject to gap release (1527 morphospecies). Greater richness estimates in reference forest are attributable to a greater proportion of macro-invertebrate species that occurred in only one grid. However, the robustness of comparisons between treatments of these bioregional estimates of richness is compromised by inadequate sampling. In contrast, for equivalent sampling effort, species accumulation was slightly greater in silviculturally treated forest than in reference forest, implying that silviculturally treated grids had a more homogenous species composition. Data were analysed using non-metric multidimensional scaling ordination and canonical analysis of principal co-ordinates (CAP) analysis. Invertebrate assemblage composition and abundance were strongly influenced by biogeographic pattern, as represented by forest ecosystem/year of collection (these factors were confounded in the design of the monitoring project). No significant effects of silvicultural treatments on morphospecies composition were detected using CAP analysis of morphospecies abundance. Retention of patches of unharvested forest adjacent to harvested forest will assist in maintaining invertebrate biodiversity at the landscape scale. The data suggest that indicator species may be of limited value for monitoring recovery after disturbance in the jarrah forest bioregion because of substantial species turnover between different forest ecosystems and years of sampling. Monitoring of invertebrates should be continued to demonstrate whether harvested coupes are sufficiently heterogeneous, so that their contribution to bioregion species diversity is equivalent to that of unharvested areas.

Wood in different stream types: Epixylic biofilm and wood-inhabiting invertebrates in a lowlandversusan upland stream

Colonization of incubated wood samples by invertebrates and biofilm was compared between a lowland and an upland stream over a 15 month period. Invertebrate densities increased during the first weeks of incubation and then decreased to rather stable densities during the remaining investigation period in both streams. Within the first incubation weeks invertebrate numbers were significantly higher in the lowland stream. Higher dissolved nutrient concentrations and water temperatures accelerated initial epixylic biofilm development in the lowland stream. Lowest invertebrate numbers on incubated branches in the lowland stream coincided with increased discharge. Extreme low flows in the upland stream resulted in lowest invertebrate numbers on incubated wood during the study. Temporal patterns of biofilm and invertebrates indicated some interactions, but statistical significance was low, which might be caused by the variety of interacting effects. Additionally, invertebrate assemblages of in-stream wood samples were collected from four lowland and four upland streams to examine differences of epixylic invertebrate assemblages between the two stream types. Invertebrate densities were significantly higher on submerged wood from lowland streams than wood from upland streams. However, no clear differences in invertebrate assemblages found between the stream types. The study results show that introduced wood in lowland and upland streams is rapidly colonized by aquatic invertebrates and provided an attachment site for biofilms. Invertebrate numbers during the first two months of incubation significantly overestimate the invertebrate numbers found on resident in-stream wood in lowland and upland streams. Analyses of taxonomic composition of wood-inhabiting invertebrate assemblages from natural wood from lowland and upland streams revealed that each stream displayed a rather specific epixylic fauna.

Host taxonomic relatedness and functional-group affiliation as predictors of seaweed–invertebrate epifaunal associations

To test the efficacy of seaweed taxonomic relatedness and morphological/functional- group membership as predictors of host-use by invertebrate epifauna, I sampled invertebrate assem- blages associated with 1652 individual thalli across 32 species of seaweed. Additionally, I tested whether seaweeds within the same functional group had the potential, in the context of species loss, to functionally replace each other as habitat. In total, I found 54 776 individuals across 98 taxa of invertebrates. Similarity of invertebrate assemblages did not decrease as taxonomic distances between seaweed hosts increased; invertebrate assemblages were as different on sibling algal spe- cies as on hosts classified in different kingdoms. The utility of seaweeds as hosts for mobile inverte- brates varied across components of invertebrate diversity. Invertebrate assemblage composition was different across most algal functional groups, whereas invertebrate taxon richness was different for ca. 25% of functional groups, and no differences in invertebrate abundance across algal functional groups were observed. There was substantial variation in host-use within seaweed functional groups, suggesting that overall functional group performance indicates little about the performance of the constituent species. Specifically, composition, richness and abundance of invertebrate assemblages were different across most hosts within each algal functional group. Therefore, in the event of sea- weed species loss, replacements by members of the same functional group generally appear unlikely. These observations bring into question the use of general frameworks for predicting performance of seaweeds as hosts for associated invertebrates; it appears that invertebrate selection of seaweed hosts is largely dependent upon the identity of the host species.

