PKI publikatsioonid

Selle valdkonna püsiv URIhttp://hdl.handle.net/10492/3348

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Chironomid incorporation of methane‐derived carbon in plankton‐ and macrophyte‐dominated habitats in a large shallow lake
(Wiley, 2018) Agasild, Helen; Kisand, Anu; Ainelo, Epp; Feldmann, Tõnu; Timm, Henn; Karus, Katrit; Kisand, Veljo; Jones, Roger I.; Nõges, Tiina; Centre for Limnology. Institute of Agricultural and Environmental Sciences. Estonian University of Life Sciences
1. While 13 C-depleted carbon derived from biogenic methane can substantially contribute to the benthic secondary production in deep stratified lakes, its role in shallow lakes is less clear. We investigated the dynamics of δ13 C and δ15 N in the larvae of Chironomus plumosus throughout an annual cycle in two ecologically distinct basins (open-water plankton-dominated and sheltered macrophyte- covered) of a large (270 km2 ), shallow, polymictic and eutrophic lake (Võrtsjärv, Estonia, North Europe). The larval stable isotopic compositions were linked to the presence of methane-oxidising bacteria (MOB) in larval guts and sediments. 2. Molecular detection of MOB revealed their presence in various sediment types, but stable isotope (SI) analysis revealed clear differences in the feeding of chironomid larvae between the plankton- and macrophyte-dominated habitats. 3. In the plankton-dominated habitat, the mean δ13 C values of larvae remained relatively constant (−38.3‰ to −35.5‰) and corresponded closely to the sediment δ13 C values. Mean δ13 C values of chironomid larvae were generally lower in macrophyte-dominated habitats (−43.4‰ to −33.0‰), and both seasonal and individual variation in larval δ13 C values were more pronounced. MOB presence in larval guts proved a dietary contribution from biogenic methane in macrophyte-dominated habitats. Both the SI and molecular results indicated that MOB could help support larvae even during the cold temperature-limited and ice- covered periods. 4. Our study indicates that methane-derived carbon makes a low but steady contri- bution to the larval chironomids throughout an annual cycle in large shallow Võrtsjärv. However, this contribution can be substantially higher in the lake habitats with abundant macrophytes. The study provides further evidence that a carbon flow pathway from biogenic methane can contribute to the benthic food web under variable habitat conditions in a shallow polymictic lake.
Contrasting responses to long-term climate change of carbon flows to benthic consumers in two different sized lakes in the Baltic area
(Elsevier, 2018) Belle, Simon; Freiberg, Rene; Poska, Anneli; Agasild, Helen; Alliksaar, Tiiu; Tõnno, Ilmar; Centre for Limnology. Institute of Agricultural and Environmental Sciences. Estonian University of Life Sciences
The study of lake sediments and archived biological remains is a promising approach to better under- stand the impacts of climate change on aquatic ecosystems. Small lakes have been shown to be strongly sensitive to past climate change, but similar information is lacking for large lakes. By identifying re- sponses to climate change of carbon flows through benthic food web in two different sized lakes, we aimed to understand how lake morphometry can mediate the effects of climate change. We recon- structed the dynamics of phytoplankton community composition and carbon resources sustaining chironomid biomass during the Holocene from the combined analysis of sedimentary pigment quanti- fication and carbon stable isotopic composition of subfossil chironomid head capsules (d13 C HC) in a large lake in the Baltic area (Estonia). Our results showed that chironomid biomass in the large lake was mainly sustained by phytoplankton, with no significant relationship between d13 C HC values and tem- perature fluctuations. We suggest that lake morphometry (including distance of the sampling zone to the shoreline, and lake volume for primary producers) mediates the effects of climate change, making large lakes less sensitive to climate change. Complementary studies are needed to better understand differ- ences in organic matter dynamics in different sized lakes and to characterize the response of the aquatic carbon cycle to past climate change.
