bluuebunny/crossref_metadata_2025 huggingface dataset:
The feeding relationships of two invertebrate predators in a New Zealand river
Authors: DEVONPORT B. F. , WINTERBOURN M. J.
Published: May 2006

The size frequency distributions and foods of the larvae of Archichauliodes diversus (Megaloptera: Corydalidae) and Stenoperla prasina (Plecoptera: Eustheniidae) were studied for a year in the Glentui River, South Island, New Zealand. These two species are the largest invertebrate predators inhabiting streams and rivers in New Zealand, where they are the only carnivorous members of their respective orders. Both species occupied the same habitat with A. diversus being slightly more abundant in most months. Many small larvae occurred within the sediments of the stream bed, whereas more larger larvae were found on stones lying on the surface. A wide size range of larvae was present throughout the year and the median size (in terms of head width) of both species was similar in most months. Larval growth could not be determined from field data and the life cycles of both species can be described as non‐seasonal. Quantitative sampling in 5 months provided estimates of population densities. These were maximal in December when values of 136/m2 for A. diversus and 114/m2 for S. prasina were obtained.

Larval Chironomidae and mayflies of the genus Deleatidium were the most frequently taken prey of both predators in all months, and no strong relationship between size or species of predator and size of prey was found. Caseless trichopteran larvae formed a less important component of the diets of both species and detritus was ingested by some individuals. No instances of cannibalism and only one example of cross‐predation by each predator was seen. Diel sampling in November showed that large Deleatidium larvae were relatively more abundant in the guts of insect predators and in nocturnal drift samples than in the benthos. This suggests that their greater activity at night may increase their susceptibility to predation by nocturnal feeders.

No clear ecological segregation of the two species with respect to habitat or prey utilization was found and there was no obvious interspecific competition for food, which appeared to be abundant at all times. Finally, the prevalence of non‐seasonal life cycles in New Zealand aquatic insects is discussed in relation to the low degree of speciation in several groups.
Assemblages ofPisidiumspecies (Bivalvia, Sphaeriidae) from localities in eastern England
Authors: BISHOP M. J. , HEWITT S. J.
Published: May 2006

Collections of Pisidium spp, were made from a large number of sites and a diversity of habitats, The concurrence of the different species was examined, An ordination of the assemblages showed no marked clusters, but could be related to habitat.
Studies on Plover Cove Reservoir, Hong Kong
Authors: HODGKISS I. J. , TAI Y. C.
Published: May 2006

The species composition and year‐month frequency together with the abundance of the four periphytic communities of Plover Cove Reservoir (the epiphyton, epilithon, epipelon and epipsammon) were compared both in terms of all species present and in terms of major (dominant/frequent) species using the ‘circle’ method. All four communities were similar in terms of overall species composition but the richest variety of species occurred in the epiphyton. The diatom floras on wood and rock surfaces closely resembled each other as did the two sand grain floras. The former floras were, however, much more diversified than the latter floras and stood distinctly apart from them. In terms of their dominant/frequent species, the epipelic/epipsammic communities and the epiphytic/epilithic communities had the same number of common taxa (three), a further indication of the closeness between the two communities in each combination. On the other hand, the fact that the three common taxa were different for each combination again reveals the distinct differences between the two combinations.

Investigations concerning the effect of the nature of the substrate on diatom growth revealed that it had little effect in qualitative terms. Quantitatively there would appear to be some effect, since differences in abundance and frequency and thus in the seasonal cycle of diatoms growing on different substrates were observed. The conditions in the microhabitats of each substrate undoubtedly determined the dominance and abundance of the flora. However, the effect of the nature of the various substrates on diatom growth varied from species to species and in general, the substrates showed little qualitative selectivity. Thus, no truly differential species were found to any great extent on any of the four substrates.

The relationships between the growth of these four periphytic diatom communities and the physical and chemical conditions have also been investigated in terms of cell number and chlorophyll content. Both graphical and statistical analyses of the results are discussed, and it is suggested that fluctuations in water level, temperature and nutrients (especially silica, nitrate and phosphate) are the major factors governing the seasonal patterns of variation in periphyton standing crop. Thus, diatom growth is maximum when nutrient concentrations and water level are high and when water temperature is low, and as temperature increases and nutrients decrease so diatom growth falls. It is probable that an interplay of these factors, together with the detrimental effects of heavy rainfall and typhoons during summer, is responsible for the seasonal changes in periphyton in Plover Cove Reservoir exhibiting a winter peak as opposed to the commonly occurring spring and autumn growth peaks.
Studies on Plover Cove Reservoir, Hong Kong
Authors: HODGKISS I. J. , CHAN L. T. H.
Published: May 2006

The zooplankton fauna of the Plover Cove Reservoir has been investigated using two sampling series. The first series involving a 3‐year investigation using 6‐ft vertical hauls at three stations in the reservoir, revealed the presence of two copepod and four cladoceran species with little variation in terms of seasonal peak occurrence and abundance in any of the stations and so no evidence of the horizontal distribution patterns referred to by other authors. In all three stations Diaptomus gracilis was the dominant copepod species and Diaphanosoma leuchtenbergianum the dominant cladoceran species.

