bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous conditions in the south‐eastern Bering Sea 1997: linkages among climate, weather, ocean, and Biology
Authors: Napp Jeffrey M. , Hunt George L.
Published: March 2003

In 1997, the Bering Sea ecosystem, a productive, high‐latitude marginal sea, demonstrated that it responds on very short time scales to atmospheric anomalies. That year, a combination of atmospheric mechanisms produced notable summer weather anomalies over the eastern Bering Sea. Calm winds, clear skies, and warm air temperatures resulted in a larger‐than‐normal transfer of heat to surface waters and the establishment of a shallow mixed layer. In spring, significant new production occurred below the shallow pycnocline over the Middle Shelf, depleting the subpycnocline nutrient reservoir that normally exists during summer. Following the depletion of nitrate and silicate from the system, a sustained (≥ 4 months) bloom of coccolithophores (Emiliania huxleyi) was observed – a phenomenon not previously documented in this region. Summer Middle Shelf Domain copepod concentrations were higher for some species in 1997 than in the early 1980s. Warmer surface water and lack of wind mixing also changed the basic distribution of hydrographic regimes on the south‐eastern shelf and altered the strength and position of fronts or transition zones where apex predators seek elevated food concentrations. The Inner Front was well inshore of its normal position, and adult euphausiids (the primary prey of short‐tailed shearwaters, Puffinus tenuirostris) were unavailable at, and shoreward of, the front in autumn. High shearwater mortality rates followed the period of low euphausiid availability. Some, but not all, of these anomalous conditions re‐occurred in 1998. These observations are another demonstration that the structure and function of marine ecosystems are intimately tied to forcing from the atmosphere. Alteration of climatological forcing functions, expressed as weather, can be expected to have large impacts on this ecosystem and its natural resources.
On the temporal variability of the physical environment over the south‐eastern Bering Sea
Authors: Stabeno P. J. , Bond N. A. , Kachel N. B. , Salo S. A. , Schumacher J. D.
Published: March 2003

During 1997 and 1998, unusual physical conditions occurred in the Bering Sea: strong May storms and calm conditions in July; record high sea surface temperature; a shallow wind mixed layer; a fresher‐than‐normal water column; and abnormal cross‐shelf currents. Accompanying these conditions were changes in the dominant phytoplankton, a die‐off of seabirds, increased sightings of large whales and diminished returns of salmon. Changes to the physical environment during 1997 and 1998 are placed in context of historical meteorological and oceanographic data sets. Although 1997 had the warmest sea surface temperature ever observed on the south‐east Bering Sea shelf, the heat content of the water column was cooler than average. In contrast, during 1998, the sea surface temperature was cooler than in 1997 but the water column had significantly higher heat content. During recent years, the water column has freshened over the middle shelf because of increased sea ice and reduction of on‐shelf transport of the saline, high‐nutrient water from the slope. The timing of the spring bloom is directly related to the presence of ice. When ice is advected over the south‐east shelf during March/April an early, sharp phytoplankton bloom occurs. The absence of ice during this critical time is associated with a May/June bloom.
The potential for advective exchange of the early life stages between the western and eastern Baltic cod (Gadus morhua L.) stocks
Authors: Hinrichsen H.‐H. , Böttcher U. , Oeberst R. , Voss R. , Lehmann A.
Published: March 2003

In order to clarify mechanisms influencing the reproductive success of Baltic cod (Gadus morhua L.), a modelling exercise was performed to examine the effects of the wind‐driven circulation on the transport of early life stages between the western and eastern Baltic. Because the different stocks spawn in different areas and environments at different times of the year, the occurrence of variable age/length distributions of juveniles within the different potential nursery areas can be explained by the circulation pattern. A three‐dimensional circulation model of the Baltic was utilized to investigate the temporal evolution of egg and larval distributions of the western Baltic cod stock, which spawns preferentially in the Danish Straits, in Kiel Bay as well as in Mecklenburg Bay. For different scenarios (1988 and 1993), within‐ and between‐year variability of egg and larval transport showed large differences, primarily due to variations in wind forcing. In 1988, relatively low and variable wind forcing prevailed, whereas, due to sustained strong, mainly westerly, winds, in January 1993, the recent major Baltic inflow to the Baltic Sea occurred. Differences in contributions of early life stages from the western to the eastern cod stocks, depending on the physical forcing conditions, suggest that this process can be controlled by variations of atmospheric forcing conditions. The potential for early life stages from the western Baltic cod stock to drift into the Arkona Basin and the Bornholm Basin, and to contribute there to the juvenile population, has been recognized as being mainly due to strong westerly winds. During cold winters, retention of eggs, larvae and juveniles within their original spawning grounds may predominate. Transport of cod early life stages from the Øresund, as well as from the Great Belt, can occur only during periods of strong westerly winds, but significant eastwards orientated drift from Kiel Bay and Mecklenburg Bay was also evident during periods of minor westerly wind influence.
Relationships among vertically structured in situ measures of turbulence, larval fish abundance and feeding success and copepods on Western Bank, Scotian Shelf
Authors: Reiss ChristianS. , Anis Ayal , Taggart Christopher T. , Dower JohnF. , Ruddick Barry
Published: March 2003

