bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of the exotic Daphnia lumholtzii and native macro‐zooplankton in a subtropical chain‐of‐lakes in Florida, U.S.A.
Authors: Havens Karl E. , East Therese L. , Marcus Joseph , Essex Patrick , Bolan Benjamin , Raymond Stephanie , Beaver John R.
Published: March 2003

1. Seasonal dynamics of the exotic Daphnia lumholtzii and native macro‐zooplankton species were studied for 2 years in six inter‐connected lakes in Florida, U.S.A. The lakes ranged widely in pH, colour and trophic status, and were dominated by copepods.  2. All six lakes contained both D. lumholtzii and the native D. ambigua, but the two species did not overlap in time. D. ambigua was dominant in autumn–spring, coinciding with lower water temperature, higher transparency and lower nutrient and chlorophyll a (Chl a) concentrations than in summer, when D. lumholtzii was dominant.  3. Based on the field observations, temperature optima were 24 °C for D. ambigua and 29 °C for D. lumholtzii, suggesting that temperature plays a role in determining dominance among the daphnids of subtropical Florida lakes.  4. D. lumholtzii has not displaced native cladocerans but occupies a ‘vacant’ seasonal niche, unexploited due to the inability of native taxa to tolerate high temperature. Furthermore, D. lumholtzii did not significantly alter algal–zooplankton interactions. There was evidence of top–down control by grazing, but it was primarily attributable to the native taxa.
Influence of stream flow regime and temperature on growth rate of the riparian tree, Platanus wrightii, in Arizona
Authors: Stromberg Juliet C.
Published: March 2003

1. The growth of riparian trees in semi‐arid regions is influenced by stream flow regime, but the relative importance of base flow and seasonal floods on growth has not been explored. I examined abiotic influences on the growth of Platanus wrightii in four stream reaches in Arizona. All reaches had a bimodal pattern of discharge, but only two had continuous flow throughout the growing season.  2. In two reaches of Sycamore Creek without perennial flow, a large percentage of the annual variation in radial growth rate of P. wrightii was explained by annual and growing season flow rate. Growth was related to these same variables in a perennial reach of Sycamore Creek, but trees maintained higher growth during drought years than they did in the temporary reaches. At Oak Creek, a larger perennial stream, P. wrightii growth showed a bell‐shaped relationship with flow. These data suggest that growth rate is frequently limited by water availability at Sycamore Creek, but not at Oak Creek.  3. At both rivers, much of the annual surface flow occurs as winter floods. Oak Creek, however, maintains a high summer base flow even during years with no floods. Platanus wrightii growth was significantly related to winter flood frequency only at Sycamore Creek. The positive relationship of growth with stream flow and winter flood frequency at Sycamore Creek presumably occurs because the P. wrightii trees are dependent on the winter flows to recharge the shallow alluvial aquifer and to raise the level of ground water within the root zone.  4. Frequent summer floods increased the growth of trees in perennial and non‐perennial reaches alike. At perennial Oak Creek, summer flood frequency was the only variable linearly related to growth of P. wrightii. Summer flood frequency was a significant, but secondary, component of multiple‐regression growth models for trees in the perennial and non‐perennial reaches of Sycamore Creek. Summer floods may stimulate growth, in part, by replenishing limiting nutrients.  5. High temperature was negatively associated with the growth of P. wrightii at Sycamore Creek. The combination of drought and high temperature resulted in very low growth rate.  6. These results have implications for the management of flood and base flow regimes on regulated, diverted and pumped rivers.
Inter‐specific differences in photosynthetic carbon uptake, photosynthate partitioning and extracellular organic carbon release by deep‐water characean algae
Authors: Sorrell Brian K. , Hawes Ian , Schwarz Anne‐Maree , Sutherland Donna
Published: March 2003

1. The effect of light intensity on photosynthesis and the fate of newly fixed organic carbon was compared for three characean algae collected at the same depth (10 m) but differing in their depth distributions. For each species we determined photosynthesis–irradiance (P–E) responses, the partitioning of newly fixed carbon into four intracellular pools (low molecular‐weight compounds, polysaccharides, lipids and proteins) and the extracellular organic carbon (EOC) release at a range of photon flux densities (PFD) 0–60 μmol m–2 s–1.

2. The P–E responses differed between the three species, with the light compensation point (Ec) and dark respiration rate highest in the shallowest species (Chara fibrosa), intermediate in the mid‐range species (C. globularis) and lowest in the deepest species (C. corallina). Photosynthetic efficiency (α) and photosynthesis: respiration ratios were lowest in C. fibrosa and highest in C. corallina.

3. In all three species, the low molecular weight pool was the principal photosynthetic product (>60% of fixed C) at 3 μmol m–2 s–1 PFD, but its proportional contribution decreased rapidly with increasing irradiance. Polysaccharide rose to become the major product (>35% of fixed C) at saturating PFD (35 μmol m–2 s–1).

4. Protein synthesis was saturated at 5 μmol m–2 s–1 in all species and was consistently a lower proportion of the fixed carbon in C. corallina than the other species. The fraction incorporated in the lipid pool increased slightly with irradiance but was always less than 10% of fixed C, while the proportion lost as EOC was unaffected by light, being significantly higher in C. fibrosa than the other species.

