bluuebunny/crossref_metadata_2025 huggingface dataset:
A field technique for the determination of zooplankton grazing on natural bacterioplankton
Authors: BJøRNSEN PETER KOEFOED , LARSEN JENS BRENNER , GEERTZ‐HANSEN OLE , OLESEN MICHAEL
Published: May 2006

SUMMARY. 1. A method for the determination of zooplankton community grazing rates on natural populations of bacteria is described.

2. Undisturbed zooplankton samples were incubated with 3H‐thymidine‐labelled bac teriioplankton, and animals and their food subsequently separated by size.

3. Prehandling of zooplankton by concentration before incubation reduce the grazing rates by a factor ranging from three to four.

4. Time series experiments showed that appropriate incubation periods ranged from 40 min at 14°C to 60 min at 10°C.

5. Spatial variability in the zooplankton was the main source of the overall standard error. This was considerably reduced by using composite samples.
Fluxes of free amino acids in three Danish lakes
Authors: JøRGENSEN NIELSO. G.
Published: May 2006

SUMMARY. 1. Heterotrophic assimilation rates and concentrations of dissolved free amino acids (DFAA) were followed during diel studies in the eutrophic Lake Mossø, Lake Esrom and Lake øm in spring and summer in 1982. In all three lakes, three to four fold diel variations in concentrations and assimilation rates were measured. These fluctuations appeared to be iindependent of phytoplankton and bacteria production. Pools of DFAA varied from 380 nM (Lake Mossø) to 2430 nM (Lake ørn), with serine, glycine, alanine and ornithine as dominant free amino acids.

2. When similar water samples were incubated in a natural light‐dark cycle or in total darkness, different pools of DFAA were measured in light and dark.

3. Decomposition of organic matter or zooplankton activity (rather than e.g. phytoplankton exudates) appear to be responsible for the concentration changes.

4. Observed discrepancies between simultaneous concentration changes and assimilation rates are discussed in relation to the applied tracer procedure and the concentration measurements.

5. Assimilation of DFAA sustained from 6% to 25% of the bacterial carbon requirement, corresponding to 2–12% of the phytoplankton production in the lakes.
Life history and body size evolution in Holopedium gibberum Zaddach (Crustacea, Cladocera)
Authors: TESSIER ALAN J.
Published: May 2006

SUMMARY. 1. Body size, development, sheath size and relative egg size were examined in two populations of Holopedium gibberum Zaddach. The populations were chosen because of differences in juvenile versus adult mortality.

2. The population subject to food limitation and predation from icthyoplankton (high juvenile mortality) exhibited large size at birth and maturity, large sheath size, and eggs which were relatively large compared to the adult. In contrast, individuals in the population exposed to predation by golden shiner (high adult mortality) were smaller at birth and maturity, had a smaller sheath, and produced relatively small eggs.

3. I contrast body size and relative egg sizes of these H. gibberum populations with literature values for all Cladocera, and propose a general hypothesis for the evolution of relative egg size in Cladocera.
The spectral distribution and attenuation of underwater irradiance in Tasmanian inland waters
Authors: BOWLING L. C. , STEANE M. S. , TYLER P. A.
Published: May 2006

SUMMARY.1. Measurements were made of the attenuation and spectral distribution of downwelling and upwelling photosynthetically‐available radiation (PAR) in all the principal types of natural waters found in Tasmania.

2. Most lakes in the State are clear and non‐turbid, with water itself and the low concentrations of gilvin being the principal determinants of the green underwater light climate. Many others are deeply coloured by dissolved and colloidal organic material (gilvin, gelbstoff) which rapidly attenuates short wavelengths, specifying a shallow, predominantly red euphotic zone.

3. A spectrophotometric measure of colour, the absorption coefficient at 440 nm, is statistically related to measurements on the platinum scale with good precision.

4. Few Tasmanian lakes are turbid but in those that are the underwater light climate is almost identical to that of non‐turbid, humic lakes.

5. Reflectance,R, varied with depth but not in the asymptotic way previously encountered. A linear relationship existed between the scattering coefficient,b, and nephelometric turbidity, but not at the approximate 1:1 ratio reported elsewhere.

6. Most Tasmanian lakes are oligotrophic or dystrophic and phytoplankton rarely influenced the underwater light field.

7. Seasonal variation in optical character is not great in natural lakes and their optical properties and light fields can be used typologically.

8. Simple and multiple regression analysis showed that Secchi depth was a poor predictor of euphotic depth but the optical properties and the underwater light field of inaccessible lakes could be reasonably predicted from laboratory measurements made on small water samples, using regressions developed for a wide range of lake types and by reference to the quantaradiometric scans of lakes with comparable optical properties.

9. An optical classification of Tasmanian lakes made by cluster analysis agreed reasonably well with one based on edaphic, vegetational and chemical criteria.
The consumption of eggs of the perch, Perca fluviatilis L., by macroinvertebrates in the field
Authors: DIAMOND MARK , WAKEFIELD PHILIP M.
Published: May 2006

SUMMARY. 1. Perch egg masses, in a late stage of development, were collected from a small stillwater and the composition of the egg masses and the number of invertebrates which colonized them was recorded.

2. All of the invertebrates that colonized the egg masses were tested serologically for the presence of perch eggs and the ability of some invertebrates to eat live and dead perch eggs in the laboratory was determined.

3. Of the nineteen taxa that colonized the egg masses, only two species of flatworm and three species of caddisfly larva ate perch eggs in the field and, of these, only one genus of caddisfly larva ate live eggs in the laboratory.

