bluuebunny/crossref_metadata_2025_split huggingface dataset:
Allozyme diversity in brown trout (Salmo trutta) from Central Spain: Genetic consequences of restocking
Authors: Machordom A. , Garcåa‐Marån J. L. , Sanz N. , Almodçvar A. , Pla C. 
Published: March 2003

1.  The brown trout (Salmo trutta) represents one of the main freshwater resources in Spain, but habitat alterations and overharvesting have contributed to the decline or disappearance of numerous natural populations. In addition, reinforcement programs of wild populations based on releases of hatchery reared fish of exogenous origin compromise the conservation of remnant native trout resources.2.  We present allozymic data from Central Spain trout populations including stocked and unstocked populations. Although the levels of genetic variation observed were low and affected by hatchery releases (p = 18.23%, Ho= 3.39%), they were within the range observed in other European areas.3.  The effective introduction of hatchery reared fish is genetically homogenising the populations in the studied area and disturbing the ancestral pattern of genetic variation that distinguishes the Tajo and Duero basins. Within the eight natural populations analysed, seven had alleles assigned to the foreign trout. The introgression in these populations, following the LDH‐5*90 allele frequency, ranged between 2% and 29.4%, but those values are not in concordance with the respective stocking effort undertaken in each population. Moreover, the release of hatchery‐reared fish does not solve the problems related to the reduced size of wild populations and their recruitment instability.
Life history and production of Paranephrops zealandicus in a forest stream, with comments about the sustainable harvest of a freshwater crayfish
Authors: Whitmore Nathan , Huryn Alexander D. 
Published: March 2003

1. Life history and production were assessed for the crayfish Paranephrops zealandicus in three reaches of a headwater stream with a catchment of regenerating coniferous‐broadleaf forest in the south‐east of the South Island of New Zealand.2. Crayfish density ranged from 3 to 4 m−2 in riffles and 4–12 m−2 in pools, depending on reach. Crayfish biomass (4–33 g AFDW m−2) and annual production (2–11 g AFDW m−2) were high compared with values reported elsewhere, while P:B ratio was low (0.33–0.43). This substantial production was dependent primarily upon high biomass rather than high growth rate.3. The crayfish of this population rank amongst the longest lived and slowest growing ever recorded. Individuals estimated to be 16+ year of age were not uncommon. Females became reproductively active at 6+ year. Fewer than 4% of females carried eggs, and young remained attached to females for at least 15 months.4. We propose that characteristics of this population are the consequence of a cool thermal regime (mean daily stream temperature = 7.0 °C, range 1.8–11.9 °C), and that low biomass turnover and poor reproductive rate precludes any sustainable commercial harvest of crayfish from streams in New Zealand with similar thermal regimes.
This is not the end of limnology (or of science): the world may well be a lot simpler than we think
Authors: Harris Graham 
Published: March 2003

1.Reynolds (1998)recently wrote a short piece in this journal lamenting the state of the art of freshwater ecology. Others have recently foreshadowed the end of science altogether. It is my argument here that the end of science is not nigh and that there are fundamental advances to be made in understanding ecosystem function. Despite changes to the funding base of freshwater ecology over the years, the discipline can continue to make fundamental contributions to ecology. We have an excellent base of raw material to work with, however, collected.2. As a rebuttal Reynolds (1997)I present evidence that ecosystems (and freshwater ecosystems in particular) may well be a lot simpler than we think. Buried deep within a very complex world there are some general modes of behaviour, determined by fundamental principles, which impart certain kinds of high level order and predictability.3. By means of six propositions I argue the case for the existence of these fundamental principles and present empirical evidence for each.4. In conclusion it is clear that there is a need for fundamental information about the role of biodiversity in ecosystem function. There is also a need to understand the interplay between environmental perturbations, biodiversity and functional groups which together determine the cycling of energy and materials within freshwater and estuarine systems. While we have considerable information about northern hemisphere aquatic ecosystems less is known about southern hemisphere systems.
Changes in agricultural intensity and river health along a river continuum
Authors: Harding JoN. S. , Young Roger G. , Hayes JohN. W. , Shearer Karen A. , Stark JohN. D. 
Published: March 2003

