bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlocal wind‐driven fjord–coast advection and its potential effect on plankton and fish recruitment
Authors: Asplin Lars , Salvanes Anne Gro Vea , Kristoffersen Jon Bent
Published: March 2003

The Bergen Ocean Model (BOM), a three‐dimensional physical coastal ocean model, was used for a numerical simulation experiment to investigate short‐term effects of wind‐generated coastal upwelling and downwelling on the dynamics of adjacent large outer and smaller inner fjords. The effect of the real alongshore wind regime on advection for an idealized fjord topography, resembling Masfjorden, western Norway, is used as an example. This modelling exercise is a supplement to, and its predictions support, the various hypotheses investigated in ecosystem simulation studies of the Masfjorden. The model predicts that coastal winds from the north cause upwelling and transport the upper water layer out from the fjords. Winds from the south cause downwelling and transport the upper water layer into the fjords. The transport is rapid and ≈50% of the upper water layer may be replaced within 1–2 days. Implications of these physical processes for the dispersal and retention of planktonic organisms and the early life stages of fish are discussed. If strong southerly winds occur frequently, this will transport planktonic organisms into the fjord and may increase the carrying capacity for planktivorous fish. In contrast, frequent strong northerly winds may reduce the abundance of planktonic organisms, including the early life stages of marine fish, and thus possibly reduce recruitment to fjord fish populations. Frequent shifts between southerly and northerly winds would cause an exchange of early life stages between neighbouring fjords and thus enhance genetic exchange.
Relationship between freshwater input to the coastal zone and the historical landings of the benthic/demersal fish Eleginops maclovinus in central‐south Chile
Authors: Quiñones R. A. , Montes R. M.
Published: March 2003

The ecosystem off central‐south Chile is one of the most productive marine systems in the world, providing approximately 4% of worldwide fish captures. We analysed the effect of freshwater input (river runoff and rainfall) to the coastal zone in central‐south Chile (36°00′–37°30′ lat. S) on the landings of the Róbalo (Eleginops maclovinus) using the following data: Róbalo annual landing statistics, monthly mean and annual mean runoff of Itata (1975–91) and Bio‐Bio rivers (1975–94), and cumulative monthly rainfall and annual mean rainfall (1975–94). Time series were smoothed using three‐point equally weighted running means. To analyse the relationship between Róbalo’s landing and river runoff, as well as rainfall, Pearson’s product‐moment correlation analyses were conducted at relevant lag times. The statistical significance of correlation coefficients was calculated taking into account intraseries autocorrelation. Our results showed that Róbalo’s landings were significantly correlated to freshwater input to the coastal zone in central‐south Chile. Thus, significant correlation coefficients were found between annual Róbalo’s landings and: (i) annual mean runoff of the Itata (r=−0.94) and Bio‐Bio (r=−0.80) rivers lagged 3 and 4 years, respectively, and (ii) annual mean rainfall lagged 4 years (r=−0.75). The lag time at which highest correlation coefficients between annual mean environmental and annual landing time series took place (i.e. 3–4 years) corresponded to the age at which Róbalo reaches the minimum exploitation size. Accordingly, we hypothesize that river runoff and rainfall strongly influence the survival rate of Róbalo’s early stages during the first year of life.
Using patch studies to link mesoscale patterns of feeding and growth in larval fish to environmental variability
Authors: Dower John F. , Pepin Pierre , Leggett William C.
Published: March 2003

We present results from a series of three patch studies designed to examine links between environmental variability and mesoscale patterns of feeding and growth of larval radiated shanny (Ulvaria subbifurcata). We examine the effects of variability in temperature, turbulence and prey concentration on both the mean (i.e. population level) and the variance (i.e. individual level) of larval feeding and growth rates among the three bays. Although both gut fullness and growth rates differ significantly between bays, our results show only weak environmental influences. When larvae are pooled across bays (i.e. treated as independent observations), environmental factors generally explain <4% of the variability in gut fullness. When treated as daily mean residuals, however, temperature accounts for 41% of the variability in mean gut fullness, while both temperature and prey concentration also explain significant portions of the variance in gut fullness (38 and 43%, respectively). Between‐bay differences in larval growth rates are consistent with patterns of temperature variation but not with patterns of prey availability. Studies relying on tracking a single patch of larvae typically suffer from having too few observations to detect significant relationships between feeding or growth and environmental variables. By following three patches we collected a larger number of observations. However, as we encountered only a limited range of environmental conditions it remains difficult to adequately assess the role of environmental factors. In part, this problem stems from the inability of fisheries oceanographers to track the recent environmental history of individual larvae on the same fine scales currently employed to collect biological data (e.g. guts and otoliths) on individuals.
The feeding ecology of larval Pacific hake (Merluccius productus) in the California Current region: an updated approach using a combined OPC/MOCNESS to estimate prey biovolume
Authors: Cass‐Calay Shannon L.
Published: March 2003

