A study on the faeces of some chalk stream invertebrates

An account is given of the size, form, texture, colour, cohesion and composition of the faeces of 41 species of invertebrates found in chalk streams. The relationships between the character of the faeces and the taxonomic positions and habits of the producers are considered.The importance of faeces production relative to the bulk of stream bed sediments is discussed. Faeces of different origins accumulate in different areas of the stream bed and these differences may be associated in part with their form and structure and in part with the distribution of the species from which they originate. In the summer months tubificid worms alone may be responsible for reworking between 0.3% and 0.5% of the fine particulate material in sediments every day.     

Biology of epiphytic Chironomidae (Diptera:Nematocera) in chalk streams

Submerged macrophytes are a conspicuous feature of chalk stream ecosystems, supporting large populations of diatoms and invertebrates, including larvae of the nematocerous family Chironomidae. Close temporal and spatial association is evident between chironomid larvae and diatoms, and diatoms are frequently a major component of the food of midge larvae. Larvae provided with food that is rich in diatoms survive better and grow and develop more quickly than larvae that are supplied with food that is predominantly fine organic detritus. First instar larvae selectively feed on diatoms but it is likely that selection is on the basis of particle size, rather than for diatoms per se. Three species of epiphytic larvae (2 Cricotopus spp. and Eukiefferiella ilkleyensis) transfer to a diet that is predominantly of fresh plant material (Ranunculus calcareus leaves) in the third and fourth instar. The life cycle strategies of many species of Orthocladiinae equip them to exploit temporarily favourable environmental conditions very rapidly and effectively. This fact helps to explain the coexistence of species with similar strategies of resource utilization, as part of the normal epiphytic fauna of chalk streams.     

Spatial and temporal occurrence of invertebrates in a chalk stream,Berkshire, England

The invertebrate assemblages of the River Lambourn and its tributary, the Winterbourne stream, were investigated as part of a broad ecological study prior to water resource development in the catchment. The longitudinal distribution of the invertebrate fauna within the Winterbourne stream was examined in detail and supporting data for the R. Lambourn revealed that the upstream intermittent section of each water course had an invertebrate assemblage which was distinct from the fauna downstream where flow was permanent. Within the perennial zone taxon richness tended to increase downstream.A one-year programme of monthly quantitative sampling on five distinct biotopes (Ranunculus, Berula, Callitriche, gravel and silt) at two contrasted sites (shaded and unshaded) was undertaken in the lower perennial of the R. Lambourn below the confluence with the Winterbourne. On each study site, the taxon richness, numerical abundance and biomass of invertebrates were significantly higher on the three macrophytes than on gravel and silt. There were also statistically significant seasonal changes in the biomass of invertebrates on each site. Estimates of total biomass of invertebrates per site revealed a late spring peak (May/June) and a late autumn (November/December) peak, neither of which coincided with the summer peak biomass of macrophytes. This suggested that, in the lower perennial, the level of food resources (epiphytic algae in late spring and fallen tree leaves plus decaying macrophytes in autumn) rather than available habitat, were a major influence on population levels for most of the year.Quantitative sampling of each biotope on each site continued in June and December only for a period of 8 years (1971–78), during which time the river experienced a minor drought (1973) and a severe drought (1976). The Chironomidae showed a strong positive response to conditions of low flow in June of 1973 and 1976, when exceptionally high densities of larvae were recorded. Although further between-year differences were recorded in several other major components of the invertebrate fauna, which may have been related to conditions of low discharge, they did not have long-term consequences for the fauna in the lower perennial of the R. Lambourn.In contrast, in the upper perennial, the prolonged drought of 1976 resulted in the loss of wetted perimeter and macrophytes, coupled with deposition of silt, all of which had deleterious effects on the invertebrate assemblages. The following year, despite a normal discharge regime and the removal of silt, some submerged macrophytes were slow to return to their pre-drought condition. In the intermittent section, the drought of 1976 resulted in the total loss of flow for a 16 month period instead of a more typical four month period of water loss.Thus, chalk streams encompass within a single system both stable and extreme hydrological regimes which offer unique opportunities for investigating the processes of community formation and maintenance.     