5. A kinetic experiment with C. fibrosa at 35 μmol m–2 s–1 PFD revealed a continued increase in net polysaccharide, protein and lipid synthesis during a 22.5‐h light period, whereas the net size of the low molecular weight pool remained constant. In a subsequent dark period, protein and lipid synthesis continued at the expense of the polysaccharide and low‐molecular‐weight pools. The EOC release rose to a constant low release in the light, then peaked slightly immediately after the dark–light transition before returning to the same rate as in the light. Extrapolating these data over 24 h suggests that the proportion of fixed carbon lost as EOC may be as high as 10% in this species.

6. The interspecific differences in carbon acquisition between the three species reflected their depth distributions, with the deeper species having more efficient photosynthetic metabolism, lower P:R ratios and less EOC release, although no apparent differences in internal partitioning of photosynthate.
Abrupt change in primary productivity in a littoral zone of Lake Biwa with the development of a filamentous green‐algal community
Authors: Nozaki Kentaro
Published: March 2003

1. Some characteristics of the photosynthesis and primary production of benthic and planktonic algal communities were investigated in a littoral zone covered with gravel in the north basin of Lake Biwa, paying special attention to the recent development of filamentous green algae (FGA) in the benthic algal community.

2. Pmax (maximum gross photosynthesis rate) values of the benthic algal community (0.1–1.2 mg C mg chl. a−1 h−1) obtained from photosynthesis–irradiance (P–I) curves were lower than those of the planktonic algal community (2.4–11.5 mg C mg chl. a−1 h−1). This is apparently a result of the high degree of self shading in the benthic algal community and its low turnover as compared with that of the planktonic algal community.

3. Relatively high Ik values (150–200 μmol photon m−2 s−1) were observed in the benthic algal community only in June–July when a FGA, Spirogyra sp., was abundant. This reflected a photosynthetic characteristic of the Spirogyra itself, in which photosynthesis was saturated at high light intensity.

4. The FGA community established in the layer between planktonic and sessile (benthic algae except for FGA) algal communities. It brought about extraordinarily high organic matter production in the littoral zone at the expense of production in the sessile algal community.
Evaluation of methods for estimating macroinvertebrate species richness using individual stones in tropical streams
Authors: Melo Adriano S. , Froehlich Claudio G.
Published: March 2003

1. The most straightforward way to assess diversity in a site is the species count. However, a relatively large sample is needed for a reliable result because of the presence of many rare species in rich assemblages. The use of richness estimation methods is suggested by many authors as a solution for this problem in many cases.

2. We examined the performance of 13 methods for estimating richness of stream macroinvertebrates inhabiting riffles both at local (stream) and regional (catchment) scales. The evaluation was based on (1) the smallest sub‐sample size needed to estimate total richness in the sample, (2) constancy of this size, (3) lack of erratic behaviour in curve shape and (4) similarity in curve shape through different data sets. Samples were from three single stream sites (local) and three from several streams within the same catchment basin (regional). All collections were made from protected forest areas in south‐east Brazil.

3. All estimation methods were dependent on sub‐sample size, producing higher estimates when using larger sub‐sample sizes. The Stout and Vandermeer method estimated total richness in the samples with the smallest sub‐sample size, but showed some erratic behaviour at small sub‐sample sizes, and the estimated curves were not similar among the six samples. The Bootstrap method was the best estimator in relation to constancy of sub‐sample sizes, but needed an unacceptably large sub‐sample to estimate total richness in the samples. The second order Jackknife method was the second best estimator both for minimum sub‐sample size and constancy of this size and we suggest its use in future studies of diversity in tropical streams. Despite the inferior performance of several other methods, some produced acceptable results. Comments are made on the utility of using these estimators for predicting species richness in an area and for comparative purposes in diversity studies.
Life on the edge: the plankton and chemistry of Beaver Lake, an ultra‐oligotrophic epishelf lake, Antarctica
Authors: Laybourn‐Parry Johanna , Quayle Wendy C. , Henshaw Tracey , Ruddell Andrew , Marchant Harvey J.
Published: March 2003

1. Beaver Lake, a large epishelf lake in eastern Antarctica was sampled on two occasions during the austral summer of 2000. Two sites, one 1 km offshore and another 6 km offshore were sampled at intervals to depths of 40 and 110 m, respectively.

2. The lake is an end member of ultra‐oligotrophic lake systems with a very low carbon pool. Dissolved organic carbon concentrations ranged between 95 and 652 μg L–1. Nutrient levels were generally low with soluble reactive phosphorus ranging from undetectable to 8.4 μg L–1, ammonium ranged between 1.8 and 5.0 μg L–1, nitrate from undetectable to 161 μg L–1 and nitrite 1.1–5.3 μg L–1.

3. Chlorophyll a concentrations (0.39–4.38 μg L–1) showed an unusual distribution with the highest levels close to the lake bottom at the offshore site (110 m) where the phototrophic nanoflagellates (PNAN) displayed strong autofluorescence.

4. Bacterial concentrations were low, with a maximum of 7.60 × 107 L–1, as were the concentrations of heterotrophic nanoflagellates that exploit them.