A combined optical particle counter (OPC) and multiple opening and closing net and environmental sensing system (MOCNESS) was used to obtain simultaneous measurements of the fine‐scale distribution of ‘prey‐sized’ particles and the vertical distribution of larvae of Pacific hake (Merluccius productus). Physical properties were also measured. The data were used to describe the feeding ecology of Pacific hake larvae, and to explore the effects of prey abundance, time of day, temperature and depth on feeding. Pacific hake larvae consumed a wide variety of prey including copepod eggs, nauplii, copepodites, and euphausiid metanauplii. Calanoid copepodites comprised > 75% of the ingested prey volume. First‐feeding larvae were 2.5–3.0 mm SL. These larvae consumed prey 40–200 μm wide. Larvae 3.0–6.5 mm long ingested prey 40–400 μm wide and larvae > 6.5 mm long ingested prey 400–700 μm wide. There were clear diel patterns in feeding incidence and prey volume ingested. Feeding commenced between 06:01 and 08:00 hours PST and continued until ∼ 16:00 hours. Ingested prey items remained in the gut until complete gut evacuation occurred near dawn. The volume of food ingested was estimated using two indices, the cube root of the prey volume (CRPV) and the cube root of the stomach volume (CRSV). Standard length, log elapsed time since gut evacuation, depth and particle biovolume contributed significantly to variation in both indices. Temperature did not contribute to variability in either CRPV or CRSV.
The relationship between the skipjack tuna (Katsuwonus pelamis) fishery and seasonal temperature variability in the south‐western Atlantic
Authors: Andrade H. A.
Published: March 2003

The spatio‐temporal distribution of tuna fishing effort has been related to oceanographic circulation and features in several seas of the world. Understanding the relationship between environmental variables and fishery resource dynamics is important for management decisions and to improve fishery yields. The relationship between sea temperature variability and the pole‐and‐line skipjack tuna (Katsuwonus pelamis) fishery in the south‐western Atlantic Ocean was investigated in this work. Data from logbooks, satellite images (sea surface temperature), and oceanographic surveys were used in the analyses. Skipjack are caught in warm tropical waters of the Brazil Current (BC). The north–south displacement of fishing effort was strongly associated to seasonal variation of the surface temperature, which was coupled to the tropical BC flow. Oceanographic fronts from autumn to spring and a shallow thermocline in summer probably induces the aggregation of skipjack schools over the shelfbreak, favouring fishing operations. Hypotheses are proposed to explain the relationship between peaks of fishing events and the presence of topographic peculiarities of the shelfbreak.
Light availability as a possible regulator of cyanobacteria species composition in a shallow subtropical lake
Authors: Havens Karl E. , Phlips Edward J. , Cichra Mary F. , Li Bai‐lian
Published: March 2003

1. Variations in the relative biovolumes of dominant cyanobacterial taxa were evaluated in the context of environmental conditions using canonical correlation analysis (CCorrA) and Redundancy Analysis (RDA). The objective was to test a conceptual model in which underwater irradiance determines dominance by bloom‐forming (high light adapted) or non‐blooming (low light adapted) taxa.

2. The data set consisted of 404 contiguous observations, collected over a 3‐year period at eight pelagic sites, in shallow Lake Okeechobee, Florida, U.S.A. Data included species biovolumes, total phosphorus (TP), total nitrogen (TN), dissolved oxygen (DO) and chlorophyll a concentrations, as well as two indices: underwater irradiance (Secchi depth) and the ratio of Secchi:total depth.

3. The first environmental canonical variable was strongly correlated with the two light‐related indices, and negatively correlated with TP. This reflects the predominant role of resuspended P‐rich lake sediments in controlling underwater irradiance in the shallow lake. The first species canonical variable displayed a strong negative correlation with Lyngbya limnetica and L. contorta, and positive correlations with Anabaena circinalis, Aphanizomenon flos aquae and Microcystis spp. The results support the conceptual model; the first pair of canonical variables explained 55% of the variation in the species–environmental data set. RDA results provided further support for the hypothesis that irradiance was the major force controlling community structure.

4. One unexpected result was a positive association between Oscillatoria spp. dominance and indicators of high irradiance. This conflicts with past research indicating that Oscillatoria is a low light adapted taxon, and the finding that it is the most abundant taxon in Lake Okeechobee. This may reflect the fact that the two Lyngbya taxa were more strongly associated with low light conditions than Oscillatoria. CCorrA results indicated that Oscillatoria densities are strongly controlled by water temperature. There is a need for more detailed studies of cyanobacteria ecophysiology in order to explain fully the seasonality of phytoplankton in this and other shallow subtropical lakes.
Epiphytic algae and macroinvertebrates on submerged and floating‐leaved macrophytes in an Italian lake
Authors: Cattaneo Antonella , Galanti Gaetano , Gentinetta Silvia , Susana And
Published: March 2003

1. The presence of contiguous beds of submerged (Myriophyllum spicatum, Ceratophyllum demersum and Najas marina) and floating‐leaved (Trapa natans) vegetation in a north Italian lake allowed us to test the effect of the different host architecture on epiphytic algae and invertebrates and to predict the consequences for the lake of changes in the predominant vegetation.

