bluuebunny/crossref_metadata_2025 huggingface dataset:
Population structure, life histories and abundance of copepods in Tjeukemeer, the Netherlands
Authors: VIJVERBERG J.
Published: May 2006

SUMMARY. The copepod zooplankton of Tjeukemeer was sampled at weekly intervals for 3 years (1969–1971), and ten species were recorded. Five species contributed more than 99% of all individuals collected. Acanthocyclops robustus is the most abundant species (66%), followed by Mesocyclops leuckarti (13%), Cyclops vicinus (11%), Eurytemora affinis (9%) and Diacyclops bicuspidatus (1%).

The ecology of the A. robustus population in Tjeukemeer differs from other A. robustus populations in that it dominates the open water zone. This is an additional argument for a taxonomic revision of the A. vernalis‐robustus complex.

Seasonal periodicity in abundance of each species was very similar in 3 successive years.

All cyclopoid species went into diapause, A. robustus and M. leuckarti during winter, D. bicuspidatus and C. v. vicinus during summer. Most species diapause in a particular copepodite stage.

The seasonal variation in the population structure, the fecundity and the sex ratio are described. Both population structure and sex ratio were influenced by diapause and size‐dependent mortality. The fecundity was more influenced by the water temperature and the age structure of the female population than by food situation or size of the females.
Selective feeding and its effect on polymorphism and sexuality in the rotifer Asplanchna sieboldi
Authors: GILBERT JOHN J.
Published: May 2006

SUMMARY.
Campanulate females of A. sieboldi (clone 12C1) attack Asplanchna brightwelli and A. girodi much more readily than either the alga Volvox aureus or the rotifer Brachionus calyciflorus. Pre‐feeding campanulates on B. calyciflorus prior to testing does not appreciably affect their response to this prey. Discrimination during feeding occurs immediately after the campanulate's corona contacts a potential food organism and is probably mediated by chemoreceptors. Once a food organism is attacked, the probabilities of it being captured and subsequently swallowed are high and similar for each of the four organisms tested.

Since food organisms other than Asplanchna. such as V. aureus and B. calyciflorus, induce campanulates in this clone to produce cruciform, and thus frequently sexual, females in succeeding generations, a tendency of these campanulates to select congeneric prey would favour the maintenance of the campanulate morphotype and thus the continuation of parthenogenetic reproduction in the ensuing population.
Effect of temperature on the hatching time of eggs of Ephemerella ignita (Poda) (Ephemeroptera:Ephemerellidae)
Authors: ELLIOTT J. M.
Published: May 2006

SUMMARY.
Eggs of Ephemerella ignita (Poda) were kept at eight constant temperatures (range 5.9–19.8°C) in the laboratory. Over 85% of the eggs hatched in the temperature range 10.0–14.2°C but the percentage decreased markedly to 39% at 5.9°C and 42% at 19.8°C. Hatching time (days after oviposition) decreased with increasing water temperature over the range 5.9–14.2°C and the relationship between the two variables was well described by a hyperbola. Therefore, the time taken for development was expressed in units of degree‐days above a threshold temperature. Mean values (with 95%CL) were 552 (534–573) degree‐days above 4.25°C for 10% of the eggs hatched, 862 (725–1064) degree‐days above 3.57°C for 50% hatched and 1383 (1294–1486) degree‐days above 3.14°C for 90% hatched. These values can be used to predict hatching times at temperatures below 14.68°C for 10% hatched, 14.54°C for 50% hatched and 14.45°C for 90% hatched. At higher temperatures, the hatching time and the number of degree‐days required for development both increased with increasing temperature. Equations were developed to estimate the number of degree‐days required for development at these higher temperatures.

Eggs were also placed in the Wilfin Beck, a small stony stream in the English Lake District. Maximum and minimum water temperatures were recorded in each week and the summation of degree‐days was used to predict the dates on which 10%, 50% and 90% of the eggs should have hatched. There was good agreement between these estimates and the actual hatching times. Only 10–15% of the eggs hatched between October and late February with most of the eggs hatching in March, April and May. Nymphs hatching in October and November probably did not survive the winter.
A quantitative sampler for air‐breathing aquatic insects
Authors: HENRIKSON LENNART , OSCARSON HANS
Published: May 2006

SUMMARY.
A quantitative funnel‐trap sampler for air‐breathing aquatic insects is described. Performance tests with special reference to adult Glaenocorisa propinqua are presented. Abundance was calculated from pilot surveys with the funnel‐trap sampler during 1976 and compared with results from a trial with the capture‐recapture method. The influence of temperature on the frequency with which adult Glaenocorisa propinqua renews the bubble gilt was measured.
Cyclomorphosis in natural populations ofDaphnia cephalataKing
Authors: HEBERT PAUL D. N.
Published: May 2006

SUMMARY.Daphnia cephalataKing is a major component of the zooplankton in freshwater ponds of eastern Australia. Phenotypic variation in head shape both within and between populations is striking. Some of this variation is ontogenetic, but among individuals of similar size head length still varies by a factor of two. The causes of this variation have been investigated by analysing head size in thirty‐four populations ofD. cephalataover a 17‐month period. An annual cycle in crest size, apparently related to seasonal changes in mean temperature, was evident when the data were pooled. Large differences in head size were commonly observed, however, among samples collected simultaneously. Some of this variation was correlated with local differences in resource availability, which were due, in part, to local variation inDaphniadensity. Other consistent interpopulation differences in head size were related to stable environmental differences among sites and probably also to genetic differences among populations.
Trace elements in the Upper Fly River, Papua New Guinea
Authors: BOYDEN C. R. , BROWN B. E. , LAMB K. P. , DRUCKER R. F. , TUFT S. J.
Published: May 2006