The second series, involving a 13‐month investigation of vertical sets of water samples collected both day and night at 4‐h intervals for 24‐h periods, revealed that in terms of seasonal vertical distribution, all six species occurred at all depths during the survey, but with a tendency to be concentrated in the surface waters.

In terms of diurnal vertical distribution, differences in the migration pattern occurred from season to season in the case of Diaptomus gracilis. Thus, during spring, summer and autumn, concentrations occurred at the surface at 10.00 and 22.00 hours followed by migration to greater depth, whereas in winter, surface accumulations persisted even into the daylight hours. However, both Cyclops hyalinus and Diaphanosoma leuchtenbergianum showed surface accumulations at night and a movement away from the surface by day during all seasons.

Investigations of the seasonal variation in environmental parameters conducted during both sampling series revealed that, as in the case of similar surveys, water temperature was the major controlling factor governing the seasonal variation in composition of the zooplankton fauna as well as its seasonal vertical distribution since in the case of Diaptomus gracilis and Ceriodaphnia reticulata low water temperatures corresponded with peak seasonal occurrence whereas in the case of the other species high water temperatures corresponded with peak seasonal occurrence, and since Diaptomus gracilis and Diaphanosoma leuchtenbergianum showed maximum concentration near the surface when surface water temperatures were high, whereas the remaining species showed their maximum concentration near the surface when lower water temperatures prevailed.

It would also appear, however, that seasonal changes in zooplankton densities closely followed algal densities since Diaptomus gracilis, Diaphanosoma leuchtenbergianum and Bosmina longirostris had their maxima in late spring and Cyclops hyalinus in late summer while algal densities in this reservoir were highest in early spring and early summer.

With regard to the diurnal vertical distribution of the zooplankton, light appeared to be the only factor alternating by an amount likely to be correlated with such diurnal vertical changes in zooplankton density.
Respiratory behaviour of larvae of four species of the Family Polycentropodidae (Trichoptera)
Authors: PHILIPSON G. N. , MOORHOUSE B. H. S.
Published: May 2006

Larvae of Plectrocnemia conspersa and Polycentropus flavomaculatus from flowing water and Cyrnus flavidus and Holocentropus picicornis from still water were selected for study.

In the above sequence, these larvae are associated with increasing ranges of temperature in their natural habitats. Experimental determination of lethal temperatures and investigations on ventilation frequency indicated that the larvae were increasingly tolerant of temperature in the same sequence of species.

C. flavidus and H. picicornis showed infrequent ventilation which was little affected over wide ranges of temperature and dissolved oxygen but was stimulated erratically by water flow. P. conspersa and P. flavomaculatus showed more active ventilation which was more sensitive to changes in temperature and dissolved oxygen and was decreased by water flow.

Consideration of ventilation in relation to oxygen uptake in P. conspersa and P. flavomaculatus suggests that ventilation activity may account for some 60–70% of active oxygen uptake. Differences in ventilation behaviour may thus be important in limiting larval distribution in stream systems.
Dominant diatoms in Tjeukemeer (The Netherlands)
Authors: MOED J. R. , HOOGVELD H. L. , APELDOORN W.
Published: May 2006

A situation is described where silicon depletion affected a population of diatoms, mainly Diatoma elongatum and Melosira spp., in the shallow lake Tjeukemeer (The Netherlands). After Si‐deficiency the numbers of cells dropped quickly, whereas at least for the upper layer (0–1 m) a big increase in the percentage of biprotoplastic D. elongatum cells was observed. Probably the major part of the D. elongatum population arrived alive at the bottom. Heavy winds occurring 2 weeks later stirred up considerable numbers of both diatoms. The numbers of dead D. elongatum cells was then 40–50%, presenting some evidence that a large scale dying of D. elongatum cells occurs rather shortly after arrival at the bottom of Tjeukemeer. In the following weeks, at low Si‐concentration, numbers of D. elongatum almost doubled with once again a relatively high percentage of biprotoplastic cells, whereas numbers of Melosira spp. decreased. In the relevant conditions it seems that D. elongatum can take up silicon faster than Melosira spp.
Changes in the zooplankton of Lakes Mutanda, Bunyonyi and Mulehe (Uganda)
Authors: GREEN J.
Published: May 2006

Samples taken from Lake Mutanda in 1975 indicate that the specific composition of the zooplankton has changed from that in 1962. This change is very similar to that which occurred in Lake Bunyonyi sometime between 1931 and 1962. The most important aspect of the change is the disappearance of three species of Daphnia, together with Ceriodaphnia reticulata, Metadiaptomus aethiopicus, and Caridina nilotica. The 1975 samples indicate lower standing crops of zooplankton in all three lakes, and lower ratios of nauplii to copepodids than in 1962. The possibility of these changes being attributable to human activities is discussed.
Sediment development and its influence on the distribution and tube structure of Chironomus plumosus L. (Chironomidae, Diptera) in a new impoundment
Authors: McLACHLAN A. J. , CANTRELL M. A.
Published: May 2006

