bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature dependence of food intake, ammonia excretion and respiration in Ceriodaphnia reticulata (Jurine) (Lake Kinneret, Israel)*
Authors: GOPHEN MOSHE
Published: May 2006

The abundance of Ceriodaphnia reticulata (Jurine) in Lake Kinneret is restricted every year to the period March to June with a peak in May. The most constant parameter accompanying the peak is temperature with a range of 20–22° C. An attempt was made to clarify whether the estival high average temperatures observed in the epilimnion of this lake (27–28° C) could explain the decrease of the Ceriodaphnia population.

Three physiological parameters: food intake, ammonia excretion and respiration rates, were measured experimentally at three temperatures (15, 22 and 27° C). The dry weight of individuals of the winter and summer populations were measured, and the percentages of egg‐bearing females in the populations were calculated.

It was found that temperature increase accelerates the rates of ammonia excretion and food ingestion. The acceleration was greater in the lower temperature range (15–22° C) than in the higher one (22–27° C). Conversely, the enhancing of respiration rate is higher in the upper temperature range. The resulting deficit of energy at high temperatures causes a reduction in body size and a significant diminution of egg production, which leads to a progressive decline of the population.
A key to larvae and pupae of Sericostoma personatum (Spence) and Notidobia ciliaris (Linné) (Sericostomatidae : Trichoptera) in Britain
Authors: WALLACE I. D.
Published: May 2006

SUMMARY. Certain larvae and pupae have been identified as Notidobia ciliaris (Linné) by rearing field‐collected larvae to the adult stage and by rearing larvae from eggs laid by a female in captivity. The larvae differ in many important respects from larvae of this species described by earlier workers. Characters are provided to distinguish these larvae and their associated pupae from those of Sericostoma personatum (Spence). The habitat and distribution of both species in Britain is outlined.
Chironomid communities in small prairie ponds: some characteristics and controls
Authors: DRIVER E. A.
Published: May 2006

SUMMARY. In a study of small prairie ponds in Central Saskatchewan, chironomid diversity was dependent on the stage of development of the plant community within a moisture gradient. Changes in the moisture regime affect the plant community directly, which in turn influences the diversity of the chironomid community. Rapid or complete water level reduction in a pond maintains a very simple chironomid community, three to ten species, and a simple plant community of two to three dominant species. Increased water levels eliminate emergent and submergent plants, thereby eliminating those chironomid species which live in association with the plants. Pond morphometry (mean depth, maximum depth, surface area) and water chemistry (pH and bicarbonate) showed positive relationships with chironomid diversity. The precise nature of these relationships was not determined.

Chironomid diversity increases gradually from very temporary ponds to permanent ponds, therefore, chironomids can be used as indicators of pond permanency.
Seasonal changes in the abundance and distribution of planktonic rotifers in Grasmere (English Lake District)
Authors: ELLIOTT JUDITH I.
Published: May 2006

SUMMARY. The planktonic rotifers of Grasmere, a small lake in the English Lake District, were studied from August 1969 to December 1972. Twenty‐four species were recorded but five were very rare. The remaining species were divided into three groups according to their seasonal occurrence: spring to autumn species (Keratella quadrata. K. cochlearis, Gastropus stylifer, Asplauduia priodonta. Kellicottia Umgispina, Conochilus hippocrepis)., spring to early summer species (Polyarthra dolichoptera, Synchaeta tremula, S. pectinata, S. stylata, S. oblonga, C. unicornis), summer to autumn species (Polyarthra vulgaris, P. major. Filinia terminalis, S. grandis, Ploesoma hudsoni, Trichocerca capucina, T. similis). The months in which each species was abundant are given.

Keratella quadrata and Filinia terminalis were most abundant in the deepest stratum, Kellicottia longispina and Conochilus spp. were most abundant in the upper and middle strata. Trichocerca spp. showed no pronounced vertical distribution, and all the remaining species were most abundant in the upper stratum. Keratella cochlearis and Kellicottia longispina attained their highest densities over a wide range of temperature and oxygen concentration. Filinia terminalis, Conchihis spp., Asplanchna priodonta. K. quadrata, and Polyarthra spp., attained their highest densities within a narrow range of temperature and oxygen concentration. Optimum ranges are given for each species.

Major changes occurred between 1971 and 1972 when Asplanchna priodonta. Kellicottia longispina, Conochilus unicornis and Filinia terminalis increased in abundance, whilst Keratella quadrata. Gastropus stylifer, C. hippocrepis, Polyarthra spp., Synchaeta spp. and Ploesoma hudsoni decreased in abundance. These changes are discussed in relation to the temperature and oxygen requirements of each species and also to the probable enrichment of the lake after the opening of a new sewage works in June 1971.
Relative abundance and growth of mussels (Mollusca: Eulamellibranchia) in pools 8,9 and 10 of the Mississippi River
Authors: COON THOMAS G. , ECKBLAD JAMES W. , TRYGSTAD PAUL M.
Published: May 2006

