bluuebunny/crossref_metadata_2025_split huggingface dataset:
Distribution and abundance of the larval black porgy, Acanthopagrus schlegeli (Bleeker), in coastal waters and an estuary of western Taiwan
Authors: HUANG W. B. , CHIU T. S. 
Published: March 2003

AbstractThis study compared the distribution, abundance and body length of larval black porgy, Acanthopagrus schlegeli (Bleeker), to relative environmental conditions in the coastal waters near Wan‐kung and the Da‐du estuary of western Taiwan to evaluate the utilization of these two water bodies as nursery grounds. Sampling was carried out on spring tides from October 1993 to September 1994. In the coastal waters, salinity (mean = 31.50/00) and current speed (39.1 cm s−1) were significantly higher than those in the estuary (28.30/00 and 29.6 cm s−1). Most of the larvae occurred from late winter to early spring. The period of occurrence was longer and the density was higher in the coastal waters. The mean body length in the coastal waters (9.28 mm) was greater than that in the estuary (7.33 mm), but the coefficient of variation of body length was smaller (coastal waters, 8.15%; estuary, 19.87%). The occurrence of the larvae in the two regions was negatively correlated with water temperature and positively with salinity and dissolved oxygen, and the change of density of larval black porgy was similar to that of all larval species discriminated by principal component analysis. The range and mode of the length‐frequency distributions were different between the two regions. It was concluded that coastal waters are overall a better nursery habitat for black porgy.
Biophysical dynamics of western transition zones: a preliminary synthesis
Authors: Olson Donald B. 
Published: March 2003

The nature of the western portions of the biogeographic temperate or transition zones in the North Pacific and North Atlantic is reviewed. The physical transport of nutrients and biomass into them from the Kuroshio and Gulf Stream as well as from the poleward sides are estimated. The conclusion is that the upwelling in the two western boundary currents makes the largest contribution to the nutrient and biomass fluxes into these transition zones. A conservative estimate of the amount of upwelled fluid is derived from absolute velocity sections in the Gulf Stream. The estimate suggests that upwelling into the euphotic zone exceeds 2 × 106 m3 s–1. This implies that upwelling in these western boundary currents matches or exceeds that in eastern boundary currents such as the California Current. The two western boundary regimes have very different poleward situations. The Oyashio extension flows parallel to the Kuroshio and is a deep current. The North Atlantic Shelf Front flow is to the west where it is ultimately entrained into the edge of the Gulf Stream. There does not seem to be any tendency for this to occur in the Kuroshio. Despite these differences in the northern and western boundaries, the two transition zones are similar with large amplitude meanders, anticyclonic rings and streamers dominating their physical structure. The physical features responsible for the transfer of materials from the boundary current extensions into the transition zones are similar in both systems. Ring formation contributes only ˜ 10% of the transfer, while ring‐induced streamers contribute 30%. The rest of the transport is contributed by branching of the boundary current front. Both currents have well developed secondary fronts consisting of subtropical surface water pulled into the transition zone.Biologically, the upwelling in both western boundary currents leads to a biomass maximum along the boundary in both secondary producers (copepods) and in small pelagic fish. In the Kuroshio, the latter are the Japanese sardine, Sardinops melanostictus, that spawn in the Kuroshio and then enter the transition zone for the summer and fall months. In the Gulf Stream, the dominate species are menhaden, Brevoortia tyrannus and B. smithi. These species make use of the coastal environments of North America and although the adults spawn in the Gulf Stream, they are not thought to play a major role in the Slope Water, transition zone. The similar differences in the use of the Kuroshio and the Gulf Stream ecosystems occurs in the behaviour of bluefin tuna, squid and other large pelagics. The Gulf Stream system also lacks an equivalent to Pacific saury, Cololabis saira. The biology therefore is at least subtly different, with saury and sardines being replaced by mid‐water fish in the North Atlantic. A fuller comparison of the biology with quantitative methods in both systems should be encouraged.
Assessing zooplankton advection in the Barents Sea using underway measurements and modelling
Authors: Edvardsen A. , Slagstad D. , Tande K. S. , Jaccard P. 
Published: March 2003