4. It is concluded that the invertebrates present were not important predators of perch eggs.
Ovipositional behaviour ofSimulium argyreatumandS. variegatumand its relationship to infection by the fungusErynia conica(Entomophthoraceae)
Authors: HYWEL‐JONES N. L. , LADLE M.
Published: May 2006

SUMMARY.1. At two sites in DevonS. argyreatumandS. variegatumonly oviposited on water‐splashed boulders. The oviposition season was from 15 March to 9 November at Steps Bridge and from 28 March to 7 December at Fingle Bridge. Flies laid eggs only during a brief period after sunset.

2. Flies infected with the fungusE. conicareturned to the oviposition sites at the same times as healthy flies, but infected flies appeared to be unable to lay eggs.

3. At least 10.9% of healthy flies were found to have infective conidia ofE. conicaon their wings after laying eggs.
The role of fish in the regulation of nutrient cycling in Lake Balaton, Hungary
Authors: TÁTRAI ISTVÁN , ISTVÁNOVICS VERA
Published: May 2006

SUMMARY. 1. In 1984 an enclosure experiment was carried out in order to elucidate the importance of nutrient supply from fish to phytoplankton during the critical summer period in eutrophic Lake Balaton. One enclosure was stocked with fish and the other left empty.

2. Two peaks were recorded in primary production reaching maximum values in the fish enclosure.

3. In the enclosure with fish, inorganic nitrogen concentrations increased gradually till the end of the experiment, with ammonia making up the largest component. Lower dissolved phosphorus concentrations in the fish enclosure, with its higher primary production rate, may indicate an intense cycling of this nutrient.

4. The biological and chemical changes occurring in the enclosure suggest that bream removal can be an effective tool in water quality control for Lake Balaton.
Respiration studies and population metabolism of the gastropod Theodoxus jordani (Sowerby)
Authors: AL‐DABBAGH KHALID Y. , LUKA JAMAL Y.
Published: May 2006

SUMMARY. 1. The oxygen consumption of the gastropod snail T. jordani was determined at six different temperatures corresponding to those experienced in the field.

2. The respiration rate increasing linearly with increasing tissue weight at all temperatures studied. Regression equations describing the respiration rate‐live weight relationship were significantly different (P<0. 001).

3. The respiration rate‐temperature relationship was linear for seven weight classes of the population. The extent of change in the respiration rate with increasing temperature differed between the different weight classes. The Q10 value was highest (2.5) for the smallest weight class and decreased with increasing size.

4. The annual respiratory loss by the whole population was estimated to be 334.75 kJ m−2.
The incidence of predation on lake‐dwelling leeches
Authors: YOUNG J. O. , SPELLING S. M.
Published: May 2006

SUMMARY. 1. Erpobdella octoculata (L.), Glossiphonia complanata (L.) and Helobdella stagnate (L.) were eaten readily by larval and adult dytiscid beetles, larval caddisflies and Sialis, nymphal odonatans and various fish in laboratory experiments.

2. A serological technique showed that very few lake‐collected specimens of these predatory taxa, plus triclads, leeches and stone fly nymphs, had been feeding on leeches.

3. A literature survey of lake studies on fish diet indicated that usually less than 6% of individuals with gut contents had eaten leeches. Few detailed records of waterfowl feeding on leeches have been documented.

4. It is concluded that predation pressure on lake‐dwelling leeches is light, and is more severe from fish than invertebrates, less on populations inhabiting stony shores than in vegetation, and greater on the erpobdellid than the two glossiphoniid species.
Gemmules of Anheteromeyenia ryderi and Heteromeyenia tubisperma (Porifera: Spongillidae) from southern New England undergo diapause
Authors: BAZER LAURENCE J. , FELL PAUL E.
Published: May 2006

SUMMARY. 1. The annual cycle of the freshwater sponge, Anheteromeyenia ryderi, was studied in a seepage pond in Connecticut. The adult form of the sponge persisted throughout the year, although some specimens at the edge of the pond degenerated by late summer. During the middle of the winter, adult sponges had a simplified tissue morphology with reduced numbers of flagellated chambers.

2. Gemmules of A. ryderi were also present during all seasons. Gemmule germination occurred during the spring, and some specimens produced new gemmules by late spring.

3. The gemmules of A. ryderi underwent a protracted diapause which was broken under both natural and laboratory conditions by several months exposure to low temperatures (≤5°C).

4. The gemmules of Heteromeyenia tubisperma were also shown to undergo diapause, but in this case diapause was broken by a relatively short cold treatment (1 month).
The role of periphyton abundance and quality in the microdistribution of a stream grazer, Helicopsyche borealis (Trichoptera: Helicopsychidae)
Authors: VAUGHN CARYN C.
Published: May 2006

SUMMARY. 1. A series of laboratory and field experiments was performed to determine if the preference of larvae of Helicopsyche borealis (Trichoptera: Helicopsychidae) for exposed rock surfaces in streams was related to patchiness of periphyton food.

2. At low current velocities in the laboratory larvae preferred food‐saturated as opposed to food‐depleted portions of substrata and drifted off the substratum in response to low food levels.

3. When offered a choice of three potential foods—a diatom, a green filamentous or a blue‐green filamentous alga—larvae showed no preference.

4. Larval densities on artificial subtrata in field experiments were highest in areas of high algal chlorophyll a.

5. In laboratory experiments more adults emerged from cultures containing green algae or diatoms than cultures with blue‐green algae or bacteria alone.

