bluuebunny/crossref_metadata_2025_split huggingface dataset:
Prey selection and diets of bluegill Lepomis macrochirus with differing population characteristics in two Nebraska natural lakes
Authors: Olson N. W. , Paukert C. P. , Willis D. W. , Klammer J. A. 
Published: March 2003

Abstract
Environmental prey samples and stomach contents of bluegill
Lepomis macrochirus (Rafinesque) were collected in spring and summer 2000 from two Nebraska Sandhill lakes. Watts Lake contained a low‐density bluegill population, whereas Cozad Lake contained a high‐density bluegill population. Bluegill diets from both lakes were compared to determine if bluegill prey preference differed between the two populations. The highest median per cent (by calories) of zooplankton in the diet was 1.3%; the remainder was macroinvertebrates. Watts Lake bluegills preferred (based on Manly's alpha) amphipods in spring and chironomids in summer. Cozad Lake bluegills did not show a strong preference (compared with Watts Lake) for any macroinvertebrates, but still utilized amphipods and chironomids during both seasons. Larger bluegills in Watts Lake preferred chironomids in summer, but Cozad Lake bluegills did not exhibit this relationship. The higher density Cozad Lake bluegill population appeared to be more opportunistic than the lower density Watts Lake population, but both preferred macroinvertebrates.
Decadal change in abundance of surface migratory myctophid fishes in the Kuroshio region from 1957 to 1994
Authors: Watanabe Hikaru , Kawaguchi Kouichi 
Published: March 2003

AbstractDecadal change in abundance of surface migratory myctophid fishes was examined in the Kuroshio region of the western North Pacific for the 35 yr from 1957 to 1994 in relation to the Kuroshio regime shift, indicated by changes in its transport volume and sea surface temperature in the early 1970s. Each year, samples were collected from the 0‐ to 1‐m depth layer at night, from January to March, at 83 stations on average. Ten species belonging to five genera occurred. Juveniles [standard length (SL) ≤ 40 mm] and adults (SL > 40 mm) of each species were analysed. In juveniles, Myctophum asperum, M. nitidulum, Symbolophorus evermanni and Centrobranchus brevirostris accounted for 91.1% of the total catch (7419 individuals), while M. nitidulum contributed 82.4% of the total adult catch (494 individuals). The abundance of juvenile S. evermanni, C. brevirostris and M. nitidulum showed prominent peaks in 1971, together with adult M. nitidulum. These peaks corresponded to extraordinarily high zooplankton abundance in the Kuroshio region in 1971, suggesting high recruitment success and low adult mortality in surface migratory myctophids. Smaller changes in abundance in other years were species‐specific, and the fluctuation patterns were mainly explained by year‐to‐year fluctuations in the strength of the Kuroshio and the geographical distribution of each species, i.e. an increased Kuroshio flow volume resulted in an increase in tropical species and a decrease in temperate species, but no change in the pan‐Kuroshio species.
Intercalibrating SCOR, NORPAC and bongo nets and the consequences for interpreting decadal‐scale variation in zooplankton biomass in the Gulf of Alaska
Authors: Mckinnell S. M. , Mackas D. L. 
Published: March 2003

AbstractThe Canadian weathership time series of zooplankton wet weight biomass, collected at Ocean Station Papa in the Gulf of Alaska from 1956 to 1981, is one of the most comprehensive of its kind in marine science. In 1966, the sampling gear changed from a white North Pacific (NORPAC) net to a black Scientific Committee on Oceanic Research (SCOR) net and it was recently discovered that insufficient intercalibration samples were collected to understand how their sampling properties differed. A Canada‐GLOBEC project to redo the intercalibration of these net types and to understand how they relate to current sampling gear (bongo net) started in 1997. Seventy replicates of the three net types were collected in deep water in the Gulf of Alaska. The major finding is that all nets have similar sampling characteristics, whereas earlier reports indicated that NORPAC biomass values should be multiplied by a factor of 1.538 to be equivalent to the SCOR net. It now appears that this factor arose because flowmeters were not used in the original 1956–81 sampling (volume filtered was estimated from tow length × mouth area). A positive bias was introduced into the SCOR values because relatively more water passed through the SCOR net (undetected without a flow meter) than through the NORPAC net. This means that the unmetered NORPAC samples from 1956 to 1966 should not be adjusted and the unmetered SCOR values should be reduced by a factor that is related to wire angle. The general effect on the entire series is to lower the average biomass estimates, but more so for the early portion of the series than the later years.
The distribution of dippers,Cinclus cinclus(L.), in the acid‐sensitive region of Wales 1984–95
Authors: Buckton  , Brewin  , Lewis  , Stevens  , Ormerod  
Published: March 2003