1. The impact of agricultural activities on waterways is a global issue, but the magnitude of the problem is often not clearly recognized by landowners, and land and water management agencies.2. The Pomahaka River in southern New Zealand represents a typical lowland catchment with a long history of agricultural development. Fifteen sites were sampled along a 119‐km stretch of the river. Headwater sites were surrounded by low‐intensity sheep farming, with high‐intensity pasture and dairying occurring in the mid‐reach and lower reaches.3. Water clarity decreased significantly from about 6 m in the headwaters to less than 2 m in the lower reaches. Benthic sediment levels increased significantly downriver, peaking at 35 mg m−−2 below several tributaries with high‐intensity agriculture in their catchments. Periphyton levels were also significantly greater in the lower reaches than the headwaters, and coincided with increased nitrogen (DIN) and phosphorus (SRP) concentrations.4. Macro‐invertebrate species richness did not change significantly throughout the river, but species composition did with Ephemeroptera, and to a lesser extent, Plecoptera and Trichoptera dominating the headwater sites (where there was high water clarity, and low nutrient and periphyton levels). Downriver these assemblages were replaced by molluscs, oligochaetes and chironomids.5. Canonical correspondence analysis indicated that agricultural intensity and physical conditions associated with agriculture activity (e.g. impacted waters, high turbidity and temperature) were strongly associated with the composition of benthic assemblages at differing reaches down the Pomahaka River.6. The present results indicate that quantifying agricultural intensity within a catchment, particularly relative livestock densities, may provide a useful tool for identifying threshold levels above which river health declines.
Predicting community characteristics from habitat conditions: fluvial fish and hydraulics
Authors: Lamouroux Nicolas , Olivier Jean‐Michel , Persat Henri , PouilLy MarC. , Souchon YveS. , Statzner Bernhard 
Published: March 2003

1. One current approach to the prediction of community characteristics is to use models of key local‐scale processes (e.g. niche dimensions) affecting individuals and to estimate the effects of these attributes over larger scales. We tested this approach, focusing on how the hydraulic habitat structures fluvial fish communities.2. We used a recent statistical habitat model to predict fish community characteristics in eleven reaches in the Rhône river basin in France. Predictions were made ‘blindly’ since most reaches were not used to calibrate the model. The model reflects species preferences for local hydraulics. We made predictions of the fish community from the local hydraulic conditions found in the reaches under low flow conditions. The overall abundance and the relative abundance (both as indices) of fish species, specific size classes and species traits (i.e. reproductive, trophic, morphological and others) were predicted. We summarized our predictions of the relative abundance of species as two ‘community structure indices’ using Principal Component Analysis.3. Our predictions from low‐flow hydraulics were compared with long‐term observations of fish communities. The relative abundance of species actually observed depended largely on zoogeographic factors within the Rhône basin which could not be predicted by the model. The model predicted 13% of the variance in the indices of relative abundance at the species level and 23% of this variance at the trait level for all zoogeographic regions combined. However, when focused on reaches within a geographic region, the model explained up to 47% of the same variance. Therefore, geographic regions act as ‘filters’ on the relative abundance of species, but hydraulics do affect fish communities within a given geographical context.4. For the synthetic ‘community structure indices’, we obtained good predictions from hydraulics independently of the geographical context (variance explained up to 95%). These indices were linked to simple key hydraulic characteristics of river reaches (Froude and/or Reynolds number). The indices enabled interpretations of the links between hydraulics, geomorphology, discharge and community patterns. These links were consistent with existing knowledge of species and their traits.5. In addition to the above validations, the habitat model partly explained the observed effects of impoundment on fish communities.6. The present results show that stream hydraulics strongly impact fish community structure. Consequently, our findings confirm that community characteristics can be predicted using models of the local‐scale habitat requirements of the species forming the community.
Habitat use by crayfish in stream pools: influence of predators, depth and body size
Authors: Englund Göran , Krupa James J. 
Published: March 2003

