bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seasonal dynamics of the planktonic community in Lake Druzhby, Princess Elizabeth Land, Eastern Antarctica
Authors: LAYBOURN‐PARRY JOHANNA , BAYLISS PETER 
Published: November 2003

1. The temporal abundance and composition of the plankton of a continental Antarctic lake (Lake Druzhby) situated in the Vestfold Hills, Eastern Antarctica was investigated from December 1992 to December 1993. The system was dominated by microbial plankton (cyanobacteria, heterotrophic bacteria and protozoans) with few metazoans.2. Chlorophyll a concentrations ranged between 0.15 and 1.1 μg l–1 and showed highest levels from late winter to spring.3. Heterotrophic bacteria ranged between 75 and 250 × 106 l–1 with highest abundances in late winter/spring. Mean bacterial biovolumes showed considerable seasonal variation (0.05–0.31 μm3). Largest biovolumes occurred in summer and this was the time of highest community biomass.4. Heterotrophic nanoflagellates reached highest abundances in late summer (maximum 14 × 105 l–1). Their mean biovolume also exhibited considerable seasonal variation, ranging between 1.77 and 27.0 μm3, with largest size resulting in community biomass peaking in early summer. Ciliated protozoa were poorly represented and sparse. Phototrophic nanoflagellates were sparse in this lake; instead the phototrophic plankton was dominated by a small rod‐shaped cyanobacterium which constituted the largest carbon pool in the system. It was common throughout the year, its biomass peaking in autumn. Its presence is discussed in relation to lake morphometry and light climate.5. Heterotrophic flagellate grazing rates ranged from 6.78 bacteria cell–1 day–1 at 2 °C to 11.8 bacteria cell–1 day–1 at 4 °C. They remove around 2% of the bacterial carbon pool per day during summer and winter.6. Nutrient levels were low and recorded in pulses. Dissolved and particulate organic carbon were also low, usually less than 3 mg l–1 and 600 μg l–1, respectively. The carbon pools were derived from autochthonous sources. This lake system is driven by bottom‐up forces and lacks top‐down control, which fits into the picture currently seen for continental Antarctic lakes.
The ecology of a subterranean isopod, Caecidotea tridentata
Authors: EDLER C. , DODDS W.K. 
Published: November 2003

1. The blind isopod Caecidotea tridentata is the dominant invertebrate in a simple community of subterranean organisms inhabiting the local, shallow aquifer under Konza Prairie, Kansas, U.S.A.2. The ecology of this karst aquifer was explored by sieving water from a spring, collecting water samples for analysis, and manipulating sediments and invertebrates in the laboratory. The size frequency distribution was stable and gravid females were present throughout the year, suggesting continuous reproduction.3. The number of isopods collected per litre was negatively correlated with discharge and the abundance of bacteria, but positively related to the numbers of an amphipod (Bactrurus hubrichti). This may be explained if both the isopods and the amphipods track the saturated zone below the top of the water table; at lower discharge, the top of the water table is closer to the spring outlet. The suspended bacteria wash out in greater numbers with high discharge.4. When isopods and carbon were added in a pairwise experimental design to sediments collected from the aquifer, the isopods significantly stimulated numbers and activity of planktonic and sedimentary bacteria, while carbon had no effect. This suggests that invertebrates can affect the microbes locally in an aquifer.
Responses of the predatory rotifer Asplanchna intermedia to prey species differing in vulnerability: laboratory and field studies
Authors: IYER NANDINI , RAO T. 
Published: November 2003

1. We have studied the numerical and functional responses of campanulate morphs of Asplanchna intermedia fed five species of rotifer (Brachionus rubens, B. patulus, B. calyciflorus, Hexarthra mira and Filinia longiseta). The vulnerability of the prey varied with their morphology and mode of swimming.2. To test the numerical and functional responses, prey species differing in their morphology and mode of swimming were provided. Responses were also tested with mixtures of evasive and non‐evasive prey provided in three different ratios.3. A. intermedia showed a type II functional response to all the prey species provided.4. The population growth rate of A. intermedia on the various prey species provided ranged from a minimum of –0.24 to a maximum of 0.68. There was a significant correlation between the capturability of a prey species and the population growth rate of the predator feeding on it. The capturability of a prey species also has a significant influence on the maximal predator density but not on the time taken to reach it.5. Observations from a field study undertaken over a 10‐month period to study the prey preferences of A. intermedia in nature were corroborated by the laboratory findings.
A multivariate analysis of phytoplankton and food web changes in a shallow biomanipulated lake
Authors: ROMO SUSANA , VAN DONK ELLEN , GYLSTRA RONALD , GULATI RAMESH 
Published: November 2003

