SwePub - search: L773:0046 5070 OR L773:1365 24...

Enumeration	Reference	Cover	Find
1.	Bjerring, Rikke, et al. (author) Subfossil Cladocera in relation to contemporary environmental variables in 54 Pan-European lakes 2009 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 54:11, s. 2401-2417 Journal article (peer-reviewed)abstract P>1. Changes in cladoceran subfossils in the surface sediments of 54 shallow lakes were studied along a European latitude gradient (36-68 degrees N). Multivariate methods, such as regression trees and ordination, were applied to explore the relationships between cladoceran taxa distribution and contemporary environmental variables, with special focus on the impact of climate. 2. Multivariate regression tree analysis showed distinct differences in cladoceran community structure and lake characteristics along the latitude gradient, identifying three groups: (i) northern lakes characterised by low annual mean temperature, conductivity, nutrient concentrations and fish abundance, (ii) southern, macrophyte rich, warm water lakes with high conductivity and high fish abundance and (iii) Mid-European lakes at intermediate latitudes with intermediate conductivities, trophic state and temperatures. 3. Large-sized, pelagic species dominated a group of seven northern lakes with low conductivity, where acid-tolerant species were also occasionally abundant. Small-sized, benthic-associated species dominated a group of five warm water lakes with high conductivity. Cladoceran communities generally showed low species-specific preferences for habitat and environmental conditions in the Mid-European group of lakes. Taxon richness was low in the southern-most, high-conductivity lakes as well as in the two northern-most sub-arctic lakes. 4. The proportion of cladoceran resting eggs relative to body shields was high in the northern lakes, and linearly (negatively) related to both temperature and Chl a, indicating that both cold climate (short growing season) and low food availability induce high ephippia production. 5. Latitude and, implicitly, temperature were strongly correlated with conductivity and nutrient concentrations, highlighting the difficulties of disentangling a direct climate signal from indirect effects of climate, such as changes in fish community structure and human-related impacts, when a latitude gradient is used as a climate proxy. Future studies should focus on the interrelationships between latitude and gradients in nutrient concentration and conductivity.
2.	Blindow, I, et al. (author) How important is the crustacean plankton for the maintenance of water clarity in shallow lakes with abundant submerged vegetation? 2000 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 44:2, s. 185-197 Journal article (peer-reviewed)abstract 1. We measured the abundance and biomass of filter-feeding microcrustacean zooplankton and calculated their grazing impact on phytoplankton biomass during summer in five shallow, mesotrophic to eutrophic lakes. For three of the lakes data exist both from years with dense submerged vegetation and low turbidity (the clearwater state), as well as from years characterised by sparse vegetation and high turbidity (the turbid state). In the other two lakes data are available only for clearwater conditions. 2. In all lakes conditions of dense vegetation and clear water coincided with a low abundance of crustacean plankton during summer. In the three lakes that shifted, the calculated biovolume ingested by crustacean plankton (filtering rate) was 3-11 times lower during clearwater conditions compared with turbid conditions. Because phytoplankton biomass was lower during clearwater conditions, however, daily grazing pressure from microcrustacea (expressed as percentage of phytoplankton biomass) did not differ between states. In three of the five lakes, grazers were estimated to take less than 10% of the phytoplankton biomass per day, indicating filtration by zooplankton was not the most important mechanism to maintain clearwater conditions. 3. High densities of Cladocera were found in three of the lakes within dense stands of Charophyta. However, these samples were dominated by plant-associated taxa that even during the night were rarely found outside the vegetation. This indicates that plant-associated zooplankton has no major influence on the maintenance of water clarity outside the vegetation. 4. Spring peak abundance of Cladocera was observed in three of the lakes. In two of these, where seasonal development was studied in both the clearwater and the turbid state, spring peaks were lower during the clearwater state. 5. Predation, low food availability or a combination of both may explain the low zooplankton densities. Phytoplankton may be limited by low phosphorus availability in the lakes dominated by Charophyta. Our results indicate that the importance of zooplankton grazing may have minor importance for the maintenance of the clearwater state in lakes with dense, well-established submerged vegetation.
3.	Carlsson, Nils, et al. (author) Lethal and non-lethal effects of multiple indigenous predators on the invasive golden apple snail (Pomacea canaliculata) 2004 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 49:10, s. 1269-1279 Journal article (peer-reviewed)abstract 1. We investigated the individual and combined effects of two predators (the climbing perch, Anabas testudineus, and the wetland crab, Esanthelphusa nimoafi) indigenous to wetlands in Laos, on the behaviour and survival of the invasive South American golden apple snail (Pomacea canaliculata). The snail is considered a pest, consuming large amounts of rice and other aquatic vegetation in the region. 2. Snail avoidance reactions to released predator chemical cues were investigated in aquaria while the effects of predators on a mixed snail population were studied in field enclosures that contained native aquatic plants (Salvinia cucullata, Ludwigia adscendens and Ipomoea aquatica). 3. In the aquaria experiment, neonate (2-3 mm) and medium-sized snails (8-10 mm) responded to fish chemical cues by going to the surface, whereas adult snails (35-40 mm) went to the bottom. In contrast, no size class of snails reacted to chemical cues released by crabs. 4. In the field experiment, fish reduced the abundance of neonate snails, and crabs reduced the abundance of all size classes. The effect of the combined predators could not be predicted from the mortality rate observed in single predator treatments. The survival of neonate and medium-sized snails was greater and of adults less than expected. The presence of predators did not affect egg production. Snails consumed significant amounts of plants despite the presence of predators. 5. Our findings suggest that some indigenous Asian predators have lethal and sublethal effects on P. canaliculata that depend on snail size and predator type. When in the presence of several predators the response of snails to one predator may either increase or decrease the vulnerability of snails to the others.
