| 1. |
- Becares, Eloy, et al.
(författare)
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Effects of nutrients and fish on periphyton and plant biomass across a European latitudinal gradient
- 2008
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Ingår i: Aquatic Ecology. - : Springer Science and Business Media LLC. - 1386-2588 .- 1573-5125. ; 42:4, s. 561-574
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Tidskriftsartikel (refereegranskat)abstract
- Replicated, factorial mesocosm experiments were conducted across Europe to study the effects of nutrient enrichment and fish density on macrophytes and on periphyton chlorophyll a (chl-a) with regard to latitude. Periphyton chl-a densities and plant decline were significantly related to nutrient loading in all countries. Fish effects were significant in a few sites only, mostly because of their contribution to the nutrient pool. A saturation-response type curve in periphyton chl-a with nutrients was found, and northern lakes achieved higher densities than southern lakes. Nutrient concentration and phytoplankton chl-a necessary for a 50% plant reduction followed a latitudinal gradient. Total phosphorus values for 50% plant disappearance were similar from Sweden (0.27 mg L-1) to northern Spain (0.35 mg L-1), but with a sharp increase in southern Spain (0.9 mg L-1). Planktonic chl-a values for 50% plant reduction increased monotonically from Sweden (30 mu g L-1s) to Valencia (150 mu g L-1). Longer plant growing-season, higher light intensities and temperature, and strong water-level fluctuations characteristic of southern latitudes can lead to greater persistence of macrophyte biomass at higher turbidities and nutrient concentration than in northern lakes. Results support the evidence that latitudinal differences in the functioning of shallow lakes should be considered in lake management and conservation policies.
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| 2. |
- de Eyto, E, et al.
(författare)
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The distribution of chydorids (Branchiopoda, Anomopoda) in European shallow lakes and its application to ecological quality monitoring
- 2003
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Ingår i: Archiv für Hydrobiologie. - : Schweizerbart. - 0003-9136. ; 156:2, s. 181-202
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Tidskriftsartikel (refereegranskat)abstract
- This study describes the chydorid (Branchiopoda, Anomopoda) assemblages from 66 European shallow lakes, and presents data relating the assemblages to lake type and ecological quality. Forty species, out of a total recorded European fauna of 60 species, were found in the study sites. No significant differences were found between chydorid assemblages associated with rock and plant substrata. Patterns of distribution were best explained primarily by latitude and pH. Chlorophyll-a, total phosphorus, water temperature and Secchi depth were also correlated with assemblage descriptors. Alonopsis elongata, Alona rectangula, Alonella excisa and Pleuroxus uncinatus were shown to have higher prevalence in certain lake types. The dominance of Chydorus sphaericus in a third of the study sites was linked to eutrophication and high levels of chlorophyll-a. The relationship between chydorids and lake ecological quality was more apparent at species rather than community level. This study identifies important typological factors affecting chydorid distribution, and confirms that patterns of chydorid distribution previously reported from regional studies hold true across Europe.
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| 3. |
- Gyllström, Mikael, et al.
(författare)
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Bioturbation as Driver of Zooplankton Recruitment, Biodiversity and Community Composition in Aquatic Ecosystems
- 2008
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 11:7, s. 1120-1132
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Tidskriftsartikel (refereegranskat)abstract
- In an experimental study we assessed if benthic bioturbating invertebrates affect the recruitment (hatching) of zooplankton from the sediment, and if this effect persists as differences in the zooplankton community in the water column, that is, if bioturbation quantitatively stimulates benthic-pelagic coupling. We investigated the effects of four different benthic invertebrates (Asellus aquaticus, Chironomus plumosus, Tubifex tubifex in the presence or absence of the predator Sialis lutaria). In total, 45 zooplankton taxa hatched from the sediment and the hatching success of some of these was dependent on the species identity of the bioturbating invertebrate. The predator Sialis reduced the abundance of all three invertebrate species, but tended to positively influence the zooplankton recruitment rates, possibly through increasing the activity of the bioturbating invertebrates. The most striking effect of bioturbation on the hatching and pelagic zooplankton community properties was that, on average, 11% more species hatched in the Asellus treatment than in any other treatment. This was also mirrored in the zooplankton water column community where, on average, 7% more species established a viable population in treatments with Asellus as bioturbator. In a complementary field survey, Asellus was more common in littoral than in profundal sediments. Because Asellus strongly affected recruitment of zooplankton in our experiment, we argue that bioturbation may partly explain why recruitment of resting stages of both phyto- and zooplankton is generally higher in littoral than in profundal areas.
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| 4. |
- Gyllström, Mikael, et al.
