bluuebunny/crossref_metadata_2025 huggingface dataset:
Humus forms in two secondary semi‐evergreen tropical forests
Authors: Loranger G. , Ponge J. F. , Lavelle P.
Published: March 2003

The dynamics and function of humus forms in tropical forests are still poorly understood. Humus profiles in two secondary semi‐evergreen woodlands in Guadeloupe (French West Indies) were analysed micromorphologically. The humus forms are described under the canopy of five dominant tree species at two sites: under Pisonia subcordata and Bursera simaruba in a secondary forest on a Leptosol (Rendzina), and under Swietenia macrophylla, Tabebuia heterophylla and B. simaruba in a plantation on a calcareous Vertisol.

In the secondary forest, two distinct humus forms were observed. A calcareous Amphimull, characterized by an OH horizon comprising the faecal pellets of millipedes, is formed under the canopy of P. subcordata, which produces a litter that is rich in nitrogen. A Dysmull with a thick root mat (OFRh horizon) develops under the canopy of B. simaruba, which produces a litter rich in lignin and phenol that is consumed slowly by the soil fauna. In the plantation on the Vertisol, the activity of the endoanecic earthworm Polypheretima elongata has led to the rapid disappearance of litter and the mixing of organic and mineral material. The humus form is a Eumull and is similar under all three tree species present.
Movement of wild and experimentally stocked brown trout, Salmo trutta L., before and after a flood in a small Austrian stream
Authors: Weiss S. , Kummer H.
Published: March 2003

Weirs and traps were used to monitor the movement of two strains of stocked brown trout, Salmo trutta L. Within 24 h of stocking, 15% (n = 13) of a Danish strain and 21% (n = 19) of a hybrid strain moved at least 100 m from their release site. In the following 5–6 days, no further movement was found for Danish fish, but hybrid fish continued to move, totaling 32% (n = 29) of the fish stocked. During this same period, 36 wild brown trout (≈ 3.5% of the population) were captured, moving over the weirs. Two weeks later, and one week after a flood, 70% (n = 59) of the Danish strain were recovered within their release sites and 89% (n = 76) were recovered during an electric fishing survey within the 3.5‐km‐long experimental area. In contrast, 43% (n = 31) of the hybrid strain were recaptured in their release sites and 49% (n = 45) within the experimental area. The total recapture of wild adult fish was only 16% (n = 41). The flooding event was insignificant in comparison with strain‐specific behaviours in determining patterns of movement and residency.Austria, brown trout, floods, movement, stocking.
Larval fish movement in the River Lohajang,Tangail, Bangladesh
Authors: De Graaf G. J. , Born A. F. , Uddin A. M. K. , Huda S.
Published: March 2003

Larval fish drift and distribution patterns were studied in the River Lohajang, a tributary of the River Jamuna, Bangladesh, during the monsoon seasons (June ‐ October) of 1992, 1993 and 1994. Larval fish drift peaks with the water levels of the River Jamuna. In all three years, the Indian carp, Catla catla, Labeo rohita L. and Cirrhinus mrigala, were associated with the first pulses, but were absent from drift samples after September. Hilsa species and other non‐identified fish species were found throughout the monsoon season. The highest larval fish densities were found in the upper strata of the river, near the shore. The drift densities of these fish became evenly distributed through time. Water turbidity probably influenced the vertical and horizontal distribution, and the absence of diel patterns. The most important species in the larval drift were Hilsa spp., followed by Labeo rohita L., Glossogobius giuris L. and Rasbora daniconius. Among the major carp, Labeo rohita was the dominant species, contributing 80‐90%. The impact of flood control programmes on the reproduction of riverine and larval fish drift is discussed.
Downstream migration of European lake trout, Salmo trutta f. lacustris L., and resident brown trout, Salmo trutta f. fario L., progeny in a Lake Constance affluent river
Authors: SCHULZ U. H.
Published: March 2003

Abstract  The local migratory behaviour of lake trout, Salmo trutta L., and resident brown trout, S. trutta L., progeny from an inflowing stream of Lake Constance was compared. No differences were detected with respect to emigration rate (3.5% and 4.2% for lake trout and resident trout, respectively), rate of residency (6.8% and 8.2% for lake trout and resident trout, respectively) and rate of survival (12.3% and 12.1% for lake trout and resident trout, respectively) one year after stocking. Some of the resident brown trout offspring became migrants and vice versa. The results indicate that the progeny of riverine brown trout contribute considerable numbers to lake trout stock.
Applications and characteristics of angler diary programmes in Ontario, Canada
Authors: Cooke S. J. , Dunlop W. I. , Macclennan D. , Power G.
Published: March 2003