SUMMARY.
Measurements were made of calcium, magnesium and eight trace elements (Cu, Zn, Fe, Mn, Ni, Pb, Cd, Co) in waters, sediment and biota at eight sites in the Upper Fly River, Papua New Guinea. Determinations from streams draining an area rich in copper ore showed relatively low values for soluble copper and this was attributed to the small amount of ore exposed to weathering, heavy rainfall and high pH of water associated with the limestone bedrock. More iron was transported in a soluble form down a headwater tributary (Alice River) than in the Fly River but higher iron concentrations were associated with particulate matter in the Fly than in the Alice. The geochemistry of the catchment and the distance from the headwaters were important influences on the amount of particulate iron and its distribution between soluble and particulate forms.

Levels of metals in the biota generally reflected the background concentrations of metals encountered at each site. Concentrations of Cu, Cd, and Zn were lower in starved invertebrates compared with unstarved individuals but no consistent changes were observed in Fe or Mn content.
The effects of temperature on the development and mortality of eggs of perch, Perca fluviatilis
Authors: GUMA'A S. A.
Published: May 2006

SUMMARY.
The rate of development and mortality of perch Perca fluviatilis was studied at ten different constant temperatures. The rate of development was inversely related to the incubation temperature, whereas the rate of mortality was directly related to the incubation temperature. The sum of heat (ΣH, degree‐days) required for 10, 50 and 90% of the eggs to hatch was found to be constant, regardless of the incubation temperature, with mean values (with 95% confidence limits) of 91.4 (83.3–102.0) degree‐days above 4.6°C for 10% hatched, 97.0 (90.9–104.2) degree‐days above 4.9°C for 50% hatched and 101.0 (94.3–108.7) degree‐days above 5.0°C for 90% hatched. Mortality among the different embryological stages was highest for the pre‐hatching stage (i.e. when eye‐pigment has been formed) at all temperatures. High mortality among the early stages occurred at temperatures below 8°C and above 12°C.
Variations in the shallow water form of Potamogeton richardsonii induced by some environmental factors
Authors: SPENCE D. H. N. , DALE H. M.
Published: May 2006

SUMMARY.
Populations of Potamogeton richardsonii in Sparrow Lake, Ontario, vary greatly in leaf dimensions and internode length. Leaf length/breadth (L/B) ratio is increased by low irradiance, significantly at 4% daylight and, in a contrary fashion, by ontogenetic drift at high irradiances of shallow water. L/B ratio was not correlated with substrate. These findings suggest that this ratio is of doubtful value taxonomically or as an integrator, as specific leaf area is confirmed to be, of factors like photosynthetically active radiation (PAR). Longest internodes belong to plants from deep(1.8 m) water, and, in a summer‐grown high‐density population, internode length decreases logarithmically as depth lessens; both observations implicate PAR and ageing. Relative to undisturbed, shallow‐water shoots, young transplants in full daylight elongate almost twice as fast because of the production of more, and longer, internodes. Young shoots in 12% daylight lengthen even more rapidly than those in full daylight (and four times faster than undisturbed shoots) in the same period because of quicker elongation of the same number of internodes. At ambient summer temperatures, this rate of elongation is inversely related to PAR. Experimental and seasonal field data indicate that maximal internode extension occurs on young shoots in very low irradiances at temperatures of 9–15°C; in nature, effects of increasing water temperatures are depressed by increasing irradiances and ageing until minimal extension takes place in old shoots at mid‐ to late‐summer temperatures and in high irradiances. In tanks (40 m3) in full daylight, nutrients limit growth of plants on sand before they limit growth on clay (with marl intermediate) whereas, at 12% daylight, light limits growth on sand before soil nutrients do. The leaf area index on silty sand on an exposed shore was 0.4 at 0.5 m depth, in contrast to a cultured population where it was 4.0 in silty loam at the same depth. Thus, while it has not been possible to explain some variations in leaf morphology of P. richardsonii in environmental terms, the differential effects of ontogeny, PAR and temperature on shoot growth have been assessed, along with overall effects of light and nutrients on biomass and of shelter on leaf area index.
Salamander drift
Authors: STONEBURNER D. L.
Published: May 2006

SUMMARY.
Interpretation of data collected from a spring‐fed stream suggests the existence of a phenomenon in running water that has not been previously described — salamander drift. Stream substrate and drift collections indicated that pre‐metamorphic salamanders (Eurycea bislineata) entered the water train and drifted during the months of April, May and June. Post‐metamorphic salamanders, and individuals about to undergo metamorphosis, did not appear in the stream drift.
Aspects of the ecology of Prymnesium parvum (Haptophyta) and water chemistry in the Norfolk Broads, England
Authors: HOLDWAY P. A. , WATSON R. A. , MOSS BRIAN
Published: May 2006

SUMMARY.
Prymnesium parvum, an ichthyotoxic phytoplankter, has been recorded, at times abundantly, in the River Thurne, Norfolk, and its associated Broads. Its occurrence has been apparently more frequent and its population sizes probably larger since the late 1960s than previously and fish mortalities due to it now occur almost annually.