Response of the flora and macroinvertebrate fauna of a chalk stream site to changes in management

1. Temporal changes in a series of habitats and their macroinvertebrate assemblages were examined on a 50‐m section of a chalk stream in Berkshire, England between June 1975–79 and June 1997–2001. 2. The site was part of a trout fishery in 1975–79, when river management included instream weed cutting together with control of bankside trees and riparian vegetation. Management ceased in the 1980s and by 1997–2001, the site was heavily shaded by trees and riparian vegetation. 3. The mean area of instream macrophytes decreased by 50% between the first and second sampling period. In contrast, gravel and silt increased and invading marginal vegetation formed a new habitat. 4. Changes in macroinvertebrate family richness between sampling periods were scale dependant. Although there were, on average, significantly more families in individual replicates in 1975–79 than in 1997–2001, total family richness for the site in each year did not differ significantly between sampling periods. 5. Sixty families of macroinvertebrates were recorded during the study, 50 in both sampling periods, 53 in 1975–79 and 57 in 1997–2001. This small increase in site family richness may be due to the invading marginal plants. 6. Total macroinvertebrate abundance was significantly lower in the second sampling period. A major drought in 1976 resulted in significantly higher densities of macroinvertebrates, partly through the exploitation of epiphytic diatoms by chironomid larvae. A drought in 1997 failed to elicit a similar response because of the limited macrophytes and diatoms under heavy shading by trees and marginal vegetation. 7. Significant increases in important shredders and decreases in some scrapers between the early and later sampling years largely reflected changes in available food resources. 8. Whereas macroinvertebrate family richness has been conserved under the recent ‘no management’ regime, the site is now less attractive as a fishery because of poor access and lower densities of some macroinvertebrates taken by brown trout.     

Long-term investigations of trophic relationships in southern chalk streams

SUMMARY. 1. An understanding of the feeding relationships of organisms is fundamental to our capability to conserve and manage aquatic systems. At one extreme we must study the cyclic and erratic physical processes which govern the reproduction, survival and growth of consumers and their'prey'and at the other the rates of food consumption, the assimilation of nutrients and the energetic interactions of plants, animals and micro-organisms.
2. Since the commencement of freshwater science in this country, our understanding of the mechanisms by which producers and consumers interrelate has increased greatly. Information is required basically on three levels: (1) Short-term laboratory and field studies designed to provide detailed data on aspects such as habitat selection, growth, feeding behaviour, etc. (2) Investigation of patterns of change which show periodicities of weeks, months or even a few years associated with the life cycles of many plants and animals and with the seasonal variations in physical and chemical parameters. (3) Long-term surveillance and monitoring, often in a superficial manner, of particular aspects of river ecology in order to detect trends of change or patterns of variation over tens or hundreds of years and, if possible, to relate these to recorded climatic changes.
3. Long-term data collection, in the scale of human longevity, is most appropriate to phenomena which show readily indentifiable periodic maxima or minima or which occur at well defined times (for example the discharge of a river or the start and finish of flow in a winterbourne). Alternatively, information which is amenable to automatic or semi-automatic monitoring (temperature, water chemistry, fish migration) or integrated sampling (insect abundance, annual removal of cut water weeds) may also provide valuable evidence of long-term change.     

The occurrence and significance of Cladocera (Crustacea) in some streams of Central Indiana,U.S.A.