Angler diary programmes (n=46, 1979–1997) implemented in Ontario by the Ontario Ministry of Natural Resources are reviewed, and the different uses of angler diary programmes, levels of participation and differences in programme design are reported. In Ontario, angler diary use is common, but successful application is limited. This review revealed a variety of uses and approaches for administering angler diary programmes. Problems arise when programmes are initiated without the complete commitment of the administrators and agency, or when there is no regular review so adaptive changes can be made. If administrators realize the potential biases and problems associated with diaries, and design programmes to control them, angler diaries can provide favorable cost‐effective results. With reduced funding and staffing constraints, angler diary programmes could become the primary method of data collection for specialized and remote fisheries.
Homing patterns of Baltic salmon, Salmo salar L., from smolts released from two hatcheries in the River Dalälven, Sweden
Authors: Insulander C. , Ragnarsson B.
Published: March 2003

The River Dalälven Baltic salmon, Salmo salar L., population has been maintained by stocking reared fish since the early 1920s. Initially, all rearing was carried out at one hatchery, but since the late 1980s two have been used. Both hatcheries are situated 9–10 km from the river mouth but some 600 m apart. All broodfish were caught in a single fish trap situated some 700 m upstream of the upper hatchery. The salmon smolts were released just below the water outlets of each hatchery, respectively. About 2% of the released smolts from each hatchery were tagged annually with Carlin tags. Total recapture rates were higher for smolts from the lower hatchery. A higher proportion of recaptured fish was reported from the home river for salmon from the upper hatchery. The migration within the river to the fish trap was more precise for fish from the upper station. Strays were very late in the season and of a higher number from the lower hatchery. Observations of jumping salmon by the outlet from the lower station indicated that salmon returned to that point. The lower recaptures in the trap were considered a result of a shorter river migration of salmon from the lower hatchery.
Do different seagrass species support distinct fish communities in south‐eastern Australia?
Authors: ROTHERHAM D. , WEST R. J.
Published: March 2003

Between spring 1998 and autumn 1999, a fine mesh seine net was used to sample fish communities at three locations in south‐eastern Australian estuaries, two located near Sydney [Botany Bay (BB) and Port Hacking (PH)] and one located approximately 150 km to the south [Sussex Inlet (SI)]. At each location, fish were collected from adjacent beds of the seagrasses Posidonia australis Hooker and Zostera capricorni Ascherson. These seagrass species differ markedly in morphology and life history. Fish communities displayed significant differences between seagrass species with respect to abundances and lengths of economically important species, and the structure of assemblages at locations in PH and BB, but not in SI. Differences appeared to be related to the recruitment of juveniles of several inshore species, such as Acanthopagrus australis (Günther), Rhabdosargus sarba (Forskaal) and Girella tricuspidata (Quoy & Gaimard) to Zostera beds at BB and PH during spring and early summer. These differences were not evident over the wider spatial scale, however, the SI location did support a distinct assemblage of fish compared with locations in PH and BB. These results suggested that local recruitment events and differences in estuarine geomorphology may be important in structuring these seagrass fish communities.
From carbon flux to regime shift
Authors: STEELE JOHN H.
Published: March 2003

The basic assumption in biological oceanography – and in GLOBEC – is that physical forcing at a wide range of space and time scales determines most of the dynamics of marine populations. This has been very productive and provides the global context for GLOBEC and other programmes. How far can it take us in the future; and, alternatively, what role is played by community interactions?
Comparison of models for defining nearshore flatfish nursery areas in Alaskan waters
Authors: NORCROSS BRENDA L. , BLANCHARD ARNY , HOLLADAY BRENDA A.
Published: March 2003

Because it is unrealistic to assess fishes in all locations, models are needed to characterize the nursery habitats of flatfish species. Descriptive habitat models of species presence and categorical analysis regression tree (CART) models of species abundance have been developed in previous studies. Based on collections around Kodiak Island, Alaska in 1991 and 1992, these models have been developed for: age‐0 flathead sole (Hippoglossoides elassodon); age‐0 Pacific halibut (Hippoglossus stenolepis); age‐1 yellowfin sole (Pleuronectes asper); and age‐0 rock sole (Pleuronectes bilineatus). In 1995, collections were made in bays along the Alaska Peninsula (an area never before sampled for juvenile flatfishes) and were compared with the previous models developed for Kodiak Island in 1991 and 1992. Very simple descriptive models for Kodiak Island (
Norcross et al., 1995
, Neth. J. Sea Res. 34: 161–175) accurately predicted the abundance along the Alaska Peninsula of flathead sole (78%), Pacific halibut (96%), yellowfin sole (75%) and rock sole (99%) in specific depth ranges and on specific substrate types. More complex CART models of species abundance (
Norcross et al., 1997
, Fish. Bull. (US) 95: 504–520) were more precise but not as accurate as the descriptive models because some parameters were not always available at the test locations. Flathead sole were found at temperatures ≤ 8.9°C on mud and mixed mud substrates in similar proportions in 1995 (66%) as in 1991–92 (71%). Similarly, Pacific halibut were ≤ 7.9 km inside bays and at depths ≤ 40 m in 93% of the sites of this study, compared with 89% previously. Seventy‐five per cent of yellowfin sole were at depths ≤ 28 m on mixed substrates in both study periods. Rock sole were found on sand and muddy sand substrates at temperatures above 8.7°C in 52% of the sites in present and 69% of the sites in previous studies. This field test demonstrated that both descriptive and CART models were very useful at identifying juvenile habitat parameters, but are insufficient for areas not previously sampled. The resource‐selection models verified the importance of a subset of parameters used in earlier models and provided a statistical means (78–87% correct) for prediction of fish distribution in similar areas of the eastern North Pacific.
Climate change and Adriatic ichthyofauna
Authors: Dulc˘ić  , Grbec
Published: March 2003