(författare)
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Dormancy in freshwater zooplankton: Induction, termination and the importance of benthic-pelagic coupling
- 2004
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Ingår i: Aquatic Sciences. - : Springer Science and Business Media LLC. - 1420-9055 .- 1015-1621. ; 66:3, s. 274-295
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Forskningsöversikt (refereegranskat)abstract
- For a short-lived organism, such as a freshwater zooplankter, the ways of coping with years of local recruitment failure are either to disperse between habitats and recolonise or to disperse in time through diapause. Diapause is common among freshwater zooplankton and is generally seen as a way to escape periods of harsh environmental conditions. The egg-bank or pool of diapausing copepodites in lake sediments resulting from the production of diapausing stages has several implications for zooplankton ecology, genetics, and evolution which we outline in this review. The presence of a benthic dormant stage also creates a coupling between the benthic habitat and the pelagic, and we argue that zooplankton phenology is a result of selective forces in both habitats. The spatial distribution of diapausing eggs appears to be governed by random resuspension dynamics coupled with higher hatching rates in shallow waters. For diapausing copepodites, however, an active choice of where and how deep to enter the sediment may affect their distribution. In a reanalysis of published data, we found a size-dependent bathymetric distribution and vertical distribution in the sediment of diapausing cyclopoid copepodites. Our review of published laboratory studies showed that predictors of seasonal change such as photoperiod and temperature were the only type of cues used for the termination of diapause. We also found a relation between generation length and the type of cue used for diapause induction: copepods mainly used seasonal cues from the abiota, rotifers mainly used cues from the biotic environment, and cladocerans used a mix of both types. We describe patterns in emergence timing and contribution to population dynamics from studies using in situ estimation of emergence, and conclude that hatching from dormant stages may qualitatively and quantitatively affect zooplankton population dynamics and seasonal succession.
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| 5. |
- Gyllström, Mikael
(författare)
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Ecology of zooplankton communities: climate, dormancy, and benthic-pelagic coupling
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes how influences, such as top down and bottom up forces, shape zooplankton communities in shallow lakes. I have also extended the traditional food-web theory by investigating the effects of climate on total biomass, taxonomic composition, and temporal properties of zooplankton communities. A field experiment showed that the total biomass of both phytoplankton and zooplankton increased with nutrient enrichment. This increase was, however, lower for zooplankton and higher for phytoplankton when planktivorous fish was present, indicating cascading effects of top down forces from fish to phytoplankton. A study of 81 lakes, covering a climate gradient from Southern Spain to Northern Sweden, confirmed the role of lake productivity (total phosphorus concentration) as the most important predictor of total phytoplankton and zooplankton biomass. Moreover, macrophyte cover and climate also significantly affected total zooplankton biomass. Increased macrophyte cover led to an increase in total zooplankton biomass through its positive effect on macrophyte associated and benthic taxa. Enrichment mainly affected pelagic taxa and the main effect of enrichment was an increase in cyclopoid copepods relative to calanoid copepods and an increased proportion of Daphnia of the total cladoceran biomass. Warmer climate was associated with lower biomass of zooplankton, mainly through its negative impact on pelagic species. Enrichment and increased temperature (especially the combination of these two) also reduced the temporal stability of zooplankton communities. Zooplankters are usually considered to be short-lived, transient creatures, but their ability to produce resistant dormant stages can prolong their life span considerably and carry populations through periods during which active stages are unable to survive. Dormancy has implications for zooplankton ecology, genetic diversity and evolution of species. In a field study hatching from diapausing eggs was shown to affect seasonal succession in a cladoceran community only during spring. An analysis of published data together with my own data suggest that cues, used to break dormancy, are exclusively of an abiotic type, signalling seasonal change. The type of cues used to induce diapause, on the other hand, appears related to the generation length or life span with long-lived taxa relying more on seasonal cues, whereas short-lived taxa rely on cues signalling environmental change on a shorter time scale. The presence of large pools of dormant eggs or individuals in lake sediments also suggest that in studies of zooplankton populations, the dynamics of both active and dormant stages should be considered. Spatial distribution of dormant stages in lake sediments seems to be the result of passive processes for diapausing eggs but possibly an active process for copepodites. Reanalysis of earlier studies regarding diapausing copepodites revealed a size-dependent distribution both horizontally in the lake and vertically in the sediment. Predation, or risk of predation, from benthivorous fish is proposed as one potential factor creating these patterns. This exemplifies the importance of viewing zooplankton life histories as the product of both benthic and pelagic selection pressures.
