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Abstract

Fish are an important source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for birds, mammals and humans. In aquatic food webs, these highly unsaturated fatty acids (HUFA) are essential for many physiological processes and mainly synthetized by distinct phytoplankton taxa. Consumers at different trophic levels obtain essential fatty acids from their diet because they cannot produce these sufficiently de novo. Here, we evaluated how the increase in phosphorus concentration (eutrophication) or terrestrial organic matter inputs (brownification) change EPA and DHA content in the phytoplankton. Then, we evaluated whether these changes can be seen in the EPA and DHA content of piscivorous European perch (Perca fluviatilis), which is a widely distributed species and commonly consumed by humans. Data from 713 lakes showed statistically significant differences in the abundance of EPA- and DHA-synthesizing phytoplankton as well as in the concentrations and content of these essential fatty acids among oligo-mesotrophic, eutrophic and dystrophic lakes. The EPA and DHA content of phytoplankton biomass (mg HUFA g− 1) was significantly lower in the eutrophic lakes than in the oligo-mesotrophic or dystrophic lakes. We found a strong significant correlation between the DHA content in the muscle of piscivorous perch and phytoplankton DHA content (r = 0.85) as well with the contribution of DHA-synthesizing phytoplankton taxa (r = 0.83). Among all DHA-synthesizing phytoplankton this correlation was the strongest with the dinoflagellates (r = 0.74) and chrysophytes (r = 0.70). Accordingly, the EPA + DHA content of perch muscle decreased with increasing total phosphorus (r2 = 0.80) and dissolved organic carbon concentration (r2 = 0.83) in the lakes. Our results suggest that although eutrophication generally increase biomass production across different trophic levels, the high proportion of low-quality primary producers reduce EPA and DHA content in the food web up to predatory fish. Ultimately, it seems that lake eutrophication and brownification decrease the nutritional quality of fish for human consumers.

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... EPA and DHA are mainly produced by algae and subsequently transferred through the food web to fish and top consumers via zooplankton and benthic macroinvertebrates. Increased loading of nutrients and dissolved organic carbon from the watershed have been linked with decreased mass fractions of EPA and DHA in game fish Taipale et al., 2016). EPA and DHA have significant health benefits also for humans (Harris et al., 2021), and decreased mass fractions in fish may affect EPA and DHA intake and nutritional quality for humans (Strandberg et al., 2018). ...
... Eutrophication and climate warming may affect phytoplankton production and EPA and DHA concentrations directly by altering the fatty acid profiles within specific phytoplankton taxa (Fernandes et al., 2016;Guchina and Harwood, 2006;Hazel, 1995;Hixson and Arts, 2016) or indirectly by altering phytoplankton community structure (Galloway and Winder, 2015;Taipale et al., 2016). The direct effects are usually investigated with algal monocultures (Fernandes et al., 2016, Hixson andArts, 2016) while the indirect effects are inferred from field studies or simulations (Taipale et al., 2016, Strandberg et al., 2020. ...
... Eutrophication and climate warming may affect phytoplankton production and EPA and DHA concentrations directly by altering the fatty acid profiles within specific phytoplankton taxa (Fernandes et al., 2016;Guchina and Harwood, 2006;Hazel, 1995;Hixson and Arts, 2016) or indirectly by altering phytoplankton community structure (Galloway and Winder, 2015;Taipale et al., 2016). The direct effects are usually investigated with algal monocultures (Fernandes et al., 2016, Hixson andArts, 2016) while the indirect effects are inferred from field studies or simulations (Taipale et al., 2016, Strandberg et al., 2020. The fatty acid compositions of algae and cyanobacteria are strongly driven by phylogeny (Taipale et al., 2013;Galloway and Winder, 2015), albeit with some environmental influence, and these taxonomic differences are so distinct that seston fatty acid composition can be used to infer phytoplankton community structure (Strandberg et al., 2015;Cañavate, 2019). ...
Article
Climate change and eutrophication are among the main stressors of shallow freshwater ecosystems, and their effects on phytoplankton community structure and primary production have been studied extensively. However, their combined effects on the algal production of polyunsaturated fatty acids (PUFA), specifically, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are currently unresolved. Moreover, the proximate reasons for changes in phytoplankton EPA and DHA concentrations are unclear, i.e., the relative importance of ecological (changes in the community composition) vs. ecophysiological (within taxa changes in EPA and DHA levels) factors. We investigated the responses of phytoplankton EPA and DHA concentrations to warming (IPCC climate scenario) and nutrient additions in mesocosms which had been run continuously at varying temperature and nutrient levels for 15 years prior to this study. Nutrient treatment had a significant effect on phytoplankton EPA and DHA concentrations and about 59 % of the variation in EPA and DHA concentrations could be explained by changes in the phytoplankton community structure. Increased biomass of diatoms corresponded with high EPA and DHA concentrations, while cyanobacteria/chlorophyte dominated mesocosm had low EPA and DHA concentrations. Warming had only a marginal effect on the EPA and DHA concentrations in these mesocosms. However, a significant interaction was observed with warming and N:P ratio. Our findings indicate that direct nutrient/temperature effects on algal physiology and PUFA metabolism were negligible and the changes in EPA and DHA concentrations were mostly related to the phytoplankton community structure and biomass. These results also imply that in shallow temperate lakes eutrophication, leading to increased dominance of cyanobacteria, will probably be a greater threat to phytoplankton EPA and DHA production than warming. EPA and DHA are nutritionally important for upper trophic level consumers and decreased production may impair secondary production.
