bluuebunny/crossref_metadata_2025_split huggingface dataset:
Grazer control and nutrient limitation of phytoplankton biomass in two Australian reservoirs
Authors: MATVEEV VLADIMIR , MATVEEVA LILIAN 
Published: November 2003

1. Grazer and nutrient controls of phytoplankton biomass were tested on two reservoirs of different productivity to assess the potential for zooplankton grazing to affect chlorophyll/phosphorus regression models under Australian conditions. Experiments with zooplankton and nutrients manipulated in enclosures, laboratory feeding trials, and the analysis of in‐lake plankton time series were performed.2. Enclosures with water from the more productive Lake Hume (chlorophyll a = 3–17.5 μg l–1), revealed significant zooplankton effects on chlorophyll a in 3/6, phosphorus limitation in 4/6 and nitrogen limitation in 1/6 of experiments conducted throughout the year. Enclosures with water from the less productive Lake Dartmouth (chlorophyll a = 0.8–3.5 μg l–1), revealed significant zooplankton effects in 5/6, phosphorus limitation in 5/6 and nitrogen limitation in 2/6 of experiments.3. While Lake Hume enclosure manipulations of the biomass of cladocerans (Daphnia and Diaphanosoma) and large copepods (Boeckella) had negative effects, small copepods (Mesocyclops and Calamoecia) could have positive effects on chlorophyll a.4. In Lake Hume, total phytoplankton biovolume was negatively correlated with cladoceran biomass, positively with copepod biomass and was uncorrelated with total crustacean biomass. In Lake Dartmouth, total phytoplankton biovolume was negatively correlated with cladoceran biomass, copepod biomass and total crustacean biomass.5. In both reservoirs, temporal variation in the biomass of Daphnia carinata alone could explain more than 50% of the observed variance in total phytoplankton biovolume.6. During a period of low phytoplankton biovolume in Lake Hume in spring–summer 1993–94, a conservative estimate of cladoceran community grazing reached a maximum of 0.80 day–1, suggesting that Cladocera made an important contribution to the development of the observed clear‐water phase.7. Enclosure experiments predicted significant grazing when the Cladocera/Phytoplankton biomass ratio was greater than 0.1; this threshold was consistently exceeded during clear water phase in Lake Hume.8. Crustacean length had a significant effect on individual grazing rates in bottle experiments, with large Daphnia having highest rates. In both reservoirs, mean crustacean length was negatively correlated with phytoplankton biovolume. The observed upper limit of its variation was nearly twice as high compared to other world lakes.
Coprophagy: a supplementary food source for two freshwater gastropods?
Authors: BRENDELBERGER HEINZ 
Published: November 2003

1. The freshwater pulmonate snail Radix peregra voluntarily and regularly fed on its faeces, whereas Bithynia tentaculata (Prosobranchia) did not.2. With high‐quality faeces as food (faeces with C : N‐values below ten) Radix could grow and survived for 11 weeks. Growth was 24–30% of that achieved with control food (lettuce, Chlamydomonas and Tetramin), and body mass was close to the expected value.3. As with real food, the percentage organic content of faeces was reduced during gut passage, with the exception of very low‐quality faeces.4. Faeces contained living cells of green algae (Chlamydomonas reinhardii) and diatoms (Achnanthes lanceolata, Eunotia pectinalis), which survived the gut passage of R. peregra and B. tentaculata. Faecal material was also rich in bacteria, with up to 150 × 106 cells mg–1 dry mass. Bacteria increased in abundance in faeces which had been evacuated for 7 days or more.5. A further degradation of partly digested food in the faeces was indicated by the activity of the extracellular digestive enzymes cellobiase and chitobiase. These enzymes hydrolysed material with an activity of 0.2–14.5 pkat mg–1 faecal dry mass in 1–12‐day‐old faeces. In faeces of Bithynia fed control food or incubated sycamore leaves, chitobiase activity was correlated with bacterial abundance.6. Coprophagy is considered to be a suitable strategy for further degradation and utilization of refractory material for which one gut passage is too short and/or too inefficient.
Annual production of leaf‐decaying fungi in a woodland stream
Authors: SUBERKROPP KELLER 
Published: November 2003