AbstractThe coastal shelf of northern Norway and the Barents Sea is highly advective and mainly affected by the North Atlantic Current and the Norwegian Coastal Current. The oceanographic conditions are an important factor for the spatial and temporal distribution of zooplankton in the region. To quantify zooplankton advection over the western border of the Barents Sea, a Scanfish/Optical Plankton Counter (OPC), Acoustic Doppler Current Profiler (ADCP), Multiple Opening and Closing Nets and Environmental Sampling System (MOCNESS), and hydrodynamic model were used. This study provides data from two time windows (June and July 1998) by continuous measurements between northern Norway and Bear Island. The zooplankton community structure was obtained by net tows and zooplankton abundance fields were mapped by an OPC counting zooplankton in the size range 0.7–14 mm equivalent spherical diameter. A simple zooplankton community structure was found with the copepod Calanus finmarchicus (CIII–CV) as the dominant species in this size fraction. Ocean currents were measured by a ship‐mounted ADCP and the residual currents were calculated by subtracting the tidal component obtained from a hydrodynamic model. Two measurements conducted in June and July 1998 shows a net eastward transport of water of 3.5 and 1.3 Sverdrup over the section. For the same two periods, zooplankton biomass transport is also positive towards east but varies by two orders of magnitude between the two measurements.
Seasonal heterotrophic flagellate and bacterial plankton dynamics in a large oligotrophic lake– Loch Ness, Scotland
Authors: Laybourn‐Parry Johanna , Walton Mark 
Published: March 2003

1. Bacterial production in the 0–30 m water column of Loch Ness was measured using a dual labelling procedure with [3H] thymidine and [14C] leucine between May 1993 and June 1994. In most cases the uptake of the two labels did not covary, suggesting unbalanced growth. Rates of bacterial production varied from undetectable to 46.2 μg C l–1 day–1. Highest production coincided with the period of highest primary production, but carbon derived from this source was insufficient to meet the bacterial carbon demand, which was met by allochthonous humic inputs to the system.2. Heterotrophic flagellate (HNAN) grazing rates, measured using fluorescently labelled bacteria, ranged between 10.3 and 24.5 bacteria cell–1 day–1 at temperatures between 5 and 15 °C. They removed up to 27% of the bacterial production per day.3. Heterotrophic flagellate specific growth rates ranged from 0.043 to 0.093 h–1 between 5 and 15 °C, giving generation times of 7.4–16.1 h.4. bacterial and HNAN abundances were not coupled, but the highest HNAN grazing impact related to a time of high bacterial productivity.
Effects of an invasive bivalve on the zooplankton community of the Hudson River
Authors: Pace Michael L. , Findlay Stuart E. G. , Fischer David 
Published: March 2003

1. Previous studies documented that zebra mussels became abundant in the Hudson River during 1992 causing an 80–90% reduction in phytoplankton biomass. This study used intervention time series analysis of abundance, biomass and reproduction over the period 1987–95 to assess changes in zooplankton in response to the invasion.2. Zebra mussels caused a size‐dependent decline in zooplankton. Microzooplankton, including tintinnid ciliates, rotifers and copepod nauplii all declined in 1992 and were scarce thereafter. Mean abundances of post‐naupliar copepods and of cladocerans were also lower following the invasion but these changes were not statistically significant (P > 0.05). Egg ratios and clutch sizes for the dominant cladoceran, Bosmina freyi, were not significantly related to zebra mussels, even though relatively low egg ratios were observed after the invasion.3. The strong declines in microzooplankton were probably caused by direct zebra mussel predation. Estimated consumption rates by mussels were roughly equivalent to maximum microzooplankton growth rates.4. The total biomass of zooplankton in the Hudson River declined by more than 70% following the invasion. Annual average zooplankton biomass was correlated with chlorophyll, but biomass per unit chlorophyll in the Hudson River was much lower than in lakes. The present study hypothesizes that this lower biomass reflects limitations by riverine flow and by predation during summer.
Primary nutrients and the biotic integrity of rivers and streams
Authors: Miltner Robert J. , Rankin And Edward T. 
Published: March 2003

