The reproductive cycle in the population of Saccostrea cuccullatta (Born) from the coast of Karachi,Pakistan

Periphytic diatom communities on clay tile and sterilized rock substrates were compared with those on natural substrates. Clay tiles yielded diatom communities with the least variability between replicate samples, and the greatest similarity to the natural substrate assemblage. The advantages of utilizing introduced substrate communities and problems encountered with their simulation of the natural substrate community are discussed.     

Emigration and immigration can be important determinants of benthic diatom assemblages in streams

SUMMARY.

• 1 Interspecific differences in diatom abundances in stream drift (plankton), immigration, and natural benthic assemblages were compared to assess the importance of emigration and immigration in benthic diatom community dynamics. Water samples were collected throughout a 24-h period to measure diel changes in diatom drift abundances and to estimate benthic diatom emigration rates. Immigration was assessed with 24-h colonization of bare tiles.
• 2 Dissimilarity in species composition of drift, immigration, and natural substrate assemblages indicated differential emigration and immigration among diatom species.
• 3 A mathematical model indicated that reproduction by diatoms in the plankton could not account for diel drift peaks and that diel variation in drift was an informative measure of benthic diatom emigration.
• 4 Emigration and immigration of some species constituted substantial proportions of diatom abundances on natural substrata. We conclude that emigration into the drift and immigration onto substrata can be important processes that regulate benthic diatom species composition and standing crop in streams.

     

Unsuitability of introduced tiles for sampling blackfly larvae (Diptera: Simuliidae)*

SUMMARY. 1. Blackfly larvae were collected from twenty-one stations in five lake outlets in Southern Quebec. Tiles (total area=500cm²) were introduced in early March, and collected 4 weeks later: randomly selected rocks (30–500cm) from the surrounding area were collected at the same time. 2. Larval densities on tiles were significantly less variable than on rocks. The variance of density estimates on tiles averaged 36% of the observed variance on natural rocks, or 67% when variance on rocks was corrected for average rock size. 3. Tiles significantly overestimated densities on rocks in some streams, and significantly underestimated them in others. These differences could not be explained by microhabitat differences (distance from the lake, depth, current velocity) between rock and tile samples. The bias that tiles introduce in density estimates precludes their use in comparisons among sites.     

The relation between invertebrate drift and two primary controls,discharge and benthic densities,in a large regulated river

相似文献   

The effects of habitat complexity and hydraulic conditions on the establishment of benthic stream macroalgae

相似文献   

Wind‐driven thermocline movements affect the colonisation and growth of Achnanthidium minutissimum,a ubiquitous benthic diatom in lakes

相似文献   

Productivity modifications to flour beetles (Coleoptera: Tenebrionidae) by gamma radiation (60Co) of one or both sexes and by the addition of radiated males or females to population

The effects on productivity by the addition of various numbers of radiated adult males or females to populations of two densities were determined for two species of flour beetles. Modifications in productivity after exposure to gamma radiation from⁶⁰Co included:

1. females of T. confusum were sterilized by an exposure between 2620 to 5230 R.
2. females of T. castaneum were not sterilized by 10, 200 R.
3. males were not sterilized by 10, 200 R.
4. sterile females may serve as depositories for normal sperm thereby reducing the productivity. Addition of such females to populations of flour beetles did not reduce the numbers of progeny.
5. since sterile females did not suppress population development, and since they destroy grain and cereal products, they should be eliminated from control programs featuring the sterile insect release technique.
6. population density decreased the numbers of progeny.

The use of the sterile insect release technique to control insects of stored grain products does not seem likely with present day sanitary standards since large numbers of insects need be added to effect control.     

Influence of the colonizing substrate on diatom assemblages and implications for bioassessment: a mesocosm experiment

Although diatoms are important bioindicators of ecological quality, their ecological traits are still not well understood. A major issue is that of substrate preferences, which may result in differences in production, and assemblage structure and composition, and which should therefore be taken into account for ecological quality assessment studies. Thus, in this work, the periphyton grown on sand and ceramic tiles in indoor controlled channels were compared to understand whether substrate differences lead to differences in: periphyton production (chlorophyll-a), chlorophyll-b and c concentrations, diatom assemblages (diversity-Shannon-Wiener, cell density, taxonomic composition, trait proportions), and ecological quality assessments (IPS-‘Indice de Polluosensibilité Spécifique’). A combined inoculum of periphyton from four Portuguese streams was introduced to the running channels (six sand and six tile) and left to colonize for 35 days. Epilithic (tiles) and epipsammic (sand) assemblages were sampled at days 14 and 35. We verified that there were no differences in chlorophyll-a concentration over time and between substrates. On both sampling occasions, the epipsammic assemblages had higher concentration of chlorophyll-c and diatom density but without significant differences over time in each substrate. The taxonomic composition was different between substrates and over time. However, these differences were not reflected in ecological quality assessment. The diversity was also similar between substrates in both sampling occasions, but it was higher at day 14. Mobile and stalked species were more abundant over the entire study and differed significantly between substrates, with the epipsammic assemblages presenting higher abundances of both traits. We concluded that the colonizing substrate influences diatom assemblages but not the ecological quality assessment.     

