bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modelling the impact of the regulation of estuarine drift‐netting on the declared rod catch of Atlantic salmon	Salmo salarL. in the River Usk
Authors: Bowker  , Ferns  , Phillips  , Mawle  
Published: March 2003

1. A novel method was used to determine if the statutory regulation of drift‐netting at the mouth of the River Usk in Wales was associated with a significant improvement in the stock and rod catch of salmon in the river upstream.2. A linear regression model was constructed, in which the annual rod catch of salmon declared from the Usk between 1977 and 1988 was the dependent variable and the simultaneous annual catch declared from the nearby River Wye was the independent variable. The model was extrapolated to project the annual rod catches of salmon on the Usk, relative to the Wye, between 1989 and 1995.3. The model accurately projected the actual rod catches declared from the Usk in 1989, 1990 and 1991. However, between 1992 and 1995 the declared catches deviated significantly (P≤ 0.05) from those projected by the model. The upsurge in rod catches declared after 1992 from the Usk, relative to the Wye was concomitant with the regulation of estuarine drift‐netting.4. It was concluded that diminished estuarine exploitation had a beneficial impact on salmon angling success on the Usk. However, the utility of the model was restricted by inconsistencies in the methods used to generate the data, by changes in fishery management policies and by a lack of essential information on the interrelationships between catch, effort, stock and environmental conditions.
The fauna in the upper stony littoral of Danish lakes: macroinvertebrates as trophic indicators
Authors: Brodersen Klaus P. , Dall Peter C. , Lindegaard Claus 
Published: March 2003

1. The macroinvertebrate fauna living on stones in the exposed stony littorals of thirty‐nine Danish lakes were examined by multivariate numerical methods. The data were derived from 125 semi‐quantitative samples and a species list of 126 taxa. The mean number of individuals per sample was 960, and among the most common taxa were Asellus aquaticus, Gammarus, Oulimnius, Tinodes, Cricotopus and Dicrotendipes.2. The total number of species and fourteen individual taxa were positively correlated to mean depth of the lakes and eleven taxa were correlated to the total phosphorus concentration. The Shannon diversity was negatively correlated to the chlorophyll a concentration ([Chl a]).3. Community patterns were examined by detrended correspondence analysis (DCA), and the relationship between species data and selected environmental variables was analysed by canonical correspondence analysis (CCA). Mean lake depth was found to be the strongest environmental variable in explaining the species data. The [Chl a] and Secchi depth also explained significant variation in the distribution of the stony littoral invertebrates. Wind fetch and relative exposure did not explain any variation in the faunal composition among sites.4. The abilities of the macroinvertebrates to predict the lake trophic state, expressed as log ([Chl a]), were explored by means of weighted averaging (WA) regression and calibration. Two tolerance‐weighted WA models using inverse and classical regression for deshrinking are presented. The models were assessed by the root mean square error (RMSE) of prediction, using bootstrapping as cross validation, and by the correlation between observed and inferred log ([Chl a]). The model using inverse deshrinking had a RMSEboot = 0.41 and r2 = 0.63. By using classical regression, the predictability in the ends of the gradient was improved but the RMSE increased: RMSEboot = 0.46.5. Although the factors determining faunal distribution patterns in the Danish lowland lakes were highly multivariate and difficult to disentangle, it seems reasonable to use the WA estimated species optima and tolerances to [Chl a] in a bio‐assessment model.
Plasticity of Daphnia magna life history traits in response to temperature and information about a predator
Authors: Sakwińska Olga 
Published: March 2003

1. Exudates from predators often elicit early maturation in Daphnia, which may protect them from predation. Diel vertical migration (DVM) is also a predator‐avoidance device and affects life history traits because of the variable temperature experienced during migration. This study asks, therefore, how do these two effects interact and what are the net costs and benefits of the two defences combined?2. Key life history features were studied in a two factorial life table experiment in a monoclonal cohort of Daphnia magna to quantify the costs of predator‐induced defences.3. The costs of DVM, associated with low temperature, yielded a 30% decrease in the intrinsic rate of population increase. This was caused by later maturation and longer egg development time, despite a higher fecundity.4. Chemical information that predators were present resulted in smaller, more numerous offspring, but had no significant effect on size and age at first reproduction. The costs of induction were therefore associated with smaller, and thus presumably lower quality, offspring.5. Changes in life history induced by fish exudates were independent of the shifts caused by low temperature.6. The measure of fitness chosen to assess the costs of induced defences is important because the costs often depend on the environment.
Does sediment resuspension have persistent effects on phytoplankton? Experimental studies in three shallow lakes
Authors: Ogilvie Brett G. , Mitchell Stuart F. 
Published: March 2003