4.	Carlsson, Nils, et al. (author) Size-dependent effects of an invasive herbivorous snail (Pomacea canaliculata) on macrophytes and periphyton in Asian wetlands 2006 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 51:4, s. 695-704 Journal article (peer-reviewed)abstract 1. The invasive golden apple snail (Pomacea canaliculata), native to South America, is a serious pest on rice seedlings in south-east Asia and has also been shown to consume large amounts of macrophytes in natural wetlands, with large effects on ecosystem functioning. Earlier studies suggest that the snail undergoes an ontogenetic diet shift, feeding on algae and detritus as juveniles and shifting to aquatic macrophytes as adults. 2. Here, we study the effects of snail populations with a size-structure typical of either populations at an invasive front or the size-structure of established populations. In an enclosure experiment performed in a wetland in Laos, we compared treatments with small snails only (3 mm; invasive treatment) to treatments with small, medium sized (10 mm) and adult (> 25 mm) snails (established treatment). The effects of snail grazing on three aquatic macrophyte species and periphytic algae were quantified. 3. We found that snails of all sizes had a strong negative effect on the biomass of all macrophyte species and periphytic algae. There was no evidence of an ontogenetic diet change, i.e. snails in both the invasive and established treatments affected macrophyte biomass. Foraging was size-dependent in that small snails had higher relative foraging capacity (g plant consumed per g of snail) compared with medium and adult snails. Small snails, therefore, depressed growth of medium snails at increasing densities through exploitative competition for preferred resources, while adult snails did not grow at all in the presence of small snails. 4. Density dependence is common in freshwater invertebrates, including gastropod populations, but differences in size dependent foraging- and competitive-ability have rarely been demonstrated in this group of organisms. Knowledge about intra-specific differences in ecological performance may, however, both deepen our understanding of the processes that underlie population dynamics in invertebrates such as gastropods, and help develop control strategies for invasive golden apple snails.
5.	Gutseit, Kelly, et al. (author) Essential fatty acids and phosphorus in seston from lakes with contrasting terrestrial dissolved organic carbon content 2007 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 52:1, s. 28-38 Journal article (other academic/artistic)abstract 1. It is often assumed that lakes highly influenced by terrestrial organic matter (TOM) have low zooplankton food quality because of elemental and/or biochemical deficiencies of the major particulate organic carbon pools. We used the biochemical [polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA) - 20:5 omega 3] and elemental (C : P ratio) composition of particulate matter (PM) as qualitative measures of potential zooplankton food in two categories of lakes of similar primary productivity, but with contrasting TOM influence (clear water versus humic lakes). 2. C : P ratios (atomic ratio) in PM were similar between lake categories and were above 400. The concentration (mu g L-1) and relative content (mu g mg C-1) of EPA, as well as the particulate organic carbon concentration, were higher in the humic lakes than in the clear-water lakes. 3. Our results show high fatty acid quality of PM in the humic lakes. The differences in the biochemical quality of the potential zooplankton food between lake categories can be attributed to the differences in their phytoplankton communities. 4. High biochemical quality of the food can result in high efficiency of energy transfer in the food chain and stimulate production at higher trophic levels, assuming that zooplankton are able to ingest and digest the resource available.
6.	Gutseit, Kelly, et al. (author) Food quality for Daphnia in humic and clear water lakes 2007 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 52:2, s. 344-356 Journal article (peer-reviewed)abstract 1. Growth and reproduction of Daphnia fed lake seston were measured in two categories of meso- to eutrophic lakes differing with respect to terrestrial organic matter influence (humic and clear water lakes). The content of highly unsaturated fatty acids (HUFA), P and N, as well as the taxonomical composition of seston were analysed.2. Seston HUFA and C : P ratios were similar between lake categories, whereas C : N ratios were lower in the clear water lakes in both spring and summer. Despite the similarity in HUFA and P content of seston, Daphnia growth rate, clutch size and the proportion of gravid females were, respectively, about 1.5, 3 and 6 times higher in the clear water lakes.3. Differences in growth and reproduction were related to a combination of higher N content and good fatty acid quality of the seston in the clear water lakes. Relatively high biomass of edible algae, such as Rhodomonas sp. and Cryptomonas sp., in the clear water lakes, and differences in water pH likely contributed to the observed differences in Daphnia growth and reproduction between lake categories. Additionally, it is possible that Daphnia was energy limited in the humic lakes despite high particulate organic carbon (POC) concentrations, as the contribution of non-algal and detrital C to the POC pool was high.4. Our results suggest that dietary HUFA content has the potential to improve herbivore growth and reproduction if N and P are not limiting. N merits more attention in studies of zooplankton nutrition.