During the last 25 years (1973–1998), changes in the quantitative and qualitative composition of the Adriatic ichthyofauna have been noted. The numbers of thermophilic species have increased; several species, previously scarce or rare, have become more abundant, while others are new records. There are also some examples of the disappearance or increasing scarcity of some species. These observations can be related to oceanographic changes in the Adriatic Sea.
Behaviour of immature yellowtails (Seriola quinqueradiata) observed by electronic data‐recording tags
Authors: Kasai Akihide , Sakamoto Wataru , Mitsunaga Yasushi , Yamamoto Shotaro
Published: March 2003

The long‐term behaviour of immature yellowtails, Seriola quinqueradiata, was studied using electronic data‐recording tags in Sagami Bay, Japan, during the autumn and early winter. Temperature or depth data were continuously recorded for 5–69 days on six yellowtails. The temperature recorded from the 0‐year‐old yellowtails showed only small variations (<0.5°C day−1) around the SST on the coast, indicating the 0‐years stayed in the immediate coastal area with little horizontal movement. The 1‐year‐old yellowtail showed larger temperature variations that reached 3°C day−1, which implies distinctly larger horizontal movements than the 0‐year‐olds. Depth records showed the 0‐years stayed around 10 m while the 1‐year yellowtail swam in deeper water (mainly 10–30 m) with large variations. The latter often dived to 40 m in the daytime, but shallower than the depth of the thermocline. Both temperature and depth records showed apparent diurnal patterns. Comparing the fish data with environmental conditions, it is suggested that 1‐year yellowtails stay close to the coast during the night, move at dawn to feed in the daytime and return at dusk via a frontal zone. In addition, wind stress could change yellowtails’ behaviour.
A dynamic optimisation model for the behaviour of tunas at ocean fronts
Authors: Kirby David S. , Fiksen Øyvind , Hart Paul J. B.
Published: March 2003

We present a model that simulates the foraging behaviour of tunas in the vicinity of ocean fronts. Stochastic dynamic programming is used to determine optimal habitat choice and swimming speed in relation to environmental variables (water temperature and clarity) and prey characteristics (abundance and energy density). By incorporating submodels for obligate physiological processes (gastric evacuation, standard and active metabolic costs) and sensory systems (visual feeding efficiency), we have integrated into a single fitness‐based model many of the factors that might explain the aggregation of tunas at ocean fronts. The modelling technique describes fitness landscapes for all combinations of states, and makes explicit, testable predictions about time‐ and state‐dependent behaviour. Enhanced levels of searching activity when hungry and towards the end of the day are an important feature of the optimal behaviour predicted. We consider the model to be particularly representative of the behaviour of the warm‐water tunas or Neothunnus (e.g. skipjack, Katsuwonus pelamis, and yellowfin, Thunnus albacares) and for surface‐dwelling temperate tunas (e.g. young albacore, Thunnus alalunga), which are often observed to aggregate near fronts. For the bluefin group (i.e. older albacore; northern and southern bluefin, Thunnus thynnus and Thunnus maccoyii), for which extended vertical migrations are a significant and as yet unexplained component of behaviour, the model is able to reproduce observed behaviour by adopting the lower optimal temperature and standard metabolic rate of albacore. The model cannot explain why physiological differences exist between and within the different tuna species, but it does show how differences in susceptibility to thermal stress will permit different behaviour.
The importance of retention processes in upwelling areas for recruitment of Octopus vulgaris: the example of the Arguin Bank (Mauritania)
Authors: Faure Valerie , Inejih Cheikh Abdellahi , Demarcq Herve , Cury Philippe
Published: March 2003

The relationship between recruitment of octopus (Octopus vulgaris) populations and environmental conditions off the Arguin Bank (Mauritania) in the main nursery ground was investigated between 1990 and 1996. Three environmental indices (coastal upwelling intensity, coastal retention and wind‐induced turbulence indices) are derived from satellite infrared imagery (METEOSAT) and from the COADS (Comprehensive Ocean–Atmosphere Data Set) data to quantify the coastal retention process and productivity, both believed to be important factors for recruitment success. The octopus recruitment index as well as environmental indices fluctuate annually and seasonally. Linear regression and generalized additive models (GAM) are used to relate recruitment indices and the environmental conditions prevailing during the early‐life planktonic stage, known to be the main critical period of the octopus life cycle. Coastal retention especially appears to be a key factor for recruitment success. Owing to seasonal variations in enrichment and mixing processes, larvae benefit from retention in the spring but are negatively affected by a breakdown in retention in the autumn. Increasing upwelling intensity is beneficial for octopus recruitment, as the Arguin Bank limits the detrimental dispersive effects linked to upwelling.
Spatial correlation patterns in coastal environmental variables and survival rates of salmon in the north‐east Pacific Ocean
Authors: Mueter Franz J. , Ware Dan M. , Peterman Randall M.
Published: March 2003