1. The persistence of effects of sediment resuspension on chlorophyll a, phytoplankton production and plant nutrients was examined by artificially resuspending sediment in enclosures in three shallow lakes and monitoring concentrations for 4–8 days. Realism was assessed by relating initial suspended solids concentrations to those observed during natural wind events.2. Positive effects on the phytoplankton, persisting for at least 4–6 days were detected in eight of the nine experiments, and similar effects on nutrient concentrations were also common, although suspended solids had normally returned to control levels within 24 h3. The phytoplankton during the periods of persistence was normally dominated by planktonic rather than benthic/meroplanktonic genera.4. Several of the positive responses appeared to be associated with relief of nitrogen deficiency in the algae.5. Persistent effects from previous resuspension events may cause baseline concentrations of phytoplankton and nutrients in shallow lakes to be overestimated and the effects of resuspension on phytoplankton and nutrients to be underestimated
Snail reaction to watercress leaf tissues: reinterpretation of a mutualistic ‘alarm’ hypothesis
Authors: Kerfoot W. C. , Newman R. M. , Hanscom Z. 
Published: March 2003

1. Both emergent and submersed growth forms of the amphibious mustard watercress (Nasturtium officinale) contain appreciable concentrations of glucosinolate that deter feeding by a variety of aquatic grazers. Glucosinolate and myrosinase are stored separately in plant tissues, but undergo hydrolysis upon tissue damage to form characteristic isothiocyanates and nitriles.2. Snails of the genus Physella readily consume yellowed, senescing leaves of watercress, yet are reluctant to attack fresh, green leaves. Laboratory behavioural studies confirm that these preferences are related to intrinsic properties of the leaves independent of periphyton concentrations. Snails are attracted to crushed yellow leaves, yet are actively repulsed by isothiocyanates liberated by crushed, green leaves, despite the higher nitrogen content of the green tissue.3. The aversion response to crushed green leaves confirms reports by Haynes & Taylor (1984) and others that snails avoid crushed leaves of watercress. However, our interpretation of the interaction is distinctly different from theirs. Rather than a damaged plant signalling imminent danger to host periphyton grazers, the liberation of the compound 2‐phenylethyl isothiocyanate from damaged tissues acts as a deterrent that protects the plant against opportunistic herbivores, which include certain snail species.
Diel emigration and colonization responses of blackfly larvae (Diptera: Simuliidae) to ultraviolet radiation
Authors: Donahue William F. , Schindler David W. 
Published: March 2003

1. Total counts of blackfly larvae densities over 30‐ and 57‐h periods in experimental channels during May of 1996 & 1997 indicate that ultraviolet radiation (UV; 290–400 nm) may be important in stimulating emigration.2. Under experimentally controlled solar UV exposure, larval densities at dawn in UV‐shielded channels were 161% and 168% higher than in the UV‐exposed channels. Larval densities in UV‐exposed channels then decreased by 68.2% and 81.1% between dawn and early afternoon of the two days; density decreases in UV‐shielded channels were slight, and not statistically significant, during the same periods.3. Larvae within UV‐exposed channels occupied shaded microhabitats during hours of intense solar radiation, suggesting that simuliid larvae can detect and respond to UV radiation over very short periods of time.4. A cyclical pattern of UV‐induced emigration during hours of increasing solar flux (06.30–13.30) and net immigration in the hours of decreasing solar flux and at night emerged. Thus stream invertebrates may be very sensitive to environmental changes, resulting in either increased UV flux or decreased shading of streams. Diel cycles in invertebrate densities should be taken into account in research designs and sampling protocols in order to identify and interpret correctly results of both periodic surveys and experiments.
Leaf breakdown and associated macroinvertebrates in alpine glacial streams
Authors: Robinson Christopher T. , Gessner Mark O. , Ward J. V. 
Published: March 2003