Invertebrate assemblages in relation to habitat types on a floating mat in Mizorogaike Pond, Kyoto, Japan

Abiotic environmental variables and invertebrate assemblages were compared among four habitat types (bare hollow, sphagnum-rich hollow, pool, and mat edge) on a floating mat in Mizorogaike Pond, Kyoto. We found differences in abiotic environments between two hollows and two inundated habitats (pool and mat edge); pH was significantly lower in hollow habitats than in inundated habitats, and water depths were significantly shallower in sphagnum-rich hollows than in inundated sites. The composition of invertebrate assemblages in the hollow was distinct from that in the inundated habitats. The abundances of some dominant invertebrate taxa or functional feeding groups on the floating mat differed between the hollows and inundated habitats, and were correlated with water temperature, pH and depth. These results indicate that habitat heterogeneity created by the coexistence of hollows and inundated habitats contributes to species diversity on the floating mat in Mizorogaike Pond. A comparison of the pH values in different wetlands revealed that both bog- and fen-specific components coexist within this system. In order to adequately manage and conserve peatland ecosystems, it is necessary to consider the importance and vulnerability of both hollows and inundated habitats in peatlands.

Response of taxonomic groups in streams to gradients in resource and habitat characteristics

SummaryCompared to other ecosystem types, a wide variety of biomonitoring methods are available for rivers. Few studies have, however, compared the response of bioindicators (i.e. different river inhabiting taxonomic groups) to different types of environmental stress.We regressed diversity, taxonomic distinctness and assemblage composition of fish, invertebrates, macrophytes and benthic diatoms to multivariate gradients in nutrient enrichment and habitat degradation using data from 66 lowland and 77 mountain streams.In lowland streams, the composition of benthic diatom assemblages, measured by Detrended Correspondence Analysis, showed the strongest response to elevated nutrient concentrations (R2 = 0·830), followed by macrophytes (0·711), fish (0·443) and invertebrates (0·391). Macrophyte richness was slightly better correlated with the habitat gradient (0·253) than diatom richness (0·235) and both were better predictors than either fish (0·147) or invertebrate (0·140) assemblage composition.For mountain streams, invertebrate assemblage composition was the best predictor of changes in nutrient concentrations (R2 = 0·749), followed by macrophyte (0·396) and benthic diatom (0·325) assemblages and fish diversity (0·099). Invertebrate assemblage composition was also slightly better correlated with the habitat gradient (0·391) compared to macrophyte richness (0·323) and both were better than either benthic diatom assemblage composition (0·206) or fish abundance (0·161).Macrophyte and benthic diatom assemblages in lowland streams and fish and invertebrate assemblages in mountain streams were correlated with the other taxonomic groups, implying that these taxonomic groups may be used as surrogates for indicating wholesale change in diversity.Synthesis and applications. Our findings show that response trajectories differ between taxonomic groups and stressor, and even with stream type. For this reason, streams and other ecosystem type's response signatures and first and second principle relations should be considered in the selection of robust, complementary and cost‐effective measures for biomonitoring. For instance, our findings of asymmetric response to stress show how different taxonomic groups can be used to strengthen inference of change.

Changes in arthropod diversity along a land use driven gradient of shrub cover in savanna rangelands: identification of suitable indicators

Shrub encroachment linked to heavy grazing has dramatically changed savanna landscapes, and is a major form of rangeland degradation. Our understanding of how shrub encroachment affects arthropod communities is poor, however. Here, we investigate the effects of shrub encroachment on abundance and diversity of ground-dwelling (wingless) arthropods at varying levels of shrub cover in the southern Kalahari. We also ascertain if invertebrate assemblage composition changes with habitat structure and identify which aspects of habitat structure (e.g., grass cover, herbaceous plant cover, shrub density) correlate most strongly with these changes. Ant, scorpion and dung beetle abundance increased with shrub cover, whereas grasshoppers and solifuges declined. Spider and beetle abundance exhibited hump-shaped relationships with shrub cover. RTU richness within orders either mirrored abundances, or exhibited no trend. Shrub density was the habitat component most correlated with similarities between invertebrate assemblages. Ground-dwelling arthropods showed clear shifts in species assemblage composition at a similarity level of 65% according to shrub density. Changes in indicator species showed that within the Tenebrionidae (darkling beetles), certain species respond positively to shrub thickening, replacing other species within the Family. Small-bodied, wingless Scarabaeidae (dung beetles) tended to increase with increased shrub density and three species emerged as significant indicators of more thickened habitats, although this might be a response to greater dung availability, rather than habitat structure itself. We conclude that because ground-dwelling invertebrates showed such clear responses in species assemblage composition, they present excellent candidates for use as indicator species in further studies into bush encroachment.

