bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alkaline phosphatase activity in two planktonic desmid species and the possible role of an extracellular envelope
Authors: Spijkerman Elly , Coesel Peter F. M. 
Published: March 2003

1. Cosmarium abbreviatum var. planctonicum, a desmid from oligo‐mesotrophic lakes, had a higher maximum alkaline phosphatase activity (APA) and affinity constant under both continuous and pulsed inorganic phosphorus (Pi) limitation than Staurastrum chaetoceras, a desmid predominantly encountered in eutrophic lakes.2. APA of both species increased when measured in starved cells subjected to pulsed Pi conditions when compared to continuous Pi limitation.3. The portion of extracellular relative to cellular APA was higher in S. chaetoceras than in C. abbreviatum, indicating that S. chaetoceras secreted the enzymes more readily into its environment.4. The difference in APA could explain the dominance of C. abbreviatum during competition between these two species under conditions of continuous organic P (Po) limitation, but not the outcome under a pulsed Po shortage. The dominance of S. chaetoceras in the latter experiment can, however, be explained by species‐specific Pi‐uptake characteristics.5. After a saturating pulse of Pi, no increase in Pi in the extracellular mucus layer of C. abbreviatum was found and it was therefore concluded that the mucilage sheath does not store P. However, the sheath could have a main function as an accumulation site of cellular APA, providing the cell with Pi.
The state of freshwater ecology
Authors: Reynolds Colin S. 
Published: March 2003

1. The case is advanced that freshwater ecologists need to champion the relevance of their work to the development of ecological theory and to the understanding of ecosystem function and behaviour, not least for its importance in addressing pressing applications to the stewardship of the biosphere. An essential step is to review, and update where necessary, the paradigms of aquatic ecology.2. It is proposed that the major constraint on the organisms, their attributes and adaptations are related first to the physical properties of the medium in which they live. The drives to grow and reproduce relate to the trophic transfer of reduced carbon with important microbial interventions. General principles of ‘emergy’ apply. The supportive capacities of given environments may be set by chemical constraints, but it is suggested that, with the exception of chronically resource‐deficient waters, population dynamics relate to opportunities incumbent upon system variability and the consequent pulsation of resources.3. Variability affects diversity, through frequent revision of the thermodynamic base. Frequent structural change promotes species diversity and, because function is maintained, it appears that efficient function is dependent upon high diversity. Caution is necessary because high productivity and high diversity are both products of the disturbances consequent upon external forcing and manifestly non‐equilibrium conditions.4. Reactions to these statements are canvassed.
Genetic structure of the stonefly, Yoraperla brevis, populations: the extent of gene flow among adjacent montane streams
Authors: Hughes Jane M. , Mather Peter B. , Sheldon Andrew L. , Allendorf Fred W. 
Published: March 2003

1. Gene flow in populations of stream insects is expected to depend on the distance between and the connectedness of sites in stream networks, and on dispersal ability (i.e. larval drift and adult flight).2. Yoraperla brevis (Banks) is an abundant and characteristic stonefly of smaller streams in the northern Rocky Mountains. The present authors analysed genetic structure at 27 sites in sevenz streams flowing into the Bitterroot River in western Montana, USA. Cellulose acetate electrophoresis identified five variable loci with 16 alleles.3. Genotype frequencies conformed to Hardy–Weinberg expectations. Within‐stream differentiation was low and among‐stream variation (Fst) was an order of magnitude higher.4. UPGMA grouped sites within streams and also grouped adjacent streams. The tree produced by the Neighbour Joining Method was similar although not quite so clear cut.5. This orderly pattern (i.e. Hardy–Weinberg proportions, homogeneity within streams and geographical structure) contrasts strongly with patterns observed in invertebrates from subtropical streams in Australia. Yoraperla brevis maintains large populations in predictable environments, has a long life‐cycle with a likelihood of cohort mixing, emerges synchronously in large breeding populations and occupies streams separated by areas of high relief; the Australian situation is the opposite in most respects.6. Further analysis of a range of species is required to determine whether the different genetic structure in Y. brevis compared to the Australian species occurs more generally in North American stream insects.
Leaf litter breakdown in a Mediterranean stream characterised by travertine precipitation
Authors: Casas J. J. , Gessner M. O. 
Published: March 2003

