A qualitative analysis of macrofaunasampling in ditches

Summary A comparison is made of macrofauna taxa between ditches that are similar according to criteria that are also used for making inventories. Four complexes of ditches were selected in the Eempolder. An extended sampling programme was carried out in the same diches the Department of Water Works of the Province of Utrecht sampled because of their inventory of natural communities. The results of the two sampling programmes are compared and a minimum sample size is calculated.     

Current and substrate preferences of benthic invertebrates in the rivers of the Hindu Kush-Himalayan region as indicators of hydromorphological degradation

The study introduces an approach to obtaining information about the preferences of benthic invertebrates for substrate and current velocity in a region with little prior knowledge of benthic invertebrates. These preferences are then used for river assessment. Substrate-specific sampling of 271 reference sites was conducted in lower mountainous and lowland areas of the Hindu Kush-Himalaya region. Statistical analysis revealed significant preferences for substrate type and current velocity for 50 taxa of Ephemeroptera, Plecoptera, Trichoptera, Coleoptera, Diptera, Odonata, Mollusca, and Oligochaeta. A 20-point system was developed to assign scores for substrate and current preferences. Scores from seven taxa of Ephemeroptera and Trichoptera revealed low ecological potential in response to habitat alteration. These data were used to develop four preference metrics. The Lithal metric is composed of 34 taxa with significant preferences for stony substrates (fine gravel to bedrock size). The Lithophile metric contains 21 taxa with strong statistical links to stony substrates, which were also found on other substrates. The Lithobiont metric consists of 13 taxa exclusively found on stones. The Lotic metric consists of 11 taxa with significant preferences for moderate-to-fast current velocities. Multi-habitat sampling was conducted at 181 sites reflecting a hydromorphological gradient. The Mann–Whitney U test and box-and-whisker plots were applied to test the relationship of the new metrics to hydromorphological stress. Of the four new metrics, the Lithal, Lithophile, and Lotic were able to detect impacts of hydromorphological degradation.     

Resource seasonality and fish diets in an Illinois stream

Synopsis The purpose of this study was to evaluate the intensity of competition for food among 9 species of stream fishes that primarily eat aquatic invertebrates. The taxonomic and size composition, and numerical abundance of aquatic invertebrates were monitored for one year using drift and benthic samples. Diet data were obtained from stomachs of fishes captured at the same time and place that invertebrate sampling was done. Diet characteristics examined included taxonomic and size composition, number of prey per fish, and diet breadth. Drifting invertebrates were more abundant early in the year (March–June) than later (July–January). The summer-early fall scarcity of invertebrates was especially notable among those>3.6 mm long, which comprised the bulk of prey found in fish stomachs. Average prey size eaten by a fish species was positively correlated with fish mouth size, but interspecific overlap in prey size was extensive. Cyprinids as a group (5 species) ate proportionally fewer small (< 3.6 mm long) prey from July to January than did the centrarchids and stonecat. Taxonomic compositions of available invertebrates and fish diets varied markedly among sampling dates, but the use of prey taxa by fishes was not correlated with the availability of those taxa. Use of aquatic prey taxa was generally similar among fish species, but cyprinids as a group ate proportionally more terrestrial prey from July to January than did the centrarchids and stonecat. Diet breadths for all species increased as food levels declined, indicating that these fishes experienced resource depression. Food scarcity was evidently more severe for cyprinids since their stomachs contained few prey through the summer and fall relative to the centrarchids and stonecat. Though the fish species studied probably compete for food in the summer and fall, this competition did not account for the community structure observed.     

The influence of periphyton, detritus and shelter on invertebrate colonization of aquatic bryophytes

