bluuebunny/crossref_metadata_2025 huggingface dataset:
Conservation and management of brown trout, Salmo trutta, in Ireland
Authors: FAHY EDWARD
Published: May 2006

SUMMARY. .1. Ireland's fauna and flora are, compared with those of Britain and Continental Europe, relatively impoverished as a consequence of our glacial history. Salmonids are, however, well represented here and, because cyprinids are not. they make up a large proportion of the freshwater fish biomass.

2. It may be more accurate to regard our trout fauna as a mosaic of subspecies and races rather than a single species. Two principal immigrations are thought to have contributed to the extant strains one of which includes the valuable long‐lived sea trout and freshwater ferox. Their fidelity to specific spawning areas isolates and maintains the purity of trout strains but certain aspects of spawning behaviour may leave some of them susceptible to cross fertilization with others.

3. Strains of trout may take distinguishable external forms or they may not be easily recognized by eye. In spite of their great interest in the conservation and management of trout, anglers are largely unaware of their genetic status.

4. Artificial restocking of salmonids has been carried out in Ireland since the nineteenth century; most effort has been expended on Atlantic salmon but, in the last 25 years, the restoration of trout populations depleted by pollution and arterial drainage has been the object of these exercises. There is concern for the consequences of wild trout strains being diluted by these efforts although, to date, evidence to support that happening is sparse.

5. Problems associated with deterioration in water quality have multiplied over the past 20 years and trout is the species most affected by fish kills. These tend to be seasonal, exacerbated by low water and dry weather. The smallest streams, which may be as narrow as 30 cm, which are the stronghold of trout in many catchments, are at greatest risk.

6. Ireland's cyprinid fauna results from introductions but it is rapidly developing ‐ as is coarse angling. Roach is the species spreading fastest. Studies show that roach will share the diet of trout and. possibly more significant, will compete with them for the angler's fly.
Experimental investigations of diel vertical movements by lotic mayflies over substrate surfaces
Authors: GLOZIER NANCY E. , CULP JOSEPH M.
Published: May 2006

SUMMARY. 1. The vertical distribution within the substrate of three lotic mayflies (Rhithrogena sp., Paraleptophlebia sp. and Baetis tricaudalus Dodds) was examined in laboratory streams to determine if diel patterns of vertical movement across substrate surfaces existed and whether light intensity, temperature, substrate composition or food availability influenced the observed movement patterns.

2. Rhithrogena sp. and B. tricaudatus exhibited significant diel movement from lower substrate surfaces during the day to upper surfaces at night, although >64% of B. tricaudalus occupied the upper surfaces throughout the 24 h period. In contrast, Parakplophlebia sp. larvae did not change their vertical distribution over the 24 h period.

3. The proportion of mayflies occupying substrate surfaces was influenced by the amount of upper and lower surface area available in the substrate and, possibly, crevice sizes associated with lower surfaces.

4. The movement of Rhiihrogena sp. from lower surfaces during the day to the upper surfaces during the night was influenced by changes in light intensity, but not by changes in food availability or water temperature.

5. The diel patterns of vertical movement exhibited by lotic mayflies in this investigation raise the possibility that at least some biotic interactions may vary over a diel cycle. These could include competitive interactions or temporal cycling of prey availability to predators.
A comparison of the effects of prey and non‐prey neighbours on foraging rates of Epischura nevadensis (Copepoda: Calanoida)
Authors: FOLT CAROL L. , BYRON EARL R.
Published: May 2006

SUMMARY. 1. Adults of the calanoid copepod, Epischura nevadensis, aggregate in situ near the thermocline in Lake Tahoe, California‐Nevada. together with adults of another species of calanoid copepod, Diaptomus tyrelli and juveniles of both species. With a series of laboratory predation and algal clearance trials, we show that foraging rates of adult E. nevadensis are determined not only by the density of co‐occurring potential prey (small copepods), but also by the presence of co‐occurring non‐prey neighbours (large, adult copepods). These effects occur at densities and in zooplankton assemblages found naturally, emphasizing the ecological importance of neighbours other than prey on zooplankton feeding.

2. Neighbours are distinguished primarily by size. Although predation rates increase linearly with the densities of small copepods. both algal clearance and predation rates decrease in the presence of large copepods. We also show, with a field predation experiment using small enclosures, that adults are size selective within species and that Diaptomus are selected over conspecifics of the same size.

3. We hypothesize that by reducing foraging rates in the presence of large zooplankton. E. nevadensis avoids predators and reduces predation risk at the cost of reduced energy consumption.
Standard hemispheres as indicators of flow characteristics in lotic benthos research
Authors: STATZNER BERNHARD , MÜLLER RAINER
Published: May 2006

SUMMARY. 1. Standard hemispheres of identical size and surface but different densities were exposed on a horizontal plane at the bottom of streams. The heaviest hemisphere moved was used as an indicator of flow conditions close to the substrate.

2. Techniques of manufacture, maintenance, and use of the equipment were considered in detail.

3. The method was an easily applicable and integrated indicator of key hydraulic characteristics (turbulence or force of flow prevailing at the stream bottom) previously measured in lotic benthos research, and can replace these more laborious techniques.

4. The hemispheres enabled a rapid flow characterization in stream reaches, in smaller areas where the benthos was being quantitatively sampled, and in en/exclosure cages used in experimental studies.