5. Primary production ranged between 19.7 and 25.49 μg C L–1 day–1 and bacterial production from 0.32 to 1.15 μg C L–1 day–1.

6. In common with other continental Antarctic lakes, the system was dominated by a microbial plankton. However, a dwarf variety of the calanoid copepod, Boeckella poppei, occurred below 25 m at concentrations of 3–5 L–1.

7. The data suggest that primary production and bacterial production were not limited by nutrient availability, but by other factors, e.g. in the case of bacterial production by organic carbon concentrations and primary production by low temperatures.
The effects of vertical mixing on a phytoplankton community: a modelling approach to the intermediate disturbance hypothesis
Authors: Elliott J. A. , Irish A. E. , Reynolds C. S.
Published: March 2003

1. Connell’s (1978) intermediate disturbance hypothesis (IDH) has been proposed as one explanation of why diversity is often highest at intermediate levels of disturbance. We used a model phytoplankton responses to environmental change (PROTECH) to investigate the validity of this hypothesis.

2. In a simulated phytoplankton assemblage of eight species, we found that the relationship between the increased intensity of a single forcing event and diversity was described by a positively skewed curve.

3. A progressive increase in forcing frequency introduced a sharp decrease in diversity at a threshold frequency. However, the highest diversity values were found at an intermediate frequency of disturbance.

4. We described the shape of this breakpoint response as like a ‘cliff’ and reconcile it with multiple stable‐point theory. It is argued that the IDH should possibly be represented by this ‘cliff’ relationship, which may be applied to (or encourage the re‐examination of) many previous studies.
Geographical patterns of species turnover in aquatic plant communities
Authors: Virola Teija , Kaitala Veijo , Lammi Antti , Siikamäki Pirkko , Suhonen Jukka
Published: March 2003

1. A classic theory in biogeography predicts that high latitude communities are unstable. This may be because of decreased species richness or decreased environmental predictability and productivity towards the poles.

2. We studied latitudinal patterns in long‐term community persistence of aquatic vascular plants in 112 Finnish lakes, situated within a 1000‐km range from the northernmost to the southernmost lake.

3. Contrary to theoretical predictions, we found that the turnover rate of plant species in 45 years was inversely related to latitude. That is, plant communities in northern lakes were more persistent than communities in southern lakes. When we used multiple regression to find the best predictors of species turnover rate (TR), latitude was the only variable that was highly significantly related to species turnover rate. Area, species number, water transparency, pH and change in transparency did not notably explain the gradient observed.

4. The latitudinal trend was mainly because of lower species immigration rates at higher latitudes, whereas extinction rate did not so strongly decrease with increasing latitude. Immigrations and extinctions in the lakes were not in balance: the species numbers between the 1930s and 1980s increased more strongly in the southern than northern lakes.

5. We suggest that the inverse relationship between latitude and plant species TR in Finland is most probably caused by human influence on lakes, especially eutrophication and immigration of new species in southern latitudes. In addition, although species richness per lake did not decrease towards the north, the total species pool probably does, which means that in the north there are fewer species that can actually immigrate.
A hydrogeomorphological context for ecological research on alpine glacial rivers
Authors: Smith Barnaby P. G. , Hannah David M. , Gurnell Angela M. , Petts Geoffrey E.
Published: March 2003

1. This paper presents a framework for the analysis of glacial stream ecosystems based upon the hierarchy of physical processes that operate over timescales varying from diel to millennial. Linked conceptual models propose interrelationships between climate, hydrology and fluvial geomorphology in alpine catchments.

2. These conceptual models are illustrated using data from the Taillon/Gabiétous catchment, French Pyrénées. Secondary sources provide information concerning the long‐term sequence of climatic and geomorphological controls on contemporary catchment processes. Detailed hydrogeomorphological field data collected over three consecutive summer melt seasons (1995–97) permit identification of marked changes in shorter‐term (diel, seasonal and inter‐annual) physical processes.

3. Clear differences in the response of water quality and quantity variables were observed between years as climatic conditions varied. In two of the three study years, a precipitation‐driven regime was imposed upon the typical ablation‐driven river discharge pattern in alpine streams. Clear changes in water quality and quantity were evident with increasing distance from the glacier: (i) discharge increased although specific discharge decreased markedly, (ii) the mean and variability in water temperature increased, and (iii) base concentrations of suspended solids decreased.

4. The physical processes incorporated in the conceptual models presented in this paper have ecological implications because they underpin a nested suite of disturbance regimes operating over timescales from diel to millennial.
Effects of light and nutrients on the net accumulation and elemental composition of epilithon in boreal lakes
Authors: Frost Paul C. , Elser James J.
Published: March 2003

1. Two experiments in the Experimental Lakes Area (ELA) in north‐western Ontario, Canada examined the effects of light and two key elements on the net accumulation and elemental composition of epilithon. In Lake (L) 224, benthic algae were grown under different light intensity and phosphorus supply, while in L302S we provided three levels of two different carbon sources (bicarbonate and glucose) to algae colonizing nutrient‐diffusing substrata. After 1 month of accumulation, we sampled biofilms for chlorophyll (chl), carbon (C), phosphorus (P) and algal C.