6. Periphyton quality was not as important as abundance in controlling H. borealis microdistribution. By selecting exposed surfaces of rocks, H. borealis larvae place themselves in the microhabitat most likely to contain both abundant and high quality food patches.
Zooplankton associations in some Ethiopian crater lakes
Authors: GREEN J.
Published: May 2006

SUMMARY. 1. The zoopiankton associations in five crater lakes in Ethiopia were examined in April 1984. The two least alkaline lakes had the most diverse zoopiankton.

2. The large diaptomid copepod Lovenula africana was present in the lakes with alkalinities between 10 and 63 meq l−1, but was absent from Lake Chitu (239 meq l−1).

3. The contribution of the zoopiankton to the nocturnal deoxygenation of Lake Aranguadi is negligible.
Diet and predation by three leaf‐associated stoneflies (Plecoptera) in an Arkansas mountain stream
Authors: FEMINELLA JACK W. , STEWART KENNETH W.
Published: May 2006

SUMMARY. 1. Life cycles, food habits, mouthpart morphologies, prey preferences, and predator‐prey size relationships were investigated for the three most common stoneflies in leaf packs in the Little Missouri River, Arkansas: Clioperla clio (Newman), Isoperla namata Prison, and Perlesta spp. Each species was univoltine and had a fast seasonal cycle, with extended egg or nymphal diapause, rapid nymphal growth and emergence in spring to early summer.

2. Foregut analysis showed predictable dietary shifts by C. clio and Perlesta spp., from detritus and diatoms in early instars to invertebrate prey in later instars. Isoperla namata fed facultatively on insects, detritus and diatoms, with no conspicuous ontogenetic shifts. The mouthparts of all three species strongly reflected their diet.

3. Electivity analysis indicated opportunistic feeding by the three species, with feeding rarely differing significantly from random.

4. Sizes of stonefly predators and their ingested prey were highly correlated (P<0.01). However, rather than shifting toward larger prey sizes, growing predators expanded their size thresholds and continued to include numerous small prey items in their diet. Prey choice was governed most directly by prey availability, because stoneflies selected the most abundant groups, irrespective of size or taxon.

5. The likelihood of competition among the three stoneflies for prey was minimized by timing of their life cycles, differential food use and probably the temporary nature of leaf pack habitats.
Variations in carbon fractions within a dimictic and a meromictic basin of the Junius Ponds, New York
Authors: PENDL MICHAEL P. , STEWART KENTON M.
Published: May 2006

SUMMARY. 1. The Junius Ponds, a unique series of proximate glacial kettle basins located between the cities of Rochester and Syracuse. New York, U.S.A., contain basins of dimictic and meromictic nature. This study focused upon differences in partitioning of total inorganic carbon (TIC), paniculate organic carbon (POC), and dissolved organic carbon (DOC) within the dimictic Junius Pond 7 (JP7, ∼8m) and the meromictic Junius Pond 5 (JP5, ∼17m).

2. For TIC, variations with depth were much greater in JP5 than in JP7. However, seasonal variations were greater in JP7 than in JP5. We attribute these variations to differences in the mictic nature of the basins.

3. Concentrations of POC were substantially less in the relatively clear mixolimnion of JP5 than in the epilimnion of JP7. Distinct POC layers formed at the oxic‐anoxic boundary in both basins during late summer.

4. The lower monimolimnion of JP5 is believed to have the warmest water occurring under ice (8.2–8.6°C) of any natural body of water in the continental United States east of the Mississippi River. The monimolimnetic region of JP5 has unusually low DOC:POC ratios of ≤1:l.
Suspended bacteria in calcareous and acid headstreams: abundance, heterotrophic activity and downstream change
Authors: RIMES CARRIE A. , GOULDER R.
Published: May 2006

SUMMARY. 1. Concentration of total suspended bacteria and heterotrophic activity (as turnover rate and turnover rate per bacterium for glucose assimilation by a trace‐addition approach) were determined at distance intervals along four high‐trophic‐status calcareous headstreams in the Yorkshire Worlds and along four low‐tropic‐status acid headstreams in the Galloway Hills.

2. Mean concentration of suspended bacteria was marginally greater in the calcareous streams while turnover rate and turnover rate per bacterium were substantially greater.

3. Further determinations of heterotrophic activity (as turnover rate, turnover rate per bacterium, Vmax and Vmax per bacterium for glucose mineralization by a kinetic approach) supported the conclusion that heterotrophic activity was greater in the calcareous streams.

4. Mean cell volume of suspended bacteria, measured by electron microscopy, was found to be greater in the calcareous streams.

5. In the calcareous streams the concentration of total bacteria and turnover rate usually increased substantially, in a straight‐line relationship, with distance downstream from the source. In the acid streams such downstream increase was less usual, the rate of increase per unit length of stream was less, curvilinear relationships were more frequent and on some occasions downstream decrease was observed.

6. The calcareous and acid streams thus formed two distinct groups on the basis of heterotrophic activity, cell volume and rate of downstream increase of suspended bacteria. This division was not necessarily caused solely by difference in pH but might be due to the combined effects of the many environmental variables which change in parallel with pH.
Species segregation during predator evasion in cyprinid fish shoals
Authors: ALLAN JOHN R. , PITCHER TONY J.
Published: May 2006

SUMMARY. 1. When a predator attacks a mixed‐species group, individual prey arc faced with a conflict between retaining the advantages of large group size and the disadvantages of remaining among aliens. Experiments were designed to show how this conflict is resolved in fish shoals.