5. The method also has the potential to characterize and compare physics of flow in individual running water segments with regard to frequencies and intensities of disturbances caused by long‐term variations in discharge.

6. The hemispheres could be used as a standard in benthic research. since they offer a well defined scale that is directly comparable not only between studies in running waters but also in wave‐exposed shores of lakes and oceans.
Salamander predation and vertical distributions of zooplankton
Authors: HOLOMUZKI JOSEPH R.
Published: May 2006

SUMMARY. 1. The impact of different predation regimes of zooplanktivorous larval tiger salamanders, Ambystoma tigrinum nebulosum, on the vertical temporal distributions of Daphnia pulex, Diaptomus nudus and larval Chaoborus flavicans was studied in limnetic enclosures in a pond in east‐central Arizona. Zooplankton densities were monitored 1‐2 h before sunset, at sunset, and 1‐2 h after sunset at three depths (0‐0.4, 1.0 and 2.0 m) in four salamander treatments (0, 20, 40 salamanders per enclosure, and unenclosed limnetic areas).

2. Densities and body size of Daphnia pulex were consistently greater in salamander‐free enclosures than in other treatments. More Daphnia were generally nearer the surface (0‐1.0 m) than along the bottom before and at sunset than after sunset in enclosures without salamanders. After sunset, Daphnia was by far most dense along the bottom. Densities were uniform among depths and sample times in treatments with salamanders. Salamanders moved throughout the water column. Frequencies of D. pulex spined morphs (with prominent dorsal crest) did not differ among salamander treatments.

3. Chaoborus densities were positively correlated with D. pulex distributions among depths and sample times in treatments. Spatio‐temporal distributions of Chaoborus were influenced more by their daphnid prey than by risk of predation from larval salamanders.

4. Densities of Diaptomus nudus were highest in open water controls and lowest in enclosures without salamanders. Diaptomus was generally more dense between 0 and 1 m than at 2.0 m depths in all treatments, and vertical distributions were not dependent on salamander density.
A model of surface water acidification in Cumbria and its uses in long‐term research
Authors: TIPPING E.
Published: May 2006

SUMMARY. 1. A description is given of a simple process‐based model of deposition‐catchment interactions in areas of Cumbria underlain by rocks of the Borrowdale Volcanic Series. The processes considered are evapotranspiration, nitrogen uptake by plants, dissolution and precipitation of A1(OH)3, basecation weathering, hydrolysis of Al3+, reactions of the carbonate system, and water flow routing. Model parametersare estimated from 1980s data for deposition and streamwater chemistry. It is shown that the‐ model is also applicable to tarns (small lakes). Analysis of 1970s streamwater data highlights uncertainties about deposition concentrations of NH4+ and catchment transformations of nitrogen.

2. Using estimates of past deposition compositions, past compositions of tarn waters are estimated and indicate declines in pH I of up to 1 unit between c. 1850 and c, 1950, These changes are similar to those estimated independently from analysis of sediment diatoms. The model also shows that the historical pH trends are consistent with other paiaeolimnological evidence that Cumbrian soils have been acid for several thousand years. The model output is also consistent with direct evidence suggesting that the chemical compositions of Cumbrian tarns have altered little during the past 30 years.

3. The model is used to estimate water compositions during high‐flow episodes at various times in the past, and shows that even a small increase in depositional acidity would have made high‐flow waters sufficiently acid and aluminum‐rich to limit faunal abundance. This is consistent with the limited amount of observational evidence that is available.

4. The model can be used (a) for prediction, given scenarios for future deposition compositions or catchment behaviour, and (b) as a framework for planning future studies and interpreting data. Further work on the model should improve the reliability of its parameters, find better descriptions of processes dealt with in the current version, and introduce processes currently ignored. The present analysis indicates that fieldwork is needed to study nitrogen transformations, soil properties and biological responses to changes in streamwater chemistry.
The relative effects of enrichment and climate change on the long‐term dynamics of Daphnia in Esthwaite Water, Cumbria
Authors: GEORGE D. G. , HEWITT D. P. , LUND J. W. G. , SMYLY W. J. P.
Published: May 2006

SUMMARY. 1. The factors influencing the seasonal and inter‐annual variations in the numbers of Daphnia hyalina in Esthwaite Water between 1956 and 1972 are analysed. Esthwaite Water has always been eutrophic. but the phosphorus and nitrogen loadings to the lake increased significantly in the mid 1960s.

2. Qualitatively, the phytoplankton and zooplankton populations in the lake changed relatively little during the period of study. Quantitatively, however, eutrophic species of algae became more abundant and the numbers of Eudiaptomus declined as the numbers of Daphnia increased.

3. The seasonal dynamics of the Daphnia was governed partly by the seasonal temperature cycle, and partly by the periodicity of edible algae. The birth rate of the Daphnia was constrained by temperature from January to April and from October to December. At other times their rate of increase was governed by the relative abundance of edible and inedible algae.

4. Edible and inedible species of algae tended 10 appear in a recurring annual sequence. Diatoms such as Asterionella were abundant in the spring, the early summer phytoplankton was dominated by edible flagellates, but inedible algae such as Aphanizomenon and Microcystis become dominant later in the year.