1. Phytoplankton dynamics, food chain changes and resilience in Lake Zwemlust, a shallow lake in The Netherlands, are described for the period 1986–94.2. After biomanipulation in 1987, the lake moved through two alternative states, while the external nutrient loadings were maintained. A clear‐water phase, mostly dominated by macrophytes, persisted from 1987 to 1991, and a rather turbid state, dominated by algae, occurred in the summers of 1992–94, after several consecutive and sustained perturbations affecting different parts of the food web in the lake. These two periods were characterized by different community structures.3. The phytoplankton assemblage gradually changed in a pattern that reverted in later years towards that of the pre‐biomanipulation stage, although the same species composition was not regained. This agrees with some mathematical models. During the clear‐water phase, nutrient shortage, light climate and zooplankton feeding selected in favour of small, high surface : volume ratio and rapidly reproducing algae. However, in mid‐summer of 1992–94, nutrient availability and cladoceran grazing on edible algae favoured cyanophytes.4. Nutrients were transferred to higher trophic levels or lost from the system at relatively high rates when the lake was in a piscivore–macrophyte‐dominated state, while they tended to accumulate in the algae in a planktivore‐dominated chain without macrophytes. The role of weed beds was central for nutrient competition (mostly nitrogen) with algae, as well as a refuge and a base for alternative food sources to grazers. Weed beds seemed to have a strong effect in increasing connectedness, resilience and stability of the lake community.5. The complete return of Zwemlust to a turbid state dominated by phytoplankton seems to have depended upon turnover of the limiting nutrient, which was retarded by macrophytes and stimulated by planktivorous fish and waterfowl.
Epiphytes from a deep‐water characean meadow in an oligotrophic New Zealand lake: species composition, biomass and photosynthesis
Authors: HAWES IAN , SCHWARZ ANNE‐MAREE 
Published: November 2003

1. The epiphytic flora of a characean meadow in Lake Coleridge, a deep, oligotrophic lake on the South Island of New Zealand, was dominated by diatoms, particularly Eunotia pectinalis and Achnanthes minutissima. The meadows occupied a depth range from 5 to 30 m. Adnate taxa predominated at all depths below 5 m, while increased taxonomic diversity at 5 m resulted from an increased abundance of erect taxa, including chlorophytes and stalked diatoms.2. Seasonal changes in epiphyte biomass were followed using artificial substrata and by estimating epiphyte chlorophyll a concentration on host plants. The latter required development of a novel technique utilizing the consistent relationship between fucoxanthin and chlorophyll a concentrations in the epiphyton. Epiphyte chlorophyll a on host plants varied with depth and host species between 0.1 and 0.3 mg g–1 dry weight. Maximum epiphyte biomass was at 10–15 m depth. At depths of 15 m and less, epiphyte chlorophyll a reached a maximum of ≈ 200–300 mg m–2 in mid‐summer, while at greater depths maximum biomass was less and coincided with a period of clear water in spring.3. Photosynthetic carbon fixation was estimated from photosynthesis–radiation curves and estimates of radiation flux at sampling depths. At depths greater than 10 m, variability of the vertical extinction coefficient of lake water rather than seasonal fluctuations in incident radiation were responsible for determining the temporal pattern of production. Chlorophyll a‐specific photosynthesis was estimated to peak in summer at 5 m (8 mg mg–1 day–1), and in spring at all other depths.4. Annual epiphyte production was estimated as 27 g C m–2 year–1 at 5 m depth, falling to 15 g C m–2 year–1 at 15 m and 1 g C m–2 year–1 at 30 m. Areal biomass changes tended to be temporally but not quantitatively coupled to estimated in situ photosynthesis, and we hypothesize that epiphyte biomass may have been controlled by grazing gastropod snails.
Scales of observation of riparian forests and distributions of suspended detritus in a prairie river
Authors: JOHNSON SHERRI , COVICH ALAN 
Published: November 2003