1. Fungi are thought to be important mediators of energy flow in the detritus‐based food webs of woodland streams. However, until recently, quantitative methods to assess their contribution have been lacking. Growth rates of leaf‐decaying fungi can be estimated from rates of acetate incorporation into ergosterol which, together with estimates of fungal biomass from ergosterol concentrations, enables calculation of fungal production. In this study, I used this method to estimate total production of leaf‐decaying fungi over an annual cycle in a small woodland stream, Walker Branch, Tennessee, U.S.A. To calculate fungal biomass and production on an areal basis, I determined the amount of leaf litter occurring in the stream by sampling transects randomly selected in each of ten 10‐m sections every 20–50 days. Subsamples of leaves chosen from five of the transects were used to determine ergosterol concentrations and in situ rates of acetate incorporation into ergosterol.2. Leaf litter, fungal biomass m–2, and fungal production m–2 were highly seasonal. Leaf litter ranged from 249 g m–2 in November to less than 5 g m–2 during the summer. Fungal biomass as percentage of leaf litter ranged from 4.4 to 8.8% during the year, but on an areal basis ranged from 11 to 13 g m–2 during November to January to 0.25 g m–2 in June, primarily due to the seasonal variation in amount of leaf litter present. Fungal growth rates averaged 2.6% day–1 (0.9–7.0% day–1) during the year. Daily production of leaf‐decaying fungi ranged from 0.49 g m–2 in November, when the amount of leaf litter was at its maximum, to 0.006 g m–2 during the summer when the amount of leaf litter was low. Annual production of leaf‐decaying fungi was 34 g m–2, with an annual production to biomass ratio (P/B) of 8.2.3. Fungal spore concentrations in the stream were also seasonal and were correlated with amount of leaf litter m–2 and fungal biomass m–2. Spore concentrations varied between one and four spores ml–1 throughout most of the year, but increased to eighteen spores ml–1 shortly after the greatest amount of leaf litter was present in the stream during November.
Habitat segregation and interactive effects of multiple predators on a prey assemblage
Authors: GONZÁLEZ MARÍA , TESSIER ALAN 
Published: November 2003

1. In a field experiment we examined the interactive effects of two common predators of zooplankton, bluegill sunfish (Lepomis macrochirus) and Chaoborus spp. on the growth rate and habitat use of three congeneric prey species (Daphnia). Bluegill and Chaoborus both consume Daphnia, but bluegill also prey on Chaoborus. The prey species, Daphnia pulicaria, D. rosea and D. retrocurva, differed in body size and vertical distribution. We expected the largest species, D. pulicaria, to be most vulnerable to fish predation and the smallest species, D. retrocurva, to be most vulnerable to Chaoborus predation.2. As we expected, the population growth rate of D. pulicaria was significantly reduced by fish. However, Chaoborus also significantly reduced the growth rate of this species. No significant interaction effect was detected, indicating that the effect of these predators was additive. The growth rates of D. rosea and D. retrocurva were significantly reduced by Chaoborus, but a significant interaction effect indicated that the effect of Chaoborus was stronger in the absence of fish than when fish were present. Therefore the impact of Chaoborus and fish on D. rosea and D. retrocurva was non‐additive. The interactive effect of the two predators on D. retrocurva was greater in magnitude than on D. rosea.3. In the absence of predators, the three Daphnia species showed no differences in mean habitat depth between day and night. Both predators significantly affected diel habitat use of D. pulicaria and D. rosea. Fish caused both of these Daphnia species to move deeper during the day, whereas Chaoborus caused Daphnia to move into shallower water at night. Daphnia retrocurva tended to migrate upwards at night in all predator treatments, but no significant differences in migration were observed among the predator treatments. The effects of predators on habitat use were not interactive for any prey species.4. Our results suggest that body size, habitat use and the diel migratory response to predators are important factors mediating the interactive effects of multiple predator types on zooplankton.
Structure and diversity of stream invertebrate assemblages: the influence of temperature with altitude and latitude
Authors: JACOBSEN DEAN , SCHULTZ RIKKE , ENCALADA ANDREA 
Published: November 2003