1. Dippers were surveyed along seventy‐four acid‐sensitive streams in upland Wales in 1984 and again in 1995. At forty‐eight of the sites, and in an additional twenty‐three to twenty‐nine adjacent catchments, changes in acid‐base status and macroinvertebrate communities were assessed. River habitat surveys (RHS) and GIS (Geographical Information System) provided information on habitat features.2. pH means across all the sites were higher on average by 0.12 pH units in 1995 than 1984, accompanied by significantly increased total hardness and reduced sulphate. However, geometric mean aluminium concentrations increased significantly, while the abundances of important dipper prey either remained constant (Ephemeroptera) or declined (Trichoptera; Plecoptera).3. As in 1984, dipper distribution in 1995 was related to acid‐base status: aluminium concentrations were significantly higher, and pH significantly lower, at sites where dippers were absent. In both surveys, there were significantly more bankside broadleaves and fewer conifers where dippers were present.4. Although dippers occurred in 1995 on a similar number of streams as in 1984, there were both gains and losses, and an overall significant reduction in the number of visits on which birds were recorded (= registrations) per survey reach. Gains and losses were not related to habitat structure or acid‐base status, and might be stochastic. Mean aluminium concentrations increased more (P < 0.06) at sites where dipper registrations fell, than where they increased, but changes were large enough to explain altered occupancy at only five sites. Plecopteran abundances declined most at sites losing birds.5. We conclude that recovery from acidification has not yet been large or sustained enough to allow widescale increase in the Welsh dipper population, and continued decline cannot be excluded. There is a need for better understanding of how recovery processes will permeate foodwebs to reach top predators in acidified streams, and of the geographical scale of recovery required to increase populations in dispersed organisms such as birds. Such uncertainties, together with the mismatch in trends revealed by stream chemistry and dippers, illustrate reasons why chemical data alone are inadequate for the assessment of changing river quality.
Mitochondrial DNA polymorphism among alpine populations of Gammarus lacustris (Crustacea, Amphipoda)
Authors: Meyran  , Taberlet  
Published: March 2003

1. Mitochondrial DNA sequence analysis was used to investigate the phylogeographic structure among populations of the amphipod Gammarus lacustris isolated in high altitude lakes from the Northern to the Southern Alps, and to investigate the historical and demographic events that may have accompanied this differentiation.2. The comparison of a 376‐base segment of the mitochondrial cytochrome c oxidase I gene in fifty‐four specimens from nine different populations reveals no variation within populations. However, northern populations appear divergent from those from the Southern Alps. A particular population, located at the limit between the Northern and Southern Alps shows an intermediate haplotype related to the southern lineage.3. Consideration of the different mitochondrial lineages, together with geographical differences among populations, suggests a scenario for the post‐glacial colonization of G. lacustris in the alpine lakes.
Macroconsumer effects on insect detritivores and detritus processing in a tropical stream
Authors: Rosemond Amy D. , Pringle Catherine M. , Ramírez Alonso 
Published: March 2003

1. Few studies have assessed the effects of macroconsumers, such as fishes and shrimps, on detritus and detritivores.2. We used an underwater electric field to prevent macroconsumers from feeding in and on leaf packs in a lowland stream in Costa Rica and thus to determine their effects on the density of insect detritivores and decay rates of leaves.3. Exclusion of macroconsumers resulted in significantly higher densities of small invertebrates inhabiting leaf packs. Most of these were collector–gatherers, none were shredders.4. Despite the increase in invertebrate density, decay rates of leaves were not statistically different. These findings contrast with results from temperate streams showing that increases in the density of invertebrates in leaf packs typically result in an increased rate of decay.5. Leaf decay rates and invertebrate densities were also compared between leaf packs placed in electric exclusion treatments and those placed in coarse (2 cm) plastic net bags (as used in many previous studies). Our results suggest that using such netting in tropical streams may deter macroconsumers, which can affect insect density and, potentially, decay rates of organic matter.
Effects of eutrophication on seasonal patterns of mesozooplankton in a tropical reservoir: a 4‐year study in Pampulha Lake, Brazil
Authors: Pinto‐coelho Ricardo M. 
Published: March 2003