7.	Hansson, Lars-Anders, et al. (author) Conflicting demands on wetland ecosystem services: nutrient retention, biodiversity or both? 2005 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 50:4, s. 705-714 Journal article (peer-reviewed)abstract 1. Wetland ecosystems may, besides having considerable economical value, increase landscape biodiversity and function as traps for nutrients from land to freshwater- and marine systems. As a result of these features, wetlands are nowadays often protected and restored, and many countries have even initiated wetland construction programmes. 2. In the present study, we aim at increasing the knowledge on how to improve the design of a wetland with respect to both biodiversity and nutrient retention, by analysing physical, chemical and biological features of a large set of constructed wetlands. 3. Our results show that a combination of the wetland features, namely shallow depth, large surface area and high shoreline complexity are likely to provide a high biodiversity of birds, benthic invertebrates and macrophytes and to have high nitrogen retention, whereas a small, deep wetland is likely to be more efficient in phosphorus retention, but less valuable in terms of biodiversity. 4. Hence, among the features used to design new wetlands, area, depth and shoreline complexity have fundamental, and sometimes conflicting, effects on nutrient retention and biodiversity. This means that there are, within limits, possibilities to direct the ecosystem function of a specific wetland in desired directions.
8.	Hansson, Lars-Anders, et al. (author) Cyanobacterial chemical warfare alters zooplankton commuinty composition 2007 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 52:7, s. 1290-1301 Journal article (peer-reviewed)abstract 1) Toxic algal blooms widely affect our use of water resources both with respect to drinking water and recreation. However, it is not only humans, but also organisms living in freshwater and marine ecosystems, that may be affected by algal toxins. 2) In order to assess if cyanobacterial toxins affect the composition of natural zooplankton communities, we quantified the temporal fluctuations in microcystin concentration and zooplankton community composition in six lakes. 3) Microcystin concentrations generally showed a bimodal pattern with peaks in early summer and in autumn, and total zooplankton biomass was negatively correlated with microcystin concentrations. Separating the zooplankton assemblages into finer taxonomic groups revealed that high microcystin concentrations were negatively correlated with Daphnia and calanoid copepods, but positively correlated with small, relatively inefficient phytoplankton feeders such as cyclopoid copepods, Bosmina and rotifers. 4) In a complementary, mechanistic laboratory experiment using the natural phytoplankton communities from the six lakes, we showed that changes in in situ levels of microcystin were coupled with reduced adult size and diminished juvenile biomass in Daphnia. 5) We argue that in eutrophic lakes, large unselective herbivores, such as Daphnia, are ”sandwiched” between high fish predation and toxic food (cyanobacteria). In combination, these two mechanisms may explain why the zooplankton community in eutrophic lakes is generally comprised of small forms (e.g. rotifers and Bosmina) and selective raptorial feeders, such as cyclopoid copepods, whereas large, unselective herbivores, such as Daphnia, are rare. Hence, this cyanobacterial chemical warfare against herbivores may add to our knowledge on population and community dynamics among zooplankton in eutrophic systems.
9.	Hansson, Lars-Anders, et al. (author) Responses to fish predation and nutrients by plankton at different levels of taxonomic resolution 2004 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 49:12, s. 1538-1550 Journal article (peer-reviewed)abstract 1. To improve mechanistic understanding of plankton responses to eutrophication, a mesocosm experiment was performed in the shallow littoral zone of a south Swedish lake, in which nutrient and fish gradients were crossed in a fully factorial design. 2. Food chain theory accurately predicted total biomass development of both phyto- and zooplankton. However, separating zooplankton and algae into finer taxonomic groups revealed a variety of responses to both nutrient and fish gradients. 3. That both nutrients and fish are important for phytoplankton dynamics was seen more clearly when viewing each algal group separately, than drawing conclusions only from broad system variables such as chlorophyll a concentration or total phytoplankton biovolume. 4. In some taxa, physiological constraints (e.g. sensitivity to high pH and low concentrations of free CO2) and differences in competitive ability may be more important for the biomass development than fish predation, grazing by herbivorous zooplankton, and nutrient availability. 5. We conclude that food chain theory accurately predicted responses in system variables, such as total zooplankton or algal biomass, which are shaped by the dynamics of certain strong interactors ('keystone species'), such as large cladocerans, cyanobacteria and edible algae (<50 mum), whereas responses at finer taxonomic levels cannot be predicted from current theory.