How long-term water level changes influence the spatial distribution of fish and other functional groups in a large shallow lake
(Elsevier, 2020) Bhele, Upendra; Öğlü, Burak; Tuvikene, Arvo; Bernotas, Priit; Silm, Maidu; Järvalt, Ain; Agasild, Helen; Zingel, Priit; Seller, Siim; Timm, Henn; Nõges, Peeter; Nõges, Tiina; Cremona, Fabien; Chair of Hydrobiology and Fishery. Institute of Agricultural and Environmental Sciences
We numerically explored the effects of long-term water level changes on biotic biomass and spatial distribution of fish in a large shallow lake. We calibrated Ecospace model (Ecopath with Ecosim modelling suite) with data from various functional groups (ranging from phytoplankton to piscivorous fish), and considered 14 different habitats. Two scenarios representing, respectively, a long-term water-level increase and decrease by 1 m were constructed and run for a period of thirty eight years (1979–2016). The results showed a very uneven spatial distribution of fish biomass in the lake, with the highest con- centration in the southern basin. The 1 m decrease scenario caused a diminution in the biomass of all groups but piscivorous fish. The 1 m increase scenario saw a weak decrease in most species biomass. Consequently, in both scenarios, long-term water level changes would be generally detrimental to the lake biota. In the context of more frequent climate-induced hydrological fluctuations, we encourage the use of these simulations as effective tools for future prediction and assessment of ecosystem-based fisheries management and ecological status maintenance of shallow lakes.
How warming and other stressors affect zooplankton abundance, biomass and community composition in shallow eutrophic lakes
(Springer Nature, 2020) Cremona, Fabien; Agasild, Helen; Haberman, Juta; Zingel, Priit; Nõges, Peeter; Nõges, Tiina; Laas, Alo; Chair of Hydrobiology and Fishery. Institute of Agricultural and Environmental Science
We aimed to investigate the influence of environmental factors and predict zooplankton biomass and abundance in shallow eutrophic lakes. We employed time series of zoo- plankton and environmental parameters that were measured monthly during 38 years in a large, shallow eutrophic lake in Estonia to build estimates of zooplankton community metrics (cladocerans, copepods, rotifers, ciliates). The analysis of historical time series revealed that air temperature was by far the most important variable for explaining zooplankton biomass and abundance, followed, in decreasing order of importance, by pH, phytoplankton biomass and nitrate concentration. Models constructed with the best predicting variables explained up to 71% of zooplankton biomass variance. Most of the predictive variables had opposing or antagonistic interactions, often mitigating the effect of temperature. In the second part of the study, three future climate scenarios were developed following different Intergovernmental Panel on Climate Change (IPCC) tem- perature projections and entered into an empirical model. Simulation results showed that only a scenario in which air temperature stabilizes would curb total metazooplankton biomass and abundance. In other scenarios, metazooplankton biomass and abundance would likely exceed historical ranges whereas ciliates would not expand. Within the metazooplankton community, copepods would increase in biomass and abundance, whereas cladocerans would lose in biomass but not in abundance. These changes in the zooplankton community will have important consequences for lake trophic structure and ecosystem functioning.
Importance of ciliates as food for fish larvae in a shallow sea bay and a large shallow lake
(Elsevier, 2019) Zingel, Priit; Agasild, Helen; Karus, Katrit; Buholce, Linda; Nõges, Tiina; Centre for Limnology. Institute of Agricultural and Environmental Research
We estimated the consumption of planktonic ciliates by fish larvae in the Väinameri Sea (a shallow semi-enclosed bay of the Baltic Sea) and Lake Võrtsjärv (a shallow and eutrophic lake). Our primary hypothesis was that planktonic ciliates constitute a substantial component of the diet of fish larvae in both environments. We also assumed that the contribution of ciliates to larval nutrition is bigger in lacustrine than in marine environment because ciliates are usually more abundant in lakes. The nutrition of field collected larval fish was determined by gut content analysis using epifluorescence microscopy. Our study revealed that ciliates occurred in the alimentary tracts of all fish species examined. We discovered that the consumption of ciliates by first-feeding fish larvae contributed approximately 40 and 60% of their total consumed carbon in the Väinameri and in Võrtsjärv, respectively. Ciliates represent essentially important food for fish larvae and sufficient protozoan food may enhance larval growth in the beginning of the exogenous feeding and shorten the most vulnerable period in larval stage before shifting to larger prey.