1. Detrital inputs from riparian forests can provide the main source of energy to aquatic consumers in stream communities. However, the supply of coarse organic detritus to stream communities is difficult to predict. Patchy riparian inputs and connectivity between reaches have complicated studies and disrupted patterns of the distribution of suspended coarse particulate organic matter within streams and rivers.2. In this study we emphasize the importance of spatial and temporal scales in determining potential distribution of instream leaf litter. Although large pulses of detritus are transported by streams during storm flows, the main supply of benthic leaf litter used by shredders and of suspended particulate organic matter used by filter feeders is transported during prolonged periods of baseflow. The local, fine‐scale distribution of this organic matter is determined by the location and continuity of leaf litter sources (riparian vegetation) and specific features of channel roughness (such as woody debris, roots and rocks).3. Viewing riparian vegetation at several scales results in variable conclusions regarding the amount of potential source area of leaf detritus. The percentage of suspended whole leaves at sites in the Little Washita River, Oklahoma, U.S.A. was best explained by the percentage of riparian forest cover in 500 m and 1000 m reaches upstream of the sites, as viewed by remote sensing imagery. The amount of leaf fragments was best explained by distance downstream along the longitudinal gradient. Ash‐free dry mass of suspended coarse particulate matter did not correlate with any measures of riparian cover.4. Our results suggest that leaves originate over longer reach lengths than those generally considered as source areas. Scale is an important consideration in studies of riparian patterns and related instream processes because of the need to integrate point dynamics as well as upstream influences.
The relationship between land use and physicochemistry, food resources and macroinvertebrate communities in tributaries of the Taieri River, New Zealand: a hierarchically scaled approach
Authors: TOWNSEND COLIN , ARBUCKLE CHRIS , CROWL TODD , SCARSBROOK MIKE 
Published: November 2003

1. The relationship between land use and stream conditions was investigated, including physicochemistry, the availability of primary food resources and species richness, species composition and trophic structure of stream macroinvertebrate communities. The survey involved eight subcatchments of the Taieri River (New Zealand) encompassing reasonably homogeneous examples of four major land uses: native forest, native tussock grassland, plantations of introduced pine and agricultural pasture.2. Each land use was represented by two subcatchments, each subcatchment by two to four tributaries, and each tributary by two to three sampling sites. These three sampling scales each represent typical designs for stream community studies. By recording responses at all scales, it can be determined explicitly whether the scale of sampling influences interpretation of community structure.3. Elevation, riffle length, proportion of large substrata in the bed, total phosphorus and alkalinity were significantly related to land use, as were canopy cover and the relative abundance of leaves and wood in the streams. Principal components analysis of invertebrate density data identified nine orthogonal community types, the distributions of two of which were significantly related to land use. The role played by browsers and shredders in the stream community depended on land use.4. Primary analysis was at the level of the tributary. When it focused on sites within tributaries, more variables were related to land use and at a higher level of significance. This was largely a result of enhanced statistical power due to increased replication. When whole subcatchments were the focus of attention, statistical power was so low, even with six to eleven subsamples to generate overall means, that few significant patterns could be identified. However, the community patterns that were revealed were similar whatever the scale of sampling.
Reconciling landscape and local views of aquatic communities: lessons from Michigan trout streams
Authors: WILEY MICHAEL , KOHLER STEVEN , SEELBACH PAUL 
Published: November 2003

