bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of two scales of habitat architecture on benthic grazing in a river
Authors: Robson Belinda J. , Barmuta Leon A. 
Published: March 2003

1. This experiment studied the effects of differing levels of the complexity of substratum architecture at two spatial scales on the distribution and abundance of benthic algae and invertebrates, and the strength of the trophic interaction between invertebrate grazers and algae. Some estimates of the effects on invertebrate colonization rates were also made.2. Four levels of microhabitat architectural complexity were created using artificial substrata (clay tiles) and placed in Mountain River, Tasmania, in two riffle types (bedrock and boulder‐cobble) of differing large‐scale substratum complexity. After a colonization period, invertebrate grazers were removed from half the tiles to measure the effects of grazing. Invertebrates on the tiles were also counted and identified. At the end of the experiment, algae were removed from the tiles and analysed for chlorophyll a.3. Invertebrate grazers did not reduce algal biomass during the experiment, and microhabitat‐scale architecture influenced algal biomass more strongly than riffle‐scale architecture. Highly complex microhabitat architecture increased algal biomass by providing more surface area, but once standardized for surface area, algal biomass decreased as the complexity of microhabitat architecture increased.4. Microhabitat‐scale architecture was also predominant in determining invertebrate density and the identity of the dominant grazer species. In contrast to algal biomass, invertebrate densities and species density increased with the complexity of microhabitat architecture, suggesting that refuges from flow (and possibly predation) were as important to river invertebrates as the distribution of their food source.5. Riffle‐scale architecture had some effect on the colonization of two slow‐moving grazer taxa, but, overall, the colonization processes of slow‐moving grazers were determined mostly by the complexity of microhabitat‐scale architecture.
Long‐term recovery of a mountain stream from clear‐cut logging: the effects of forest succession on benthic invertebrate community structure
Authors: Stone Michael K. , Wallace J. Bruce 
Published: March 2003

1. Changes in benthic invertebrate community structure following 16 years of forest succession after logging were examined by estimating benthic invertebrate abundance, biomass and secondary production in streams draining a forested reference and a recovering clear‐cut catchment. Benthic invertebrate abundance was three times higher, and invertebrate biomass and production were two times higher in the disturbed stream.2. Comparison of invertebrate community abundance 1, 5 and 16 years after clear‐cutting indicated that the proportion of scrapers had decreased, whereas shredders had increased. Functional group percentage similarity indicated that the invertebrate community in the disturbed stream 16 years after clear‐cutting was more similar to the reference than to that found earlier in the disturbed stream.3. The five indices calculated from data collected over the past 16 years, as well as the abundance, biomass and production data collected during this study, proved to be of differing value in assessing recovery of the disturbed stream from logging. Percent dominant taxon and EPT (Ephemeroptera, Plecoptera and Trichoptera) taxon richness failed to show any initial differences between reference and disturbed streams, indicating that these indices may not be useful for measuring recovery from logging. The percentage Baetis and shredder–scraper indices showed significant differences only during the 1977 study and suggest recovery (no difference between reference and disturbed) by 1982. The North Carolina Biotic Index showed continued differences during 1982 in the riffle and depositional habitats and recovery by 1993. Total macroinvertebrate abundance, biomass and production, as well as EPT abundance, indicated continued differences between the reference and disturbed streams in the 1993 study.
The effect of temperature on the response of Daphnia to toxic cyanobacteria
Authors: Claska Mary E. , Gilbert John J. 
Published: March 2003

1. In a set of life‐table experiments, cohorts of neonate Daphnia pulex were exposed to a toxic strain of Anabaena affinis and A. flos‐aquae, and to a pure cyanobacterial toxin (anatoxin‐a), at 12 or 14, 19, and 25 °C. The fecundity and survival of individual animals were assessed at 1‐, 2‐ or 3‐day intervals, depending on the temperature, through to the fifth brood of the control cohort. The sensitivity of D. pulex to the cyanobacteria and the toxin at each temperature was measured by determining its finite population growth rate (λ) in an experimental treatment as a fraction of that in a control treatment. Tests with three concentrations of cyanobacteria (1.0, 2.5 and 5.0 μg mL–1) and one concentration of anatoxin‐a (1 μg mL–1), and with two clones of D. pulex, showed a consistent and statistically significant pattern of increasing sensitivity at higher temperatures.2. Anabaena affinis affected both survivorship and fecundity, while A. flos‐aquae and its toxin, anatoxin‐a, primarily affected fecundity. Presence of cyanobacteria affected brood size, brood number, time to first reproduction and interclutch interval. Temperature affected time to first reproduction and interclutch interval at all concentrations of cyanobacteria. Brood number and brood size were little affected by temperature except at the highest concentrations of cyanobacteria. Increasing the concentration of A. flos‐aquae affected demographic parameters, especially at the lower temperatures, while increasing the concentration of A. affinis had less effect.3. The study suggests that increasing water temperatures in natural systems should exacerbate the inhibitory effect of toxic cyanobacteria on daphniid population growth rates.
The increasing divide between First and Third Worlds: science, collaboration and conservation of Third World aquatic ecosystems
Authors: Wishart  , Davies  
Published: March 2003