... For example, cryptomonads (Cryptophyceae), diatoms (Bacillariophyceae), dinoflagellates (Dinophyceae), and euglenoids (Euglenophyceae) have typically high EPA and DHA content (Taipale et al. 2013, Peltomaa et al. 2017. Green algae (Chlorophyceae, Conjugatophyceae, and Trebouxiophyceae) and cyanobacteria do not usually contain long-chain EPA and DHA (Taipale et al. 2016, Peltomaa et al. 2017), but can have relatively high amounts of ALA and SDA and saturated fatty acids. However, there are also taxa-specific variations in the biomolecule contents within the previously listed taxonomic groups (Ahlgren, Gustafsson, and Boberg 1992, Taipale et al. 2013, Peltomaa et al. 2017. ...
... These vital biomolecules are also beneficial for human neural development, neural and immune function, also decreasing e.g., cardiovascular disease risks (Swanson et al. 2012). Some studies have suggested that reducing PUFA trends in the primary producers, and primary consumers along environmental change would cascade to secondary and tertiary consumers, potentially impacting the quality for human consumed aquatic taxa as well (e.g., Taipale et al. 2016, Colombo et al. 2020). ...
... If the predicted environmental shift in time corresponded to the spatial gradient in environmental factors, space could be used to replace time to model future change (e.g., Pickett 1989). Space-for-time substitution is a widely used study method in ecological studies to bypass the problem with the lack of long-term datasets (Jeppesen et al. 2000, Taipale et al. 2016, Laske et al. 2019Senar et al. 2021). Long-term datasets, including relatively new techniques such as fatty acid content analysis, are still scarce (but see Lind et al. 2018) but would give presumably the most precise predictions when modeling future change in ecosystems, at least in a local scale (Blois et al. 2013). ...
Thesis
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Climate change and intense land-use activities are promoting lake eutrophication and browning, affecting community structure and food web processes. In this thesis, space-for-time approach was used to study the environmental change impacts on food web structure, energy pathways, and organism nutritional quality (defined with fatty acids and mercury content) in subarctic and boreal regions. Only specific algal taxa can synthesize eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are important polyunsaturated fatty acids (PUFA) for consumer growth and reproduction. Mercury is a toxic heavy metal that, bioaccumulates to organisms via diet. In subarctic lakes, increasing temperature and productivity negatively affected EPA+DHA content of seston and zooplankton. However, no such changes were observed from boreal regions. Seston and cladoceran PUFA contents were uncorrelated in the boreal zone where cladoceran preferred to feed on high-quality algae. European perch (Perca fluviatilis (L.)) showed slight decreasing trends in their muscle DHA content from more transparent lakes towards shallower and murkier ones in the boreal areas. In subarctic climate–productivity gradient, the decreasing prey item quality (zooplankton and profundal benthos) did not affect fish muscle EPA+DHA content at community level. Perch in boreal low pH lakes and highly forested catchments rely more on terrestrial energy sources than eutrophic lakes with neutral pH. This likely resulted in higher mercury and omega-6 PUFA content in perch muscle. Increasing temperature and productivity fundamentally alter subarctic lake communities' structure and function, resulting in an increasing share of cyanobacteria, smaller-bodied zooplankton, smaller benthos taxa, and warmer-water-adapted cyprinid fishes. Positive trends in biomass at each second trophic level (phytoplankton and invertivorous fish) were observed along with climate-productivity gradient shaping biomass pyramids. Food web processes and PUFA dynamics seem to differ between boreal and subarctic lakes. Future studies with harmonized methodology and wide lake gradients are needed to evaluate wheter methodology or ecology are driving these observed differences.
... Eutrophication of aquatic ecosystems modifies phytoplankton community structure by increasing the abundance of cyanobacteria and green algae, resulting in a decrease in the dietary quality of phytoplankton for zooplankton and fish (Jørgensen, 2001;Taipale et al., 2016c). Cyanobacteria and green algae do generally not contain longchain PUFA but ALA and stearidonic acid (SDA; 18:4ω3) (Los and Mironov, 2015;Taipale et al., 2016a). ...