1. Artificial bryophytes were placed in a shaded and an unshaded New Zealand alpine stream to investigate why invertebrates colonized these structures and, by inference, real plants. Three experiments were conducted to investigate the influence of (i) periphyton and detritus (ii) shelter, and (iii) time, on invertebrate colonization. 2. In the first experiment, seven taxa at the unshaded site displayed a preference for substrata with high detrital and periphyton biomass, presumably reflecting a food relationship. At the shaded, less stable site, only two taxa displayed such a relationship. 3. Reducing substratum ‘stem’ density (i.e. ‘shelter’) in the second experiment had little effect on the biomass of periphyton at each site, and only at the shaded site was detrital biomass reduced on low-density substrata. Abundances of most of the twenty-two invertebrate taxa analysed were unaffected by stem density reduction: densities of only four taxa at the unshaded site, and two at the shaded site were reduced. 4. Stepwise multiple regression showed that invertebrate abundance was little affected by stem density at either site. Indeed, shelter was the primary factor influencing abundance of only two of twenty-two taxa at the unshaded site, and none at the shaded site. Abundances of most taxa were related to periphyton or detrital biomass at each site. 5. The third experiment investigated temporal relationships between invertebrate density, periphyton and detrital biomass, and exposure time of artificial bryophytes. Regression analyses indicated that of twenty-two taxa at the stable, unshaded site, eight were influenced by periphyton biomass, three by detrital biomass, and two by exposure time. At the unstable shaded site, abundances of only eight of twenty-two taxa were significantly related to the measured variables, of which exposure time was most important (four taxa).     

Factors Affecting Macroinvertebrate Richness and Diversity in Portuguese Streams: a Two‐Scale Analysis

We analysed the spatial patterns in macroinvertebrate taxon richness and abundance at two scales: sampling unit and basin. We sampled 12 stream sites in three zones of Portugal, differing in climate geomorphology and water chemistry. At a sampling unit scale, substratum organic matter content, depth and the dominant size of substratum particles were correlated with numbers of taxa and individuals. We propose that the number of taxa at a small scale depends on the number of individuals, which in turn is the result of organic matter accumulation, hydrologic and substratum characteristics. The environmental parameters better explaining the large‐scale biological data were temperature, minimum size of substratum particles and pH. Regardless of the relative importance of variable types and mechanisms regulating stream invertebrates along the climatic gradient, rivers from the North and Centre appeared to be richer in taxa than the typically Mediterranean streams in the South.     

Long-Term Changes in the Invertebrates Associated with the Litter of <Emphasis Type="Italic">Phragmites australis</Emphasis> in a Managed Reedbed

Faunal changes within a managed bed of the common reed (Phragmites australis (Cav.) Trin.) were monitored by bi-monthly sampling over 6 years. The reedbed was subject to an annual cycle of summer draw-down and winter reflooding. Water level fluctuations annually result in two distinct communities becoming established, a wet (submersion) community composed of aquatic invertebrates and a dry (exposure) community composed of terrestrial and semi-aquatic taxa. The most numerous family found in the sampling programme was the Chironomidae. Reedbeds are ecotonal wetlands with the fauna being opportunistic resulting principally from range extension of communities in the neighbouring aquatic and terrestrial areas of permanence. Colonization from aquatic refugia following flooding is relatively slow. The alternation annually between the submergence and exposure conditions is highly disruptive and results in low species diversity and a reduction in invertebrate numbers. The high degree of inter-annual variability recorded demonstrates the importance of long-term sampling programmes.     

An experimental study of the influence of periphytic algae on invertebrate abundance in a Hong Kong stream

1. Small cages (294cm²) containing unglazed clay quarry tiles were used to investigate the influence of periphytic algae on macroinvertebrate abundance in a Hong Kong stream. Algal biomass was manipulated by shading cages with plastic sheets. Individual cages were assigned to one of three treatment groups: unshaded, shaded and deeply shaded. Invertebrate densities and algal biomass within cages were monitored after 23, 37 and 65 days. 2. Multiple-regression analysis revealed that algal biomass, invertebrate morphospecies richness and total abundance declined with greater shading intensity. The responses of individual invertebrate taxa varied: some (especially Trichoptera) were unaffected by shading, whereas grazers (Baetidae, Psephenidae and Elmidae) declined as shading increased. 3. Significant regressions of the densities of individual taxa upon algal and detrital standing stocks in cages had positive slopes, but algal biomass increased during the study while detrital standing stocks declined. Abundance of invertebrates declined or remained rather stable over time. Density increases resulting from a positive association with algae were apparently offset by declines in abundance correlated with reductions in detritus. 4. Declines in algal biomass were associated with greater shading to which animals may respond directly. To uncouple the link between scarcity of algae and reduction of light intensity, the plastic covers on two groups of cages (deeply shaded and unshaded) which had been placed in the stream for 28 days were reversed so that cages which had been shaded became unshaded and vice versa. The cages were recovered on day 33, Only Coleoptera demonstrated a positive association with atgae inside cages; no relationship between population densities and algal biomass or light intensity was apparent for other taxa. However, the design may have been confounded by deposition of sediment in the cages (due to declining stream discharge) which reduced population densities of colonizers. 5. This study documents changes in invertebrate abundance and morphospecies richness in response periphyton and detritus standing stocks within patches. Summation of such responses may account for observed variations in benthic communities among Hong Kong streams which differ in the extent of shading by riparian vegetation.     