1. Ten of the leading journals in the field of freshwater ecology were identified using the Science Citation Index’s Journal Citation Reports. These journals were surveyed to assess the levels and patterns of collaboration in research initiatives in regions of the Third World. Membership demographics of five professional societies in this field were also examined to elucidate distribution patterns of practitioners in the field.2. In total, 8960 papers were surveyed, of which only forty were published in a language other than English. Senior authors came from 114 of the 130 different countries listed among authors’ addresses. Of these, forty‐five were from Third World countries and sixty‐nine from the First World. Five countries were responsible for 60.64% of the papers submitted; the United States = 25.65%; Canada = 11.55%; Australia = 10.15%; the United Kingdom = 6.73%; New Zealand = 6.56%. Multi‐authored papers accounted for 73.05% of all papers.3. Papers by authors from Third World countries accounted for only 10.93% of single‐author papers and less than 10% of multi‐authored papers. Collaboration was found in 73.05% of the papers surveyed, the vast majority of which (87.39%) was between authors from First World countries. Only 825 (9.21%) of the papers surveyed involved authors from different countries. Most of this collaboration (72.36%) was between authors from different First World countries.4. Some 1038 papers surveyed included research undertaken in, or included authors from, Third World countries. The majority of these papers (69.08%) were submitted by authors from Third World countries, involving either multiple or single authorship. The third most common publication relating to research in Third World regions (17.4%) came from single‐author papers in which the authors were from a First World country. Only four of the papers surveyed were submitted by single authors from Third World countries working in First World countries.5. There is a disproportionate representation of taxonomic (20.3%) and marine (10.5%) papers from the Third World regions in comparison to both lentic (8.0%) and lotic (7.4%) papers.6. Membership demographics of the professional societies surveyed continue to reflect the historical origins of freshwater ecology. More than 80% of members in the three largest societies examined are registered in Europe and North America, while membership of the remaining societies remains largely regional.7. It is argued that present levels of collaboration and technology transfer from the First World to the Third World are inadequate and that, given the widening gulf in terms of personnel and resources, the future of essential research on inland waters in the Third World does not bode well unless in situ capacity building within Third World countries becomes a target of First World research and funding agencies.
In situ experiments on predatory regulation of a bivalve mollusc (Dreissena polymorpha) in the Mississippi and Ohio Rivers
Authors: Thorp James H. , Delong Michael D. , Casper And Andrew F. 
Published: March 2003

1.
In situ exclosure experiments in the Mississippi and Ohio Rivers determined the importance of fish predation in regulating zebra mussels (Dreissena polymorpha), an increasingly important constituent of the benthic invertebrate assemblages in both rivers.2. We evaluated the effects of predatory fish on the density, biomass and size distribution of zebra mussels in a floodplain reach of the upper Mississippi River and in a naturally constrained reach of the Ohio River. Fifty, six‐sided, predator‐exclusion cages and fifty ‘partial’ cages (mesh at the upstream end only) were deployed, with half the cages containing willow snags and half clay tiles suspended 12–16 cm above the bottom. A single snag or tile sample unit was removed from each cage at approximately monthly intervals from July to October 1994. Types and relative abundances of molluscivorous fish were evaluated by electrofishing near the cages in both rivers. Actual and potential recruitment of young zebra mussels on to the substrata were measured using benthic samples in both rivers and estimated (Ohio River only) from counts of planktonic veligers.3. Zebra mussels were consumed by at least three fish species in the upper Mississippi River (mostly carp, Cyprinus carpio, and redhorse suckers, Moxostoma sp.) and five species in the Ohio River (primarily smallmouth buffalo, Ictiobus bubalus, and channel catfish, Ictalurus punctatus), but potential recruitment seemed adequate to replace consumed mussels, at least in the Ohio River. The number of juvenile benthic mussels showed no apparent link with the density of veligers soon after initiation of reproduction. Recruitment of juveniles on snags and tiles was not affected by cage type (thus eliminating a potentially confounding ‘cage effect’).4. Fish significantly influenced mussel populations, but the impact was often greatest among low density populations in the upper Mississippi. Density and biomass differed in both rivers for cage type (higher inside cages), substratum (greater on tiles), and date (increased over time). Presumed size‐selective predation was present in the Mississippi (greater on larger size classes) but was not evident in the Ohio. We hypothesize that fish in the Mississippi can more easily select larger prey from the low density populations; whereas size‐selective predation on tightly packed zebra mussels in the Ohio would be difficult.5. Although fish can reduce numbers of Dreissena polymorpha in the two rivers, current levels of fish predation seem insufficient to regulate zebra mussel densities because of its great reproductive capacity. The recent invasion of zebra mussels, however, could lead to larger fish populations while promoting greater carbon retention and overall ecosystem secondary production.
Phytoplankton responses to experimental enhancement of grazing pressure and nutrient recycling in a small Andean lake
Authors: Queimaliños Claudia P. , Modenutti Beatriz E. , Balseiro Esteban G. 
Published: March 2003