Field and laboratory evidence is presented to demonstrate that colonization of a new impoundment by the early invader, Chronomus plumosus L., is strongly influenced by sediment, the depth of which affects both larval abundance and tube shape. Larvae avoid areas with little sediment, such as eroded or newly inundated shores. In laboratory experiments, larvae constructed horizontal tubes in sediments between 3 and 10 mm depth, but in deeper sediments (11–30 mm) most of the larval tubes were vertically orientated. Of these about 70% were U‐shaped and the remainder J‐shaped. Larval abundance was positively correlated with sediment depth in the range 0–10 mm.
Decomposition of aquatic biota and sediment formation: lipid components of two blue‐green algal species and of detritus resulting from microbial attack
Authors: CRANWELL P. A.
Published: May 2006

To simulate early stages in the diagenesis of algal material in lakes, microbial attack was allowed to proceed on natural populations of two blue‐green algal species, Gloeotrichia echinulata (J. E. Smith) P. Richter and Oscillatoria agardhii var. isothrix Skuja. Changes in composition and abundance of the major lipid fractions were related to differences in the ease of microbial attack and to the effect of oxygen on the decay process. The loss of labile unsaturated compounds during diagenesis is consistent with the small amount of these compounds in most lake sediments.
Types of parasitism by larvae of water mites (Acari: Hydrachnellae)
Authors: BÖTTGER KLAUS
Published: May 2006

The larvae of Hydrachnellae can be divided into three types, based on the habits of the parasitic (larval) stage in the life cycle. (1) The larvae do not leave the water. Parasitizing aquatic insects, they are permanently submerged and wet. Only some species of the family Hydrachnidae belong to this type. (2) The larvae leave the water. The parasitic phase occurs either on insects living on the water surface, or in the air stores of aquatic insects. In both cases the larvae are not in direct contact with water during the parasitic phase. The Limnocharidae, Eylaidae and some species of the Hydrachnidae belong to this type. (3) The larvae parasitize insects which live in the air and which can leave the direct proximity to water; therefore it may be difficult for the mite larva to return to water. Except for the Hydrachnidae, Limnocharidae and Eylaidae, all families of the Hydrachnellae belong to this type.
Experiments on feeding and growth of the amphipod Gammarus pulex (L.) related to its distribution in the River Duddon
Authors: WILLOUGHBY L. G. , SUTCLIFFE D. W.
Published: May 2006

Individuals of Gammarus pulex were kept at 15°C for periods of 23–70 days on diets comprised of elm or oak leaves, Tricladium and Clavariopsis (Hyphomycete fungi), Molinia (grass), Zygogonium (alga), Nardia (liverwort). Both the mean interval between moults (mi), and daily increments in body wet weight, were related to diet. The lowest value for mi was 14·6 days on a diet of naturally decaying elm and oak leaves. The largest weight gains also occurred on this diet; the average daily gain in weight (Dw) = 130·8 μg/day, the mean specific gain in weight (Gw) = 1·69 μg %/day. On green Molinia and fungi diets Dw ranged from nil to 60·7 μg/day, and mi= 17·4–18·4 days was significantly (P<0·01) longer than mi on leaf diets. Survival and growth were poor on brown Molinia. Nardia did not support growth or survival. A mixed diet of Tricladium, Zygogonium, Nardia and decaying grasses was not sufficient to promote an increase in body weight, and mi= 21·8 days. This diet represents the commonly available food materials in Mosedale Beck, an acid stream in the upper Duddon catchment. Survival and growth of G. pulex on fungi and leaf diets in media containing low concentrations of potassium ions are also described and discussed briefly in relation to the distribution of G. pulex in the upper catchment of the R. Duddon.
Seasonal and diel periodicity in the drift of aquatic insects in a subtropical Florida stream
Authors: COWELL BRUCE C. , CAREW WARREN C.
Published: May 2006

A study of insect drift was conducted in a small, subtropical Florida stream from December 1971 to December 1972 to describe the seasonal and diel periodicity and to determine factors influencing behavioural drift. Paired samples of 2 h duration beginning 15 min after sunset were taken biweekly, and hourly collections over a 24‐h period were made quarterly. Benthic invertebrates were collected on each date from three habitats (riffle, pool and aquatic vegetation) and temperature, dissolved oxygen and current velocity were measured.

Drift rates ranged from 100 to 2125 organisms/m2. h (0·03 to 0·49 organisms/m3) and were greatest in winter and early spring; minimal rates occurred in the summer months. The following six taxa, in order of relative abundance, comprised 87% of the drift: Baetis intercalaris, Cheumatopsyche sp., Stenonema exiguum, Chironomidae, Stenelmis fuscata and Simulium sp. Total drift showed no significant correlation with temperature, dissolved oxygen or mean benthic abundance and only slight correlation with current velocity (r=0·34). Stepwise, multiple regression analyses indicated that riffle density and mean size of drifting organisms were important factors influencing the drift rates of B. intercalaris (R=0·67) and S. exiguum (R=0·82); mean size, riffle density and water temperature influenced the drift of Cheumatopsyche sp. (R=0·78). The other taxa of drifting insects showed no significant correlation with the variables measured.