2. Increased C supply did not significantly affect algal growth (C or chl) or elemental composition (C/P ratios) in L302S. However, P enrichment increased chl and algal C, dramatically reduced the C/P ratio of epilithon, and did not affect total organic C in L224. Phosphorus enrichment also increased the proportion of algal material in the total particulate organic matter and altered the taxonomic composition of algae in L224 biofilms. Shading had no significant effect on the C/P ratio and total organic C in epilithon from the L224 experiment.

3. Our results demonstrate that P supply affects the elemental composition of organic matter that collects on rock substrata. It thus appears that low availability of P relative to C and light drives the formation and retention of high C/P organic matter on rock surfaces in oligotrophic boreal lakes.
Changes in genetic structure of North American Bythotrephes populations following invasion from Lake Ladoga, Russia
Authors: Berg David J. , Garton David W. , Macisaac Hugh J. , Panov Vadim E. , Telesh Irena V.
Published: March 2003

1. We used allozyme electrophoresis to compare Bythotrephes longimanus (Crustacea: Onychopoda: Cercopagididae) from recently founded North American populations with those from native European populations, and to examine changes in genetic structure of North American populations over time.

2. The genetic structure of North American populations in 1996 was similar to that of European populations, because of the disappearance of founder effects which distinguished North American from European populations in 1989.

3. The Lake Ladoga, Russia population was more closely related to North American populations than to other European populations, consistent with non‐genetic evidence implicating Lake Ladoga as the source of North American populations.

4. Our results provide additional evidence of the presence of an invasion corridor that allows Urasian and Ponto‐Caspian species to be introduced into North American freshwater ecosystems, and show that founder effects can erode over time following establishment of invasive species.
Growth and emergence of the stonefly Leuctra nigra in coniferous forest streams with contrasting pH
Authors: THOMSEN ANNE G. , FRIBERG NIKOLAI
Published: March 2003

1. Growth and emergence of the acidification tolerant stonefly Leuctra nigra were studied in four coniferous forest streams with contrasting pH. Invertebrate samples were taken bimonthly during May 1997 to April 1998. Emerging L. nigra were captured in two of the streams during April to July 1998 using pyramidal emergence traps. In addition, a laboratory experiment was conducted to evaluate growth of L. nigra in response to variations in food quality (neutral or acid conditioned leaves) and water pH.

2. The invertebrate community in low pH streams had lower diversity and density compared with neutral streams. Abundance of L. nigra was also lower, despite the dominance of this stonefly in the invertebrate community in the acidic streams.

3. Secondary production of L. nigra was 2.04 and 3.07 g DW m–2 year–1 in the neutral streams compared with 1.02 and 1.27 g DW m–2 year–1 in the acidic streams. The P/B ratio differed only slightly among streams.

4. More adult L. nigra emerged in the neutral stream compared with the acidic stream, despite the density of the pre‐emerging fifth instar nymphs of L. nigra being similar in the two streams. Adult size (expressed as wing length) and female fitness were also significantly greater in the neutral stream.

5. Laboratory growth of L. nigra nymphs was significantly lower when fed acid conditioned alder leaves rather than neutral conditioned leaves. There was no difference in growth when nymphs were fed neutral conditioned leaves in acid and neutral water.

6. Our study shows multiple, sub‐lethal effects on life history of the acidification tolerant stonefly L. nigra in coniferous streams with low pH. The results suggest that these effects could be mediated primarily by low food quality. These findings add to the existing evidence that coniferous plantation forestry has a negative impact on stream ecosystems.
The effects of Daphnia on nutrient stoichiometry and filamentous cyanobacteria: a mesocosm experiment in a eutrophic lake
Authors: PATERSON M. J. , FINDLAY D. L. , SALKI A. G. , HENDZEL L. L. , HESSLEIN R. H.
Published: March 2003

1. Stoichiometric theory predicts that the nitrogen : phosphorus (N : P) ratio of recycled nutrients should increase when P‐rich zooplankton such as Daphnia become dominant. We used an enclosure study to test the hypothesis that an increased biomass of Daphnia will increase the relative availability of N versus P sufficiently to decrease the abundance of filamentous cyanobacteria. The experiment was conducted in artificially enriched Lake 227 (L227) in the Experimental Lakes Area (ELA), north‐western Ontario, Canada. Previous studies in L227 have shown that the dominance of filamentous, N‐fixing cyanobacteria is strongly affected by changes in the relative loading rates of N and P.

2. We used a 2 × 2 factorial design with the addition or absence of D. pulicaria and high or low relative loading rates of N and P (+NH4, –NH4) in small enclosures as treatment variables. If Daphnia can strongly affect filamentous cyanobacteria by altering N and P availability, these impacts should be greatest with low external N : P loading rates. The phytoplankton community of L227 was predominantly composed of filamentous Aphanizomenon spp. at the start of the experiment.

3. Daphnia strongly reduced filamentous cyanobacterial density in all enclosures to which they were added. The addition of NH4 had only a small impact on algal community composition. Hence, we conclude that Daphnia did not cause reductions in cyanobacteria by altering the N : P ratio of available nutrients.