SUMMARY. Twenty‐three species of unionid mussels were sampled during the summer of 1975 from a 76‐mile reach of the Upper Mississippi River; this represented eight species fewer than were recorded in a 1930–31 survey for the same section of the river. Of the 244 sites sampled in 1975, mussels were found at 116 sites and the ten most productive sites accounted for 40.8% of the 1205 mussels collected. There were as many as thirteen different mussel species taken from one sampling site. The two most abundant species (Amblema peruviana and Megalonaias gigantea) constituted 54.5% of the mussels sampled in 1975; these two species made up only 8.3% of the 1930–31 survey. Individuals of the twelve most abundant mussel species were aged, and shell‐length growth equations were determined. In addition, shell‐free dry weight growth rate and shell weight growth rate was determined for Amblema peruviana. The calculated annual production for A. peruviana (assuming a mean density of 1 per m2) was 482 mg/m2 shell‐free dry weight, and 14.471 g/m2 shell weight.
The spring development of phytoplankton in Lake Erken
Authors: BOSTRÖM BENGT , PETTERSSON KURT
Published: May 2006

SUMMARY. In Lake Erken there is a regular phytoplankton peak at ice‐breakup in the spring. Pechlaner (1970) studied the spring outburst of 1960. We carried out a similar study in 1973, when the climatic factors were completely different, with only 10 cm of ice and almost no snow. Thus, due to light penetration, there was a high phytoplankton biomass under the ice as early as March.

Stephanodiscus astraea (Ehr.) Grun. and Asterionella formosa Hass. dominated the biomass during the spring development in 1973 instead of the normally dominating S. hantzschii v. pusillus Grun.

The nutrient decrease was slower in 1973 than in 1960. A comparison of carbon assimilation and the decrease of nitrate and phosphate indicate sufficient nutrient supply in 1973. In 1960, the population grew logarithmically until the nutrients became limiting. In 1973, the average biomass was greater, but the mean probable primary production was only half that of 1960. From the activity coefficients for the 2 years it is also clear that, in 1960, S. hantzschii v. pusillus was highly productive during its short but intensive growth period. Its minute size and high surface/volume ratio enabled it to take up nutrients rapidly and efficiently. The chlorophyll content of S. astraea in 1973 was only half as much as that of S. hantzschii v. pusillus in 1960. Since the light conditions under the ice in March 1973 were more unfavourable than during the exponential phase of 1960, production was much lower.
The significance of alkaline phosphatase activity in Lough Neagh
Authors: STEVENS R. J. , PARR MARY P.
Published: May 2006

SUMMARY. A study of the eutrophic Lough Neagh was undertaken to ascertain the use of alkaline phosphatase activity as an indicator of phosphorus‐limited algal growth. Lough Neagh and its surrounding rivers were monitored during 1974 and 1975. Alkaline phosphatase activity increased in the lough when the algal crop increased and depleted orthophosphate to a growth‐limiting concentration. Enzyme activity was appreciable, however, at all other times of the year and may on occasions have been associated with zooplankton. The enzyme activity in the inflowing rivers was much greater than in the lough itself. Depending on enzyme stability the enzyme inputs from rivers could contribute significantly to the lough activity. Sewage disposal works effluent appeared to be a major source of enzyme activity in river water. As the alkaline phosphate activity in Lough Neagh resulted from several sources, increased activity could not be used as a reliable indicator of phosphorus limited algal growth.
The downstream drifting of larvae of Dixa (Diptera: Dixidae) in two stony streams
Authors: ELLIOTT J. M. , TULLETT P. A.
Published: May 2006

SUMMARY. Larvae of Dixa, especially D. puberula Loew., were a significant component of the invertebrate drift in the Walla Brook in southwest England, the Wilfin Beck and the River Duddon in the English Lake District, and the River Estibère in the French Pyrenees. The drifting of the larvae increased markedly at night and showed a definite diel periodicity with maximum numbers usually in the early hours of the night. Seasonal peaks in the density of larvae in the drift frequently occurred in months when adults and especially pupae were present. Most drifting larvae were in the fourth and final instar, and their drift rate usually increased when they were searching for suitable pupation sites.
A sampling device for the invertebrate fauna of aquatic vegetation
Authors: MINTO M. L.
Published: May 2006

SUMMARY. A sampler designed to provide a quantitative estimate of the benthic invertebrates of littoral/sub‐littoral zones dominated by Sphagnum moss is described. Data obtained from a small oligotrophic lake at a depth of 1 m using this sampler are presented. Optimum sample size was determined and samples comprising five sampling units were found to be adequate in terms of the number of invertebrate species present and their relative abundance. Similarity of such samples was greater than 90%.
Uptake and respiration of organic compounds and heterotrophic growth in Pediastrum duplex (Meyen)*
Authors: BERMAN THOMAS , HADAS ORA , KAPLAN BINA
Published: May 2006

SUMMARY. Axenic cultures of Pediastrum duplex, a green alga prominent in Lake Kinneret, Israel, assimilated and respired amino acids, acetate, glucose, glycollate and glycerol under conditions of light or darkness. Increased rates of uptake and respiration were observed in nutrient (P and N) depleted medium. Although ineffective in moderate light (30–100 μ Einstein m−2 s−1) glycerol, glucose and leucine, but not glycollate, stimulated growth and yields under faint light (∼ 2 μ Einstein m−2 s−1). In the dark, glycerol (and sometimes leucine) permitted growth. Kinetic studies with leucine indicated an active uptake mechanism effective at substrate concentrations from 0.5 to 47 μg 1−1.
Absence of pigmentation in corixid bugs (Hemiptera) after the use of the aquatic herbicide dichlobenil
Authors: TOOBY T. E. , MACEY D. J.
Published: May 2006

