bluuebunny/crossref_metadata_2025 huggingface dataset:
Prey selectivities of threespine sticklebacks (Gasterosteus aculeatus) and phantom midge larvae (Chaoborus spp.) in Newfoundland lakes
Authors: CAMPBELL CHRISTINE E.
Published: May 2006

SUMMARY.
1. Threespine stickleback (Gasterosteus aculeatus) and Chaoborus (C. punctipennis and C. trivittatus) planktivore populations were sampled from several oligotrophic lakes on the Avalon Peninsula of Newfoundland, Canada. Pelagic zooplankton communities in these lakes consist of Daphnia catawba, Holopedium gibberum, Eubosmina longispina, Leptodiaptorma minutus, Epischura nordenskioldi, Cyclops scutifer and rotifers (Conochilus unicornis, Keratella and Kellicottia spp.).

2. Comparison of gut contents of G. aculeatus and crop contents of later instar Chaoborus larvae with lake zooplankton communities indicated that the vertebrate and invertebrate plank tivores show contrasting species and size selectivities in their choice of zooplankton prey. Prey selectivities were quantified by means of the selectivity index α.

3. G. aculeatus showed positive selectivity for larger zooplankton (greater than 0.76 mm in length), typically the cladoceran D. catawba, while Chaoborus larvae showed positive selectivity for smaller zooplankton (less than 0.50 mm in length), typically the cladoceran E. longispina. While rotifers never featured in the diet of the sticklebacks, these zooplankters were a common component of the chaoborid diet. H. gibberum, with its gelatinous sheath, was rarely found in the gut contents of G. aculeatus and was never found in the crop contents of Chaoborus larvae.

4. Selective predation by these planklivores in the relatively shallow and well‐mixed oligotrophic Avalon lakes may influence species composition and size structure of the pelagic zooplankton communities.
Comparison of epilithic and epixylic biofilm development in a boreal river
Authors: SINSABAUGH ROBERT L. , GOLLADAY STEPHEN W. , LINKINS ARTHUR E.
Published: May 2006

SUMMARY.
1. We assessed substratum effects on lotic biofilm development by placing glass and white pine sampling units in a fourth‐order boreal river, and analysing, at 6‐week intervals, upper‐surface biofilms for ATP, chlorophyll, ergosterol, and the activities of nine exoenzymes.

2. All parameters, except chlorophyll standing stock (range 80–320 μg dm−2) and β‐xylosidase activity (range 0.4–4.8 μmol h−1 dm−2), were significantly greater for epixylic biofilms than for epilithic ones, but the magnitude of the increases varied from 2 to 5 fold, showing that, even under similar hydrodynamic conditions, epilithic and epixylic biofilms are structurally and functionally distinct. For example, ergosterol concentrations ranged from undetectable to 0.93 μg dm−2 for epilithon and from 11–49 μg dm−2 for epixylon; corresponding ranges for ATP were 1.6–3.7 (epilithon) and 4.2–7.7 μg dm−2 (epixylon), for acid phosphatase activity: 2.3–4.9 and 20–41 μmolh−1dm−2, and for alkaline phosphatase activity: 1.9–8.1 and 29–150 μmol h−1dm−2, respectively.

3. The more extensive epixylic development was attributed to utilization of the wood substratum as a supplemental carbon source and to a higher density of microbial attachment sites.
Predation by chaoborids on typical and spined Daphnia pulex
Authors: PAREJKO KEN
Published: May 2006

SUMMARY.
1. In laboratory predation experiments, predation rates were determined for fourth‐instar larvae of the chaoborids (Insecta: Diptera) Mochlonyx sp. and Chaoborus americanus preying on four juvenile instars and adult Daphnia pulex (clone SBL). In the case of Mochlonyx, predation was most intense on second‐instar juvenile Daphnia while Chaoborus preyed equally on second and third instars.

2. Mochlonyx and Chaoborus induced an antipredator defence (neck‐teeth) which was most frequently expressed in second‐instar juvenile Daphnia. Expression of this antipredator phenotype was correlated with a reduced rate of Mochlonyx predation.
Invertebrate grazer‐periphyton interactions in a eutrophic marsh pond
Authors: HANN B.J.
Published: May 2006

SUMMARY.
1. The effects of two different invertebrate grazer guilds on the periphytic algal community were studied in a marsh pond in Manitoba, Canada over one entire open‐water season.

2. Microcrustaceans (cladocerans, copepods, ostracods), which were numerically dominant in the unperturbed grazer community, effectively reduced the periphytic algal biomass to a persistent, depauperate residual assemblage throughout the season.

3. The perturbed grazer community, enclosed and treated with ro‐tenone, was composed primarily of chironomids and oligochaetes. This community permitted a more diverse algal community to develop except when grazer numbers peaked.

4. When grazer numbers in the perturbed community were at a maximum, the algal assemblage appeared to be ‘overgrazed’. Algal biomass was reduced below the minimum characteristic of the unperturbed community.

5. There was an inverse relationship between algal biomass and grazer numbers in both perturbed and unperturbed communities, but variation in degree of response was much greater in the perturbed system than in the unperturbed one.
Regional and temporal variation in pH, alkalinity and carbon dioxide in Danish streams, related to soil type and land use
Authors: REBSDORF A. , THYSSEN N. , ERLANDSEN M.
Published: May 2006

SUMMARY 1. The Weichsel glaciation has divided Denmark into two regions with different susceptibility to acidification. East of the Weichselian terminal moraine, soils are usually clayey and calcareous, and the streams are alkaline (mean alkalinity 2.24 mmol 1‐‐1) and resistant to inputs of acidifying substances.