1. Breakdown of four leaf species (Platanus orientalis, Populus nigra, Salix atrocinerea, Rubus ulmifolius) was studied in a Mediterranean second‐order stream characterised by abundant travertine precipitation, a history of fire in its catchment, and a recently revegetated alluvial corridor.2. Compared to breakdown rates reported in the literature for congeneric species, breakdown of the four species was slow (k = 0.0024–0.0069 day−1 for the tree species, and 0.0103 and 0.0111 day−1 for Rubus), in spite of high water temperatures, indicating that the travertine layer that quickly covered submerged leaves impeded decomposer activity and physical fragmentation losses.3. Breakdown rates nevertheless differed between leaf species in a predictable manner, suggesting that the observed mass loss was largely due to biological processes.4. The observed tendency towards increasing leaf nitrogen and phosphorus concentrations during breakdown suggests that microorganisms were actively involved in leaf breakdown; however, this interpretation must be viewed with caution because of potentially confounding effects by nutrients contained in the travertine layer.5. Leaf breakdown of the three indigenous species was faster than that of the exotic species P. orientalis. Due to the recalcitrance of its leaves, the frequent use of Platanus in revegetation schemes following the destruction of indigenous vegetation by fire, exacerbates the negative effect of travertine precipitation on leaf breakdown and, by extension, energy flow in Mediterranean karst streams.
Assessment of river condition at a large spatial scale using predictive models
Authors: Turak EreN. , Flack Lloyd K. , Norris Richard H. , Simpson Justen , Waddell Natacha 
Published: March 2003

Summary1. RIVPACS‐type predictive models were developed at a relatively large spatial scale for the Australian state called New South Wales (NSW, 801 428 km2). Aquatic macroinvertebrate samples and physical and chemical data were collected from 250 reference sites (little affected by human activities) and 23 test sites (with known human impacts) throughout NSW in autumn and spring 1995 and identified mostly to family level. Reference sites were grouped based on their macroinvertebrate data using classification (UPGMA) and ordination techniques. Relationships between macroinvertebrate and environmental data were established using principal axis correlations and stepwise multiple discriminant function analysis. models for predicting invertebrate assemblages were developed separately for edge and riffle habitats for autumn and spring data sets and for combined autumn and spring data sets.2. Sites in the lowland sections of the western flowing rivers were characterized by low taxonomic richness and were distinct from the sites in the eastern part of the state. Sites on the western slopes of the Great Dividing Range in southern and northern NSW mostly fell into separate groups. In eastern NSW, site groups did not represent a north, central and south division. Sites on highland streams, coastal fringe streams and large rivers mostly formed distinct groups, but most of the sites on east‐flowing rivers fell into large site groups that did not have clear geographic boundaries.3. Environmental variables that were strongly correlated with ordinations of macroinvertebrate presence/absence at sites were water temperature, altitude, longitude and maximum distance from source. The predictor variables determined by DFA for the six models created included alkalinity, altitude, location (longitude and/or latitude), stream size and substratum composition. These are generally in common with the variables determined for other large geographic areas in Australia and the United Kingdom.4. Model outputs from reference sites suggest that, among the six models, the riffle model combining autumn and spring is likely to give the most reliable predictions. The combined edge model also performed well but refinements are needed for single season models to provide reliable outputs.5. Combined season models both for riffles and for edges detected biological impairment at all but one of the test sites. Single season riffle models also detected impairment while single season edge models characterized sites as unimpaired despite other models’ indications of impaired fauna. Riffle models may be more sensitive than edge models but the sampling of riffles is often limited by flow. Edge habitats are available at most sites but there may be few riffles in floodplain rivers. Available resources, desired model sensitivity, and river type should be considered jointly to determine the most useful habitat to sample.
Biomass allocation in three macrophyte species in relation to the disturbance level of their habitat
Authors: BARRAT‐SEGRETAIN MARIE‐HELENE 
Published: March 2003