10.	Hargeby, Anders, et al. (author) Increased growth and recruitment of piscivorous perch, Perca fluviatilis, during a transient phase of expanding submerged vegetation in a shallow lake 2005 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 50:12, s. 2053-2062 Journal article (peer-reviewed)abstract 1. In this study, we examine how a 7-year period of expanding submerged stonewort (Chara spp.) vegetation during a shift from turbid to clear water in a shallow lake influenced individual growth and population size structure of perch (Perca fluviatilis). We expected that a shift from phytoplankton to macrophyte dominance and clear water would improve feeding conditions for perch during a critical benthivorous ontogenetic stage, and enhance the recruitment of piscivorous perch. 2. Growth analysis based on opercula showed that growth during the second year of life was significantly higher in years with abundant vegetation than in years with turbid water and sparse vegetation. Growth was not affected during the first, third and fourth year of life. Stable isotope analyses on opercula from 2-year-old perch showed that the increase in growth coincided with a change in carbon source in the diet. Stable nitrogen ratio did not change, indicating that the increased growth was not an effect of any change in trophic position. 3. Following the expansion of submerged vegetation, perch size range and abundance of piscivorous perch increased in central, unvegetated areas of the lake. In stands of stoneworts, however, mainly benthivorous perch were caught, and size range did not change with time. 4. Our findings provide empirical support for the notion that establishment of submerged vegetation may lead to increased recruitment of piscivorous perch, because of improved competitive conditions for perch during the benthivorous stage. This is likely to constitute a benthic-pelagic feedback coupling, in which submerged vegetation and clear water promote the recruitment of piscivorous perch, which, in turn, may increase water clarity through top-down effects in the pelagic.
11.	Karlsson-Elfgren, I, et al. (author) Factors regulating recruitment from the sediment to the water column in the bloom-forming cyanobacterium Gloeotrichia echinulata 2004 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 49:3, s. 265-273 Journal article (peer-reviewed)abstract 1. The influence of light, temperature, sediment mixing and sediment origin (water depth) on the recruitment of the cyanobacterium Gloeotrichia echinulata was examined in the laboratory. 2. Light and temperature were the most important factors initiating germination in G. echinulata. 3. The extent of germination (recruited biovolume) was mainly regulated by temperature and sediment mixing. Furthermore, sediment mixing significantly enhanced the frequency of observed heterocysts and colonies. 4. Despite the fact that the deep and shallow sediments contained a similar number of akinete colonies, the highest recruitment occurred from shallow sediments, indicating that akinetes from shallow sediments have a higher viability than those from deeper parts of the lake. 5. Our results support the hypothesis that shallow sediments are more important than profundal sediments for the recruitment of G. echinulata to the pelagic zone.
12.	Lakowitz, Thomas, et al. (author) Tuning in to multiple predators: conflicting demands for shell morphology in a freshwater snail. 2008 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 53:11, s. 2184-2191 Journal article (peer-reviewed)abstract 1. We examined the response to chemical cues from fish and crayfish, two predators with contrasting feeding modes, and their single and combined effect on shell morphology in the freshwater snail Radix balthica. 2. Snails were subjected to four treatments: tench (Tinca tinca), signal crayfish (Pacifastacus leniusculus), a combination of tench and signal crayfish and no predators (control). Shell shape, crushing resistance and shell thickness were quantified. We also analyzed whether shape or shell thickness contributes most to crushing resistance. 3. Chemical cues from the fish induced a rounder shell shape in R. balthica, a thicker shell and a higher crushing resistance, whereas crayfish chemical cues had no effect on shell morphology, shell thickness or crushing resistance. Shell shape contributed more to crushing resistance than shell thickness. 4. The combined predator treatment showed an intermediate response between the fish and crayfish treatments. Shell roundness was reduced compared to the fish treatment, but the reduced crushing resistance that comes with a less rounded shell was compensated by an increased investment in extra shell material, exceeding that of the fish treatment. 5. Our study extends previous studies of multipredator effects on phenotypically plastic freshwater snails by showing that the snails are able to fine tune different elements of morphology to counter predator specific foraging modes.
13.	Moss, B, et al. (author) Continental-scale patterns of nutrient and fish effects on shallow lakes: synthesis of a pan-European mesocosm experiment 2004 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 49:12, s. 1633-1649 Journal article (peer-reviewed)abstract 1. Results are analysed from 11 experiments in which effects of fish addition and nutrient loading on shallow lakes were studied in mesocosms. The experiments, five in 1998, six in 1999, were carried out in six lakes, distributed from Finland to southern Spain, according to a standard protocol. 2. Effects of the treatments on 29 standard chemical, phytoplankton and zooplankton variables are examined to assess the relative importance of bottom-up (nutrient enrichment) and top-down (fish predation) effects. For each year, the experiments in different locations are treated as replicates in a meta-analysis. Results of individual experiments are then compared in terms of the patterns of significant influences of nutrient addition and fish predation with these overall results (the baseline), and between years in the same location. 3. The overall meta-analysis gave consistent results across the 2 years, with nutrient loading influencing all of the chemical variables, and on average 31% of primary producer and 39% of zooplankton variables. In contrast, fish influenced none of the chemical variables, 11% of the primary producer and 44% of the zooplankton variables. Nutrient effects on the system were thus about three times greater than fish effects, although fish effects were not inconsiderable. 4. The relative importance of nutrients and fish in individual experiments often differed between years at the same location and effects deviated to varying degrees from the baseline. These deviations were treated as measures of consistency (predictability) of conclusions in repeat experiments. Consistency increased southwards and this is interpreted as a consequence of more variable annual weather northwards. 5. The influence of nutrient loading was greater southwards and this was probably manifested through naturally greater annual macrophyte abundance in warmer locations in consequence of the longer plant growing-season. There was no trend in the relative importance of fish effects with latitude but this may partly be an artefact of the simple fish community used. These findings suggest that nutrient control should be a greater priority than biomanipulation in the restoration of eutrophicated shallow lakes in warm temperate regions. 6. Starting conditions affected the outcome of experiments. High initial concentrations of total phosphorus and planktonic chlorophyll a concentration (created by local conditions prior to the experiment) led to de-emphasis of the importance of nutrient loading in the experiment.
