bluuebunny/crossref_metadata_2025 huggingface dataset:
Variability in performance in wild Atlantic salmon, Salmo salar L., fry from a single redd
Authors: García De Leániz C. , Fraser N. , Huntingford F. A.
Published: March 2003

Dispersal and growth were studied in Atlantic salmon, Salmo salar L., fry from a natural isolated redd. The distribution of fry leaving the redd was strongly peaked, 80% being caught within a 2‐week period. Early in the dispersal period, all fry leaving the redd had remnants of yolk sac and had not fed; by half way through the dispersal period, no fry had any visible yolk, but 35% still had empty stomachs. Fry leaving the redd during the first half of the dispersal period tended to settle in different first feeding sites than those dispersing later. Predation on fry by larger salmonids was frequent, especially during dispersal. Coefficients of variation for length, weight and condition factor increased significantly over the study period and for individually recognised fry, growth rates varied markedly. Thus, individual salmon fry differ in physical status on emergence from the redd and these differences are amplified during the first few weeks after emergence.
Carbon sources of Amazonian fisheries
Authors: Benedito‐Cecilio E. , Araujo‐lima C. A. R. M , Forsberg B.R. , Bittencourt M.M. , Martinelli L. C.
Published: March 2003

Variation in the seasonal and spatial isotopic composition of plant C4 (aquatic macrophytes) and C3 (forest, C3 aquatic macrophytes and algae), and that of fish [Prochilodus nigricans Agassiz, Mylossoma duriventre (Cuvier), Colossoma macropomum (Cuvier), Semaprochilodus insignis (Schomburgk) and S. taeniurus Steindachner in the Amazon floodplain were analysed to test whether the fisheries deliver plant carbon to the population of Manaus in the same proportion as it is available in the floodplain. The contribution of C4 plants was significantly lower in 13C during the season of high water levels and increased toward the west of the basin. Mylossoma duriventre and C. macropomum changed δ13C levels, while the δ13C of P. nigricans and C. macropomum shifted spatially. The contribution of C4 to the fisheries yield was small. C3 plants (excluding phytoplankton) also contributed less than expected. This was explained by the importance of detritivores to the yield of the fisheries and the dependence of these species on algal carbon.
Factors determining the structure of fish communities in Pantanal lagoons (MS, Brazil)
Authors: Súarez Y. R. , Petrere Jr M. , Catella A. C.
Published: March 2003

The fish communities of lagoons in the Nhecolândia Pantanal were studied to determine the factors which are responsible for the composition and abundance of species. Fishes were collected in 19 lagoons during August 1997, after their isolation from the River Negro, using beach seines (15 × 1.5 m; 2 mm mesh). A total of 51 species were collected. In the lagoons, or in parts with dense macrophytes, a screened box trap was used. Fishing was also accomplished with hooks of several sizes. Species richness was estimated by the jack‐knife procedure, after adjustment to the log‐normal distribution and with von Bertalanffy’s equation (asymptotic). The most important factors in the community organization were macrophyte cover, piscivore abundance and depth of the lagoons. The role of these habitats in the Pantanal ecosystem was discussed.
Investigation of the Negombo estuary (Sri Lanka) brush park fishery, with an emphasis on community‐based management
Authors: AMARASINGHE U. S. , AMARASINGHE M. D. , NISSANKA C.
Published: March 2003

The Negombo estuary brush park fishery in Sri Lanka was investigated from June 1998 to March 1999. The mean fish yield (all species) in the fishery was 12.46 t ha−1 yr−1. Fin fish species formed about 91% of the yield and the rest was formed by penaeid shrimps and crabs. Fish yield and the twig density in the brush park exhibited a second order polynomial relationship indicating a minimum yield at an intermediate value of twig density in the brush parks. The relationship between fish yield and duration of implantation of brush parks showed an optimal period of 30–40 days for high fish yields. Income levels of fishermen, availability of construction material and suitable sites for implantation of brush parks are some of the factors determining size and number of brush parks per fisherman and duration of installation. Indigenous knowledge within the fishing community about the effect of salinity variations, twig density and mangrove species used on the harvests greatly contribute to effective operation of this fishing practice. Cultivation of mangroves to obtain twigs and branches is a unique feature in this estuary. Indigenous knowledge on mangroves has led to the adoption of sound silvicultural practices. Although cultivating mono‐specific mangrove stands may not increase diversity of mangrove forests, it reduces denudation of naturally occurring mangrove forests because of brush park construction, and retains habitats for other organisms. Mangrove management plans in the Negombo estuary should therefore be viewed and treated in an integrated manner that takes into account both resource and social components.
Spawning habitat of the Atlantic menhaden in Onslow Bay, North Carolina
Authors: Checkley, Jr  , Ortner  , Werner  , Settle  , Cummings
Published: March 2003