Species aggregation: the influence of detritus in a benthic invertebrate community

Species aggregation with detritus was examined in a zoobenthic stream community. Detritus was quantified (dry weight in particle size categories) in contiguously arranged quadrats along four transects within a 40m stream section. Total organism density was found to be positively related to increasing detrital biomass (dry weight) in all transects, although the magnitude of this association was influenced by the detrital particle size distribution in each quadrat. Eliminating certain particle size categories of detritus resulted in substantial changes in the magnitude of association. For example, in one transect, total organism density and total detrital biomass showed no association. However, when one particle size category (greater than 10 mm) was removed a highly significant relationship was found. Total detrital biomass was found to be a useful predictor of organism distribution, however, inordinately high detrital biomass and variance within larger particle size categories can mask a relationship. This result suggests that the use of discrete size categories is necessary when considering species/ detrital relationships.Significant associations were found between the density of particular species and total biomass of detritus. The magnitude, as well as significance, of these associations were found to vary when correlations were calculated with restricted particle size categories of detritus. Species associations were often not consistent between transects, possibly due to local characteristics of detritus or overriding environmental factors. Current velocity was found to be unimportant in determining the detrital biomass held in the substrate. Likewise, few associations were found between current velocity and organism density in three out of four transects. Results of this study suggest that habitat selection by some taxa is influenced by local variation in detrital biomass, as well as detrital particle size composition.     

The effects of electrofishing on the invertebrates of a Lake District stream

Summary The experiments were performed in Dale Park Beck, a stony stream in the English Lake District. Two operators electrofished the sampling area (length 20 m in April and July 1970, and 40 m in May 1971) three times (runs 1, 2, 3) in each experiment.Electrofishing caused a marked increase in the number of invertebrates drifting out of the sampling area, and nearly all taxa taken in the bottom samples were also found in the drift samples. The fish shocker was chiefly responsible for the increased drifting of Plecoptera, Ephemeroptera and Gammarus pulex, and these taxa were dislodged from the substratum more easily than Trichoptera, Coleoptera, Diptera and Polycelis felina. The increased drifting of the latter taxa was chiefly due to the disturbance of the substratum by the two operators.Most of the invertebrates drifting from the upstream end of the experimental section returned to the bottom within the sampling area. The invertebrate drift out of the sampling area came chiefly from the downstream end of the section, and was equivalent to a loss of only 5% from the total benthos in the sampling area (losses varied between <1 and 13% for individual taxa).     

The adequacy of collecting techniques for estimating species richness of grassland invertebrates

1.  There is still considerable debate about the most effective methods of sampling invertebrates in monitoring and assessment programmes.
2.  The above-ground invertebrates of a limestone grassland in north-east England were compared between samples from pitfall traps and from a D-vac suction trap combined with a lightweight swish net (SW/DV).
3.  Over 14 000 individuals were captured, with similar numbers in the pitfall and SW/DV samples. A total of 480 species of Hemiptera, Coleoptera, Diptera and Araneae was identified and placed into 14 taxa for further analysis.
4.  The pitfall sample produced species/specimen curves from which it was possible to estimate species richness for all the Coleoptera and Araneae taxa and the calypterate Schizophora. The SW/DV sample was adequate to estimate the species richness of Hemiptera, most Diptera taxa, herbivorous Coleoptera and Linyphiidae.
5.  The proportion of Coleoptera and Araneae taxa that were method-unique was higher in the pitfall sample than the SW/DV sample and vice versa for the Hemiptera and Diptera taxa. Nevertheless, a relatively high proportion of method-unique species of most taxa was found in both sample types, indicating that they can each contribute to assessing species assemblages in grasslands.
6.  Both pitfall traps and SW/DV samples are needed to estimate species richness in grasslands for all taxa except Heteroptera, Homoptera and Lycosidae. Herbivorous Coleoptera and Linyphiidae were collected in numbers adequate for assessing richness in both sample types, but more specimens were required in one or other sample for the remaining taxa.     