SUMMARY. Unpigmented nymphs and adults of the corixid bugs Sigara dorsalis and Corixa punctata were found in ponds treated with the aquatic herbicide dichlobenil. Tissue residues accumulated rapidly in nymphs exposed to dichlobenil, and pigmentation was inhibited during ecdysis. However, dichlobenil residues were rapidly eliminated from the tissues of unpigmented nymphs placed into clean water, and pigmentation returned during the following ecdysis.
Ecological studies on Oligochaeta inhabiting depositing substrata in the Irwell, a polluted English river
Authors: EYRES J. P. , WILLIAMS N. V. , PUGH‐THOMAS M.
Published: May 2006

SUMMARY.
Oligochaete worms dominate the macroinvertebrate fauna of the River Irwell, in north west England. The river is polluted by domestic and industrial wastes. Tubificids constituted 86.8% of the worm fauna, with three dominant species; Tubifex tubifex (Müller), representing 43.1% of the total oligochaetes, Limnodrilus hoffmeisteri Claparède, representing 26.8% and Limnodrilus udekcmianus Claparède, representing 16.7%. The Naididae were the next most abundant worms, representing 6.1% of the oligochaete fauna, with Nais elinguis Müller comprising 5.0%.

T. tubifex and L. hoffmeisteri were abundant along the length of the river, but reached their greatest numbers in the organically polluted lower reaches at Agecroft and Salford. The density of L. udekemianus was low in the Irwell above the entry point of the heavily polluted River Roch, but high below this point. N. elinguis was abundant above the Roch entry point and scarce below it.

In the three dominant tubificids, the main population recruitment occurred during the summer months (April to September for T. tubifex, May to November for L. hoffmeisteri and June to October for L. udekemianus). In N. elinguis, there was massive recruitment in April.
A review of the biology of British Naididae (Oligochaeta) with emphasis on the lotic environment
Authors: LEARNER M. A. , LOCHHEAD G. , HUGHES B. D.
Published: May 2006

SUMMARY.
Naidids live in a wide range of aquatic habitats but are particularly important numerically as part of the benthic fauna of rivers with stony substrates. In general they graze on bacteria and algae although some, particularly Chaetogaster spp., are mainly predaceous, and C. limnaei vaghini is a parasite of molluscs, chiefly Gastropoda. Food selection seems to be based largely on particle size although the food quality of the particles within the appropriate size‐range influences rates of growth and reproduction.

Major factors determining the distribution and abundance of naidid species are the nature of the substratum and the presence and kind of vegetation. Plants with a highly dissected form, a thick growth habit, and which permit the greatest periphyton development generally support the most abundant naidid populations. The oligochaete fauna of coarse substrates (stones and gravels) is often dominated by the Naididae but both species‐richness and abundance of naidid populations are generally reduced where fine substrates (silts and muds) occur. The occurrence of worms within the substratum is also determined by its nature; naidids penetrate to depths of 20–70 cm in coarse substrates but rarely penetrate below 6 cm in mud. The principal factor limiting both depth penetration and the dominance of naidids in fine substrates is probably oxygen availability.

Naidids reproduce both asexually and sexually, the former method predominating for most of the year. Asexual reproduction usually involves the budding‐off of zooids but a few species fragment. Sexual reproduction is often infrequent; populations of some species produce few or no sexually mature individuals. In mature worms asexual reproduction virtually ceases. In populations that produce mature individuals there is apparently one sexual generation a year, usually occurring during the summer and autumn. Adults die soon after laying their cocoons.

In general, naidids are most abundant during the summer months when rates of growth and asexual reproduction are stimulated by higher temperatures and a plentiful supply of food. A few species, however, e.g. Nais elinguis and Paranais litoralis, are more abundant in the spring.

The response of naidid species to different kinds of pollution is varied but generally organic enrichment of rivers which have stony substrates results in a considerable (ten‐ to twenty‐fold) increase in naidid abundance. Nais elinguis, N. barbata, N. communis, N. variabilis, and Chaetogaster diaphanus are often abundant in such rivers, the foremost species reaching densities of 200 000 m−2. Nais alpina, N. bretscheri, and N. pardalis appear to be relatively intolerant of organic enrichment. A substantial increase in naidid abundance is also promoted by the deposition of biologically inert particles (coal dust, china clay, sand) on the river bed.

The importance of Naididae in relation to pollution surveillance of fresh waters is discussed.
Spatial variation in epilithic algae in a stony stream (Wilfin Beck) with particular reference to Cocconeis placentula
Authors: JONES J. G.
Published: May 2006

SUMMARY.
Epilithic algae in a small softwater stream in the English Lake District were studied using a direct counting epifluorescence technique. A small trickling filter sewage treatment plant discharged into the stream and cattle grazed in fields adjoining the upper reaches. Both increased the inorganic nitrogen and phosphorus concentrations in the stream but the effect of the cattle was of a more intermittent nature. Cocconeis placentula was the dominant diatom but large numbers of encrusting green, blue‐green and red algae also occurred in samples from the middle reach, which was heavily shaded by trees in summer. Although it was possible to demonstrate the effect of the sewage effluent on the rate of colonization of clean surfaces placed in the stream, it was only during periods of stable water flow that this was reflected in the standing crop of algae on the stones. The Cocconeis counts below the sewage outfall tended to be highest in the autumn whereas those of the other diatoms were highest in the spring. The results were, however, extremely variable and apart from the effect of the nutrient inputs, the Cocconeis standing crops were largely related to the rate of water flow. Counts decreased and the variability between and within stones increased as higher rainfall and flow caused instability and scouring of the stones. A similar decrease in standing crop and high variability occurred in conditions of very low water flow but this could not be explained.
The influence of turbidity on net phytoplankton photosynthesis in some Irish lakes
Authors: JEWSON D. H. , TAYLOR J. A.
Published: May 2006