... Although carbohydrates are an important energy source for herbivores (or species at lower trophic levels), lipids are usually the most important energy source for carnivorous (or higher trophic level) fish species (Biro et al., 2004;Le Gall and Behmer, 2014;Lee et al., 2006;Skiba-Cassy et al., 2013). The increase of terrestrial organic matter in freshwater ecosystems is predicted to increase the availability of carbohydrates that can support the energy demand for somatic growth and reproduction of herbivorous zooplankton and help them spare essential biomolecules (Taipale et al., 2016c). However, high allochthonous diets decrease the lipid content in zooplankton and consequently in fish fry (Taipale et al., 2018) and can thus also decrease the somatic growth of juvenile fish (Meng et al., 2019) and winter survival for the young fish populations (Hurst and Conover, 1998). ...
... Carbohydrate, lipid, and protein content in each trophic level were analyzed using previously described methods (Taipale et al., 2016c). Briefly, total carbohydrate content was analyzed using Dubois's method in which glucose is dehydrated to hydroxymethylfurfural in a hot acidic medium (Dubois, 1956). ...
Article
Diet quality is crucial for the development of offspring. Here, we examined how the nutritional quality of prey affects somatic growth and the lipid, carbohydrate, protein, amino acid, and polyunsaturated fatty acid content of rainbow trout (Oncorhynchus mykiss) fry using a three-trophic-level experimental setup. Diets differed especially in their content of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are physiologically essential polyunsaturated fatty acids for a fish fry. Trout were fed with an artificial diet (fish feed, DHA-rich), marine zooplankton diet (krill/Mysis, DHA-rich), or freshwater zooplankton diet (Daphnia, Cladocera, DHA-deficient). The Daphnia were grown either on a poor, intermediate, or high-quality algal/microbial diet simulating potential changes in the nutritional prey quality (EPA-content). Trout fed with the fish feed or marine zooplankton entirely replaced their muscle tissue composition with compounds of dietary origin. In contrast, fish tissue renewal was only partial in fish fed any Daphnia diet. Furthermore, fish grew five times faster on marine zooplankton than on any of the Daphnia diets. This was mainly explained by the higher dietary contents of arachidonic acid (ARA), EPA, and DHA, but also by the higher content of some amino acids in the marine zooplankton than in the Daphnia diets. Moreover, the fatty acid-specific carbon isotopes revealed that trout fry could not biosynthesize ARA, EPA, or DHA efficiently from their precursors. Our result suggests that changes in the zooplankton and macroinvertebrate communities' structure in freshwater habitats from DHA-rich to DHA-poor species may reduce the somatic growth of fish fry.
... Rather, the composition of fatty acids in fish is largely dependent on the phytoplankton species present at the base of the food web and modified by physiological requirements (Henderson and Tocher 1987). Because the fatty acid composition of fish differs among species and by age of fish depending on diet, fatty acids have been used as dietary tracers (Sahu et al. 2013;Taipale et al 2016, Fujibayashi et al. 2018. Differences in the lipid and protein composition of the axial muscle of fish has been reported to influence the concentrations metalloids (Charette et al. 2021). ...
... EPA is considered to be metabolically costly for fish to produce, and therefore must be acquired from their diet (Brett and Muller-Navara 1997). A low abundance of EPA, and high abundance of PAL, LIN, and OLE, has been reported in aquatic organisms from waterbodies containing a high biomass of cyanobacteria (Sharathchandra and Rajashekhar 2011;Sahu et al. 2013;Taipale et al. 2016). In the year prior to this study, the cyanobacteria in Dairy Farm Lake made up 90% of the phytoplankton by biovolume during summer and 10% during winter (Cianci-Gaskill et al., in preparation). ...
... A high abundance of cyanobacteria during the study period was also indicated by a phycocyanin: chlorophyll ratio 0.2:1 to 0.4:1 during summer and 0.1:1 during fall (Cianci-Gaskill et al., in preparation). Taipale et al. (2016) also reported that the abundance of EPA and DHA in predatory fish was negatively correlated with the percentage of cyanobacteria in the waterbody, and that EPA and DHA was lower in fish from eutrophic waterbodies in comparison to fish from oligo-mesotrophic and dystrophic waterbodies. The FA composition of fish in this study should not be assumed to reflect the seasonal changes in FA in LMB for other waterbodies. ...
Article
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Largemouth bass (LMB, 265–475 mm) were collected to document whether changes in fish condition and reproductive status influenced the concentration of total mercury (Hg) and selenium (Se) in axial muscle by season and sex. The fatty acid (FA) composition of fish was also examined to describe seasonal and sexual differences and identify whether arachidonic acid (ARA) could be used as a biomarker of Hg toxicity. There was a trend for females to have lower (p < 0.062) Se concentrations than males. The concentration of Se for females during spring (mean ± SD, 686 ± 51 ng/g dw) was 15% lower than males (806 ± 67 ng/g dw). Lower Se concentrations in females than males continued through summer and fall. Concentration of Hg for females during spring (152 ± 39 ng/g ww) was also 59% lower than males (373 ± 303 ng/g ww), but the difference was not significant (p > 0.2). The percent of lipids was greatest in fall and winter (3%) and comprised primarily of omega-3 fatty acids (35 g/100 g lipid). Fish condition as measured by percent lipids and relative weight was negatively (p < 0.02) related to Hg concentration for females and males. Lipid content for both sexes was also positively (p < 0.05) related to the Se:Hg ratio. Relative weight was positively related to the Se:Hg ratio for females during all seasons (p = 0.014), but only during spring and summer for males (p < 0.007). A low Se:Hg value was associated with an elevation in ARA for both sexes and a reduced hepatosomatic index in males. Data suggested that females transferred muscle stores of Se and Hg to developing oocytes during spring. This study generates hypotheses regarding the physiological drivers of seasonal and sexual variability in Hg, Se, and FA in LMB that may be applicable to other species and have implications for fisheries health and management.