2. Epiphyton development, measured as carbon, nitrogen, phosphorus, chlorophyll a (Chl a), phaeophytin and as algal and macroinvertebrate density, was significantly higher on submerged plants than on T. natans. The C : Chl a ratio, a proxy of the ratio of heterotrophs to autotrophs, was higher on the floating‐leaved plants. The elemental (C : N : P) and pigment (Chl a : phaeophytin) ratios were not significantly different between the two vegetation types.

3. The taxonomic composition of epiphytic algae and invertebrates was similar on the different plants. The more varied morphology of the floating‐leaved T. natans resulted in a higher diversity of epiphytic algae, however, but not of macroinvertebrates.

4. There was a significant inverse relationship between epiphyton biomass and the standing crop of the host plant, suggesting a key role for light and water exchange in epiphyton development.

5. Replacement of floating‐leaved by submerged plants would increase the total biomass of epiphytic algae and invertebrates.
Influence of diet shifts in underyearling fish on phosphorus recycling in a hypertrophic biomanipulated reservoir
Authors: Mehner Thomas , Mattukat Frank , Bauer Dirk , Voigt Hanno , Benndorf Jürgen
Published: March 2003

1. In addition to effects of direct predation by planktivorous fish, nutrient recycling by fish may also contribute to structuring foodwebs in lakes. There is little evidence, however, about whether underyearling fish undergoing several ontogenetic diet shifts may have a comparable bottom‐up impact.

2. This study examined seasonal patterns of phosphorus (P) concentration and external load, phytoplankton, zooplankton and benthos, and diet shifts in three underyearling fish [perch (Perca fluviatilis), roach (Rutilus rutilus) and ruffe (Gymnocephalus cernuus)] in the shallow, hypertrophic biomanipulated Bautzen reservoir, Germany. Phosphorus metabolism of fish was calculated by a balanced bioenergetics model on the basis of fish diet, growth and water temperature.

3. The fish showed several shifts from planktivory to other food sources during the sampling period from May to September. These shifts were probably caused by the seasonal succession of the zooplankton community, mainly the midsummer decline of Daphnia galeata.

4. The diet shifts in fish also had consequences for the amount of P consumed and released. During periods of dominant zooplanktivory, the excretion of P did not exceed the removal of P stored in pelagic prey. By contrast, if benthivory dominated, fish subsidized the pelagic P pool by excreting more P from benthic prey than had been removed from the pelagic area. This occurred predominantly in perch and ruffe during periods of low zooplankton biomass, whereas the roach ate more algae and therefore excreted less P of benthic origin.

5. Phosphorus release by underyearling fish was estimated at a maximum of 0.1 mg m–3 JY day–1. This value was negligible compared with both the external load of P to Bautzen reservoir and the concentration of P in the pelagic area during summer. It is therefore concluded that both the predominance of underyearling zooplanktivorous fish and the high Daphnia biomass during certain periods of the year in the Bautzen reservoir may be the reason that nutrient release by the fish structured the foodweb only marginally. 6. This study suggests that biomanipulation has altered both top‐down and bottom‐up impacts of fish in Bautzen reservoir. The highest efficiency of foodweb manipulations may be obtained after reduction of the external P loading below a certain threshold. In turn, if external restoration of eutrophied lakes is not accompanied by changes in fish community, then the combined forces of strong zooplanktivory and high P recycling of dense stocks of zooplanktivorous and benthivorous fish may hold the water in a eutrophic‐like stage, even if external load has been significantly reduced.
An assessment of the influence of recruitment from the sediment on the development of planktonic populations of cyanobacteria in a temperate mesotrophic lake
Authors: Head R. M. , Jones R. I. , Bailey‐Watts A. E.
Published: March 2003

1. A number of planktonic cyanobacteria species form resting stages that survive in the sediments of lakes. The significance of this life history strategy to the ecology of new planktonic populations was investigated in Esthwaite Water, a mesotrophic lake in the English Lake District.

2. A simple trapping technique was used to quantify vertical movements of five species of buoyant gas‐vacuolate cyanobacteria from close to the sediments, along a depth transect.

3. ‘Recruitment’ from the sediments was found to be widespread amongst the cyanobacteria species associated with the summer phytoplankton community.

4. Estimates of the vertical upward fluxes of cyanobacteria based upon trap catches could not account for observed increases in the planktonic populations suggesting that ‘recruitment’ was not a significant source of biomass.

5. Vertical upward movements of Anabaena solitaria were recorded prior to this species becoming established in the plankton suggesting that benthic populations might be a source of cells for initial pelagic growth of populations of this species.