The Thurne system is brackish and may have become more so, due to exploitation by drainage pumps, of a saline water table, in recent years. Evidence for this is conflicting, but in any case an increase in salinity is unlikely to have made increased Prymnesium growth more likely. Eutrophication of some Broads in the system is most likely to have increased the populations of Prymnesium since the late 1960s and data are presented on the present water chemistry of the system for comparison with previous records, and on current phytoplankton and Prymnesium crops in different parts of it.

P. parvum has been isolated from the system as a unialgal culture and compared in morphology, salinity tolerance and ichthyotoxicity with a strain of P. parvum from Israel. The Broads strain differs slightly in size and pigmentation, but not in salinity tolerance. In culture it produces more ichthyotoxin than the Israeli strain.
The adaptive significance of cyclomorphosis in Daphnia: more possibilities
Authors: HEBERT PAUL D. N.
Published: May 2006

SUMMARY.Morphological variability inDaphniapopulations has often been uncritically ascribed to phenotypic plasticity. For instance, detailed study revealed that the ‘cyclomorphic species’D. carinatas. l. was a complex of nine species. Several of these species often cohabit and seasonal change in their relative frequencies causes phenotypic cycles which mimic true cyclomorphosis. Intraspecific genetic variation in head shape also seems widespread and is likely to be important in explaining phenotypic changes in many single species populations.

The hypothesis that helmet formation inDaphniais primarily related to predator avoidance is not supported by work on theD. carinatagroup. Seasonal trends in species composition can be explained without reference to differential predation. Natality differences exist between species with disparate head size suggesting that helmet formation may have direct effects on fitness. Two possibilities are considered. The length of the anterior adductor muscle is directly correlated with helmet size and such variation may affect swimming efficiency. In addition the laminar design of helmets suggests a role in gas exchange.
Community production and respiration by ciliated protozoa in the benthos of a small eutrophic loch
Authors: FINLAY BLAND J.
Published: May 2006

SUMMARY.
The results of laboratory experiments on ciliate reproductive and respiratory rates have been combined with field data for ciliate numbers, to produce estimates of production and respiratory energy losses by communities of benthic ciliates. Annual production decreased with increasing depth, and it was estimated to be 345, 149 and 40 J cm−2 year−1 at three sites in Airthrey Loch, Scotland. A similar trend with increasing depth was recorded for annual respiratory energy losses, being 16, 11 and 4 J cm−2 year−1 at the three sites. The corresponding annual net production efficiencies (%) were 95.2, 93.1 and 91.5. When net production efficiencies were calculated for each period (the time between successive sampling occasions) as 100 (daily production/daily assimilation), the range extended from 63 to 98. The energetic efficiencies of the ciliate populations are discussed with reference to data in the literature for higher organisms.
Dissolved organic carbon fluxes in the Shetucket River of eastern Connecticut, U.S.A.*
Authors: KLOTZ R. L. , MATSON E. A.
Published: May 2006

SUMMARY.
Seasonal changes in dissolved organic carbon (DOC) concentrations were monitored biweekly for 1 year at seven stations in the Shetucket River watershed in eastern Connecticut, U.S.A. Nine monthly diurnal studies revealed 24‐h fluctuations of up to 53% of the seasonal range of 250–2200 μm DOC.

Net DOC removal along a 1.9‐km stretch below a secondary sewage treatment plant (activated sludge effluent diluted to a final average volume of 1.4% in the river) ranged from 0 to 1600 and averaged 68 ± 64 mmol m−2 day−1. Removal of DOC further downstream could only be observed during a severe 3‐h October storm when net uptake ranged from 16 to 92 mmol m−2 h−1, using upstream‐downstream techniques. Oxygen respiration could account for about half of the net DOC removal during the October storm.

Even though net uptake was somewhat greater than reported in other lotic studies, about 97% of the DOC potentially available to benthic heterotrophs was exported further downstream.
The natural prey of larvae of the damselfly, Ischnura elegans (Odonata: Zygoptera)
Authors: THOMPSON DAVID J.
Published: May 2006

SUMMARY.
A method for determining the prey of a damselfly larva under natural conditions is described, with its shortcomings.

Within the limits of the method, it would appear that Ischnura elegans consumes different prey items in roughly the same proportions as their occurrence in the field.

Anomalous results are explained in terms of differences in encounter rates between predator and prey and/or ease with which prey can be handled.
Growth and survival of Atlantic salmon (Salmo salar) in Llyn Dwythwch, North Wales
Authors: PEDLEY R. B. , JONES J. W.
Published: May 2006

SUMMARY.
Atlantic salmon fry have been annually stocked into Llyn Dwythwch, North Wales, since 1969, in an attempt to increase the natural stocks of the area. The growth and survival of 1‐ and 2‐year‐old salmon were investigated, and compared with that of other lake‐reared populations and also with salmon in the natural stream environment. Lake‐reared salmon follow the same patterns of slow and rapid growth as found for river fish, but the growth rate was superior in the former. The variation in length – weight relationship with age and sex was investigated. Survival rates in general compared favourably with the survival in rivers, with high mortality rates of salmon in Llyn Dwythwch resulting from predation at spring stocking by the resident brown trout. This was later avoided by stocking larger fish in the autumn.
The limnology of Cabora Bassa, Moçambique, during its first year
Authors: BOND W. J. , COE NANCY , JACKSON P. B. N. , ROGERS K. H.
Published: May 2006

SUMMARY.
Cabora Bassa, a new impoundment in the Middle Zambezi River, was closed in December 1974, filling rapidly to 12m below full supply by May 1975.