Invertebrate Sampling in the Substratum of an Experimental Recirculating Stream

In order to determine the efficacy of sampling benthic invertebrates to a depth of 100 mm as compared with 200 mm, the gravel substratum of an experimental recirculating stream was sampled to both depths. Except for 6 taxa which were significantly more numerous in the shallower samplers, there was no significant difference between the densities determined from the two depths.     

Characterisation of the biofouling community on a floating wave energy device

Wave energy devices are novel structures in the marine environment and, as such, provide a unique habitat for biofouling organisms. In this study, destructive scrape samples and photoquadrats were used to characterise the temperate epibenthic community present on prototypes of the Pelamis wave energy converter. The biofouling observed was extensive and diverse with 115 taxa recorded including four non-native species. Vertical zonation was identified on the sides of the device, with an algae-dominated shallow subtidal area and a deeper area characterised by a high proportion of suspension-feeding invertebrates. Differences in species composition and biomass were also observed between devices, along the length of the device and between sampling dates. This research provides an insight into the variation of biofouling assemblages on a wave energy device as well as the potential technical and ecological implications associated with biofouling on marine renewable energy structures.     

The feeding behaviour of some common lotic insect species in two streams of differing detrital content

The trophic relationships of the benthic invertebrates at two places of differing detrital content in an oligotrophic stream system were examined during a 12 month period.
The sites are described and their detrital contents and other abiotic features compared.
The faunal list at each site is fairly similar but certain species are more common at or restricted to one or other site. The reasons for this are briefly discussed.
The predators and omnivores are in two groups: the first feed only on certain prey and are thus limited by the distribution of their prey. The others consume a wide range of prey and have wider distributions.
The predator species are non-selective in their choice of prey which are devoured in an intensity which cannot however be related to their density in the benthos.
In poorer trophic conditions predators adapt by consuming a greater quantity of algae and detritus; cannibalism and interpredator-predation occur. The prey species are more intensely consumed under poor trophic conditions.
The ecology of two species of predatory Plecoptera is examined and the results indicate that competition probably occurs between them.     

Towards the global monitoring of biodiversity change

Governments have set the ambitious target of reducing biodiversity loss by the year 2010. The scientific community now faces the challenge of assessing the progress made towards this target and beyond. Here, we review current monitoring efforts and propose a global biodiversity monitoring network to complement and enhance these efforts. The network would develop a global sampling programme for indicator taxa (we suggest birds and vascular plants) and would integrate regional sampling programmes for taxa that are locally relevant to the monitoring of biodiversity change. The network would also promote the development of comparable maps of global land cover at regular time intervals. The extent and condition of specific habitat types, such as wetlands and coral reefs, would be monitored based on regional programmes. The data would then be integrated with other environmental and socioeconomic indicators to design responses to reduce biodiversity loss.     

How can habitat size influence leaf litter decomposition in five mid-Appalachian springs (USA)? The importance of the structure of the detritivorous guild

Although habitat size is known to influence both structural and functional properties of ecosystems, there have been few attempts to assess the influence of habitat size on ecosystem processes. Here we investigated the relationships between leaf litter decomposition and ecosystem surface area, macroinvertebrates and physico-chemical factors in five freshwater springs located in Huntingdon County (Pennsylvania, U.S.A.). Leaves of Ulmus americana L. were used to study leaf litter breakdown with the litter-bag technique. Field work was carried out at one sampling station per spring, each with eight replicates per sampling time (3, 20, 40 days), from April to May 2004. American elm leaves decomposed at different rates in the different springs, varying inversely with the spring area. The leaf bags were colonized by 16 taxa of benthic macrofauna, amongst which scrapers and shredders were the most common guild. Macroinvertebrate species richness co-varied with spring area, but not with other physico-chemical variables. Moreover, a significant inverse relationship was observed between American elm leaf decay rate and taxonomic richness. In the studied springs, habitat area was an ecosystem feature indirectly affecting detritus processing by influencing the structure of the detrital food web within the systems.     