Although Cladocera are collected often in large rivers, their importance in streams has been under-estimated. This paper summarizes the results of a preliminary study of the benthic Cladocera in the streams of three watersheds in South Central Indiana. Seventeen sites were sampled with respect to species of benthic Cladocera present, their relative abundance, population size, and population dynamics.Cladocera were present in all streams and sites in the three watersheds. Nineteen species were collected: 13 species from the family Chydoridae, 3 Daphniidae, 2 Macrothricidae, and 1 Bosminidae. Just four species — Alona circumfimbriata, Chydorus brevilabris, Pleuroxus denticulatus, and Macrothrix laticornis — made up 68–96% of the numbers at all sites.Density of Cladocera ranged from 3–5200 m^–2 and they reproduced and maintained populations in the streams sampled. Numbers were generally high in October and early November and decreased to near zero in late December and January. The most important factor appearing to affect population sizes was discharge. Numbers at almost all sites decreased significantly after a rainfall increased discharge.A Principal Components and clustering analysis grouped sites with similar physical parameters in a continuum of low to high order. Sites with low numbers of Cladocera were generally shallow, narrow, and had a loose unconsolidated substrate. Sites with high population numbers were generally deep, wide, and had a stable substrate that accumulated detritus.     

The chironomid larvae of a small chalk stream in Berkshire, England

Abstract. 1. The longitudinal distributions of larval Chironomidae (Diptera) were examined for 1 year in the intermittent and perennial sections of the Winterbourne, a small chalk stream in Berkshire, England.
2. Forty-nine chironomid taxa were recorded at ten major sites which were sampled on six occasions and four additional taxa were recorded at sites sampled only once.
3. Cluster analyses using data from the major sampling sites identified three groups of sites. A pond in the stream channel which had a distinct chironomid fauna was distinguished from all other sites before the remaining intermittent sites were separated from all perennial sites on the basis of the chironomid fauna.
4. In the perennial stream, a site heavily shaded by trees had low species richness compared with partially and unshaded sites further downstream. The lowest site, which was near to the confluence with a larger chalk stream, the River Lambourn, had the highest number of taxa (thirty-five), including several which were frequent in the Lambourn.
5. By recording the occurrence of prepupae, an indication of emergence periods was obtained and many taxa were shown to have extended periods of emergence.     

Faecal pellets in streams: their binding, breakdown and utilization

1. Faecal pellets of Gammarus (shredders) and Simulium larvae (suspension feeders) are bound by exopolymers. Immediately after egestion, Gammarus pellets are covered by a peritrophic membrane that breaks up within hours, although pellets remain intact because of internal binding materials. 2. Although they expand soon after egestion, the faecal pellets of Gammarus and Simulium remain intact for more than 30 days. Their internal structure is altered and the main agents of this change are bacteria that have survived passage through the gut (and become bound within pellets). 3. When disrupted physically, freshly egested (1‐ to 2‐day old) Simulium faecal pellets break up into relatively large pieces whereas freshly egested Gammarus faecal pellets break apart into much smaller pieces. Disruption of 30‐day old Simulium faecal pellets results in similar sized pieces to those from freshly egested pellets, but disruption of 30‐day old Gammarus pellets produces pieces that are two orders of magnitude larger than those resulting from disruption of freshly egested pellets. 4. Faecal pellets of Gammarus and Simulium are eaten by stream invertebrates and are sites of microbial breakdown. Faecal pellets are a source of organic matter for benthic invertebrates, bacteria and, indirectly, for plants.     

The temperatures of nine flowing waters in southern England

The authors analyse water temperatures in seven streams and two watercress beds in southern England, and examine some of the biological implications.     

A comparison of the relative contributions of temporal and spatial variation in the density of drifting invertebrates in a Dorset (U.K.) chalk stream