5. Daphnia could only reproduce in late summer when there were periodic regrowths of edible algae. Such regrowths were most likely to occur when there had been some entrainment of deep nutrients by episodic wind mixing. Calm weather encouraged the growth of blue‐green algae that effectively‘blocked’the development of the Daphnia for the remainder of the summer.

6. The factors that controlled the seasonal dynamics of the Daphnia also influenced the average number recorded in a particular year. The average number of Daphnia increased in the early sixties when Cryptomonas was abundant and decreased in the late sixties when blooms of Aphanizomenon appeared in mid summer. Detailed analyses showed that a similar increase in the numbers of Aphanizometion had occurred in the late fifties. The critical factor throughout was the prolonged period of calm resulting in stable stratification.

7. This ‘weather’ effect was highlighted by comparing de‐trended timeseries of Daphnia and Aphanizometion numbers with a simple measure of thermocline stability. De‐trending removed the superimposed effects of progressive enrichment and revealed a 10‐year cycle of thermocline stability that matched the temperature cycle recently reported in Windermere, These cycles are related to the movement of weather systems in the Atlantic so could change if the pattern of atmospheric circulation is altered by global warming.

8. The possible effects of climate change on Daphnia dynamics are discussed in relation to the findings in Esthwaite Water.
A network for long‐term ecological research in the United States
Authors: MAGNUSON J. J. , BOWSER CARL J.
Published: May 2006

SUMMARY. 1. A network of seventeen long‐term ecological research sites funded by the National Science Foundation (NSF) and spanning sites in arctic to tropical climates, low to high altitudes and wet to dry environments, provides evidence for the increasing popularity of sustained ecological research in the U.S.A.

2. The sites function as regional or national facilities for long‐term research as well as for comparative and process studies by investigators from the operating institutions and by visiting researchers.

3. The aquatic habitats include a variety of lakes ponds, wetlands and a playa; montane, woodland, tundra and prairie streams; as well as salt marsh, estuary, ocean beach and inshore oceanic sites.
Comparison of biotic index values for invertebrate collections from natural and artificial substrates
Authors: MODDE TIMOTHY , DREWES HENRY G.
Published: May 2006

SUMMARY. 1. We evaluated the use of a biotic index in a small mountain stream on the basis of collections of benthic macroinvertebrates from both artificial and natural substrates in years of above and below normal discharge.

2. Invertebrate composition sampled from artificial and natural substrates exhibited inverse trends in density associated with discharge patterns.

3. Biotic index values derived from artificial substrates provided a more consistent and accurate description of the water quality of a small stream between years of high and low discharge than did those determined from natural substrates.
The seasonal response of diatom communities to variable water quality in some English urban lakes
Authors: GUZKOWSKA M. A. J. , GASSE F.
Published: May 2006

SUMMARY. 1. Five diatom assemblages and their corresponding site groups were associated with the urban lakes. When treated as a single dataset, DC A and PCA grouped these diatom assemblages along an environmental gradient from circum natural. dilute waters to strongly alkaline, concentrated, nutrient‐rich waters.

2. When treated as individual datasets, 75% of the known variance was explained by the first axis of DCA in all five diatom assemblages; this indicated the existence of a strong primary environmental gradient. The PCA results showed that the identity of this primary environmental gradient can be different for each assemblage.

3. The statistical analyses showed that the physicochemical gradients were continuous and not discrete. Nevertheless, fine‐scale analysis can identify smaller, more precise species and site groups.

4. Two types of species response could be identified within most sub‐assemblages in the urban lakes: the first was a quasi‐seasonal response and was characterized by a gradual rise to a peak relative abundance of one dominant or several co‐dominant species which could be sustained for a period of weeks before a gradual decline. A quasi‐seasonal response was sometimes interrupted by a storm response. The storm response was characterized by a sudden increase in the relative abundance of one or more diatom species following a storm, after which the species declined to pre‐storm abundances within 7 days.

5. The effects of urban runoff on the water quality of urban lakes can override the effects of true seasonal factors such as water temperature and day length on the relative abundance of species.
The distribution of micro‐arthropods in some southern English streams: the influence of physicochemistry
Authors: RUNDLE SIMON D. , HILDREW ALAN G.
Published: May 2006

SUMMARY. 1. Micro‐arthropods were surveyed during October 1986 at thirty stony, stream riffle sites in the Ashdown Forest, southern England.

2. The importance of a number of physicochemical variables in determining both the distribution of micro‐arthropod taxa and community structure was assessed.

3. Acidic sites had an impoverished fauna. Total micro‐arthropod species richness and densities were highest under circumneutral conditions. and the same patterns were shown by the Hydrachnellae, Harpucticoida and Cladocera. A number of species seemed indifferent to acidic conditions and were widespread and, as a group, the cyclopoid copepods showed no relationship with pH.

4. Multiple regression showed that other environmental variables, in particular annual mean temperature and maximum discharge, were also important in explaining the between‐site distribution of separate micro‐arthropod groups and individual species.

5. Other multivariate techniques (ordination, classification and multiple discriminant analysis) showed that impoundment linkage, source distance and conductivity, along with pH, were the most important variables in explaining patterns of species composition between sites.
Complex and flexible life history of a freshwater benthic harpacticoid species
Authors: SARVALA JOUKO
Published: May 2006

SUMMARY. 1. The life history of the benthic harpacticoid paracamptus schmeili (Crustacea: Copepoda) in the oligotrophic lake Pääjärvi, South Finland, was described from quantitative field data of all developmental stages. The generation time of P. schmeili was exceptionally long for a meiobenthic animal and varied with depth from 1 year in the littoral (depths of 1 and 2m) to 2 years in the upper profundal (13 and 14 m). and to 3 years in the lower profundal (40 m).