2. Simulated attacks with a model predator were made upon mixed and single species shoals of three cyprinid species under semi‐natural conditions in a fluvarium.

3. Measurements of elective group size, neighbour identity and distance, and encounters within and between species revealed behaviour which sorted fish into species at the onset of predator attack.

4. A control experiment demonstrated the same effect for fish of matched size.

5. The value to the individual of segregative behaviour in response to predator threat is discussed.
Fish communities in the perennial wetland of the Sudd, southern Sudan
Authors: HICKLEY P. , BAILEY R. G.
Published: May 2006

SUMMARY. 1. Cyperus papyrus and Typha domingensis swamps were recognized as the major ecological zones in the perennial wetland of the Sudd.

2. Fish sampling, chiefly by gill‐netting and electric fishing, was concentrated in the open‐waters of channels and lakes together with submerged, fringing and marginal vegetation in the accessible papyrus zone. Sixty‐two species were recorded including fifteen catfishes. thirteen characoids, seven cyprinids, seven mormyrids and seven cichlids.

3. The highest diversity and abundance of tishes was obtained in the shallow Sudd lakes which revealed considerable uniformity in population structures. The most numerous species in gill‐nets were Alestes dentex, Synodontis frontosus and S. schall, whereas Heterotis niloticus, Mormyrus cashive and Distichodus rostratus assumed importance in terms of biomass. Micralestes avutidens and cichlids were abundant among the small fishes inhabiting fringes of Eichhornia crussipes, and air‐breathing species occurred beneath the vegetation mat.

4. Flowing‐water habitats exhibited a similar but restricted fauna. Catches were dominated by Synodontis frontosus in open‐water and by Micralestes acutidens and Chelaethiops bibie in the margins. The latter species was shown to have a clear preference for running water.

5. Peak catches in a representative river‐lake could be interpreted as the arrival of fish for breeding or their migration through the lake for reproduction elsewhere. The capture of fry or juveniles of many species in fringing or marginal vegetation indicates that the permanent floodplain of the Sudd provides suitable spawning and rearing grounds.

6. Access to the extensive Typha zone was limited but from available evidence it was inferred that air‐breathing fishes, notably Heterotis and Gymnarchus, may penetrate the swamps to reach areas remote from perennial transmission channels.
A new window trap used in the assessment of the flight periods of Chironomidae and Simuliidae (Diptera)
Authors: JÓNSSON ERLENDUR , GARDARSSON ARNTHÓR , GÍSLASON GÍSLIMÁR
Published: May 2006

SUMMARY. 1. A window trap is described which has been found useful in the study of the fight periodicity of chironomids and simuliids. the trap is simple to construct and can be operated in high winds.

2. Window traps were operated in 1977 and 1478 at Lake Myvatn. Iceland, when thirty‐nine chironomid species and two simuliid species were caught. Most of the chironomids had two peaks in flight activity per year. e.g. Eukiefferietla minor, Cricotftpus tibialis. Pogonocladius consohrinus, Tanytaraus gracilentus and Micropsectra airofasciata. Chironomus islandicus and Heterotrissocladius grimshawi had one peak in activity in all traps. The flight activity of Prodadius istandicus, Orthocladius oblidens and Micropsectra Undrothi varied greatly between traps and years. Simulium vittatum had two peaks in flight activity, corresponding to the two generations developing per year. Variation in trap catches of .S. vittatum reflected populalion changes measured independently in a study of larval population dynamic
Production of the chironomid Procladius bellus in an annual drawdown reservoir
Authors: SEPHTON THOMAS W. , PATERSON COLIN G.
Published: May 2006

SUMMARY. 1. In Laurel Creek Reservoir. Ontario, a small, eutrophic annual drawdown reservoir, some individuals of the chironomid Procladius bellus survive the winter drawdown.

2. With refilling of the reservoir in spring, colonization by P. bellus is continuous and there were three generations a year.

3. Production estimated by the size‐frequency method was 117.12 kg (175 mg m−2) in 1980 and 70.14 kg (105 mg m‐2) in 1981. Annual P:B was about 13 in both years.

4. Substantial slation‐to‐station variations in production occurred and overall production was lower than in shallow habitats.
Phosphorus inactivation in a eutrophic lake by the direct addition of ferric aluminium sulphate changes in phytoplankton populations
Authors: FOY R. H. , FITZSIMONS A. G.
Published: May 2006

SUMMARY. 1. Reduced total phosphorus concentrations in the summer which followed the addition of iron aluminium sulphate to White Lough failed to reduce significantly the phytoplankton. which continued to be dominated by Oscitlatoria agardhii var. isothrix Skuja.

This species was present throughout the 4 years studied, forming over 50% of the algal volume in 80% of samples. In contrast, species which occurred principally in the summer months were found to be severely curtailed when sediment release of phosphorus was suppressed.

2. The phosphorus: carotenoid ratio was used to assess the extent of phosphorus limitation because laboratory studies on O. agardhii var. isothrix showed that this ratio was a much beter indicator of cell phosphorus content than the phosphorus: chlorophyll a ratio. Reduced summer phosphorus concentrations in White Lough caused a transition from intermittent to continuous phosphorus limitation rather than a proportional reduction in the summer phytoplankton.