SUMMARY.
An important influence on gross photosynthetic rates per unit area is the success with which phytoplankton competes for the available light with non‐algal suspended material and dissolved organic compounds. Using a range of Irish lakes, with euphotic zones varying between 0.7 and 20 m and with chlorophyll‐α values between 1 and 860 mg m−3, the effect on gross rates of photosynthesis is analysed for changes in the balance between the factors contributing to light attenuation. Net values per unit area are also likely to be modified in well‐mixed systems as the ratio of light to dark regions in the water column are altered with changes in light penetration. Depth gradients in dark respiration are reported for L. Neagh which vary according to previous light history and nutrient stress. Possible cases of restraint on phytoplankton growth are discussed for optically deep situations.
Laboratory experiments on prey selection by perch fry (Perca fluviatilis)
Authors: FURNASS TREVOR I.
Published: May 2006

SUMMARY.
In laboratory experiments, prey selection of zooplankters by starved perch fry (Perca fluviatilis) from Windermere, English Lake District, is temporally variable and there is usually, in the short‐term, a persistent succession from one actively selected prey species to another. Provided that the prey is visible, the patterns of prey selection are maintained irrespective of the accessibility of the prey. The fish do not optimize their energy intake per effort. The method of observing predation activity by fish shows qualitative and quantitative prey selection as time progresses in great detail.
Seston sedimentation
Authors: REYNOLDS C. S.
Published: May 2006

SUMMARY.
Three experiments are described in which the rates of loss from suspension of Lycopodium spores introduced at the water surface in a large butyl rubber enclosure (‘Lund Tube’) were monitored. Rates of arrival at the mud surface and in sediment traps placed in the water column were also measured. Results obtained by each method are compared with the predetermined intrinsic sinking behaviour of the individual particles. The experiments, which were carried out under differing conditions of water‐column stability (isothermal mixing, thermal microstratification, and autumnal destratification), demonstrate the importance of turbulent mixing in determining the effective settling rate of seston. A simple predictive model is developed to relate sinkinglosses to the vertical extent of broadly defined water layers. Recoveries in sediment traps can give an accurate synopsis of net sedimentation when they are operated in non‐turbulent water layers, but trap performance in turbulent flow is significantly modified by hydrodynamic perturbation generated by the traps themselves.
A simple tubular phytoplankton sampler for vertical profiling in lakes
Authors: NICHOLLS K. H.
Published: May 2006

SUMMARY.
A description is given of a tubular phytoplankton sampler with a self‐activating closing valve. It can be constructed to any length, but a 2‐m or 3‐m sampler is convenient and allows the most important portion of a lake's vertical profile to be examined with relatively few hauls. Samples can be pooled for a single analysis of a sample representing the euphotic zone or other selected interval of depth within a lake. Alternatively, a series of taps in the sidewall of the tube enables subsampling of the contents and consequently, detailed determination of vertical inhomogeneities in phytoplankton distribution. Some data obtained with the sampler from two Ontario lakes are presented.
Biochemical genetics and taxonomy in Plumatella fungosa and P. repens (Bryozoa: Phylactolaemata)
Authors: MUNDY S. P. , THORPE J. P.
Published: May 2006

SUMMARY.
Some authors have recently concluded that, using morphological criteria, the freshwater bryozoans Plumatella repens and P. fugosa cannot be separated and should be regarded as conspecific. To test this conclusion, electrophoretic techniques have been used to examine genetic differences between the two nominate species at several enzyme loci. Significant variation at a malate dehydrogenase locus and three aminopeptidase loci establish beyond doubt that P. repens and P. fugosa are separate but related species. No significant variation was found between two populations of P. repens. Morphological characters for the distinction of the two species are discussed and evaluated.
Composition and zonation of benthic invertebrate communities in a New Zealand kauri forest stream
Authors: TOWNS D. R.
Published: May 2006

SUMMARY.
The macro‐invertebrate fauna of Waitakere River and its tributaries, a northern New Zealand kauri forest stream, was surveyed in January 1974 and January and June 1975, as part of a study on stream community dynamics. This survey and regular samples in the study area provided 144 taxa, almost three times the maximum number previously recorded from a New Zealand stream. Many species were restricted in distribution to a high gradient tributary, or the low gradient mainstream. These did not follow the division into rhithron and potamon families suggested for New Zealand.
A sample holder for decomposing and processing delicate biological materials for scanning electron microscopy
Authors: LAUTENSCHLAGER K. P. , KAUSHIK N. K. , ROBINSON J. B.
Published: May 2006

SUMMARY.
A simple, inexpensive sample holder was developed to permit delicate biological materials (faecal pellets) to be decomposed in aquatic environments and thereafter to be processed by dehydration and critical point drying procedures. Part of the holder itself is used to mount the sample onto specimen studs. Delicate materials are therefore never subjected to physical damage during handling at any stage of their processing for scanning electron microscopy.
Physiological and environmental constraints in the ecology of the planktonic dinoflagellate Ceratium hirundinella
Authors: HARRIS G. P. , HEANEY S. I. , TALLING J. F.
Published: May 2006