Diel (24 h) studies of the major taxa showed marked differences in the periodicity, both within and between taxa, indicating the need for long‐term studies with frequent sample intervals in subtropical habitats. A new drift pattern for the family Chironomidae, alternans type, was observed for late instars of Polypedilum halterale.
Chironomid pupal exuviae in the River Chew
Authors: WILSON R. S.
Published: May 2006

SUMMARY. Weekly skim‐net samples of chironomid pupal exuviae were collected at a single station on the River Chew, Avon, England, from September 1972 to September 1973. Eighty‐six types of exuviae were characterized in this study, of which sixty‐four made up only 4% of the year's catch. Thirty ‐eight percent of the year's catch was referable to Micropsectra atrofasciata Kieffer.

The samples showed the expected maxima of numbers and species in spring and early summer. The emergence periods for many of the more common species were very extended, with one or more peaks.
The effect of the impoundment of Lake Kainji, Nigeria, on the indigenous species of mormyrid fishes
Authors: BLAKE B. F.
Published: May 2006

SUMMARY. Changes in the numbers and species composition of mormyrid fishes since the impoundment of the Niger (Lake Kainji) are analysed. An initial decline after impoundment appears to have been reversed and these fish are now increasing. The increase is, however, restricted to a few species only; many forms common in the river are still declining or have disappeared altogether. Marked seasonal variations in abundance are described and possible explanations discussed.
The effect of environmental factors on estimated viable and total populations of planktonic bacteria in lakes and experimental enclosures
Authors: JONES J. G.
Published: May 2006

SUMMARY. The difference between the results of viable and total counting procedures for bacteria are exemplified by vertical profiles from a deep and a shallow lake and from seasonal changes in the epilimnion and hypolimnion of a shallow eutrophic lake. The viable count was, on average, 0.25% of the total count, the greatest difference being noted in the anoxic hypolimnion, probably due to the inadequacy of the viable counting procedure for the isolation of bacteria from such samples. There was a general trend for the more nutrient‐rich waters to support larger bacterial populations but such observations did not provide any further information on the factors responsible for the population changes observed. Seasonal fluctuations in the counts are studied and the qualitative and quantitative changes resulting from artificial enclosure of water are discussed. Not all the temporal changes could be explained and short‐term changes resulting from nutrient additions to the experimental enclosures were not always reproducible. Horizontal variability was examined, found to be significant and could play an important role where water movement and turbulence is considerable. Results from six sites sampled between 1969 and 1974, representing total and viable bacterial population estimates and a total of eighteen independent or regressor variables were then subjected to principal components analysis. Results taken from the whole water column showed the overwhelming effect of the process of stratification on the bacterial population accounting for 30%‐60% of its variability. Secondary components representing algal productivity could account for 10% to 20% of the variability. Many of the chosen regressor variables were acting as measures of the same phenomenon without providing significant information on what affected the bacterial population. To overcome this problem results from the hypolimnion and epilimnion were analysed separately. The analysis demonstrated the importance of seasonal changes in nutrient concentrations in the epilimnion and the development of anoxic conditions in the hypolimnion. Algal biomass, phosphate concentration and the interaction of pH and ammonia appeared to be important. It was concluded that most of the variability in the bacterial population estimates could have been explained by five of the regressor variables and that the factors most likely to provide more information would include some measure of predation and lake retention time.
Short‐term effects of highway construction on the limnology of a small stream in southern Ontario*
Authors: BARTON BRUCE A.
Published: May 2006

SUMMARY. A limnological investigation was carried out to document the effects of constructing a modern highway across a small stream in southern Ontario. During construction, suspended solids increased to as high as 1390 mg/l but later returned to pre‐construction levels of <5 mg/l. Similarly, sediment deposition increased ten‐fold to 0. 61 g dry wt/cm2. day directly below the construction site during stream rechannelization after completion of the culvert. Decreased proportion of organic matter in sediments indicated that they came from the construction site. Sediments were readily removed by spates and apparently settled out in downstream ponds. There was no change in water chemistry. Standing crop of fish was reduced from 24 to 10 kg/ha immediately below the site. This decrease did not occur further downstream and fish populations at the affected site returned to original levels after construction. No change in numbers of riffle macroinvertebrates was observed during or after construction. However, there was a noticeable shift in species composition. Invertebrates present during construction activities may have remained in sheltered areas avoiding sedimentation effects. Evidence from invertebrate sampling in denuded areas around the site strongly suggests that organisms which may have been removed during construction were replaced quickly by drift.
The fecundity of dace, Leuciscus leuciscus (L.) in Emral Brook, Clwyd, North Wales
Authors: WILKINSON DUNCAN R. , JONES J. W.
Published: May 2006