SUMMARYCrayfish in headwater streams are subjected to predation from two sources: (a) fish; and (b) terrestrial predators including wading birds and mammals. Field observations of the mortality of tethered crayfish of two size classes were used to examined how predation risks imposed by the two types of predators varied with water depth and crayfish size. We also examined the depth distribution of large and small crayfish in stream pools with and without predatory fish.Predatory fish, mostly green sunfish,Lepomis cyctuellus, and creek chub,Semotilus atromaculatus, rapidly consumed tethered small crayfish (body length = 25–30 mm) in deep areas (0.4–0.7 m), but not in shallow areas (0.05–0.15 m) of stream pools. Tethered large crayfish (body length = 50–75 mm) suffered little mortality from fish at either depth. Terrestrial predators such as racoons,Procyou lotor, and herons,ButoridesandArdea, caused little crayfish mortality in deep areas, but rapidly consumed both small and large crayfish exposed in shallow areas.A comparison of habitat use by crayfish in pools with and without fish suggests that small, but not large, crayfish shift their distributions to shallow water in the presence of fish. In pools without fish, the distribution of small crayfish was independent of depth, whereas large crayfish occupied deep water.
Morphological deformities occurring in Belarusian chironomids (Diptera: Chironomidae) subsequent to the Chernobyl nuclear disaster
Authors: Williams D. Dudley , Nesterovitch Andrei I. , Tavares Annette F. , Muzzatti Ernest G. 
Published: March 2003

1. Chironomid larvae and adults were collected from several freshwater habitats around the Chernobyl site from 1990 to 1994 (4–8 years after a nuclear accident) and examined for morphological deformities.2. Deformities were found in larvae of nine of the 13 species collected, and were most obvious in headcapsule structures, particularly the antennae, mentum, mandibles and epipharyngeal pectens.3. In species of Chironomus, the most abundant genus, there was a positive linear relationship between the incidence of deformity and radiation level. Indices of severity of deformity showed similar trends. It is suggested that these deformities resulted largely from ingestion of irradiated, plant‐derived, fine particulate food.4. Among adult male Ch. riparius, the deformity index decreased both with increasing time from the accident and with increasing distance from the reactor, although these trends were not statistically significant. There was also a trend of increased severity of deformity closer to the accident, both in time and space.5. Overall, there was a greater incidence of deformity in the larvae than in the adults (e.g. 60 versus 20%, respectively, at the Krasnoselye site and 33 versus 20%, respectively, at the more distant Dron’ki site).6. It was not possible to determine whether the deformities were inherited from previous generations or were somatic occurrences in each new generation as a consequence of the radiation that continues to pervade the region.
Nutrient limitation of bacterioplankton and phytoplankton in humic lakes in northern Sweden
Authors: Jansson Mats , Bergström Ann‐Kristin , Drakare Stina , Blomqvist Peter 
Published: March 2003

1. Two small humic lakes in northern Sweden with concentrations of dissolved organic carbon (DOC) between 15 and 20 mg L–1 were fertilized with inorganic phosphorus (P) and inorganic nitrogen (N), respectively. A third lake was unfertilized and served as a control. In addition to this lake fertilization experiment, data from different regional surveys were used to assess the role of different limiting factors.2. The P fertilization had no effects on bacterioplankton or phytoplankton, while phytoplankton were significantly stimulated by N fertilization. Inorganic nutrient limitation of bacterioplankton was a function of DOC concentration in water of the investigated region and nutrient‐limited bacteria were found only in lakes with DOC concentrations less than around 15 mg L–13. The fertilization experiments demonstrated that the DOC‐rich experimental lakes contained a bioavailable pool of P that was not utilized to its full potential under natural conditions. The overall mobilization of energy (bacterioplankton plus phytoplankton) in the experimental lakes was restricted by lack of inorganic N.
Fitness and sexual response to population density in Daphnia pulex
Authors: Berg  , Pálsson  , Lascoux  
Published: March 2003