1. Structure and diversity of the macroinvertebrate fauna were studied in relation to altitude and latitude among three groups of streams from Ecuador (lowland: 100–600 m, Central Valley: 2600–3100 m, páramo: 3500–4000 m), and one group from the temperate lowland region of Denmark. The streams in the four regions were comparable with regard to physical characteristics such as size, current and substratum.2. In terms of faunal composition the Ecuadorian highland streams bore more resemblance to the Danish lowland streams than the Ecuadorian lowland streams. The greater similarity between the Ecuadorian highland and the Danish streams, however, was due to the large number of insect families in the Ecuadorian lowlands, many of which were not found in the other regions. Of ten physico‐chemical parameters measured, maximum stream temperature explained by far the most variability in faunal composition.3. The number of insect orders and families increased linearly with maximum stream temperature and therefore decreased with altitude and latitude. A compilation of literature data on insect richness and maximum water temperature from streams around the world confirmed this pattern, yielding a common linear relation for both temperate and tropical streams. This pattern may arise due to a direct temperature effect on speciation but is probably also related to geological history and the influence of climatic changes on stream ecosystems. We estimate that small, tropical, lowland streams have, on average, a two‐ to fourfold higher species richness than temperate lowland streams.
Structural characteristics of phytoplankton assemblages in tidal and non‐tidal freshwater systems: a case study from the Schelde basin, Belgium
Authors: MUYLAERT KOENRAAD , VAN KERCKVOORDE ANDY , VYVERMAN WIM , SABBE KOEN 
Published: November 2003

1. The Schelde estuary, its side basins and their tributaries were sampled in August 1995 and April 1996 for phytoplankton abundance, biomass, diversity and species composition. In order to clarify the underlying causes of differences in phytoplankton communities, the results were related to some important abiotic variables.2. Although species richness and diversity did not differ significantly between the riverine and the freshwater tidal stations, multivariate ordination techniques based on species abundances differentiate between these two ecosystems. While in the rivers phytoplankton standing stocks were as high in summer as in spring, standing stocks in the freshwater tidal estuary were significantly higher in the August samples.3. It is postulated that due to the resuspension of suspended solids by estuarine currents, light is limiting phytoplankton development in the freshwater tidal reaches in spring. At that stage, phytoplankton populations have already developed in the rivers. In summer, zooplankton prevent any further increase of riverine phytoplankton populations. In the freshwater tidal estuary, however, increased light levels, a higher residence time compared to rivers and the absence of zooplankton due to low oxygen concentrations permit phytoplankton populations to bloom.
Reproduction and adult longevity of five species of planktonic cyclopoid copepods reared on different diets: a comparative study
Authors: HOPP ULRICH , MAIER GERHARD , BLEHER RAINER 
Published: November 2003

1. The nutritional value of a pure algal food, the phytoflagellate Chlamydomonas reinhardtii, and a mixed diet was tested for five planktonic cyclopoid copepods (Acanthocyclops robustus, Cyclops vicinus, Cyclops abyssorum, Mesocyclops leuckarti and Thermocyclops crassus). The algae were offered at high density (4.5 × 105 cells ml–1; 22.5 mg C l–1) in a flow‐through system. The mixed diet consisted of concentrated natural plankton (rotifers, copepod nauplii, small copepodites and large phytoplankton forms) in the size range 50–150 μm and with a dry mass > 20 mg l–1. Reproductive parameters (clutch size, interclutch periods, number of clutches produced) and adult longevity were monitored as indicators of nutritive value.2. All species had a significantly lower reproductive output and a shorter or unchanged adult lifespan on the algal compared with the mixed diet.3. The species differed considerably in their ability to use algae. Mesocyclops leuckarti produced no clutches with algae, and females died earlier than with the mixed food. Acanthocyclops robustus and C. vicinus produced smaller and fewer clutches, displayed a longer interclutch period and shorter (A. robustus) or similar (C. vicinus) lifespan on the algal food than on the mixed food. Thermocyclops crassus and C. abyssorum produced smaller clutches with the algal food, but interclutch period was shorter with the algal than with the mixed diet (T. crassus) or of the same length with both diets (C. abyssorum). Adult lifespan was the same under both food regimes. Unfed females produced no eggs.4. The ability to utilize algae, the reproductive output and the reproductive allocation were not related to body size. Acanthocyclops robustus, a species of intermediate size, produced by far the largest clutches and the most eggs per lifetime under both food regimes and invested more in reproduction than the other species.5. Reproduction was costly. Unfed and non‐reproducing females of C. vicinus and C. abyssorum reached the same age or lived longer than fed and reproducing ones.6. The adult cyclopoids tested are primarily omnivorous, but utilize algae which are frequently sufficient for egg production.
Relationships between benthic biota and hydrological indices in New Zealand streams
Authors: CLAUSEN BENTE , BIGGS BARRY 
Published: November 2003