SUMMARY.
Constraints upon the vertical distribution of a population of Ceratium hirundinella, in a productive English lake during the summer stratification of 1976, are considered. They are interpreted in relation to vertical gradients of temperature, dissolved oxygen and irradiance, and to rates of photosynthesis and respiration measured as oxygen exchange in long‐ and short‐term exposures. The motile cells tended to aggregate at an intermediate depth in the epilimnion, associated with a relative irradiance level of c. 10% or c. 140 μ einsteins m−2s−1 as measured with a horizontal PAR sensor. Higher irradiances, and conditions below the oxycline, were apparently unfavourable, but the intervening layer was severely compressed at the height of summer stratification, when concentrations of inorganic nitrogen were also minimal. Thus the population apparently passed through a critical period, at which the cellular content of chlorophyll‐α was much reduced. The preferred irradiance level in the lake corresponded to that at which measured rates of net photosynthesis were maximal. Increased rates of oxygen evolution were measured at higher irradiances in very short exposures; this behaviour may be of importance to cells experiencing vertical movement in nature.
The annual cycle of intraovarian egg size and fecundity of the barbel Barbus barbus in the River Severn
Authors: HANCOCK R. S.
Published: May 2006

SUMMARY.
The annual cycle of intraovarian egg size in 124 mature barbel caught during a 3‐year period was investigated. Storage methods, subsampling and measuring procedures were assessed and found to be reliable. Estimates of fecundity were made on thirty‐two barbel containing developing ripening eggs. A new egg separation and counting technique was used modified from the volumetric ratio method described by Bagenal & Braum (1968). Fecundity estimates were found to be accurate by comparison with manual counts. Barbel ovaries contained two egg groups throughout the year. A third large, ripening egg group developed prior to spawning. The diameter of the ripening eggs, measured in arbitrary optical units, was significantly correlated with fork length. Large fish spawned bigger eggs than small fish. Fecundity was logarithmically related to fork length and ovary weight and linearly related to somatic weight. The mean diameter of the ripening intraovarian egg group was also logarithmically related to ovary weight. Heavier ovaries contained proportionally fewer, but larger, ripening eggs than small ovaries.
Diel patterns of reproduction in rotifer populations from a tropical lake
Authors: SAUNDERS JAMES F.
Published: May 2006

SUMMARY.
The diel patterns of reproduction were studied for three rotifer populations from Lake Valencia, Venezuela. Significant departures from uniformity were recorded for egg eclosion and egg deposition rates in Keratella americana and Brachianus calyciflorus, but only from egg deposition rates in B. havanaensis. The existence of non‐random reproduction has practical ramifications for studies of population dynamics and secondary production.
Early composition and biomass of the crustacean Zooplankton in Bough Beech Reservoir, south‐east England
Authors: MUNRO I. G. , BAILEY R. G.
Published: May 2006

SUMMARY.
The crustacean Zooplankton community in Bough Beech, a flooded valley reservoir in south‐east England, was investigated in the early years of impoundment. The nutrient status and phytoplankton were typical of a lowland eutrophic lake, and this was reflected in the composition of the Zooplankton. At any given time, the latter comprised one or two cladoceran and two or three copepod species, of which the cladocerans were generally numerically predominant. Marked alterations in the Zooplankton community occurred in the first 2 years of the study and were related to changes in predation pressure by fishes. By the end of the third year, the composition of the Zooplankton community had stabilized.

The cladoceran biomass was normally in excess of that of the copepods, with maxima in spring and autumn. Peaks in copepod biomass occurred within 2 months of those of the Cladocera.
The use of bird rings for the individual recognition of fish
Authors: BELLAMY G. C.
Published: May 2006

SUMMARY.
Fish bearing celluloid bird rings on the anterior edge of the dorsal fin can be recognized individually in the field for several weeks. Grayling Thymallus thymallus, over 20 cm long, in a fast‐flowing river retained recognisable rings for a mean of 47 days. Brown trout Salmo trutta, retained rings for comparable periods. Rings could be seen at distances up to 10 m, irrespective of the orientation of the fish to the observer. This marking technique compares favourably with others.
An opto‐electronic sediment detector and its use in the chemical micro‐profiling of lakes
Authors: CUNNINGHAM C. R. , DAVISON W.
Published: May 2006

SUMMARY.
A device for detecting (with minimum disturbance) the sediment‐water interface in lakes is described. It is based on a commercially available slotted ‘opto‐switch’ incorporating a light emitting diode and a phototransistor. The design of an audible and visual indicator is given. Possible uses are discussed and an example of chemical micro‐profiling near to the sediment with the aid of the device is reported.
Colonization of artificial substrata by macro‐invertebrates in a stream and variations according to stone size
Authors: KHALAF G. , TACHET H.
Published: May 2006

SUMMARY. Plastic cages containing artificial substrata were placed on the stony bottom of a stream in a section where the environmental conditions appeared to be homogeneous. The section was divided into eight equal sub‐sections (A‐H) and four cages were placed in each sub‐section. The stone‐size of the artificial substrata was similar within each cage but differed between the four cages with average diameters of 14, 24, 48 and 96 mm, respectively. The baskets were removed one month later and the catches of macro‐invertebrates were recorded.