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| 6. |
- Gyllström, Mikael
(författare)
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Induction and termination of diapause in a freshwater zooplankton community
- 2004
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Ingår i: Archiv für Hydrobiologie. - : Schweizerbart. - 0003-9136. ; 161:1, s. 81-97
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Tidskriftsartikel (refereegranskat)abstract
- I examined production of, and emergence from, diapausing eggs, together with planktonic dynamics of three cladoceran genera (Bosmina, Ceriodaphnia, and Daphnia) for 16 months in a shallow lake. In a complementary field experiment I manipulated environmental variables potentially important as cues for induction and termination of diapause. Ceriodaphnia and Daphnia, but not Bosmina, were dependent on emergence to initiate planktonic populations in spring. During the rest of the season, emergence was unimportant for population and community dynamics. The timing of diapausing-egg production differed between genera, but tended to coincide with peaks in abundance. No hatching was found in any of the experimental treatments, but diapausing-egg production was found in high nutrient treatments with no fish. Field study and experiment together imply that the types of environmental cues involved in diapause induction are different from the ones stimulating its termination. Seasonal cues such as photoperiod appear to govern the hatching of diapausing eggs. In comparison, the induction of diapausing-egg production seems less dependent on season and more on biotic factors.
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| 7. |
- Gyllström, Mikael, et al.
(författare)
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The role of climate in shaping zooplankton communities of shallow lakes
- 2005
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Ingår i: Limnology and Oceanography. - 1939-5590. ; 50:6, s. 2008-2021
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Tidskriftsartikel (refereegranskat)abstract
- We analyzed data from 81 shallow European lakes, which were sampled with standardized methods, for combined effects of climatic, physical, and chemical features of food-web interactions, with a specific focus on zooplankton biomass and community structure. Multiple-regression analysis showed that total phosphorus (TP) generally was the most important predictor of zooplankton biomass and community structure. Climate was the next most important predictor and acted mainly through its effect on pelagic zooplankton taxa. Benthic and plant-associated taxa (typically almost half the total zooplankton biomass) were, however, affected mainly by macrophyte coverage. Neither climate nor TP affected the relation between small and large taxa, and we found only a weak trend with increasing TP of increasing mean crustacean body mass. Dividing the data set into three climate zones revealed a pronounced difference in response to lake productivity between cold lakes, with long periods of ice cover, and the two warmer lake types. These ‘‘ice’’ lakes differed from the others with respect to the effect of TP on chlorophyll a, the zooplankton : chlorophyll a ratio, the chlorophyll a :TP ratio, and the proportion of cyclopoids in the copepod community. Our data suggest that bottom-up forces, such as nutrient concentration, are the most important predictors of zooplankton biomass. In addition, climate contributes significantly—possibly by affecting top-down regulation by fish—and may interact with productivity in determining the zooplankton standing biomass and community composition. Hence, the present study suggests that food-web dynamics are closely linked to climatic features.
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| 8. |
- Hansson, Lars-Anders, et al.
(författare)
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Responses to fish predation and nutrients by plankton at different levels of taxonomic resolution
- 2004
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 49:12, s. 1538-1550
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Tidskriftsartikel (refereegranskat)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.
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| 9. |
- Moss, B, et al.
(författare)
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Continental-scale patterns of nutrient and fish effects on shallow lakes: synthesis of a pan-European mesocosm experiment
- 2004
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 49:12, s. 1633-1649
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Tidskriftsartikel (refereegranskat)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.
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| 10. |
- Moss, B, et al.
(författare)
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The determination of ecological status in shallow lakes - a tested system (ECOFRAME) for implementation of the European Water Framework Directive
- 2003
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Ingår i: Aquatic Conservation: Marine and Freshwater Ecosystems. - : Wiley. - 1052-7613. ; 13:6, s. 507-549
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Tidskriftsartikel (refereegranskat)abstract
- 1. The European Water Framework Directive requires the determination of ecological status in European fresh and saline waters. This is to be through the establishment of a typology of surface water bodies, the determination of reference (high status) conditions in each element (ecotype) of the typology and of lower grades of status (good, moderate, poor and bad) for each ecotype. It then requires classification of the status of the water bodies and their restoration to at least 'good status' in a specified period. 2. Though there are many methods for assessing water quality, none has the scope of that defined in the Directive. The provisions of the Directive require a wide range of variables to be measured and give only general guidance as to how systems of classification should be established. This raises issues of comparability across States and of the costs of making the determinations. 3. Using expert workshops and subsequent field testing, a practicable pan-European typology and classification system has been developed for shallow lakes, which can easily be extended to all lakes. It is parsimonious in its choice of determinands, but based on current limnological understanding and therefore as cost-effective as possible. 4. A core typology is described, which can be expanded easily in particular States to meet local conditions. The core includes 48 ecotypes across the entire European climate gradient and incorporates climate, lake area, geology of the catchment and conductivity. 5. The classification system is founded on a liberal interpretation of Annexes in the Directive and uses variables that are inexpensive to measure and ecologically relevant. The need for taxonomic expertise is minimized. 6. The scheme has been through eight iterations, two of which were tested in the field on tranches of 66 lakes. The final version, Version 8, is offered for operational testing and further refinement by statutory authorities.
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