Using vertically stratified data of the abundance of silver hake (Merluccius bilinearis) larvae and concentrations of copepods collected in the field, we examine relationships among the vertical distribution of larval fish, their potential prey, feeding success and water column turbulence. Water column turbulence and associated stratification parameters were estimated from: (i) in situ measures of turbulent kinetic energy dissipation (ɛ) provided by an EPSONDE profiler; (ii) in situ wind speed; (iii) the Richardson number (Ri); and (iv) the buoyancy frequency (N2). Small (< 5 mm total length) silver hake were more abundant in the least turbulent waters (i.e. at a minimum in the rate of dissipation of turbulent kinetic energy, ɛ < 10–7 W kg−1; Ri > 0.25; N2 > 0.001 (rad s–1)2). Partial correlations amongst ɛ, N2 and small hake larvae were significant only for N2. The abundance of larger (> 5 mm total length) hake larvae was positively correlated with depth and was not associated with either ɛ or N2. Vertical distributions of three potential prey (classified by stage) were variable. Early stage copepodids were positively correlated with N2 and negatively correlated with ɛ. We found no evidence of diel distribution patterns for small (< 5 mm total length) hake larvae or for any of the developmental stages of the copepods examined. Neither estimate of water column turbulence inferred from wind speed nor from Ri was meaningfully related to in situ estimates of ɛ or to larval fish abundance. Feeding success, measured either as prey items (gut)–1, average prey length, or total prey volume (gut)–1, was not related to predicted encounter rates between days. However, the average prey length (gut)–1 was significantly (P < 0.01) related to water column turbulence. These conflicting results suggest that the relationship between larval feeding and the environment is more complicated than assumed. We conclude that without substantial high resolution in situ examination of the relationship between the vertical distributions of turbulence, larvae and their prey, the growing acceptance in the secondary literature that turbulence has a positive and biologically meaningful effect on trophic interactions between fish and their zooplankton prey (a generalization based largely on modelling and laboratory experiments) is premature.
Denitrification in river sediments: relationship between process rate and properties of water and sediment
Authors: García‐ruiz  , Pattinson  , Whitton
Published: March 2003

1. A survey was made of denitrification and nitrous oxide (N2O) production in river sediments at fifty sites in north‐east England during one season in order to investigate the relationship between rates and environmental factors likely to influence these processes. The sites were chosen to represent a wide range of physical and chemical conditions. Denitrification rate and N2O production were measured within 5 h of sampling using the slurry acetylene blockage technique.

2. Denitrification rate ranged from less than 0.005–260 nmol N g–1 DW h–1, tending to increase in a downstream direction. N2O production ranged from negative values (net consumption) to 13 nmol N2O‐N g–1 DW h–1 and accounted for 0–115% of the N gases produced.

3. Denitrification rate and N2O concentration in the sediment were correlated positively with nitrate concentration in the water column, water content of the sediment and percentage of fine (< 100 μm) particles in the sediment.

4. The variation in denitrification rate was satisfactorily explained (64% total variance) by a model employing measurements of water nitrate and water content of sediments. No simple or multiple relationship was found for N2O production.
Differences in predation among morphotypes of the rotifer Asplanchna silvestrii
Authors: Hampton Stephanie E. , Starkweather Peter L.
Published: March 2003

1. Interactions were observed between three morphotypes of the predatory rotifer Asplanchna silvestrii and six different prey (Brachionus plicatilis, B. rotundiformis, B. pterodinoides, B. satanicus, Hexarthra jenkinae and copepod nauplii) to understand the differences in feeding abilities among morphotypes that may have led to the evolution of this predator polymorphism. The outcome of predation events was affected significantly, both by predator morphotype and prey type. Predator morphotypes also interacted differently with different prey types.

2. The two smaller morphotypes, the saccate and the cruciform, responded similarly to prey overall, except that the smallest morphotype (saccate) was unable to ingest the most mobile prey (nauplii) and less able to ingest relatively large prey (B. plicatilis). The largest morphotype, the campanulate, had the highest encounter rate with prey, but the lowest probability of attack after encounter, so that it consumed far fewer prey per feeding bout than did the smaller morphotypes. This may have been because campanulates prefer larger prey than used in this study.

3. Highly mobile prey (H. jenkinae and copepod nauplii) were much less susceptible to predation than the less mobile Brachionus species. While evasiveness reduced attacks by saccates and cruciforms, campanulates did not have a significantly lower attack rate on H. jenkinae and copepod nauplii than on less evasive prey. Large body size moderately defended B. plicatilis against ingestion by saccates only. The short‐spined B. satanicus was the only prey that was rejected after capture, resulting in lower ingestion probabilities for B. satanicus than other brachionid prey.
Manipulation of habitat quality: effects on chironomid life history traits
Authors: Stanko‐Mishic Sandra , And J. Kevin Cooper , Silver Pamela
Published: March 2003

1. To understand how habitat heterogeneity affects organisms, the present authors measured the response of chironomid life‐histories to single patch types in a controlled laboratory experiment. The objective was to determine whether the size and type of leaf particles in the substratum affect development rate and survival of larvae, and the fecundity of the resulting adults.