1. The hypothesis was tested that perennial plants surviving in habitats frequently disturbed by floods should demonstrate the ability to escape the frequently scoured surficial zone by using refugia located deeper in the substrate. As a consequence, they should allocate more biomass to their underground parts than when growing in rarely disturbed habitats.2. The allocation of biomass of three aquatic macrophytes (Berula erecta, Groenlandia densa, Myriophyllum spicatum) to their different organs (underground and above‐ground parts) was measured in former river channels organized along a gradient of scouring flood disturbances.3. For each species, biomass allocation to underground parts varied between sites: from 10.2 to 37.5% in B. erecta, from 14.9 to 31.1% in G. densa and from 8.4 to 23.2% in M. spicatum. It was correlated to the flood disturbance level of the site for B. erecta and M. spicatum but not for G. densa. No relationship was found between biomass allocation to underground parts and sediment richness.4. The plasticity in biomass allocation of these three macrophyte species appears to be an adaptation to the variability in environmental conditions and implies difficulties in the classification of plant primary strategies, when this type of plasticity is ignored.
Dynamics of submerged macrophyte populations in response to biomanipulation
Authors: Strand John A. , Weisner Stefan E. B. 
Published: March 2003

1. A 6‐year study (1992–97) of changes in submerged vegetation after biomanipulation was carried out in the eutrophicated Lake Finjasjön, Southern Sweden. Ten sites around the lake were revisited each year. At each site five samples of above‐ground biomass were taken at 10 cm water depth intervals. An investigation of the seed bank at the 10 sites, and a grazing experiment where birds and large fish were excluded was also conducted.2. Between 1992 and 1996, in shallow areas (water depth < 3 m), vegetation cover increased from < 3 to 75% and above‐ground biomass from < 1 to 100 g DW m–2. Mean outer water depth increased from 0.3 to 2.5 m. Elodea canadensis and Myriophyllum spicatum accounted for > 95% of the increase in biomass and plant cover. The following year (1997), however, cover and above‐ground biomass decreased, mainly attributable to the total disappearance of E. canadensis. Secchi depth increased after biomanipulation until 1996, but decreased again in 1997.3. Total and mean number of submerged species increased after biomanipulation, probably as a result of the improved light climate. However, after the initial increase in species number there was a decrease during the following years, possibly attributed to competition from the rapidly expanding E. canadensis and M. spicatum. The lack of increase in species number after the disappearance of E. canadensis in 1997 implies that other factors also affected species richness.4. A viable seed bank was not necessary for a rapid recolonization of submerged macrophytes, nor did grazing by waterfowl or fish delay the re‐colonization of submerged macrophytes.5. Submerged macrophytes are capable of rapid recolonization if conditions improve, even in large lakes such as Finjasjön (11 km2). Species that spread by fragments will increase rapidly and probably outcompete other species.6. The results indicate that after the initial Secchi depth increase, probably caused by high zooplankton densities, submerged vegetation further improved the light climate. The decrease in macrophyte biomass in 1997 may have caused the observed increase in phosphorus and chlorophyll a, and the decrease in Secchi depth. We suggest that nutrient competition from periphyton, attached to the macrophytes, may be an important factor in limiting phytoplankton production, although other factors (e.g. zooplankton grazing) are also of importance, especially as triggers for the shift to a clear‐water state.
Growth of an acid‐tolerant stonefly on epilithic biofilms from streams of contrasting pH
Authors: Ledger Mark E. , Hildrew Alan G. 
Published: March 2003