The Continuous, Underway Fish Egg Sampler (CUFES) was used to sample pelagic eggs of the Atlantic menhaden (Brevoortia tyrannus) from 3‐m depth off North Carolina in winter 1993–94 and 1994–95. Simultaneous measurements were made of temperature, salinity, and the concentration of chlorophyll a. The maximal concentration of eggs was 346 eggs m−3. Eggs were highly aggregated in patches which occurred between the Gulf Stream and mid‐shelf fronts (17–23°C, 36.0–36.4‰). Unexpectedly, eggs were found almost exclusively in water of 20–60 m (mode 20 m) bottom depth. Thus, spawning appears related to bathymetry as well as hydrography. Variograms for egg concentration indicated a mean (± SE) patch scale of 3.6 ± 1.7 km and a high degree of spatial variance explained by CUFES sampling. Lagrangian modelling of particles moving in response to tides, winds, and a prescribed flow from the north indicated that the region of observed, maximal occurrence of eggs is favourable for the retention of eggs and larvae on the shelf adjacent to inlets used to enter nursery areas.
Wind‐generated transport of fictitious passive larvae into shallow tidal estuaries
Authors: Blanton  , Werner  , Kapolnai  , Blanton  , Knott  , Wenner
Published: March 2003

Four 14‐day field experiments were conducted to determine the densities of postlarval white shrimp and blue crab megelopae moving into a tidal inlet along the south‐eastern United States. Certain winds directions were statistically associated with peaks in abundance, a result which motivated us to use a high resolution finite‐element numerical model to simulate passive larval transport under a variety of wind directions into the inlet. The passive particles were initially distributed uniformly in a zone of the continental shelf which extended 20 km offshore and 20 km alongshore in either direction. Each simulation was conducted for five tidal cycles (2.5 days) under constant wind stress. These simulations indicated that larvae are withdrawn from the continental shelf into the inlet from a narrow zone parallel to the shoreline but extending less that 5 km offshore. The withdrawal zone changed to one directly offshore of the inlet mouth only for a wind direction that pointed directly toward the inlet mouth. Under downwelling‐favourable winds, particles originating in the surface accumulate along the downwind boundary and drift shoreward with time thus causing a ‘pooling’ of larvae along the coast. This scenario is repeated with less efficiency for upwelling‐favourable winds with particles originating near bottom. The ‘pooling’ process occurs over the scale of the particle domain. A second and smaller scale is indicated by the relatively few particles which are withdrawn into the inlet as they pass inside the 7‐m isobath (within 5 km of the coast). Those that do pass become available for inlets farther downstream.
Skipjack tuna fishery in relation to sea surface temperature off the southern Brazilian coast
Authors: Andrade Humber Agrelli , Garcia Carlos Alberto Eiras
Published: March 2003

Several oceanographic studies have associated tuna fisheries to sea surface temperature (SST) fields, although catch per unit of effort (CPUE) has not shown a clear relationship with SST. However, most results concerned species that occur deep in the water column. In this paper, we present a study on the relationship between SST and CPUE for the skipjack tuna fisheries off the southern Brazilian coast, which take place at the sea surface. We use historical data from the Japanese fleet, which operated in the area from July 1982 to June 1992. Fishing sets occurred only in areas where SST ranged from 17°C to 30°C. Frequency of occurrence vs. SST showed a Gaussian distribution, with highest CPUEs in waters of SST 22°‐26.5°C. The relationship between CPUE (or fishing set occurrence) and SST varied seasonally. Largest CPUEs occurred in summer, independently of SST. Therefore, temperature alone could not be used as a determinant of CPUE, suggesting that seasonal variability of other environmental parameters has a stronger effect on the CPUE than does SST. However, when the seasonal cycle was excluded from the data sets, a relationship between the interannual variability of SST and CPUE became apparent. Cross‐correlation analysis between CPUE and SST has shown that oscillations in CPUE anomalies precede oscillations in SST anomalies by a month, but the mechanism relating them in this way is unknown.
Variability of community structure of Copepoda related to El Niño 1982–83 and 1987–88 along the west coast of Baja California Peninsula, Mexico
Authors: Hernandez‐Trujillo Sergio
Published: March 2003

Copepod community structure and abundance of the most abundant species were studied during 15 cruises made between 1982 and 1989 along the west coast of the Baja California Peninsula, Mexico. The number of species and species diversity (Shannon’s index) for each sampling station of the oceanographic cruises were obtained. Though the zone was dominated during the year by the tropical copepod component, similarities between El Niño 1982–83 and 1987–88 were observed. Tropical‐equatorial populations were added to the regular tropical composition (50%) of the community of copepods resulting in a wide distribution of those populations in 1982–83 and in 1987–88. The scenario in 1984–89 (without 1987–88) was significantly different from both El Niños because of the sea surface temperature, the species diversity, and the tropical copepod component, although 1982 was similar to 1985 in diversity index and number of species. Environmental conditions prevailing along the west coast of Baja California during El Niño indicate that in 1982–83 the effect on the copepod community was greater than during the 1987–88 event.
Stock size fluctuations in chub mackerel (Scomber japonicus) in the East China Sea and the Japan/East Sea
Authors: Hiyama Yoshiaki , Yoda Mari , Ohshimo Seiji
Published: March 2003