2. Chironomus riparius larvae were raised in sand supplemented with dogwood, Cornus florida, (a rapid decomposer) or American sycamore, Platanus occidentalis, (a refractory decomposer) leaves fully crossed in a factorial design with four leaf particle sizes (0.2, 0.5, 1 and 5 cm2), or in sand only.

3. Development time was shorter in dogwood habitats than sycamore habitats, and shorter in sycamore habitats than in sand habitats. Survival was higher and larval head capsule lengths of instars III and IV were larger in dogwood than in sycamore or sand habitats. Development time was longer and head capsule lengths of instars III and IV were smaller in habitats with 5‐cm2 leaf particles than in 0.2‐, 0.5‐ and 1‐cm2 particle size treatments. Female thorax length (a measure of fecundity) did not differ among treatments.

4. The present authors conclude that, for C. riparius confined to a single patch type, fitness is significantly enhanced when the patch contains small particles of dogwood (labile) leaves.
Examination of endopelic and epilithic algal community structure employing scanning electron microscopy
Authors: Greenwood J. L. , Clason T. A. , Lowe R. L. , Belanger S. E.
Published: March 2003

1. Biological community structure within a stream periphyton mat and sediment core was examined using scanning electron microscopy. Samples were fixed, freeze‐fractured and viewed under normal conditions with a scanning electron microscope.

2. This technique enabled the analysis of orientation and spatial distribution of algal cells within the three‐dimensional algal communities.

3. Fractured samples from a periphyton mat and sediment core at the Procter & Gamble Experimental Stream Facility showed layering of some dominant diatom species, such as Nitzschia dissipata, Melosira varians and Gyrosigma attenuatum. The spatial relationship of nematodes as potential algal predators was also revealed.

4. Advantages, disadvantages and potential future applications of this freeze fracture technique are discussed.
Demographic responses of adult Mesocyclops thermocyclopoides (Copepoda, Cyclopoida) to different plant and animal diets
Authors: Kumar R.A.M. , Ramakrishna Rao T.
Published: March 2003

1. We studied the effects of food type on adult females of the cyclopoid copepod Mesocyclops thermocyclopoides.

2. The test diets, covering a size range of 5–1250 μm, included a toxic strain of Microcystis aeruginosa, three algae (i.e. Chlorella vulgaris, Scenedesmus acutus and Chlorogonium elongatum), three ciliates (i.e. Tetrahymena pyriformis, Stylonychia notophora and S. mytilus), two rotifers (i.e. Brachionus angularis and B. calyciflorus) and two cladocerans (i.e. Ceriodaphnia cornuta and Moina macrocopa), and a selected subset of them in a second experiment.

3. Experimental diets were started with the last juvenile instar (C5) and data were collected on the newly moulted adult females. The survival of the copepod was less affected by food type than its reproductive output. Net reproductive rate was significantly higher with animal than with plant food. Algal diets enriched with organic extracts supported higher reproductive rates than unenriched diets of the same algal species. The large and motile alga Chlorogonium gave performances which approached those of ciliate diets.

4. The pre‐reproductive period of M. thermocyclopoides was shorter and its post‐reproductive period longer with animal than with plant diets, the latter being chiefly caused by a briefer period between clutches.

5. The frequency of infertile clutches increased in later clutches, indicating possible sperm limitation in females which have mated only once.

6. There was a significant, positive correlation between the size of food particles and the lifetime reproductive output of M. thermocyclopoides, with more than an order of magnitude difference in the total fecundity between the largest and the smallest food items.

7. Mesocyclops thermocyclopoides achieved the highest total fecundity with ‘mixed’ food, and thus, reflected the adaptive value of omnivory for this species.
Diversity, distribution and larval habitats of North Swedish blackflies (Diptera: Simuliidae)
Authors: Malmqvist Björn , Zhang Yixin , Adler Peter H.
Published: March 2003

1. Blackfly species richness and community structure were analysed at fifty‐six sites in northern Sweden in two seasons. The sites were situated in a wide range of streams and rivers from small springbrooks, bog streams and lake‐outlet streams to medium‐sized forest rivers and large rivers draining montane regions.

2. Thirty‐nine blackfly species were found, with between two and thirteen species per site. Neither species richness nor abundance could be related to the environmental variables measured.

3. An analysis of labral fan size of blackflies indicated a clear trend for the prevalence of larvae with small fans in large rivers and larvae with larger fan size in small streams. Similarly, fan size related to current velocities so that large fans were associated with slow current velocities and small fans with high velocities.

4. A strong relationship existed between species composition and habitat, as seen in ordination by non‐metric multidimensional scaling. The relationship found between fan size and habitat size‐related variables, such as channel width, depth, velocity and substratum particle size, along with longitude and altitude, in partial least squares regression analysis offered an explanation of the species composition–habitat relationship.