Comparison of two methods for sampling invertebrates: vacuum and sweep‐net sampling

ABSTRACT With numerous invertebrate sampling techniques available, deciding which technique to use under certain circumstances may be difficult. Many researchers interested in invertebrate abundance and availability relative to the foraging ecology of birds may use a technique (e.g., vacuum sampling or sweep‐netting) without understanding the impacts their choice may have on the samples collected and the ability of the method to meet research objectives. We compared the characteristics, including overall biomass, morphospecies richness, average size, diversity, and body length categories, of invertebrates collected using a sweep‐net and a Dietrick vacuum sampler along paired transects in Woodward County, Oklahoma, from May to July 2007 and 2008. These sampling techniques differed in the taxa collected, with the orders Diptera, Homoptera, and Hymenoptera dominating vacuum samples and the orders Homoptera, Orthoptera, and Araneae dominating sweep‐net samples. Although morphospecies richness was similar for the two techniques, the mean size of invertebrates collected and overall invertebrate biomass were greater for sweep‐netting than vacuum sampling. Vacuum sampling was more effective at collecting small (e.g., <5 cm) invertebrates, whereas sweep‐netting captured large (>5 cm) Orthopteran and Lepidopteran larvae at higher rates. Thus, our results indicate that neither sampling method effectively sampled all invertebrate families and investigators should be aware of the potential biases of different sampling techniques and be certain that the technique selected will allow study objectives to be met.     

Community structure and spatial distribution of benthic fauna in the Bellingshausen Sea (West Antarctica)

The structure and spatial distribution of the macrofauna community of the Bellingshausen Sea in the western sector of Antarctica was studied during the ‘BENTART–06’ oceanographic expedition. This is one of the least explored Antarctic seas. A total of 20 box cores were sampled at 11 stations ranging from 157 to 3,304 m depth, using an USNEL-type box corer (BC) dredge. Representatives of 25 higher taxa of invertebrates were collected. Deeper sampling sites were less rich in taxa (4–7 taxa), whereas the figures were higher at shallower sites (up to 17 taxa). Faunal density on the sea bottom revealed a horizontal spatial gradient from the western sites with extremely low figures (90 indiv./m²) towards the eastern ones with the highest figures (1,360 indiv./m²) close to the Antarctic Peninsula. Several abiotic factors (depth, redox, organic matter, carbonates and particle size of surficial sediments) were measured simultaneously on the sea floor to characterise the substrate preferences of the fauna. Positive correlations were found between the faunal distribution and a combination of depth, redox values, and organic matter content of sediments. This indicates decreasing availability of food in the deeper bottoms of the Bellingshausen Sea with a prevalence of depauperated bottoms dominated almost exclusively by a foraminiferans community.     

Native and alien macroinvertebrate richness in a remnant of the former river Rhine: a source for recolonisation of restored habitats?

Rivers are among the most endangered ecosystems of the world with dramatically decreasing biodiversity. Rehabilitation programmes aiming at restoration of riverine ecosystems rely on the recolonisation of native macroinvertebrates from refuges. We examined whether a relatively natural remnant of the former river Rhine (Altrhein) harbours a higher richness of benthic macroinvertebrates than two sites of the modified Rhine with artificial and semi-natural embankments near Basel. All three sites were bimonthly sampled between May 2007 and May 2008 using three techniques: Kick and Sweep, drifting animals collected from pieces of stone turned by hand, and animals collected from stone surfaces. Taxa richness was higher in the Altrhein than in the two sampling sites in the river Rhine, but it was mainly a result of the large number of individuals sampled at this site. Despite 17% of taxa recorded were alien, the three sampling sites differed neither in the number of alien taxa nor in their abundances. However, lower percentages of both alien taxa and individuals were recorded in the Altrhein than at the other two sites in the Rhine. Indicator value analysis showed that the macroinvertebrate community of the Altrhein maintains several native and specific taxa. Multivariate analyses supported the separation of the communities collected at different sampling sites and also the uniqueness of the community in the Altrhein. The observed patterns, however, strongly depended on the sampling method applied, thereby calling the attention to the application of standard sampling methods and also to the restriction of result comparisons on projects using identical sampling methodology. Our study shows that the remnant of the former river Rhine serves as a refuge for macroinvertebrates which may facilitate future restoration of the river embankment.     