1. The relationship between macroinvertebrate assemblages and the breakdown of alder [Alnus viridis (Chaix), Dc.] leaves was examined by exposing leaf packs in four streams in an alpine glacial floodplain over 8 months. Although glacially fed, the four sites (pro‐glacial, glacial lake outlet, main channel, and a side‐channel with a mix of water sources) differed physically and contained different benthic communities.2. Leaf breakdown and associated fungal properties differed widely among sites. Leaf decay rate varied by an order of magnitude (k ranged from 0.0029 to 0.0305 day–1), and was fastest at the lake outlet (< 20% leaf mass remaining by day 45) and slowest at the pro‐glacial site (> 75% remaining on day 45). Rapid processing at the lake outlet was because of the presence of Acrophylax zerberus Brauer, a shredding caddisfly.3. There were few macroinvertebrate taxa at the pro‐glacial site (two to four taxa present in packs) and leaf breakdown was attributed primarily to micro‐organisms. Leuctra abundance in leaf packs was strongly correlated with fungal biomass but not with the sporulation activity of any specific aquatic hyphomycete. Other taxa, such as Baetis and chironomids, showed no relationship with any leaf characteristic, suggesting that leaf packs were used mainly as a habitat and not as a food resource.4. The predatory stonefly Isoperla was significantly associated with the abundance of macroinvertebrate prey (Baetis, Chironomidae and Leuctra) in leaf packs at the main and side‐channel sites. The results indicate that leaf breakdown can vary widely in alpine lotic environments, reflecting site‐specific differences in habitat characteristics, and in macroinvertebrate and fungal composition.
Predation by longfin smelt (Spirinchus thaleichthys) on the mysidNeomysis mercedisin Lake Washington
Authors: Chigbu P. , Sibley T. H. 
Published: March 2003

Summary1. Longfin smelt and mysid samples collected in Lake Washington from 1988 to 1992 were examined, and historic data on smelt and mysid abundance were reviewed to assess the impacts of smelt predation on Neomysis mercedis. The feeding habits of smelt were also examined for differences between odd and even years, and seasonal and ontogenetic variations in smelt diet were described.2. A reciprocal relationship in the abundance of 1+ smelt and Neomysis suggested that smelt regulate mysid abundance in the lake.3. The proportion of smelt diet contributed by mysids was higher for less abundant year classes of smelt.4. These results indicate that intraspecific competition for scarce mysids occurs in the even‐year classes of smelt.
Do xeric landscapes increase genetic divergence in aquatic ecosystems?
Authors: Thomas E. Perry , Blinn Dean W. , Keim Paul 
Published: March 2003

Summary1. Previous investigations of the ecological genetics among amphipods in south‐western U.S.A. suggested a xeric landscape promoted genetic divergence among passively dispersed freshwater invertebrates, thereby enhancing speciation events. We predicted that less divergence would occur among amphipod populations across similar geographic distances in mesic regions.2. EightHyalella aztecapopulations were sampled along a 200‐km transect in western Oregon, U.S.A. Genetic distances among populations were estimated from randomly amplified polymorphic DNA (RAPD). Genetic analyses indicated much less divergence among Oregon populations than among Arizona populations in an arid environment.3. Behavioural observations support the genetic data: Oregon populations exhibit little differentiation in swimming behaviour, whereasHyalellapopulations in Arizona exhibit extremes in swimming behaviour.4. These results provide preliminary support for the hypothesis that a xeric landscape promotes genetic and behavioural divergence among amphipods. Many aquatic invertebrates classified as panmictic populations may encompass genetically distinct groups; those isolated by a xeric landscape are especially prone to diversification.
Nutrient dynamics at the interface between surface waters and groundwaters
Authors: Dahm Clifford N. , Grimm Nancy B. , Marmonier Pierre , Valett H. Maurice , Vervier Philippe 
Published: March 2003