The stock size of chub mackerel (Scomber japonicus) in the East China Sea and the Japan/East Sea has shown a continuous decrease, with fluctuations, from 1975 to 1990. After a remarkable increase in 1992–96, the stock size fell to its lowest level in 1997–99. The spawning success (number of recruits/spawning biomass) fluctuates periodically with a period of several years, although there are no clear relationships between the spawning biomass and the number of recruits. Spawning success was inversely correlated with sea surface temperature (SST). On the contrary, the catch amount and the catch per unit effort (CPUE) of spotted mackerel (Scomber australasicus) has increased since 1997.
Empirical biomass model for the Japanese sardine, Sardinops melanostictus, with sea surface temperature in the Kuroshio Extension
Authors: Noto Masayuki , Yasuda Ichiro
Published: March 2003

An Empirical Biomass Model for the Japanese sardine, Sardinops melanostictus, was developed on the basis of the relationship between February sea surface temperature (SST) in the Kuroshio Extension (30–35°N, 145–180°E) and the mortality coefficient during the period from egg to age 1, observed in 1979–94, to examine the long‐term variation of biomass. The periods of the good and bad catch, the year of the biomass peak, and the speed of the biomass decline in the period from 1957 to 1994 were successfully reproduced, except for the biomass increase in the early 1970s. When the model also included with a density‐dependent effect, the whole history of the observed catch during 1957–94 was almost perfectly reproduced. These results suggest that the environment in the Kuroshio Extension region, represented by winter–spring SST, is regarded as a leading factor for determining fluctuations of the sardine biomass in the long term, and that the density effect has a secondary contribution.
Predator–prey interactions between larval damselflies and mining larvae of Glyptotendipes gripekoveni (Chironomidae): reduction in feeding activity as an induced defence
Authors: Koperski Pawel
Published: March 2003

1. The feeding methods and intensity of predation by larvae of the damselfly Erythromma najas on leaf‐mining larvae of the chironomid Glyptotendipes gripekoveni were examined in artificial habitats differing in complexity. The experiments assessed the influence of chemical stimuli from the predator, light and the concentration of suspended food on the feeding activity of G. gripekoveni inside and outside of the mine.

2. Erythromma najas preyed upon G. gripekoveni as the latter grazed outside mines. The intensity of this predation decreased significantly at night in a habitat offering alternative prey.

3. When the food concentration for the chironomid was high, it significantly reduced both filtering activity and activity outside mines in response to the kairomone produced by E. najas. Feeding activity did not change when food was scarce.

4. The induced reduction in filter‐feeding and deposit‐feeding activity probably reduced predator success by reducing the probability of long‐distance detection of a mine and location of the chironomid’s hole.

5. The predator can detect and catch mining prey in either the light (visually) or dark (mechanically). This may explain the lack of diel periodicity in the chemically induced differences in prey activity.

6. Reduced feeding activity of mining larvae in the chemically simulated presence of a larval damselfly can be explained as an induced antipredator behaviour, illustrating the trade‐off between feeding demands and predation risk in a poorly known link of the littoral foodweb.
Breakdown of	Ficusand	Eucalyptusleaves in an organically polluted river in India: fungal diversity and ecological functions
Authors: Raviraja  , Sridhar  , Bärlocher Felix
Published: March 2003

1. At two organically polluted sites in the River Nethravathi, banyan and eucalypt leaves were colonized by one or two species of aquatic hyphomycetes. A total of three or four species were identified at the two sites in samples of water and naturally occurring leaves.

2. Spore production from stream‐exposed leaves by aquatic hyphomycetes was lower by a factor of up to 1 million compared with an earlier study in geographically close but unpolluted streams.

3. Exponential decay rates and loss rates of phosphorus and calcium, were not statistically different from an earlier study in unpolluted streams. Nitrogen increased during decomposition more slowly in the current study.

4. The microbial community on both leaves released enzymes active against starch, pectin, cellulose and xylan.

5. Banyan leaves conditioned for 12 weeks were more palatable to the gastropod Notopala sp. than unconditioned leaves.

6. Together with earlier data from unpolluted streams, the study provides evidence that organic pollution severely restricts diversity of aquatic hyphomycetes and their reproductive output, but does not have an equally strong effect on ecological functions generally associated with this group.
Selective predation on an introduced zooplankter (Bythotrephes cederstroemi) by lake herring (Coregonus artedii) in Harp Lake, Ontario
Authors: Coulas Robert A. , Macisaac Hugh J. , Dunlop Warren
Published: March 2003

1.Bythotrephes cederstroemi(Crustacea: Onychopoda: Cercopagidae) invaded Harp Lake, Ontario in 1993, since when the zooplankton community has shifted from dominance of small‐bodied to large‐bodied species. During 1995 diets of adult lake herring (Coregonus artedii), Harp Lake’s primary planktivorous fish, were examined to determine the extent to which this conspicuous zooplankter has become integrated into the lake’s foodweb and whether fish condition has been affected in consequence.

2.BythotrephesandDaphnia galeata mendotaewere strongly preferred prey, whilstHolopedium gibberumand calanoid and cyclopoid copepods were negatively selected by lake herring. Predation onBythotrephesandHolopediumwas not size‐selective, althoughD. galeata mendotaeand calanoid copepods (Leptodiaptomus minutusandL. sicilis) consumed by herring were significantly larger than co‐occurring conspecifics in the lake.

3. Caudal spines ofBythotrephesmay form boluses in lake herring stomachs. However, the number of caudal spines in fish digestive tracts did not differ significantly from the number ofBythotrephes’ mandible pairs, indicating that the former were not differentially retained.