The lake, with five basins, lies along a west–east axis almost parallel to prevailing south‐easterly winds. Limnological records, from several stations along the lake axis, indicated homoiothermal conditions until September, the hot dry season. From then until records ceased in December, thermoclines and oxyclines were present in the deeper eastern basins. Hydrogen sulphide was recorded in hypolimnial waters towards the end of the year. Open water of the shallow, wind‐ and wave‐swept eastern basins remained oxygenated throughout the year.

Water transparency increased fivefold from April to December, increasing too from east to west. pH was alkaline becoming more acid in cool winter months and in bottom waters of stratified basins. Conductivity ranged from 95 to 119 °S cm−1 with higher values in shallow lake margins. Chemical content of surface waters showed little seasonal or spatial variation and was, in general, comparable with pre‐impoundment levels.

Duration of the initial ‘productive phase’ will probably be shorter than Kariba due to more rapid lake water exchange but indications are that productivity will be higher in the maturation phase.
Mortality patterns in trout (Salmo trutta and S. gairdneri) exposed to an anionic detergent in relation to concentration and mechanisms of toxic action
Authors: ABEL P. D.
Published: May 2006

SUMMARY.
Histological and electron microscopical study of the gills of fish poisoned by the anionic detergent sodium lauryl sulphate indicates that the nature of the toxic action changes at a concentration of about 120 mg I−1. Toxicity tests were conducted to determine whether this change could be detected in the test data, using brown trout (Salmo trutta) and rainbow trout (S. gairdneri).

Toxicity curves showed no indication of the change in toxic action, but at concentrations of 120 and 130 mg I−1 of sodium lauryl sulphate ‘split’ probit lines occurred, and the lines for 150 mg I−1 consistently differed in slope from other lines.
Life‐history and distribution of Simulium austeni (Diptera: Simuliidae) in relation to phytoplankton in some southern English rivers
Authors: HANSFORD R. G.
Published: May 2006

SUMMARY.
Regular sampling of larval and pupal simuliids in the River Stour (Dorset) showed that Simulium austeni produces a single generation of larvae per year, pupating in late April‐early May. The species is abundant in the middle and lower reaches of the Stour and its larger tributaries, but in nearby rivers of comparable size it is rare or absent, Unlike these other rivers, the Stour supports a true phytoplankton dominated by small centric diatoms (Stephanodiscus hantzschii). Peak concentrations of particulate chlorophyll‐α sometimes correspond with the growth period of S. austeni larvae. The distribution of S. austeni relative to that of phytoplankton is discussed and the importances of suspended bacteria and water chemistry are briefly considered.
Comparative estimations of the energy content of fish tissue from bomb calorimetry, wet oxidation and proximate analysis
Authors: CRAIG J. F. , KENLEY M. J. , TALLING J. F.
Published: May 2006

SUMMARY.
Four methods were used to determine the energy content of somatic tissues of Perca fluviatilis. Two forms of direct calorimetry (both adiabatic and non‐adiabatic) and wet (dichromate) oxidation gave similar results. When energy contents were calculated from proximate analysis using accepted conversion factors (9.45 cal mg−1 for lipid, 5.65 cal mg−1 for protein) results were higher than those from the other methods. The discrepancy was eliminated when a lower, directly determined energy content for the extracted lipid fraction was used.

Some historic and technical aspects of the comparison are discussed.
Statistical analysis of nitrate concentrations from the River Frome (Dorset) for the period 1965–76
Authors: CASEY H. , CLARKE R.T.
Published: May 2006

SUMMARY.
Statistical analysis has been carried out on 11 years (1965–75) weekly data of nitrate concentrations and discharge values from the R. Frome (Dorset). The results have shown a trend over the 11‐year period with nitrate concentrations increasing by 0.11 mg NO3‐N 1−1 per year. A predictive model for nitrate concentrations for 1976 was made and even though discharge conditions were extreme, the mean predicted nitrate concentration of 3.37 ± 0.136 mgNO3‐N1−1 was very close to the observed mean nitrate concentration of 3.44mgN03‐N1−1.
Changes in phytoplankton physiology and morphology in response to dissolved nutrients in Lough Neagh, N. Ireland
Authors: GIBSON C. E. , STEVENS R. J.
Published: May 2006

SUMMARY.
Cell phosphorus and anthrone‐reactive carbohydrate contents were measured over a 6‐month period in the phytoplankton of Lough Neagh, N. Ireland. When all the soluble reactive phosphorus had disappeared from the water column, cell phosphorus contents began to decrease, reaching a minimum value of 0.4% ash‐free dry weight. At this time, cell carbohydrate contents greatly increased and phosphorus sorption assays showed rapid uptake of orthophosphate. Following a presumed sediment phosphorus release, cell carbohydrate and phosphorus uptake rate decreased greatly and there was a subsequent increase in cell phosphorus content to 1.6% ash‐free dry weight. As the cell phosphorus content declined, blue‐green algal filaments became progressively shorter. On the basis of these responses it is likely that phosphorus limitation occurred over a 4‐week period.
The influence of some ecological factors on the metabolism—temperature curve of the larvae of Limnephilus rhombicus (Trichoptera, Limnephilidae)
Authors: ROUX C.
Published: May 2006

SUMMARY.
The oxygen uptake of Limnephilus rhombicus, a typical inhabitant of lentic waters, was measured in three different experimental situations: in still water with a plastic mesh as a substrate, in stirred water with a plastic mesh and in still water without any substrate. Water flow caused a small increase in oxygen uptake at all temperatures but principally above 15°C. The presence or absence of the plastic substrate had little influence on oxygen uptake; L. rhombicus can be active over the whole range of temperatures studied but its activity is always small. Its metabolism—temperature curve stands out in having a plateau between 5 and 10°C, with a steeper part between 10 and 20°C, the slope of which varies according to the conditions. Maximum oxygen uptake at high temperatures was relatively low (1235 ± 153 μl O2g dry wt‐1h‐1 at 25°C).