1. Pampulha Lake has undergone rapid eutrophication. Annual maxima of total phosphorus and conductivity increased steadily from 1993 to 1996. Nitrogen quickly decreased after macrophyte removal in 1994, but increased again in the following years2. The zooplankton was dominated by Daphnia gessneri, D. laevis, Diaphanosoma birgei and Thermocyclops decipiens. The biomass of major zooplankton organisms, including Daphnia and rotifers, increased during the period covered in this study.3. Autocorrelation coefficients have confirmed the existence of recurrent seasonal patterns for both chemical and biological variables.4. Daphnia, calanoid copepods and rotifers showed clear and recurrent seasonal patterns. Cyclopoid copepods and Diaphanosoma had temporal patterns more affected by long‐term trophic changes. Other organisms such as Moina, Ceriodaphnia and Bosmina exhibited high temporal variability with no recurrent patterns.5. There was a strong and positive correlation between total phosphorus and Daphnia biomass. Seasonal patterns of this cladoceran were also inversely associated with sestonic C:P ratios. Thus, Daphnia may be limited primarily by phosphorus and not by total food availability as expressed by particulate carbon.6. This study suggests that increasing eutrophication has changed the structure as well as seasonal patterns of the zooplankton community in Pampulha Reservoir.
Does body storage act as a food‐availability cue for adaptive adjustment of egg size and number in Daphnia magna?
Authors: Glazier Douglas S. 
Published: March 2003

1. The hypothesis that body storage is used by daphniids as a physiological cue for adaptively adjusting egg size and number to food availability was tested.2. Egg size and number were examined to see whether they are related to individual variation in body storage independent of maternal size, genotype and food level. Egg mass and brood size (number of eggs in a brood) were compared to somatic mass, all adjusted to maternal body length, at two food levels in two parthenogenetic clones of Daphnia magna.3. The prediction that adjusted brood size should increase with body storage, whereas adjusted egg mass should decrease with increasing body storage, was not fulfilled as seven of eight comparisons failed to fit the expectation.4. It is concluded that body storage is probably not the food‐availability cue used by daphniids to control intrabrood resource allocation. Other possibilities, such as chemical cues emitted by food organisms and by coexisting cladocerans, are briefly discussed.
Effects of solar radiation on bacterial and fungal density on aquatic plant detritus
Authors: Denward C. M. T. , Edling H. , Tranvik L. J. 
Published: March 2003

Summary1. The effects of solar radiation on bacterial and fungal growth on aquatic macrophyte detritus were studied in a microcosm experiment. Senescent leaves of Phragmites australis were incubated for 63 days in shallow water in the shade under photosynthetically active radiation (PAR) together with ultraviolet radiation, or under filters removing either ultraviolet B (UVB) or both UVB and ultraviolet A (UVA).2. Bacterial abundance and bacterial 3H‐leucine incorporation in the water were measured, together with α‐ and β‐D‐glucosidase activity. In addition, bacterial abundance and fungal biomass associated with the litter were measured.3. The results indicate that both PAR and UVA affect the micro‐organisms involved in the decomposition of leaf litter. The α/β‐D‐glucosidase activity ratio was less than one in irradiated and more than one in shaded microcosms, suggesting a change in the substrate dissolved organic matter composition towards more β‐ than α‐glycosidic linkages as a result of solar radiation.4. Microcosms receiving UVB displayed a significantly higher β‐D‐glucosidase activity than shaded microcosms, and those exposed to PAR or PAR + UVA, demonstrating the potential importance of UVB radiation.5. The free‐living bacteria tended to be dominated by filamentous forms in microcosms subject to solar radiation, especially PAR, and attached microbial communities showed a greater tendency to be dominated by bacteria in irradiated microcosms than in shaded microcosms.
Effects of prey dispersal on predator–prey interactions in streams
Authors: Dahl J. , Greenberg L. 
Published: March 2003