2. In the littoral, egg‐bearing females were found from April to October, with peaks in spring and late summer, while in the profundal a single summer egg peak was present.

3. In the littoral and in the lower profundal there were three, in the upper profundal) probably four, simultaneous parallel cohorts over‐wintering as adults, medium‐sized (at 13 m also large) copepodids and medium‐sized nauplii. Reproductive isolation of the parallel cohorts was possible at all depths.

4. The between‐depth variation in the life history of P. schmeili was probably mainly a phenotypic response to the changing level and seasonal course of temperature and food supply. Growth and reproduction were confined to summer months, and the lengthening generation times with depth accompanied decreasing summer temperatures.

5. The cessation of growth in winter was probably due to a shortage of food, which may also have accentuated the size differences of the overwintering groups through intraspecific competition.
Patterns in the distribution of heptageniid (Ephemeroptera) species in Saskatchewan, Canada
Authors: WHITING ERIC R. , SHEARD J. W.
Published: May 2006

SUMMARY. 1, The distribution patterns of twenty‐one species of heptageniid mayflies were examined in Saskatchewan and west‐central Manitoba, Canada. Presence/absence data from 174 stream sites were analysed using two complementary multivariate techniques, classification (Ward's method with Euclidean distance) and ordination (detrended correspondence analysis).

2. Multivariate analyses revealed two large, distinct groups of sites within the study area. The first included sites characterized by the presence of Heptagenia elegantula (Eaton) and Stenonema terminatum (Walsh). The second included sites characterized by the presence of Stenonema vicarium (Walker), Leucrocuta hebe (McDunnough) and/or Nixe species. The two groups contained, respectively, three and four subgroups.

3. Groups and subgroups defined by multivariate analyses were compared using large‐scale environmental features obtained from topographic and other maps. Differences in environmental features between the two groups were mainly in stream order, terrestrial vegetation and annual number of degree‐days (calculated from air temperature). The first group could be characterized as warm, large river habitat in grassland and parkland vegetation regions. The second included cooler, small to midsized streams and rivers in boreal forest. Most differences among subgroups were also in stream order, terrestrial vegetation and degree‐days, although some subgroups in the second group differed also in stream gradient.

4. The observed groups and subgroups were not associated with drainage basins.
Inhibitory effects of high molecular weight dissolved organic matter upon metabolic processes in biofilms from contrasting rivers and streams
Authors: FREEMAN CHRISTOPHER , LOCK MAURICE A. , MARXSEN JÜRGEN , JONES SUSAN E.
Published: May 2006

SUMMARY. 1. The effect of removal of organic manor >1000 apparent molecular weight (AMW) upon biofilm processes was determined in three contrasting streams in West Germany and three contrasting rivers in the U.K. This process removed 66–85% of the dissolved organic matter supply.

2. Elevations in extra cellular enzyme activity (β‐glucosidase, phosphatase and esterase), metabolic heat‐output, bacterial density and poly‐beta‐hydroxy alkanoate (PHA) content (a prokaryote storage product) were noted throughout the study in response to the removal of organic matter. This suggests that there are inhibitory substances present in the dissolved organic matter pool >1000 AMW. Evidence is presented to suggest that phenolics play a role in this inhibition.

3. Decreases in metabolic heat output, β‐glucosidase activity and PHA content were noted at four sites in response to the removal of >1000 AMW material.

4. The divergent responses of the six river/stream biofilms are indicative of radically differing metabolic/catabolic processes, on a spatial and/or temporal basis, to a major organic supply perturbation.
Epiphytic diatoms in two freshwater maritime Antarctic lakes
Authors: OPPENHEIM DEBORAH R. , GREENWOOD RICHARD
Published: May 2006

SUMMARY.

 An ecological study of two small maritime Antarctic lakes on Signy Island, South Orkney Islands, was undertaken from January 1986 to March 1987. Analysis of diatom counts from the lakes provided examples of oligotrophic and mesotrophic ecosystems.

 A diverse community of 104 epiphytic taxa was identified. Twenty‐eight taxa had a percentage abundance greater than 1% in both lakes. Distinctive dominant taxa were identified from each lake.

 A variety of ordination techniques was performed on the abundance data and a principal components analysis demonstrated differences in the diatom assemblages between the two lakes. Clear separations of sites and species were evident between the lakes, and accounted for the greatest percentage variance.

 Species composition varied with depth within each lake and was also important in influencing changes in assemblage composition between sites.

 A redundancy analysis indicated that species composition was correlated to concentrations of nitrogen and phosphorus but the total variance accounted for by the four physical and chemical factors measured was low (24%).
The population dynamics of Chydoridae and Macrothricidae (Cladocera: Crustacea) from the River Thames, U.K.
Authors: ROBERTSON ANNE L.
Published: May 2006

SUMMARY.