1. Invertebrate drift is commonly investigated in streams, with the majority of studies focussed on temporal (typically diel) variation. In comparison, few studies have investigated spatial variation in drift and there is little consensus among them. We tested the hypothesis that spatial variation in invertebrate drift is as important as temporal variation. 2. The density of drifting invertebrates in a chalk stream was sampled using an array of nets arranged to determine vertical, lateral and longitudinal variation. Samples were collected at dawn, during the day, at dusk and by night, on four separate monthly occasions. Insecta and Crustacea were analysed separately to identify the effect of differing life history strategies. The density of drifting debris was also recorded, to act as a null model. 3. Time of day and vertical position together explained the majority of the variance in invertebrate drift (79% for Insecta and 97% for Crustacea), with drift densities higher at dusk and night, and nearer the stream bed. Independently, time of day (38%, Insecta; 52%, Crustacea) and vertical position (41%, Insecta; 45%, Crustacea) explained a similar amount of the observed variance. Month explained some of the variance in insect drift (9%) but none for Crustacea. 4. Variation in the density of drifting debris showed little in common with invertebrate drift. There was little variation associated with time of day and only 27% of the observed variation in debris could be explained by the factors investigated here, with month explaining the largest proportion (20%). We suggest the difference in drifting debris and invertebrates provides further evidence for a strong behavioural component in invertebrate drift. 5. Spatial variation in invertebrate drift can be of the same order of magnitude as the much‐described diel temporal variation. The extent of this spatial variation poses problems when attempting to quantify invertebrate drift and we recommend that spatial replication should be incorporated into drift studies.     

Structure and grazing of stone surface organic layers in some acid streams of southern England

SUMMARY.

• 1 Stone surface organic layers were investigated at five sites on small, acid streams in the Ashdown Forest, southern England. Sites differed in stream water pH (means 4.3–6.6) and some other physicochemical features.
• 2 Organic layers at the stream bed surface differed between sites in structure and in the amount of organic carbon present. Algae were abundant at the sites with higher conductivity and pH, iron bacteria (mainly Leptothrix sp.) predominated in the iron-rich Broadstone stream, whereas the surface layer at the most acid site was predominantly a rather structure less organic film with few living organisms.
• 3 Amounts of organic carbon on stones buried within the stream bed for 3 months were almost identical at all sites. When viewed with the scanning electron microscope (SEM), organic layers on buried stones were rather structure less with some amorphous, floceulent material. The paucity of microflora suggests that these layers may have been formed primarily by abiotic mechanisms.
• 4 X-ray microanalysis of organic layers indicated that complexes of organic matter with the metals iron, aluminium and manganese were present.
• 5 Laboratory experiments with seven species of invertebrates showed that all were able to remove and at least partially ingest organic layers and underlying sandstone. The weight of material removed was highest on microbially impoverished layers from the most acid site, and was substantially lower where algae were abundant. 6. The role of stone surface organic layers in stream systems is discussed. They may be important sites of dissolved organic matter (DOM) uptake and transfer to the benthos. A major impact of acidity on running water could be through its effect on the structure and function of organic layers.

     

Distribution patterns of some subterranean Crustacea in the territory of the former Yugoslavia

A selection of the most representative distribution patterns of stygobiont animals is presented. The range of a genus may extend beyond the Dinaride karst, while some species exhibit a holo-Dinaric distribution. The mero-Dinaric distribution is organised in two vicarious centres (in the NW and SE) as well as an epilittoral and a paralittoral belt. The paralittoral distribution is a result of paleogeographic rather than present-day ecological conditions. Important differences between the interstitial faunas of Slovenia (and NE Italy) and Macedonia are probably the result of their different sources. Some other distribution patterns are discussed or summarized from the existing literature. The distribution patterns of this stygobiont fauna are extremely diverse, and are influenced by the geological complexity of the territory as well as by the richness of the fauna concerned. New distribution data for some Copepoda, Thermosbaenacea, and Amphipoda are appended.     