... However, the fate of other terrestrial origin biomolecules (e.g., amino acids) in the aquatic food webs is not known, and most of current knowledge is related to indirect consequences. For example, browning has a great impact on the phytoplankton composition, and the synthesis and transfer of physiologically essential long-chain polyunsaturated fatty acids (PUFA), such as eicosapentaenoic acid (EPA, 20:5ω3) and docosahexaenoic acid (DHA, 22:6ω3) (Taipale et al., 2016b;Strandberg et al., 2016); PUFA are required for optimal growth and reproduction of zooplankton, fish and mammals (Arts et al., 2009). Since EPA and DHA are synthesized only by certain phytoplankton taxa (Taipale et al., 2016b), changes in the phytoplankton community influence EPA and DHA availability for herbivorous zooplankton, and their transfer in the food web. ...
... For example, browning has a great impact on the phytoplankton composition, and the synthesis and transfer of physiologically essential long-chain polyunsaturated fatty acids (PUFA), such as eicosapentaenoic acid (EPA, 20:5ω3) and docosahexaenoic acid (DHA, 22:6ω3) (Taipale et al., 2016b;Strandberg et al., 2016); PUFA are required for optimal growth and reproduction of zooplankton, fish and mammals (Arts et al., 2009). Since EPA and DHA are synthesized only by certain phytoplankton taxa (Taipale et al., 2016b), changes in the phytoplankton community influence EPA and DHA availability for herbivorous zooplankton, and their transfer in the food web. Browning might have opposite impacts on the phytoplankton composition in different climatic zones and biomes. ...
... For example, Senar et al. (2019) found that browning favored cyanobacteria and decreased sestonic EPA and DHA content in temperate lakes. However, in boreal lakes, strong browning is known to inhibit cyanobacteria (Taipale et al., 2016b;Senar et al., 2021), but favor the raphidophyte Gonyostomum semen (Lepistö et al., 1994;Lebret et al., 2018) which might result in an apparent increase on EPA even though G. semen is too large to be consumed by most zooplankton (Gutseit et al., 2007;Strandberg et al., 2020). ...
Article
Full-text available
Water browning or brownification refers to increasing water color, often related to increasing dissolved organic matter (DOM) and carbon (DOC) content in freshwaters. Browning has been recognized as a significant physicochemical phenomenon altering boreal lakes, but our understanding of its ecological consequences in different freshwater habitats and regions is limited. Here, we review the consequences of browning on different freshwater habitats, food webs and aquatic-terrestrial habitat coupling. We examine global trends of browning and DOM/DOC, and the use of remote sensing as a tool to investigate browning from local to global scales. Studies have focused on lakes and rivers while seldom addressing effects at the catchment scale. Other freshwater habitats such as small and temporary waterbodies have been overlooked, making the study of the entire network of the catchment incomplete. While past research investigated the response of primary producers, aquatic invertebrates and fishes, the effects of browning on macrophytes, invasive species, and food webs have been understudied. Research has focused on freshwater habitats without considering the fluxes between aquatic and terrestrial habitats. We highlight the importance of understanding how the changes in one habitat may cascade to another. Browning is a broader phenomenon than the heretofore concentration on the boreal region. Overall, we propose that future studies improve the ecological understanding of browning through the following research actions: 1) increasing our knowledge of ecological processes of browning in other wetland types than lakes and rivers, 2) assessing the impact of browning on aquatic food webs at multiple scales, 3) examining the effects of browning on aquatic-terrestrial habitat coupling, 4) expanding our knowledge of browning from the local to global scale, and 5) using remote sensing to examine browning and its ecological consequences.
... Increased algal and cyanobacterial blooms threaten the functioning of aquatic ecosystems, fisheries, and human health [3,4]. Increased cyanobacteria dominance and warming have been suggested to decrease the basal production of n-3 and n-6 polyunsaturated fatty acids (n-3 and n-6 PUFA) [5,6]. The decreased basal production of n-3 and n-6 PUFA is predominantly caused by changes in the phytoplankton community structure because the composition of PUFA in algae and cyanobacteria is phylogenetically determined [7,8]. ...