4. Lake herring weight‐at‐length relationships in lakes in Muskoka, Ontario, invaded byBythotrephesdid not differ from those in adjacent non‐invaded lakes, indicating thatBythotrephesinvasion of lakes apparently has not affected condition of lake herring.
Abiotic aspects of channels and floodplains in riparian ecology
Authors: Huggenberger P. , Hoehn E. , Beschta R. , Woessner W.
Published: March 2003

1. The ecology of riparian zones is enormously influenced by the heterogeneous sedimentary structures and associated complex hydrologic flow paths that mediate surface‐ and groundwater exchanges. Sedimentary structures form a three‐dimensional, dynamic framework that controls subsurface flow and the vertical and horizontal exchange of water between channels and floodplains in gravel bed rivers. The modern structure of the bed sediments reflects the legacy of cut and fill alluviation for a particular river basin.

2. Highly permeable sedimentary textures, particularly open framework gravels, allow rapid exchange between surface and groundwaters.

3. Ground penetrating radar provides high resolution information on the nature and three‐dimensional distribution of the sediments within the shallow subsurface (4–25 m) of gravel bed rivers. Bed sediments can be mapped at the decimeter scale.

4. Exchange and mixing of ground and channel water occurs along losing, gaining and flow‐through reaches as determined by the hydraulic gradient and transmissivity of the bed sediments.

5. Spatial and temporal patterns of surface‐ and groundwater interactions can be quantified by mass flux measurements and by assessing geochemical contrasts. Natural tracers, such as temperature or radon, are well suited for mapping exchange sites and quantifying interactions. Artificial signals produced by injecting anions, like chloride, bromide and organic dyes are also useful.

6. The study of riparian ecosystems requires an understanding of the geomorphic structures and processes that build and maintain bed sediments and flow pathways through them.
Effects on phytoplankton of nutrients added in conjunction with acidification
Authors: Findlay D. L. , Hecky R. E. , Kasian S. E. M. , Stainton M. P. , Hendzel L. L. , Schindler E. U.
Published: March 2003

1. The effects of nitric acidification on phytoplankton were studied in a small, eperimentally manipulated, oligotrophic lake (L302N) in the Eperimental Lakes Area of Canada. The focus was altered after 9 years of acidification to investigate the possibility of using nutrient additions to stimulate recovery, followed by a controlled incremental recovery, in which the pH was increased to a predetermined target level.

2. Five years of additions of HNO3 to L302N reduced its pH from 6.5 to 6.1. Nitrate concentration increased because the algal community was severely P deficient. The phytoplankton community structure and productivity were not significantly affected by these additions.

3. The phytoplankton community was significantly affected when pH was subsequently decreased over three successive years from 6.1 to 5.1 by the addition of HCl. Dominance shifted from chrysophytes to a co‐dominance of chlorophytes and dinoflagellates, which altered the size structure of the community. Species diversity significantly decreased, although phytoplankton productivity remained unchanged.

4. At pH 5.1 nitrate and sulphate additions were made, creating conditions like those in lakes in eastern North America, which receive high loadings of nitrogen from the atmosphere. The phytoplankton assemblage shifted to dominance by small coccoidal chlorophytes. However, biomass and productivity were unaffected.

5. Finally, phosphate, as phosphoric acid, was added, along with nitrate and sulphate, to the epilimnion, which stimulated internal alkalinity generation and productivity. It is concluded that CO2 concentrations and the form of N (nitrate vs. ammonia) affect algal composition but that P determines algal biomass and productivity. Chlorophytes were found to be good competitors for P when N and CO2 were high; it is epected that cyanobacteria would be more competitive for P in low CO2 systems. Conversely, dinoflagellates are most competitive in systems with low pH and high P, such as that which occurred in L302N. Although the P additions reduced N concentrations and created alkalinity, this is not a recommended remedial procedure in acidified lakes because it enhanced dinoflagellate abundance, which has been associated with fish kills.

6. When all additions ceased, the pH of L302N recovered from 5.1 to 5.8, chrysophytes and chlorophytes became more abundant and dinoflagellates decreased in abundance. Phytoplankton biomass decreased and species diversity increased. Phytoplankton productivity remained unchanged
E‐mail: J.Laybourn‐Parry@nottingham.ac.ukAnnual plankton dynamics in an Antarctic saline lake
Authors: Bell Elanor M. , Laybourn‐Parry Johanna
Published: March 2003

1. The plankton dynamics of Ace Lake, a saline, meromictic basin in the Vestfold Hills, eastern Antarctica was studied between December 1995 and February 1997.

2. The lake supported two distinct plankton communities; an aerobic microbial community in the upper oxygenated mixolimnion and an anaerobic microbial community in the lower anoxic monimolimnion.

3. Phytoplankton development was limited by nitrogen availability. Soluble reactive phosphorus was never limiting. Chlorophyll a concentrations in the mixolimnion ranged between 0.3 and 4.4 μg L−−1 during the study period and a deep chlorophyll maximum persisted throughout the year below the chemo/oxycline.