We examined spatial correlations for three coastal variables [upwelling index, sea surface temperature (SST), and sea surface salinity (SSS)] that might affect juvenile salmon (Oncorhynchusspp.) during their early marine life. Observed correlation patterns in environmental variables were compared with those in survival rates of pink (O. gorbuscha), chum (O. keta), and sockeye (O. nerka) salmon stocks to help identify appropriate variables to include in models of salmon productivity. Both the upwelling index and coastal SST were characterized by strong positive correlations at short distances, which declined slowly with distance in the winter months, but much more rapidly in the summer. The SSS had much weaker and more variable correlations at all distances throughout the year. The distance at which stations were no longer correlated (spatial decorrelation scale) was largest for the upwelling index (> 1000 km), intermediate for SST (400–800 km in summer), and shortest for SSS (< 400 km). Survival rate indices of salmon showed moderate positive correlations among adjacent stocks that decreased to zero at larger distances. Spatial decorrelation scales ranged from approximately 500 km for sockeye salmon to approximately 1000 km for chum salmon. We conclude that variability in the coastal marine environment during summer, as well as variability in salmon survival rates, are dominated by regional scale variability of several hundred to 1000 km. The correlation scale for SST in the summer most closely matched the observed correlation scales for survival rates of salmon, suggesting that regional‐scale variations in coastal SST can help explain the observed regional‐scale covariation in survival rates among salmon stocks.
Influence of invasive macrophytes on channel morphology and hydrology in an open tropical lowland stream, and potential control by riparian shading
Authors: Bunn S. E. , Davies P. M. , Kellaway D. M. , Prosser I. P.
Published: March 2003

1. The catchments of many tropical lowland streams in far north Queensland have been extensively cleared for the cultivation of sugar cane to the extent where very little of the native riparian vegetation remains. Stream channels are often choked by a matrix of introduced pasture grass (Brachiaria mutica, or para grass) and accumulated sediment from cropland erosion.

2. Detailed transects across Bamboo Creek, a fourth order cane‐land stream, revealed an estimated sediment load of 20 000 t km–1. This has resulted in an estimated 85% reduction in the predicted bankful discharge of the original stream channel. Channel capacity has been reduced from 2.3 times to 0.3 times the predicted Q50 flood discharge of 140 m3 s–1.

3. Shade cloth treatments of 50% and 90% across the stream were used to mimic the effect of shading by riparian vegetation. Three months of shading resulted in a substantial reduction in the height and standing biomass of para grass in both shade treatments, compared to open plots (0% shade). The most dramatic effect was in the 90% treatment, where a mean reduction of 63% in height and 52% in total biomass was recorded. This was despite high net primary production of para grass in the open plots of 2.8 g dry wt m–2 day–1, which resulted in a overall increase of 11% and 28% in plant height and total biomass, respectively.

4. These data suggest that restoration of native riparian vegetation will be an effective long‐term means of controlling invasive macrophytes in disturbed cane‐land stream channels. Reduction of excessive macrophyte growth and the mobilisation of accumulated sediment are essential to the restoration of natural hydrological and ecological processes.
Sublethal parameters in morphologically deformed Chironomus larvae: clues to understanding their bioindicator value
Authors: De Bisthoven L. Janssens , Nuyts P. , Goddeeris B. , Ollevier F.
Published: March 2003

1. Parameters of condition between normal and deformed fourth instar larvae of

Chironomus

gr.

thummi

(Kieffer 1911) were compared in four populations: one reference (PE) and two metal‐polluted sites (NP and SCH) in the River Dommel, and one site polluted by domestic sewage and copper in the River Ijse (NEI).

2. The site PE ranked lowest for metal body burdens, deformities, mortalities and emergence duration, while SCH and NEI ranked highest.

3. Deformed and non‐deformed larvae most often did not differ in length and weight (

in situ

end‐points for growth); when differences occurred, deformed larvae tended to be smaller.

4. The energy content and dry weights in one population (NEI) were lower in normal larvae than in the weakly deformed ones. The percentage of ash‐free dry weight was lower in deformed larvae of the polluted Dommel sites, compared to the normal ones.

5. The

in vitro

emergence rate (end‐point for development of fourth instars) for the reference population PE, both in its own sediment and in artificial cellulose substrate, was better than for the other sites. In two populations (NEI, SCH) the development of deformed larvae in their own sediment was slower, with higher mortality, than for the normal larvae. In one population (NP), normal and deformed larvae survived and developed equally well. The emergence rates of the respective populations were similarly ranked when the larvae were raised in an artificial cellulose substrate.

6. Elution peaks of alleged metal‐binding proteins were lower in deformed larvae from SCH and NEI, but higher in deformed larvae from NP, than in normal larvae.