14.	Nilsson, Anders (author) Book review 2008 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 53:7, s. 1489-1490 Review (other academic/artistic)
15.	Nilsson, Erika, et al. (author) Facilitation and interference among three predators affect their consumption of a stream-dwelling mayfly 2006 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 51:8, s. 1507-1514 Journal article (peer-reviewed)abstract 1. We experimentally tested if a multiplicative risk model accurately predicted the consumption of a common mayfly at risk of predation from three predator species in New Zealand streams. Deviations between model predictions and experimental observations were interpreted as indicators of ecologically important interactions between predators. 2. The predators included a drift-feeding fish [brown trout (T), Salmo trutta], a benthivorous fish [galaxiid (G), koaro, Galaxias brevipennis] and a benthic predatory stonefly (S; Stenoperla sp.) with Deleatidium sp. mayflies as prey. Eight treatments with all predator species combinations and a predator-free control were used. Experiments were performed in aquaria with cobbles as predator refuges for mayflies and we measured the proportion of prey consumed after 6 h for both day and night trials. 3. Trout consumed a higher proportion of prey than other predators. For the two predator treatments we found less than expected prey consumption in the galaxiid + trout treatment (G + T) for both day and night trials, whereas a higher than expected proportion of prey was consumed during night time in the stonefly + trout (S + T) treatment. 4. The results indicate interference (G + T) and facilitation (S + T) between predators depending on predator identity and time of day. Thus, to make accurate predictions of interspecific interactions, it is necessary to consider the ecology of individual species and how differences influence the direction and magnitude of interactions.
16.	Nyström, Per, et al. (author) Crayfish in lakes and streams: individual and population responses to predation, productivity and substratum availability 2006 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 51:11, s. 2096-2113 Journal article (peer-reviewed)abstract 1. In a correlative study, we investigated the relative importance of fish predation, refuge availability and resource supply in determining the abundance and size distributions of the introduced and omnivorous signal crayfish (Pacifastacus leniusculus) in lakes and streams. Moreover, the biomass and food selection of predatory fish was estimated in each habitat type and stable isotopes of carbon and nitrogen were measured in perch (Perca fluviatilis), the dominant predator in the lakes, and in its potential food sources (crayfish, juvenile roach and isopods). 2. In lakes, crayfish were the most frequent prey in large perch (46%), followed by other macroinvertebrates (26%, including the isopod Asellus aquaticus) and small fish (25%). Crayfish and fish dominated the gut contents of large perch with respect to biomass. Nitrogen signatures showed that perch were one trophic level above crayfish (approx. 3.4 parts per thousand) and a two-source mixing model using nitrogen isotope values indicated that crayfish (81%) contributed significantly more to perch isotope values than did juvenile roach (19%). A positive correlation was found between the abundance of crayfish and the biomass of large perch. Crayfish abundance in lakes was also positively correlated with the proportion of cobbles in the littoral zone. Lake productivity (chlorophyll a) was positively correlated with crayfish size, but not with crayfish abundance. 3. In streams, brown trout (Salmo trutta) were the most abundant predatory fish. Gut contents of large trout in a forested stream showed that terrestrial insects were the most frequently found prey (60%), followed by small crayfish (27%) and isopods (27%). In contrast to lakes, the relative abundance of crayfish was negatively correlated with the total biomass of predatory fish and with total biomass of trout. However, abundance of crayfish at sites with a low biomass of predatory fish varied considerably and was related to substratum grain size, with fewer crayfish being caught when the substratum was sandy or dominated by large boulders. The mean size of crayfish was greater at stream sites with a high standing stock of periphyton, but neither predator biomass nor substratum grain size was correlated with crayfish size. 4. Our results suggest that bottom-up processes influence crayfish size in lakes and streams independent of predator biomass and substratum availability. However, bottom-up processes do not influence crayfish abundance. Instead, substratum availability (lakes) and interactions between predation and substratum grain size (streams) need to be considered in order to predict crayfish abundance.