Microdistribution of benthic invertebrates in a rocky mountain (U.S.A.) stream

A study of the benthic invertebrate community inhabiting a small, foothill trout stream in the Rocky Mountains of Idaho was conducted over a two-year period. Monthly Hess samples and short-term experiments using substratum-filled trays were used to describe the spatial dispersion of the benthos and to examine the response of invertebrate populations to substratum and current. A method was devised for measuring available surface area which involved coating individual stones with latex and measuring the area of the print resulting from inking the impression left on the latex mold.The dispersion of all populations was clumped throughout the year. Alteration of the cross-sectional pattern of current velocity and stream bed composition changed the pattern of distribution but not the extent of clumping. Collections made in areas of depositing and eroding substrata revealed a more diverse fauna in the latter. Most groups of organisms found in the riffle were scarcer in the pools or absent from them. The pool fauna contained no important additions over those found in the riffles.After a year's study of invertebrate populations in an otherwise undisturbed riffle, the substratum was altered and the flow made more uniform; an increase in the abundance of most of the benthic invertebrates followed. No single factor was responsible for the increase, but the change in substratum size and degree of compaction accounted for most of the change. Interpretation of the results was aided by findings from experiments using substratum-filled trays.Two series of stream experiments using the trays were conducted: one to test the relative importance of current and substratum and the other to test the effect of particle size on the distribution of the benthic fauna. In the first series, placement of trays of stones in a pool resulted in an increase in numbers of some but not all of the invertebrates over numbers usually occurring in the pool. Trays filled with stones and placed in a riffle supported fewer animals than found on the adjacent stream bed but more than in the pool. Variations are attributed to differences in current velocity and amounts of imported organic and inorganic debris. Three different relationships of population numbers to current velocity were found for different members of the community (direct, indirect, and parabolic) over the range of 10 to 60 cm/sec. The second series of experiments consisted of two sets of trays filled with stones of medium or large pebbles, respectively. Nine taxa, as well as all of the combined taxa, showed a preference for trays of small stones over the natural stream bed. A few taxa were noticeably more abundant on the small substratum than on the large but most of the fauna showed only slight increases in numbers or remained constant on the two substrata. Only three taxa showed a direct relation of numbers to total surface area presented by the stones.Number and kinds of organisms found in trays filled with a uniform size of substratum did not correspond to those taken in Hess samples from the natural stream bed. This has important implications in terms of currently recommended pollution monitoring techniques. However, it is suggested that if the substratum composition of the trays more nearly matched that of the stream, the correspondence would be much better. The results of the present study also throw considerable doubt on the adequacy of generalizations derived from earlier studies of responses to substratum size and suggest several reasons for reevaluating current ideas regarding the influence of substratum on invertebrate distribution.     

Temporal and Taxonomic Variability in Response of Fauna to Riparian Restoration

Evaluating the success of restoration projects requires well‐designed studies. Among the decisions that need to be made are what taxonomic groups to study and when to conduct the monitoring. To explore how these decisions can influence assessments of restoration success, we examined species richness and composition data collected over several years on different terrestrial fauna (landbirds, rodents, bees, and beetles) at Sacramento River restoration and remnant riparian sites. Our selection of study organisms enabled us to ask whether variability in species richness among restoration sites is less for vagile taxa than for sedentary taxa, and if invertebrates display greater variability among sites than vertebrates. Our results demonstrate that responses to restoration can vary depending upon the season when it is assessed, and the taxa that are studied. For all taxa except bees, there was considerable variability in the relative performance of taxa at restoration sites from one sampling date to the next, such that the relative ranking of the sites often changed dramatically. Comparisons of β ‐diversity (variability in species richness across sites) revealed that certain taxonomic groups were more spatially variable in their response to restoration than others. Among vertebrates, sedentary taxa (rodents) had significantly higher variability in species richness across sites than highly vagile taxa (birds); however, no such pattern was observed for invertebrates. Overall, vertebrates had lower variability than invertebrates, suggesting that evaluations of restoration success based on a few better‐known taxonomic groups (e.g., birds, rodents) may be inadequate to represent the biodiversity response of other groups (e.g., insects).