7. A different development rate and mortality of deformed larvae in non‐adapted populations and the possibility of metal adaptation, as in site NP, may modulate the final outcome of deformity frequencies, thus having an impact on the biomarker value of deformities in benthic midge larvae.
Aquatic plant diversity in riverine wetlands: the role of connectivity
Authors: Bornette Gudrun , Amoros Claude , Lamouroux Nicolas
Published: March 2003

1. The hypothesis was tested that intermediate connectivity to a river results in propagule inputs to wetlands, whereas excessive connectivity impedes recruitment, and insufficient connectivity causes less competitive species to be eliminated, with no recruitment of new species. As a consequence, very low or very high nutrient levels should decrease species richness by selecting specialized species, whereas intermediate nutrient levels should favour the co‐occurrence of species with contrasting nutrient requirements.

2. Among cut‐off channels with high sinuosity and which are infrequently flooded by the river (low flood scouring), one example possesses high species richness because most species are saved from extinction by long‐term isolation of the channel and cold groundwater supplies. Other channels are poorly supplied with groundwater and show a lower richness of species, because of low propagule inputs and low recruitment potential.

3. Cut‐off channels with low sinuosity and which are flooded at intermediate frequencies were divided into three groups. The first group was species‐poor, being closely connected to the river through downstream backflows which maintain nutrient‐rich and turbid waters, in keeping with the hypothesis. The second group presents intermediate richness caused by: (i) lower river backflows; and (ii) floods that partly scour substrate and plants, and afford regeneration niches for transported propagules. The third group was species‐poor because of excessive groundwater supplies, which probably acted as a limiting factor for species growth and recruitment.

4. The most frequently flooded channel shows the highest species richness, and occurrence of rare and fugitive species, because of floods which compensate competition by scouring sediments and plants, and afford regeneration niches for propagules. In this case, conservation of biodiversity necessitates propagule sources at the level of the river landscape.
Alkaline phosphatase activity in two planktonic desmid species and the possible role of an extracellular envelope
Authors: Spijkerman Elly , Coesel Peter F. M.
Published: March 2003

1. Cosmarium abbreviatum var. planctonicum, a desmid from oligo‐mesotrophic lakes, had a higher maximum alkaline phosphatase activity (APA) and affinity constant under both continuous and pulsed inorganic phosphorus (Pi) limitation than Staurastrum chaetoceras, a desmid predominantly encountered in eutrophic lakes.

2. APA of both species increased when measured in starved cells subjected to pulsed Pi conditions when compared to continuous Pi limitation.

3. The portion of extracellular relative to cellular APA was higher in S. chaetoceras than in C. abbreviatum, indicating that S. chaetoceras secreted the enzymes more readily into its environment.

4. The difference in APA could explain the dominance of C. abbreviatum during competition between these two species under conditions of continuous organic P (Po) limitation, but not the outcome under a pulsed Po shortage. The dominance of S. chaetoceras in the latter experiment can, however, be explained by species‐specific Pi‐uptake characteristics.

5. After a saturating pulse of Pi, no increase in Pi in the extracellular mucus layer of C. abbreviatum was found and it was therefore concluded that the mucilage sheath does not store P. However, the sheath could have a main function as an accumulation site of cellular APA, providing the cell with Pi.
The state of freshwater ecology
Authors: Reynolds Colin S.
Published: March 2003

1. The case is advanced that freshwater ecologists need to champion the relevance of their work to the development of ecological theory and to the understanding of ecosystem function and behaviour, not least for its importance in addressing pressing applications to the stewardship of the biosphere. An essential step is to review, and update where necessary, the paradigms of aquatic ecology.

2. It is proposed that the major constraint on the organisms, their attributes and adaptations are related first to the physical properties of the medium in which they live. The drives to grow and reproduce relate to the trophic transfer of reduced carbon with important microbial interventions. General principles of ‘emergy’ apply. The supportive capacities of given environments may be set by chemical constraints, but it is suggested that, with the exception of chronically resource‐deficient waters, population dynamics relate to opportunities incumbent upon system variability and the consequent pulsation of resources.

3. Variability affects diversity, through frequent revision of the thermodynamic base. Frequent structural change promotes species diversity and, because function is maintained, it appears that efficient function is dependent upon high diversity. Caution is necessary because high productivity and high diversity are both products of the disturbances consequent upon external forcing and manifestly non‐equilibrium conditions.

4. Reactions to these statements are canvassed.
Genetic structure of the stonefly, Yoraperla brevis, populations: the extent of gene flow among adjacent montane streams
Authors: Hughes Jane M. , Mather Peter B. , Sheldon Andrew L. , Allendorf Fred W.
Published: March 2003

1. Gene flow in populations of stream insects is expected to depend on the distance between and the connectedness of sites in stream networks, and on dispersal ability (i.e. larval drift and adult flight).