SUMMARY. Estimates of the fecundity of dace were made on 105 mature females using the dry method of Simpson (1959). The reliability of the counting procedure was assessed and found to be satisfactory. Fecundity was examined in relation to fork length (cm), somatic weight (g), ovary weight (g) and age (years). Logarithmic multiple regressions of fecundity on these variables showed that neither log fork length nor log somatic weight contributed significantly towards explaining the observed variations in fecundity. The best prediction equation for fecundity, incorporated both log ovary weight and log age. Incidents of extensive follicular atresia were found in the ovaries of 19% of the female dace examined and the frequency of occurrence of this phenomenon increased with age.
Habitat and substrate influences on population and production dynamics of a stream caddisfly, Ceraclea ancylus (Leptoceridae)
Authors: RESH VINCENT H.
Published: May 2006

SUMMARY. Population and production dynamics of Ceraclea ancylus (Vorhies), a leptocerid caddisfly with a univoltine life cycle, five larval instars, and a single cohort population, were examined in Brashears Creek, Kentucky. A systematic sampling approach that included analysis in riffle, pool, and waterwillow bed habitats was used and fourteen sampling transects were taken across Brashears Creek between May 1971 and July 1972. For each of the 70 m2 samples taken along a transect, the depth, habitat, and substrate type were recorded. The number of C. ancylus cases and numbers and dry weights of each larval instar were determined.

The majority of the C. ancylus population was in the second larval instar in July, the third larval instar in August, the fourth larval instar in September, and the fifth larval instar from October through May. The spring population was 30% of the early instar maximum estimated the previous August. The spatial distribution of C. ancylus reflects a logarithmic pattern with early instar larvae more highly clumped than the late larval instar and pupal populations. Initial standing stock estimates were less than 1% of the standing stock biomass. A production estimate of 9.9 mg/m2·year (dry weight) was determined using the instantaneous growth method, Allen's Curve method, and the Hynes method of estimating secondary production. Turnover ratios (7.0 annual TR, 5.7 cohort TR) were higher than estimates reported as typical for benthic macroinvertebrates because of the low initial to final mean individual weight of the C. ancylus larvae (0.4%).

Production estimates calculated for C. ancylus populations in waterwillow bed (4.4 mg/m2·year) and pool (13.7 mg/m2·year) habitats were less than calculated for the riffle population (19.9 mg/m2·year). The annual turnover ratio (10.2) was higher in the pool population than in other habitats because of spring larval migration into the pool from other habitats. A trend of higher production estimates with larger sized substrate particles and increased numbers of particles may reflect the increase in available food sources or attachment sites. The accuracy of production estimates and their applicability to water resource management may be limited by a failure to consider the spatial distributions of the population being sampled and the tendency for sampling procedures to be confined to single habitats.
Feeding selectivity of a tropical Chaoborus population
Authors: LEWIS WILLIAM M.
Published: May 2006

SUMMARY. The Chaoborus population of Lake Lanao, Philippines, was sampled weekly over a 65‐week period. Specimens representing all four instars, all times of the year, and two points in the daily migration cycle were dissected for determination of gut contents.

Major items in the diet of Lanao Chaoborus include Bosmina, Diaphanosoma, and the copepodid and adult stages of cyclopoid and calanoid copepods. Items that are available but seldom eaten include nauplii and rotifiers except Keratella. Feeding rate averages 2.5% of body weight per day in instars 3–4.

Predator size affects but does not fully explain prey selection. Electivity values are much higher for Bosmina and Diaphanosoma than for copepods, even though these food items overlap in size. Bosmina, which has the highest electivity value of any prey, is virtually identical in size to the calanoid nauplius, which has one of the lowest electivity values. This and other similar data suggest that prey of the same size differ greatly in palatability or vulnerability.

There is a marked variation in feeding rate and food composition from day to night. The smallest Chaoborus feed more during the day than at night, but the opposite is true for Chaoborus of moderate to large size. Large Chaoborus switch from a daytime emphasis on copepod copepodids and adults to a nighttime emphasis on Cladocera.

Diurnal variation between instars in food composition cannot be explained simply on the basis of the vertical distributions of predators and prey. An interaction of vertical distribution with prey density and predator selectivity does explain the overall Chaoborus feeding pattern, however. During the day, larger Chaoborus move deep into the water column where food is scarce. Their daytime feeding rate is lower due to low prey density at great depths. Low prey density is partially compensated by relaxation of preference. At night, upward migration of large Chaoborus into an area of high prey density permits a resumption of marked selectivity and high feeding rates. Small Chaoborus do not descend deep into the water column during the day, as their lower hunting efficiency apparently requires higher food density and use of visual cues to sustain adequate feeding rates. Prey density thus affects both the vertical distribution and feeding selectivity of the Chaoborus population.
Influence of zinc on lotic plants
Authors: SAY P. J. , DIAZ B. M. , WHITTON B. A.
Published: May 2006