6. Low numbers of vegetative filaments of Anabaena flos‐aquae, Aphanizomenon flos‐aquae and Oscillatoria agardhii were observed in the plankton through the winter. These small overwintering populations appeared to be the primary source of inocula for the large summer populations of these species.
Defining and measuring river health
Authors: Karr James R.
Published: March 2003

1. Society benefits immeasurably from rivers. Yet over the past century, humans have changed rivers dramatically, threatening river health. As a result, societal well‐being is also threatened because goods and services critical to human society are being depleted.

2. ‘Health’— shorthand for good condition (e.g. healthy economy, healthy communities) — is grounded in science yet speaks to citizens.

3. Applying the concept of health to rivers is a logical outgrowth of scientific principles, legal mandates, and changing societal values.

4. Success in protecting the condition, or health, of rivers depends on realistic models of the interactions of landscapes, rivers, and human actions.

5. Biological monitoring and biological endpoints provide the most integrative view of river condition, or river health. Multimetric biological indices are an important and relatively new approach to measuring river condition.

6. Effective multimetric indices depend on an appropriate classification system, the selection of metrics that give reliable signals of river condition, systematic sampling protocols that measure those biological signals, and analytical procedures that extract relevant biological patterns.

7. Communicating results of biological monitoring to citizens and political leaders is critical if biological monitoring is to influence environmental policies.

8. Biological monitoring is essential to identify biological responses to human actions. By using the results to describe the condition, or health, of rivers and their adjacent landscapes and to diagnose causes of degradation, we can develop restoration plans, estimate the ecological risks associated with land use plans in a watershed, or select among alternative development options to minimize river degradation.
Emergence and lateral dispersal of adult Plecoptera and Trichoptera from Broadstone Stream, U.K.
Authors: Petersen Irene , Winterbottom Julie H. , Orton Stuart , Friberg Nikolai , Hildrew Alan G. , Spiers D. C. , Gurney† W. S. C.
Published: March 2003

1. Emergence and inland dispersal of adult stoneflies (Plecoptera) and caddisflies (Trichoptera) from Broadstone Stream, an acidic and iron‐rich stream in southern England, were studied over 10 months in 1996–1997. Fifteen pyramidal emergence traps were placed randomly in a 200‐m stretch. Three Malaise traps were placed above the stream and six more on each side (one wooded, one open) along a transect at distances of 1, 15, 30, 45, 60 and 75 m from the channel.

2. More than 16 000 stoneflies, belonging to 11 species, and just under 400 caddisflies (22 species) were caught. Four dominant stoneflies (Leuctra fusca, Leuctra nigra, Leuctra hippopus and Nemurella pictetii) accounted for 96% and 95% of the catches in the emergence and Malaise traps, respectively. Two caddisflies (Plectrocnemia conspersa and Potamophylax cingulatus) accounted for 63% of the catch in the Malaise traps. Few caddisflies were taken in emergence traps.

3. The emergence periods of L. fusca, L. nigra and L. hippopus were well‐defined and unimodal, whereas that of N. pictetii was prolonged and erratic. Overall, more females (1285) emerged than males (740).

4. Female stoneflies and caddisflies were in the majority in the Malaise traps above the stream. On land, significantly more females than males of L. fusca, L. nigra and P. cingulatus were caught. The sex ratio of the remaining species did not deviate significantly from 1:1.

5. The three Malaise traps placed above the stream caught most of the stoneflies though there was also dispersal away from the channel, the numbers caught declining with distance. Exponential models explained between 67% and 99% of the variation in numbers of individuals with distance from the channel in the four common stoneflies. Half the individuals went less than 11–16 m from the stream, while 90% travelled less than 51 m. Significantly more L. nigra and N. pictetii were caught in the woodland than on the open side, whereas L. hippopus showed no overall preference for either side.
Macrophyte diversity and composition in relation to substratum characteristics in regulated and unregulated Danish streams
Authors: Baattrup‐Pedersen Annette , Riis Tenna
Published: March 2003

1. The objective of the present study was to examine how the physical stream environment in regulated and unregulated lowland streams affects the diversity and distribution of macrophyte communities. We analysed the abundance, distribution and composition of macrophytes, together with physical parameters, in seven regulated and seven unregulated unshaded Danish stream reaches.

2. Total macrophyte coverage was similar in the regulated and unregulated streams, but species richness and Shannon diversity were higher in the unregulated streams. Overall, we found fifty‐two different species in the regulated stream reaches and sixty‐two in the unregulated stream reaches. The spatial distribution of macrophytes on the stream bottom was more heterogeneous in the unregulated streams.

3. We found positive correlations between the coverage and diversity of macrophytes and the coverage of coarse‐textured substratum types on the stream bottom, as well as between macrophyte coverage and diversity and substratum heterogeneity. We also found that the macrophytes were more heterogeneously distributed where substratum heterogeneity was greater.