1. Rapidly advancing geographical information systems (GIS) technologies are forcing a careful evaluation of the roles and biases of landscape and traditional site‐based perspectives on assessments of aquatic communities. Viewing the world at very different scales can lead to seeming contradictions about the nature of specific ecological systems. In the case of Michigan trout streams, landscape analyses suggest a predictable community shaped by large‐scale patterns in hydrology and geology. Most site‐based studies, however, suggest these communities are highly variable in structure over time, and are strongly shaped by site‐specific physical and biological dynamics. As the real world is comprised of processes operating both at local and landscape scales, an analytical framework for integrating these paradigms is desirable.2. Decomposition of variances by factorial ANOVA into time, space and time–space interaction terms can provide a conceptual and analytical model for integrating processes operating at landscape and local scales. Using this approach, long‐term data sets were examined for three insects and two fishes common in Michigan trout streams. Each taxon had a unique variance structure, and the observed variance structure was highly dependent upon sample size.3. Both spatially extensive designs with little sampling over time (typical of many GIS studies) and temporally extensive designs with little or no spatial sampling (typical of population and community studies), are biased in terms of their view of the relative importance of local and landscape factors. The necessary, but in many cases costly, solution is to develop and analyse data sets that are both spatially and temporally extensive.
Seasonal variation in vertical and horizontal movement of the freshwater bivalve Elliptio complanata (Mollusca: Unionidae)
Authors: AMYOT JEAN‐PIERRE , DOWNING JOHN 
Published: November 2003

1. Vertical and horizontal movement were studied in the freshwater bivalve Elliptio complanata at a sandy site in an oligotrophic lake over 3 years. Mussel movement did not vary significantly between day and night. On average, between 2 and 8% of 527 mussels moved each month during the ice‐free season and the distance travelled by moving mussels averaged 0.6 cm day–1.2. Mussels were endobenthic during the winter, emerged from the sandy substrate in mid‐May, peaked in sediment surface abundance in July, and descended into the sediments for the winter in September–October. Vertical displacement of mussels was closely correlated with water temperature although daylength may play a role. Mussels apparently move very little beneath the sediment during the winter.3. The number of mussels moving horizontally at any given time was linearly correlated with daylength, but the distance travelled during a sampling period was related to daylength in a non‐linear fashion. Greatest horizontal displacement of epibenthic mussels was found during spring and early summer, coincident with spawning in E. complanata
Internal shell annuli yield inaccurate growth estimates in the freshwater mussels Elliptio complanata and Lampsilis radiata
Authors: KESLER DAVID , DOWNING JOHN 
Published: November 2003

1. The objective of this study was to compare, in freshwater bivalves, growth rates inferred from the spacing of internal annuli to those obtained directly by measuring annual changes in shell length.2. The unionid mussels studied were Elliptio complanata and Lampsilis radiata from a pond in the north‐eastern U.S.A. Age was inferred from internal lines of 157 E. complanata and twenty‐five L. radiata. Actual length change was determined from comparisons of annual remeasurements of marked E. complanata (n = 520) in 1992–95 and L. radiata (n = 81) in 1993–95.3. High retrieval rates of painted mussels demonstrated the efficacy of the marking method.4. Annual length changes determined by remeasurement were significantly lower than annual length changes predicted by length‐at‐age data from internal annuli. Should this be a common occurrence, past estimates of annual growth based on annuli are probably too large, and unionid mussels may be much older than previously assumed.
Seasonal, discharge‐driven patterns of mayfly assemblages in an intermittent Neotropical stream
Authors: NOLTE ULRIKE , DE OLIVEIRA MARIA JOSÉ , STUR ELISABETH 
Published: November 2003

1. Streams in the seasonal wet and dry tropics have highly dynamic discharge regimes. Our study stream, located in mid‐western Brazil, drains into the Pantanal, South America’s largest wetlands, and is characterized by frequent spates in the rainy season and several weeks of interrupted flow in the dry season.2. In order to understand how these seasonal flow patterns influence the aquatic fauna, floating litter was studied because: (i) this habitat is exposed to the current, and thus is likely to be most affected abiotically and biotically by changes in flow; and (ii) this habitat is abundant in unaltered tropical streams. Studies were conducted in a third‐ and a fourth‐order reach. Mayflies were chosen as study organisms because they were frequent and species‐rich on floating litter, and because they should to be responsive to changes in current velocity.3. In the course of 15 months, covering one rainy and two dry seasons, mayflies showed pronounced seasonal patterns at family and genus level, which were evidently driven by discharge. Two periods of high mayfly densities were observed in the course of one year. One maximum coincided with the peak of the rainy season, the other with the peak of the dry season, and both were distinct in faunistic composition. At high current velocities the leptophlebiid Farrodes sp. was dominant and Leptohyphes sp., Acerpenna sp. and Paracloeodes sp. were frequent. In the dry season, when the river was reduced to isolated standing waters, 86–93% of all mayflies were Caenis sp.4. Altogether sixteen mayfly genera from the families Baetidae, Caenidae, Leptohyphidae, Leptophlebiidae and Oligoneuriidae were recorded. Two genera are new to science, the baetid Aturbina was recently described (among others, from material from our study river), Acerpenna and Paracloeodes are new records for South America, and Miroculis and Terpides are recorded for the first time south of the Amazon.
The role of carbon dioxide in the initiation and maintenance of blue‐green dominance in lakes
Authors: SHAPIRO JOSEPH 
Published: November 2003