1. The objective of this study was to identify the most ecologically relevant hydrological indices for characterizing hydrological regimes in New Zealand streams. To do this we related measures of periphyton chlorophyll a, ash‐free dry mass (AFDM), species richness, and diversity and invertebrate density, species richness and diversity, to thirty‐four hydrological variables derived from daily flow records at eighty‐three sites. The hydrological variables included some describing average flow conditions, flow variability, floods, and low‐flow characteristics.2. A principal components analysis showed that the interrelationship between many of the hydrological variables was high, and most variables correlated significantly with Principal Component 1 (PC1). The flood frequency variables formed a distinct component of the flow regime and were the main contributor to PC2.3. We found that both the average flow conditions and some measure of variability were significantly related to most of the biological variables, and these individual hydrological variables were more strongly correlated to the biological measures than the composite principal components. Only four of the thirty‐four flow variables were significantly correlated (P < 0.05) with measures of periphyton biomass (chlorophyll a and AFDM), whereas twenty‐four variables were correlated with periphyton diversity. Conversely, thirty‐one of the thirty‐four flow variables were correlated with total invertebrate density, whereas only four variables correlated with diversity.4. We selected the flood frequency (FRE3), where a flood is defined as flows higher than three times the median flow, as the most ecological useful overall flow variable in New Zealand streams because it explained a significant amount of the variance in four out of the six main benthic community measures, and it had a clear mechanism of control of the biota which was commensurate with current stream ecosystem theory. Periphyton biomass decreased with increasing FRE3, whereas invertebrate density had an increasing/curvilinear relationship with FRE3. Periphyton species richness and diversity decreased with increasing FRE3.
Interactive effects of diet and thermal regime on growth of the midge Pseudochironomus richardsoni Malloch
Authors: GRESENS SUSAN 
Published: November 2003

1. Larvae of Pseudochironomus richardsoni were reared to pupation in individual enclosures, in one of three thermal habitats in a northern California stream. The average temperature range in cold seeps was 15–21 °C, while the main channel ranged from 20 to 27 °C, and side pools ranged from 18 to 33 °C. Diet consisted of either diatoms or algal detritus.2. Specific growth rate ranged from 0.057 to 0.267 day–1. Specific growth and developmental rates were highest on a diatom diet, and increased with temperature. Regressions of growth rate on mean microsite temperature were also significantly altered by diet. Differences in specific growth rate due to diet are magnified at higher temperatures.3. Pupae reared on diatoms were larger than those reared on detritus. The mass of pupae reared on detritus decreased with increasing temperature. However, there was no significant relationship between pupal mass and temperature for larvae reared on diatoms.4. The combined effects of food quality and thermal environment on growth of the midge P. richardsoni are significantly different from the independent effects of diet and temperature. Interactive effects of food quality and temperature may influence the contribution of certain aquatic habitats (algal mats) to invertebrate secondary production.
Spatial and temporal response of stream bacteria to sources of dissolved organic carbon in a blackwater stream system
Authors: KOETSIER III PETER , McARTHUR VAUN , LEFF LAURA 
Published: November 2003