2. Trend analysis of pH and alkalinity of water samples taken over 15 years in two streams with alkalinities above 1.5 mmol 1−1 in eastern Jutland, showed no trends of acidification.

3. West of the terminal moraine the soils are sandy and leached and alkalinity is lower (mean 0.59 mmol 1−1). Although such streams with medium alkalinity are believed not to be vulnerable to acidification, we have documented significant decreases in their pH and alkalinity over 12 years.

4. Trends of pH and alkalinity in four western streams with mean alkalinities between 0.05 and 0.79 mmol 1−1 showed annual decreases of 0.027 pH units and 4.7 nmol 1−1 in alkalinity.

5. Overall, Danish streams contain about 7.9 times more calculated free CO2 (pCO2=10−2.6 atm) than water in equilibrium with air (pCO2= 10−3.5 atm). The calculated free CO2 content has increased significantly in western Danish streams over the study period (6.9 μmol 1−1 yr‐1). This increase cannot be explained by the prevailing global increase in atmospheric pCO2 which only can account for 0.54 pmol 1−1 yr−1 at maximum.

6. Reasons for the ongoing stream acidification in the western part of Denmark are discussed. We suggest that atmospheric deposition causes stream acidification in a heath‐covered catchment without agriculture. In heavily cultivated regions the main acidification factor is argued to be proton production in the soil through nitrification of ammonium‐containing fertilizers.
Prey behaviour and size‐selective predation by fish
Authors: MACCHIUSI FRANK , BAKER ROBERT L.
Published: May 2006

SUMMARY 1. We investigate the role of differential activity of chiro‐nomids as an explanation for the size selection of small larvae by fish.

2. In the laboratory, pumpkinseed sunfish (Lepomis gibbosus L.) selectively consumed large larvae of Chironomus tentans Fab. when no tube‐building materials were available. Small larvae were selectively consumed when a mud substrate was provided but there was no difference in predation rates on large and small larvae in sand.

3. Small larvae spent more time out of their tubes than large larvae in the presence of fish, which may explain the selection for small larvae in mud. Large larvae apparently compensated for decreased foraging activity in the presence of fish by increasing activity when fish were absent. Visibility of large larvae inside tubes may account for their increased mortality in sand.

4. Our results suggest that differential activity is important in explaining the size‐selective mortality observed in the field.
Growth of the medicinal leech, Himudo medicinalis, under natural and laboratory conditions
Authors: WILKIN P. J. , SCOFIELD A. M.
Published: May 2006

SUMMARY 1. The growth of the medicinal leech, Hirudo medicinalis L., was studied in the wild by a mark and recapture technique, and in the laboratory. Growth in the wild, even after 2 years, was generally small and variable.

2. After being offered regular feeds of various preparations of bovine blood through a pig‐ileum membrane and being allowed to feed to satiation, hatchling leeches in the laboratory showed a saltatory pattern of weight gain with increases greatly in excess of those seen in the wild. Twelve of twenty‐five leeches starved from hatching survived for about 250 days. The ability to survive for long periods without feeding may well be important for the overwintering survival of late hatchlings.
A continuous‐flow system for measuring in vitro oxygen and nitrogen metabolism in separated stream communities
Authors: PRAHL C. , JEPPESEN E. , SAND‐JENSEN K. , MOTH‐IVERSEN T.
Published: May 2006

SUMMARY.
1. This paper describes a continuous‐flow system that we have used extensively for measurement of oxygen exchange and nitrogen transformations in different communities of lowland streams, i.e. the water, the sediment, and the macrophyte—biofilm community. The system, which is set up on the stream bank, consists of several macrophyte and sediment chambers equipped with a double‐flow system that ensures an internal water velocity close to that in the stream and which, by continuously renewing the water, mimics diel fluctuation in stream temperature and water chemistry. Water temperature and dissolved oxygen are measured continuously and the data stored on magnetic tape. Water samples are collected in a refrigerator and analysed using standard chemical procedures.

2. The application of the system is illustrated using results obtained during a 2‐day summer experiment in a shallow macrophyte—rich stream. The biological processes in the stream were mainly associated with the macrophyte—biofilm community and the sediment, those in the water being negligible. Oxygen release was confined to the macrophyte—biofilm community, the sediment consuming oxygen both by day and by night. Whole‐system gross production and dark respiration occurred at similar rates (6–7g O2 m−2 day−1), net balance being about zero. Inorganic nitrogen was consumed both by the sediment and to a greater extent by the macrophytes, the diel average consumption being 1g N m−2 day−1.

3. The sum of the activity in the macrophyte and sediment chambers corresponded to the overall activity of the stream section as determined by upstream/downstream mass balance. This indicates that the results obtained with the continuous‐flow chambers realistically describe the oxygen and the nitrogen metabolism of the stream.
Extracellular enzyme activity associated with suspended matter in the River Rhine
Authors: ADMIRAAL W. , TUBBING G.M.J.
Published: May 2006

SUMMARY.
1. Spatial and temporal variations in exoenzymatic proteolysis and alkaline phosphatase activity in the River Rhine were measured fluorometrically using L‐leucyi (ß‐naphthylamide and methylumbelliferyl phosphate (MUFP), respectively, as test substances.