3. Reduced autumn grazing pressure by Daphnia hyatina Leydig allowed large algal populations to develop in the winters following phosphorus reduction despite a 50% decline in total phosphorus. The combination of increased winter phytoplankton and lower total phosphorus reduced soluble reactive phosphorus concentrations to less than 5,μg P l−1 which in turn curtailed the spring diatom pulse.
Variation in the C:P ratio of suspended and settling seston and its significance for P uptake calculations
Authors: UEHLINGER U. , BLOESCH J.
Published: May 2006

SUMMARY. 1. In 1981–84 limnocorral (LC) experiments were performed in Lake Lucerne. Switzerland, to manipulate the planktonic community by varying P fertilization and by removing large zooplankton (with a 95 μm screen).

2. The C:P ratios in both suspended and entrapped seston exceeded the ‘ideal’ C:P ratio of 106 proposed by Redfield, Ketchum & Richards (1963) when P was limiting algal growth.

3. P fertilization could decrease the sestonic C:P ratio to 106 only when P did not limit algal growth; P additions far exceeding the P loading of eutrophic lakes were necessary to obtain this situation.

4. Changes in epilimnetic C:P ratios were usually related to short‐ term changes in primary production, caused by variable in situ light conditions and turbulence, and subsequent variation in POC concentrations.

5. Entrapped seston in the 95 μm‐filtered LCs showed C:P ratios slightly higher than those of suspended seston, indicating fast P release and slower C mineralization in the epilimnetic nutrient cycle.

6. Removing large crustacean zooplankton enhanced epilimnetic P mineralization, and C:P ratios of entrapped seston in the 95 μm‐filtered LCs were increased.

7 Detritus formed a relatively high proportion of the seston and amounted to more than two‐thirds of the measured POC concentration.

8. Calculations of algal P uptake using information on sestonic C:P ratios and 14C uptake rates are questionable, as long as detritus cannot be separated from algae and net carbon uptake cannot be accurately measured.
Prey selection by juvenile cyprinids from running water
Authors: SCOTT ALASDAIR
Published: May 2006

SUMMARY. 1. The juveniles of dace (Leuciscus leuciscus (L.)) and roach (Rtuihts rtuihis (L.)) and yearling minnows (Phoxtnus phoxinus(L.)) exhibited generally similar patterns of feeding behaviour and preferences for particular prey types.

2. Factors affecting prey selection included predator and prey size, prey activity and environmental conditions.

3. All three species preferred prey sizes approximately 0.6x their maximum gape.

4. Prey motion was essential to induce attack, and prey were usually selected in proportion to their relative activities.

5. Specialization on one prey type was observed in still water, and was always directed at the most active prey type. In flowing water no specialization was observed, and size selection was suppressed in the juvenile fish. Yearling minnows, however, were size selective in both still and flowing water.

6. The presence of macrophyte cover did not significantly change the pattern of prey selection, but did reduce the predation rale.

7. These results are discussed in the context of previous studies of prey selection and optimal foraging.
Response of the freshwater marsh species, Panicum hemitomon Schult., to increased salinity
Authors: PEZESHKI S. R. , De LAUNE R. D. , PATRICK W. H.
Published: May 2006

SUMMARY. 1. Panicum hemitomon Schult. plants were colleeted from Louisiana's Mississippi River deltaic plain freshwater marsh and subjected to salinities of 5–12 ppt under controlled environment conditiotis.

2. The condition was designed to simulate salt stress resulting from storm surges, brine spills associated with oil recovery operations and salt water intrusion due to rapid subsidence and parallel increases in apparent sea level in Louisiana's coastal areas.

3. Plant stomatal conductance was reduced between 55 % and 80% and net photosynthesis declined between 20% and 67% in response to the different salinities within 1 day of salt application. Both responses lasted throughout the entire experiment.

4. Salinities ranging between 10 and 12 ppt resulted in tissue death in the plants 4 days after salt exposure.

5. In addition to the short‐term impact of salt water influx on gas exchange of P, hemitomon reported here, the potential long‐term effects on habitat change are discussed.
Distributional patterns of immature Simuliidae (Diptera) in northwestern North America
Authors: CORKUM LYNDA D. , CURRIE D. C.
Published: May 2006

SUMMARY. 1. Major landscape features and hydrological parameters indicative of black fly species assemblages were examined at 101 stream sites in Alberta, northern British Columbia, the Yukon and Alaska during the summer. Forty‐one black fly taxa were recorded at seventy‐ nine sites using qualitative sampling procedures. River sites lacking black flies had significantly higher conductivity, greater depth, shallower slope and were farther from the Pacific Ocean than sites with black flies.

2. Classification of sites by taxon occurrence using hierarchical cluster analysis suggested five groupings: A. Simulium tuberosum(Lundstrëm) complex + several taxa. B, S. venustum Saylverecundum Stone and Jamnback complexes +S, tuberosum complex; C. 5. arcticum Malloch complex +S. corbis Twinn complex; D, Gymnopais Stone/Prosimulium Roubaud; and E. P. onychodactytum Dyar and Shannon complex + several taxa.

3. Multiple discriminant analysis (MDA) was used to predict group membership of the seventy‐nine sites using nineteen environmental variables; 71% of the sites were classified correctly. MDA identified latitude and distance from stream source as important factors separating group D from other groups. Stream width and drainage basins entering the Arctic Oeean and Hudson Bay delineated group B. There was no clear separation among groups A. C or E. The presence of sibling species probably accounts for the overlap of black fly assemblages.