 A study was made of the population dynamics of benthic cladocerans in the River Thames, U.K. These included three species of Chydoridae (Alona affinis Leydig, Disparalona rostrata (Koch 1841) and Leydigia leydigi Schodler) and one species of Macrothricidae Iliocryptus sordidus (Lievan).

 The pattern of chydorid abundance was similar to that found in many lakes: a midsummer peak followed by a sharp decrease in numbers and subsequent low abundance. This was caused by a temporary decrease in natality, possibly due to food limitation, and a more permanent increase in mortality, thought to be due to predation.

 Iliocryptus sordidus differed considerably from the chydorids, the major population peak occurring in the autumn. The lifestyle and adult size of Iliocryptus sordidus (Lievan) must render adults less vulnerable to invertebrate and fish fry predation.

 A literature survey showed that the assemblage of species found in the unvegetated littoral of lakes and rivers included a taxocene of cladocerans.
Distribution and production of Chironomidae (Diptera) in the lower course of the Grabia River (Central Poland)
Authors: GRZYBKOWSKA M. , WITCZAK J.
Published: May 2006

SUMMARY.

 A fifth‐order section of the Grabia River was investigated over two years: 1984/85 (low water level) and 1985/86 (high spate). Chironomidae (thirty‐nine species) dominated the macrobenthos in both years.

 In 1984/85 (mean annual water temperature 10.2°C), the number of Chironomidae species in coarse sediment was highest in spring (thirty‐three species) while in sand it was highest in summer (fifteen species). A decrease in species richness was recorded in autumn and winter at each of the established sites. The estimated Chironomidae production for the whole river section was 5.37 g dry wt m−2 yr−1, but it differed widely amongst the study sites, ranging from 3.75 to 12.07 g m−2 yr−l.

 In 1984/85 (mean annual temperature 8.1°C) there occurred a summer spate which was more intense than any recorded over the previous 20 years. This substantially reduced the number of species, the greatest reduction being in the coarse sediment, which was buried with sand during the spate. Production for the whole section decreased to 1.17 g m−2 yr−1, and the variability amongst sites ranged from 1.04 to 1.45 g m−2 yr−1.
Effect of selective planktivory by fry of Rhamdia sapo (Pimelodidae: Pisces) on zooplankton community structure
Authors: ZAGARESE HORACIO ERNESTO
Published: May 2006

SUMMARY.

 The direct and indirect effects of predation by larval fish (Rhamdia sapo) on zooplankton in rearing tanks are analysed. Rhamdia sapo larvae showed an unusual species‐selectivity for Acanthocyclops robustus, the main invertebrate predator present.

 Acanthocyclops robustus populations were markedly reduced, presumably as a direct consequence of species‐selective removal. Other zooplanktonic prey were not significantly affected by R. sapo predation.

 Rotifers increased in tanks with fish, but this was not related to herbivorous crustacean variables (biomass, mean weight, abundance and species composition). On the contrary, rotifer biomass was negatively correlated with some A. robustus variables (biomass and mean weight of adults + copepodites and nauplii biomass). Thus, the rotifer increase appears to be an indirect effect of predation on A. robustus by R. sapo larvae.
Effect of food concentration on growth, reproduction and survivorship ofBosmina longirostris(Cladocera)
Authors: URABE JOTARO
Published: May 2006

SUMMARY.1. Body growth, reproduction and survivorship ofBosmina longirostriswere monitored at four food concentrations (0.05, 0.10, 0,25 and 2.50 ing Cl−1) to examine the extent to which food concentration affects these life‐history parameters.

2. Food concentration had a significant effect on growth, and most of the reproductive parameters (size and age at maturation, brood size, instar duration and egg development time). More than 60% of animals died before maturation at the lowest food concentration, although most animals survived until maturation at other food concentrations.

3. Change in life‐history parameters resulted in a decrease in rate of population growth (r) from 0.310 to 0.020 day−1with decreasing food concentration, showing that this cladoceran is highly food‐limited in many lakes.

4. Importance of the effect of food concentration on egg development time was emphasized in relation to analysis of natural populations.
Cladoceran assemblages, seasonal succession and the importance of a hypolimnetic refuge
Authors: TESSIER ALAN J. , WELSER JENNIFER
Published: May 2006

SUMMARY.
1. We investigate the importance of a refuge from fish predation to the abundance, species composition and seasonal succession of zooplankton. Thirty lakes representing a range of depths were sampled twice in summer for physical/chemical parameters and zooplankton community structure.

2. We define the refuge from centrarchid predators to be that space between the thermocline and the zone of anoxia. As lakes vary in rate of oxygen depletion from the hypolimnion. the refuge size and lake depth are independent: refuge size decreases during the summer period.

3. Lake depth and refuge size independently explain variation among lakes in zooplankton species composition, but seasonal community change within lakes is best predicted by loss of refuge size.

4. Refuge size also explains the substantial variation in the relative dominance of the two major daphnid species. Lakes possessing a large refuge are dominated by D. pulicaria; those with a small refuge are dominated by the smaller, D. galeata mendotae. We suggest that lakes of intermediate refuge size, which are characterized by high species diversity, represent a more equitable balance of predation and competition.
Taxonomic structure of phytoplankton assemblages in Crater Lake, Oregon, U.S.A.
Authors: DEBACON M. K. , MCINTIRE C. D.
Published: May 2006

SUMMARY.
1. A taxonomic analysis of 171 phytoplankton samples obtained from Crater Luke, Oregon, between 1985 and 1987 revealed 132 taxa in the upper 250 m of the water column. The greatest temporal variation in taxonomic structure occurred between 40 and 80 m below the water surface, a depth range which corresponded to the zone of maximum primary production.