2. Extracellular proteolytic activity measured in the lower 150‐km reach of the river during 1988 followed the changes in the concentration of particulate nitrogen associated with the occurrence of phytoplankton blooms. Alkaline phosphatase activity was not related to the concentration of particulate phosphate and correlated weakly with particulate nitrogen and phytoplankton concentrations.

3. Seasonal observations (1989) in the lower River Rhine and transport studies in a 660‐km‐long reach of the river (1990) indicated that the variations in the exoenzyme activities were unrelated (or not closely related) to fluctuating bacterial numbers. Exoproteolytic activity correlated well with thymidine incorporation and algal density, confirming indications in the literature that the exoenzyme activity is related to the overall metabolic rate of the bacterial populations.

4. The exoproteolytic activities in the Rhine are similar to the highest observed in eutrophic freshwaters, indicating a rapid turnover of proteins in the river. Bacterial phosphatase activities, measured with MUFP, were similar to those in the few marine and inland waters studied so far. However, phosphate‐limited algal blooms, such as reported for the plume of the Rhine in the North Sea, are likely to contribute substantially to hydrolysis of natural organic phosphates.
The fauna of North American temperate cold springs: patterns and hypotheses
Authors: GLAZIER D.S.
Published: May 2006

SUMMARY.
1. The relative abundance of six classes of macroinvertebrates in fifteen mid‐Appalachian and thirteen other North American cold springs is briefly reviewed. In both surveys peracaridans, molluscs, and triclads dominated the hard‐water limestone springs, whereas insects dominated the relatively acidic soft‐water springs.

2. A hypothetical framework is offered to explain the dominance of non‐insect taxa in hard‐water limestone springs. The importance of a non‐emergent lifestyle and high population densities in springs is emphasized. Some evidence is offered in support of the proposed hypotheses, but most of the testing remains to be done.
Spring bloom development of microbenthic algae and associated invertebrates in two reaches of a small lowland stream with contrasting sediment stability
Authors: IVERSEN TORBEN MOTH , THORUP JENS , KJELDSEN KARINA , THYSSEN NIELS
Published: May 2006

SUMMARY.

The microbenthic algal biomass and the invertebrate fauna were quantified during an algal spring bloom in two reaches of a small Danish lowland stream which, although similar with regard to stream velocity, water chemistry and irradiance, differed with regard to substrata and sediment stability. Due to channelization, one reach (Ellerup I) had low variation in depth, unstable sand midstream and mud along the banks; the other reach (Ellerup II) had more variable depth and more different and stable substrata.

At Ellerup I, maximum mean algal biomass was 74 ± 28 mg chl m −2. Algal biomass primarily developed in muddy areas near the banks, whereas midstream algal biomass remained low.

At Ellerup II, maximum mean algal biomass was 161 ± 41 mg chl m−2 on fine‐grained sediments and 64 ± 21 mg chl m−2 on stones. Algal biomasses near the banks and midstream were similar, but seasonal development on the two main substrata was significantly different, suggesting that algal development on the two substrata was regulated by different factors.

At Ellerup I, the invertebrate fauna was dominated by Oligochaeta and invertebrate density and diversity were generally higher near the banks than midstream. Such differences did not occur at Ellerup II, where total invertebrate density was significantly higher than at Ellerup I and the fauna was dominated by Orthocladiinae, Simuliidae and Baetis sp.

It was concluded that stream channelization and maintenance, through their effects on sediment variation and stability, profoundly affect algal biomass distribution and development and invertebrate distribution, density and community structure.
Calibration of FST‐hemispheres against bottom shear stress in a laboratory flume*
Authors: STATZNER B. , KOHMANN F. , HILDREW A.G.
Published: May 2006

SUMMARY.

Fliesswasserstammtisch (FST)‐hemispheres of identical size but different densities were exposed on a horizontal plane on the pebble‐covered bottom of a laboratory flume at streaming to shooting, turbulent and fully developed flow. The heaviest hemisphere moved was used as an indicator of shear stress, a flow force acting on the flume bottom.

The relationship between shear stress and hemisphere density was practically the same for three different sets of hemispheres, namely one prototype set newly prepared for the calibrations, one prototype set intensively used in the field prior to calibrations, and one randomly selected new set bought commercially.

Shear stress (y, dyn cm−2) was related to hemisphere density (x, g cm−3) by y= x2.85 (n= 69; r2= 0.993). For lighter hemispheres this relationship was better explained by the linear model y= 7.32x– 6.60 (n= 35; r2=0.983).
Invertebrate recolonization of small patches of defaunated hyporheic sediments in a Sonoran Desert stream
Authors: BOULTON A.J. , STIBBE S.E. , GRIMM N.B. , FISHER S.G.
Published: May 2006

SUMMARY.

Fine mesh (63 nm) traps filled with defaunated sediment and open to recolonization from upstream, downstream or below were buried 30 cm deep in the hyporheic zone of a gravel run in a desert stream and recovered after 1, 3, 7, 14 and 27 days. Temporal changes in organic matter and faunal composition and abundance were compared among treatments and with those in completely closed ‘control’ traps.

Closed traps consistently contained tittle detritus (<30mg AFDM per 5000 cm3). Traps facing upstream accumulated significantly more organic matter than those facing below or downstream, indicating downstream hyporheic transport of fine particulate detritus.