SUMMARY. Field and laboratory studies have been carried out on the tolerance to zinc of the filamentous green algae Hormidium rivulare Kütz., H. flaccidum Kütz. and H. fluitans (Gay) Heering growing in flowing waters. Forty‐seven different sites in England, France, Germany and Ireland were included, the majority of them chosen to represent examples of zinc pollution resulting from past or present mining activities. All three species were widespread both in waters free of zinc pollution and waters with zinc pollution, and H. rivulare and H. flaccidum were frequent at a site with the highest zinc level included in the survey (mean of 22.8 mg l−1, maximum of 30.2 mg l−1 Zn passing through a filter). At sites with higher zinc levels, populations showed increased resistance to zinc of the filamentous green algae Hormidium rivulare Kütz., H. flaccidum creased resistance being largely, if not entirely, the result of genetic adaptation. An increased frequency of geniculations can occur both as an environmental and a genetic response to very high zinc levels. The application of various statistical analyses to the data suggests that two groups of chemical factors may be influencing the toxicity of zinc in the field. The first group which appears to increase the toxicity of zinc includes cadmium and lead, while the second group, which decreases the toxicity of zinc, includes magnesium, calcium and various hardness factors. As the occurrence of zinc, cadmium and lead in the field are all strongly intercorrelated, it is not possible to distinguish clearly the effects of one from the other, although the data do suggest that cadmium is more likely than lead to influence zinc toxicity. The ‘amelioration’ factors are also strongly intercorrelated in the field, so it is difficult to comment on their relative importance. There is some indication for H. rivulare at least, that an increase in PO4‐P and a decrease in pH may also reduce zinc toxicity.
The recent history of the chironomid fauna of Lough Neagh, from the analysis of remains in sediment cores
Authors: CARTER C. E.
Published: May 2006

SUMMARY. Analysis of sub‐fossil chironomid remains in the top of Lough Neagh sediments shows a change from a mainly Tanytarsus fauna to a mainly Chironomus one. This has been accompanied by an exponential increase in numbers of head capsules deposited per m2 per year. Tentative dating places this change within the last 130 years, with the most rapid increase in numbers post‐1945
Development of the macro‐invertebrate fauna of Cow Green reservoir (Upper Teesdale) in the first five years of its existence
Authors: ARMITAGE PATRICK D.
Published: May 2006

SUMMARY. The development of marginal (shore‐line), sub‐littoral (3–6 m) and profundal (15–18 m) fauna was followed using timed collections in shallow water and artificial substrata in deeper regions.

The reservoir started filling in July 1970 and was close to top water level in the autumn of that year. Samples in the marginal zone contained drowned terrestrial organisms and some Cladocera (Chydoridae) in February 1971 but by October, Chironomidae and Oligochaeta became abundant and micro‐crustaceans (copepods and cladocerans) formed about 98% of the total catch. Peak densities of micro‐crustaceans in the marginal zone were reached in the summer of 1971, but chironomids and oligochaetes were most abundant in the second year after filling. The numbers of marginal zone animals were greatest at the most sheltered site, and lowest at a site on the windward shore. At a stream mouth the rheophilic fauna present in April 1971 was replaced with limnophilic organisms (Chironomidae and Tubificidae) by September 1971.

In the sub‐littoral, Hydra, Enchytraeidae, Orthocladiinae Tanytarsini and oribatoid mites were the most abundant taxa, whereas Naididae, Hirudinea, Ostracoda, Gammarus pulex, Chironomini and Pisidium spp. were numerous in the profundal zone.

Total faunal numbers and biomass were greatest in the profundal zone in all years. The highest annual mean estimate of biomass in the sub‐littoral was 3.07 g (wet wt)m−2 in the second year after filling, thereafter both numbers and biomass fell. In the profundal the maximum biomass (about 29 gm−2) was observed in the third and fourth years after filling. An estimate of total standing crop of benthic organisms below the drawdown limit, made in July 1974, gave a figure of about 43 tonnes, wet weight.

Biomass estimates at Cow Green were compared with those in eighteen other reservoirs and were found to be high especially in relation to those from other upland areas.
Growth rates of the stonefly, Amphinemura sulcicollis Stephens, in the upper River Wear
Authors: SVENSSON E.
Published: May 2006

SUMMARY. Growth rates of Amphinemura sulcicollis were investigated at five main stations in the upper River Wear, Northern England. Retardation of growth was noted during November, December and January and comparison was made of the degree of such retardation at high and low stations.
An analysis of seasonal dynamics of a mixed population of Daphnia, and the associated cladoceran community
Authors: ALLAN J. DAVID
Published: May 2006

SUMMARY. The dynamics of a mixed population of Daphnia(D. ambigua and D. parvula) are analysed over 9 months in a small eutrophic lake. A spring peak of D. ambigua occurred shortly after ice break‐up. Decline of D. ambigua coincided with a high occurrence of sexual reproduction, the appearance of D. parvula which did not become abundant, and a substantial increase in Ceriodaphnia quadrangula. A third cladoceran, Bosmina longirostris, was abundant before and after the period of numerical dominance by D. ambigua, but declined to very low numbers coincident with the increase in D. ambigua.