4. Bacterioplankton abundance showed considerable seasonal variation related to light and substrate availability. Autotrophic bacterial abundance ranged between 0.02 and 8.94 × 108 L−−1 and heterotrophic bacterial abundance between 1.26 and 72.8 × 108 L−−1 throughout the water column.

5. The mixolimnion phytoplankton was dominated by phytoflagellates, in particular Pyramimonas gelidicola. P. gelidicola remained active for most of the year by virtue of its mixotrophic behaviour. Photosynthetic dinoflagellates occurred during the austral summer, but the entire population encysted for the winter.

6. Two communities of heterotrophic flagellates were apparent; a community living in the upper monimolimnion and a community living in the aerobic mixolimnion. Both exhibited different seasonal dynamics.

7. The ciliate community was dominated by the autotroph Mesodinium rubrum. The abundance of M. rubrum peaked in summer. A proportion of the population encysted during winter. Only one other ciliate, Euplotes sp., occurred regularly.

8. Two species of Metazoa occurred in the mixolimnion; a calanoid copepod (Paralabidocera antarctica) and a rotifer (Notholca sp.). However, there was no evidence of grazing pressure on the microbial community. In common with most other Antarctic lakes, Ace Lake appears to be driven by ‘bottom‐up’ forces.
Dissolved organic matter and phosphorus leached from fresh and ‘terrestrially’ aged river red gum leaves: implications for assessing river–floodplain interactions
Authors: Baldwin D. S.
Published: March 2003

1. The rates of leaching, speciation and bioavailability of dissolved organic matter (DOM) and dissolved phosphorus (P) leached from fresh leaves of the river redgum, Eucalyptus camaldulensis Dehnh, were compared to those from leaves which had been aged on the flood plain for 5_months. The DOM and P leaching rates from microbially inhibited aged leaves were first‐order with respect to leaf quantity. The kinetics of DOM and P leaching from fresh leaves were more complex; DOM leaching from fresh leaves appeared to be self‐inhibitory, while P leaching from leaves was potentially enzymatically mediated.

2. The speciation and microbial bioavailability of DOM from fresh and aged leaves were completely different. At lower leaf biomass, almost all the DOM from fresh leaves was utilized by an introduced microbial consortium; at higher biomass, microbial utilization appeared to be nutrient limited. Conversely, only about 30% of the DOM leached from aged leaves was utilized by the introduced microbial consortium during the course of the experiment. The difference in microbial utilization could be a result of changes in DOM speciation as a consequence of terrestrial ageing.

3. Weak‐anion exchange chromatograms of microbially inhibited fresh leaf extracts showed numerous (unassigned) DOM peaks, most of which could be used by the microbial consortium present. The weak‐anion exchange chromatograms of sterile aged leaves showed only three broad peaks and a number of smaller spikes. Only one of the broad peaks could be utilized by the microbial consortium.

4. Phosphorus speciation was also determined by weak‐anion exchange chromatography. Most of the P leached from both fresh and aged leaves was free orthophosphate, and therefore, readily available. Two organic‐P species leached from microbially inhibited fresh leaves were also found to be readily available to the microbiota.
The importance of physical habitat assessment for evaluating river health
Authors: Maddock Ian
Published: March 2003

1. Physical habitat is the living space of instream biota; it is a spatially and temporally dynamic entity determined by the interaction of the structural features of the channel and the hydrological regime.

2. This paper reviews the need for physical habitat assessment and the range of physical habitat assessment methods that have been developed in recent years. These methods are needed for assessing improvements made by fishery enhancement and river restoration procedures, and as an intrinsic element of setting environmental flows using instream flow methods. Consequently, the assessment methods must be able to evaluate physical habitat over a range of scales varying from the broad river segment scale (up to hundreds of kilometres) down to the microhabitat level (a few centimetres).

3. Rapid assessment methods involve reconnaissance level surveys (such as the habitat mapping approach) identifying, mapping and measuring key habitat features over long stretches of river in a relatively short space of time. More complex appraisals, such as the Physical Habitat Simulation System (PHABSIM), require more detailed information on microhabitat variations with flow.

4. Key research issues relating to physical habitat evaluation lie in deciding which levels of detail are appropriate for worthwhile yet cost‐effective assessment, and in determining those features that are biologically important and hence can be considered habitat features rather than simple geomorphic features.

5. The development of new technologies particularly relating to survey methods should help improve the speed and level of detail attainable by physical habitat assessments. These methods will provide the necessary information required for the development of the two‐and three‐dimensional physical and hydraulic habitat models.

6. A better understanding of the ways in which the spatial and temporal dynamics of physical habitat determine stream health, and how these elements can be incorporated into assessment methods, remains a key research goal.
The effects of disturbance events on phytoplankton community structure in a small temperate reservoir
Authors: Barbiero R. P. , James W. F. , Barko J. W.
Published: March 2003

1 The effects of disturbances, in the form of storm events, on phytoplankton community structure were examined over the course of four years in Eau Galle Reservoir, Wisconsin, USA.

2 Disturbances consistently brought about significant, but highly transient, increases in apparent phytoplankton species richness. It is likely that these resulted from temporary increases in the biomass of previously undetected rare species.

3 Substantial shifts in community dominance were confined to large, early season events, and were seldom long‐lived. Later ‘climax’ communities were highly resistant to any changes in dominance, even when increases in species richness occurred.