1. The switch between asexual and sexual reproduction is an important fitness component in cyclically parthenogenetic populations as it is the key to persistence in unstable habitats and because it influences population genetic characteristics such as linkage disequilibrium and population genetic structure.2. Genetic variation for sexual and asexual reproductive rate (RC) was examined, under varying population density, in Daphnia pulex sampled from a rockpool system and two other distinct European localities.3. Density affected the switch to sexual behaviour, as found in other studies and reduced Rc. Production of males was not correlated with sexual reproduction, promoting outcrossing.4. Genetic variation was found for the response to density, both within and between populations. There was substantial variation within the rockpools despite their demographic instability, indicating rapid recovery of life‐history variation or maintenance during bottlenecks.
Species traits in relation to habitat variability and state: neotropical juvenile fish in floodplain creeks
Authors: Mérigoux Sylvie , Dolédec Sylvain , Statzner Bernhard 
Published: March 2003

1. Ecological theory predicts that (1) proportions of fish having particular life history strategies should vary with habitat conditions, and (2) biological traits of species should change across spatio‐temporal variability gradients (River Habitat Templet).2. We used data on juvenile fish and biological traits of the species, temporal (i.e. hydrology) and spatial (e.g. depth, bottom substrate, litter type) habitat variability and state (i.e. mean conditions) to test these predictions for communities comprising 57 fish taxa in floodplain creeks of the Sinnamary River (French Guiana).3. We did not confirm predictions on habitat use according to groupings based on life history strategies. However, we found 10 significant relationships between species traits and habitat variability (e.g. size at maturity, diameter of mature oocytes, parental care and relative body height decreased with increasing temporal variability; size at maturity and mean diameter of mature oocytes increased with increasing spatial variability). In addition, state variables such as mean water level, dissolved oxygen, mean width or mean depth could explain much of the variation in species traits.4. Thus, our results generally supported the River Habitat Templet but suggested that state, in addition to variability, should be included in habitat descriptions.
Viruses in the plankton of freshwater and saline Antarctic lakes
Authors: Laybourn‐Parry Johanna , Hofer Julia S. , Sommaruga Ruben 
Published: March 2003

1. Virus‐like particle (VLP) abundances in nine freshwater to saline lakes in the Vestfold Hills, Eastern Antarctica (68° S) were determined in December 1999. In the ultra‐oligotrophic to oligotrophic freshwater lakes, VLP abundances ranged from 1.01 to 3.28 × 106 mL–1 in the top 6 m of the water column. In the saline lakes the range was between 6.76 and 36.5 × 106 mL–1. The lowest value was found in meromictic Ace Lake and the highest value in hypersaline Lake Williams. Virus to bacteria ratios (VBR) were lowest in the freshwater lakes and highest in the saline lakes, with a maximum of 23.4 in the former and 50.3 in the latter.2. A range of morphologies among VLP was observed, including phages with short (Podoviridae) and long tails, icosahedric viruses of up to 300 nm and star‐like particles of about 80 nm diameter.3. In these microbially dominated ecosystems there was no correlation between VLP and either bacterial numbers or chlorophyll a. There was a significant correlation between VLP abundances and dissolved organic carbon concentration (r=0.845, P < 0.01).4. The data suggested that viruses probably attack a spectrum of bacteria and protozoan species. Virus‐like particle numbers in the freshwater lakes were lower than values reported for lower latitude systems. Those in the saline lakes were comparable with abundances reported from other Antarctic lakes, and were higher than most values published for lower latitude lakes and many marine systems. Across the salinity spectrum from freshwater through brackish to hypersaline, VLP concentrations increased roughly in relation to increasing trophy.5. Given that Antarctic lakes have a plankton almost entirely made up of bacteria and protists, and that VLP abundances are high, it is likely that viruses play a pivotal role in carbon cycling in these extreme ecosystems.
Flight activity of insects along a mountain stream: is directional flight adaptive?
Authors: Winterbourn Michael J. , Crowe Anna L. M. 
Published: March 2003