2. Yoraperla brevis (Banks) is an abundant and characteristic stonefly of smaller streams in the northern Rocky Mountains. The present authors analysed genetic structure at 27 sites in sevenz streams flowing into the Bitterroot River in western Montana, USA. Cellulose acetate electrophoresis identified five variable loci with 16 alleles.

3. Genotype frequencies conformed to Hardy–Weinberg expectations. Within‐stream differentiation was low and among‐stream variation (Fst) was an order of magnitude higher.

4. UPGMA grouped sites within streams and also grouped adjacent streams. The tree produced by the Neighbour Joining Method was similar although not quite so clear cut.

5. This orderly pattern (i.e. Hardy–Weinberg proportions, homogeneity within streams and geographical structure) contrasts strongly with patterns observed in invertebrates from subtropical streams in Australia. Yoraperla brevis maintains large populations in predictable environments, has a long life‐cycle with a likelihood of cohort mixing, emerges synchronously in large breeding populations and occupies streams separated by areas of high relief; the Australian situation is the opposite in most respects.

6. Further analysis of a range of species is required to determine whether the different genetic structure in Y. brevis compared to the Australian species occurs more generally in North American stream insects.
Leaf litter breakdown in a Mediterranean stream characterised by travertine precipitation
Authors: Casas J. J. , Gessner M. O.
Published: March 2003

1. Breakdown of four leaf species (Platanus orientalis, Populus nigra, Salix atrocinerea, Rubus ulmifolius) was studied in a Mediterranean second‐order stream characterised by abundant travertine precipitation, a history of fire in its catchment, and a recently revegetated alluvial corridor.

2. Compared to breakdown rates reported in the literature for congeneric species, breakdown of the four species was slow (k = 0.0024–0.0069 day−1 for the tree species, and 0.0103 and 0.0111 day−1 for Rubus), in spite of high water temperatures, indicating that the travertine layer that quickly covered submerged leaves impeded decomposer activity and physical fragmentation losses.

3. Breakdown rates nevertheless differed between leaf species in a predictable manner, suggesting that the observed mass loss was largely due to biological processes.

4. The observed tendency towards increasing leaf nitrogen and phosphorus concentrations during breakdown suggests that microorganisms were actively involved in leaf breakdown; however, this interpretation must be viewed with caution because of potentially confounding effects by nutrients contained in the travertine layer.

5. Leaf breakdown of the three indigenous species was faster than that of the exotic species P. orientalis. Due to the recalcitrance of its leaves, the frequent use of Platanus in revegetation schemes following the destruction of indigenous vegetation by fire, exacerbates the negative effect of travertine precipitation on leaf breakdown and, by extension, energy flow in Mediterranean karst streams.
Assessment of river condition at a large spatial scale using predictive models
Authors: Turak EreN. , Flack Lloyd K. , Norris Richard H. , Simpson Justen , Waddell Natacha
Published: March 2003

1. RIVPACS‐type predictive models were developed at a relatively large spatial scale for the Australian state called New South Wales (NSW, 801 428 km2). Aquatic macroinvertebrate samples and physical and chemical data were collected from 250 reference sites (little affected by human activities) and 23 test sites (with known human impacts) throughout NSW in autumn and spring 1995 and identified mostly to family level. Reference sites were grouped based on their macroinvertebrate data using classification (UPGMA) and ordination techniques. Relationships between macroinvertebrate and environmental data were established using principal axis correlations and stepwise multiple discriminant function analysis. models for predicting invertebrate assemblages were developed separately for edge and riffle habitats for autumn and spring data sets and for combined autumn and spring data sets.

2. Sites in the lowland sections of the western flowing rivers were characterized by low taxonomic richness and were distinct from the sites in the eastern part of the state. Sites on the western slopes of the Great Dividing Range in southern and northern NSW mostly fell into separate groups. In eastern NSW, site groups did not represent a north, central and south division. Sites on highland streams, coastal fringe streams and large rivers mostly formed distinct groups, but most of the sites on east‐flowing rivers fell into large site groups that did not have clear geographic boundaries.

3. Environmental variables that were strongly correlated with ordinations of macroinvertebrate presence/absence at sites were water temperature, altitude, longitude and maximum distance from source. The predictor variables determined by DFA for the six models created included alkalinity, altitude, location (longitude and/or latitude), stream size and substratum composition. These are generally in common with the variables determined for other large geographic areas in Australia and the United Kingdom.

4. Model outputs from reference sites suggest that, among the six models, the riffle model combining autumn and spring is likely to give the most reliable predictions. The combined edge model also performed well but refinements are needed for single season models to provide reliable outputs.