Summary1. The surface water/groundwater (SW/GW) interface is a crucial control point for lateral nutrient fluxes between uplands and aquatic ecosystems and for upstream/downstream (longitudinal) processes in lotic ecosystems.2. Hydrological and biogeochemical dynamics of the SW/GW ecotone are linked to the degree of channel constraint and the sediment characteristics of the floodplain and stream bed.3. The availability of specific chemical forms of electron donors and electron acceptors affects the spatial distribution of biogeochemical processes at the SW/GW interface. Temporal change in discharge is also a major factor affecting the rate and extent of these processes.4. The magnitude of SW/GW interactions in lotic ecosystems is predicted to be a major determinant of solute retention. Channel morphology, stream bed composition and discharge are predicted to be important controls on SW/GW interactions.5. Interdisciplinary research involving hydrologists, geomorphologists, aquatic ecologists, microbial ecologists and landscape ecologists is needed to further our present understanding of this critical interface linking terrestrial and aquatic ecosystems.
Response of stream fish to improved water quality: a comparison between the 1960s and 1990s
Authors: Eklöv A. G. , Greenberg L. A. , Brönmark C. , Larsson P. , Berglund O. 
Published: March 2003

Summary1. The effect of improved water quality on fish assemblages in streams in southern Sweden was assessed by comparing species composition at 161 sites and water quality at twenty‐nine sites in the 1960s and the 1990s.2. Water quality had improved and there was an increase in the number of sites or catchments with brown trout (Salmo trutta), stone loach (Barbatula barbatula) and eel (Anguilla anguilla). The response was greatest for brown trout and was best explained by increased oxygen concentrations.3. The number of sites with nine‐spined stickleback (Pungitius pungitius), ide (Leuciscus idus) and brook lamprey (Lampetra planeri) decreased between the 1960s and 1990s. The decrease was greatest for nine‐spined stickleback and was related to the increase in sites with trout, suggesting that nine‐spined stickleback may be sensitive to predation or competition.4. Improved water quality has led to recolonization by brown trout, probably enabling biotic interactions to play a larger role in structuring fish assemblages. Improving water quality was an effective method for rehabilitating fish populations in streams where natural colonization was possible.
The hydrogeomorphic approach to functional assessment of riparian wetlands: evaluating impacts and mitigation on river floodplains in the U.S.A.
Authors: Hauer F. Richard , Smith R. Daniel 
Published: March 2003

Summary1. The ’hydrogeomorphic‘ approach to functional assessment of wetlands (HGM) was developed as a synthetic mechanism for compensatory mitigation of wetlands lost or damaged by human activities. The HGM approach is based on: (a) classification of wetlands by geomorphic origin and hydrographic regime (b) assessment models that associate variables as indicators of function, and (c) comparison to reference wetlands that represent the range of conditions that may be expected in a particular region. In this paper, we apply HGM to riparian wetlands of alluvial rivers.2. In the HGM classification, riverine wetlands are characterized by formative fluvial processes that occur mainly on flood plains. The dominant water sources are overbank flooding from the channel or subsurface hyporheic flows. Examples of riverine wetlands in the U.S.A. are: bottomland hardwood forests that typify the low gradient, fine texture substratum of the south‐eastern coastal plain and the alluvial flood plains that typify the high gradient, coarse texture substratum of western montane rivers.3. Assessment (logic) models for each of fourteen alluvial wetland functions are described. Each model is a composite of two to seven wetland variables that are independently scored in relation to a reference data set developed for alluvial rivers in the western U.S.A. Scores are summarized by a ’functional capacity index‘ (FCI), which is multiplied by the area of the project site to produce a dimensionless ’functional capacity unit‘ (FCU). When HGM is properly used, compensatory mitigation is based on the FCUs lost that must be returned to the riverine landscape under statutory authority.4. The HGM approach also provides a framework for long‐term monitoring of mitigation success or failure and, if failing, a focus on topical remediation.5. We conclude that HGM is a robust and easy method for protecting riparian wetlands, which are critically important components of alluvial river landscapes.
Α comparison of alternative techniques for prediction of the fauna of running‐water sites in Great Britain
Authors: Moss D. , Wright J. F. , Furse M. T. , Clarke R. T. 
Published: March 2003