1. Flight activity of Trichoptera, Plecoptera and Ephemeroptera was studied by sticky trapping for 12 months at five sites along a New Zealand mountain stream. Over 19 000 insects were captured by the traps, which were located in forest and grassland reaches, including a reach with intermittent flow.2. Most species occurred predominantly in forest or grassland, although some were trapped throughout the stream. Longitudinal distributions of adults and their larvae were strongly correlated.3. Flight periods of 24 caddisflies, three mayflies and four stoneflies ranged from 2 to 12 months. Six species were trapped in all months and 17 (55%) in more than 5 months.4. The most abundant forest‐dwelling caddisfly species were over‐represented on the downstream sides of sticky traps located in, and immediately below, forest indicating a majority was flying upstream. Upstream flight compensates for downstream drift of larvae and should maximize the likelihood that forest‐dwelling species will locate preferred habitat for egg, larval and/or adult development. Unlike the caddisflies, the stonefly Spaniocerca zelandica was over‐represented on the upstream sides of traps, suggesting that some adults may float or fly downstream following emergence.5. In contrast to forest‐dwelling species, only one common caddisfly (Oxyethira albiceps) was over‐represented on the downstream sides of traps at grassland sites. Unlike the forest‐dwelling species, most species taken at the downstream sites probably came from a variety of sources, including a nearby stream.
Food limitation of planktonic rotifers: field experiments in two mountain ponds
Authors: Cordova Susan E. , Giffin Joy , Kirk Kevin L. 
Published: March 2003

1. Resource competition is thought to be important in controlling zooplankton population dynamics and structuring zooplankton communities. Resource competition requires that resources are limiting. Ten field experiments were conducted to determine the presence and intensity of resource limitation of herbivorous planktonic rotifers in two mountain ponds. The intensity of food limitation was measured as Δr, the difference between population growth rates in food supplemented versus control enclosures.2. Rotifers were significantly food limited (Δr > 0) in most experiments. The intensity of food limitation varied between species. In Grady Lake, mean Δr was 0.26 day−1 for Polyarthra vulgaris and 0.43 day−1 for an unidentified Synchaeta sp. In L1 Pond, mean Δr was 0.07 day−1 for Keratella cochlearis and 0.28 day−1 for S. oblonga. The frequent and intense food limitation suggests that edible phytoplankton in both ponds were often present at low densities, were of low nutritional quality, or both. The intensity of food limitation often changed rapidly over time, indicating rapid temporal variation in resource availability.3. For P. vulgaris, Δr was not correlated with its population growth rate in Grady Lake. Thus, although food limitation was common, population dynamics may have been more strongly affected by other factors. For K. cochlearis, Δr increased as population density increased, suggesting the existence of intraspecific resource competition that may regulate population dynamics.
Response of plankton communities to whole‐lake Ca(OH)2 and CaCO3 additions in eutrophic hardwater lakes
Authors: Zhang Ying , Ghadouani Anas , Prepas Ellie E. , Pinel‐Alloul Bernadette , Reedyk Sharon , Chambers Patricia A. , Robarts Richard D. , Méthot Ginette , Raik Assia , Holst Meike 
Published: March 2003

1. The impact of whole‐lake lime (slaked lime, Ca(OH)2, and/or calcite, CaCO3) addition on plankton communities was evaluated in eutrophic hardwater lakes on the North American Boreal Plain.2. Two lakes received a single treatment of lime (Ca(OH)2 at 74 or 107 mg L–1), two lakes received multiple treatments with Ca(OH)2 and/or CaCO3 (5–78 mg L–1), and four lakes were untreated and served as reference systems.3. Over the long‐term (> 1 year), phytoplankton biomass was reduced in multiple‐dose lakes, but not in single‐dose lakes. Cyanobacteria typically dominated the algal community in the years before, during and after lime treatment in both single‐ and multiple‐dose lakes.4. In the single‐dose lakes, randomized intervention analysis showed no significant change in the biomass of zooplankton after lime addition.