Protozoan communities in chalk streams

This study assessed the individual effects of three mayflies (Paraleptophlebia sp., Ephemerella subvaria McDunnough and Epeorus sp.) and one caddisfly (Psilotreta sp.) on periphyton communities associated with clay tiles and leaves. Algal densities were estimated for leaf discs and tiles from experimental chambers (with individual grazers) and control chambers (i.e., no grazers). Scanning electron micrographs (SEM) of leaf discs and tiles also were taken for all mayfly grazing experiments. Densities of algae on leaf discs were two to five times lower than on tiles. Mouthpart morphology influenced how different insects grazed the periphyton community. Paraleptophlebia had typical collector-gatherer mouthparts and had no effect on diatom densities associated with leaves whereas diatom densities on grazed tiles were higher than densities on tiles from control chambers. Epeorus had brusher mouthparts and had little impact on diatom densities regardless of substratum type. The other two grazers had the blade-like mandibles of a scraper. Psilotreta did not reduce the numerical abundance of diatoms on either substratum, but did alter community structure by significantly reducing densities of stalked Gomphonema olivaceum and large species of Navicula and Nitzschia; densities of smaller diatoms (Achnanthes spp) increased. However, E. subvaria reduced densities of most algal species regardless of size on both substrata and also significantly altered community structure. SEMs of substrata grazed by mayflies showed reductions in fungal hyphae on all grazed leaf discs, decreases in filamentous algal forms on grazed tiles, and greatly shortened stalks of G. olivaceum (Paraleptophlebia only). Thus, periphyton communities are different on leaves versus tiles and grazers with different mouthpart morphologies have varying effects on both algal and heterotrophic microbial community structure.     

Ecology of streams draining forested and non-forested catchments in an area of central Scotland subject to acid precipitation

A study of 12 streams draining forested and non-forested catchments was made in an area of central Scotland where slow-weathering bedrock was predominantly quartzite, schists and slates. Sitka spruce (Picea sitchensis Carriere) was the most common tree species. Precipitation in the area had an annual mean pH in the range 4.3–4.5. Streams within the planted zone were always more acid than those outside and had higher concentrations of aluminium and manganese. With one exception, trout were absent from streams within long-established forests and planted salmon eggs (Salmo salar L.) died within a few weeks. A high proportion of such eggs survived in streams outside the forest. Siphlonurus lacustris Eaton was the only mayfly nymph found in the most acid streams in summer collections. In winter samples, mayfly nymphs, Heptagenia lateralis (Curtis) were found in only one forest stream but several species were present in the non-forested catchments. It is suggested that spruce forests can effectively collect acid pollutants which are subsequently washed out, thus accelerating the acidification of the soil. Streams therefore become increasingly acid as the neutralisation capacities of their catchments decrease.     

Effect of flagella expression on adhesion of Achromobacter piechaudii to chalk surfaces

Aims: To examine flagella role and cell motility in adhesion of Achromobacter piechaudii to chalk. Methods and Results: Transmission electron microscopy revealed that stationary cells have thicker and longer flagella than logarithmic cells. SDS‐PAGE analysis showed that flagellin was more abundant in stationary cells than logarithmic ones. Sonication or inhibition of flagellin synthesis caused a 30% reduction in adhesion to chalk. Preincubation of chalk with flagella extracts reduced adhesion, by 50%. Three motility mutants were isolated. Mutants 94 and 153 were nonmotile, expressed normal levels of flagellin, have regular flagella and exhibited reduced adhesion. Mutant 208 expressed low levels of flagellin, no flagella and a spherical cell shape but with normal adhesion capacity. Conclusions: Multiple cell surface factors affect the adhesion efficiency to chalk. Flagella per se through physical interaction and through cell motility contribute to the adhesion process. The adhesion behaviour of mutant 208 suggests that cell shape can compensate for flagellar removal and motility. Significance and Impact of the Study: Physiological status affects bacterial cell surface properties and hence adhesion efficiency to chalk. This interaction is essential to sustain biodegradation activities and thus, remediation of contaminated chalk aquifers.     