2. Phytoplankton cell biovolume in the upper 20 m of the water column was relatively high during the summer months, a period when Nitzschia gracilis was dominant in the epilimnion. However, 72% or more of the cell biovolume between 0 and 200 m was distributed below 20 m and, during the winter and spring months, 61% was found below 80 m.

3. Cluster analysis identified a sparse, temporally ubiquitous flora which was modified to various degrees when environmental conditions became favourable for the growth of a few dominant taxa. These surges ot dominance by individual taxa accounted for 2 to 5‐fold increases in cell biovolume and generated a pronounced taxonomic discontinuity between the floras in the epilimnion and hypolimnion.

4. While the taxonomic structure of the phytoplankton in the epilimnion corresponded closely with the structure found in a 1978–80 study, the flora below the metalimnion was more diverse and less predictable in species composition than the pattern reported in the earlier study.
Exploitation of prey by a river bird, the dipper Cinclus cinclus (L.), along acidic and circumneutral streams in upland Wales
Authors: ORMEROD S. J. , TYLER STEPHANIE J.
Published: May 2006

SUMMARY.
1. The diet of the Eurasian dipper Cinclus cinclus. a riverine bird from a globally widespread genus, was assessed through all stages of its annual cycle using published data and field studies from streams of contrasting chemistry. Time‐activity budgets were also compiled throughout the year and used to estimate annual energy requirements from the stream ecosystem.

2. The annual energy requirements for a territorial pair ranged from 148,000 to 158,000 kJ yr−1 depending on whether one or two broods were reared. After allowing for assimilation efficiency, these requirements were estimated to represent 10.5–11.0 kg dry mass of fish and invertebrates. Using representative values for territory size (4680–11,250 m2), annual exploitation of secondary production was estimated at 0.93–2.35 g dry mass m−2.

3. Several features combined to focus the predatory load on certain organisms over different stages of the annual cycle. These included the availability and selection of alternative prey, the need to provision nestlings with large items such as trichopteran larvae, and the use by females of calcium‐rich prey such as fish prior to egg formation.

4. Across their range of territory size, annual exploitation (dry mass) by dippers was estimated at 0.06–0.29 g m−2 for Plecoptera. 0.02–0.22 g m−2 for Ephemeroptera. 0.59–1.11 g m−2 for Trichoptera and 0–0.78 g m−2 for fish. Exploitation of Ephemeroptera. I richoptera and fish were all highest in circumneutral streams, but exploitation of Plecoptera was highest in acidic streams because other prey were scarce.

5. Cottids dominated the fish component of the diet. Influences on their density could be substantial according to available data on production in Welsh streams. Hydropsychids and limnephilids dominated the trichopteran component, with exploitation again representing potentially substantial amounts of production. Contemporaneous data are required on benthic production and exploitation by the birds.

6. The ecological role of birds in rivers particularly, and aquatic ecosystems generally, is currently neglected but worthy of considerable research effort.
Ecology of leptocerid caddisfly larvae in an intermittent South Australian stream receiving Eucalyptus litter
Authors: TOWNS D. R.
Published: May 2006

SUMMARY.
1. Brown Hill Creck, a small intermittent stream in dry sclernphyll forest in South Australia, flows for about 6 months during winter and spring. When flow ceases the stream dries to isolated pools which receive high summer inputs of Eucalyptus obliqua litter. Decomposition of this material in remnant pools causes extremely dark waters and depressed oxygen concentrations for up to 90 days.

2. Only two fully aquatic insect species, Lepntorussa darlingtoni and Lectrides varians (Trichoptera: Leptoceridae), persist under these conditions. Both utilize litter as food, but have different feeding strategies. The more abundant L. darlingtoni ingests organic and microbial material from leaf surfaces, whereas L. varians is a leaf shredder.

3. Larval processing budgets based on laboratory and fleid experiments indicated that L. variant has a greater impact on litter decomposition rates than L. darlingtoni. However, because of low density, low oxygen concentrations in pools during summer, and rapid flushing of litter from pools once flow recommences. L. variaus larvae process a small proportion of the total litter input.
Emergence and dynamics of cyclopoid copepods in an unpredictable environment
Authors: WYNGAARD GRACE A. , TAYLOR BARBARA E. , MAHONEY DIANE L.
Published: May 2006

SUMMARY.
1. We studied species composition, abundance and population dynamics of cyclopoid copepods emerging from dormancy from the sediments of a temporary pond in South Carolina in 1985, 1988 and 1989. During a drought in 1988–89, the maximum hydroperiod was 19 days; in 1985 and late 1989‐early 1990, the hydroperiods were 57 and 118 days. We also report on species present in 1984 and 1987, two years that had longer hydroperiods, and on abundance of cyclopoids in 1984.

2. Within a day after standing water appeared, fourth‐instar copepodids of Diacydops haueri and D. crassicaudis brachycercus became active. These two species appeared every time the pond filled in winter, spring, or autumn. Other species, including Acanthocyclops vernalis, were usually not collected until weeks or months after the pond filled. Because the times and durations of fillings were extremely variable, species composition differed among years, with the most species (eleven) appearing in 1984, the year with the longest hydroperiod.