5. In addition to testing that distributions of blackfly larvae reflect morphological traits, we tested two general hypotheses pertaining to distribution patterns: (a) that blackfly communities show bimodal distributions; and (b) that their distributions are nested. Neither of these two hypotheses was supported by our observations. However, widespread blackfly species were locally more abundant than those found at relatively few sites, thus showing a positive abundance–occupancy relationship.
Community concordance between the fish and aquatic birds of lakes in northern Alberta, Canada: the relative importance of environmental and biotic factors
Authors: Paszkowski Cynthia A. , Tonn William M.
Published: March 2003

1. Community concordance measures the degree to which patterns in community structure in a set of sites are similar between two different taxonomic groups. Although seldom incorporated into studies of lake ecosystems, aquatic birds can be influenced by the same environmental features of lakes which affect fish and invertebrates, and can interact with these organisms directly as predators, competitors or prey. We surveyed lakes in north‐central Alberta, Canada, to determine if co‐occurring fish and aquatic bird assemblages displayed concordance, and assessed the relative importance of environmental and biotic factors in contributing to observed concordance.

2. In 41 lakes (3–305 ha), we encountered seven species of fish and thirty‐one avian taxa which subsequently were used in multivariate analyses. Fish assemblages dominated by large piscivores were in large deep lakes, whereas fishless lakes and lakes with only small‐bodied fish were small and shallow, and thus, prone to winter hypoxia. Bird assemblages displayed three general patterns: (a) small shallow lakes supported a ‘core’ of widespread species (between three and eight species per lake); (b) large, deep lakes supported more species (between 11 and 16), including large, aerially foraging piscivores; and (c) large, shallow lakes supported the most species (between 15 and 23), including many ducks.

3. Randomization tests of matrix concordance and Mantel tests both showed that fish and bird assemblages were significantly concordant. Concordance reflected the fact that both groups were strongly affected by the same key environmental factors, principally lake size and maximum depth, and to a lesser extent, productivity and geographic isolation. Direct interactions between birds and fish, such as predation and competition, appeared to play much smaller roles in shaping the two assemblages.
Calcium carbonate deposits reduce predation pressure on Gammarus fossarum from salamander larvae
Authors: Ruff Heike , Maier Gerhard
Published: March 2003

We studied the lime deposits on Gammarus fossarum from a tufa brook in Southern Germany. Between 20 and 75% of the gammarids collected carried calcium carbonate deposits at the dorsal part of the pleon segments. Average weight of deposits ranged between 0.6 mg on small and 1.7 mg on large specimens and constituted 60–20% of specimens' dry weights.

Predator‐prey experiments with salamander larvae and gammarids showed that significantly fewer prey with deposits were eaten than without deposits and that the differences in predation risks between prey with vs. prey without deposits were greatest in small and medium sized specimens.

Lime deposits changed the feel or taste and the activity patterns of gammarids. Gammarids with deposits were rejected significantly more often by the predators than gammarids without deposits. Medium sized specimens with deposits, which suffered a great predation risk, were significantly less active than specimens of the same size category without deposits.

Lime deposits did not increase conspicousness or decrease escape ability of prey. Prey with deposits were attacked by predators with the same frequency and captured with the same success as prey without deposits.

Lime deposits may afford effective protection from salamander predation in some natural habitats. Predation impact on gammarids by salamander larvae may be low, however, because larval density was very low in most places (< 1 m‐2) and because larvae are only present for a limited time until they start metamorphosis.
Littoral microcrustacea in Lake 302S in the Experimental Lakes Area of Canada: acidification and recovery
Authors: Hann Brenda J. , Turner Michael A.
Published: March 2003

The littoral microcrustacean community (Cladocera and Copepoda) was examined from 1989 to 1991 in a lake experimentally acidified to pH 4.5, and from 1992 to 1997 during the early stages of pH recovery.

Cladoceran abundance declined significantly from 1989 to 1991 (pH 4.5), but species richness did not change. Acantholeberis curvirostris, Simocephalus serrulatus, Latona spp. (Latona setifera, L. parviremis), and all species of chydorid Cladocera declined markedly in abundance while at pH 4.5. The abundance of cyclopoid copepods was low and Ceriodaphnia and calanoid copepods were absent.

Recovery of the community was subsequently monitored as pH was incrementally changed to a target pH 5.1 in 1992 and 1993, and to 5.8 in 1994–97. Species richness remained unchanged. Chydorid cladocerans remained at low abundance in 1992, and only Chydorus cf. brevilabris increased substantially from 1993 to 1996. Non‐chydorid Cladocera increased in abundance in 1992, declined again in 1993, then gradually increased (mainly due to Ophryoxus gracilis) in 1994–96. All species declined in 1997 as minnows recolonized the lake. The calanoid copepod Leptodiaptomus minutus was present in low numbers in 1997.

The microcrustacean community in the littoral zone of Lake 302S has not yet shown consistent signs of recovery from acidification.
Factors governing nutrient status of mountain lakes in the Tatra Mountains
Authors: Kopàcöek JiR. öå , Stuchlåk& Evzö.E. N. ,   dagger, Strasökrab VeörA. , Psöenàk Petra
Published: March 2003

1. Nutrient and chlorophyll a levels, and bacterial numbers of 84 glacial lakes in the Tatra Mountains (Slovakia and Poland, Central Europe) were determined to assess the impact of catchment vegetation and water acidity on lake trophic status.