Habitat use by the fish assemblages of two chalk streams

Patterns of habitat use by fish assemblages in two chalk streams in southern England were examined to identify species preferences with respect to major habitat gradients. Both study sites, although differing in some physical habitat characteristics, mainly channel width, water temperature and instream cover, could be arranged similarly along a continuum extending from erosional to depositional habitats. Twelve fish species were collected from stream surveys conducted during July 1993. The habitat was partitioned into six fish species associations that could be assigned to three habitat guilds: depositional ( Barbatula barbatula, Gasterosteus aculeatus and Anguilla anguilla ), riffle ( Leuciscus leuciscus, Thymallus thymallus and Salmo salar ) and generalist ( Salmo trutta, Phoxinus phoxinus, Gobio gobio, Cottus gobio, Lampetra planeri and Pleuronectes flesus ). At low to moderate densities the different species associations were collected in the same habitat patch, but at higher densities there was a clear tendency to mutual avoidance. In particular, large trout appeared as strong interactors that tended to exclude other species from their territories. It is hypothesized that the fish assemblage of the Mill Stream and Bere Stream have partitioned the habitat in such a way as to minimize potential Competition.     

The biology of Oligochaeta from Dorset chalk streams

Fewer species and more individuals of Tubificidae were present in the soft sediments of a polluted ditch than in the relatively unpolluted Bere Stream. Changes in width frequency of natural populations of Tubifex tubifex and Limno-drilus hoffmeisteri throughout the year were similar at both the sites investigated. In laboratory experiments larger populations of Tubifex tubifex developed in fine sediments than coarse. By means of a width-dry-weight relationship it was possible to estimate the weight of the experimental populations.     

Primary production and potential availability of autochthonous carbon in southern Ontario streams

Primary production was measured in forested and open streams in southern Ontario to identify the main factors influencing algal growth, and to test the assumption that autochthonous inputs are negligible in forested headwater streams. In low order streams in southern Ontario, primary production is related primarily to light, temperature, and substrate, and appears to be largely independent of location on the river continuum. Net primary production on rock averaged 2.24 and 0.098 g Cm^–2 day^–1 during the summer at meadow and forested sites, respectively, showing peaks in the spring and fall at the forested sites. Net primary production on sediment was significant, averaging 20% (range of 6 to 82%) of net primary production on rock. When adjusted for assumed invertebrate assimilation efficiency, autochthonous production in riffles at forested sites could provide an estimated 30% of total carbon inputs potentially available to aquatic invertebrates.     

An index of biotic integrity based on fish assemblages for subtropical streams in southern Brazil

Several methods for calculating indices of biological integrity (IBIs) have been developed for different ecogeographic regions of the world. All of them calculate IBI scores by comparing against reference sites or historical data on fish assemblage composition. Because of intensive agriculture and urbanization in our study area, we located no reference sites, and historical information about fish assemblage composition did not exist. Instead, we developed hypothetical reference scores based on seasonal electrofishing surveys at six study sites in adjacent but geomorphologically different watersheds. Our IBI included 10 metrics that varied with degree of degradation. We found that Shannon–Wiener indices varied significantly between seasons, indicating significant changes in species composition. Therefore, we calculated seasonal IBI scores also, but these did not significantly differ from each streams general IBI score, which was calculated on the basis of four samples per site. General stream IBI scores reflected differing levels of anthropogenic disturbance.     

The water mites (Acari: Hydrachnidia) of streams in The Netherlands: Distribution and ecological aspects on a regional scale

The water mites of running waters in The Netherlands have been surveyed for the period 1987–1992. The aims were to investigate their present distribution, to make a comparison with historical data and to identify differences in water mite assemblages on a regional scale. The investigation covered 821 sites in eight different drainage areas. In spite of the scarcity of historical data, it may be concluded that in the course of this century about 40% of rheophilic water mites have become extinct. In canalized streams lentic species are dominant. In springs and spring streams, lotic species can survive, but the assemblages consist mainly of euryoecious water mite species.Multivariate techniques were used to show regional differences. These differences are mainly determined by stream hydraulics. The area of Zuid-Limburg can easily be demarcated by its relatively high number of rheophilic species. The man-made streams (sprengen) at the east side of the Veluwe area are characterized by a number of species which indicate undisturbed circumstances. The response of water mites to pollution of running waters is discussed.