3. The abundances of emerging Diacydops were much lower in 1988 and 1989 (range of means from seven fillings in spring and autumn: 675–7382 animals m−2) than 1985 (range of means from three fillings in winter: 26,037–107,418 animals m−2). Low abundances of emerging animals could have been caused by poor survival of dormant animals, poor production during preceding seasons, or incomplete emergence of the dormant populations.

4. Substrate samples from the dry pond were collected in spring, summer, and autumn 1988 and winter 1989 to measure emergence of the cyclopoids in laboratory incubations. Population densities of emerging animals were much lower in 1988 and 1989 (range of means from seven experiments: 0–120 animals m−2 over the first 3 days) than in similar experiments in 1984 (Taylor & Mahoney, 1990, means from two experiments: 3630 and 6890 animals m−2).

5. Despite the low abundance of animals emerging from dormancy in late 1989, the cyclopoid populations in 1990 reached similar densities of copepodids (104−‐105 animals m−2) to those reached in 1984 and 1985. These results suggest that short generation time and high reproductive capacity permit rapid recovery from population reductions.
Consequences of pH measurement errors
Authors: HOENICKE RAINER , STAPANIAN MARTIN A. , ARENT LORI J. , METCALF RICHARD C.
Published: May 2006

SUMMARY.
1. The pH range over which the effects of acidification on freshwater organisms become apparent may be quite narrow, in some cases less than half a pH unit. Therefore, accurate measurement is important, particularly in dilute surface waters near the biologically critical threshold of hydrogen ion activity.

2. A hypothetical example based on data from two species of fish illustrates the potential errors in predicting mean mortality when pH is measured by probes of varying accuracies, placing our results into an ecosystem management perspective. For a given error, there will be greater uncertainty in predicting mean mortality for species sensitive to increased hydrogen ion activity than for more tolerant species.

3. We review field pH measurement errors, and present unique laboratory (measurements at 1°C and under argon) and field comparisons of current instruments used for continuous, in situ pH monitoring, including the only instrument comparison in low conductivity waters during snow melt. Four operator or sampler‐caused measurement errors and three electrode‐caused pH measurement errors are illustrated with data from four common types of pH probes and meters.

4. Studies providing no confidence intervals for a set of pH measurements due to the lack of rigorous quality control and assurance procedures are of limited quantitative value to future investigators attempting to analyse temporal trends of surface water acidification. Management and policy decision attempts will remain seriously hampered until more interpretable results are routinely generated.
An experimental study of the effects of predatory fish on macroinvertebrates in a Hong Kong stream
Authors: DUDGEON* DAVID
Published: May 2006

SUMMARY.
1. Predation upon macroinvertebrates by the loach Oreonectes platycephalus Günther (Cobitidae) was studied using predator inclusion/exclusion cages in a series of pools along a Hong Kong stream. Treatments employed were predator exclusion, medium (approximately natural) predator densities (1 fish cage−1) and high predator densities (2 fish cage−1). Macroinvertebrate abundance in cages was monitored after 2 and 4‐weeks exposure to predators.

2. The presence of fish was associated with significant declines in the total numbers of macroinvertebrates colonizing cages. However, taxa were influenced differently, with mayflies decreasing by a factor of two while the more mobile shrimps (Atyidae) were unaffected. Chironomid abundance (largely Chironominae) was unaffected by predator density and increased in week 4. Detritus acted as a confounding variable at this time because chironomid abundance was significantly correlated with the weight of accumulated detritus in cages.

3. While invertebrates were more abundant in cages lacking fish, there were no fewer invertebrates in cages with 2 fish than with 1 fish. This may indicate the presence of secure refuges among substrates in the cages, preventing the additional fish from depleting prey further, or a lack of precision of methods due to natural variations in prey densities and spatial patchiness.

4. No significant effects of predators on relative prey abundance or species richness were detected.

5. The impact of predation on prey abundance weakened on week 4, perhaps due to extra refuges among the accumulated detritus. However, drying of the stream increased fish densities in pools so that cages may have become zones of relative safety that were colonized readily by macroinvertebrates. This result highlights the need for year‐round investigations to quantify predation effects in Hong Kong's seasonal tropical climate.
Competition, survivorship and growth in macrophyte communities
Authors: WILSON SCOTT D. , KEDDY PAUL A.
Published: May 2006

SUMMARY.
1. Transplant experiments tested the proposition that the intensity of competition within macrophyte communities varies with standing crop in a freshwater marsh in Ontario, Canada.

2. Transplants of three species (Carex lasiocarpa, Juncus brachycephalus, Scripus validus) were grown at sixty‐six locations chosen to represent a range of standing crop values. At each location, transplants were grown in plots with all neighbours removed and in adjacent plots with all neighbours present.

3. The effect of neighbours on transplant growth did not vary with standing crop, soil, or water depth, with the exception of one species which was most suppressed by neighbours in shallow water. In contrast, the effect of neighbours on the survivorship of transplants was greatest on organic soils supporting high values of standing crop in shallow water, and least on mineral soils supporting low values of standing crop in deeper water.