The results are compared with those obtained previously for the larvae of Microptema testacea which inhabit flowing zones in brooks. L. rhombicus larvae appear both as cold‐water animals and as animals from highly variable biotopes. They are in fact very ubiquitous and occupy all lentic biotopes from cold and mountainous districts to temperate lowlands.
The food and feeding habits of Physailia pellucida and Schilbe mystus with notes on the diets of S. uranoscopus and Siluranodon auritus, family Schilbeidae (Osteichthyes: Siluriformes) in Lake Kainji, Nigeria
Authors: OLATUNDE AKINOLA A.
Published: May 2006

SUMMARY.
The food and feeding patterns of four schilbeids in Lake Kainji were studied between November 1974 and October 1975. Physailia pellucida, a small but abundant species, fed on small crustaceans and immature insects, while Schilbe mystus, a larger but less common schilbeid, fed principally on fish, with insects as a supplementary item in its diet. The rare species, Schilbe uranoscopus, was piscivorous, Siluranodon auritus, another small and rare species, is a herbivore feeding mainly on algae, with some crustaceans and immature insects taken as a source of animal protein. Preferential food selection by different length groups was found in S. mystus and P. pellucida. There were seasonal changes in the dietary items. Competition for food within the family was assumed not to occur in view of the different feeding habits of the species.
Effects of temperature and current discharge on the concentration and photosynthetic activity of the phytoplankton in the upper Mississippi River
Authors: BAKER ALAN L. , BAKER KATHLEEN KROMER
Published: May 2006

SUMMARY.
Temperature and current discharge regulated phytoplanktonic concentration, chlorophyll‐a concentration, the light‐saturated rate of photosynthesis (Pmax), and photosynthetic capacity (Pcap) in the Mississippi River at Prairie Island, Minnesota. The chlorophyll‐a maximum was 48 mg m−3 in 1975, a wet year with a high current discharge, and 190 mg m−3 in 1976, a relatively dry year. The highest values of Pmax were 0.37 (mgO2 I−1h−1) in 1975 and 1.60 in 1976. Pcap varied from 3 to 21 (gO2 per g chlorophyll‐a h−1) both years, and its value was highly correlated with temperature. The temperature optimum shifted from 16°C for Pcap in the spring, to greater than 28°C in the summer. Multiple regression analysis indicated a second‐order relationship of Pcap in the spring to temperature. Other independent variables explained only negligible variation of Pcap.
Periphyton production in Fort River, Massachusetts
Authors: SUMNER WILLIAM T. , FISHER STUART G.
Published: May 2006

SUMMARY.
The primary production and general ecology of a periphyton community of a New England, lowland stream were studied over a seventeen‐month period. Temperature, light, periphyton chlorophyll‐α, and community structure were monitored regularly. Seasonally distinct chlorophyll peaks coincided with the light maximum in early May, just prior to the appearance of leaves of riparian trees, and again in autumn after terrestrial leaf fall. During midwinter, despite low light and temperature levels and high stream discharge, mean chlorophyll concentrations remained similar to summer values.

A mathematical expression relating periphyton photosynthesis per unit chlorophyll‐α to temperature, light and periphyton density was established with submersible light‐dark chambers in situ. Survey data collected over the study period were employed in the empirical equation to estimate seasonal variations in periphyton primary production. Weekly mean daily estimates of periphyton gross production ranged from < 0.1 g O2 m−2, during midwinter, to 6.5 g O2 m−2 during early May. Estimated annual periphyton gross production and respiration were 0.58 and 1.27 kg O2 m−2, respectively. Factors influencing seasonal variations of Fort River periphyton standing crop are discussed.
Exclusion of phytoplankton in the proximity of dominant water‐soldier (Stratiotes aloides)
Authors: BRAMMER ERIK S.
Published: May 2006

SUMMARY.
Profuse growth of the submerged macrophyte, Stratiotes aloides, in two similar locations, one in central Sweden and one in the Masurian lake district of north‐eastern Poland, exerted a negative influence upon contiguous populations of phytoplankton. The Polish location offered an additional possibility to investigate chemical and biological gradients between the littoral community of S. aloides and the prevailing limnetic population of cyanophytes (mainly Anabaena planctonica and Oscilatoria spp.). A considerable decline in planktonic chlorophyll was accompanied by decreases in electrolytic conductivity, carbonate alkalinity and contents of calcium, potassium and sodium. Low concentrations of molybdate‐reactive phosphorus in the water of the Stratiotes community was credited to co‐precipitation with calcium carbonate on the leaf surfaces of the submerged plants. Thus, rather than allelopathy, competition for esssential nutrients together with changes in the ionic composition of the water seemed to be a more likely explanation for the decline in phytoplankton.
Energetics of a population of the isopod Asellus aquaticus: Life history and production
Authors: ADCOCK J. A.
Published: May 2006

SUMMARY.
A population of Asellus aquaticus in Wistow Lake, England, was sampled at monthly intervals from September 1973 to September 1974. The mean population density was 586 m−2 in autumn 1973 but it fell to 67 m−2 by autumn 1974. Evidence suggests that the lower density in autumn 1974 was due to premature mortality of gravid females. The cause of this is not known.