4. The species growing both submerged and emergent were more abundant in the regulated streams, whereas species growing only submerged were more abundant in the unregulated streams. Species growing submerged, species growing both submerged and emergent, and species only growing emergent segregated differently in a canonical correspondence analysis ordination. The submerged species were primarily associated with coarser‐textured substrata, whereas species growing both submerged and emergent, and species growing only emergent were associated with finer‐textured substrata.

5. The most abundant species in the regulated streams, Sparganium emersum, accounting for almost one‐third of the total macrophyte coverage, was primarily associated with clay and sandy bottom substrata, whereas the most abundant species in the unregulated streams, Batrachium peltatum, was primarily associated with gravel and stony substrata.
Velocity gradients and turbulence around macrophyte stands in streams
Authors: Sand‐Jensen Kaj , Pedersen Ole
Published: March 2003

1. Submerged macrophytes strongly modify water flow in small lowland streams. The present study investigated turbulence and vertical velocity gradients using small hot‐wire anemometers in the vicinity and within the canopies of four macrophyte species with the objective of evaluating: (a) how plant canopies influence velocity gradients and shear force on the surfaces of the plants and the stream bed; and (b) how the presence and morphology of plants influence the intensity of turbulence.

2. Water velocity was often relatively constant with water depth both outside and inside the plant canopies, but the velocity declined steeply immediately above the unvegetated stream bed. Steep vertical velocity profiles were also observed in the transition to the surface of the macrophyte canopy of three of the plant species forming a dense shielding structure of high biomass. Less steep vertical profiles were observed at the open canopy surface of the fourth plant species, growing from a basal meristem and having the biomass more homogeneously distributed with depth. The complex distribution of hydraulic roughness between the stream bed, the banks and the plants resulted in velocity profiles which often fitted better to a linear than to a logarithmic function of distance above the sediment and canopy surfaces.

3. Turbulence increased in proportion to the mean flow velocity, but the slope of the relationships differed in a predictable manner among positions outside and inside the canopies of the different species, suggesting that their morphology and movements influenced the intensity of turbulence. Turbulence was maintained in the attenuated flow inside the plant canopies, despite estimates of low Reynolds numbers, demonstrating that reliable evaluation of flow patterns requires direct measurements. The mean velocity inside plant canopies mostly exceeded 2 cm s−−1 and turbulence intensity remained above 0.2 cm s−−1, which should be sufficient to prevent carbon limitation of photosynthesis in CO2‐rich streams, while plant growth may benefit from the reduced physical disturbance and the retention of nutrient‐rich sediment particles.

4. Flow patterns were highly reproducible within canopies of the individual species despite differences in stand size and location among streams. We propose that individual plant stands are suitable functional units for analysing the influence of submerged macrophytes on flow patterns, retention of particles and biological communities in lowland streams.
Nutrient enhancement, food quality and community dynamics in a tropical rainforest stream
Authors: Pearson R. G. , Connolly N. M.
Published: March 2003

A mixed nutrient supplement was added to stream‐side experimental channels in a closed canopy rainforest in tropical Queensland over a 7‐month period, raising nitrogen and phosphorus concentrations well above ambient.

Nutrient supplements enhanced decomposition of some leaf species, but levels of chlorophyll a and fine particulate organic matter did not differ between treatment and control channels.

Shredding by Anisocentropus kirramus (Trichoptera) had a significant effect on leaf litter breakdown, but nutrient supplements did not enable A.kirramus to shred more material; however, biochemical analysis of A. kirramus showed that nutrient supplements enhanced the nutritional quality of the litter for this species.

Treatment channels contained 75% more invertebrates than control channels, but significant differences in abundance (all positive) were detected in only five of the 109 invertebrate species present. There was no change in species richness or evenness between treatment and control channels.

The limited community response indicates that (a) variables other than nutrients (e.g. light) restricted primary productivity, (b) low nutrient concentrations limit invertebrate production, (c) invertebrate community composition in this closed canopy, forest stream is resistant to nutrient enhancement, and (d) there was no direct relationship between productivity and diversity in this tropical stream.
Transient physicochemical microhabitats facilitate fish survival in inhospitable aquatic plant stands
Authors: Miranda L. E. , Driscoll M. P. , Allen M. S.
Published: March 2003