... Global climate change is predicted to increase surface water temperatures in summer and strengthen the thermal stratification in lakes [35], which in turn have been noted to increase the frequency, intensity, and duration of cyanobacteria blooms [36]. In general, cyanobacteria have a lower n-3/n-6 ratio than eukaryotic algae and most cyanobacteria genera do not produce C 20 PUFA, thus cyanobacteria blooms have been suggested to decrease the basal production of physiologically important PUFA, such as EPA [6]. Microcystis is one of the most common bloom-forming cyanobacteria [4], and the desaturation of C 20 precursors in Chironomus may indicate a higher-than-expected availability of EPA and ARA to upper trophic level consumers in lakes exposed to nontoxic Microcystis blooms. ...
... Climate-induced increase in cyanobacteria biomass and the direct temperature effects on the cyanobacterial fatty acids together with the decreased trophic upgrading of C 20 precursors in chironomids may have cascading effects throughout the food web. The estimated decrease in algal production of EPA and DHA, due to cyanobacteria dominance, correlated with lower levels of EPA and DHA in fish [6]. Chironomus contains only trace amounts of DHA even if abundant in the diet [16,24]. ...
Article
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Cyanobacteria dominance and warming have been suggested to decrease the production of polyunsaturated fatty acids (PUFA) in freshwater ecosystems. Physiological adaptations of poikilothermic animals to higher temperatures may further decrease PUFA levels in aquatic food webs. We conducted diet manipulation experiments to investigate the combined effects of dietary PUFA and warming on the proportions of eicosapentaenoic acid (EPA) and arachidonic acid (ARA) in Chironomus riparius. The experimental diet consisted of a nontoxic cyanobacterium Microcystis, which contained C20 PUFA: 20:3n-3, 20:4n-3, and 20:3n-6, but no EPA or ARA. Additionally, we used TetraMin® fish flakes as a control treatment. A temperature increase from 20 °C to 25 °C decreased the proportion of n-3 C20 PUFA and the n-3/n-6 ratio in Microcystis. Diet manipulation experiments indicated that Chironomus desaturated dietary C20 precursors to EPA and ARA, but warming decreased this bioconversion and resulted in lower levels of EPA and ARA in Chironomus. Warming did not alter the proportions of EPA and ARA in Chironomus larvae if these PUFA were readily available in the diet (TetraMin® control treatment). In conclusion, warming and cyanobacteria dominance may decrease the production and trophic transfer of physiologically important PUFA in freshwaters by (1) decreasing the n-3/n-6 ratio and the abundance of n-3 C20 precursors in Microcystis, and (2) decreasing the bioconversion of n-3 and n-6 C20 precursors to EPA and ARA in chironomids. These changes may have cascading effects throughout the food web and decrease the content of EPA in fish, potentially affecting its availability to humans.
... Since plankton organisms are the first trophic link in pelagic food webs, anthropogenic changes both in the quantity and nutritional quality of planktonic biomass can result in altered trophic transfer of essential biochemical compounds (Müller-Navarra et al., 2004;Boëchat et al., 2011Boëchat et al., , 2014Winder et al., 2017) and affect biomass production and nutritional quality of higher-level consumers, including those commonly used as food sources for humans, such as mollusks and fish (Taipale et al., 2016). Therefore, detecting both the type and degree of human impacts on aquatic ecosystems is not only crucial for conservation and mitigation efforts but also understanding the impacts on aquatic ecosystem services such as food production. ...
... High contributions of saturated fatty acids (SFAs) and some monounsaturated fatty acids (MUFAs) are found in bacteria and cyanobacteria (Volkman et al., 1998;Watson, 2003), and marine seston has a higher ω3:ω6 ratio than freshwater seston and terrestrial plants (Bergé and Barnathan, 2005). Moreover, single FAs and FA metricse.g., palmitic acid and stearic acid as well as various FAs typical for bacteriaare effective markers for human activities, such as urbanization, sewage discharge and different types of agriculture practices (Boëchat et al., 2011(Boëchat et al., , 2014Gomes et al., 2016;Taipale et al., 2016). Finally, FAs can be detected in different environmental media, such as seston, sediment, and plant and animal tissues, and are associated to key physiological processes, such as cardiac and neural functioning, hormone synthesis, and tissue repair processes (Gomes et al., 2016;Calder, 2018). ...
... Changes towards a more SFA or PUFA rich community may affect the transfer of essential compounds to high-level consumers (Taipale et al., 2016). As final consumers in food webs, humans are particularly interested in the nutritional quality of their food resources. ...