Gravid females were present from February to June and July to September, giving rise to spring and autumn cohorts. The larger members of the spring cohort reproduced in the autumn, the remainder in the following spring. The autumn cohort reproduced mainly in the following spring but later than the spring cohort. The bimodal length‐frequency curves were analysed to separate the two cohorts and to estimate growth and production of each cohort separately. The overwintering spring cohort had a faster relative growth rate than the smaller individuals of the autumn cohort. Thus the spring cohort showed a P/B ratio of 2.62 for the period September–April compared with a ratio of 1.81 for the autumn cohort. The highest ratio of 6.42 was shown by the spring cohort in the summer (May–September).

Annual population production (P) was 3004.9 mg dry wt m−2 from a mean biomass (B) of 757.2 mg dry wt m−2. The P/B ratio of 3.96 is double the value reported for A. aquaticus in Sweden.
Feeding on gastropods by lake‐dwelling Polycelis in the absence and presence of Dugesia polychroa (Turbellaria, Tricladida)
Authors: REYNOLDSON T. B. , PIEARCE BRONWEN
Published: May 2006

SUMMARY.
Using a serological technique, the extent of feeding upon snails by Polycelis tenuis was compared in habitats lacking and containing Dugesia polychroa which is the major triclad predator of snails. It was found that P. tenuis ate significantly more snails when D. polychroa was absent. It was concluded that in the field interspecific competition for snails between these two triclad species was a more powerful process than any social feeding by P. tenuis on snails captured by D. polychroa.

Feeding on snails as a group by P. tenuis and P. nigra in the habitat where the two triclads co‐existed was of a similar magnitude and this was also true of their feeding on the common snail species and genera. Approximately 10% of the triclads gave a positive reaction to snail antisera.

Feeding on snails by P. nigra in the three habitats lacking D. polychroa was similar in extent and did not differ from that of P. tenuis. It was concluded that P. nigra would be similarly affected by the presence and absence of D. polychroa as shown for P. tenuis.

No definitive seasonal pattern was detected in the incidence of feeding upon snails by either Polycelis species but this may have been obscured by seasonal changes in the detection period of snail antigens due to temperature effects. There was some evidence that such feeding increased during the period when small snails were present in the population.
Some physiological‐biochemical characteristics of planktonic blue‐green algae during bloom formation in three Salopian meres
Authors: ROTHER J. A. , FAY P.
Published: May 2006

SUMMARY.
Levels of cellular orthophosphate concentration, alkaline phosphatase activity, photosynthesis and nitrogenase activity of natural populations of blue‐green algae collected during the summer of 1976 from the surface waters of three eutrophic lakes were determined under controlled conditions. Intracellular concentrations of surplus stored phosphorus remained high and alkaline phosphatase activity remained low during the formation and decline of the surface bloom, which indicated that available phosphorus does not become limiting to growth. In contrast, declining rates of nitrogenase activity and net photosynthesis were recorded, particularly in those blooms of shorter duration. An increase in numbers of bacteria during the summer may account for the observed fall of net photosynthetic rates, since gross rates did not change as markedly. There was appreciable nitrogenase activity proceeding and during the differentiation of akinetes, and the cellular C/N atomic ratio of sporulating populations was lower than in non‐sporulating algae. It is suggested that the onset of sporulation in surface blooms is initiated by an imbalance of the normal vegetative growth of the algal cells and of their carbon and nitrogen metabolism.
The effect of impoundment on the water chemistry of Lake Asejire, Nigeria
Authors: EGBORGE AUSTIN B. M.
Published: May 2006

SUMMARY.Following the impoundment of the River Oshun to form Lake Asejire, Nigeria, in 1970, changes in the water chemistry were monitored. Chemical stratifications followed closely the pattern of thermal stratifications as the lake was chemically stratified from February to April and destratified from June to September and in January.
The occurrence and ecological importance of dissolved ATP in fresh water
Authors: RIEMANN BO
Published: May 2006

SUMMARY.
Dissolved ATP, defined as ATP which passes through 0.2 μm filters, was found in fresh water. During the spring diatom bloom in two eutrophic Danish lakes, concentrations of dissolved ATP varied between 0.1 and 3.8 μgl−1, constituting 14–76% of the total ATP (particulate plus dissolved ATP). The kinetics of the light emission obtained from mixing firefly enzyme with dissolved ATP demonstrated that the major proportion of the dissolved ATP was in fact ATP. Despite some variations, the seasonal changes in dissolved ATP paralleled the changes in the increasing phytoplankton population during the rise of the diatom blooms. The dissolved ATP increased after the diatom peak, indicating that release of ATP from the phytoplankton due to mortality may be a major source of dissolved ATP.