Lateral and longitudinal patterns within the stygoscape of an alluvial river corridor

In landscape ecology, landscapes are viewed as hierarchically-organized groups of interacting components or zones. This perspective is applied in studies of riverscapes with increasing frequency,particularlyin studies ofchannel habitats and channel-floodplain interactions. Stygoscapes, the subsurface portions of riverscapes, have received less attention. Stygoscapes are composed of three saturated zones beneath and lateral to river channels: the hyporheic, parafluvial and riparian zones. These zones are differentiated on the basis of hydrological, biological and chemical conditions, and the degree of interaction with the channel surface. In this paper, we describe lateral and longitudinal patterns in the shallow (30 cm - 10 m depth) stygoscape of the alluvial Selwyn River, New Zealand. We used abutting hyporheic, parafluvial and riparian zones in large-scale downwelling (losing) and upwelling (gaining) sections of the river mainstem to compare physico-chemical and biological conditions across a broad stygoscape. The stygoscape zones had the same arrangement in both sections: hyporheic zones within the wetted channel, riparian zones furthest from the channel, and parafluvial zones between the hyporheic and riparian zones. Nitrate and dissolved reactive phosphorus concentrations and electrical conductivity were significantly higher, and dissolved organic phosphorus concentrations and pH levels lower, in the gaining section than the losing section. In both sections, ammonium, dissolved reactive phosphorus, and dissolved organic carbon concentrations and pH were higher in the hyporheic zone than the riparian zone. Within the losing section, DON and DOP concentrations were higher in the hyporheic zone than the riparian zone. Physico-chemical conditions were intermediate in the parafluvial zones of both river sections. These among-zone differences suggest that hyporheic zones are sinks for dissolved nutrients, and that effects of hyporheic sinks are greatest in losing river sections with unidirectional flow from the surface to the hyporheic zone. There were large differences among stygoscape zones in invertebrate assemblage composition, and smaller differences between the losing and gaining sections. Invertebrate densities, taxon richness and % insect taxa were higher in hyporheic zones than riparian zones. Invertebrate densities were intermediate in the parafluvial zones, and taxon richness and % insect taxa were similar in parafluvial and riparian zones. The spatial patterns we observed in the Selwyn River suggest that hydrological connectivity between zones, and permeability within zones, are among the most important determinants of chemical and biological dynamics in stygoscapes. Differences in large-scale upwelling and downwelling, and differences in water source (runoff and groundwater) appeared to be of secondary importance.

Oceanographic gradients and patterns in invertebrate assemblages on offshore oil platforms

Abstract Page, H. M., Culver, C. S., Dugan, J. E., and Mardian, B. 2008. Oceanographic gradients and patterns in invertebrate assemblages on offshore oil platforms. – ICES Journal of Marine Science, 65: 851–861. We explored variability in the composition and cover of subtidal macroinvertebrate assemblages, and the recruitment and growth rates of selected invertebrate species, on seven offshore oil and gas platforms arrayed across a gradient in oceanographic conditions in the Santa Barbara Channel, CA, USA. The major macroinvertebrate taxa (sea anemones, mussels, barnacles, tubiculous amphipods, hydroids, and sponges) were common to all platforms. However, discriminant function analysis (DFA) revealed that the assemblages of two platforms (Gilda and Gail) clearly differed from the other platforms, a pattern attributable, in part, to the presence of conspicuous exotic species (the anemone, Diadumene sp., and encrusting bryozoan, Watersipora subtorquata) on these platforms. If these exotic species were excluded from the analysis, platforms in proximity to each other generally tended to have invertebrate assemblages more similar to each other than to platforms located farther away. Spatial variation in barnacle recruitment onto ceramic plates and mussel growth rate reflected prevailing oceanographic gradients. The existence of along-channel patterns in the composition of platform invertebrate assemblages, and in invertebrate recruitment and growth associated with oceanographic gradients, suggests that assemblages attached to platforms or other artificial structures may be useful barometers of short and perhaps longer term change in ocean climate.