1. We hypothesized that changes in bacterial colony growth would be correlated to shifts in riparian vegetation (via leachate quality) along a river continuum of a south‐eastern, blackwater stream (U.S.A.). Spatially, we expected bacterial assemblages from downstream reaches to utilize more sources of leachate and at higher concentrations than bacteria collected from headwater reaches. Temporally, we predicted higher colony growth on leachate from autumn‐shed (senescent) leaves compared with leachate from fresh, green leaves.2. We examined spatial differences in assemblage growth by culturing bacteria sampled along the stream continuum on gradient plates using leachates from four common riparian species (Taxodium distichum, Carya spp., Acer rubrum and Decumaria barbara). Bacteria from the lowest site were able to use all sources provided and at all concentrations, whereas bacteria from upper reaches could not. Colony density was correlated to relative leachate concentration at all sites along the continuum.3. Leachates from fresh and senescent A. rubrum leaves were used to determine temporal differences. Winter assemblages of bacteria could not grow on fresh leaf leachate at any concentration but grew well on autumn leaf leachate at higher concentrations. Differential response of bacterial assemblages indicated local adaptation to potential sources of dissolved organic matter.4. Growth response of stream bacterial colonies appeared to be dependent on the timing and source of leachate as well as on sources of dissolved organic carbon from further upstream. Growth of bacterial assemblages exhibited ‘generalist’ characteristics in headwater reaches and ‘specialist’ characteristics at the mouth of our study stream drainage. Thus, our findings lend support to the argument that variable resource habitats favour a small, generalist assemblage, while environments with stable resource supplies allow for highly diverse assemblages dominated by specialists.
Size‐dependent flight initiation by a lotic mayfly in response to a predatory fish
Authors: SCRIMGEOUR GARRY , CASH KEVIN , CULP JOSEPH 
Published: November 2003

1. Laboratory experiments were performed to determine whether flight initiation by lotic mayfly larvae of Baetistricaudatus exposed to the longnose dace (Rhinichthyscataractae) is affected by an individual’s size and its physiological state.2. We used a three factorial ANOVA design to test whether flight initiation distances (FIDs) were affected by Baetis size (small, large), starvation level (low, high), and the length of a predator‐free foraging period (short, long).3. FIDs were significantly affected by the interaction between Baetis size and starvation level, and the main level effects of starvation and Baetis size. FIDs of small larvae were unaffected by starvation level and the length of the predator‐free feeding period, whereas starvation reduced FIDs of large larvae 2‐fold.4. Subsequent experiments showed that size‐dependent differences in FIDs could not be attributed to size‐specific differences in the economics of rates of food intake or gut evacuation. For both small and large larvae, food intake rates declined with increasing time spent foraging and both small and large larvae consumed the majority (70–75%) of food within the first 3 h of the 12‐h feeding period. Similarly, gut evacuation declined with increasing starvation time and rates of evacuation did not differ between small and large larvae. These data suggest that size‐dependent differences in flight initiation by Baetis larvae do not involve the energetics of food intake or processing.
Landscape influences on water chemistry in Midwestern stream ecosystems
Authors: JOHNSON LUCINDA , RICHARDS CARL , HOST GEORGE , ARTHUR JOHN 
Published: November 2003

1. Landscape characteristics of sixty‐two subcatchments within the Saginaw Bay Catchment of central Michigan were examined to identify relationships with stream water chemistry. Land use, land cover and elevation were quantified for both entire catchments and the upland–river ecotone (100 m stream buffer strip). Catchment and ecotone data were then empirically compared with stream water chemistry using multivariate and regression analyses. Redundancy analysis was used to partition variance among land use, geology, and the shared influence of land use and geology.2. Major catchments dominated by rowcrop agriculture had the highest alkalinity, total dissolved solids and nitrate + nitrite concentrations.3. Strong seasonal differences were observed in total nitrogen and nitrite + nitrate, but not in total phosphorus or suspended solids. Land use and landscape structure factors such as slope and patch density (number of land use patches per km2) accounted for most of the observed variance in summer.4. In both autumn and summer, landscape factors accounted for much of the observed variation in total dissolved solids and alkalinity. During autumn, geological factors and the shared influence of geology/landscape structure plus land use exerted more influence than did land use alone.5. Total phosphorus and total suspended solids were much better explained by land use within the stream ecotone in summer than in other seasons. However, total nitrogen, nitrate, orthophosphate and alkalinity were equally well explained by land use within the ecotone and throughout the whole catchment. Only total dissolved solids in summer and ammonium in autumn were explained better by the whole catchment than the ecotone.6. Our results show that relatively coarse spatial databases can provide useful descriptors of regional water quality.