4. Our findings are briefly discussed in the context of stream classification systems, notably the river continuum concept.
A comparison of chlorophyll a and carotenoid concentrations as indicators of algal volume
Authors: FOY R. H.
Published: May 2006

SUMMARY. 1. Carotenoid concentration, as measured hy absorbance at 480 nm. was a better indicator of algal volume than chlorophyll a when the results from two lakes and laboratory studies on Osciltaloria agardhii var. isothrix Skuja were compared. The correlation between algal volume and carotenoid in White Lough (r=0.91) was significantly higher (0.001 P<0.01) than ihat between algal volume and chlorophyll a(r=0.77). The Lotigh Neagh correlation coefficient lor algal volume with carotenoid (r=0.89) was only marginally stronger than that with chlorophyll a(r=0.87).

2. The relatively weak correlation between algal volume and chlorophyll a in White Lough was a result of a summer decline in the chlorophyll a content of O. agardhii var. isothrix, which dominated the phytoplankton. The chlorophyll a content of the phytoplankton was depressed by high summer daily totals ol light hours received by the phytoplankton in White Lough of up to 14 h in comparison to a maximum value of 3.8 h in Lough Neagh. where no seasonal cycle of chlorophyll a content was evident.

3. Laboratory studies demonstrated that while chlorophyll a per unit algal volume of O. agardhii var. isothri.x declined with increasing light dose, carotenoid content did not. Nitrogen and phosphorus limitation depressed the carotenoid content but to a lesser degree than was observed for chlorophyll a.
Zooplankton populations and the diets of three Chaoborus species (Diptera, Chaoboridae) in a tropical lake
Authors: HARE LANDIS , CARTER JOHN C. H.
Published: May 2006

SUMMARY. 1. Zooplankton populations in a small, natural, tropical lake are dominated by a few, small‐sized taxa including the copepod Thermo‐ cyclops consimilis, the cladoceran Moina micrura and several rotifer species.

2. Moina micrura and adults of Thermocyclops consimilis undergo diel vertical migrations within the water column. Population densities of T. consimilis show marked intra‐annual variations which may to some extent be related to variations in rainfall and to lunar periodicities In predator abundance.

3. The diets of Chaoborus lavae include other Chaoborus, Cladocera, Copepoda. Rotifera and the dinoflagellate Peridinium. The diets of late instars of the largest species, edulis, were dominated by Crustacea, while those of the two smaller species. C, ceratopogones and C. anomalus, were dominated by Rotifera and the dinoflagellate alga Peridinium, as were the diets of early instars of all species. Algae have not been previously reported to be a large component of the diet of Chaoborus populations in nature.

4. Some of the dietary differences among Chaoborus instars and species are related to the size of each prey species in relation to the mouth gape of each instar. However, there are also important differences in electivity among instars of different species of the same size.
Time‐course of inorganic nitrogen uptake and incorporation by natural populations of freshwater phytoplankton
Authors: PRISCU JOHN C.
Published: May 2006

SUMMARY. 1. Time‐course measurements of NH4+ and NO3−uptake were made on the natural phytoplankton populations in a eutrophic lake at a time when these nutrients were at their lowest annual concentration.

2. Both NH4+ and NO3− uptake was increased at least five‐fold during the first 5 min of incubation following near saturating pulses of these nutrients.

3. Elevated uptake was also observed following low level (∼2μg N 1−1) pulses of NH4+ and NO3−, but substrate depletion during the first hour of incubation may have been partially responsible for this apparent enhancement.

4. Incorporation of I5N into TCA‐insoluble material (protein) following the saturating NH4+ pulse was increased less than total cellular 15N uptake, whereas no elevation of 15N incorporation into protein was observed following a saturating NO3−pulse.

5. The percentage of I5N incorporated into protein, with respect to total cellular uptake, was ∼32% and ∼12% for NH4+ and NO3−, respectively, following 5 h of incubation.
Regulation of damseifly populations: the effects of larval density on larval urvival, development rate and size in the field
Authors: BANKS MICHAEL J. , THOMPSON DAVID J.
Published: May 2006

SUMMARY. 1. The popuhttion density of Coenagrion pttella larvae was monitored in five populations, and of Ischntira elegans in two populations, between October 1982 and May 1983.

2. There was no measurable mortality of larvae over winter and no larval growth until April. Larvae in high density populations were smaller than those in low density populations and were more likely to have a semi‐ voltine life history.

3. The population density of C. ptiella was also monitored (more frequently) in two populations with differenl initial densities between July and November 1983. In the high density population there was a constant rate of larval mortality, while in the low density population there was no detectable larval mortality, indicating that larval mortality may be density dependent. Larvae in the high density population were again smaller, and more likely to be semi‐voitine, than those in the low density population.

4. The role of density dependent larval growth, development and mortality in the regulation of damseifly populations is discussed.
Methods for the activation of the resting eggs of Daphnia
Authors: SCHWARTZ STEVEN S. , HEBERT PAUL D. N.
Published: May 2006

SUMMARY. 1. The conditions required to initiate development of resting eggs of thirty‐six clones of Daphnia representing seven species were investigated.

2. The temperature of both dark incubation and subsequent light treatment are shown to affect hatch success. By varying these parameters the majority of resting eggs from each test clone were stimulated to develop. Arctic clones required a low hatching temperature (7°C), whereas clones from warmer climates hatched best at 14–21°C.