Longitudinal patterns of benthic invertebrates along a stream in the temperate forest in Japan: in relation to humans and tributaries

Abstract. The relationship between benthic invertebrate assemblage composition and surrounding land use has been examined in various ways, but most studies are undertaken at a coarse scale, or they compare obviously different landscapes. In Japan, these obvious differences in landscape are rare, and humans reside even in remote montane areas. In order to clarify the influence of human residence on benthic invertebrate assemblages, seasonal and site differences among benthic samples collected from a 15‐km stretch of Kuroson Stream and their relation with riparian land use were examined. The number of individuals and genera differed significantly both spatially and temporally. Multivariate assemblage structure also differed significantly across space and time along the stream. Increase of residential areas affected the in‐stream benthic invertebrate assemblage. Site differences along the stream and the effect of human residence were not masked by the potentially homogenizing influence of tributary streams. The composition of surrounding vegetation was the most important factor influencing benthic community structure. The presence or absence of human residential areas and seasonal change were also important variables. Benthic invertebrates may be carried and migrate to main streams from tributaries; however, this phenomenon was not observed. Assemblages of benthic invertebrates that inhabit a particular site do not change and are considered to vary seasonally across a certain range.

Plant-associated invertebrates and hydrological balance in the large volcanic Lake Bracciano (Central Italy) during two years with different water levels

Lakes in the Mediterranean region experience an altered hydrological balance with large water level reductions and/or fluctuations within and between years. To date, little is known about the reaction of invertebrate assemblages inhabiting the littoral zone to water level changes in natural lakes. Here, we present the case of the volcanic Lake Bracciano, one of the largest and deepest Italian lakes. We compared the numerical composition and taxonomic richness of plant-associated invertebrate assemblages sampled from three sites and three depth ranges (0–4 m, 4–8 m and 8–15 m) between years with different water levels. Using historical data, we built a hydrological balance model to assess the role of different water budget components on the water levels. The hydrological balance showed that the volume of water currently abstracted for human use exceeds the potential changes caused by the projected warming of climate and decreasing amount of precipitation by nearly an order of magnitude. In a low water level year, littoral macrophytes and invertebrate assemblages exhibited qualitative and quantitative differences at all sampling sites and depths. The invertebrate assemblage showed a reduced taxonomic richness and lower numerical abundance of the more sessile forms (water mites, gastropods, nematodes, naidid oligochaetes), which feed directly on living plants or epiphytic algae, and an increase of more mobile and/or detritivore taxa.

Functional approaches for assessing plant and invertebrate abundance patterns in arable systems