Article
Fatty acids (FAs) and their metrics have been used to detect and assess the impacts of urbanization and agriculture on aquatic ecosystems. Here, we investigated whether seston FAs are also useful to characterize and understand early-stage aquaculture impacts in a large tropical reservoir (Furnas Reservoir, SE Brazil). We tested the hypothesis that single FAs, as well as selected FA metrics in the seston fraction, are efficient markers of net-cage fish farming effects. In general, fish farming had only minor effects on standard water chemical variables, mainly small increases in ammonium, nitrate, and dissolved organic nitrogen concentrations. By increasing concentrations of several polyunsaturated FAs, early-stage fish farming improved sestonic food quality in the more oligotrophic branch of the reservoir under drought conditions. However, in general, increases in concentrations of bacterial FAs, due to fish farming, suggested organic matter (OM) subsidies from non-ingested and non-assimilated fish feed. In the more eutrophic reservoir branch, seston FA profiles suggested that fish farming caused an increase of low-quality food resources, such as cyanobacteria. Thus, background impact levels may determine the biochemical responses of tropical reservoirs to fish farming. Higher contributions of potentially sewage-derived and bacterial FAs during drought conditions, especially at reference sites of the more oligotrophic branch, suggested that drought shifted OM inputs towards anthropogenic sources, thereby overwriting land-use related differences between reservoir branches and homogenizing their environmental conditions. In conclusion, FA variables were useful to evaluate and understand environmental conditions, as well as the effects of early-stage fish farming and drought, and should be considered in impact assessments in tropical lentic ecosystems.
... Only certain algae groups, such as dinoflagellates, diatoms and cryptophytes, are able to produce EPA and DHA efficiently and are abundant in cold and nutrient-poor lakes (Taipale et al., 2013. However, warm and eutrophic lake primary producer communities, often dominated with cyanobacteria, are inefficient in EPA and DHA production (Müller-Navarra et al., 2000, 2004Taipale et al., 2013Taipale et al., , 2016. ...
... Second, we hypothesized (H2) that cyanobacteria form an increasing proportion of the phytoplankton communities in warmer and more productive lakes (Przytulska et al., 2017), thus lowering nutritional quality of primary producers. As such, we expected that this difference would be passed through all higher trophic levels (Müller-Navarra et al., 2000;Taipale et al., 2016). Finally, we hypothesized (H3) that increasing temperature and productivity would increase total community biomass including an increase in physiologically important EPA and DHA of the total lake community Jeppesen et al., 2000). ...
... Fatty acids were analysed as methyl esters (e.g. Taipale et al., 2016), identified and quantified using a gas chromatograph attached to mass spectrometer. Samples were spiked with nonadecylic acid (PLFA c19:0). ...
Article
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Climate change in the Arctic is outpacing the global average while land-use is intensifying due to exploitation of previously inaccessible or unprofitable natural resources. A comprehensive understanding of how the joint effects of changing climate and productivity modify lake food web structure, biomass, trophic pyramid shape and abundance of physiologically essential biomolecules (omega-3 fatty acids) in the biotic community is lacking. We conducted a space-for-time study in 20 subarctic lakes spanning a climatic (+3.2°C and precipitation: +30%) and chemical (dissolved organic carbon: +10mg L−1, total phosphorus: +45µg L−1 and total nitrogen: +1000µg L−1) gradient to test how temperature and productivity jointly affect the structure, biomass and community fatty acid content (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]) of whole food webs. Increasing temperature and productivity shifted lake communities towards dominance of warmer, murky-water adapted taxa, with a general increase in the biomass of primary producers, and secondary and tertiary consumers, while primary invertebrate consumers did not show equally clear trends. This process altered various trophic pyramid structures toward an hour glass shape in the warmest and most productive lakes. Increasing temperature and productivity had negative fatty acid content trends (mg EPA+DHA g−1 dry weight) in primary producers and primary consumers, but not in secondary and tertiary fish consumers. The massive biomass increment of fish led to increasing areal fatty acid content (kg EPA+DHA ha−1) towards increasingly warmer, more productive lakes, but there were no significant trends in other trophic levels. Increasing temperature and productivity are shifting subarctic lake communities towards systems characterised by increasing dominance of cyanobacteria and cyprinid fish, although decreasing quality in terms of EPA+DHA content was observed only in phytoplankton, zooplankton and profundal benthos.
... However, Rasmussen (2010) presented stable isotope evidence of algae being more selectively assimilated by stream invertebrates than allochthonous sources. Allochthonous carbon sources are poor in essential biochemical compounds, especially essential fatty acids (Brett et al. 2009;Taipale et al. 2014Taipale et al. , 2016, and thus considered low-quality food for aquatic consumers (Brett et al. 2017). ...
... Boreal lakes are characterized by relatively high inputs of brown-colored, allochthonous organic matter (Algesten et al. 2004;Kortelainen et al. 2006), which is predicted to increase in the future due to recovery from acid deposition and increased precipitation, soil erosion, and terrestrial runoff induced by climate change (Monteith et al. 2007;Weyhenmeyer et al. 2014;De Wit et al. 2016). Consequently, lake browning and eutrophication will alter algal and invertebrate community composition, which has negative impacts on the availability and trophic transfer of EPA and DHA in lake food webs (Strandberg et al. 2015;Taipale et al. 2016;Kesti et al. 2021). By suppressing benthic primary and secondary productivity due to lower light and oxygen, darker water, and intensified stratification, a decline in the relative importance of benthic trophic pathways is expected (Vadeboncoeur et al. 2003;Solomon et al. 2015). ...