Estimates of egg hatching rate at various temperatures demonstrate that these three cladocerans have different rate responses to temperature, and that seasonal succession of species is predictable from temperature alone. The importance of temperature versus species interactions in controlling species succession is discussed.
The phased division of the freshwater dinoflagellate Ceratium hirundinella and its use as a method of assessing growth in natural populations
Authors: HELLER M. D.
Published: May 2006

SUMMARY. The nocturnal phasing and partial synchrony of cell division in Ceratium hirundinella was investigated on four occasions for dense planktonic populations in a small productive lake (Esthwaite Water). The population growth rates deduced from the proportion of cells dividing per day are compared with the rates of increase of cell density in the lake. The maximum proportion of Ceratium cells found dividing at any time was 5.8 ± 1.0%, and the time of optimum division was 03.00 hours G.M.T. The daily rate of division during the main phase of population increases was similar to that deduced from the overall population increments at that time, although during the week of collection the increase had apparently ceased temporarily. On the other three occasions, either increase of cell numbers had ceased or the population was declining, but a continued low rate of division (c. 3% day−1) was found.

The nocturnal division of Ceratium in Esthwaite Water is compared with the division phasing of dinaflagellates described from elsewhere. Some general problems associated with the derivation of estimates of population growth rate from division frequency are also considered.
The effect of current velocity and sediment on the drift of the mayfly Ephemerella subvaria Mcdunnough
Authors: CIBOROWSKI JAN J. H. , POINTING P. J. , CORKUM LYNDA D.
Published: May 2006

SUMMARY. Experiments conducted in an artificial stream showed that significantly more nymphs drifted from an inorganic substrate at a mean current velocity of 28.5 cm s−1 than at 18.5 cm s−1. Drift density, however, was not affected. Disproportionately large numbers of nymphs drifted while current velocities were being increased from 18.5 to 28.5 cm s−1.

Both drift numbers and drift density were greater in turbid water, after the addition of large amounts of inorganic sediment, than under clear‐flowing conditions during dark periods but not in the light. The interaction of increasing current velocity and sediment levels resulted in a significantly greater number of drifting nymphs under lighted conditions.

Minor spates which do not seriously disturb the stream bed may initiate significant increases in macroinvertebrate drift.
Primary production studies in two linked but contrasting Welsh lakes
Authors: PENTECOST ALLAN , HAPPEY‐WOOD CHRISTINE M.
Published: May 2006

SUMMARY.
Llyn Padarn and Llyn Peris have distinct phytoplankton populations. During 1975–76, the standing crop measured as chlorophyll‐a was 5.5 times greater in Padarn than in Peris and the production rate, determined by the 14CO2 method, was faster by 3.4 times. These differences were attributed to the higher concentrations of phosphorus in the lower lake caused by treated sewage effluent. Incident light intensity, which was slightly lower in Peris due to mountain shading, and temperature, which was 1–4°C higher in Padarn, made little significant contribution to these differences during the summer. The reduced transparency of Padarn water, compared with that of Peris, resulted from denser phytopiankton crops in Padarn. During the summer, Padarn exhibited carbon dioxide depletion which correlated with the chlorophyll concentration. Light inhibition at the surfaces of both lakes correlated with solar radiation intensity. However, the relationship between pigment content and maximum photosynthetic rate was poor. Extracellular products accounted for about 16% of the total production in the lakes. Uptake of 14C‐labelled acetate was low compared with that of 14CO2 uptake.
Comparative limnology of a deep‐discharge reservoir and a surface‐discharge lake on the Madison River, Montana
Authors: MARTIN DAN B. , ARNESON RONALD D.
Published: May 2006

SUMMARY.
Phytoplankton standing crop, primary production, light penetration, temperature, and various chemical concentrations were measured in a man‐made, deep‐discharge, reservoir and in a natural, surface‐discharge, lake in order to relate limnological conditions in the two bodies of water to their depth of outflow. The quantity and depth distribution of heat stored during the summer varied markedly. The reservoir functioned as a heat trap, whereas heat was readily dissipated from the lake. Salinity increased more in the lower layer of the lake. Throughout the summer, nutrient‐rich water was discharged from the reservoir whereas nutrient‐poor water was discharged from the lake. Phytoplankton standing crops were greater in the lake and were dominated by flagellates and diatoms. In the reservoir, blue‐green algae were predominant. Rates of primary production and respiration were higher in the lake, but estimated algal turnover times were faster in the reservoir. It was concluded that depth of outflow has a direct and predictable effect on certain physical and chemical conditions within these two bodies of water; but effects of discharge depth on phytoplankton were secondary and thus difficult to ascertain.
A study of the food and feeding of perch, Perca fluviatilis L., in Windermere
Authors: CRAIG J. F.
Published: May 2006

SUMMARY.
Perch were sampled for their stomach contents at regular intervals throughout 24 h from June until October in 1973 and from February 1975 until January 1976. They were found to feed on benthic organisms from November until April, on benthos and plankton during May and June and on perch fry and zooplankton from July until October. Perch over a wide size range feed on similar prey. Fish showed great variability in the weight of their stomach contents. A method based on a points system was developed to estimate the weight of food in the stomach for a given weight of fish at a known time. A diel feeding pattern which varied with the season was apparent from these data. Rates of gastric evacuation were assumed to be exponential and were calculated from the drop in night‐time stomach content weights when food intake was assumed to be zero. The rates ranged from 0.18 mg h−1 at a mean water temperature of 11°C in May to 0.35 mg h−1 at a mean water temperature of 17°C in July. Assuming that food consumption followed a linear rate of intake, the standard Bajkov method was considered an adequate model to calculate daily food consumption. Daily food consumption (mg dry weight) was calculated for 150 g perch for all months of the year (November to April and September and October being combined). A second series of values was calculated making corrections for the time spent in the fishing gears when food intake was zero but gastric evacuation continued. Daily food consumption figures for 150g male perch based on Winberg's hypotheses (1956) and growth data showed no significant differences from this second series of values, when both were expressed in energy terms. When certain assumptions have been tested, growth data and Winberg's equations together may be a suitable method for calculating an energy budget for the Windermere perch population.
A simple syringe sampler for sampling bottom waters
Authors: GIBBS M. M.
Published: May 2006