4. Despite the lack of evidence that Daphnia affected filamentous cyanobacteria by altering the relative availability of N and P, we found changes in nutrient cycling consistent with other aspects of stoichiometric theory. In the presence of Daphnia, total P in the water column decreased because of an increase in P sedimentation. In contrast to P, a decrease in suspended particulate N was offset by an increase in dissolved N (especially NH4). Hence, dissolved and total N : P ratios in the water column increased with Daphnia as a result of differences in the fate of suspended particulate N versus P. There was minimal accumulation and storage of P in Daphnia biomass in the enclosures.

5. Our experiment demonstrated that Daphnia can strongly limit filamentous cyanobacterial abundance and affect the biogeochemical cycling of nutrients. In our study, changes in nutrient cycling were apparently insufficient to cause the changes in phytoplankton community composition that we observed. Daphnia therefore limited filamentous cyanobacteria by other mechanisms.
Reproductive traits of stream‐dwelling brown trout Salmo trutta in contrasting neighbouring rivers of central Spain
Authors: NICOLA G. G. , ALMODÓVAR A.
Published: March 2003

1. Reproductive traits were studied in seven wild populations of resident brown trout in Spain. We examined whether growth, and certain environmental conditions such as water temperature or food abundance, could explain interpopulation variation in the reproductive characters.

2. The results indicated that nearby populations subjected to a wide variation in environmental conditions exhibited a similar reproductive performance.

3. Age distributions and sex ratios were not significantly different among populations. Age ranged from 0+ to 4+ years but the populations were dominated by the 0+ to 2+ groups. In all rivers females matured at age 2+ as opposed to age 1+ and 2+ for males. Mean length at the end of the growth period differed significantly among populations. However, annual growth rate was similar among rivers and was not significantly correlated with either biomass of the benthos or water temperature during the growth season.

4. Reproductive effort, body condition, fecundity and egg size did not correlate significantly with either the abundance of benthic invertebrates or water temperature. Once the effect of body length on both egg size and number was removed, a significant negative correlation was found between these two traits among populations.
A stable isotope study of linkages between stream and terrestrial food webs through spider predation
Authors: Collier Kevin J. , Bury Sarah , Gibbs Max
Published: March 2003

SUMMARY 1. Transfer of carbon from freshwater to terrestrial ecosystems can occur through predation on adult aquatic insects, but the significance of this trophic pathway to the energetics of riparian communities is poorly understood. We used stable isotopes of carbon and nitrogen to explore linkages between aquatic insect production and the nutrition of web‐building and free‐living spiders alongside two streams in the North Island of New Zealand.

2. δ13C values for riparian tree leaves (means for each site = −32.2 and −30.3‰) were distinct from those of lichens collected from stream channel rocks and instream algae, both of which were similar (−23.4 to −22.4‰). δ15N values for leaves were similar at both sites (−3.4 and −2.7‰), but algae were considerably more depleted in δ15N atonesite suggesting significant differences in instream nitrogen sources between the twostreams.

3. Isotope values for potential aquatic prey of spiders indicated that aquatic algal production was their primary carbon source at both sites. Terrestrial invertebrates collected and assumed to be potential prey reflected a range of carbon sources and represented several trophic levels.

4. At one site, δ13C values indicated a primarily algae‐aquatic insect pathway of carbon transfer to both web‐building and free‐living spider guilds. The other site appeared to have a primarily terrestrial carbon pathway for the free‐living spider guild, and a mixed aquatic‐terrestrial pathway for the web‐building guild.

5. Overall, web‐building spiders were estimated to obtain around 61% of their body carbon from aquatic production compared with 55% for free‐living spiders. Our findings suggest that consumption of prey derived from aquatic sources can provide significant nutrition for spiders living along some stream channels. This pathway may represent an important feedback mechanism contributing to the energetics of riparian communities at sites where aquatic insect production is high.
Comparing the responses of diatoms and macro‐ invertebrates to metals in upland streams of Wales and Cornwall
Authors: Hirst Heike , Jüttner Ingrid , Ormerod S. J.
Published: March 2003

SUMMARY1. Surprisingly few data compare the apparent responses of diatoms and macroinvertebrates to metals in streams. We examined variation in metals, diatoms and macroinvertebrates between 51 streams in metal‐mining areas of Wales and Cornwall, U.K., using a survey design with multiple reference and polluted sites.

2. To quantify variations in metals between sites, we calculated cumulative criterion unit (CCU) scores, a recently defined measure of total stream metal concentration and toxicity, to account for additive effects of each metal relative to putative toxic thresholds. We compared assemblage responses among epilithic diatoms and macroinvertebrates to CCU scores or individual metal concentrations using correlation and detrended correspondence analysis (DCA).

3. Macroinvertebrate diversity, richness and total abundance declined and evenness increased with increasing copper concentrations. Trends with CCU scores were significant but less pronounced. Some individual macroinvertebrate taxa varied significantly in abundance with CCU scores, copper or zinc, but overall assemblage composition correlated only with manganese, pH and nitrate.

4. Among diatoms, pH and conductivity explained the major variations in assemblage composition, and neither diversity, richness nor evenness varied with metal concentration. Nevertheless, the single strongest predictor of diatom assemblages on ordination axis 2 was the CCU score. The abundances of some macroinvertebrate taxa, particularly grazers, also explained significant variations in diatom assemblages that were linked to both metals and acid–base status.