Article
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We studied how physiologically important long-chain polyunsaturated fatty acids (PUFA) in benthic macroinvertebrates (Asellus aquaticus, Chironomidae, and Oligochaeta) were related to those in periphyton and terrestrial organic matter (tree leaves), collected from littoral areas of 17 boreal lakes that differed in their dissolved organic carbon (DOC) and nutrient (phosphorus and nitrogen) concentrations. We also analyzed fatty acid (FA)-specific stable carbon isotopes (δ 13 C FA) to investigate the dietary origin (periphyton vs. terrestrial organic matter) of PUFA in the consumers. In contrast to periphyton, terrestrial organic matter was deprived of long-chain PUFA, such as eicosapentaenoic acid (EPA), but rich in short-chain PUFA. The FA composition of macroinvertebrates was primarily taxon-specific despite the large differences in DOC and nutrient concentrations of the lakes. An increase in DOC concentration had a negative impact on the EPA content of Asellus, chi-ronomids, and oligochaetes as well as the total FA content of chironomids and oligochaetes. However, the FA content of macroinvertebrates was not related to lake total phosphorus concentrations, although the total FA and EPA content of periphyton increased with the trophic status of the study lakes. The δ 13 C PUFA values of macroinvertebrates were positively related with the δ 13 C PUFA of periphyton and weakly with δ 13 C PUFA of terrestrial leaf material. The results indicate that EPA in the studied macroinvertebrate taxa was mainly derived from an algal-based diet and not via biosynthesis from allochthonous precursor FA. Thus, macroinvertebrate production in lakes may be limited by the available algae-based food sources.
... Long-chain PUFAs are selectively retained in fish as the proportion of these molecules is often higher in the fish than its food sources. Thus, changes in phytoplankton community structure due to changes in lake chemistry (eutrophication and browning) are believed to impact directly on the PUFA content of organisms at higher trophic levels (Müller-Navarra et al., 2004;Strandberg et al., 2016;Taipale et al., 2016b;Taipale et al., 2018). It has been demonstrated that perch are capable of biosynthesizing ARA and DHA from αlinolenic (18:3n3, ALA) and linoleic acid (18:2n6, LIN), respectively (Geay et al., 2016). ...
... Perch muscle DHA content was slightly higher in larger and clearer lakes than in shallower and murkier lakes, that was in accordance with a previous study (Strandberg et al., 2016). This could be related to differences in the primary producer community structure, where murkier lakes have less n3 PUFA synthesizing phytoplankton taxa (Taipale et al., 2016b;Taipale et al., 2018). ...
Article
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Environmental change, including joint effects of increasing dissolved organic carbon (DOC) and total phosphorus (TP) in boreal northern lakes could potentially affects food web energy sources and the biochemical composition of organisms. These environmental stressors are enhanced by anthropogenic land-use and can decrease the quality of polyunsaturated fatty acids (PUFAs) in seston and zooplankton, and therefore, possibly cascading up to fish. In contrast, the content of mercury in fish increases with lake browning potentially amplified by intensive forestry practises. However, there is little evidence on how these environmental stressors simultaneously impact beneficial omega-3 fatty acid (n3-FA) and total mercury (THg) content of fish muscle for human consumption. A space-for-time substitution study was conducted to assess whether environmental stressors affect Eurasian perch (Perca fluviatilis) allochthony and muscle nutritional quality [PUFA, THg, and their derivative, the hazard quotient (HQ)]. Perch samples were collected from 31 Finnish lakes along pronounced lake size (0.03–107.5 km²), DOC (5.0–24.3 mg L⁻¹), TP (5–118 μg/ L) and land-use gradients (forest: 50.7–96.4%, agriculture: 0–32.6%). These environmental gradients were combined using principal component analysis (PCA). Allochthony for individual perch was modelled using source and consumer δ²H values. Perch allochthony increased with decreasing lake pH and increasing forest coverage (PC1), but no correlation between lake DOC and perch allochthony was found. Perch muscle THg and omega-6 fatty acid (n6-FA) content increased with PC1 parallel with allochthony. Perch muscle DHA (22:6n3) content decreased, and ALA (18:3n3) increased towards shallower murkier lakes (PC2). Perch allochthony was positively correlated with muscle THg and n6-FA content, but did not correlate with n3-FA content. Hence, the quality of perch muscle for human consumption decreases (increase in HQ) with increasing forest coverage and decreasing pH, potentially mediated by increasing fish allochthony.
... A comparable loss of EPA and DHA contents in feeds, as described for ocean warming, is suspected to happen in freshwaters. Taipale et al. (2016) reported that eutrophication (increase of nutrients) and brownification (increase of terrestrial humic substances due to global warming and reduced acid rain deposition) in boreal and subarctic lakes have an adverse impact on the trophic transfer of EPA and DHA. Both impacts change the phytoplankton EPA and DHA contents. ...
... Regression equations with R 2 and lines with 95% confidence limits are also shown. All linear regressions were significant (P < 0.05) (From Taipale et al. (2016), credit Elsevier) prominent keystone grazer in the planktonic food chain. However, an N-related reduction in secondary production can, as mentioned several times, affect higher trophic levels, such as fishes. ...