1. Aquatic plants add structural complexity to aquatic environments, provide resources for the food web and generally promote diversity and stability of aquatic fauna. However, plants also alter the abiotic properties of the water and at high densities can produce physical and chemical conditions intolerable to fish.  2. We identified substantial horizontal and vertical, as well as spatial and temporal, variability in oxygen and temperature over micro‐scales within macrophyte stands. Areas with suitable dissolved oxygen and temperature occurred close to areas with hypoxic and hyperthermic levels regarded as highly stressful to lethal for fish. Fish densities within the plant stands did not change between dusk and dawn, suggesting that fish did not leave the vegetation when conditions became adverse.  3. Variability in oxygen and temperature within the plant bed conceivably provided refugia for fish. Portions of the macrophyte bed, particularly the surface, provided suitable conditions during times of the day when oxygen tensions in deeper water were low, but not during times when surface conditions were hyperoxic and hyperthermic. During periods of low oxygen, fish may rise to the surface and either remain there, or use the surface as a corridor to travel until oxygenated pockets are located.  4. Aquatic plant stands may be thought of as a mosaic landscape composed of patches of transient physicochemical microhabitats. Within this landscape, physicochemical conditions can be precarious and fish may have to continuously change microhabitats to avoid being trapped in unsuitable locations during the daily reshuffling of physical and chemical conditions.
The costs of moulting in Daphnia; mineral regulation of carbon budgets
Authors: Hessen Dag O. , Alstad Rukke Nina
Published: March 2003

1. Zooplankton differ in their elemental contents. For the essential elements calcium (Ca) and phosphorus (P), Daphnia spp. have particularly high contents, and thus high demands, compared with other cladocera and copepods.  2. There are recent indications that the growth of zooplankton, notably Daphnia, may be directly constrained by the availability of P and Ca.  3. Major pools of P and Ca are associated with the carapace, and the moulting process represents a constant drain of these elements, as well as carbon (C), from the animals.  4. The demands for P and Ca for moulting may pose constraints on the carbon accumulation in the animals, and thus the extensive needs for these elements may translate into a total loss of C transported in the pelagic food web.  5. While the costs of moulting are substantial for the zooplankton, the export of minerals bound in the moult will play only a minor role for the epilimnetic element budgets in most lakes.
An investigation of dominance in phytoplankton using the PROTECH model
Authors: Elliott J.A. , Reynolds C.S. , Irish A.E.
Published: March 2003

1. Using a model (PROTECH‐C) that simulates the simultaneous daily growth of eight phytoplankton species, the following hypotheses were tested: (i) for each given set of simulated conditions, the species with the most appropriate trait, as predicted by a functional group classification, should dominate the community; (ii) with removal of this dominant species, the next best‐adapted species should dominate and should be from the same, or a close, functional group where available; (iii) a reduction in the inoculum size of the initially dominant species will not prevent its eventual dominance of the community.  2. For clearer insight into the mechanisms underlying these community processes, a functional group classification based upon species morphology has been used to produce a matrix analogous to Grime's CSR (C, competitor; S, stress tolerator; R, ruderal) paradigm. The effects upon this phytoplankton community of temperature, grazing, limiting light and nutrients over a simulated year were recorded.  3. The results supported all three hypotheses. It was found that, for a given selective constraint, functional traits provided excellent predictors of the dominant types. Also, under conditions of resource competition, the number of functional groups represented decreased. Competition was greatest within functional groups where niche overlap was high, but one species was always clearly the strongest competitor, i.e. its superiority over its nearest functional competitor was regularly expressed even when the difference in inoculum size was great (1000‐fold). These conclusions emphasized the power that trait selection can have in the shaping of communities.
Evidence for local adaptation in neighbouring Daphnia populations: a laboratory transplant experiment
Authors: Declerck Steven , Cousyn Christophe , De Meester Luc
Published: March 2003

1. We tested whether two neighbouring Daphnia galeata populations (from Lake Blankaart and Fish Pond), separated only by 5 m of land and with the occasional exchange of water were genetically differentiated in allozyme markers and life history traits. Allozyme electrophoresis revealed that the populations differed in allelic as well as in genotypic composition.  2. In a laboratory transplant experiment, in which animals of four clones of each of the populations were raised in the water of both ponds, survival in Blankaart water was high for both the Blankaart and Fish Pond clones, whereas survival in Fish Pond water was high for the Fish Pond clones, but low for the Blankaart clones.  3. Fish Pond clones produced fewer neonates than Blankaart clones when cultured in Blankaart water. High egg mortality was observed for animals that were raised in Blankaart water, and this egg mortality was higher for Fish Pond clones than for Blankaart clones.  4. Our results provide evidence for genetic differentiation between Daphnia populations inhabiting neighbouring water bodies and suggest local adaptation to environmental conditions other than direct predation.
Effects of urbanization on streams of the Melbourne region, Victoria, Australia. I. Benthic macroinvertebrate communities
Authors: Walsh Christopher J. , Sharpe Andrew K. , Breen Peter F. , Sonneman Jason A.
Published: March 2003

1. Macroinvertebrate community composition was assessed in small streams of the Melbourne region to test the effects of (a) urban density (catchment imperviousness 0–51%) and (b) stormwater drainage intensity (comparing the intensively drained metropolitan area with urban areas of the hinterland, which had open drains and some localized stormwater drainage).

2. Hinterland communities separated into two groups of sites correlating strongly with patterns of electrical conductivity (EC), basalt geology and annual rainfall. Community composition varied little in the high‐EC, western group (imperviousness 0.2–1.2%), but in the eastern group it was strongly correlated with catchment imperviousness (0–12%), with lower taxon richness in more impervious catchments.