1. Controls to reduce loadings of primary nutrients to maintain biotic integrity in rivers and streams have not been widely implemented because the relation between nutrients and chlorophyll, and its consequences for higher trophic levels, is confounded in lotic ecosystems by their openness, the variable degree of nutrient limitation and by the effect of physical factors.2. The relationship between primary nutrients and biotic integrity in rivers and streams was tested using biological, physical and chemical information collected since 1982 from similar locations in streams throughout Ohio using standard procedures.3. There was a negative correlation between nutrients, especially total phosphorus, and biotic integrity. The deleterious effect of increasing nutrient concentration on fish communities in low order streams was detectable when nutrient concentrations exceeded background conditions (total inorganic nitrogen and phosphorus > 0.61 mg L–1 and 0.06 mg L–1, respectively).4. These results suggest that the control of release of toxins and oxygen‐demanding wastes to rivers is insufficient to protect aquatic life, and confirm the importance of non‐point sources of pollution in catchment planning as well as the combined effect of habitat and riparian quality on nutrient assimilation.
Forestry impacts and the vertical distribution of stream invertebrates in south‐western Australia
Authors: Trayler K. M. , Davis J. A. 
Published: March 2003

1. Vertical distributions of invertebrates (> 53 μm) were compared between two logged and two undisturbed headwater streams in south‐western Australia. The abundance and composition of invertebrates from core samples (4 cm diameter, 30 cm depth) were determined at intervals of 0–1 cm, 1–5 cm, 5–15 cm and 15–30 cm.2. In addition to examining the effects of clearfell logging, this study provides the first description of the interstitial communities of Australian sandy streams. The interstitial fauna of the undisturbed streams were concentrated in the upper 5 cm of the bed and were numerically dominated by nematodes, a characteristic more typical of marine and lentic habitats than lotic systems.3. The invertebrate community structure was substantially altered in the logged streams, with fewer taxa collected than in undisturbed streams. Invertebrate densities in the logged and undisturbed streams did not differ in the upper 5 cm of the bed, but, below this, densities were significantly lower in the logged streams. Increased sedimentation did not appear to be responsible for the differences in community structure between logged and undisturbed streams.4. The impact of clearfell logging to the extent shown here has not previously been demonstrated in south‐western Australia. As a consequence it is strongly recommended that sampling of the benthic meiofauna is included in future biomonitoring protocols for the sandy streams of this region.
Development of vegetation and environmental conditions in an oligotrophic Danish lake over 40 years
Authors: Riis  , Sand‐jensen  
Published: March 2003

1. Oligotrophic ‘Lobelia‐lakes’ are rare in Denmark. The few that have survived widespread eutrophication are in uncultivated sandy regions and are threatened by acidification and increased nutrient deposition from the atmosphere. Grane Langsø was considered the clearest lake in Denmark in the 1950s, when isoetids grew to 5.5 m depth and characeans covered the deepest part of the lake bottom at 11.5 m. The goal of the study reported here was to examine whether the lake has maintained this high quality by studying the development of macrophyte distribution and composition in relation to the changes in pH, nutrient conditions and transparency over the past 40 years.2. Aquatic mosses now dominate the vegetation rather than rooted isoetids, probably as a result of acidification (summer median pH was 5.60 in 1958–1963 compared to 5.07 in 1976–1994). Along with a reduced median pH, annual pH fluctuations have increased from about 0.3 units 40 years ago to 0.9 units today.3. The depth limit of isoetid species has declined markedly and Nitella flexilis, which previously dominated the dense bottom vegetation in the hypolimnion, has disappeared. These changes can be accounted for by reduced light penetration and an increased cover of filamentous green algae and mosses on the isoetid species.4. The decline in light penetration was mainly caused by increased humic content following storm falls in 1981–84, but increased nutrient deposition may also have stimulated the growth of phytoplankton and filamentous green algae. The restricted macrophyte growth in the hypolimnion during summer can account for the change from oxygen supersaturation 40 years ago to anoxia today. The reduced light penetration has resulted in cooling of the hypolimnion, thereby increasing the stability and duration of thermal stratification. This increases the likelihood of anoxia in August–September. Profound changes in the plant community and in oxygen conditions have occurred, even though the decline of pH has been small and long‐term changes in nutrient concentration have been difficult to detect.
Intraspecific life history variation in the threatened Louisiana pearlshell mussel,Margaritifera hembeli
Authors: Johnson Paul D. , Brown Kenneth M. 
Published: March 2003