1. The apparent absence of a specialist herbivorous grazer guild from many acid streams suggests that algae‐grazer linkages in acid‐stream food webs are weak or absent. It has been hypothesized that the absence of herbivores is a consequence of the low quality and/or quantity of biofilms in acid streams.2. We compared the taxonomic composition, biomass and potential nutritional quality of epilithic biofilms from four acid and four circumneutral streams, and examined whether nymphs of a herbivore–detritivore, the stonefly Nemurella pictetii (Plecoptera: Nemouridae), could grow equally well when fed on eight biofilms from four acid and four circumneutral streams.3. Biofilms from acid and circumneutral streams differed strongly in algal composition, the former having relatively more coccoid green algae but fewer diatoms and filamentous green algae. Diatom floras differed with stream water pH.4. The quantity (i.e. area‐specific chlorophyll content, algal numbers and AFDM) and quality (biomass‐specific protein and soluble carbohydrate content) of biofilms differed significantly, both among sites of similar pH, and overall between the groups of acid and circumneutral streams.5. Nymphs of N. pictetii grew successfully on biofilms for 8–10 weeks up to emergence. However, no systematic differences in growth rate were found between the two groups of acid and circumneutral streams. Differences in the digestibility of benthic algae from different sources, and the adjustment of nymphal feeding rates, are discussed in the light of a lack of a clear relationship between growth and food quality.
Effects of snow cover on the benthic fauna in a glacier‐fed stream
Authors: Schütz Cornelia , Wallinger Manfred , Burger Rainer , Füreder Leopold 
Published: March 2003

1. Alpine streams above the tree line are covered by snow for 6–9 months a year. However, winter dynamics in these streams are poorly known. The annual patterns of macroinvertebrate assemblages were studied in a glacial stream in the Austrian Alps, providing information on conditions under the snow.2. Snow cover influenced water temperature, the content of benthic organic matter and insect development. Taxa richness and abundance of macroinvertebrates did not show a pronounced seasonal pattern. The duration of the autumn period with stable stream beds was important in determining the abundance and composition of the winter fauna.3. There were significant differences in species composition between summer and winter. Two potential strategies in larval survival were evident: adaptation to the extreme abiotic conditions in summer (e.g. Diamesa spp.) or avoidance of these conditions and development during winter (e.g. Ephemeroptera and Plecoptera).4. A comparison of a stream reach with continuous snow cover and a stream reach that remained open throughout winter showed that conditions under snow are suboptimal. At the open stream site, with higher water temperatures and greater food supply (benthic organic matter content), abundance and taxa richness was higher and larval growth was faster. Several taxa were found exclusively at this site.5. Winter conditions did not provide an entirely homogeneous environment, abiotic conditions changed rapidly, especially at the onset of snowfall and at snowmelt. Continuous monitoring is necessary to recognize spatial and temporal heterogeneity in winter environments and the fauna of alpine streams.
Export of invertebrates and detritus from fishless headwater streams in southeastern Alaska: implications for downstream salmonid production
Authors: WIPFLI MARK S. , GREGOVICH DAVID P. 
Published: March 2003

1. We examined the export of invertebrates (aquatic and terrestrial) and coarse organic detritus from forested headwaters to aquatic habitats downstream in the coastal mountains of southeast Alaska, U.S.A. Fifty‐two small streams (mean discharge range: 1.2–3.6 L s−1), representing a geographic range throughout southeast Alaska, were sampled with 250‐μm nets either seasonally (April, July, September) or every 2 weeks throughout the year. Samples were used to assess the potential subsidy of energy from fishless headwaters to downstream systems containing fish.2. Invertebrates of aquatic and terrestrial origin were both captured, with aquatic taxa making up 65–92% of the total. Baetidae, Chironomidae and Ostracoda were most numerous of the aquatic taxa (34, 16 and 8%, respectively), although Coleoptera (mostly Amphizoidae) contributed the greatest biomass (30%). Mites (Acarina) were the most numerous terrestrial taxon, while terrestrial Coleoptera accounted for most of the terrestrial invertebrate biomass.3. Invertebrates and detritus were exported from headwaters throughout the year, averaging 163 mg invertebrate dry mass stream−1 day−1 and 10.4 g detritus stream−1 day−1, respectively. The amount of export was highly variable among streams and seasons (5–6000 individuals stream−1 day−1 and <1–22 individuals m−3 water; <1–286 g detritus stream−1 day−1 and <0.1–1.7 g detritus m−3 water). Delivery of invertebrates from headwaters to habitats with fish was estimated at 0.44 g dry mass m−2 year−1. We estimate that every kilometre of salmonid‐bearing stream could receive enough energy (prey and detritus) from fishless headwaters to support 100–2000 young‐of‐the‐year (YOY) salmonids. These results illustrate that headwaters are source areas of aquatic and terrestrial invertebrates and detritus, linking upland ecosystems with habitats lower in the catchment.
Coping with warmer, large rivers: a field experiment on potential range expansion of northern quagga mussels (Dreissena bugensis)
Authors: Thorp James H. , Alexander James E. , Cobbs Gary A. 
Published: March 2003