Upstream‐facing traps also captured significantly greater numbers of taxa and individuals. Low numbers of most taxa recolonized from all three directions within 1 day; total densities of individuals in the traps increased before levelling off after 2 weeks.

The prediction that taxa with planktonic epigean relatives (e.g. cyclopoid copepods) would predominate in upstream facing traps was unsupported, nor did unpigmented, blind phreatic forms preferentially colonize traps from below. Two closely related taxa exhibited major differences in recolonization dynamics, illustrating the risk of masking such trends when pooling data for more than one taxon.

Experimental manipulations such as this supplement the predominantly descriptive studies of the hyporheos, and demonstrate the complex dynamics of organic matter and biota in the hyporheic zone that must be considered in analyses of most stream ecosystems.
Emigration and immigration can be important determinants of benthic diatom assemblages in streams
Authors: JAN STEVENSON R. , PETERSON CHRISTOPHER G.
Published: May 2006

SUMMARY.

Interspecific differences in diatom abundances in stream drift (plankton), immigration, and natural benthic assemblages were compared to assess the importance of emigration and immigration in benthic diatom community dynamics. Water samples were collected throughout a 24‐h period to measure diel changes in diatom drift abundances and to estimate benthic diatom emigration rates. Immigration was assessed with 24‐h colonization of bare tiles.

Dissimilarity in species composition of drift, immigration, and natural substrate assemblages indicated differential emigration and immigration among diatom species.

A mathematical model indicated that reproduction by diatoms in the plankton could not account for diel drift peaks and that diel variation in drift was an informative measure of benthic diatom emigration.

Emigration and immigration of some species constituted substantial proportions of diatom abundances on natural substrata. We conclude that emigration into the drift and immigration onto substrata can be important processes that regulate benthic diatom species composition and standing crop in streams.
An experimental study of the influence of periphytic algae on invertebrate abundance in a Hong Kong stream
Authors: DUDGEON DAVID , CHAN IVAN K.K.
Published: May 2006

1. Small cages (294cm2) containing unglazed clay quarry tiles were used to investigate the influence of periphytic algae on macroinvertebrate abundance in a Hong Kong stream. Algal biomass was manipulated by shading cages with plastic sheets. Individual cages were assigned to one of three treatment groups: unshaded, shaded and deeply shaded. Invertebrate densities and algal biomass within cages were monitored after 23, 37 and 65 days.

2. Multiple‐regression analysis revealed that algal biomass, invertebrate morphospecies richness and total abundance declined with greater shading intensity. The responses of individual invertebrate taxa varied: some (especially Trichoptera) were unaffected by shading, whereas grazers (Baetidae, Psephenidae and Elmidae) declined as shading increased.

3. Significant regressions of the densities of individual taxa upon algal and detrital standing stocks in cages had positive slopes, but algal biomass increased during the study while detrital standing stocks declined. Abundance of invertebrates declined or remained rather stable over time. Density increases resulting from a positive association with algae were apparently offset by declines in abundance correlated with reductions in detritus.

4. Declines in algal biomass were associated with greater shading to which animals may respond directly. To uncouple the link between scarcity of algae and reduction of light intensity, the plastic covers on two groups of cages (deeply shaded and unshaded) which had been placed in the stream for 28 days were reversed so that cages which had been shaded became unshaded and vice versa. The cages were recovered on day 33, Only Coleoptera demonstrated a positive association with atgae inside cages; no relationship between population densities and algal biomass or light intensity was apparent for other taxa. However, the design may have been confounded by deposition of sediment in the cages (due to declining stream discharge) which reduced population densities of colonizers.

5. This study documents changes in invertebrate abundance and morphospecies richness in response periphyton and detritus standing stocks within patches. Summation of such responses may account for observed variations in benthic communities among Hong Kong streams which differ in the extent of shading by riparian vegetation.
Indirect effects of fish on foraging behaviour and leaf processing by the isopod Lirceus fontinalis
Authors: SHORT T.M. , HOLOMUZKI J.R.
Published: May 2006

1. We examined whether the isopod, Lirceus fontinalis, an important facultative shredder in low‐order streams in the eastern United States, responded to chemical cues of the skin mucus of five fish species varying in relatedness and feeding habits, and if fish‐induced alterations in the foraging activity of isopods indirectly affected leaf processing.

2. In the laboratory, isopods generally responded to the presence of fish mucus by reducing their activity. Isopods were most responsive in water containing the skin mucus of predatory sunfish (Lepomis) and least responsive in water treated with mucus from algivorous stonerollers (Campostoma anomalum).

3. Rates of leaf disc breakdown by isopods in the laboratory were significantly reduced when isopods were exposed to chemical cues of confined green sunfish (L. cyanellus).

4. The rate of leaf processing in a fishless reach of a headwater stream was four to five times greater by isopods 7—10mmTL (total length) than those ≤ 5mm TL. Rates of leaf processing by isopods in low‐order streams may be affected directly by the size structure of the isopod population and indirectly by the presence of fish.
Effects of drying and freezing autumn leaves on leaching and colonization by aquatic hyphomycetes
Authors: BÄRLOCHER FELIX
Published: May 2006

1. Drying or freezing autumn‐shed leaves of Betula papyrifera, Ulmus americana and Acer saccharum increased the leaching of soluble substances. The difference between fresh and treated leaves was most pronounced in birch.