Summary1.Margaritifera hembeliis a threatened mussel limited to twenty‐two headwater streams in the Red River drainage in central Louisiana, USA. This study evaluated intraspecific variation in density, growth, size and age structure and shell morphology among several isolated populations. This study also identified the host fish and considered the role that host fish distribution played in determining mussel recruitment.2. Mussels were aggregated in beds and average densities differed among streams. However, maximum mussel densities in beds were similar in all streams; the observed maxima were among the largest for monospecific mussel beds in North America, often exceeding 300 individuals m–2.3. The maximum size reached by individuals differed among streams, but all size distributions were skewed towards larger individuals. A repeated measures analysis of tagged mussels in four populations, over a 2‐year period, indicated 2‐fold differences in growth rates among streams, and significant variation among years. Growth rates were not affected by local population density. Maximum ages reached, determined indirectly by comparing growth rates, varied from 45 to 75 years. A canonical discriminant analysis also revealed significant differences in shell morphology across populations.4. Half of the populations showed evidence of recent recruitment, and these sites had fish assemblages dominated by the host fishNoturus phaeus(Taylor). Host fish abundance appeared more important than adult mussel density in explaining recruitment patterns.5. Considerable intraspecific life history variation suggests that management strategies for this species should be stream‐specific, with emphasis on ensuring long‐term habitat stability.
Decomposition of standing litter of the freshwater emergent macrophyteJuncus effusus
Authors: Kuehn Kevin A. , Suberkropp Keller 
Published: March 2003

Summary1. Standing dead plant litter of emergent macrophytes frequently constitutes a significant fraction of the detrital mass in many freshwater wetland and littoral habitats. Rates of leaf senescence and decomposition of the emergent macrophyte Juncus effusus were examined in a small freshwater wetland in central Alabama, U.S.A. Juncus effusus leaves in the initial stages of senescence were tagged in random plant tussocks and monitored periodically to determine in situ rates of leaf senescence and death. Fully senescent leaves were collected, placed in litter bags, and suspended above the sediments to simulate standing dead decay conditions. Litter bags were periodically retrieved over 2 years and analysed for weight loss, litter nutrient contents (N, P), associated fungal biomass and fungal taxa.2. Senescence and death of J. effusus leaves proceeds from the leaf tip to the base at an exponential rate. The rate of senescence and death of leaf tissue increased with increasing temperatures. Plant litter decomposition was slow (k = 0.40 yr–1), with 49% weight loss observed in 2 years. Both the nitrogen (N) and phosphorus (P) concentration (%) of litter increased during decomposition. However, the total amount of nitrogen (mg) in litter bags remained stable and phosphorus increased slightly during the study period.3. Fungal biomass associated with plant litter, as measured by ergosterol concentrations, varied between 3 and 8% of the total detrital weight. Values were not significantly different among sampling dates (P > 0.05, ANOVA, Tukey). Fungi frequently identified on decaying litter were Drechslera sp., Conioscypha lignicola (Hyphomycetes), Phoma spp. (Coelomycetes), Panellus copelandii and Marasmiellus sp. (Basidiomycota).4. These results support previous findings that plant litter of emergent macrophytes does not require submergence or collapse to the sediment surface to initiate microbial colonization and litter decomposition.
Hydraulic microdistribution patterns of larval fire salamanders (Salamandra salamandra salamandra) in the Weidlingbach near Vienna, Austria
Authors: Baumgartner N. , Waringer A. , Waringer J. 
Published: March 2003