3. Metropolitan communities (imperviousness 1–51%) were all severely degraded, with high abundances of a few tolerant taxa. Community composition was poorly correlated with patterns of geology, rainfall or imperviousness. Differences between metropolitan and hinterland communities were well explained by patterns of biochemical oxygen demand and electrical conductivity, which were postulated to indicate the more efficient transport of pollutants to receiving streams by the metropolitan stormwater drainage system.

4. Degradation of macroinvertebrate community composition was well explained by urban density but intensive urban drainage increased degradation severely at even low urban densities. Quantification of relationships between imperviousness, drainage intensity and stream degradation can better inform the assessment, conservation and restoration of urban streams.
Morphological variation within the diatom taxon Cyclotella comensis and its importance for quantitative temperature reconstructions
Authors: Hausmann Sonja , Lotter André F.
Published: March 2003

1. The morphologically complex taxon Cyclotella comensis Grunow had no clear relationship with environmental parameters in a study using sediment surface samples from the Swiss Alps. The morphological heterogeneity of the taxon was investigated by applying a principal component analysis (PCA) to 9000 presence/absence descriptions of valves from surface samples of six lakes from different altitudes (15 characteristics, 100 valves each lake). The PCA allowed the classification of six morphs, which differed mainly in size and length of striae. Photographs of the morphs are shown in this paper.

2. Sixty‐eight sediment surface samples were analysed using these newly defined six morphs. Summer temperature explained a major part of the variance between the morphs as assessed by a redundancy analysis (RDA). Summer temperature optima and tolerances were estimated using weighted averaging.

3. The influence of the revised C. comensis taxonomy on the diatom inferred summer temperature of a high alpine lake is discussed in a multiproxy context for the past 800 years.
Size distribution of aquatic invertebrates in two prairie wetlands, with and without fish, with implications for community production
Authors: Zimmer Kyle D. , Hanson Mark A. , Butler Malcolm G. , Duffy Walter G.
Published: March 2003

1. We compared the size distribution of aquatic invertebrates in two prairie wetlands, one supporting a population of fathead minnows and the other fishless. Both wetlands were sampled in three depth zones on three dates, allowing assessment of temporal and spatial variation.

2. We determined biomass of aquatic invertebrates in 17 log2 size classes, and used these data to develop normalized size spectra. We also coupled size distributions with an allometric model to estimate relative production at the community level.

3. The composition of the invertebrate communities differed greatly between sites, and invertebrate biomass was higher in nearly all size classes in the fishless wetland. Intercepts of normalized size spectra were significantly different between wetlands, but slopes generally were not, indicating differences in standing‐stock biomass but similar size structures between the two invertebrate communities. Higher standing‐stock biomass in the fishless wetland resulted in higher relative production per unit area, but similar size distributions resulted in similar mass‐specific production (P/B) between wetlands.

4. Our results indicate that invertebrate communities in prairie wetlands may have relatively consistent size structures in spite of large differences in community composition and standing‐stock biomass. We hypothesize that the observed differences are because of predation by the minnow population and/or differences in the macrophyte communities between the two sites. However, the relative importance of macrophytes and fish predation in structuring invertebrate communities in prairie wetlands is poorly known.
Comparing diatom species, genera and size in biomonitoring: a case study from streams in the Laurentians (Québec, Canada)
Authors: Wunsam Sybille , Cattaneo Antonella , Bourassa Nathalie
Published: March 2003

1. We studied the distribution of epilithic diatoms in streams subjected to different degrees of human impact in order to evaluate their potential as bioindicators for environmental changes such as nutrient enrichment and acidification.

2. Three descriptors of the diatom assemblages were tested with respect to their potential to predict environmental changes: species composition, genus composition and size distribution.

3. Water colour and pH explained the largest amount of variation in diatom assemblages. According to ordination analyses, water colour explained variations in size distribution (42%) better than those in generic (25%) or species composition (8%). On the other hand, pH was not correlated with size distribution while a significant fraction of variation was explained by species (11%) and especially generic (18%) composition. Only species composition responded to changes in phosphorus and grazer biomass, however.

4. Size distribution and coarse (genus level) taxonomic analyses sometimes outperformed fine taxonomy in describing the response of diatom assemblages to colour and acidity. In view of the simplicity of these alternative descriptions of diatom assemblages, their potential for routine stream monitoring should be further explored.
Distribution of chironomids (Diptera) in low arctic West Greenland lakes: trophic conditions, temperature and environmental reconstruction
Authors: BRODERSEN KLAUS PETER , ANDERSON N. JOHN
Published: March 2003

1. Surface sediment samples of subfossil chironomid head capsules from 47 lakes in southern West Greenland were analysed using multivariate numerical methods in order to explore the relationship between chironomid assemblages and selected environmental variables. The study lakes are located along a climate gradient ranging from coastal maritime conditions near the Davis Strait to a continental climate near the margin of the Greenland ice sheet.