SUMMARY 1. Zebra mussels (Dreissena polymorpha) have established a much greater range in North America and Europe than quagga mussels (D. bugensis), which occupy a very similar niche.2. We hypothesised that quaggas are physiologically capable of sustaining populations in warmer rivers currently occupied only by zebra mussels and that unidentified, non‐physiological factors account for their more limited distribution.3. Growth and survival of individually tagged mussels (976 D. bugensis from Lake Erie; 2625 D. polymorpha from Lake Erie and the Ohio River) were recorded monthly for up to 15 months in an outdoor stream mesocosm receiving unfiltered water from the Ohio River.4. Extreme temperatures stressed both species; but in contrast to several previous laboratory studies, quaggas survived high temperatures better than zebra mussels. We suspect this was the result of species‐specific differences in their ability to obtain, assimilate and/or catabolise food at high, sublethal temperatures.5. A unimodal growth pattern was observed in both species, with the highest growth rates from late spring to early autumn.6. Our survival and growth data suggest that quaggas are not physiologically limited from expanding southward.7. While lacking definitive proof that dreissenid populations in rivers are ecologically sustainable without upstream lentic ecosystems and/or unintended human intervention, we suggest that complex river currents and upstream retentive and highly productive slackwater habitats in rivers may help sustain downstream populations of these meroplanktonic, dreissenid mussels.
Comparing grazing by Dreissena polymorpha on phytoplankton in the presence of toxic and non‐toxic cyanobacteria
Authors: Dionisio Pires L. M. , Van Donk E. 
Published: March 2003

SUMMARY 1. The feeding behaviour of the zebra mussel (Dreissena polymorpha) was studied in the laboratory on different combinations of food, including a green alga (Chlamydomonas reinhardtii) and toxic and non‐toxic strains of the cyanobacterium Microcystis aeruginosa.2. The highest clearance rate of phytoplankton by zebra mussels was found when the mussels were feeding on a mixture of Chlamydomonas and non‐toxic Microcystis, the lowest on a mixture of Chlamydomonas and toxic Microcystis.3. The differences found in the clearance rates between food combinations can be partly explained by the production of pseudofaeces containing live phytoplankton cells. Zebra mussels expelled significantly more live phytoplankton cells in the presence of toxic Microcystis than in the presence of non‐toxic Microcystis. The pseudofaeces contained predominantly live Chlamydomonas cells. Proportionately much less live Microcystis cells were encountered in the pseudofaeces.4. Consequently, grazing of zebra mussels on a combination of Chlamydomonas and Microcystis may finally result in a dominance of Chlamydomonas over Microcystis. The presence of toxic Microcystis may even strengthen this shift.
Population dynamics and production of Jesogammarus annandalei, an endemic amphipod, in Lake Biwa, Japan
Authors: Ishikawa Toshiyuki , Urabe Jotaro 
Published: March 2003

SUMMARY 1. Population dynamics and production of Jesogammarus annandalei, an endemic amphipod in Lake Biwa, were examined from April 1997 to June 1998. The life cycle of this species was 1 year with the new generation beginning in early autumn. They preferred low temperature (<12 °C) and their spatial distribution varied seasonally and accordingly.2. In deep water, the abundance of J. annandalei ranged from 200 to 63 000 m−2 and decreased towards summer and the biomass (0.01∼3.6 g C m−2) was on average comparable that of zooplankton. The density was much higher than that recorded by a study conducted 35 years ago.3. Individual growth rate of this amphipod was high in winter and spring but decreased in summer. Annual production of J. annandalei (6.2 g C m−2 year−1) was only 2% of primary production but was at the higher end of the range reported for amphipods in oligo‐ and mesotrophic lakes.4. These results are consistent with the view that Lake Biwa is becoming more eutrophic, with a consequent decrease in the abundance of predatory fish in the profundal zone.