2. Catchment vegetation was the crucial factor governing nutrient content of lakes.

3. Concentrations of organic carbon, organic nitrogen, and chlorophyll a, and bacterial numbers were tightly correlated with total phosphorus (TP) content. Their levels were the highest in forest lakes, then decreased in alpine lakes with decreasing amount of catchment vegetation and soil cover, and were the lowest in lakes situated in bare rocks.

4. The above pattern was further modified by lake water acidity. Concentrations of TP, organic carbon, and chlorophyll a were lower in alpine lakes with pH between 5 and 6 than in more or less acid alpine lakes. Zooplankton was absent in all alpine lakes with pH between 5 and 6.

5. Nitrate concentrations followed an inverse trend to TP; lowest values were in forest lakes, then increased with decreasing amount of catchment soils and vegetation. Within the lakes of the same type of catchment vegetation, nitrate concentrations were negatively correlated to TP. N‐saturation of catchment areas and lake primary production were dominant processes controlling nitrate levels in lakes and nitrate contribution to lake acidification.
Response of a zooplankton community to the addition of unsaturated fatty acids: an enclosure study
Authors: Boersma Maarten , Stelzer Claus‐Peter
Published: March 2003

1. The effect of the addition of emulsions with different fatty acid composition to a semi‐natural zooplankton community was studied in enclosures.  2. The reactions of different taxa in the zooplankton community to the addition of the emulsions were different. The copepods showed almost no reaction, nor did the selective cladocerans (Bosmina) or rotifers (Synchaeta or Polyarthra). The non‐selective filterfeeding cladocerans Daphnia and Ceriodaphnia, and the rotifer Keratella, showed responses to the addition of the emulsions.  3. Keratella showed the highest density in the enclosures with high amounts of highly unsaturated fatty acids added, whereas both Daphnia and Ceriodaphnia reached the highest numbers in the enclosures where we added emulsions of saturated fatty acids only.  4. Our results suggest that different taxa may be limited by different factors, even though they use similar food sources. Hence, we conclude that it is very difficult to generalize on the limiting factors in aquatic systems.
Trophic structure, species richness and biodiversity in Danish lakes: changes along a phosphorus gradient
Authors: Jeppesen Erik , Peder Jensen Jens , SØndergaard Martin , Lauridsen Torben , Landkildehus Frank
Published: March 2003

1. Using data from 71, mainly shallow (an average mean depth of 3 m), Danish lakes with contrasting total phosphorus concentrations (summer mean 0.02–1.0 mg P L−l), we describe how species richness, biodiversity and trophic structure change along a total phosphorus (TP) gradient divided into five TP classes (class 1–5: <0.05, 0.05–0.1, 0.1–0.2, 0.2–0.4,> 0.4 mg P L−1).  2. With increasing TP, a significant decline was observed in the species richness of zooplankton and submerged macrophytes, while for fish, phytoplankton and floating‐leaved macrophytes, species richness was unimodally related to TP, all peaking at 0.1–0.4 mg P L−1. The Shannon–Wiener and the Hurlbert probability of inter‐specific encounter (PIE) diversity indices showed significant unimodal relationships to TP for zooplankton, phytoplankton and fish. Mean depth also contributed positively to the relationship for rotifers, phytoplankton and fish.  3. At low nutrient concentrations, piscivorous fish (particularly perch, Perca fluviatilis) were abundant and the biomass ratio of piscivores to plankti‐benthivorous cyprinids was high and the density of cyprinids low. Concurrently, the zooplankton was dominated by large‐bodied forms and the biomass ratio of zooplankton to phytoplankton and the calculated grazing pressure on phytoplankton were high. Phytoplankton biomass was low and submerged macrophyte abundance high.  4. With increasing TP, a major shift occurred in trophic structure. Catches of cyprinids in multiple mesh size gill nets increased 10‐fold from class 1 to class 5 and the weight ratio of piscivores to planktivores decreased from 0.6 in class 1 to 0.10–0.15 in classes 3–5. In addition, the mean body weight of dominant cyprinids (roach, Rutilus rutilus, and bream, Abramis brama) decreased two–threefold. Simultaneously, small cladocerans gradually became more important, and among copepods, a shift occurred from calanoid to cyclopoids. Mean body weight of cladocerans decreased from 5.1 μg in class 1 to 1.5 μg in class 5, and the biomass ratio of zooplankton to phytoplankton from 0.46 in class 1 to 0.08–0.15 in classes 3–5. Conversely, phytoplankton biomass and chlorophyll a increased 15‐fold from class 1 to 5 and submerged macrophytes disappeared from most lakes.  5. The suggestion that fish have a significant structuring role in eutrophic lakes is supported by data from three lakes in which major changes in the abundance of planktivorous fish occurred following fish kill or fish manipulation. In these lakes, studied for 8 years, a reduction in planktivores resulted in a major increase in cladoceran mean size and in the biomass ratio of zooplankton to phytoplankton, while chlorophyll a declined substantially. In comparison, no significant changes were observed in 33 ‘control’ lakes studied during the same period.
Plankton population dynamics: food web interactions and abiotic constraints
Authors: Rothhaupt Karl O.
Published: March 2003