1. We studied the effect of mesh size (6 and 3 mm) on interactions between brown trout (Salmo trutta) and benthic invertebrates in enclosures placed in a stream in southern Sweden. We also compared how different prey exchange rates affected interactions between trout and invertebrates.2. Trout had strong impacts on some benthic taxa, and different mesh sizes produced different patterns. Trout affected the abundance of 10 of the 21 taxa examined, six in enclosures with 3 mm mesh and six in enclosures with 6 mm mesh. The abundance of nine of the prey taxa was lower in the presence of trout, only leptocerids were more numerous in the presence of trout.3. Our measurements of prey immigration/emigration, together with trout diet data, suggest that direct consumption by trout, rather than avoidance behaviour by prey, explains most decreases in prey abundance. There was avoidance behaviour by only two of the twenty‐one prey taxa, with trout inducing emigration of the mayflies Baetis rhodani and Paraleptophlebia sp.4. Trout indirectly increased periphyton biomass in both 3 and 6 mm enclosures. The effect of trout on periphyton was probably due to strong effects of trout on the grazer, Baetis rhodani, Heptagenia sp. and Paralepthoplebia sp.5. Our results suggest that mesh size, through its effects on exchange rates of prey, may affect interactions between predators and prey in running waters, but that the effects of dispersal and predation on invertebrates are taxon specific.
Ecosystem measures of river health and their response to riparian and catchment degradation
Authors: Bunn S. E. , Davies P. M. , Mosisch T. D. 
Published: March 2003

Summary1. Measurements of ecological patterns are often used as primary biological indicators of river health. However, these patterns provide little information about important stream ecosystem processes (e.g. the sources and fate of energy and nutrients). The direct measurement of these processes is considered fundamental to the determination of the health of stream and river ecosystems.2. In this paper we used two basic approaches to assess stream ecosystem response to catchment disturbance and, particularly, to the loss of riparian vegetation in different forested biomes across Australia. Benthic gross primary production (GPP) and respiration (R24) provided measures of the amounts of organic carbon produced and consumed within the system, respectively. Stable isotope analysis was used to trace the fate of terrestrial and instream sources of organic matter in the aquatic food web. In a focal catchment in SE Queensland, additional measurements were taken of riparian attributes, catchment features and water quality.3. Baseline measurements of GPP and R24 from undisturbed forest streams provided reference values for healthy streams for comparison with sites where the catchment or riparian vegetation had been disturbed. These values of metabolism were low by world standards in all biomes examined. Preliminary data from the Mary River catchment in SE Queensland indicated that these parameters were sensitive to variations in riparian canopy cover and, to a lesser extent, catchment clearing, and predictive models were developed. The ratio P : R (GPP : R24) was used to determine whether sites were net consumers (P < R) or producers (P > R) of carbon but this was not considered a reliable indicator of stream health on its own.4. Although forest streams were typically net consumers of carbon (P < < R), stable isotope analysis of metazoan food webs indicated a high dependence on inconspicuous epilithic algae in some biomes.5. A dramatic decline in the health of forest streams was observed when GPP substantially exceeded R24, especially when instream primary producers shifted from palatable unicellular algae to prolific filamentous green algae and macrophytes. These sources of instream production do not appear to enter aquatic food webs, either directly through grazing or indirectly through a detrital loop. Accumulation of these plants has led to changes in channel morphology, loss of aquatic habitat and often a major decline in water quality in some of the streams studied.
Long‐term movements of self‐marked caddisfly larvae (Trichoptera: Sericostomatidae) in a California coastal mountain stream
Authors: Jackson J. K. , Mcelravy E.R.I.C. P. , Resh V.I.ncent H. 
Published: March 2003