5. Combined season models both for riffles and for edges detected biological impairment at all but one of the test sites. Single season riffle models also detected impairment while single season edge models characterized sites as unimpaired despite other models’ indications of impaired fauna. Riffle models may be more sensitive than edge models but the sampling of riffles is often limited by flow. Edge habitats are available at most sites but there may be few riffles in floodplain rivers. Available resources, desired model sensitivity, and river type should be considered jointly to determine the most useful habitat to sample.
Temporal shift in contribution of terrestrial organic matter to consumer production in a grassland river
Authors: Huryn Alexander D. , Riley Ralph H. , Young Roger G. , Arbuckle Chris J. , Peacock Kathi , Lyon Graeme
Published: March 2003

1. We used stable isotopes to study the temporal (early summer versus autumn) pattern of use of terrestrial and aquatic sources of organic carbon by consumers in two bedrock‐confined reaches of a grassland river in New Zealand.  2. The major sources of organic carbon available to primary consumers were expected to be terrestrial leaf‐litter and biofilm from the stream channel. These putative carbon sources showed no significant change in mean δ13C between summer and autumn. Leaf litter (mean δ13C<−26.25) was depleted in 13C compared to biofilm (mean δ13C>−19.92).  3. In contrast to leaf litter and biofilm, the δ13C of consumers changed over time, being enriched in 13C in the autumn compared with early summer. Both the magnitude (>5‰ in some cases) and rapidity of this shift (<3 months) was surprising.  4. A two‐source mixing model indicated that, during early summer, terrestrial carbon comprised> 50% of tissue carbon for 15 of the 17 taxa of aquatic consumers analysed. During autumn, terrestrial carbon comprised> 50% of the tissue carbon of only five of 25 taxa. Because the mean δ13C of putative food sources was consistent over time, the shift in δ13C values for consumers is attributed to a change in relative amounts of terrestrial and aquatic carbon available for consumption.  5. Because seston consists of a mixture of many particles of diverse origin, it may provide an integrated measure of catchment‐wide sources of organic matter entering a stream channel. Like the tissues of most consumers, mean δ13C values for seston showed a significant shift toward 13C enrichment. This indicated that the relative availability of terrestrial carbon decreased from summer to autumn.  6. The actual quantity of carbon contributed to the stream food‐web by this potential terrestrial–aquatic link is unknown. Although terrestrial carbon may comprise a high proportion of the tissue carbon of consumers prior to summer, the majority of secondary production (and carbon sequestration) probably occurs during early summer as a consequence of rising temperature and high quality food in the form of biofilm.
Control of freshwater fish and crayfish community structure in Taranaki, New Zealand: dams, diadromy or habitat structure?
Authors: Joy Michael K. , Death Russell G.
Published: March 2003

1. Freshwater fish and crayfish communities were surveyed along elevational gradients in streams radiating from Mount Taranaki, New Zealand. Six of the 38 streams surveyed had dams or weirs and 32 of the 85 sites were above these barriers.  2. Of the 15 fish and one crayfish species captured, 14 were native. The number of species declined with increasing elevation and distance from the sea. Species richness was also lower above dams even when effects of elevation and distance from the sea were accounted for.  3. Linear regression models using sites without dams were constructed to predict the effect of elevation on fish and crayfish community structure and to allow the effect of dams to be evaluated. The number of species predicted by these models was consistently higher than the number of species found at the above‐dam sites.  4. Four fish community groups were classified using two‐way indicator species analysis (TWINSPAN). One high elevation group of sites consisted of short steep streams on the west side of the mountain and a second contained longer, lower gradient streams on the east side. The other two groups (3 and 4) consisted of mid‐elevation sites and low‐elevation sites, respectively.  5. Discriminant analysis was used to predict biotic group membership using the environmental data. Overall, 80% of sites were classified correctly. Correlation of environmental variables with axis scores in the canonical variate analysis revealed that distance from the sea, site elevation and presence of dams were most strongly associated with fish distribution patterns.
Biomass allocation in three macrophyte species in relation to the disturbance level of their habitat
Authors: BARRAT‐SEGRETAIN MARIE‐HELENE
Published: March 2003

1. The hypothesis was tested that perennial plants surviving in habitats frequently disturbed by floods should demonstrate the ability to escape the frequently scoured surficial zone by using refugia located deeper in the substrate. As a consequence, they should allocate more biomass to their underground parts than when growing in rarely disturbed habitats.

2. The allocation of biomass of three aquatic macrophytes (Berula erecta, Groenlandia densa, Myriophyllum spicatum) to their different organs (underground and above‐ground parts) was measured in former river channels organized along a gradient of scouring flood disturbances.

3. For each species, biomass allocation to underground parts varied between sites: from 10.2 to 37.5% in B. erecta, from 14.9 to 31.1% in G. densa and from 8.4 to 23.2% in M. spicatum. It was correlated to the flood disturbance level of the site for B. erecta and M. spicatum but not for G. densa. No relationship was found between biomass allocation to underground parts and sediment richness.

4. The plasticity in biomass allocation of these three macrophyte species appears to be an adaptation to the variability in environmental conditions and implies difficulties in the classification of plant primary strategies, when this type of plasticity is ignored.
Dynamics of submerged macrophyte populations in response to biomanipulation
Authors: Strand John A. , Weisner Stefan E. B.
Published: March 2003

1. A 6‐year study (1992–97) of changes in submerged vegetation after biomanipulation was carried out in the eutrophicated Lake Finjasjön, Southern Sweden. Ten sites around the lake were revisited each year. At each site five samples of above‐ground biomass were taken at 10 cm water depth intervals. An investigation of the seed bank at the 10 sites, and a grazing experiment where birds and large fish were excluded was also conducted.