2. Dried and frozen leaves supported more species of aquatic hyphomycetes during early decay, and conidium production from these fungi was higher.

3. Anguillospora filiformis was the most prolific spore producer on most samples. It declined in later stages of decay, when Articulospora tetradadia became more common. Crucella subtilis, an unspecialized parasite of aquatic hyphomycetes, was quite common in many samples.

4. In the autumn of 1990, 50% of elm and maple leaves, and 30% of birch leaves were shed before the air temperature dropped below 0°C; 10% (elm, maple) to 30% (birch) experienced more than one freezing period before being shed.

5. Water‐soluble extracts from leaves inhibited radial growth of four fungal species. Maple extracts generally had the greatest inhibitory effect, followed by birch and elm.
Changes in the abundance and composition of cyclopoid copepods following fish manipulation in eutrophic Lake Væng, Denmark
Authors: HANSEN ANNE‐METTE , JEPPESEN ERIK
Published: May 2006

1. The seasonal cycle of cyclopoid copepods during and following an approximately 50% reduction in planktivorous fish biomass was studied in shallow, eutrophic Lake Vaeng, Denmark, from 1986 to 1990.

2. The dominant cyclopoid copepods changed from Cyclops vicinus and Mesacyclops leuckarti during 1986–1989 to M. leuckarti and Megacyclops viridis in 1990. The abundance of cyclopoid copepods gradually increased from 1986 to 1988–89, decreased in autumn 1989 and markedly decreased in 1990.

3. The increase in the abundance of cyclopoid copepods from 1986 to 1988 is attributed mainly to the reduction in fish predation pressure, there being no concomitant increase in edible phytoplankton. The appearance of M. viridis in 1990, and the general decrease in cyclopoid copepod density in autumn 1989 and in 1990, are attributed to the appearance of submerged macrophytes.

4. Temperature, predation and availability of edible phytoplankton appear to determine whether C. vicinus or M. leuckarti dominates the cyclopoid copepod population of eutrophic Lake Væng.
Microcrustacea in flowing water: experimental analysis of washout times and a field test
Authors: RICHARDSON WILLIAM B.
Published: May 2006

1. Flow‐chamber experiments were conducted to evaluate the ability of microcrustacea to maintain position in moving water. These results were compared to distributions of zooplankton and water velocity in a stream pool to determine the relationship of animal density to water movement and swimming ability.

2. Cladocerans exhibited negative rheotaxis (directed behaviour against a current) but poor ability to maintain position at velocities >2.5cm s−1. Daphnia and Scapholeberis were better at avoiding washout than Moina and Diaphanosoma. At velocities <2.5cm s−1Eucyclops (Cyclopoida) tended to exhibit no rheotaxis.

3. Washout of Daphnia was complete at velocities >2.5cm s−1, Scapholeberis >3.2cm s−1 and Eucyclops >7.75 cm s−1. Washout time of Daphnia and Scapholeberis was positively related to body size and negatively to water velocity and possession of eggs. Washout was inversely related to water velocity for Eucyclops.

4. Highest densities of microcrustacea in a stream pool were found in non‐flowing or downstream zones of the pool. Benthic (Hydracarina, harpacticoid copepods, ostracods) and fast‐swimming (cyclopoids) forms were most common in flowing zones. Facultatively benthic Cladocera were abundant in regions of no flow. Rotifers and immature copepods were most abundant at the downstream end of the pool.

5. Behavioural mechanisms for remaining in stream pools at times of high flow appear to include: (i) flow avoidance (Simocephalus, Chydorus, Scapholeberis and cyclopoids), (ii) use of benthic habitat (ostracods, harpacticoids, Hydracarina), (iii) strong swimming ability (cyclopoids).
Herbivory of invertebrates on submerged macrophytes from Danish freshwaters
Authors: JACOBSEN DEAN , SAND‐JENSEN KAJ
Published: May 2006

1. Invertebrate herbivory on submerged freshwater macrophytes, measured as per cent leaf area lost, was determined for sixteen species and forty‐two populations of macrophytes during peak summer biomass in Danish streams and lakes.

2. All seventeen Potamogeton populations and seventeen of the remaining twenty‐five non‐Potamogeton populations were grazed. Species of Potamogeton were significantly more heavily grazed (mean 4.2%) than non‐Potamogeton species (mean 0.8%). Herbivory losses were not significantly different between stream (mean 2.4%) and lake populations (mean 1.9%). Wide ranges in herbivory loss were observed between species from the same locality and within species from different localities. The location of main damage to either old or young leaves was not species specific but varied among localities. Additional data for four macrophyte populations showed that herbivory loss had a strong seasonal variation (e.g. 1.0–26.3% for Potamogeton perfoliatus), with maximum losses during May‐June.

3. Although the mean defoliation percentages were low during the period of maximum macrophyte biomass, they were not systematically lower than encountered for terrestrial plants.
Genetic control of predator avoidance behaviour in Daphnia
Authors: WATT PENELOPE J. , YOUNG STEPHEN
Published: May 2006

1. The vertical migration behaviour in electrophoretically distinguishable clones of Daphnia magna Straus was investigated.

2. Clones differed significantly in their tendency to stay near the surface of the tank during the light phase of the daily light/dark cycle, indicating that vertical migration has a genetic component.

3. There was a significant difference in behaviour between juvenile and adult Daphnia: overall the juveniles stayed closer to the water surface than the adults, but the characteristic pattern of clonal differences persisted in the juveniles.