4 Regardless of when they occurred, disturbances tended to favour species from a narrow range of the successional sequence.
Bacterial production measured by leucine and thymidine incorporation rates in French lakes
Authors: Petit Muriel , Servais Pierre , Lavandier Pierre
Published: March 2003

1. Production of heterotrophic bacterioplankton was estimated monthly by the tritiated thymidine and leucine incorporation methods during the draining and filling of the mesotrophic Lake Pareloup (over a 2.5‐years sampling program).

2. Rates of 3H‐leucine (leu) and 3H‐thymidine (thy DNA) incorporation generally paralleled each other but the ratio of leu/thy DNA incorporation rates was higher for the draining period (34.5 mean) than during and after filling (11.5 mean).

3. After draining, the highest ratios were observed during periods of low temperature and low bacterial specific activity, while DNA labeling by 3H‐thymidine was reduced. However, bacterial production estimates obtained by 3H‐leucine (BPL) and 3H‐thymidine (BPT) incorporation methods were generally well correlated and the average BPL/BPT ratio was equal to 0.78.

4. In addition, both methods were applied during a diel cycle in three lakes of different trophic status. An increase of leu/thy DNA incorporation rates was noted from the oligotrophic to the eutrophic system. In the absence of Cyanobacteria, BPL and BPT values were quite concordant on average.

5. In situations of unbalanced growth, BPL and BPT values can diverge but when considered over a sufficient period of time they were found to be in agreement.
Variation in growth of the detritivore‐shredder Sericostoma personatum (Trichoptera)
Authors: Friberg Nikolai , Jacobsen Dean
Published: March 2003

1. We investigated the growth of the detritivore‐shredder Sericostoma personatum by feeding groups of larvae on a fresh macrophyte, Potamogeton perfoliatus, conditioned sitka spruce needles, Picea sitchensis, conditioned alder leaves, Alnus glutinosa, conditioned ash leaves, Fraxinus excelsior, and a fresh filamentous green alga, Microspora sp. A sixth treatment group of larvae was fasted.

2. The nitrogen content of the food items ranged from 1.4% dry weight (DW) for Picea needles to 4.4% DW for Microspora filaments. Consumption of the various food items by Sericostoma differed significantly, being highest for Picea, and lowest for Potamogeton and Microspora.

3. The instantaneous growth rate ranged from −1.3% DW day−1 in the fasting group to 0.75% DW day−1 in the Alnus group. The growth rate of larvae fed on Alnus, Fraxinus and Microspora was similar, and significantly higher than that of the other three groups. An increase in the size of larval cases followed the same pattern as larval growth, although with less variation between food items.

4. Larvae fed on Microspora exhibited the greatest increase in fat content, while that of the larvae fed on Picea and those in the fasting group decreased. The gross growth efficiency (G/I%) of Sericostoma (larva + case) ranged from 2% when fed on Picea to 34% when fed on Microspora. Consumption was significantly correlated with the nutrient content of food items, whereas G/I% and growth rate were only weakly related to food quality.

5. The growth of Sericostoma varies with diet and the food items sustaining highest growth rate are not necessarily the ‘typical’ shredder food resources.
Landscape spatial patterns in freshwater snail assemblages across Northern Highland catchments
Authors: Lewis David Bruce , Magnuson JohN. J.
Published: March 2003

1. Limnologists and landscape ecologists have illustrated how the spatial position of a lake in a landscape influences many of its properties, from the physical to the social. Taking a community ecology perspective, we investigated whether freshwater gastropod assemblages respond to lake landscape position.

2. We determined: (a) whether there is any spatial pattern among lakes in either the species richness or composition of gastropod assemblages; (b) the form of any spatial pattern; and (c) if any explanatory variables (e.g. dispersal corridors and limiting local conditions) show a similar pattern.

3. In three different hydrological catchments, snail species richness increased from isolated highland lakes to stream‐connected lowland lakes, probably reflecting increased colonization potential and less limiting local factors for lowland drainage lakes. Catchments appear to differ from one another with regard to relative species abundance, both in terms of macrophyte‐associated snail fauna and snails from all habitats aggregated. One or more historical events, such as chance dispersal, may have produced this pattern. Taken together, these results suggest that within‐catchment constraints produce repeated gradients in species richness, regardless of what species composition persists in the catchment.
Role of dissolved organic carbon in the attenuation of photosynthetically active and ultraviolet radiation in Adirondack lakes
Authors: Bukaveckas Paul A. , Robbins‐Forbes Marise
Published: March 2003

1. We surveyed eighty‐five lakes located in the Adirondack Mountain Region of New York State, U.S.A., to characterize the attenuation of photosynthetically active (PAR) and ultraviolet radiation (UVR) in relation to dissolved organic carbon (DOC) concentrations and pH. Attenuation of PAR was quantified in situ. Attenuation was also inferred by measuring the light absorption of filtered lake water samples at wavelengths (300, 340 and 440 nm) representing UV‐B, UV‐A and PAR.