5. Diatom species apparently tolerant of high metal concentrations includedPsammothidium helveticum,Eunotia subarcuatoides,Pinnularia subcapitataandSellaphora seminulum. Of these,P. helveticum,E. subarcuatoidesandP. subcapitatawere abundant at lower pH thanS.seminulumand might indicate metal enrichment over different pH ranges. Sensitive species includedFragilaria capucinavar.rumpens,Achnanthes oblongellaandTabellaria flocculosa.

6. We conclude that macroinvertebrates at these sites reflected metal pollution most strongly through variations in diversity while effects on diatoms were best reflected by changes in assemblage composition. We suggest that, with further refinement, CCU scores might be useful in evaluating the possible effects of metal pollution on benthic organisms in European rivers.
Evapotranspiration at the land/water interface in a semi‐arid drainage basin
Authors: DAHM CLIFFORD N. , CLEVERLY JAMES R. , ALLRED COONROD JULIA E. , THIBAULT JAMES R. , MCDONNELL DIANNE E. , GILROY DAVID J.
Published: March 2003

1. Evapotranspiration (ET) is a major source of water depletion from riverine systems in arid and semiarid climates. Water budgets have produced estimates of total depletions from riparian vegetation ET for a 320‐km reach of the Middle Rio Grande, New Mexico, U.S.A., that have ranged from 20 to 50% of total depletions from the river.

2. Tower‐based micrometeorological measurements of riparian zone ET throughout the growing season using three‐dimensional eddy covariance provided high quality estimates of ET at the stand scale.

3. A dense stand of salt cedar (111–122 cm year–1) and a mature cottonwood (Populus deltoides ssp. wislizenia Eckenwelder) stand with an extensive understory of salt cedar (Tamaria ramosissima Ledeb) and Russian olive (Eleagnus angustifolia L.) (123 cm year–1) had the highest rates of annual ET. A mature cottonwood stand with a closed canopy had intermediate rates of ET (98 cm year–1). A less dense salt cedar stand had the lowest rates of ET (74–76 cm year–1).

4. Summer leaf area index (LAI) measurements within the four stands were positively correlated with daily ET rates. LAI measurements throughout the growing season coupled to riparian vegetation classification is a promising method for improving riverine corridor estimates of total annual riparian zone ET along a reach of river.

5. Combining recent estimates of the extent of riparian vegetation along the 320 km length of the Middle Rio Grande, from Landsat 7 imagery with annual growing season measurements of ET at the four riparian stands yields a first‐order riverine corridor estimate of total riparian zone ET of 150–250 × 106 m3 year–1. This is approximately 20–33% of total estimated depletions along this reach of river.
Phylogeographical lineages in brown trout (Salmo trutta): investigating microgeographical differentiation between native populations from Northern Spain
Authors: Cagigas M. Elena , Vázquez Emilia , Blanco Gloria , Sánchez José A.
Published: March 2003

SUMMARY 1. The large microgeographical differentiation revealed by allozyme studies in brown trout (Salmo trutta) populations is one of the most striking features of this species. Additionally, allozymes showed great genetic differences between Atlantic and Mediterranean populations on a macrogeographical scale.

2. This study was carried out in order to assess whether the great differences observed between Atlantic and Mediterranean populations persisted where the two are geographically close (the ‘microgeographical scale’). Sixteen populations of brown trout, S. trutta, were screened for genetic variation at 25 allozyme loci. The sampling sites, which occupied a relatively small geographical area, were distributed across Cantabrian (Atlantic) and Mediterranean drainages in Northern Spain.

3. The neighbour‐joining tree, inferred from Nei's genetic distance, showed that brown trout populations clustered into two different groups. These groups corresponded to the Cantabrian and the Mediterranean groups of populations, although no clear geographical pattern emerged within each of the groups. This geographical pattern is basically caused by significant differences in the frequency distribution of the CK‐A1* locus, with a higher frequency of *115 in Cantabrian samples (0.586 ± 0.091) while allele *100 was more frequent in Mediterranean samples (0.931 ± 0.038). In addition, this study revealed alleles exclusive to the Mediterranean and Cantabrian populations, agreeing with previous findings.

4. Genetic differentiation between Cantabrian and Mediterranean regions (14.19%) was similar to that estimated in Spain at a larger scale (13%), showing that most of the differences between the regions can be observed even in a small geographical area.
Predictive modelling of freshwater fish as a biomonitoring tool in New Zealand
Authors: Joy M. K. , Death R. G.
Published: March 2003

SUMMARY 1. A challenge has been issued to ecologists to find quantitative ecological relationships that have predictive power. A predictive approach has been successful when applied to biomonitoring using stream invertebrates with the River Invertebrate Prediction and Classification System (RIVPACS). This approach, to our knowledge, has not been applied to freshwater fish assemblages.

2. This paper describes the initial results of the application of a regional predictive model of freshwater fish occurrence using 200 reference sites sampled in the Manawatu–Wanganui region of New Zealand over late summer/autumn 2000. In brief (i) sites were classified into biotic groups (ii) the physical and chemical characteristics that best describe variation among these groups were determined and (iii) the relationship between these environmental variables and fish communities was used to predict the fauna expected at a site.