4. When an adult population of each clone was exposed to a fish predator in an experimental tank, the position a clone maintained in the tank at the start of the day had a direct effect on its survival. Clones remaining near to the surface of the water suffered greatest predarion.
The morphometry and hydrology of Oak Mere, a lowland kataglacial lake in the north‐west Midlands, England
Authors: SAVAGE A.A. , BRADBURNE S.J.A. , MACPHERSON A.A.
Published: May 2006

1. This paper presents geological, climatic, morphometric and hydrological data, collected from 1941 to 1991, on a lowland kataglacial lake and its catchment, as a basis for the development of a descriptive hydrological model.

2. The catchment occupies an area of 2.56 km2, at altitudes of 73–130 m above sea level, and receives an average annual net precipitation of 558 000 m3. The surface geology consists principally of sandy glacial drift and peat overlying Triassic strata which are exposed at the western extremity of the catchment.

3. The mere (lake) has an asymmetrical basin lying in sandy glacial drift and peat. The area (18.4–22.9 ha), depth (7–8 m) and volume (320000–453000m3) fluctuate in relation to net precipitation in at least two ways: an immediate response and a response with a rime lag of approximately 2 years.

4. The pH, normally <5.5 but varying from 4.0 to 7,8, and ionic composition of the mere fluctuate. The evidence suggests that the fluctuation is a response to at least two essentially separate types of water supply: a base‐poor surface supply and a base‐richer supply entering at a depth of 4m.

5. Essentially, the descriptive model postulates that the mere waters are controlled by a water‐table of varying level, in relation to net precipitation, which is base poor at the surface but becomes increasingly base rich with depth.
Distribution and feeding of the predatory nematode Anatonchus dolichurus (Mononchoidea) in the Dokka delta (Norway) and its impact on the benthic meiofauna
Authors: PREJS KRYSTYNA
Published: May 2006

A dense population of a large (over 6.5mm long), semiaquatic, predatory nematode Anatonchus dolichurus was found in the delta of the River Dokka, Norway. This is the first time it has been reported in surface fresh waters.

 Nematode distribution was related to water depth, with maximum abundance (over 24000 ind.m−2) occurring in shallow areas (0.5–2.0m). Sediments at all stations with a high density of A. dolichurus were dry and exposed to air and ice during winter and early spring, and overgrown with macrophytes during summer.

 This predator contributed a greater fraction of total numbers and biomass of the nematode fauna than predatory forms in other known freshwater nematode assemblages. It constituted up to 15.6% of numbers and up to 90% of total nematode biomass.

 Anatonchus dolichurus preyed on Nematoda, small Oligochaeta (mainly Enchyrraeidae) and Chironomidae. It was able to reduce the density of these meiofaunal taxa when present in large numbers in experimental cores.
An investigation of allelopathic effects of Daphnia
Authors: MATVEEV VLADIMIR
Published: May 2006

The hypothesis is tested that large daphnids are able to suppress their own and other species' feeding and reproduction by means of excreting an inhibitory chemical (or chemicals).

 In laboratory experiments with an Australian species, Daphnia carinata, water preconditioned with 3–67 daphnids 1‐−1 for 30 h had the effect of reducing feeding rates of D. carinata and D. lumholtzi provided with Selenastrum capricornutum.

 For the two Daphnia species, there were highly significant negative correlations between feeding rate and the preconditioning density of D. carinata.

 Water preconditioned with 20–30 daphnids 1‐−1 for 1–2 weeks reduced the grazing rates of Daphnia, Moina, and Diaphanosoma 2–3‐fold.

 Moina kept in such water for 2 days stopped feeding. Conditioned water kept for 3 days without animals still inhibited grazing by Moina. Hearing to 100°C removed the inhibitory effect.

 Given excess food, and in non‐renewed water, a gradient of D. carinata densities developed a strong negative correlation between clutch size and daphnid density after a 6‐day time lag. This result may help explain the direct density‐dependent regulation of cladoceran reproduction observed earlier in a subtropical lake.
Patterns of hydrological exchange and nutrient transformation in the hyporheic zone of a gravel‐bottom stream: examining terrestrial—aquatic linkages
Authors: TRISKA FRANK J. , DUFF JOHN H. , AVANZINO RONALD J.
Published: May 2006

The terrestrial‐aquatic interface beneath a riparian corridor was investigated as a region of hydrological and biological control of nutrient flux. Subsurface flow paths were defined from the channel toward the riparian zone and also from the riparian zone toward the channel using tracer‐injection studies. Solute transport had a rapid channel component (m min−1) and a slow hyporheic flow component (mh−1, m day−1). Subsurface flow beneath the riparian zone approximated a straight path entering at meanders but could also cross beneath the stream, possibly using relic channels.

 Dissolved oxygen (DO) concentration in the hyporheic zone ranged from <1.0 to 9.5mgl−1 due to permeability variations in bankside sediments. DO concentration was related to the proportion of stream water in the lateral hyporheic zone, indicating that the channel water was the DO source.

 The magnitude and riming of lateral water exchange was linked to previously published studies of nitrification and denitrificarion. Both nitrification potential and channel exchange decreased with distance from the channel and were absent at sites lacking effective exchange, due to low DO. Field amendment of ammonium to an aerobic flow path indicated nitrification potential under natural hydrological conditions. Denitrification potential was inversely related to channel exchange and was insignificant in channel sediments. Field amendment of acetylene plus nitrate to a flow path with low DO and minimal channel exchange indicated denitrificarion of amended nitrate.