1. In this introduction, I try to follow some developments in plankton ecology, how they have led to current research topics, and how the contributions in this issue of Freshwater Biology are related to these fields of research.  2. Due to several favourable features, such as small size, short generation time and a relatively homogeneous habitat, planktonic organisms remain ideal subjects for theoretical and experimental population ecology.  3. Important current research topics involve: (1) the control of plankton communities by external abiotic factors; (2) bottom‐up (limitation by resources) and top‐down (control by predators) effects in the food web; (3) the importance of dormant resting stages and benthic–pelagic coupling in plankton dynamics; (4) costs and benefits of the mixotrophic strategy, i.e. the ability to combine a phototrophic and a phagotrophic mode of nutrition.
Temperature reaction norms of Daphnia magna: the effect of food concentration
Authors: Giebelhausen B. , Lampert W.
Published: March 2003

1. The effects of temperature and food concentration on the fitness of Daphnia magna were tested in a 4×4 factorial flow‐through design. Food ranged from 0.1 to 1.0 mg C L−1 and temperature ranged from 15 to 30 °C.  2. The juvenile growth rate (gj) was used to construct reaction norms for temperature at varying food concentrations. Two clones isolated from the same pond at different seasons did not differ with respect to their temperature responses. Reaction norms had the shape of an optimum curve with highest values around 20 °C. There was a significant temperature–food interaction as the temperature response was most pronounced when the food was not limiting.  3. Differences in fitness were a consequence of different responses of physiological parameters to food and temperature. Age and size at first reproduction, as well as egg numbers, decreased with increasing temperature and decreasing food concentration.  4. As the temperature effect was strongest at the highest food concentrations, it can be concluded that environmental warming may affect D. magna more through a temperature rise earlier in spring rather than in summer.
Multi‐scale effects of resource patchiness on foraging behaviour and habitat use by longnose dace, Rhinichthys cataractae
Authors: Thompson Andrew R. , Petty J. Todd , Grossman Gary D.
Published: March 2003

1. We examined the response of a predatory benthic fish, the longnose dace (Rhinichthys cataractae), to patchiness in the distribution of benthic macroinvertebrates on cobbles at three hierarchical spatial scales during summer and autumn 1996, and spring 1997 in a southern Appalachian stream.  2. At the primary scale (four to five individual cobbles separated by <1 m), the intensity of foraging was not correlated with the biomass of benthic macroinvertebrates/cobble, regardless of season.  3. At the secondary scale (i.e. foraging patches <5 m in diameter) we found that benthic macroinvertebrates were patchily distributed in summer, but not in autumn or spring. Concomitantly, in summer, longnose dace foraged on cobbles with a significantly higher biomass of benthic macronvertebrates than nearby, randomly selected cobbles with similar physical conditions (i.e. longnose dace tended to avoid low‐prey foraging patches). In contrast, when benthic macroinvertebrates were distributed homogeneously (spring and autumn), dace did not select patches with a significantly higher biomass of benthic macroinvertebrates than that available on randomly selected cobbles.  4. At the tertiary scale (i.e. stream reaches 11–19 m long), the biomass of benthic macroinvertebrates (per cobble per reach) was patchily distributed (i.e. differed significantly among reaches) in all seasons. Among reaches with physical characteristics preferred by longnose dace, (i.e. erosional reaches dominated by cobble/boulder substratum and high current velocity), we detected a significant, positive correlation between the biomass of benthic macroinvertebrates/cobble and longnose dace density in all seasons.  5. Our results demonstrated that both spatial and temporal patchiness in resource availability influenced significantly the use of both foraging patches and stream reaches by longnose dace.
A model for accurate drift estimation in streams
Authors: Faulkner Hazel , Copp Gordon H.
Published: March 2003

1. This paper explores the experimental difficulties involved with the use of drift nets in small streams, and outlines a method whereby the estimation of drift density (number of specimens m−3 of water) can be improved.

2. Changes in the filtering efficiency of the net caused by trapping of organic debris (‘clogging’) has the effect of reducing net entrance velocities, causing errors in the calculation of sampled water volume, and thus drift density. A model of the reductions in net entrance velocity based on empirical measurements of trapped debris is developed.

3. Cross‐sectional velocity calculations suggest that errors can also be introduced into drift density calculations by positioning sampling nets only on the bed. A method to allow this effect is demonstrated.

4. As adjustments to the calculation of sampled volume are required when sampling in rivers that undergo marked changes in discharge during the sampling period, a method whereby these effects can be accommodated to improve drift density estimations is also outlined.

5. The results of this study imply that theoretical links between flow hydraulics and short‐term drift behaviour are poorly understood.
The mating and reproductive biology of the freshwater planktonic calanoid copepod Eudiaptomus gracilis
Authors: Berger Irmgard , Maier Gerhard
Published: March 2003

1. Quantitative aspects of the mating and reproductive biology of the freshwater planktonic calanoid copepod Eudiaptomus gracilis, including duration and frequency of mating, duration of various phases of the oviducal cycle, egg production rate and adult longevity were studied under laboratory conditions. One set of copepods was fed the alga Chlamydomonas reinhardtii whose density was adjusted to 2 × 105 cells mL−1 (about 10 mg C L−1), another set was fed a mixed diet consisting of natural plankton (copepod nauplii, small rotifers and large algae) in the size range of 50–150 μm (dry mass approximately 90 mg L−1).