17.	Nyström, Per (author) Non-lethal predator effects on the performance of a native and an exotic crayfish species 2005 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 50:12, s. 1938-1949 Journal article (peer-reviewed)abstract 1. I tested the hypothesis that the potential for non-lethal effects of predators are more important for overall performance of the fast-growing exotic signal crayfish (Pacifastacus leniusculus Dana) than for the slower growing native noble crayfish (Astacus astacus L.). I further tested if omnivorous crayfish switched to feed on less risky food sources in the presence of predators, a behaviour that could reduce the feeding costs associated with predator avoidance. 2. In a 2 month long outdoor pool experiment, I measured behaviour, survival, cheliped loss, growth, and food consumption in juvenile noble or signal crayfish in pools with either a caged predatory dragonfly larvae (Aeshna sp.), a planktivorous fish that do not feed on crayfish (sunbleak, Leucaspius delineatus Heckel), or predator-free controls. Crayfish had access to multiple food sources: live zooplankton, detritus and periphyton. Frozen chironomid larvae were also supplied ad libitum outside crayfish refuges, simulating food in a risky habitat. 3. Crayfish were mainly active during hours of darkness, with signal crayfish spending significantly more time outside refuges than noble crayfish. The proportion of crayfish outside refuges varied between crayfish species, time and predator treatment, with signal crayfish spending more time in refuges at night in the presence of fish. 4. Survival in noble crayfish was higher than in signal crayfish, and signal crayfish had a higher frequency of lost chelipeds, indicating a high level of intraspecific interactions. Crayfish survival was not affected by the presence of predators. 5. Gut-contents analysis and stable isotope values of carbon (δ13C) and nitrogen (δ15N) indicated that the two crayfish species had similar food preferences, and that crayfish received most of their energy from feeding on invertebrates (e.g. chironomid larvae), although detritus was the most frequent food item in their guts. Signal crayfish guts were more full than those of noble crayfish, but signal crayfish in pools with fish contained significantly less food and fewer had consumed chironomids compared with predator-free controls. Length increase of signal crayfish (35%) was significantly higher than of noble crayfish (20%), but signal crayfish in pools with fish grew less than in control pools. 6. This short-term study indicates that fish species that do not pose a lethal threat to an organism may indirectly cause reductions in growth by affecting behaviour and feeding. This may occur even though prey are omnivorous and have access to and consume multiple food sources. These non-lethal effects of predators are expected to be particularly important in exotic crayfish species that show a general response to fish, have high individual growth rates, and when their feeding on the most profitable food source is reduced.
18.	Olsson, Karin, et al. (author) Invasions and niche width: does niche width of an introduced crayfish differ from a native crayfish? 2009 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 54:8, s. 1731-1740 Journal article (peer-reviewed)abstract 1. Human activities have promoted the spread of species worldwide. Several crayfish species have been introduced into new areas, posing a threat to native crayfish and other biota. Invader success may depend on the ability to utilise a wide variety of habitats and resources. Successful invaders are generally expected to have broader niches and to be more plastic than non-invasive species. 2. Using stable isotope ratios of carbon and nitrogen we compared the niche widths of native noble crayfish and introduced signal crayfish, a successful invader of Swedish streams. The calculation of niche width took account of between-site differences in basal resource isotope signature ranges. We also assessed whether population density, prey biomass or prey diversity affected niche width. 3. At the species level, signal crayfish had twice the niche width of noble crayfish. However, individual populations of noble crayfish and signal crayfish in Swedish streams had similar niche widths. This suggests that signal crayfish has greater plasticity with respect to habitat utilisation and feeding than noble crayfish. Niche width in both species correlated positively with benthic invertebrate biomass and diversity, indicating that animal food sources are important for crayfish. 4. We find that assessing niche width in relation to invader success can be a useful tool trying to predict the impact of invasions on different scales. The findings in this study suggest that invaders and natives will have a similar impact on the stream scale whereas the invader will have a larger impact on the regional scale due to the ability to utilise a wider range of streams.
19.	Persson, Anders, 1956-, et al. (author) Effects of benthivorous fish on biogeochemical processes in lake sediments 2006 In: Freshwater Biology. - West Sussex, UK : Wiley-Blackwell. - 0046-5070 .- 1365-2427. ; 51:7, s. 1298-1309 Journal article (peer-reviewed)abstract 1. Studies of aquatic environments have shown that community organisation may strongly affect ecosystem functioning. One common phenomenon is a change in nutrient level following a shift in the fish community composition. Although several hypotheses have been suggested, there is no consensus on which mechanisms are involved. Our study evaluated indirect effects of benthivorous fish on the biogeochemical processes at the sediment-water interface separately from direct effects caused by nutrient excretion or sediment resuspension.2. We assigned field enclosures to three treatments representing typical pond communities; without fish, addition of approximately 10 small tench or addition of one large bream. After one summer, we monitored the water chemistry, benthic invertebrates and periphyton in the enclosures and sampled sediment cores for laboratory analysis of biochemical process rates (oxygen, phosphorus and nitrogen exchange between sediment and water, and denitrification rate).3. Fish had strong negative effects on benthic invertebrates, but weaker effects on periphyton, organic content and porosity of the sediment. Moreover, there were significant positive fish effects on both phosphorus and nitrogen concentrations in the water. However, there were no general treatment effects on sediment processes that could explain the treatment effects on water chemistry in the enclosures.4. Hence, overall treatment effects attenuated along the chain of interactions. We conclude that the observed effect of benthic fish on water chemistry was probably because of direct effects on nutrient excretion or resuspension of sediment. The similarity between bream and tench treatments suggests large niche complementarity despite their different habitat preferences.