 Comparison of hydraulic head to distribution of the biologically important solutes DO, ammonium, and nitrate was useful for interpreting previous findings and conceptualizing the riparian zone as a functioning ecotone between terrestrial and aquatic systems.
The influence of larval case design on vulnerability of Limnephilus frijole (Trichoptera) to predation
Authors: NISLOW KEITH H. , MOLLES MANUEL C.
Published: May 2006

We examined the potential selective pressures exerted by different types of predators on morphological prey defences using the case‐building larvae of the limnephilid caddisfly, Limnephilus frijole. The predators were a predaceous minnow, Gila pandora, and an aeschnid dragonfly naiad, Oplonaeschna armata.

 The influence of larval case design on vulnerability to predators was evaluated in a series of laboratory experiments. Larval L. frijole were collected from a stream without fish or dragonflies. In the laboratory, larvae still occupying their field‐built cases were exposed to the two predators, with which L. frijole co‐occurs in other streams. Following 24 h exposure of caddisfly larvae to a specific predator, the pre‐trial case length, case strength, case width, and case composition of victims and survivors were compared.

 Principal components analysis (PCA) indicated substantial independent variation for all four case parameters in the study population. The cases of larvae surviving exposure to either dragonfly naiads or fish were significantly stronger and wider than cases of victims of predation. Cases of survivors were also longer and had a greater mineral fraction than those of victims, but differences were either marginally significant or not significant.

 These results demonstrate that specific aspects of case design affect the vulnerability of caddisfly larvae. In addition, predaceous fish and predaceous invertebrates, using different predation techniques, may exert similar selective pressures on these defenses. Case aspects influencing vulnerability in these experiments are broadly consistent with natural variation in case design associated with predator‐rich and predator‐free habitats for related caddisfly species.
The impact of small chironomid grazers on epiphytic algal abundance and dispersion
Authors: BOTTS P. SILVER
Published: May 2006

A combination of field and laboratory experiments was used to assess the impact of chironomid grazers on taxonomic composition, abundance and dispersion of epiphytic algal assemblages.

 In the laboratory, Psectrodadius sp. reduced the biovolume of algal species preferred as food and increased the degree of clumping of non‐preferred species. Thienemanniella cf. fusca had both positive and negative effects (depending on the algal species) on the biovolumes of algal species preferred as food and increased the degree of clumping of non‐preferred species.

 In field exclosures, no effect of removal of chironomid larvae from the grazer assemblage could be detected in autumn or winter experiments. A third, longer removal experiment, conducted in summer, resulted in increased biovolumes of edible Cosmarium spp. and Aphanocapsa spp., preferred foods of chironomid larvae. Biovolumes of Lyngbya sp., Eulbochaete spp. and Oedogortium spp., filamentous taxa used extensively in larval case construction, also increased. Chironomid larvae had no effect on total algal biovolume or biovolume of large unicellular algae.

 Chironomid larvae can influence epiphytic algal assemblages through selective grazing by reducing the biovolumes of preferred foods and through case‐building activity by reducing the biovolumes of construction materials.
Juvenile survival of a planktonic insect: effects of food limitation and predation
Authors: FISCHER JANET M. , MOORE MARIANNE V.
Published: May 2006

An experiment was conducted to investigate potential impacts of food limitation and copepod predation on juvenile survival of Chaoborus purtctipennis. We tested the hypotheses that: (i) juvenile survival of Chaoborus is influenced more by copepod predation than by starvation in a productive environment, and (ii) food limitation and predation interact to affect survival.

 Effects of food concentration (approximately 800, 1400 and 2300 microzooplankton 1‐−1) and predator density (0, 1 and 2 Mesocydops edax 1‐−1) on Chaoborus development and survival were evaluated using a 3 × 3 factorial design. Jars containing lake water, the appropriate food and predator treatments, and two Chaoborus (<12h old) were rotated on a plankton wheel at 25°C. Survival and developmental stage were monitored daily until all individuals had either died or moulted to instar II.

 Predation by Mesocydops was the major source of mortality, causing 87.5% of Chaoborus deaths over all treatments. Chaoborus mortality was significantly higher in treatments with Mesocydops (67–100%) than in predator‐free treatment (0–13%).

 Development time was significantly longer in the low‐density food treatment than in the highest food treatment.

 No significant interaction between food limitation and predation was detected.

 These results suggest that predation by copepods may limit recruitment of juvenile Chaoborus in productive lakes.
A simple periphyton sampler for algal biomass estimates in streams
Authors: DAVIES ANNE L. , GEE JOHN H.R.
Published: May 2006

A simple periphyton sampler, which is cheap and easy to construct, is described. The key component is a disposable scouring disc which also serves to adsorb detached material.

 Field trials show that the scouring sampler is significantly more efficient at removing and retaining periphyton from stones in streams for biomass estimation than other commonly used techniques.

 The scouring sampler requires only one operator. Its small size and speed of use facilitate replication of samples. Samples can be collected from stones as small as 30mm diameter.
Behavioural response of fishes to increasing pH and dissolved oxygen: field and laboratory observations
Authors: SERAFY J.E. , HARRELL R.M.
Published: May 2006

Freshwater fish assemblages were sampled quantitatively before, during, and after naturally produced conditions of elevated pH and dissolved oxygen (DO) that occurred for 2–6h in two dense macrophyte beds. Field observations were followed by 3–4‐h laboratory behavioural experiments in which banded killifish (Fundulus diaphanus), bluegill (Lepomis macrochirus), and striped bass (Morone saxatilis) were exposed to gradually increasing levels of: (i) pH; (ii) DO; and (iii) pH and DO.