1. Three series of field experiments with different zooplankton species composition and biomass were performed in a small lake in the south Andes. We attempted to measure the responses of phytoplankton species resulting from grazing mortality and stimulation of growth by nutrient recycling.2. Nanoflagellates contributed substantially to total phytoplankton cell abundance. Chrysochromulina parva represented 93.4%, 92.2% and 95.9% of total phytoplankton density in December, January and February, respectively. This fraction was reduced in all treatments with increasing zooplankton biomass.3. A negative relationship was obtained between C. parva cell numbers and increase in dissolved P. On the other hand, a significant positive relationship between the abundance of the diatom Aulacoseira granulata and P concentration was observed. These results indicate that the ungrazed diatom was able to capitalise on the increase in nutrient availability.4. As a net result of the increase or decrease of algal species we observed a change in the nano:net phytoplankton relationship. The outcome of three‐day incubations with increased zooplankton biomass was an increasing importance of net phytoplankton.5. The results indicate the importance of the indirect effects of zooplankton (through nutrient recycling) in the increase in diatoms, and the role of grazing as a growth‐limiting factor for the flagellate C. parva.
Effects of woody debris on the habitat of juvenile masu salmon (Oncorhynchus masou) in northern Japanese streams
Authors: Inoue Mikio , Nakano Shigeru 
Published: March 2003

1. The effects of woody debris on stream habitat of juvenile masu salmon (Oncorhynchus masou) were examined at two spatial scales, stream reach and channel unit, for first‐ to third‐order tributaries of the Teshio River in northern Hokkaido, Japan. The forty‐eight study reaches were classified into three distinct types: coarse‐substrate step‐pool (CSP), coarse‐substrate pool–riffle (CPR) and fine‐substrate pool–riffle (FPR) reaches. Each reach type included reaches with different riparian settings, broadly classified as forest (relatively undisturbed forest and secondary forest after fires) or grassland (bamboo bushland and pasture).2. The reach‐scale analyses showed that neither total pool volume nor pool‐to‐pool spacing was correlated with woody debris abundance in any of the three reach types. Masu salmon density was positively correlated with both woody‐debris cover area and total cover area, but not with total pool volume in the reaches.3. Channel‐unit‐scale analyses revealed that woody debris reduced non‐pool velocity, increased pool depth and retained fine sediment in pools in FPR reaches, where the size of woody debris was very large relative to the substrate material size. However, woody debris did not influence any of the hydraulic variables (depth, velocity, substrate) in either non‐pools or pools of CSP and CPR reaches. Habitat use by masu salmon in non‐pools or pools was affected by woody‐debris cover area or total cover area rather than by hydraulic variables in any of the reach types.4. The effects of woody debris on habitat at the reach‐ and channel‐unit scales in the study area were less than those indicated by previous work in the Pacific Northwest, North America, owing to the relatively small size of the riparian trees. However, the overall results suggested that woody debris in the study area contributed to masu salmon habitat by providing cover at the smaller, microhabitat scale.
Production potential of aquatic plants in systems mixing floating and submerged macrophytes
Authors: Forchhammer Nina Cedergreen 
Published: March 2003

1. To investigate whether the areal production of aquatic plant systems can be increased by growing floating and submerged plants together, the floating fern Azolla filiculoides was grown at six densities and two nutrient availabilities in the presence and absence of the submerged macrophyte Elodea canadensis.2. High nutrient availability did not affect the total areal biomass production, but raised the internal N concentration of Azolla and Elodea by 34% and 152%, respectively, and the internal P concentration by 50% and 378%.3. High Azolla density reduced Elodea production, whereas Elodea did not affect the production of Azolla. A maximal total production of 4.0 g DW m−2 day−1 was obtained at an Azolla density at and above full surface cover, when Elodea contribute with less than 10% to the total. This contribution did not raise the combined production of Azolla and Elodea significantly above the production of Azolla grown alone. Thus, maximum production was not enhanced by growing floating and submerged macrophytes together.
Associations between stream fish and benthos across environmental gradients in southern Ontario, Canada
Authors: Kilgour Bruce W. , Barton David R. 
Published: March 2003