1. In 1993 the south basin of Squaw Lake, Wisconsin, U.S.A., was artificially circulated and injected with CO2 in an attempt to eliminate the massive quantities of blue‐greens normally present during summer. The unmixed, uninjected north basin was the control. Despite a great difference in CO2 concentration and in pH between the two basins, their blue‐green maxima began simultaneously and eventually reached the same size. The predominant algae in both basins were Aphanizomenon flos‐aquae and Anabaena flos‐aquae.2. From 13 May to 9 September, experiments were done to determine the responses of photosynthesis (oxygen production) of the phytoplankton communities in both basins to changes in pH over the range 7–9. Both the north and south basins underwent two distinct shifts in the slopes of their photosynthetic responses to pH. These shifts paralleled changes in the proportion of blue‐greens in their phytoplankton.3. Experiments with additions of KHCO3 or NaHCO3 showed that the responses to pH were really responses to CO2 concentration. Therefore, the data obtained in the photosynthesis experiments were used to calculate the kinetic parameters Ks* and Vmax*. The Ks* values varied in relation to the proportion of blue‐greens, with lower values during the period when blue‐greens predominated. The Vmax*values showed no such systematic changes.4. CO2 compensation and zero photosynthesis concentrations confirm that when the blue‐greens dominated, CO2 was taken up much more efficiently than when the phytoplankton comprised mostly non‐blue‐greens. No evidence appeared suggesting direct use of bicarbonate even at pH values of 10.0.5. Experiments with water collected seasonally from four other lakes show that Squaw Lake is not unique. In each case the response slopes (and therefore Ks* values) were high during spring when non‐blue‐greens were dominant, but decreased when the blue‐green maximum began.6. Experiments with individual species of algae confirm that blue‐greens generally have better CO2 kinetics than do greens.7. It is concluded that initiation of the blue‐green maximum does not depend upon conditions of low CO2 concentration or high pH. However, once the blue‐greens become abundant they ensure their dominance by reducing concentrations of CO2 to levels available only to themselves.
Response of littoral invertebrates to reduction of fish density: simultaneous experiments in ponds with different fish assemblages
Authors: PIERCE CLAY , HINRICHS BRUCE 
Published: November 2003

1. We experimentally reduced densities of predatory fish in replicated 2 m2 areas of the littoral zone in two ponds to test whether density and biomass of invertebrates would respond to release from fish predation. The ponds are of similar size and in close proximity, but support different fish assemblages: bluegills (Lepomis macrochirus Rafinesque) and largemouth bass (Micropterus salmoides (Lacepede)) in one pond, and bluespotted sunfish (Enneacanthus gloriosus (Holbrook)) and chain pickerel (Esox niger Lesueur) in the other. Fish densities were reduced to less than 15% of ambient levels in both experiments.2. In the bluegill–bass pond, density and biomass of most invertebrate taxa and size classes were unaffected by the fish manipulation. Total invertebrate densities did not differ significantly between fish treatments, but total invertebrate biomass was significantly greater where fish density was reduced, averaging 30% higher over the course of the study. Likewise, manipulation of fish in the bluespotted sunfish–pickerel pond had few significant effects on individual taxa and size classes. There were no significant effects on total invertebrate abundance in the bluespotted sunfish–pickerel pond.3. Our results provide direct experimental evidence consistent with the collective evidence from previous work, suggesting that the impact of fish predation on density and biomass of invertebrate prey in littoral habitats is variable, but generally weak. Invertebrates that coexist successfully with fish in littoral systems probably are adept at taking advantage of refugia offered by the structurally complex physical environment.