3. Reference sites clustered into six groups based on fish density and community composition. Using 14 physical variables least influenced by human activities, a discriminant model allocated 70% of sites to the correct biological classification group. The variables that best separated the site groups were mainly large‐scale variables including altitude, distance from the coast, lotic ecoregion and map co‐ordinates.

4. The model was further validated by randomly removing 20% of the sites, rebuilding the model and then determining the number of removed sites correctly allocated to their original biotic groups using environmental variables. Using this process 67% of the removed sites were correctly reassigned to the six predetermined groups.

5. A further 30 sites were used to determine the ability of the model to detect anthropogenic impact. The observed over expected taxa (O/E) ratios were significantly lower than the reference site O/E ratios, indicating a response of the fish assemblages to the known stressors.
The role of phosphorus release by roach [Rutilus rutilus (L.)] in the water quality changes of a biomanipulated lake
Authors: Tarvainen M. , Sarvala J. , Helminen H.
Published: March 2003

SUMMARY 1. Following fish removal, the water quality in biomanipulated lakes often improves concomitant with decreased phosphorus (P) levels. Because the decrease in P concentrations derives most probably either directly or indirectly from fish, which are the main target of biomanipulation, this study examined the P release of 0+, 1+ and 2+ roach [Rutilus rutilus (L.)] and changes in the P release during summer in a shallow eutrophic lake in Finland.

2. The P release was separated into P derived from benthic and littoral food items and into recycled P derived from feeding on zooplankton, to estimate the contribution of net P additions to the water column by the fish to the increase in P concentrations of the lake water (75–110 mg P m−3) in summer 1991–96.

3. Individual P release of roach by both egestion and excretion was estimated with a bioenergetics model. The size of the roach population was estimated with a depletion method and the proportions of different age groups from catch samples, using a programme separating mixtures of normal distributions. The sensitivity of the release estimates to variation in the growth data was estimated with the jackknife technique.

4. The biomass‐specific P release by 0+ roach (0.36–0.54 mg P g−1 day−1) was higher than that by older roach (0.07–0.16 mg P g−1 day−1) throughout the summer. The P release by the whole roach population deriving from benthic and littoral food items (0.7–2.7 mg m−3 during July to August, representing a net addition to the water column) was 5–19 times lower in 1991–96 than the recycled P release deriving from zooplankton (8.9–25.7 mg m−3), and too low to explain the increase in the P concentration of the lake water during the summer. Because the biomass‐specific P release and roach diet composition vary with fish age, it is important to consider the age structure of fish populations to obtain correct estimates of P release and net additions to the water column.

5. The removal of roach by fishing diminished the roach stock greatly, but the fish‐mediated P release to the water column changed little. This effect was because of the high compensation capacity of the roach population, leading to high recruitment of young fish with higher biomass‐specific P release rates.

6. External loading is very low during summer months and therefore it cannot explain the increase in the P concentration of water during that time. Internal loading from the sediment might be as high as 10.2 mg P m−2 day−1, i.e. 50 times higher than the maximum net P addition by the total roach population.
Effects of piscivore‐mediated habitat use on growth, diet and zooplankton consumption of roach: an individual‐based modelling approach
Authors: Hölker Franz , Haertel Susanne S. , Steiner Silke , Mehner Thomas
Published: March 2003

SUMMARY 1. We used an individual based modelling approach for roach to (i) simulate observed diel habitat shifts between the pelagic and littoral zone of a mesotrophic lake; (ii) analyse the relevance of these habitat shifts for the diet, activity costs and growth of roach; and (iii) quantify the effects of a hypothetical piscivore‐mediated (presence of pikeperch) confinement of roach to the littoral zone on roach diet, activity costs and growth.

2. The model suggests that in the presence of pikeperch, roach shifts from zooplankton as the primary diet to increased consumption of less nutritious food items such as macrophytes, filamentous algae and detritus.

3. The growth of roach between May and October was predicted to be significantly higher in the absence of pikeperch, although the net activity costs were about 60% higher compared with the scenario where pikeperch were present.

4. These modelling results provide quantitative information for interpreting diel horizontal migrations of roach as a result from a trade‐off between food availability and predation risk in different habitats of a lake.

5. Altering the habitat selection mode of planktivorous roach by piscivore stocking has the potential to reduce zooplankton consumption by fish substantially, and could therefore be used as a biomanipulation technique complementing the reduction of zooplanktivorous fish.
Biomanipulation of lake ecosystems: successful applications and expanding complexity in the underlying science
Authors: Mehner Thomas , Benndorf Jürgen , Kasprzak Peter , Koschel Rainer
Published: March 2003

SUMMARY 1. To illustrate advances made in biomanipulation research during the last decade, seven main topics that emerged after the first biomanipulation conference in 1989 are discussed in relation to the papers included in this special issue and the general literature.

2. The substantially higher success rates of biomanipulations in shallow as opposed to stratified lakes can be attributed to several positive feedback mechanisms relating mainly to the recovery of submerged macrophytes.