Summary1. The relationship between fish and benthic invertebrate communities in wadeable streams in southern Ontario, Canada, was examined using three independent and spatially distinct data sets.2. Associations between fish and benthos were always significant when benthos were identified to family and often at the level of phylum. Identification to genus improved the strength of the fish–benthos association in one case. In contrast, identification to species did not improve the strength of the fish–benthos association. Associations between benthos and fish were weaker for one study utilizing a ‘rapid’ bio‐assessment protocol involving field sorting and identification, and a second study which utilized winter benthic collections.3. In two surveys, stream temperatures were important to the distributions of both fish and benthos, while in a third survey, fish and benthos were primarily influenced by stream size. In all three studies, fish and benthos were associated with similar suites of environmental variables, suggesting that the fish–benthos associations in these streams was driven by corresponding environmental tolerances.4. Although there was significant variation in the strength of the fish–benthos association which could be attributed to differences in sampling methodologies, the findings from the present study confirm that stream fish and benthos are significantly associated. Therefore, surveys of benthos can be used to make inferences on the condition of fish community composition.
Large‐scale assessments of river health using an Index of Biotic Integrity with low‐diversity fish communities
Authors: Harris J. H. , Silveira R. 
Published: March 2003

Summary1. Effective tools are needed to measure the ‘health’ of rivers at scales large enough to be useful for management. Indicators for assessing the complex of variables that constitutes river health need to be ecologically based, efficient, rapid and consistently applicable in different ecological regions.2. A large‐scale survey of rivers in New South Wales, Australia provided data to test the Index of Biotic Integrity (IBI). The IBI employs the fish‐community attributes, identified using regional and river‐size data, expected for a river reach of excellent environmental quality. It uses metrics based on species richness, abundance, community structure and the health of individual fish. IBI metrics were established to suit a relatively low‐diversity and unspecialized freshwater fish fauna in south‐eastern Australia, totalling 55 species.3. The IBI was able to discriminate between relative levels of environmental quality within a diverse set of stream systems and four presumptive ecological regions. The index was validated by testing the repeatability of scores, and by comparison of IBI scores at eighty sites with an independent measure of potential catchment condition, the River Disturbance Index.4. Assessments of metric performance showed that eleven of the twelve metrics contributed satisfactorily. One metric based on trophic guild performed poorly and should be deleted from the index. Six other recommendations are made to enhance the performance of the IBI.5. Results show that, while all large rivers have been disturbed, rivers in the Murray region and those in many coastal montane areas are particularly degraded.6. The IBI results presented here demonstrate a validated method for large‐scale monitoring of river health based on a fish fauna of limited diversity, in the absence of suitable reference sites.
Aerial survey of waterbirds on wetlands as a measure of river and floodplain health
Authors: Kingsford R. T. 
Published: March 2003

Summary1. This study highlights the use of waterbird communities as potential measures of river and floodplain health at a landscape scale.2. The abundance and diversity of a waterbird community (54 species) was measured over 15 trips with four aerial and three ground counts per trip on a 300‐ha lake in arid Australia.3. Aerial survey estimates of individual species were significantly less precise (SE/mean) than ground counts across two (11–100 and > 1000) out of four abundance classes of waterbirds: 0–10, 11–100, 101–1000 and > 1000. Standard error/mean as a percentage decreased with increasing abundance from about 60% for the lowest abundance class to 18% for the largest abundance class.4. Aerial survey estimates were negatively biased for species in numbers of less than 10 and greater than 5000 but unbiased compared to ground counts for other abundance classes. Aerial surveys underestimated numbers of waterbirds by 50% when there were 40 000 waterbirds. Three ground counts found about seven more waterbird species than four aerial surveys. One ground count took about 150 times longer than two aerial surveys and cost 14 times more.5. Regression models were derived, comparing aerial survey estimates to ground counts for 31 of 36 species for which there were sufficient data. Aerial survey estimates were unbiased for most of these species (67%), negatively biased for six species and positively biased for one species. Estimates were negatively biased in species that occurred in small numbers or that dived in response to the aircraft.6. River system health encompasses the state of floodplain wetlands. Waterbirds on an entire wetland or floodplain may be estimated by aerial survey of waterbirds; this is a coarse but effective measure of waterbird abundance. Aerial survey is considerably less costly than ground survey and potentially provides a method for measuring river and floodplain health over long periods of time at the same scale as river management.