3. Variation in hatching cues existed between conspecific individuals from different collection sites. These differences suggest that research determining macro‐ and microgeographic patterns in hatching phenology would be fruitful.
Coidingham Loch, S.E. Scotland
Authors: BAILEY‐WATTS A. E. , KIRIKA A. A. LYLE. A. , WISE* E. J.
Published: May 2006

SUMMARY. 1. Coidingham Loch (Berwickshire. Scotland) (area. 8.4 ha, mean depth 2.9 m, max. depth 12.3 m) belongs to Hakansson's convex shape category. It lies in a basin of Silurian Greywackes rock within 0.25 km of coastal sea cliffs (c. 133 m a.s.l.). The theoretical hydraulic replacement time is 3.17 years.

2. The loch stratifies intermittently in summer. Fluctuations in oxygen concentration generally correspond to spells of mixing and stratification; low values of 10% saturation occur at the bottom.

3. The sum of the concentrations of major cations (Na+, K+, Ca2+, Mg2+) is in accordance with measured conductivities ranging between 380 μS cm−1 and 420 μS cm−1 (k.25). The ratios (by equivalents) of Na+/Cl− (0.04) are similar to those in sea‐water, whilst values for Ca+2+/Cl− (0.85–1.01) and Mg2+/Cl− (0.79–0.88) reflect the bedrock.

4. Nitrate concentrations were lowest (<0.05 mg N1−1) in summer following losses from the column of 107 mg N m−2 1−1, a rate corresponding well with published figures on microbial nitrate reduction. Nitrate increased at a rate of 8μg N I−1 d−1 to a winter maximum of 1.55 mg N I−1. Mass balance calculations show that if this rise is attributed to run‐off from surrounding land, a loss rate of 11.1 kg N ha−1 yr−1 would be required; this value is also commensurate with published figures.

5. Changes in phosphorus and factors controlling them contrast markedly with those of nitrate. The minimum concentration of 55 μg total P l−1 (mainly in soluble reactive form) occurs in spring. An increase to the maximum ofc. 300 μg l−1 in summer is sustained mainly by release from the sediments at a regular rate of 3 μg P l−1 d−1 (8.7 mg m−2 d−1). Adsorption by the sediments is considered to be the major process accounting for autumnal losses of phosphorus of 2.6 mg P M−2d−1.

6. Silica showed a less regular seasonal pattern, but varied some 45‐fold with a maximum of 2.25 mg SiO2, l−1 in August.
The biology and life cycles of Lipsothrix spp. (Diptera: Tipulidae) inhabiting wood in Western Oregon streams
Authors: DUDLEY TOM L. , ANDERSON N. H.
Published: May 2006

SUMMARY. 1. The immature stages of the craneflies Lipsothrix nigrilinea and L. fenderi are spent in galleries within decayed red alder (Atntts rtibra), in low order streams of the Pacific Northwest. L. fenderi also occurs in some coniferous wood and wood in semi‐terrestrial sites at stream margins. Larvae of both species feed on the wood and are important degraders of this material.

2. The immature stages are briefly described and behaviour of the two species is compared.

3. L. nigrilinea has a predominantly biennial life cycle. It emerges from April to August in response to receding water level. The absence of this cue results in an extension of the life span to 3 or more years. The non‐deterministic life cycle results in high variability of juvenile and adult weights.

4. L. fenderi is basically a biennial species, with a more synchronized autumn emergence. A portion of the population may emerge after 1 year if oviposition occurs early enough to allow autumnal growth of larvae or if growth is relatively rapid.

5. The extended life cycle of Lipsothrix spp. and the broad emergence of L. nigrilinea are concluded to be adaptations to a habitat/resource which is relatively stable and allows long‐term association.
Variability In the rate of egg development of the stonefly, Nemoura cinerea (Plecoptera)
Authors: EBRITTAIN JOHN , LILLEHAMMER ALBERT
Published: May 2006

SUMMARY. 1. The egg development of the widely distributed European stonefly. Nemoura cinerea Retzius. was investigated in the laboratory. There was a significant relationship between water temperature (T°C) and incubation period (Ydays), expressed by the regression equation: Y= 239 T−0.85 (r2= 0.85. P<0.001).

2. The number of day‐degrees above 0°C required for hatching showed a curvilinear relationship with water temperature, with a minimum requirement around 12°C.

3. Nemoura cinerea shows more variation in the rate of egg development than most other stoneflies. This, in part, explains the wide size range in nymphal populations and the species’ extended emergence period. Flexibility in life cycle and asynchrony in egg development enable this species to colonize a wide range of freshwater habitats.
An improved version of the Haney grazing chamber
Authors: GAWLER MEG , CHAPUIS RENE
Published: May 2006

SUMMARY An in situ grazing chamber is described which facilitates the handling of radioactive materials, improves the capture of zooplank‐ ton, and optimizes the mixing of labelled food particles into the food suspension.
Importance of hydrogen ions and aluminium in regulating the structure and function of stream ecosystems: an experimental test
Authors: HALL RONALD J. , DRISCOLL CHARLES T. , LIKENS GENE E.
Published: May 2006

1. Experiments simulating spring acidic snowmelt episodes were conducted to determine the effects of short‐term inputs of H+and Al on the chemistry and biology of a poorly buffered mountain stream. HC1 and A1C13were added in separate experiments to first‐ to third‐order reaches of a New Hampshire stream.

2. Cation exchange and Aln+dissolution reactions neutralized experimentally added H+, whereas groundwater dilution was insignificant. Mobilized Ca++, Mg++and Aln+concentrations progressively increased from third‐ to first‐order reaches during HC1 additions. Mobilization of Ca++and Mg++was greater during A1C13than HC1 addition.