2. Substantial variation in transparency was observed among lakes in this region. Attenuation depths (z1%) for PAR ranged from 0.5 to greater than 20 m, while inferred values for UV‐B and UV‐A ranged from a few centimetres to > 5 m. Median values of UV‐A penetration (0.75 m) and UV‐B penetration (0.45 m) corresponded to 11% (UV‐A) and 6% (UV‐B) of lake maximum depth.

3. Much of the variation in PAR and UVR attenuation was explained by differences in lake DOC. Univariate power models based solely on DOC accounted for 85% (PAR), 90% (UV‐A) and 91% (UV‐B) of the variation in absorption.

4. Attenuation and absorption coefficients were generally lower for recently acidified lakes compared to acidic and circumneutral lakes which have not undergone recent acidification. However, differences among these three groups of lakes were not statistically significant. Our results suggest that the effects of acidification on the optical properties of a regional population of lakes, even in an area experiencing widespread acidification, are relatively subtle in comparison with other factors contributing to inter‐lake variability.

5. The presence of near‐shore wetlands is probably a key factor influencing regional variability in DOC and light climate among Adirondack lakes. Temporal variability in climatic factors influencing wetland DOC production and export may mask more subtle influences on lake DOC associated with anthropogenic acidification.
Spatial variation in density, mean size and physiological condition of the holarctic amphipod Diporeia spp. in Lake Michigan
Authors: Nalepa Thomas F. , Hartson David J. , Buchanan Jennifer , Cavaletto Joann F. , Lang Gregory A. , Lozano Stephen J.
Published: March 2003

We examined spatial patterns in population characteristics (density, biomass, mean body length) and physiological condition (lipid content, length‐weight) of the amphipod Diporeia spp. in Lake Michigan by collecting samples at up to 85 sites in late summer 1994 and 1995. Variables were examined relative to water depth and three lake regions: south, central and north. Most major river systems are found in the south, and this region is more nutrient‐enriched compared to the north.

Over all sites, mean density was 5240‐2, biomass was 4.1g dry wt m‐2, and mean body length was 5 mm. While maximum densities were related to depth, with a peak at 30–70 m, greatest densities occurred on the west side of the lake, and low densities were found in the south‐east, north‐east and lower Green Bay. High densities in the west probably resulted from upwelling, and reduced densities in the south‐east may reflect food competition with Dreissena polymorpha (zebra mussel).

Lipid content, weight per unit length, and mean length declined with increased water depth, but depth‐related trends were most evident in the south. Overall, mean lipid content and weight per unit length were significantly lower in the south (16.6% dry wt, 0.59 mg at 5 mm body length) compared to the north (23.7% dry wt, 0.78 mg at 5 mm body length). These regional differences may have resulted from greater diatom availability in the north and competition from D. polymorpha in the south. Triacylglycerols and phospholipids were the dominant lipid classes in all three regions. Although the mean proportion of triacylglycerols, the energy‐storage lipid, was lower in the south than in the north, regional differences in proportions of lipid classes were not significant.

Mean lipid content and weight per unit length of Diporeia in the south were lower than values found in the late 1980s prior to the establishment of Dreissena. Mean lipid content of mature individuals is now at levels considered a minimum for successful reproduction.
The influence of macrophyte beds on plankton communities and their export from fluvial lakes in the St Lawrence River
Authors: Basu Ben K. , Kalff J. , Pinel‐Alloul B.
Published: March 2003

1. To determine the influence of macrophyte beds on plankton abundance within fluvial lakes of the St Lawrence River, planktonic components (macrozooplankton, heterotrophic bacteria, and phytoplankton as chlorophyll‐a [Chl‐a]) were sampled in Lake St Francis and Lake St Pierre during summer 1998. We tested the hypothesis that the abundance of planktonic components was higher within macrophyte beds in comparison to the more rapidly flushed open water areas of the fluvial lakes.  2. The large cross channel variation in zooplankton biomass was indeed correlated with the presence of dense beds of submerged macrophytes. Total macrozooplankton biomass was nine‐fold greater within the beds (mean=180 μg L−1 dry mass) than in either the open water or areas with only sparse vegetation (mean=20 μg L−1 dry mass).  3. Chl‐a and heterotrophic bacterial abundance were also higher in the beds, but only slightly so. There was no difference in total phosphorus or dissolved organic carbon concentrations between areas of dense vegetation, sparse vegetation or open water.  4. Macrophyte beds on the margins of the fluvial lakes allow the development of high planktonic abundance relative to the fast flowing central channel. Macrozooplankton biomass was much higher at the outflows of the lakes (∼50 μg L−1 dry mass) in comparison to the inflows (<20 μg L−1 dry mass). The increase is due to the transfer of organisms from submerged macrophyte beds into the central channel in the downstream quarter of the two lakes where the marginal littoral waters enter central channel waters.  5. Along rivers, shallow fluvial lakes appear to act as sources of plankton which is exported downstream during years of extensive littoral macrophyte development.
Tests of autotrophic picoplankton as early indicators of nutrient enrichment in an ultra‐oligotrophic lake
Authors: Schallenberg Marc , W. Burns Carolyn
Published: March 2003