Toxic benthic freshwater cyanobacterial proliferations: Challenges and solutions for enhancing knowledge and improving monitoring and mitigation

1. This review summarises knowledge on the ecology, toxin production, and impacts of toxic freshwater benthic cyanobacterial proliferations. It documents monitoring, management, and sampling strategies, and explores mitigation options.
2. Toxic proliferations of freshwater benthic cyanobacteria (taxa that grow attached to substrates) occur in streams, rivers, lakes, and thermal and meltwater ponds, and have been reported in 19 countries. Anatoxin- and microcystin-containing mats are most commonly reported (eight and 10 countries, respectively).
3. Studies exploring factors that promote toxic benthic cyanobacterial proliferations are limited to a few species and habitats. There is a hierarchy of importance in environmental and biological factors that regulate proliferations with variables such as flow (rivers), fine sediment deposition, nutrients, associated microbes, and grazing identified as key drivers. Regulating factors differ among colonisation, expansion, and dispersal phases.
4. New -omics-based approaches are providing novel insights into the physiological attributes of benthic cyanobacteria and the role of associated microorganisms in facilitating their proliferation.
5. Proliferations are commonly comprised of both toxic and non-toxic strains, and the relative proportion of these is the key factor contributing to the overall toxin content of each mat.
6. While these events are becoming more commonly reported globally, we currently lack standardised approaches to detect, monitor, and manage this emerging health issue. To solve these critical gaps, global collaborations are needed to facilitate the rapid transfer of knowledge and promote the development of standardised techniques that can be applied to diverse habitats and species, and ultimately lead to improved management.

     

The influence of moss on grazers in high‐altitude streams: food,refuge or both?

相似文献   

Water‐level fluctuations regulate the structure and functioning of natural lakes

相似文献   

The occurrence of benthos deep in the substratum of a stream

• 1 The vertical distribution of the benthic fauna of the Speed River, Ontario, was studied over a 13-month period from October 1970 to October 1971. Various physical and chemical parameters of this interstitial environment were also measured.
• 2 Several new techniques for sampling the interstitial environment of rivers wert devised. These methods and their relative efficiencies are considered.
• 3 The validity of the terms ‘hyporheal’ and ‘hyporheic’ are discussed and the term ‘hyporheos’ is offered to replace the former.
• 4 A brief resume of interstitial sampling methods is given with comments on their limitations for sampling deep heterogeneous substrates.
• 5 Chemical parameters are thought to be more important in the control and distribution ofthe fauna than physical parameters.
• 6 It is suggested that many larvae of stream-dwelling chironomids have over-wintering stages when they penetrate deep into the substrate to: (a) actively feed on the trapped organic detritus; (b) follow an optimum temperature for development.
• 7 It is suggested that the shape of an organism determines its success as a hypo-rheic form and examples are given.
• 8 The numbers of animals oecurring in the sub-benthic populations are shown to be very large indeed. For the Speed River, estimates of between 184,760 and 797,960 animals/m^ are made for different times of the year. Dry weight biomass is estimated o t vary between 30 9 g and 253-2 g/m^ throughout the year.
• 9 Sub-benthic or hyporheic populations are shown to exist in at least three other Canadian rivers. Some ofthe animals found are shown to be common to two or more of these rivers.
• 10 The inefficiencies of many conventional benthic samplers in sampling the total biomass of certain streams with hyporheic populations is discussed.

     

Effects of land cover type on community structure and functional traits of alpine stream benthic macroinvertebrates

1. In the European Alps, due to the current changes in land use driven by different social and economic factors, grasslands and pastures are being increasingly replaced by forests. Whereas many studies have focused on the impacts of urbanisation and intensive agricultural activities, no study has evaluated the effects of changes among types of natural to semi-natural land cover in the Alps with a focus on lotic environments.
2. Here, combining taxonomic and functional approaches, we show the effects of four different alpine land cover types (rocks, grasslands, coniferous forests, valley bottom pastures) on stream benthic macroinvertebrate communities. Irrespective of elevation, grasslands and pastures exhibited unpredicted similarity in terms of the composition of the macroinvertebrate assemblages and hosted the highest diversity of benthic organisms, whereas in each of the other land cover types, the density and diversity of the faunal assemblages showed distinct and characteristic values.
3. When analysing the functional diversity decomposed to richness, evenness, and divergence components, grasslands and pastures again showed a similar trend, being characterised by high levels of resource exploitation and niche differentiation, with the potential to host additional organisms. However, as expected, differences driven by land cover type and elevation emerged when examining the single functional traits, since elevation played a major role in terms of the distribution of traits conferring resistance and resilience.
4. Our results demonstrate that land cover type is a prominent factor influencing the taxonomic and functional variety of stream benthic macroinvertebrate communities. Moreover, alpine grasslands contained an unexpected diversity of aquatic insects, as previously assessed for other organisms (e.g. plants and snails). Overall, our study highlights the importance of the preservation of the diversity of habitats in the alpine region, with a special focus needed for valuable semi-natural landscapes, such as grasslands and pastures, particularly in a time of increasing intensification and abandonment of lands in the alpine context.