3. The role of both nutrient loading and in‐lake concentrations in predicting the success of biomanipulations is emphasised and supported by empirically defined threshold values. Nutrient recycling by aquatic organisms (such as fish) can contribute to the bottom‐up effects on lake food webs, although the degree can vary greatly among lakes.

4. Ontogenetic niche shifts and size‐structured interactions particularly of fish populations add to the complexity of lake food webs and make scientifically sound predictions of biomanipulation success more difficult than was previously envisaged.

5. Consideration of appropriate temporal and spatial scales in biomanipulation research is crucial to understanding food web effects induced by changes in fish communities. This topic needs to be further developed.

6. An appropriate balance between piscivorous, planktivorous and benthivorous fishes is required for long‐lasting success of biomanipulations. Recommended proportions and absolute densities of piscivorous fish are currently based on data from only a few biomanipulation experiments and need to be corroborated by additional and quantitative assessments of energy flow through lake food webs.

7. Biomanipulation effects in stratified lakes can be sustained in the long term only by continued interventions. Alternate stable states of food web composition probably exist only in shallow lakes, but even here repeated interventions may be needed as long as nutrient inputs remain high.

8. Biomanipulation is increasingly used as a lake restoration technique by considering the needs of all lake users (sustainability approach). The combination of water quality management and fisheries management for piscivores with positive effects for both appears to be particularly promising.

9. Biomanipulation research has contributed substantially to progress in understanding complex lake food webs, which should in turn promote a higher success rate of future whole‐lake biomanipulations.
0+ perch predation on 0+ bream: a case study in a eutrophic gravel pit lake
Authors: Beeck Peter , Tauber Sandra , Kiel Stephanie , Borcherding Jost
Published: March 2003

SUMMARY 1. We studied the population dynamics of 0+ fish in a eutrophic gravel pit lake in which predation of 0+ Eurasian perch on other 0+ fish was suspected to influence perch growth and the structure of the fish community, with effects on the lake food web.

2. The adult fish community was dominated by piscivorous species, especially perch, and the 0+ fish community was dominated by perch and bream. Bream grew to a total length of 80 mm between May and the end of August, gradually decreased in numbers during the summer, and completely disappeared in autumn. Stomach analysis revealed that 0+ perch ≥28 mm fed on 0+ bream.

3. The initially unimodal cohort of 0+ perch gradually broadened and became bimodal by the end of July. Fish of the larger, piscivorous cohort grew faster (1.4 mm day−1) than the smaller, zooplankton‐consuming fish (0.6 mm day−1). Although individuals of both cohorts later consumed zooplankton and grew at similar rates (0.5 mm day−1), only perch of the large cohort (mean TL 125 mm) were found by mid‐October. Intraspecific competition for food or cannibalism of older perch may have contributed to the disappearance of the smaller perch.

4. Early piscivory of the fast‐growing 0+ perch apparently resulted in the disappearance of 0+ bream by the end of the growing season and precocious maturation of male perch. In contrast to findings in other studies, these large 0+ perch thus avoided the juvenile bottleneck by switching to piscivory early during their ontogenetic development.

5. The observations of this study suggest that early piscivory of 0+ perch can have a long‐lasting impact on fish communities in eutrophic lakes, particularly if prey fish are abundant and the structural complexity of the lake is low. Furthermore, early piscivory of 0+ perch may help prevent the expected increase in 0+ cyprinids following reduction of adult cyprinids, which is considered important to ensure the long‐term success of biomanipulation experiments.
Contribution of omnivorous tilapia to eutrophication of a shallow tropical reservoir: evidence from a fish kill
Authors: Starling Fernando , Lazzaro Xavier , Cavalcanti Cristine , Moreira Ricardo
Published: March 2003

SUMMARY 1. We examined whether a large stock of tilapia (>750 kg ha−1, in littoral areas >1300 kg ha−1), mostly Oreochromis niloticus (L.) and Tilapia rendalli (Boulenger), could contribute to the eutrophication of a tropical reservoir (Lago Paranoá, Brasília, Brazil) by enhancing P‐loading.

2. We took advantage of an extensive fish kill (>150 tons removed) during May–August 1997 in a hypereutrophic branch of the reservoir to compare water quality characteristics 1 year before and after this event by means of BACI statistics. We also measured P‐excretion rates in laboratory trials to assess the P‐loading of the reservoir by the tilapia relative to tributary inputs and loading from a sewage treatment plant.

3. Concentrations of chlorophyll a (decline from 84 to 56 μg L−1, P=0.018) and total P (decline from 100 to 66 μg L−1, P < 0.001) decreased significantly in the branch of the reservoir affected by the fish kill, compared with a similar but unaffected branch that served as a control. Because P‐loading by both a sewage treatment plant and tributaries remained high after the incidence, the fish kill was likely to contribute to the observed water quality improvement.

4. Removing 150 tons of dead tilapia corresponded to 20 days of external total phosphorus load (TP‐load) to the branch, and resulted in a reduction of 5.1 kg P day−1 in internal recycling via tilapia excretion, which is equivalent to 12% of the external TP‐load.

5. Implementing professional tilapia cast‐net fisheries could be an efficient biomanipulation approach to improve water quality and limit the occurrence of cyanobacteria blooms and fish kills in hypereutrophic branches of Lago Paranoá and similar tropical lakes.