2. The entire mating process, from the grasping of the female by the male’s right geniculate antennule to the separation of the pair, lasted about 2 min. Spermatophore placement started at about 30 s to 1 min after mating began and took approximately 1 min. Immediately after the spermatophore had been fixed in the female’s genital segment, the pair separated.

3. The total oviducal cycle, including the gravid phase where the female carried ripe oocytes and the non‐gravid phase where the female did not carry ripe oocytes, lasted about 5–6 days. The non‐gravid phase was particularly long; it was longer than the gravid phase and constituted 62–72% of the total cycle.

4. Mating and spermatophore placement usually occurred with gravid females although occasionally (in 30 of 200 observations) spermatophores were attached in the genital segment of non‐gravid females. Generally two to four, but up to seven, spermatophores were observed at a female’s genital segment at the same time.

5. Clutch size, rate of egg production and adult longevity depended on food. When fed on C. reinhardtii, females carried 7–8 eggs clutch−1, produced a mean of 1.3 clutches and lived 14 days on average. When fed natural mixed food, females carried 10 eggs clutch−1, produced 5.6 clutches and lived 37 days on average.

6. Removal of males after the first clutch resulted in no further egg production. Re‐mating is necessary in E. gracilis for continuous clutch production and the production of fertile eggs.

7. Mating duration is comparatively short and the non‐gravid phase comparatively long in E. gracilis. This could be an adaption to the life in the pelagic zone of the lake, where fish predators are present. Fish select ovigerous females, pairs in copula and, probably, females with ripe oocytes which make them conspicuous. Thus, a short mating duration and a prolonged period without conspicuous oocytes, can be advantageous.
Behaviour of roach (Rutilus rutilus L.) altered by Ligula intestinalis (Cestoda: Pseudophyllidea): a field demonstration
Authors: Loot Géraldine , Brosse Sébastien , Lek Sovan , Guégan Jean‐François
Published: March 2003

1. We studied the influence of a cestode parasite, the tapeworm Ligula intestinalis (L.) on roach (Rutilus rutilus L.) spatial occupancy in a French reservoir (Lake Pareloup, South‐west of France).

2. Fish host age, habitat use and parasite occurrence and abundance were determined during a 1 year cycle using monthly gill‐net catches. Multivariate analysis [generalized linear models (GLIM)], revealed significant relationships (P < 0.05) between roach age, its spatial occupancy and parasite occurrence and abundance.

3. Three‐year‐old roach were found to be heavily parasitized and their location toward the bank was significantly linked to parasite occurrence and abundance. Parasitized fish, considering both parasite occurrence and abundance, tended to occur close to the bank between July and December. On the contrary, between January and June no significant relationship was found.

4. These behavioural changes induced by the parasite may increase piscivorous bird encounter rate and predation efficiency on parasitized roach and therefore facilitate completion of the parasite’s life cycle.
How well do laboratory experiments explain field patterns of zooplankton emergence?
Authors: Cáceres Carla E. , Schwalbach Michael S.
Published: March 2003

1. We conducted a laboratory experiment to explore potential mechanisms driving variation in zooplankton emergence from diapausing eggs observed in Oneida Lake, NY, U.S.A. We hypothesized that variation in timing of ice‐out (date of thawing of ice) between 1994 and 1995, which resulted in variation in photoperiod–temperature cues, contributed to the differences in the observed field patterns. Environmental chambers were used to establish weekly photoperiod–temperature combinations that reproduced natural conditions in Oneida Lake in 1994 and 1995. In addition, a third treatment (‘dark’) exposed eggs only to the changes in temperature. We recorded zooplankton emergence for 2.5 simulated ice‐free seasons.

2. Nine cladoceran taxa were found to hatch, but only Daphnia pulicaria in large numbers. Hatching of D. pulicaria was recorded throughout the season in the two light treatments and sporadically in the dark treatment. The early ice‐out treatment had the highest emergence, followed by the late ice‐out and dark treatments. Among taxa, there was temporal segregation with five hatching in the early weeks of sampling and two taxa hatching during the middle weeks. Alona hatched late in the first year, but earlier in the second year.

3. We compared our laboratory results of D. pulicaria hatching with the field data obtained by Cáceres (1998). Hatching was continuous in the laboratory, whereas a synchronous spring emergence was found in the field. However, in both the laboratory and the field, more D. pulicaria hatched under conditions reflecting ice‐out occurring in March as opposed to April. Because differences in rates and timing of emergence can affect the population and community dynamics of pelagic systems, we suggest caution when applying laboratory results to field populations.
The relative importance of shading and nutrients on algal production in subtropical streams
Authors: Mosisch Thorsten D. , Bunn Stuart E. , Davies Peter M.
Published: March 2003

1. We used artificial substrata in forested and open streams in South‐East Queensland, Australia, to determine the relative importance of shading from riparian vegetation and of nutrients on periphyton growth, and whether nitrogen and/or phosphorus limited algal productivity.