Analysis of the catches (density and number of taxa in each cage) revealed no significant differences in connection with the position of the cages in the section of stream. Cages with 48‐mm stones contained the least abundant fauna. The taxa which colonized cages with 14‐ or 24‐mrn stones were more numerous than those collected from cages with 48‐ or 96‐mm stones.

Statistical analysis by laxon confirmed the preceding results. Variability in connection with the position of the cages along the section of stream was never significant. A little more than half the taxa were distributed independently of stone size but always showed a contagious type distribution. The density of the other taxa was higher, either in cages with 14‐ or 24‐mm stones (particularly Gammarus) or only in cages with 96‐mm stones (especially Hydropsyche). Only one taxon was more abundant in cages with 48‐mm stones, the type of substratum in which the overall density was lowest.

Catches in the cages were not the same as those taken with a Surber sampler because the two samplers did not take samples from the same habitats and also because the baskets offered a more specialized habitat than the surrounding bottom. The basket with 24‐mm stones gave the least distorted picture of the natural population.
Quantification and characterization of sedimenting particulate organic matter in a shallow hypereutrophic lake*
Authors: MOLONGOSKI JOHN J. , KLUG MICHAEL J.
Published: May 2006

SUMMARY.
Sedimenting seston was collected in May‐November 1976 and 1977 in sedimentation traps anchored 0.5 m above the pelagic sediments of hypereutrophic Wintergreen Lake. Sedimentation rates differed greatly in the two years studied, ranging from 2.7 to 19.3 g m−2 day−1 in 1976 and from 2.6 to 9.5 g m−2 day−1 in 1977. Because of the shallowness of the lake (maximum depth 6.5 m), the quantity and quality of sedimenting particulate organic matter (POM) was closely linked to the production dynamics of the phytoplankton. Chemical analyses indicated that the sedimenting POM was planktonic in origin and, in contrast to that of many deeper lakes, was dominated by protein. Short sedimentation distances coupled with the close proximity of the anaerobic hypolimnion to the photic zone ensured that the majority of sedimenting POM reached the sediments in a relatively undegraded form.
Light and pressure in two freshwater lakes and their influence on the growth, morphology and depth limits of Hippuris vulgaris
Authors: BODKIN P.C. , POSLUSZNYand U. , DALE H. M.
Published: May 2006

SUMMARY.
Hippuris vulgaris was found growing down to a depth of 6 m in two clear‐water lakes. Mean summer water temperatures of the epilimnia were 15–18°C. Midsummer photosynthetically available radiation, (PAR 400–700 nm) at 6 m was 100 μeinsteins m−2s−1. In the laboratory, shoots of H. vulgaris continued to elongate at temperatures of 15 and 20°C and at pressures of 1.0, 1.8 and 2.3 atm. (corresponding to 0 m, 8.0 m and 13.3 m depths of water, respectively) providing PAR was kept above 100 °E m−2s−1. Leaf primordia were initiated further from the apex in shoots grown under a pressure of 2.3 atm., but the site of initiation is not critical for the subsequent growth of leaves in H. vulgaris. Lacunae in shoots grown under a pressure of 2.3 atm. were also larger than those in control shoots, implying that pressure does not constrict air spaces. Root growth is not inhibited by a pressure of 2.3 atm. Field measurements and laboratory experiments indicate that in warm water, PAR is the environmental factor most likely to control the depth limits of H. vulgaris in the field.
Density estimation for water‐striders (Heteroptera: Gerridae)
Authors: SPENCE JOHN R.
Published: May 2006

SUMMARY.
Estimates of relative and absolute abundance in field populations of two Gerris species were compared using regression techniques. Separate equations for each gerrid size class allow prediction of population density from timed‐catch sampling. Presence or absence of vegetation markedly affected capture rates, but capture rates were not affected by Gerris species or type of emergent vegetation. Availability for capture varied with gerrid leg length; this relationship can be used to estimate availability constants for other water‐strider species.
Habitat selection and association of stream insects: a multivariate analysis
Authors: SHELDON ANDREW L. , HAICK ROGER A.
Published: May 2006

SUMMARY.
Habitat selection and interspecies associations of stream insects were evaluated from a set of quantitative benthos samples and habitat measurements (velocity, depth, substrate, quantities of fine and leafy detritus) from a mountain stream. Substrate was characterized by an in situ grid method which effectively describes the size and distribution of the larger surficial materials within each sample unit. A principal components ordination of samples as characterized by abundance data over all species accounted for 54% of the total variance in three dimensions but implied continuous rather than discrete faunal change with habitat. Gradients in the habitat could not be identified with real confidence. Canonical correlation analysis identified three significant habitat‐fauna interactions. The first corresponded to the gradient from eroding to depositing substrates and included detritus abundance, the second distinguished areas of fine from leafy detritus and the third appeared to include velocity‐stone size interactions. A graphical technique based on ordination of physical data and clustering of associated species adequately summarized the distribution of five Ephemerella mayflies. The multivariate and interactive nature of stream bottom environments is discussed for problems involving prediction and experimental design and control.
Biomass and annual production of the freshwater mussel Elliptio complanata in an oligotrophic softwater lake
Authors: STRAYER DAVID L. , COLE JONATHAN J. , LIKENS GENE E. , BUSO DONALD C.
Published: May 2006