20.	Pålsson, Carina, et al. (author) Net heterotrophy in Faroe Islands clear-water lakes: causes and consequences for bacterioplankton and phytoplankton 2005 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 50:12, s. 2011-2020 Journal article (peer-reviewed)abstract 1. Five oligotrophic clear-water lakes on the Faroe Islands were studied during August 2000. Algal and bacterial production rates, community respiration, and CO2 saturation were determined. In addition, we examined the plankton community composition (phytoplankton and heterotrophic nanoflagellates) and measured the grazing pressure exerted by common mixotrophic species on bacteria. 2. High respiration to primary production (6.6–33.2) and supersaturation of CO2 (830–2140 μatm) implied that the lakes were net heterotrophic and that the pelagic heterotrophic plankton were subsidised by allochthonous organic carbon. However, in spite of the apparent high level of net heterotrophy, primary production exceeded bacterial production and the food base for higher trophic levels appeared to be mainly autotrophic. 3. We suggest that the observed net heterotrophy in these lakes was a result of the oligotrophic conditions and hence low primary production in combination with an input of allochthonous C with a relatively high availability. 4. Mixotrophic phytoplankton (Cryptomonas spp., Dinobryon spp. and flagellates cf. Ochromonas spp.) constituted a large percentage of the plankton community (17–83%), possibly as a result of their capacity to exploit bacteria as a means of acquiring nutrients in these nutrient poor systems.
21.	Ranåker, Lynn, et al. (author) Effects of brown and turbid water on piscivore-prey fish interactions along a visibility gradient 2012 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 57, s. 1761-1768 Journal article (peer-reviewed)abstract 1. Environmental changes such as eutrophication and increasing inputs of humic matter (brownification) may have strong effects on predatorprey interactions in lakes through a reduction in the visual conditions affecting foraging behaviour of visually oriented predators. 2. In this experiment, we studied the effects of visual range (25200 cm) in combination with optically deteriorating treatments (algae, clay or brown humic water) on predatorprey interactions between pike (Esox lucius) and roach (Rutilus rutilus). We measured effects on reaction distance and strike distance for pike and escape distance for roach, when pike individuals were exposed to free-swimming roach as well as to roach held in a glass cylinder. 3. We found that reaction distance decreased with decreasing visual range caused by increasing levels of algae, clay or humic matter. The effect of reaction distance was stronger in turbid water (clay, algae) than in the brown water treatment. 4. Strike distance was neither affected by visual range nor by optical treatment, but we found shorter strike distances when pike attacked roach using visual cues only (roach held in a cylinder) compared to when pike could use multiple senses (free-swimming roach). Escape distance for roach was longer in turbid than in brown water treatments. 5. Changes in environmental drivers, such as eutrophication and brownification, affecting the optical climate should thus have consequences for the strength of predatorprey interactions through changes in piscivore foraging efficiency and prey escape behaviour. This in turn may affect lake ecosystems through higher-order interactions.
22.	Romare, Pia, et al. (author) Variation in spatial and temporal gradients in zooplankton spring development: the effect of climatic factors 2005 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 50:6, s. 1007-1021 Journal article (peer-reviewed)abstract 1. We examined the temporal and spatial heterogeneity of zooplankton in lake surface waters during the spring of 3 years in Lake Washington, U.S.A., a large lake with a high production of sockeye salmon fry. 2. We show large within-season and among-year variation in the horizontal distribution of temperature, chlorophyll a concentration, and zooplankton in the lake. The main pattern, a delay in zooplankton population increase from the north- to the south-end of the lake, recurred in each year and was persistent within each spring. 3. The delay is primarily caused by the development of a temperature gradient during spring warming, as cold mountain water enters the south end of the lake, while warm water enters the north end via a river draining a nearby lake. Climate factors, such as air temperature and precipitation during winter and spring, appear to influence the extent of the delay of zooplankton increase. 4. If the climate continues to warm, the temporal disconnection in zooplankton development between lake areas immediately influenced by cold river inflow and areas that are influenced by spring warming may increase in magnitude. Thus, the different areas of the lake may not contribute equally to fish production.
23.	Skov, Christian, et al. (author) Evaluating stocking of YOY pike Esox lucius as a tool in the restoration of shallow lakes 2007 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 52:9, s. 1834-1845 Journal article (peer-reviewed)abstract 1. Stocking of piscivores in shallow, eutrophicated lakes to reduce cyprinid densities is a common approach in lake restorations. Young-of-the-year (YOY) pike Esox lucius are frequently used to reduce cyprinid densities, but their effectiveness is equivocal. This study uses a simple model to assess the efficacy of pike stocking as a lake restoration tool. 2. The model evaluates YOY pike consumption in relation to different survival and growth patterns, timing of stocking, degree of piscivory of pike as well as YOY cyprinid growth patterns and productivity. The parameters used in the model are obtained from field surveys in eight study lakes stocked with YOY pike as well as from the literature. 3. Our model showed that all parameters studied were important for predicting the effects of pike stocking on cyprinids. In particular, body size at stocking, cyprinid production and pike survival were good predictors of biomanipulation success. 4. However, our model showed that only under very specific circumstances will stocking of YOY pike result in a reduction of YOY cyprinid densities large enough to affect water quality. 5. The findings of this study question the efficacy of pike stocking as an appropriate and reliable tool for restoration programmes in shallow lakes, and indicate that when used efforts should be made to optimize the timing of stocking in relation to YOY cyprinid production and to increase the stocking body size of the pike.