The influence of macrophytes on the feeding of fish larvae in a shallow brackish sea
(Elsevier, 2019) Zingel, Priit; Karus, Katrit; Agasild, Helen; Nõges, Tiina; Centre for Limnology. Institute of Agricultural and Environmental Research
We studied the impact of the macrophyte stands on the feeding of fish larvae, paying special attention to feeding on ciliates. Generally, the importance of ciliates as larval food has been overlooked or underestimated. Based on our earlier observations we hypothesized that the consumption of ciliates by fish larvae is higher in vegetated areas. Studies were carried out in a shallow Väinameri Sea (semi-enclosed Baltic Sea basin). Fish were sampled over 3 years (2011−2013). We examined larval diet by gut segmentation and epifluorescence microscopy. The study revealed that: (1) larval food intake and condition factors were generally higher in vegetated areas; (2) ciliates represented a very important food source for larval fish; (3) in vegetated areas larval fish consumed more ciliates than in open water areas; (4) larvae of piscivorous fish species tended to catch larger prey items. In general our study suggests that larval growth may be better secured in vegetated areas.
Is fish biomass controlled by abiotic or biotic factors? Results of long- term monitoring in a large eutrophic lake
(Elsevier, 2020) Öglü, Burak; Bhele, Upendra; Järvalt, Ain; Tuvikene, Lea; Timm, Henn; Seller, Siim; Haberman, Juta; Agasild, Helen; Nõges, Peeter; Silm, Maidu; Bernotas, Priit; Nõges, Tiina; Cremona, Fabien; Chair of Hydrobiology and Fishery. Institute of Agricultural and Environmental Sciences.
Relationships between biomass and ecological factors including trophic interactions were examined to understand the dynamics of six fish species in Lake Võrtsjärv, a large shallow eutrophic lake located in Estonia (north-eastern Europe). The database contained initially 31 predictive variables that were monitored in situ for nearly forty years. The strongest predictive variables were selected by three parallel approaches: single correlation (Pearson), a multivariate method (Co-inertia analyses), and a machine learning algorithm (Random Forests), followed by a Generalized Least Squares model to determine meaningful relationships with fish biomass. Models with both additive and interactive effects were constructed. The results revealed that the indicators of degraded ecological conditions (high cyanobacteria biomass and their proportion in total phytoplankton, high summer temperature, high nutrient concentration) were negatively correlated to fish biomass. Benthic macroinvertebrates and other biotic predictors (biomass of specific fish prey and predators) were also important contributors to fish biomass dynamics. Together, abiotic and biotic factors explained 40–60% of the variance of fish biomass, depending of the species. Our findings suggest that both abiotic and biotic factors control fish biomass changes in this eutrophic lake.
Relationships between fisheries, foodweb structure, and detrital pathway in a large shallow lake
(Springer, 2018) Cremona, Fabien; Järvalt, Ain; Bhele, Upendra; Timm, Henn; Seller, Siim; Haberman, Juta; Zingel, Priit; Agasild, Helen; Nõges, Peeter; Nõges, Tiina; Centre for Limnology. Institute of Agricultural and Environmental Sciences. Estonian University of Life Sciences
We modeled energy transfer and trophic position of fish, plankton, and macroinvertebrates and the relative importance of top-down versus bottom-up processes in Lake Võrtsjärv, a large shallow eutrophic lake in Estonia (northeastern Europe). We employed input values based on 37 years of biomass and fishing activity monitoring for calibrating the Ecopath with Ecosim (EwE) model. Energy flows from primary producers and detritus, represented by total system throughput, were nearly equal (51 and 49%, respec- tively). Simulation revealed that top-down and bot- tom-up forces were at play, metazooplankton was not efficiently grazing phytoplankton production, and a trophic cascade proceeded through macroinverte- brates rather than through zooplankton. Detritivory was responsible for the relatively low trophic position of Võrtsjärv fish compared to other lakes. Bottom-up processes were the main drivers for the dual, primary production- and detritus-based pathways in energy flow. Our findings suggest that the predicted biomass increase of cyanobacteria in shallow lakes in the future will strengthen the reliance of consumers on the detrital pathway at the expense of the primary production pathway.