Consumption of dissolved ATP was evaluated in uptake experiments using 3H‐ATP. Rates of uptake of 3H‐ATP by micro‐organisms (diameter 0.2–0.6 μm) proved to be close to the rates for 3H‐D‐glucose uptake. The variations in 3H‐ATP uptake during the diatom blooms showed non‐systematic changes and ranged between 1.0 and 15.8% h−1 (mean = 4.9% h−1) of the quantity added. Turnover rates for dissolved ATP varied between 12 and 730 ng l−1 h−1 (mean = 175 ng l−1). These rather high rates of turnover suggest that dissolved ATP is an important compound in the metabolism of freshwater bacteria.
The distribution of Asellus aquaticus and A. meridianus (Crustacea, Isopoda) in Britain
Authors: WILLIAMS W. D.
Published: May 2006

SUMMARY.
Asellus aquaticus and A. meridianus are freshwater isopods common more or less throughout Britain. It has been suggested that the former species is replacing the latter. To investigate this, the distributions of the species were determined in the English Lake District, near Merseyside, and elsewhere. Additionally, some field transference experiments were conducted in Anglesey and near Merseyside. Particular attention was given to changes in distribution with time; many of the observations reported relate to a time span of almost 20 years. Taken together, the results provide qualified support for the suggestion that A. aquaticus is replacing A. meridianus.
Stages of infection and ecological effects of a fungal epidemic on the eggs of a limnetic copepod
Authors: REDFIELD G. W. , VINCENT W. F.
Published: May 2006

SUMMARY.
Fungal infection of calanoid copepod (Diaptomus novamexicanus) eggs was observed in each of three years in an alpine lake (Castle Lake, California, U.S.A.). Stages in the infection process were examined by light and scanning electron microscopy and evidence was obtained that the Lagenidium‐like fungus concerned was a virulent parasite. Fungal destruction of eggs varied in timing and severity from year to year. The maximum impact of the disease was an estimated 48.4% decrease in potential copepod recruitment in 1976 due to the onset of a severe epidemic early in the summer growing season. The minimum impact, a 5.6% decrease in potential recruitment, was recorded in 1975. In this year the proportion of infected eggs was reduced and large numbers of juveniles had been released before the fungal disease began. The 1974 epidemic was intermediate in severity. The effect of these epidemics on Castle Lake calanoid populations is discussed in relation to temperature, food availability and predation.
Effect of temperature on the duration of egg, nauplius and copepodite development of some freshwater benthic Copepoda
Authors: SARVALA J.
Published: May 2006

SUMMARY.
The development times of the egg, nauplius and copepodite stages of seven species of freshwater benthic copepods (Paracyclops fimbriatus, Canthocamptus staphylinus, Attheyella crassa, Moraria brevipes, M. mrazeki, Bryocamptus echinatus and Paracamptus schmeili) were determined at constant temperatures ranging from 1.5 to 24°C using detritus as food. Several regression models used earlier to describe the temperature dependence of development were tested on this material.

Species differed both in the rapidity of development and in the magnitude of the effect of temperature. Development times usually decreased with increasing temperature, but in M. brevipes temperatures exceeding 16°C retarded postembryonic development. P. fimbriatus developed at a rate comparable to that reported earlier for littoral cyclopoids. All the harpacticoid species developed more slowly than planktonic, littoral or benthic copepods previously studied, but faster than subterranean species. The effect of temperature was most marked in species reproducing in warm water.

The relationship between rate of development and temperature was not linear. None of the curvilinear temperature functions tested was statistically adequate in all cases. However, three of the models gave a reasonable fit to all egg development data, and one of these, the semilogarithmic quadratic equation, lnD= In a+T In b+T2 In c, also satisfactorily described postembryonic development. This model accommodates the retardation of development at higher temperatures, and can therefore be recommended for further testing.
The vertical distribution of macro‐invertebrates in the substratum of the upper reaches of the River Wye, Wales
Authors: MORRIS D. L. , BROOKER M. P.
Published: May 2006

SUMMARY.
A study of the vertical distribution of benthic macro‐invertebrates in the upper Wye, Wales, using basket samplers, indicated no difference between the number of organisms collected, at one sampling time, after 28, 61 and 93 days. However, densities in samples collected after periods greater than 370 days were generally lower than might have been expected. Overall, 59.4%, 22.6% and 18.0% of the benthic invertebrates were recorded in the top (0–11 cm), middle (12–22 cm) and bottom (23–33 cm) levels of the basket samplers. Some organisms were generally confined to the top level (e.g. Ephemeroptera, Simuliidae, Mollusca), others were more evenly distributed (e.g. Oligochaeta, Chironomidae) and some increased with depth at certain times (Sericostoma personatum). Except for organisms confined to the upper layer it was not possible to predict with any certainty the vertical distribution of most organisms within the substratum. The community structure and abundance of invertebrates in the basket samplers differed from collections obtained with a conventional surface sampler.
An algal pigment ratio as an indicator of the nitrogen supply to phytoplankton in three Norfolk broads
Authors: WATSON R. A. , OSBORNE P. L.
Published: May 2006

SUMMARY.
A pigment ratio representing the ratio of carotenoid pigments to chlorophyll‐a was calculated by dividing the optical density at 480 nm by that at 664 nm for a 90% acetone extract of phytoplankton. Its seasonal variation in three Norfolk broads was examined and, except for nitrogen‐fixing species, it was found to vary independently of the algal species composition.

A good inverse correlation with the particulate nitrogen to carbon ratio was found. The seasonal variation in the pigment ratio was considerably affected by measurable lake concentrations of inorganic nitrogen supplied from ttie catchment. Other sources of nitrogen such as nitrogen fixation and release from the sediment were also indicated by changes in the ratio.