SUMMARY.
An extensive survey of Mirror Lake, New Hampshire, was carried out by divers with SCUBA to assess the importance of the freshwater mussel Elliptio complanata in this softwater lake ecosystem. Density (0.032 adults m−2), biomass (52 mg m−2 as dry organic matter) and annual production (6.4 mg m−2 as dry organic matter) of the mussel population are low when compared with results from other studies, corresponding with the general observation that mussels are scarce in soft, oligotrophic waters. We reject the traditional view that the low mussel density is a result of low calcium concentrations in Mirror Lake, and propose that mussel populations may be regulated by a scarcity of appropriate fish hosts in unproductive lakes. Elliptio complanata is probably not important in the metabolism or biochemistry of the Mirror Lake ecosystem.
A portable system for measuring water temperature, conductivity, dissolved oxygen, light attenuation and depth of sampling
Authors: BENHAM D. G. , GEORGE D. G.
Published: May 2006

SUMMARY.
This paper describes the design, construction and testing of a portable monitoring system capable of measuring water temperature, conductivity, dissolved oxygen, light attenuation and depth of operation. The unit is powered by rechargeable batteries and can be used to provide instantaneous readings or continuous records of each variable when used with a suitable chart recorder. Circuits for measuring conductivity and light‐ratio are of a novel design. The conductivity circuit measures conductance by the voltage drop across a low‐value resistor connected in series with the conductivity cell. The light‐ratio circuit measures light intensities by digitizing signals from two photocells and comparing their ratios over short periods of time. The paper includes examples of results obtained with the instrument in a wide range of applications and compares the performance of the Mackereth oxygen electrode with, and without, a small water‐circulating attachment.
Algal bioassay of the water from two linked but contrasting Welsh lakes
Authors: HAPPEY‐WOOD CHRISTINE M. , PENTECOST ALLAN
Published: May 2006

SUMMARY.
A comparison of the potential water fertility of two linked lakes, Llyn Peris and Llyn Padarn, was carried out over a year using Asterionella formosa as the test organism in batch cultures. In unenriched lake water, growth was more rapid in Padarn water during autumn‐winter‐spring, but there was no significant difference between growth in water from the two lakes during the period of thermal stratification. Mean growth rates in treatments with additions of nitrogen and chelated iron were not significantly different from unenriched water samples, both between treatments and lakes during thermal stratification. Growth in water from both lakes was increased greatly by addition of phosphate. Maximum growth rates occurred on addition of nitrogen, phosphate and chelated iron, and there was no significant difference between growth rates in this treatment for the two lakes throughout the year. Comparisons of mean growth rates in bioassays by Tukey's interval estimate showed significant differences between other treatments and the two lakes. The potential fertility of water samples from the two lakes differs more during mixed water conditions than in the period of thermal stratification.

Inhibition of A. formosa growth was recorded four times in unenriched filtered water from Peris, once on addition of nitrogen and once on addition of iron. Inhibition was alleviated by the addition of nutrients.

The addition of diluted sewage effluent which enters the drainage system between the two lakes, resulted in similar rates of growth of A. formosa in water from both lakes.

Results of the bioassays are discussed in relation to differences in phytoplankton between the two lakes. Although A. formosa will grow in samples of unenriched lake water from Peris, other features, including a shorter retention time of water, lower level of incident radiation and, occasionally, inhibitory substances in the lake water, contribute to the rare occurrence of this diatom in Peris. Padarn is enriched by sewage effluent which aids the growth of A. formosa.
Population dynamics and production of the tropical freshwater shrimp Caridina nilotica (Decapoda: Atyidae) in the littoral of Lake Sibaya
Authors: HART R. C.
Published: May 2006

SUMMARY.
Seasonal changes in population structure, standing stock levels and production of Caridina nilotica were studied at three sites in the littoral margins of subtropical Lake Sibaya between January 1975 and March 1976. Average population density at these sites declined from a maximum of c. 1400 to a minimum of c. 350 individuals per m2 (3.4–0.4 g m−2 dry wt) during the study, possibly as a result of emigration into peripheral vegetation inundated by rising lake levels.

Shrimps bred perennially and, although egg stocks and instantaneous birth rates (b) were highest during summer, no corresponding increases in populaton density were observed, suggesting that the seasonally higher birth rates were offset by higher mortality rates. Population size structure and size‐specific sex ratios did not change seasonally to any marked extent. Relative abundance declined with size and females grew larger than males. Clutch size increased linearly as a function of female carapace length.

Estimates of overall mean annual somatic production (g m−2 year−1 dry wt) for the three sites between January 1975 and January 1976 ranged between c. 132 (egg‐ratio method), 37.5 (summation of growth increments) and 24 (Hynes‐Hamilton method) at an annual mean standing stock level of 2.7 g m−2 dry wt (calorific value, 20.34 kJ g−1 dry wt). Production at sites 1, 2 and 3 decreased in line with declining annual mean standing stocks (5.32, 3.67 and 0.23 g m−2, respectively). The growth increment method gave an overall mean annual P/B value of 13.9. Egg production amounted to a further 5.6, 3.6 and 0.1 g m−2 year−1 dry wt (calorific value, 28.01 kJ g−1) at sites 1, 2 and 3, or 2.7 g m−2 year−1 on average.
The resorption of zinc from scales of sea trout (Salmo trutta) during the upstream spawning migration
Authors: O'GRADY K. T.
Published: May 2006