SUMMARY.
A cheap messenger‐operated device for sampling water immediately above sediment is described.
Life‐cycle and changes in carbohydrates, proteins and lipids of Pentapedilum uncinatum Goet. (Diptera; Chironomidae)
Authors: BEATTIE D. M.
Published: May 2006

SUMMARY.
The life cycle of Pentapedilum uncinatum in the Tjeukemeer is briefly described. There are two generations of larvae per year in the mud substrate but only one generation per year in the sand substrate. Changes in chemical composition during the life cycle of P. uncinatum are described, and the data indicate that such changes are not synchronized with particular larval instars but follow a predetermined development pattern for the production of an adult insect. Development appears to be the same in both male and female larvae which results in adult insects that have almost identical percentage composition of chemical substances, but proportionately greater growth in female larvae gives an adult insect that is almost twice as heavy as the male.
A technique for predicting in‐stream flow requirements of benthic macroinvertebrates
Authors: GORE JAMES A.
Published: May 2006

SUMMARY.
A total of 225 benthic samples was taken at various riffles along the Tongue River in Montana during three separate weekly intervals in 1975. For each sample, depth, current velocity, substrate microprofile, turbulence (Froude number), and the number and kind of species present were considered.

The conditions of highest faunal diversity were 75–125 cm/s current velocity at 20–40cm depth. The optimum condition appeared to be 76 cm/s at a depth of 28 cm over medium cobble substrates.

The centroids for optimum conditions of depth and current velocity for thirty‐six common macroinvertebrates are also presented.

Representative diagrams of the tolerance ranges of some common invertebrate species are presented. Rhithrogena hageni Eaton was chosen as the indicator species since its tolerances closely matched those of the highest community diversity. The presence of Rhithrogena in future samples would indicate maintenance of adequate flow conditions for the present benthic community.

A method for applying these data to produce a minimum flow recommendation is discussed. If the optimum conditions can be plotted on composite hydrologic maps of depth and velocity in riffle areas at various discharges, one can predict the discharge at which the optimum conditions are eliminated and, thus, the recommended minimum discharge.
Water quality and the occurrence of Chironomus riparius Meigen (Diptera: Chironomidae) in a stream receiving sewage effluent
Authors: GOWER A. M. , BUCKLAND P. J.
Published: May 2006

SUMMARY.
The effects of a sewage effluent in Moat Brook, Staffordshire, were determined from regular collections of water and biological samples from directly comparable stations above and below the sewage outfall.

The eutrophic conditions below the outfall result in the replacement of Polypedilum laetum by Chironomus riparius (except in the spring) as the dominant member of the Chironominae. Continuous recruitment of first instar larvae to the population of C. riparius in summer and autumn results in much overlap of generations, but emergence trap captures suggest at least five generations in the year.

The usefulness of C. riparius as an indicator of enriched conditions in lotic ecosystems should be considered in relation to oviposition behaviour and the occurrence and seasonal variation in density of the adults and aquatic stages (including the more conspicuous third and fourth instar larvae).
The effect of sewage effluent on Grasmere (English Lake District) with particular reference to inorganic nitrogen transformations
Authors: HALL GRAHAME H. , COLLINS VERA G. , JONES J. GWYNFRYN , HORSLEY RICHARD W.
Published: May 2006

SUMMARY.
In the summer of 1971 the village of Grasmere was converted from septic tank to mains drainage with sewage treatment at an activated sludge plant. The effluent was discharged into the River Rothay, the main inflow of a nearby small lake (Grasmere). This paper describes some of the effects on the lake. The mean areal hypolimnetic oxygen deficit increased from 274 to 434 mg O2 m−2 day−1 with an accompanying marked increase in the degree of deoxygenation in the hypolimnion. Plate counts of bacteria in the surface water increased for 2 years but this increase was not sustained. The mean summer soluble reactive phosphorus concentration did, however, increase significantly (P= 0.05), but the same was not true of nitrate levels. This paper is particularly concerned with inorganic nitrogen transformations and analyses of the main inflow have shown that 50–98% of the ammonia and 10–40% of the nilrate entering in this river was derived from the sewage effluent. The concentrations in the main body of the lake were usually lower, possibly due to assimilation and denitrification in the shallower reaches of the lake. Seasonal changes in the inorganic nitrogen species in the hypolimnion showed three distinct phases of activity, ammonification, nitrification and denitrification. Nitrification accounted for approximately a quarter of the oxygen uptake in the hypolimnion.