By comparison with the distinctions of extreme, moderate and no nitrogen deficiency drawn by Healey (1975) for the nitrogen/carbon ratio, values for the pigment ratio of < 1.4, 1.4–2.4 and > 2.4 were found to indicate no, moderate and extreme nitrogen deficiency respectively in the phytoplankton. The relation ship is attributed to the measurement of secondary carotenoids in response to nitrogen deficiency.
A comparison of populations of the isopod Asellus aquaticus above and below power stations in organically polluted reaches of the River Trent
Authors: ASTON R. J. , MILNER A. G. P.
Published: May 2006

SUMMARY.
Five populations of Asellus aquaticus, subjected to different combinations of temperature and organic pollution in the River Trent, were examined over a period of 18 months. The life‐cycle was probably completed in a year or less in all the populations sampled, a larger proportion of the animals completing the life‐cycle in less than a year at warmer locations. Young animals also hatched 1 or 2 months earlier at the warmer locations.

At the locations subjected to most organic pollution, population densities and the size of animals of both sexes were the largest. The size of ovigerous females, however, appeared to be inversely related to temperature, the smallest occurring at the warmest location. Possible explanations for these differences are given in terms of the amount of food available and the effect of temperature on growth and sexual maturation.
Fossil diatoms and scales of Chrysophyceae in the recent history of Hall Lake, Washington
Authors: MUNCH C. S.
Published: May 2006

SUMMARY.
Scales of several members of the Chrysophyceae (family Synuraceae) were examined from a core of the recent sediments of Hall Lake, Washington, in conjunction with a study of fossil diatoms. Both types of microfossils revealed communities changing with the historical development of the lake. Increases in planktonic diatoms and in two species of Mallomonas occurred about the time of European settlement. Several acidophilous species among the Chrysophyta disappeared with the establishment of a sawmill and meromictic conditions in the lake. When extensive road construction around the lake ended the period of meromixis, the ratio of Synuraceae, in general, to diatoms, declined. Besides the change in ratio of Synuraceae to diatoms there was a change in the composition of the community of Synuraceae at that time. Species of Synura that had been rare before became the most abundant, and Mallomonas became relatively rare. Throughout the recent history of the lake the dominant Synuraceae seemed to respond more strongly to disturbance around the lake than the most abundant diatoms; thus, scales of Mallomonas, Synura, and other Synuraceae are valuable microfossils for paleolimnological studies.
A limnological survey of Lake Dakataua, a large caldera lake on West New Britain, Papua New Guinea, with comparisons to Lake Wisdom, a younger nearby caldera lake
Authors: BALL E. , GLUCKSMAN J.
Published: May 2006

SUMMARY.
Lake Dakataua (5°S, 150°E) is a large freshwater lake which fills the caldera at the tip of the Willaumez Peninsula on West New Britain, Papua New Guinea. A peninsula produced by post‐collapse volcanic activity divides the lake into two basins connected by a narrow channel. The surface of the lake is c. 76 m above sea level, the surface area is 48 km2, and the maximum depth c. 120 m (Lowder & Carmichael, 1970). A bathymetric map of the lake has been constructed from fathometer transects.

In October‐November, 1974, the lake was alkaline throughout with surface pH 7.6–8.2; acidity increased with depth to pH 7.1–7.5. Surface temperatures were 30.8–31.9°C. There were thermoclines at 22 m and at 40–45 m. Minimum temperature recorded was 26.8°C (at 80 m). Oxygen saturation curves were similar to the temperature curves with sharp gradients at 22 m and 40–45 m. There was no measurable O2 from 80 m downward. Living organisms were common in dredge hauls to 20 m but were not found in those from greater depths. Carbon dioxide concentration rose steadily from 1.4 mg I−1 at the surface to 19.6 mg I−1 at 80 m. Average Secchi disc transparency was 11.1 m.

Shallow water areas support dense beds of mixed aquatic plants (Najas tenuifolia and Chara sp.). Invertebrates collected included two species of sponge, a rotifer, an ostracod, six species of molluscs, seven species of Cladocera, a copepod, eight species of Hemiptera, two species of Trichoptera, ten species of Odonata, two species of Coleoptera, and seven species of Chironomidae. Vertebrates included frogs (two species) and crocodiles. Water birds, including ducks, grebes, and waders, were abundant. The biota of L. Dakataua is more diverse than that of nearby Lake Wisdom probably due to the combination of greater age and greater proximity to sources of colonists. Most species found in L. Wisdom are also found in L. Dakataua.
Seasonal distribution and life histories of Ephemeroptera in a Northumbrian River
Authors: WISE E. J.
Published: May 2006

SUMMARY.
The life histories of twelve abundant species in the River Coquet are given together with notes on certain scarce species. The life histories are compared with those recorded for other river systems and major differences in findings between studies are related to geographical location and temperature. Catastrophic mortalities noted for some populations coincided with the presence of slush‐ice in the river bed and subsequent winter spates caused by meltwaters. Extended hatching periods are apparently adaptive and compensate for such losses. Life histories are also compared along the length of the R. Coquet. Hatching periods, growth rates and emergence periods show regional differences which are apparently dependent on altitudinal variations in temperature regime.
A modified one‐metre Friedinger sampler
Authors: IRISH A. E.
Published: May 2006

SUMMARY.
A 1‐m water sampler is described together with results obtained from sampling a vertically stratified phytoplankton population of Ceratium hirundinella. These results were analysed using a one‐way analysis of variance to partition the total variance into two components. Population estimates from 1‐m sections taken sequentially from the surface waters to 5‐m depth and integrated, were not significantly different (P > 0.05) from those obtained using a 5‐m vertical tube sampler: replicate sampling units taken with both samplers showed that Ceratium was contagiouly distributed in the vertical water column.