A functional group approach was developed for plant and invertebrate assemblages from UK arable fields to assess the variation in functional composition of these highly disturbed, managed systems. Data were taken from the Farm-Scale Evaluations (FSE) of genetically modified herbicide-tolerant (GMHT) crops where the impact of management of the GMHT crop has been assessed for winter and spring sown oilseed rape, beet and maize. Twenty plant and 36 invertebrate functional groups were defined according to trophic behaviour and traits that affect resource capture, quality and availability. The functional composition of the plant community was significantly affected by season of sowing, the type of crop sown and, to a lesser extent, herbicide management. The invertebrate community composition was also affected by crop type and sowing season, but not by management. Resource and consumer groups were positively related, and data provide strong evidence for top-down control of herbivore populations. Two main interaction groups were identified within the arable food web: one between omnivores, generalist predators and detritivores, which are positively associated with monocots, and one between omnivores, parasitoids, sap feeders and leaf chewers, which have a stronger association with dicots. Although management has an impact on within-field arable biodiversity, crop type and sowing season have an overriding effect on the functional composition of plant and invertebrate assemblages in arable systems. Für Pflanzen- und Invertebratengesellschaften auf Kulturflächen in Großbritannien wurde ein Ansatz über funktionelle Gruppen entwickelt, um die Variation in der funktionalen Zusammensetzung dieser hochgradig gestörten, bewirtschafteten Systeme zu bestimmen. Die Daten stammen aus der “Farm-Scale-Evaluation” von genetisch modifizierten herbizidtoleranten Feldfrüchten (GMHT), bei der der Einfluss der Bewirtschaftung der GHMT-Feldfrüchte für Winter- und Sommerraps, Rüben und Mais abgeschätzt wurde. Es wurden 20 funktionelle Gruppen von Pflanzen und 36 von Invertebraten unter Berücksichtigung der trophischen Stellung und Eigenschaften definiert, welche die Ressourcennutzung, Qualität und Verfügbarkeit beeinflussen. Die funktionelle Zusammensetzung der Pflanzengemeinschaften wurde signifikant durch die Aussaatsaison, durch den ausgesäten Nutzpflanzentyp und in geringerem Maße durch das Herbizidmanagement beeinflusst. Die Zusammensetzung der Invertebratengemeinschaften wurde ebenfalls durch den Nutzpflanzentyp und die Aussaatsaison beeinflusst, aber nicht durch das Management. Die Ressourcen- und Konsumentengruppen standen in einer positiven Beziehung zueinander und die Daten liefern starke Hinweise auf eine top-down Kontrolle der Herbivorenpopulationen. Es wurden zwei wesentliche Interaktionsgruppen innerhalb des Kulturnahrungsnetzes gefunden: Eine zwischen den Omnivoren, unspezialisierten Prädatoren und Detritivoren, die positiv mit Monokotylen assoziiert sind, und eine zwischen Omnivoren, Parasitoiden, Saftsaugern und Blattfressern, die eine stärkere Assoziation mit Dikotylen zeigen. Obwohl die Bewirtschaftung einen Einfluss auf die Biodiversität innerhalb der Kulturfelder hat, zeigen Kulturpflanzentyp und Aussaatsaison eine überwältigenden Einfluss auf die funktionale Zusammensetzung der Pflanzen- und Invertebratengemeinschaften in Kultursystemen.

Lignite mining and stream channelization influences on aquatic macroinvertebrate assemblages along the Natchez Trace Parkway, Mississippi, USA

The article describes the effects of channelization on selected water quality parameters and benthic macroinvertebrate assemblages in four Big Black River (Mississippi, USA) tributaries crossing the Natchez Trace Parkway [U.S. National Park Service (NPS)]. Two of the streams were unchannelized (Little Bywy Creek and McCurtain Creek), and two were channelized (Big Bywy Creek and Middle Bywy Creek). Lignite mining occurs in the headwaters of Little Bywy Creek and Middle Bywy Creek. During this 3-year study, benthic macroinvertebrates were collected monthly from all four streams using Hester-Dendy Multiple plate samplers, and enumerated taxonomically and functionally. Hypotheses were tested using analyses of variance. Relationships were determined using multivariate analyses. Relative abundances of mayflies (Ephemeroptera), stoneflies (Plecoptera), caddisflies (Trichoptera) and aquatic beetles (Coleoptera) were associated with moderate to high conductivity, alkalinity, pH, and dissolved oxygen. Hellgrammites (Megaloptera), midges, blackflies, and mosquitoes (Diptera), crayfish (Crustacea: Decapoda) and leeches (Annelida: Hirudinea) were associated with lower values for these parameters. These patterns reflected seasonal rather than spatial variation (i.e., among the streams). Invertebrate assemblage composition was similar among the four streams with respect to functional groups. Invertebrate relative abundances in the two channelized streams were approximately half those of the unchannelized streams. Macroinvertebrate species richness was greater in unchannelized streams. Environmental indices categorized all four streams as having fair to good condition.

Composition, biomass and secondary production of the macrobenthic invertebrate assemblages in a coastal lagoon exploited for extensive aquaculture: Valle Smarlacca (northern Adriatic Sea)

Macrobenthic invertebrate assemblages were investigated monthly, from June 1998 to October 1999, at four sites in Valle Smarlacca pond, a north-western Adriatic coastal lagoon, in order to estimate secondary production exploitable for extensive fish aquaculture and to investigate the factors affecting this production. Benthic assemblages comprised 28 taxa, of which Hydrobia sp., Chironomus salinarius and Abra segmentum were the main contributors to both overall biomass and secondary production. Annual secondary production varied from 102.7 g AFDM m −2 y −1, in the unvegetated perimeter channel, to 152.6 g AFDM m −2 y −1 in the shallowest area where a Ruppia cirrhosa meadow was present. Multivariate correlations between environmental variables and the macrobenthic assemblage biomass highlighted the role of the water level, temperature, sediment organic carbon content and dissolved oxygen in the differentiation of the communities in the pond. Composition, biomass and secondary annual production of macrobenthic communities were dramatically affected by summer dystrophic crises. The isolation of this habitat limits the recovery of the invertebrate benthic assemblages. Only populations of two species, Hydrobia sp. and C. salinarius, seemed to be able to recover quickly after the dystrophic crises, which, in turn, could compromise the overall secondary production, with negative effects on the aquaculture activities. Water renewal and nutrient inputs should be regulated in this pond to reduce the risk of zoobenthic mass mortality and to ensure a sustainable extensive aquaculture based on natural primary and secondary production.