1. Over 140 000 larvae of the case‐building caddisfly Gumaga nigricula were self‐marked as they incorporated glitter into small portions of their cases while reared in streamside troughs. These marked individuals were released into stream pools and their movements monitored in the dry season, when base flow was low and no spates occurred, and in the wet season when base flow was high and several spates occurred.2. Of the 9,000–10 000 larvae released in each of two stream pools in the dry season, 4–20% (i.e. 377–1817 marked individuals) were observed on three sampling dates (4, 11 and 24 d after release). Most larvae (87–93%) remained within 4 m up‐ or downstream of the release line after 24 d. No larvae were found outside of the release pools, even after 37 d.3. Of the > 120 000 larvae released in one stream pool near the beginning of the wet season, 408 larvae were recaptured 130–167 d later, a period that included 30 days of high flow associated with six spates. Estimated survivorship over this period was 0.7–6.2%; there was no relationship between survival and larval size at release. Most (75%) recaptured larvae were found in the pool where they were originally released. The remaining larvae were found downstream of the release pool. Larvae had generally dispersed only a short distance downstream of the release pool (median = 18 m, maximum = 222 m). In addition, four marked pupae were later found 436 m downstream of the release pool.4. These results illustrate the sedentary nature of larval G. nigricula as well as the important role that high flow events play in larval mortality and dispersal. These case‐building larvae move very little during low flow periods, even when food resources appear limiting. In contrast, the frequency and distance of larval dispersal are much greater during periods with high flow.5. Our observations for G. nigricula support previously published inferences that larval dispersal within a stream can be limited for some aquatic insects. However, our observations also suggest that, even for a relatively sedentary species like G. nigricula, larval dispersal during periods with high flow may contribute significantly to gene flow within a stream reach.
Changes in the plankton community following introduction of filter‐feeding planktivorous fish
Authors: Fukushima Michio , Takamura Noriko , Sun Liwei , Nakagawa Megumi , Matsushige Kazuo , Xie P.I.N.G. 
Published: March 2003

1. We conducted enclosure experiments in a shallow eutrophic lake, in which a biomass gradient of the filter‐feeding planktivore, silver carp, Hypophthalmichthys molitrix Valenciennes, was created, and subsequent community changes in both zooplankton and phytoplankton were examined.2. During a summer experiment, a bloom of Anabaena flos‐aquae developed (≈ 8000 cells mL−1) solely in an enclosure without silver carp. Concurrent with, or slightly preceding the Anabaena bloom, the number of rotifer species and their abundance increased from seven to twelve species (1700–14 400 organisms L−1) after the bloom in this fish‐free enclosure. Protozoans and bacteria were generally insensitive to the gradient of silver carp biomass.3. During an autumn experiment, on the other hand, large herbivorous crustaceans were more efficient than silver carp in suppressing the algae, partly because the lower water temperature (≈ 24 °C) inhibited active feeding of this warm‐water fish and also formation of algal colonies. Heterotrophic nanoflagellate and bacterial densities were also influenced negatively by the crustaceans.4. Correspondence analysis (CA) was applied to the weekly community data of zooplankton and phytoplankton. A major effect detected in the zooplankton community was the presence/absence of silver carp rather than the biomass of silver carp, whereas that in the phytoplankton community was the fish biomass before the Anabaena bloom, but shifted to the presence/absence of the fish after the bloom.
Inhibition of phytoplankton photosynthesis by solar ultraviolet radiation: studies in Lake Titicaca, Bolivia
Authors: Villafae V. E. , Andrade M. , Lairana V. , Zaratti F. , Helbling E. W. 
Published: March 2003

1. Lake Titicaca is a large, high altitude (3810 m a.s.l.) tropical lake (16°S, 68°W) that lies on the border of Bolivia and Perú, receiving high fluxes of ultraviolet radiation (UVR) throughout the year. Our studies were conducted during September of 1997 with the main objective of studying the impact of solar UVR upon phytoplankton photosynthesis.2. Water samples were taken daily and incubated in situ (down to 14 m depth) under three radiation treatments to study the relative responses to PAR (Photosynthetic Available Radiation, 400–700 nm), UV‐A (320–400 nm), and UV‐B (280–320 nm) radiation.3. Photosynthetic inhibition by UVR in surface waters was about 80%, with UV‐A accounting for 60% and UV‐B for 20%; the inhibition by high levels of PAR was less than 20%. The inhibition due to UVR decreased with depth so that there were no significant differences between treatments at 8.5 m depth.4. The amount of inhibition per unit energy received by phytoplankton indicates that even though there was a significant inhibition of photosynthesis due to UVR, species in Lake Titicaca seem to be better adapted than species in high latitude environments.5. The cellular concentration of UV‐absorbing compounds, a possible mechanism of photoadaptation, was low in phytoplanktonic species. However, they were abundant in zooplankton, suggesting a high rate of bioaccumulation through the diet.