 Field results indicated that the macrophyte bed dominated by Hydrilla verticillata had a higher fish density than the mixed‐species (H. verticillata and Vailisneria americana) bed, but beds did not differ significantly in fish species richness or biomass. Within beds, diel changes in fish species composition, richness, density and biomass were minor.

 In the laboratory, avoidance of pH levels exceeding 9.5 was exhibited by all species tested. No significant response was observed to either DO increase treatments, or to pH and DO increase treatments.

 Results suggest fishes do not avoid areas, such as dense macrophyte beds, when high pH levels (9.5–10.0) are accompanied by high DO levels (200–260% saturation).
A simple water sampler, and a chamber for in situ incubation of plankton samples at discrete depths
Authors: TRANVIK L.J. , TRANVIK P.H.
Published: May 2006

A simple water sampler and an incubation chamber are presented. The water sampler is simpler in construction than the Ruttner sampler and other comparable devices. In addition to enclosure of water at a discrete depth, the incubation chamber releases a radioisotope or other substance of experimental interest into the sample.

 Tests of performance are presented, demonstrating efficiency in enclosure of water from discrete depths, and time course of mixing of a tracer into the sample after activation of the release mechanism.
Characterizing a zooplankton neighbourhood: small‐scale patterns of association and abundance
Authors: FOLT CAROL , SCHULZE PETER C. , BAUMGARTNER KAREN
Published: May 2006

This study compares small‐scale (i.e. neighbourhood) associations among distributions of phytoplankton, zooplankton, and zooplankton grazing rates using a combination of correlations and analyses of spatial patchiness.

 All zooplankton and phytoplankton populations had patchy distributions. On average, individuals experienced members of their same taxon at a density that was 42% greater than the mean sample density.

 The various zooplankton taxa experienced different average neighbourhoods, even within the same stratum of the lake. For example, Daphnia galeata mendotae (Birge) experienced phytoplankton concentrations that were nearly 50% greater than those experienced by Daphnia pulicaria (Forbes) at the same depth.

 The distributions of the various phytoplankton taxa were positively correlated with each other, but the distributions of zooplankton were negatively correlated, or more often, unrelated to each other.

 Phytoplankton abundance was negatively correlated with zooplankton grazing rates.

 We hypothesize that while phytoplankton distributions are driven by common external factors, the factors that determine horizontal distributions of zooplankton are species specific. In addition, zooplankton grazing appears at least partially responsible for the generation of patchiness in the distribution of phytoplankton.
Carbon and nitrogen dynamics in a maritime Antarctic stream
Authors: DAVEY MARTIN C.
Published: May 2006

The carbon and nitrogen dynamics in a maritime Antarctic lake outflow stream were investigated. The stream and the algal communities could be split into two zones: a semi‐aquatic margin consisting of a perennial cyanobacteria/diatom mat and a flowing channel with a similar perennial mat that was overgrown by annual filamentous chlorophytes during the course of the summer.

 Neither algal community was limited by nutrient availability. Major nutrients were always available in the stream water. There were slight differences in the atomic ratios of the mats, the N:P ratios in the channel mat being lower than those in the marginal mat. However, both these and the total dissolved N:P ratio in the stream water were all close to those that indicate a balanced supply.

 There was no net carbon or nitrogen accumulation by the marginal mat suggesting that uptake processes were balanced by loss processes.

 Maximum rates of carbon fixation (0.1–0.5mgCg−1 dry weight h−1) were similar to those of other perennial Antarctic algal mats. Productivity appeared to be limited by physical factors, but the effects of irradiance and temperature could not be separated.

 There were no heterocystous cyanobacteria in the mat communities and rates of atmospheric nitrogen fixation were very low (0–10ngNmg−1 mat Nh−1). Fixation accounted for only 0.3% of the nitrogen accumulation of the channel mats, but was higher in the marginal mat where uptake of other sources of nitrogen was also low.

 Nitrogen accumulation by the channel mat averaged 0.34gNm−2 day−1. Only 0.05gNm−2 day−1 was accounted for by the uptake of dissolved inorganic nitrogen (nitrate plus ammonium). The major (80%) source of nitrogen appeared to be dissolved organic nitrogen. Recycling of nitrogen within the stream ecosystem may also be important.
The nature of the fluid boundary layer and the selection of parameters for benthic ecology: reply to Lamouroux
Authors: CARLING P.A.
Published: May 2006

The near bed flow equations and definitions given originally by Carling (1992) are reviewed and are shown to be correct and unambiguous. The theoretical assumptions inate in deriving the governing equations are violated in non‐uniform, unsteady flow, such as occurs in shallow flow over rough beds, but in practice results obtained from log‐law models are often not significantly different from those derived from functions purporting to represent large‐scale roughness. This point was made carefully in the original paper.

 More complex approaches now exist for modelling gradually varying, slightly non‐uniform flow which are modifications of uniform flow models. These are not readily applicable to field data commonly available to ecologists, however, and generally give little additional insight. Advances are only likely to be made when turbulent flow structure is better understood.