1. Early versions of the river invertebrate prediction and classification system (RIVPACS) used TWINSPAN to classify reference sites based on the macro‐invertebrate fauna, followed by multiple discriminant analysis (MDA) for prediction of the fauna to be expected at new sites from environmental variables. This paper examines some alternative methods for the initial site classification and a different technique for prediction.2. A data set of 410 sites from RIVPACS II was used for initial screening of seventeen alternative methods of site classification. Multiple discriminant analysis was used to predict classification group from environmental variables.3. Five of the classification–prediction systems which showed promise were developed further to facilitate prediction of taxa at species and at Biological Monitoring Working Party (BMWP) family level.4. The predictive capability of these new systems, plus RIVPACS II, was tested on an independent data set of 101 sites from locations throughout Great Britain.5. Differences between the methods were often marginal but two gave the most consistently reliable outputs: the original TWINSPAN method, and the ordination method semi‐strong hybrid multidimensional scaling (SSH) followed by K‐means clustering.6. Logistic regression, an alternative approach to prediction which does not require the prior development of a classification system, was also examined. Although its performance fell within the range offered by the other five systems tested, it conveyed no advantages over them.7. This study demonstrated that several different multivariate methods were suitable for developing a reliable system for predicting expected probability of occurrence of taxa. This is because the prediction system involves a weighted average smoothing across site groupings.8. Hence, the two most promising procedures for site classification, coupled to MDA, were both used in the exploratory analyses for RIVPACS III development, which utilized over 600 reference sites.
Quantified small‐scale turbulence inhibits the growth of a green alga
Authors: Hondzo Midhat , Lyn Dennis 
Published: March 2003

1. Laboratory experiments were conducted to elucidate the effect of small‐scale turbulent fluid motion on the growth of laboratory cultures of the freshwater algae Scenedesmus quadricauda. Turbulent flow was generated using an oscillating‐grid apparatus. The experiments were performed under the range of fluid flow conditions similar to those occurring in nature. The only growth limiting factor was the effect of small‐scale fluid motion; all other environmental factors, such as light, temperature and nutrients, were kept constant.2. Growth of Scenedesmus quadricauda, measured in terms of chlorophyll a concentration, was inhibited when the level of turbulence in the water column was increased. Algal growth was maximum in a quiescent fluid. The inhibitory effect of fluid motion was observed independently of flow regime (laminar, transitional, turbulent) in the water column.3. Cell destruction and aggregation of dead and living cells of algae were observed in a turbulent flow. High shear rates, estimated from the dissipation of turbulent kinetic energy, caused the cell destruction, algal collision and agglomeration of algae. Data on Scenedesmus responses to small‐scale fluid motion will enhance and broaden our ability to develop predictive multispecies models for freshwater phytoplankton communities.
Prey selection and diel feeding of the freshwater jellyfish, Craspedacusta sowerbyi
Authors: Spadinger Reinhard , Maier Gerhard 
Published: March 2003

Summary1. The diet of the invasive freshwater jellyfish, Craspedacusta sowerbyi (Lankester), was assessed by analysing its stomach contents.2. The medusae ingested various zooplankton and benthic prey in the 0.1–3.0 mm size range. The selectivity indices for prey showed that larger zooplankton (0.4–1.4 mm) and active prey such as copepods were preferred; small potential prey, and the loricate rotifer Keratella cochlearis in particular, were almost never consumed. Measurements suggest that spacing between the tentacle branches could determine prey selection. Another possibility is that some prey are too small or slow to activate nematocysts after collision with the predator. Prey > 1.4 mm can probably escape or are otherwise too large to be handled.3. The medusae of Craspedacusta medusae stayed in deep water during daytime and migrated upwards at night. The greatest number of prey in freshwater jellyfish stomachs was detected at night.4. Calculation of consumption rates, based on mean stomach contents and digestion times of 4–5 h, showed that, on average, one medusa takes 190 zooplankton prey day−−1 at a mean prey density of about 100 L−−1. At the observed medusae density of 1 m−−3, the cropping rate was about 0.2 zooplankton prey L−−1 day−−1.