2. Between 1992 and 1996, in shallow areas (water depth < 3 m), vegetation cover increased from < 3 to 75% and above‐ground biomass from < 1 to 100 g DW m–2. Mean outer water depth increased from 0.3 to 2.5 m. Elodea canadensis and Myriophyllum spicatum accounted for > 95% of the increase in biomass and plant cover. The following year (1997), however, cover and above‐ground biomass decreased, mainly attributable to the total disappearance of E. canadensis. Secchi depth increased after biomanipulation until 1996, but decreased again in 1997.

3. Total and mean number of submerged species increased after biomanipulation, probably as a result of the improved light climate. However, after the initial increase in species number there was a decrease during the following years, possibly attributed to competition from the rapidly expanding E. canadensis and M. spicatum. The lack of increase in species number after the disappearance of E. canadensis in 1997 implies that other factors also affected species richness.

4. A viable seed bank was not necessary for a rapid recolonization of submerged macrophytes, nor did grazing by waterfowl or fish delay the re‐colonization of submerged macrophytes.

5. Submerged macrophytes are capable of rapid recolonization if conditions improve, even in large lakes such as Finjasjön (11 km2). Species that spread by fragments will increase rapidly and probably outcompete other species.

6. The results indicate that after the initial Secchi depth increase, probably caused by high zooplankton densities, submerged vegetation further improved the light climate. The decrease in macrophyte biomass in 1997 may have caused the observed increase in phosphorus and chlorophyll a, and the decrease in Secchi depth. We suggest that nutrient competition from periphyton, attached to the macrophytes, may be an important factor in limiting phytoplankton production, although other factors (e.g. zooplankton grazing) are also of importance, especially as triggers for the shift to a clear‐water state.
Growth of an acid‐tolerant stonefly on epilithic biofilms from streams of contrasting pH
Authors: Ledger Mark E. , Hildrew Alan G.
Published: March 2003

1. The apparent absence of a specialist herbivorous grazer guild from many acid streams suggests that algae‐grazer linkages in acid‐stream food webs are weak or absent. It has been hypothesized that the absence of herbivores is a consequence of the low quality and/or quantity of biofilms in acid streams.

2. We compared the taxonomic composition, biomass and potential nutritional quality of epilithic biofilms from four acid and four circumneutral streams, and examined whether nymphs of a herbivore–detritivore, the stonefly Nemurella pictetii (Plecoptera: Nemouridae), could grow equally well when fed on eight biofilms from four acid and four circumneutral streams.

3. Biofilms from acid and circumneutral streams differed strongly in algal composition, the former having relatively more coccoid green algae but fewer diatoms and filamentous green algae. Diatom floras differed with stream water pH.

4. The quantity (i.e. area‐specific chlorophyll content, algal numbers and AFDM) and quality (biomass‐specific protein and soluble carbohydrate content) of biofilms differed significantly, both among sites of similar pH, and overall between the groups of acid and circumneutral streams.

5. Nymphs of N. pictetii grew successfully on biofilms for 8–10 weeks up to emergence. However, no systematic differences in growth rate were found between the two groups of acid and circumneutral streams. Differences in the digestibility of benthic algae from different sources, and the adjustment of nymphal feeding rates, are discussed in the light of a lack of a clear relationship between growth and food quality.
Effects of snow cover on the benthic fauna in a glacier‐fed stream
Authors: Schütz Cornelia , Wallinger Manfred , Burger Rainer , Füreder Leopold
Published: March 2003

1. Alpine streams above the tree line are covered by snow for 6–9 months a year. However, winter dynamics in these streams are poorly known. The annual patterns of macroinvertebrate assemblages were studied in a glacial stream in the Austrian Alps, providing information on conditions under the snow.

2. Snow cover influenced water temperature, the content of benthic organic matter and insect development. Taxa richness and abundance of macroinvertebrates did not show a pronounced seasonal pattern. The duration of the autumn period with stable stream beds was important in determining the abundance and composition of the winter fauna.

3. There were significant differences in species composition between summer and winter. Two potential strategies in larval survival were evident: adaptation to the extreme abiotic conditions in summer (e.g. Diamesa spp.) or avoidance of these conditions and development during winter (e.g. Ephemeroptera and Plecoptera).

4. A comparison of a stream reach with continuous snow cover and a stream reach that remained open throughout winter showed that conditions under snow are suboptimal. At the open stream site, with higher water temperatures and greater food supply (benthic organic matter content), abundance and taxa richness was higher and larval growth was faster. Several taxa were found exclusively at this site.

5. Winter conditions did not provide an entirely homogeneous environment, abiotic conditions changed rapidly, especially at the onset of snowfall and at snowmelt. Continuous monitoring is necessary to recognize spatial and temporal heterogeneity in winter environments and the fauna of alpine streams.