3. Total phosphorus was mobilized from stream sediments during both HCI and A1C13addition. Dissolved organic carbon (DOC) decreased during A1C13addition in the second‐order but not in the third‐order reach. DOC concentration decreased during HCI addition only when Aln +mobilized from the stream bottom was >0.28 mg AI 11.

4. Production of foam at the water surface during AlCl3addition to a second‐order and HCl addition to a first‐order reach indicated a reduction in surface tension of the streamwater and may be related to complexation reactions between Al and DOC at low pH (4–5).

5. Mayfly nymphs and blackfly and chironomid larvae drifted at greater rates from HCl‐ and AlCl3treated sections of first‐ and second‐order streams than from corresponding reference areas.

6. When stream pH was lowered to 5.25–5.5 by HCI alone (15 μg monomeric inorganic Al l−1), the behaviour of aquatic invertebrates did not change, but pH reduced to the same range during Al additions (280μg Al 1−1) did affect it. Therefore, fluctuating aluminium concentrations in low‐order streams at a pH range of 4.5–5.5 may alter the biology and geochemistry of poorly buffered waters.
The diversity of macro invertebrate and macrophyte communities in ponds
Authors: FRIDAY LAURIE E.
Published: May 2006

SUMMARY 1. The range of factors which may influence the wide variation in the structure of pond communities is reviewed.

2. Factors explaining the variation in numbers of macro invertebrate and macrophyte taxa are investigated, using multiple regression analysis, for a group of ponds in which biogeographical effects are likely to be minimal.

3. Numbers of macro invertebrate taxa in these ponds are highly correlated with pH and probably, therefore, with other associated aspects of water chemistry,

4. Many invertebrate taxa, from species to entire phyla, were not found below pH 5.5, but few characteristically‘acidophilic’taxa were apparent.

5. Details of species composition of the macro invertebrate fauna differ widely even between ponds of similar pH.

6. The diversity and composition of macrophyte communities are not adequately predicted by any of the factors investigated.
The role of drift and effect of season on macroinvertebrate colonization of implanted substrata in a tropical Australian stream
Authors: BENSON L. J. , PEARSON R. G.
Published: May 2006

SUMMARY 1. Experiments using implanted substrata were conducted in Yuccabine Creek, a n upland stream in north‐eastern Australia which exhibits a strong seasonal pattern of discharge and temperature. The implanted substrata were either set in the stream bed or were raised in the water column. Three experiments were run, at different times of the year.

2. Colonization rate was dependent on benthic abundance, mobility of the fauna and distribution of resources. The rates on embedded trays were similar in the late wet season and mid dry season, but colonization rate in the late dry season was greater.

3. Drift alone could have accounted for all colonization in the late wet season, 63% of colonization in the mid dry season and less (unmeasured) in the late dry season. Drift acts to disperse early instars to patches of suitable habitat after the summer wet‐season peak in reproduction.

4. Following the wet season, stream discharge decreases, benthic abundance increases, resources become more concentrated, and movements of animals in contact with the substratum play an increasingly important role in colonization.
Sizes and daily growth rates of two algal phytoplankters in the field
Authors: COBELAS M. ALVAREZ , VELASCO J. L. , RUBIO A. , ACOSTA F. J.
Published: May 2006

SUMMARY 1. Measurements of daily growth rates, colony widths and lengths and cell widths and lengths were made on Fotterella tetrachlorelloides Buck and Staurastrum longiradiatum West & West (Chlorophyceae), collected from an eutrophic reservoir close to Madrid (Spain) on nine consecutive days of June 1983.

2. F. tetrachlorelloides exhibited growth followed by a period of decay, whilst S. longiradiatum grew more or less continuously throughout the observations.

3. A colony length‐width relationship was statistically significant throughout the growth period of F. tetrachlorelloides, but not when the population was decaying. This relationship was always statistically significant in S. longiradiatum. There was an inverse relationship between volume and daily growth rate in S. longiradiatum, but no such correlation was found in F. tetrachlorelloides.

4. The time course of statistical volume distributions and daily growth rates suggested that F. tetrachlorelloides was undergoing clonal ageing during the study.
Lake sediment microlaminae and annual mortalities of photosynthetic bacteria in an oligomictic lake
Authors: DICKMAN MIKE
Published: May 2006

SUMMARY 1. A novel mechanism of microlamina formation in oligomictic lakes is proposed. During spring and summer in Zaca Lake, an oligomictic lake in Santa Barbara, California, a light‐coloured microlamina is formed. During winter, a mass mortality of sulphur‐rich phototrophic bacteria occurs following the ventilation of the chemocline or the overturn of the lake. When this occurs, oxygen is introduced into the chemocline killing most of the anaerobic bacteria. When these sulphur‐laden bacteria die and settle to the bottom of the lake, they form a black microlamina which is rich in ferrous monosulphides.

2. The varved stratigraphy of the Zaca Lake sediment core presents an opportunity to correlate stratigraphic events in the lake's varved sediments with events reported for its catchment over the last 200 years.

3. Colonization by Europeans dates back to the 1760s, making this one of the best‐documented histories for a small lake in North America. A number of events have been correlated with stratigraphic information from the lake's varved cores.

4. Eutrophic diatom indicator species disappear downcore, where they are replaced by meso‐ and oligotrophic indicators. In addition, pollen from exotic trees planted in the lake's catchment appears at specific core depths associated with their pollen production stage.