24.	Stephen, D, et al. (author) Continental-scale patterns of nutrient and fish effects on shallow lakes: introduction to a pan-European mesocosm experiment 2004 In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 49:12, s. 1517-1524 Journal article (peer-reviewed)abstract 1. Shallow lake ecosystems are normally dominated by submerged and emergent plants. Biological stabilising mechanisms help preserve this dominance. The systems may switch to dominance by phytoplankton, however, with loss of submerged plants. This process usually takes place against a background of increasing nutrient loadings but also requires additional switch mechanisms, which damage the plants or interfere with their stabilising mechanisms. 2. The extent to which the details or even major features of this general model may change with geographical location are not clear. Manipulation of the fish community (biomanipulation) has often been used to clear the water of algae and restore the aquatic plants in northerly locations, but it is again not clear whether this is equally appropriate at lower latitudes. 3. Eleven parallel experiments (collectively the International Mesocosm Experiment, IME) were carried out in six lakes in Finland, Sweden, England, the Netherlands and Spain in 1998 and 1999 to investigate the between-year and large-scale spatial variation in relationships between nutrient loading and zooplanktivorous fish on submerged plant and plankton communities in shallow lakes. 4. Comparability of experiments in different locations was achieved to a high degree. Cross-laboratory comparisons of chemical analyses revealed some systematic differences between laboratories. These are unlikely to lead to major misinterpretations. 5. Nutrient addition, overall, had its greatest effect on water chemistry then substantial effects on phytoplankton and zooplankton. Fish addition had its major effect on zooplankton and did not systematically change the water chemistry. There was no trend in the relative importance of fish effects with latitude, but nutrient addition affected more variables with decreasing latitude. 6. The relative importance of top-down and bottom-up influences on the plankton differed in different locations and between years at the same location. The outcome of the experiments in different years was more predictable with decreasing latitude and this was attributed to more variable weather at higher latitudes that created more variable starting conditions for the experiments.
25.	Strand, John A., et al. (author) Dynamics of submerged macrophyte populations in response to biomanipulation 2001 In: Freshwater Biology. - Chichester, United Kingdom : Wiley-Blackwell. - 0046-5070 .- 1365-2427. ; 46:10, s. 1397-1408 Journal article (peer-reviewed)abstract 1. A 6-year study (1992-97) of changes in submerged vegetation after biomanipulation was carried out in the eutrophicated Lake Finjasjon, Southern Sweden. Ten sites around the lake were revisited each year. At each site five samples of above-ground biomass were taken at 10 cm water depth intervals. An investigation of the seed bank at the 10 sites, and a grazing experiment where birds and large fish were excluded was also conducted. 2. Between 1992 and 1996, in shallow areas (water depth < 3 m), vegetation cover 2 increased from < 3 to 75% and above-ground biomass from < 1 to 100 g DW m(-2). Mean outer water depth increased from 0.3 to 2.5 m. Elodea canadensis and Myriophyllum spicatum accounted for > 95% of the increase in biomass and plant cover. The following year (1997), however, cover and above-ground biomass decreased, mainly attributable to the total disappearance of E. canadensis. Secchi depth increased after biomanipulation until 1996, but decreased again in 1997. 3. Total and mean number of submerged species increased after biomanipulation, probably as a result of the improved light climate. However, after the initial increase in species number there was a decrease during the following years, possibly attributed to competition from the rapidly expanding E. canadensis and M. spicatum. The lack of increase in species number after the disappearance of E. canadensis in 1997 implies that other factors also affected species richness. 4. A viable seed bank was not necessary for a rapid recolonization of submerged macrophytes, nor did grazing by waterfowl or fish delay the re-colonization of submerged macrophytes. 5. Submerged macrophytes are capable of rapid recolonization if conditions improve, even in large lakes such as Finjasjon (11 km(2)). Species that spread by fragments will increase rapidly and probably outcompete other species. 6. The results indicate that after the initial Secchi depth increase, probably caused by high zooplankton densities, submerged vegetation further improved the light climate. The decrease in macrophyte biomass in 1997 may have caused the observed increase in phosphorus and chlorophyll a, and the decrease in Secchi depth. We suggest that nutrient competition from periphyton, attached to the macrophytes, may be an important factor in limiting phytoplankton production, although other factors (e.g. zooplankton grazing) are also of importance, especially as triggers for the shift to a clear-water state.

Skapa referenser, mejla, bekava och länka

Permalink

Träfflista för sökning "L773:0046 5070 OR L773:1365 2427 "

Refine your search

Year