Role of potentially toxic cyanobacteria in crustacean zooplankton diet in a eutrophic lake
(Elsevier, 2019) Agasild, Helen; Panksep, Kristel; Tõnno, Ilmar; Blank, Kätlin; Kõiv, Toomas; Freiberg, René; Laugaste, Reet; Jones, Roger I.; Nõges, Peeter; Nõges, Tiina; Chair of Hydrobiology and Fishery. Institute of Agricultural and Environmental Sciences
The coexistence of potentially toxic bloom-forming cyanobacteria (CY) and generally smaller-sized grazer communities has raised the question of zooplankton (ZP) ability to control harmful cyanobacterial blooms and highlighted the need for species-specific research on ZP-CY trophic interactions in naturally occurring communities. A combination of HPLC, molecular and stable isotope analyses was used to assess in situ the importance of CY as a food source for dominant crustacean ZP species and to quantify the grazing on potentially toxic strains of Microcystis during bloom formation in large eutrophic Lake Peipsi (Estonia). Aphanizomenon, Dolichospermum, Gloeotrichia and Microcystis dominated bloom-forming CY, while Microcystis was the major genus producing cyanotoxins all over the lake. Grazing studies showed that CY, and especially colonial CY, formed a significant, and also preferred component of algae ingested by the cladocerans Bosmina spp. and Daphnia spp. while this was not the case for the more selective calanoid copepod Eudiaptomus gracilis. Molecular analyses confirmed the presence of CY, including Microcystis, in ZP guts. Further analyses using qPCR targeting cyanobacterial genusspecific mcyE synthase genes indicated that potentially toxic strains of Microcystis can be ingested directly or indirectly by all the dominant crustacean grazers. However, stable isotope analyses indicated that little, if any, assimilation from ingested bloom-forming CY occurred. The study suggests that CY, and particularly Microcystis with both potentially toxic and non-toxic strains, can be widely ingested by cladoceran grazers during a bloom event with implications for control of CY abundance and for transfer of CY toxins through the food web.
Seasonal data on phytoplankton, zooplankton and zooplankton feeding from Lake Peipsi (Estonia)
(EMU DSpace, 2019) Agasild, Helen; Panksep, Kristel; Tõnno, Ilmar; Blank, Kätlin; Kõiv, Toomas; Freiberg, René; Laugaste, Reet; Jones, Roger I.; Nõges, Peeter; Nõges, Tiina
Abstract of the article : The coexistence of potentially toxic bloom-forming cyanobacteria (CY) and generally smaller-sized grazer communities has raised the question of zooplankton (ZP) ability to control harmful cyanobacterial blooms and highlighted the need for species-specific research on ZP-CY trophic interactions in naturally occurring communities. A combination of HPLC, molecular and stable isotope analyses was used to assess in situ the importance of CY as a food source for dominant crustacean ZP species and to quantify the grazing on potentially toxic strains of Microcystis during bloom formation in large eutrophic Lake Peipsi (Estonia). Aphanizomenon, Dolichospermum, Gloeotrichia and Microcystis dominated bloom-forming CY, while Microcystis was the major genus producing cyanotoxins all over the lake. Grazing studies showed that CY, and especially colonial CY, formed a significant, and also preferred component of algae ingested by the cladocerans Bosmina spp. and Daphnia spp. while this was not the case for the more selective calanoid copepod Eudiaptomus gracilis. Molecular analyses confirmed the presence of CY, including Microcystis, in ZP guts. Further analyses using qPCR targeting cyanobacterial genus-specific mcyE synthase genes indicated that potentially toxic strains of Microcystis can be ingested directly or indirectly by all the dominant crustacean grazers. However, stable isotope analyses indicated that little, if any, assimilation from ingested bloom-forming CY occurred. The study suggests that CY, and particularly Microcystis with both potentially toxic and non-toxic strains, can be widely ingested by cladoceran grazers during a bloom event with implications for control of CY abundance and for transfer of CY toxins through the food web.

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