2. High‐resolution surface water temperatures were measured through the summer season using automatic data loggers in 21 of the study lakes. The mean July surface water temperature (1999) ranged from 7.3 to 16.5 °C in the data set.

3. In all lakes, a total of 24 chironomid taxa were recorded; Micropsectra, Psectrocladius, Chironomus and Procladius were the dominant genera. There was a strong correlation between the trophic variables [total nitrogen and total phosphorus (TN, TP)] and temperature, and in redundancy analysis (RDA) the three variables explained almost equal significant amounts of variation in the chironomid data (19.8–22.3%). However, temperature lost significant explanatory power when the effect of TN was partialled out in RDA.

4. The lakes were classified using two‐way indicator species analysis (TWINSPAN) into eight groups defined by temperature, trophic variables, salinity (conductivity) and lake‐morphometric data. Fourteen chironomid taxa showed significant differences in percentage abundances among groups, with Heterotrissocladius, Micropsectra, Ablabesmyia and Chironomus as the most robust group‐indicator taxa. Forward selection of taxa in multiple discriminant analysis was used to fit chironomid assemblages into lake groups. Using only eight taxa, 95% of lakes were correctly classified at a second TWINSPAN division level (four groups) and 85% of lakes at a third division level (eight groups).

5. This study showed that there is considerable potential in using subfossil chironomid head capsules as paleoenvironmental indicators in both short‐ and long‐term (down‐core) studies of lake ontogeny and palaeoclimate conditions in West Greenland. However, because of the strong correlation between temperature and trophic variables, a quantitative reconstruction of lake‐ and habitat‐type is recommended, in combination with direct reconstruction of single variables such as temperature.
Riverine landscapes: taking landscape ecology into the water
Authors: WIENS JOHN A.
Published: March 2003

1. Landscape ecology deals with the influence of spatial pattern on ecological processes. It considers the ecological consequences of where things are located in space, where they are relative to other things, and how these relationships and their consequences are contingent on the characteristics of the surrounding landscape mosaic at multiple scales in time and space. Traditionally, landscape ecologists have focused their attention on terrestrial ecosystems, and rivers and streams have been considered either as elements of landscape mosaics or as units that are linked to the terrestrial landscape by flows across boundaries or ecotones. Less often, the heterogeneity that exists within a river or stream has been viewed as a `riverscape' in its own right.

2. Landscape ecology can be unified about six central themes: (1) patches differ in quality (2) patch boundaries affect flows, (3) patch context matters, (4) connectivity is critical, (5) organisms are important, and (6) the importance of scale. Although riverine systems differ from terrestrial systems by virtue of the strong physical force of hydrology and the inherent connectivity provided by water flow, all of these themes apply equally to aquatic and terrestrial ecosystems, and to the linkages between the two.

3. Landscape ecology therefore has important insights to offer to the study of riverine ecosystems, but these systems may also provide excellent opportunities for developing and testing landscape ecological theory. The principles and approaches of landscape ecology should be extended to include freshwater systems; it is time to take the `land' out of landscape ecology.
The influence of predatory fish on mayfly drift: extrapolating from experiments to nature
Authors: MCINTOSH ANGUS R. , PECKARSKY BARBARA L. , TAYLOR BRAD W.
Published: March 2003

1. A knowledge of how individual behaviour affects populations in nature is needed to understand many ecologically important processes, such as the dispersal of larval insects in streams. The influence of chemical cues from drift‐feeding fish on the drift dispersal of mayflies has been documented in small experimental channels (i.e. < 3 m), but their influence on dispersal in natural systems (e.g. 30 m stream reaches) is unclear.

2. Using surveys in 10 Rocky Mountain streams in Western Colorado we examined whether the effects of predatory brook trout (Salvelinus fontinalis) on mayfly drift, that were apparent in stream‐side channels, could also be detected in natural streams.

3. In channel experiments, the drift of Baetis bicaudatus (Baetidae) was more responsive to variation in the concentration of chemical cues from brook trout than that of another mayfly, Epeorus deceptivus (Heptageniidae). The rate of brook trout predation on drifting mayflies of both species in a 2‐m long observation tank was higher during the day (60–75%) but still measurable at night (5–10%). Epeorus individuals released into the water column were more vulnerable to trout predation by both day and night than were Baetis larvae treated similarly.

4. Drift of all mayfly taxa in five fishless streams was aperiodic, whereas their drift was nocturnal in five trout streams. The propensity of mayflies to drift was decreased during the day and increased during the night in trout streams compared with fishless streams. In contrast to the channel experiments, fish biomass and density did not alter the nocturnal nature nor magnitude of mayfly drift in natural streams.

5. In combination, these results indicate that mayflies respond to subtle differences in concentration of fish cues in experimental channels. However, temporal and spatial variation in fish cues available to mayflies in natural streams may have obscured our ability to detect responses at larger scales.