1. The potential of picocyanobacteria as early indicators of changes in nutrient loading and trophic status was examined in an ultra‐oligotrophic lake.  2. The study consisted of in situ, short‐term, nutrient‐addition bioassays and surveys of picocyanobacterial variables and other indices of trophic state at six sites selected to include a range of localized nutrient loadings to the lake from its catchment. The bioassays and surveys were conducted six times throughout 1 year.  3. Experimental additions of small amounts of ammonium‐N and phosphate‐P did not stimulate picocyanobacterial growth, and phosphate additions often reduced picocyanobacterial growth rates.  4. A correlation analysis using pooled data from all sites and sampling dates showed that the abundance of aggregated picocyanobacteria was strongly correlated with nutrient concentration and ratios. Other variables, including the concentration of single‐cell picocyanobacteria, chlorophyll a and primary production, were poorly correlated with nutrients.  5. The results show that picocyanobacteria in oligotrophic lakes are sensitive to extremely small changes in nutrient availability and that they can respond in complex ways. The mechanisms by which they respond to such changes require further study before they can be used as bio‐indicators of nutrient enrichment.
Effects of waves on the early growth of Vallisneria americana
Authors: Doyle Robert D.
Published: March 2003

1. The impacts of 0.15‐m waves on the survival and short‐term growth and development of young Vallisneria americana plants were studied in experimental raceways. Young plants were planted at three depths within both wave and control raceways. Wave events were designed to simulate wave disturbances caused by boat traffic and were generated five or six times each day during the 67‐day experimental growth period. The 0.15‐m waves generated produced a maximum shear velocity of about 1.4 m s−1 as they swept over the plants.  2. All plants survived at all depths in both treatments. However, plants exposed to the waves accumulated significantly less total mass than controls. The total mass accumulation of wave‐exposed plants was only 50% of that of undisturbed plants. In addition, the plants experiencing the waves had significantly shorter leaves and produced significantly fewer daughter plants.  3. While plants under both wave and no wave treatments had a similar relative growth rate and both showed a net positive growth over the experimental period, those exposed to frequent wave energy developed more slowly due to continuous leaf loss caused by the waves. Plants exposed to even modest wave energy may spread more slowly and be less resilient to recovery from other forms of disturbance.
A stable carbon and nitrogen isotope study of lake food webs in Canada’s Boreal Plain
Authors: Beaudoin Catherine P. , Prepas Ellie E. , Tonn William M. , Wassenaar Leonard I. , Kotak Brian G.
Published: March 2003

1. Stable carbon and nitrogen isotope and fish stomach content analyses were used to investigate food webs in five relatively undisturbed lakes on the Boreal Plain of Canada. Stable isotope analysis was also used to determine the importance of external and internal carbon sources.

2. Overlap in the carbon and nitrogen signatures of primary producers made it difficult to determine unambiguously the feeding habits of many invertebrates. However, isotope analysis suggested that external carbon inputs were detectable in the aquatic food chains of the one lake with a short water residence time («1 year). In the other four lakes, with water residence times ≥1 year, autochthonous carbon was the only detectable carbon source in the food webs.

3. Food webs in these lakes spanned a range of four to five trophic levels. Both invertebrates and fish appeared to eat a variety of food, often feeding at more than one trophic level.

4. With the exception of one lake (SPH20), top predators in these lakes, northern pike (Esox lucius) and fathead minnows (Pimephales promelas), occupied similar trophic positions despite large differences in body size and trophic morphology. In SPH20, where there were two additional fish species, pike occupied a higher trophic position. However, all the top predators in each lake appeared to be omnivores and generalists.

5. The prevalence of omnivory and the apparent generalist feeding habits of fish in these lakes suggest that organisms are flexible in their feeding habits and that these food webs will be resilient to disturbance.
New Zealand stream crayfish: functional omnivores but trophic predators?
Authors: Parkyn Stephanie M. , Collier Kevin J. , Hicks Brendan J.
Published: March 2003

1. The feeding ecology of the crayfish Paranephrops planifrons in streams draining catchments in native forest and pastoral land was investigated using analyses of both stomach contents and stable isotopes of carbon and nitrogen. We aimed to (1) identify the energy sources of crayfish, (2) determine whether these were affected by ontogeny or land use change, and (3) assess the functional and trophic roles of crayfish in New Zealand hill‐country streams.

2. In native forest streams, crayfish stomach contents were dominated volumetrically by leaf detritus (>60%), but in pasture streams aquatic invertebrates constituted more than 40% of stomach volumes and leaf detritus <30%. Stable isotope analyses revealed that crayfish from both native forest and pasture streams incorporated energy from aquatic invertebrates into their body tissue but did not appear to utilize detritus for growth. Therefore, deforestation had little impact on crayfish energy sources.

3. In native forest streams, adult crayfish (≥20 mm orbit‐carapace length (OCL)) consumed greater amounts of leaf detritus than juvenile crayfish, but a corresponding change in stable isotope signatures was not detected. Ontogenetic shifts in diet were not consistent between land use suggesting that change in local habitat and food resources, as a result of land use change, affect crayfish food choice more than factors related solely to age or size.

4. Crayfish appear to occupy the trophic position of a predator, but by functioning as omnivores, they have dual roles as both predators and processors of organic matter. The use of gut content analysis in conjunction with stable isotope analyses revealed that the functional and trophic roles of P. planifrons differed, with implications for the interpretation of diet studies and understanding of the role of omnivores in food webs.