4. The results indicated that establishment and survivorship of vegetative propagules was most likely to be affected by neighbours in shallow water, but that the growth of established plants was not influenced by neighbours anywhere. Growth results corroborate earlier findings that competition has little effect on aquatic macrophytes.
The distribution of chlorophylls, carotenoids and their breakdown products in Lake Kinneret (Israel) sediments
Authors: YACOBI Y.Z. , MANTOURA R.F.C. , LLEWELLYN C.A.
Published: May 2006

SUMMARY.
1. The sedimentary distribution of chlorophylls, carotenoids and their breakdown products following the winter‐spring bloom of the dinoflagellate Peridinium gatunense in Lake Kinneret was determined both spatially and vertically within the sediments, using high‐pressure liquid chromatography (HPLC).

2. All four stations (epilimnic, oxic St. J (depth = 8m) and D (12m) and hypolimnic, anoxic St. F (21 m) A (41 m) were characterized by the presence of chlorophyll a (chl‐a) chl‐b, chl‐c, phaeophytins a (ph'tin‐a) and b, phaeophorbide a (ph'bide‐a) and lutein, fucoxanthin, diatoxanthin and β‐carotene together with spectrally similar, but HPLC‐resolved, breakdown products in the surface sediments. The central deep station A (41 m), which is seasonally anoxic, trapped and preserved significantly more pigments (e.g. chl‐a= 16.35 μg g−1 organic matter) than the more erosive, oxic littoral stations (chl‐a= 1.10 and 0.76μg g−l OM at St. D and J, respectively).

3. Whereas it was possible to ascribe the presence of lutein and chl‐b to inputs of green algae and higher plants from the catchment, and fucoxanthin and chl‐c1, c2 to winter diatom blooms (e.g. Melosira granulata), there was a remarkable absence of peridinin and dinoxanthin from sediments, despite the dominance of dinoflagellates in the phytobiomass. This is consistent with the well‐known oxic lability of this epoxy carotenoid in aquatic systems, and indicates efficient breakdown of this dinoflagellate organic matter in the water column, prior to sedimentation.

4. Although pigment concentrations all decreased with depths within sediments, lutein and β‐carotene were selectively preserved compared to chl‐a and fucoxanthin which, at 40m depth at St. A, decreased to < 1% of their surface concentrations.
Seasonal trends in river biofilm storage products and electron transport system activity
Authors: BLENKLNSOPP SANDRA A. , GABBOTT PETER A. , FREEMAN CHRISTOPHER , LOCK MAURICE A.
Published: May 2006

SUMMARY.
1. Glycogen, poly‐beta‐hydroxyalkanoate (PHA) and electron transport system (ETS) activity levels were monitored seasonally in light‐ and dark‐grown biofilms from a North Wales river.

2. A spring peak was evident in glycogen, PHA and ETS activity levels per cm2 and per cell, with the exception of PHA per cell, which peaked in the winter.

3. There was a seasonal shift in the type of storage product found, perhaps reflecting seasonal changes in carbon sources.

4. The light‐grown spring biofilm yielded the greatest amount of bio‐film storage products per cm2. This should be taken into account during caloric studies of river biofilms as a food source for grazing invertebrates.

5. A model is presented of factors influencing storage product deposition in river biofilms. The thickness and cell packing of river biofilms should be noted in future studies. Storage product deposition can occur deep within thick biofilms, irrespective of the river water chemistry.
Biofilm development on leaf and wood surfaces in a boreal river
Authors: GOLLADAY S. W. , SINSABAUGH R. L.
Published: May 2006

SUMMARY 1. Biofilms are organic layers that develop on submerged surfaces. They are composed of micro‐organisms, exoenzymes, and detritus particles enclosed within a gelatinous matrix. While much is known about mineral surface biofilms, those developing on organic surfaces have not been extensively studied. We examined the influences of current velocity and substratum composition on biofilm development in a fourth‐order North American boreal river.

2. Arrays of white birch ice‐cream sticks and sugar maple leaves were placed at fast and slow current sites. Samples were collected periodically, analysed for mass loss, and assayed for microbial biomass (ATP, ergosterol, chlorophyll a) and exoenzyme activity associated with lignocellulose degradation (exo‐ and endocellulase, β‐glucosidase, phenol oxidase, peroxidase).

3. Biofilms developed rapidly on both surfaces. On leaves, biomass peaked within 30 days of exposure. On wood, ATP and chlorophyll a concentrations peaked within 30–70 days, whereas ergosterol increased throughout the study (161 days). On leaves, current velocity had little influence on biofilm development, although breakdown rates were greater at the fast flow site. On wood, ATP and chlorophyll a concentrations were greater at the fast flow site, whereas ergosterol concentrations and breakdown rates were similar at both sites. Microbial biomass was consistently greater on wood than leaves, Exoenzyme activity developed rapidly on both surfaces; current velocity had little influence on activity. Except for β‐glucosidase, activities were greater on wood than leaves.

4. Our results suggest that fungi are an important structuring element of organic surface biofilms and the physical stability of the substratum strongly influences biofilm development. Leaf surfaces are susceptible to softening and fragmentation, truncating biofilm development. In contrast, abrasion of wood surfaces removes senescent material exposing fresh substratum for colonization. Thus, wood surfaces with their greater physical stability, permit the development of more extensive biofilms. Wood surfaces may represent an overlooked but important site of metabolic activity in streams.