1. This study examined the longitudinal distribution of larval fire salamanders (Salamandra salamandra salamandra L.) in the Weidlingbach system, a first‐ to fourth‐order tributary of the Danube near Vienna, Austria. On the microhabitat scale, actual current velocities, Reynolds numbers and Froude numbers at larval locations were measured and larval positions mapped.2. Larval densities were highest in shallow first‐ and second‐order tributaries where mean current speeds were less than 20 cm s−1, mean Reynolds numbers were less than 12 000 and mean Froude numbers were less than 0.30. Young larvae appeared on 26 April, fully grown larvae were observed from 11 May and larvae started metamorphosis from 27 June. Young adults left the brook between 26 August and 8 September. A severe flood on 25 May significantly reduced larval density, especially at sites near the source.3. At a given sampling station young larvae favoured microhabitats exposed to only minor hydraulic stress. As larvae grew, they also colonized microhabitats with moderate current velocity (4–15 cm s−1). At sites with generally low discharge, larvae were distributed over a wider range of current velocities than at sites with higher discharge; at the latter, larvae were constricted to sheltered microhabitats.
Contribution of rotifers to the diet and fitness of Boeckella (Copepoda: Calanoida)
Authors: Couch Kyleigh M. , Burns Carolyn W. , Gilbert John J. 
Published: March 2003

1. The calanoid copepods, Boeckella triarticulata Sars and Boeckella hamata Brehm, are major components of the freshwater zooplankton of New Zealand. It was not known whether these copepods ingest rotifers, nor whether the inclusion of rotifers in their diets might improve their fitness. The present study aimed to identify rotifer taxa which are eaten by each copepod species, and to examine the fitness consequences of the inclusion of one species of rotifer in the diet of B. triarticulata.2. In feeding experiments using natural rotifer assemblages, both species of copepod ingested the rotifer Anuraeopsis fissa (0.4–4% of daily carbon intake), and B. triarticulata also ingested Polyarthra dolichoptera (6–30% of daily carbon intake) and Keratella cochlearis tecta (1% of daily carbon intake).3. The contribution of rotifers to the fitness of adult female B. triarticulata was assessed by comparing survival and reproduction among five diets that contained varying densities of algae (Cryptomonas sp.) and/or Polyarthra dolichoptera (4 μg C L−1). Boeckella triarticulata produced fewer clutches on a rotifer‐only diet than on a solely algal diet, and addition of rotifers to a threshold algal diet did not affect copepod fitness relative to the solely algal diets. The present results suggest that Polyarthra at 4 μg C L−1 is not a high‐quality food for B. triarticulata.
Post‐European changes to the fluvial geomorphology of Bega catchment, Australia: implications for river ecology
Authors: Brierley Gary J. , Cohen Tim , Fryirs Kirstie , Brooks Andrew 
Published: March 2003

1. Within a few decades of European disturbance in the mid‐nineteenth century, river character and behaviour were transformed in Bega catchment on the south coast of New South Wales, Australia. Ecological impacts of geomorphic changes to river structure and function throughout the catchment are assessed.2. At the time of European settlement, many water courses in Bega catchment were discontinuous, with extensive swamps along middle and upper courses. Following a series of direct and indirect human impacts, channels became continuous in the middle and upper parts of the catchment, as extensive valley fills at the base of the escarpment were incised. Along the lowland plain, the channel widened by over 300%, fundamentally altering the relationship between the channel and its adjacent floodplain.3. Geomorphic changes to river structure have modified habitat availability throughout Bega catchment. The impacts have been least pronounced in headwater streams, but have been dramatic along virtually all river courses beyond the base of the escarpment.4. Changes in river structure have been directly related to altered riparian vegetation cover, and vice versa. As a consequence of changes to river structure, bed substrate calibre (and supply volume/rate) has been modified along most streams.5. A series of indirect, secondary impacts have modified habitat viability along river courses. Lateral, longitudinal and vertical linkages within the river system have been altered, affecting the transfer of water, sediment, organic matter, nutrients and other biotic interactions.6. These direct and indirect consequences of geomorphic changes in river structure suggest that ecologists need to adopt a longer‐term, catchment‐framed view of human disturbance to river ecosystems.7. Effective, sustainable ecological rehabilitation of river courses is dependent on an understanding of geomorphic processes and determination of appropriate river structure at differing positions in catchments.