Invertebrates Colonization on Native Tree Leaves in a Neotropical Stream (Brazil)

AbstractWe evaluate the composition and structure of invertebrate assemblages during leaf breakdown of five native tree species (Myrcia guyanensis, Ocotea sp., Miconia chartacea, Protium brasiliense and Protium heptaphyllum) and a mixture of them in a headwater stream, Southeastern Brazil. Coarse mesh litter bags were used over a 120‐day period. P. heptaphyllum showed the slowest breakdown rate, while Myrcia showed the fastest. Total densities and biomass values of associated invertebrates were different among leaf types and incubation periods. The highest values of total abundance were found in P. heptaphyllum, while Ocotea sp. and Miconia were few colonized. Gathering‐collectors feeding group dominated all leaf types, followed by predators and shredders. Shredders were more abundant in Myrcia than in Miconia and the mixed pack. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Soil macroinvertebrate fauna of a Mediterranean arid system: Composition and temporal changes in the assemblage

Temporal variability is a key factor to understand the structure of belowground communities. Seasonal and annual variations are especially relevant in unpredictable desert ecosystems, where macroinvertebrates are poorly known, despite constituting an important group of soil organisms. In the present study, we analyse the composition and temporal (seasonal and annual) variations of soil macroinvertebrates in an arid area of southern Spain. During two years, macroinvertebrates were sampled in litter and belowground levels by means of soil cores. Results show that the assemblage was dominated by arthropods, especially Formicidae and Coleoptera. The assemblage differed between litter and belowground levels. In litter, detritivores dominated the community, while belowground fauna showed a similar proportion of detritivores and herbivores and a low percentage of predators. Litter and belowground assemblages showed seasonal variations in richness, abundance, biomass and composition, although variations were more marked in litter than belowground. Patterns of seasonal variation also differed between the two study years for both litter and belowground invertebrates. The seasonal and annual variability of the assemblage has potentially important implications for community dynamics in the study system, since the changes in species composition and trophic structure of soil invertebrate assemblages may affect species interactions and food web dynamics over time. Therefore, integrating temporal variability is likely to be crucial to understand soil community dynamics and food webs, especially in heterogeneous, variable systems as deserts.

Effects of catchment disturbance on stream invertebrates: comparison of different habitats (vegetation, benthic and interstitial) using bio-ecological groups.

The intensification of agriculture has drastically modified the structure of rural landscapes, changing field size, destructing hedgerow networks, and increasing nutrients and fine sediments fluxes to rivers. To evaluate the effects of these disturbances at the catchment scale, we studied the surface and interstitial water chemistry and the invertebrate assemblages in three different habitats: the vegetation, the benthic, and the interstitial. Six headwater streams ranging from undisturbed to disturbed forests (wind-fallen area) and from traditional agriculture to intensive farming areas were studied. Differences between forested and agricultural streams lie in changes in water chemistry, in habitat quality, and in the composition of the assemblages with little reduction in species richness. The forested streams were only disturbed by large-scale modifications of their catchments (i.e. wind-fallen area along the stream), which made the invertebrate assemblages similar to those of agricultural streams, even if water characteristics were not modified. In contrast, large scale modifications of landscape structure near the agricultural streams (hedgerow removal) had little effect on the fauna, but the destruction of the riparian strip (with direct access of the cattle to the river) profoundly affected the system with drastic modifications of in-stream habitat quality and invertebrate assemblage composition. The effects of these disturbances differed according to the habitat considered, with increasing differences between assemblages from the interstitial, to the benthic, and to the vegetation habitats. Finally, groups of organisms based on bioecological traits appeared as efficient tools for the evaluation of catchment disturbances, at least for the benthic and the vegetation fauna.