2. Nutrient‐diffusing substrata consisting of agar enriched with N, P and N + P, and controls without nutrients, were deployed in duplicate at 15 sites in headwater streams with riparian canopy cover ranging from 0 to 88%.

3. Shading was the over‐riding factor controlling periphyton biomass accrual on the artificial substrata, with nutrients playing a relatively minor role. Microscopic examination of periphyton scrapings taken after 7 weeks revealed that diatoms dominated on the artificial substrata in shaded streams, whereas filamentous green algae dominated the algal assemblage in the more open canopy streams.

4. Whilst nutrients had little effect on the accrual of algal biomass compared with riparian shading, there was evidence that nitrogen, and not phosphorus, stimulated periphyton production in streams with sufficient light.
Phosphorus release from sediments in hardwater eutrophic lakes: the effects of redox‐sensitive and ‐insensitive chemical treatments
Authors: Burley Kim L. , Prepas Ellie E. , Chambers Patricia A.
Published: March 2003

1. Phosphorus (P) release from bottom sediments is an important source of nutrient enrichment in many lakes in sedimentary basins, such as those in western Canada. On the Boreal Plain, sediment P release is particularly strong during periods of seasonal anoxia.

2. In this study, the effects of reduction–oxidation (redox)‐sensitive and ‐insensitive chemicals on P release were examined in sediment cores collected from three eutrophic lakes.

3. Contrary to expectations, redox‐sensitive treatments were no more effective at lowering total phosphorus (TP) in sediment cores than some redox‐insensitive treatments. Redox‐sensitive treatments with FeCl3 and FeCl3 + O2 reduced TP to 8 and 6%, respectively, of reference concentrations, whereas redox‐insensitive treatments with alum or lime + alum reduced TP to 14% of reference concentrations. Lime and O2 treatments reduced TP concentrations to 35 and 52% of reference concentrations, respectively.

4. The fraction of P that adsorbed and co‐precipitated with iron and aluminium in the sediment cores was low (non‐apatite phosphorus fractions < 5%), suggesting that P release was controlled by apatite solubility and bacterial metabolism.
Primary production and phytoplankton composition in relation to DOC input and bacterioplankton production in humic Lake Örträsket
Authors: Drakare Stina , Blomqvist Peter , Bergström Ann‐Kristin , Jansson Mats
Published: March 2003

1. The biomass and production of picophytoplankton, large phytoplankton and heterotrophic bacterioplankton were measured in humic Lake Örträsket, northern Sweden during four consecutive summers.

2. High flow episodes, carrying fresh dissolved organic carbon (DOC) into the lake, always stimulated heterotrophic bacterial production at the expense of primary production. Primary production never exceeded bacterial production for approximately 20 days after such an episode had replenished epilimnial DOC. We suggest that allochthonous DOC is an energy source that stimulates bacterioplankton that, because of their efficient uptake of inorganic nutrients, are then able to outcompete phytoplankton. After the exhaustion of readily available DOC, phytoplankton were able to dominate epilimnion production in Lake Örträsket.

3. Biomass production was higher when dominated by phytoplankton than by bacterioplankton, despite a similar utilization of nutrients in the epilimnion throughout the summer. We propose that different C : N : P ratios of bacterioplankton and phytoplankton permit the latter to produce more carbon (C) biomass per unit of available inorganic nutrients than bacterioplankton.
Effects of substratum stability on diversity of stream invertebrates during baseflow at two spatial scales
Authors: Miyake Yo , Nakano Shigeru
Published: March 2003

1. The effects of substratum stability on the diversity of stream invertebrates were assessed at two spatial scales in a Japanese stream during baseflow, from May to June 1998. Deposition and erosion were examined separately as distinct elements of substratum stability by a newly developed method using small steel pins. Stream invertebrates were sampled after 28 days of measurement of substratum stability. We also measured physical environmental variables, current velocity and depth, and food resource parameters including periphyton and particulate organic matter (POM) standing crops.

2. At the scale of the habitat patch, the effects of substratum stability on invertebrates were overwhelmed by those of POM standing crop. Moreover, higher taxon richness at high abundance may simply result from a higher likelihood of more taxa being included in samples. Therefore, this small scale revealed no role for substratum stability in explaining spatial pattern of community diversity.

3. At the reach scale (n=10), taxon richness and evenness peaked at an intermediate level of deposition, whereas invertebrate abundance did not show any significant relationship. This result, and the pattern of relative abundance of common taxa, implies that the diversity of stream invertebrates was determined by subtle substratum movements and by the habitat preference of each taxon.

4. The difference in the determinant of community parameters between the habitat patch and the reach affirm the importance of a cross‐scale analysis to choose an appropriate spatial scale for investigating the community structure of stream invertebrates. Prominent effects of substratum stability, particularly the deposition of substratum particles, during baseflow suggest that subtle and constant movement of small substratum particles can contribute to determine the diversity of stream invertebrates.