     

A manipulative study of macroinvertebrate grazers in Hong Kong streams: do snails compete with insects?

相似文献   

Benthic dinoflagellates: Testing the reliability of the artificial substrate method in the Macaronesian region

The suitability of the ‘artificial substrate’ method, i.e. standardized surfaces of fiberglass screens, for the quantification of four benthic harmful algal bloom (BHAB) dinoflagellates (Gambierdiscus, Ostreopsis, Prorocentrum and Coolia) was tested relative to estimates from natural macroalgal substrates. Sampling took place in a variety of intertidal and subtidal coastal habitats under different water motion conditions, at depths from 1 to 7 m, in two archipelagos of the Macaronesia region: The Canary Islands and Cape Verde. An immersion time of 24 h was sufficient to adequately estimate dinoflagellate abundances. Seven replicates were established as the ideal replication level, considering both reproducibility and sampling effort. In most cases, cell abundances of the four dinoflagellate genera showed lower variability on artificial substrates than on macroalgae, leading to more reliable estimates of abundances. The ratio of mean cell abundances on artificial substrates to mean cell abundances on macroalgae highly varied among sampling sites for each genus. This was especially true for Ostreopsis and Coolia. Thus, given the potentially harmful nature of benthic dinoflagellates, the transformation of abundances expressed as cells g⁻¹ of macroalgae to abundances expressed as cells cm^-2 is risky, and it should not be attempted in monitoring and management programs of harmful microalgae. In summary, results of this study support the use of artificial substrates in monitoring programs of BHAB dinoflagellates, while the risks of using macroalgae are stressed.     

Estimating abundance of introduced Chinese muntjac Muntiacus reevesi and native roe deer Capreolus capreolus using portable thermal imaging equipment

• 1 Managing the conservation impacts of deer requires knowledge of their numbers. However, estimating densities in forested areas is problematic, with pellet‐group‐based methods subject to error and uncertainty in estimating defecation and decay rates in addition to sampling variance. Use of thermal imaging equipment allows direct census by distance sampling.
• 2 Densities of introduced Chinese muntjac Muntiacus reevesi and native roe deer Capreolus capreolus were estimated in 12.8 km² of conifer forest in eastern England by thermal imaging distance transects. Estimated density of introduced muntjac (±95% confidence intervals [CI]: 20 ± 8 km⁻²) exceeded that of native roe deer (16 ± 6 km⁻²); 95% CI of c. 40% were achieved in 10 days of fieldwork.
• 3 Density estimates were not sensitive to the number of width bands applied during analysis. Detectability functions differed, with narrower effective strip widths (ESW) for muntjac (74 m) than roe deer (123 m). Thus, it is important to discriminate between species when censusing mixed assemblages. Detectability and ESW also differed among plantation growth stages. Stratification by habitat may therefore improve accuracy of density estimates but would require additional survey effort.

     

Can replacement of native by non‐native trout alter stream‐riparian food webs?

相似文献   

Top‐down and bottom‐up control of periphyton by benthivorous fish and light supply in two streams

相似文献   

Communities in high definition: Spatial and environmental factors shape the micro-distribution of aquatic invertebrates

1. According to metacommunity theories, the structure of natural communities is the result of both environmental filtering and spatial processes, with their relative importance depending on factors including local habitat characteristics, functional features of organisms, and the spatial scale considered. However, few studies have explored environmental and spatial processes in riverine systems at local scales, explicitly incorporating spatial coordinates into multi-taxa distribution models. To address this gap, we conducted a small-scale study to discriminate between abiotic and biotic factors affecting the distribution of aquatic macroinvertebrates, applying metacommunity concepts.
2. We studied a mountain section in each of three perennial streams within the Po River Basin (northern Italy). We sampled macroinvertebrates both in summer and winter, using specific in situ 50-point random sampling grids. Environmental factors, including benthic organic matter (BOM), flow velocity, water depth, and substrate were recorded together with spatial coordinates for each sampling point. The relationships between community metrics (taxon richness, abundance, biomass, biomass–abundance ratio, and functional feeding groups) and explanatory variables (environmental and spatial) were assessed using generalised additive models. The influence of the explanatory variables on community structure was analysed with joint species distribution models.
3. Environmental variables—primarily BOM—were the main drivers affecting community metrics, whereas the effects of spatial variables varied among metrics, streams, and seasons. During summer, community structure was strongly affected by BOM and spatial position within the riverbed, the latter probably being a proxy for mass effects mediated by biotic and stochastic processes. In contrast, community structure was mainly shaped by hydraulic variables in winter.
4. Using macroinvertebrate communities as a model group, our results demonstrate that metacommunity concepts can explain small-scale variability in community structure. We found that both environmental filtering and biotic processes shape local communities, with the strength of these drivers depending on the season. These insights provide baseline knowledge that informs our understanding of ecological responses to environmental variability in contexts including restoration ecology, habitat suitability modelling, and biomonitoring.

     

Life history of the Asian longhorn beetle Anoplophora glabripennis (Coleoptera Cerambycidae) in southern Europe

相似文献