SUMMARY.
The concentration of zinc in the scales of unripe, prespawning, estuarine sea trout was compared to that in the scales of sea trout about to spawn in fresh water. Zinc concentrations in scales from estuarine sea trout were in agreement with a published concentration factor but those from fresh water were not — a 43–52% reduction in the zinc concentration of the scales was observed. This withdrawal of trace metals from scales was also likely for iron but these data were less conclusive. This reclamation of trace metals from scales may represent the withdrawal of stored nutrients from body reserves to be used in gonad development and maturation.
The eutrophication of Cayuga Lake: a historical analysis of the phytoplankton's response to phosphate detergents
Authors: GODFREY PAUL JOSEPH
Published: May 2006

SUMMARY. Phytoplankton surveys of Cayuga Lake over the past 60 years indicate that summer algal crops have doubled and spring algal crops have increased 20‐fold. The pattern of algal seasonal succession has changed from a summer maximum comprised of a mixture of diatoms, greens and blue‐greens to a spring maximum comprised of diatoms followed by diminished summer levels with dominance by greens and blue‐greens. Summer algal standing crop and the shift to a spring pulse are shown to be related phenomena resulting from the pattern of phosphorus loading to the lake. The combination of data on algal biomass, chlorophyll and Secchi disc transparency serve to describe the long‐term trend in the lake's trophic state and demonstrate a large increase in algal standing crop in the period roughly coincidental with the advent of phosphorus‐based detergents. The increase in algal standing crop from pre‐1940 levels to present levels closely corresponds with that predicted by the Oglesby—Schaffner regression model from the increase in phosphorus loading due to phosphorus‐based detergents.
The macro‐invertebrate fauna of a small Andean stream
Authors: TURCOTTE P. , HARPER P. P.
Published: May 2006

SUMMARY. The benthic fauna of a small headwater stream in the Amazon drainage in Ecuador was studied from August 1976 to July 1977. The sampling station was at an altitude of 3300 m in a typical paramo habitat of constant and cool temperatures. The fauna is dominated numerically by Hydracarina, Insecta, Copepoda and Oligochaeta, The major insect groups are Ephemeroptera, Plecoptera, Trichoptera, Elmidae (Coleoptera) and Chironomidae (Diptera). Benthos densities followed a bimodal pattern of rapid decreases and intervening gradual recoveries; similar patterns occur in most taxa, but are more pronounced in smaller animals such as Copepoda and Hydracarina. An analysis of the size‐frequency distribution of three species of mayfly, two of stonefly and six of caddisfly suggest non‐seasonal life‐cycles except for Anacroneuria sp. Spates are thought to be the major factor regulating benthic densities in such non‐seasonal environments.
Nutrient retention and transformation in relation to hydraulic flushing rate in a small impoundment
Authors: TURNER RALPH R. , LAWS EDWARD A. , HARRlSS ROBERT C.
Published: May 2006

SUMMARY. The fluxes of water, chloride, silicale and various forms of nitrogen and phosphorus into and out of a 3925 ha impoundment (Lake Taiquin) in north Florida were examined over a 3 year period. Annual hydraulic flushing rates for the lake varied by a factor of more than 2 during the study period and provided an opportunity to examine the effect of flushing rate on nutrient cycling within the lake. The results support the hypothesis that nutrient retention and transformation in lakes and impoundments with high flushing rates (> 1 year‐1) are appreciably influenced by annual variations in flushing rates. Higher fractions of input silicate and total phosphorus were retained by Lake Taiquin during the years with average flushing rates (8 year‐1) than during a year with abnormally high flushing rate (16 year‐1). Nitrogen was not appreciably retained during any of the three study years, and thus N: P ratios in the lake outflow were higher than in the inflow.

Phytoplankton productivity was appreciably higher (70%) during the year with the higher flushing rate, apparently in response to higher reactive phosphorus concentrations in the lake and perhaps to a higher standing crop of phytoplankton during that year. Reactive phosphorus and dissolved inorganic nitrogen inputs could account for only about 30% and 25%, respectively, of the phosphorus and nitrogen required to support observed photosynthetic rates in all three study years. Recycling of nutrients apparently accounted for most of the remainder, although nitrogen fixation could not be ruled out as a factor in the nitrogen budget.
The impact of zooplankton feeding on the epilimnetic bacteria of a eutrophic lake
Authors: PEDRÓS‐ALIÓ CARLOS , BROCK T. D.
Published: May 2006

SUMMARY. The members of the zooplankion eat bacteria in natural systems, but the impact of this mechanism of removal of bacterial biomass on the bacterioplankton of freshwaters is unknown. Zooplankton abundance and biomass were followed for 2 years in Lake Mendota. Bacterial biomass and heterotrophic production were also assessed. Feeding of zooplankton on bacteria was measured by a cell counts method in 1979 and using radioactively labelled natural assemblages of bacteria in 1980. Total feeding was calculated and was found to account for l‐60% of the bacterial biomass daily. Annually, it accounted for 1–10% of the bacterial heterotrophic production. Since bacterial biomass does not change significantly from year to year and yet bacterial production is very high compared to feeding by zooplankton, mechanisms other than feeding must exist which remove biomass from the epilimnetic bacteria in larger amounts.