Chapter
Central of the trophic transfer is its efficiency, the ratio between production of one trophic level and that of the previous one. Long-chain polyunsaturated fatty acids (LC-PUFAs), particularly docosahexaenoic acid (DHA), are preferentially retained by higher trophic levels in disfavor of nonessential FAs and bulk carbon. Traditional beliefs have to be revised: Autochthonous LC-PUFA sources prevail even in lotic headwater food webs. The hypothesis that (marine) single-cell factories, sensitive to global warming, are the sole source of ω3 LC-PUFAs is being challenged by the identification of the widespread occurrence of ωx genes in animals and by finding potentially additional sources.
... These acids were dominant among the PUFAs in macrophytes of Lake Gusinoe [40]. This lake belongs to oligotrophic lakes [41,42], where the taxon of cryptophytic, dinophytic, and diatom algae are inhabitants, synthesizing EPA and DHA in large quantities [43,44]. It is accepted that fish inhabiting such water bodies may have a higher nutritional value in terms of PUFA content [44]. ...
... This lake belongs to oligotrophic lakes [41,42], where the taxon of cryptophytic, dinophytic, and diatom algae are inhabitants, synthesizing EPA and DHA in large quantities [43,44]. It is accepted that fish inhabiting such water bodies may have a higher nutritional value in terms of PUFA content [44]. ...
Article
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This paper describes the study of the fatty acid (FA) composition of three fish species (roach, perch, and pike) from Lake Gusinoe (western Transbaikalia). Using principal component analysis, the fatty acid composition of the studied fish species was shown to be species specific. The muscle tissue of roach, perch, and pike was found to contain high levels of polyunsaturated fatty acids (PUFA), including essential docosahexaenoic (DHA), eicosapentaenoic (EPA), and arachidonic acids. Indicators of nutritional quality based on the fatty acid composition showed that the values of the hypocholesterolemic/hypercholesterolemic (HH) ratio indices were sufficiently high. The atherogenicity (AI) and thrombogenicity (TI) indices, which are indicators for the nutritional value, were less than 1 in the studied fish. In terms of flesh lipid quality (FLQ), pike and perch had the highest proportion of total EPA + DHA. According to the obtained data for the composition of fatty acids in the muscle tissue of the studied fish from Lake Gusinoe, the anthropogenic load exerted on Lake Gusinoe has not yet statistically significantly affected the fish muscle quality.
... Compared to the number of organisms that rely on DHA, the number that are able to synthesize and accumulate DHA de novo efficiently is rather limited. The main producers of DHA are the Bacillariophyceae, Cryptophyceae, Dinophyceae and Prymnesiophyceae, which primarily inhabit oligotrophic aquatic ecosystems (Ahigren et al., 1996;Taipale et al., 2016). Besides microalgae, thraustochytrids, belonging to the kingdom Chromista and closely resembling a zoosporic fungi, are able to accumulate significant amounts of DHA (up to 12.5% of their dry mass), however, their total ecosystem biomass, as a saprophyte, is rather low (Kimura et al., 2001;Raghukumar, Ramaiah & Raghukumar, 2001;Fan et al., 2007;Lee Chang et al., 2012). ...
... Besides microalgae, thraustochytrids, belonging to the kingdom Chromista and closely resembling a zoosporic fungi, are able to accumulate significant amounts of DHA (up to 12.5% of their dry mass), however, their total ecosystem biomass, as a saprophyte, is rather low (Kimura et al., 2001;Raghukumar, Ramaiah & Raghukumar, 2001;Fan et al., 2007;Lee Chang et al., 2012). Eutrophication leads to an increase in density of cyanobacteria and this decreases the trophic transfer of LC-PUFA to higher trophic levels and, consequently, the nutritive quality of fish for human consumption (Müller-Navarra et al., 2004;Taipale et al., 2016). However, it should be noted that total LC-PUFA production increases with the availability of nutrients and in many eutrophic lakes cyanobacteria blooms typically occur in summer. ...
Article
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In recent decades, much conceptual thinking in trophic ecology has been guided by theories of nutrient limitation and the flow of elements, such as carbon and nitrogen, within and among ecosystems. More recently, ecologists have also turned their attention to examining the value of specific dietary nutrients, in particular polyunsaturated fatty acids (PUFA), among which the omega-3 PUFA, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) play a central role as essential components of neuronal cell membranes in many organisms. This review focuses on a new neuroecological approach stemming from the biochemical (mechanistic) and physiological (functional) role of DHA in neuronal cell membranes, in particular in conjunction with G-protein coupled receptors (GPCRs). We link the co-evolution of these neurological functions to metabolic dependency on dietary omega-3 PUFA. We outline ways in which deficiencies in dietary DHA supply may affect, cognition, vision, and behaviour, and ultimately, the biological fitness of consumers. We then review emerging evidence that changes in access to dietary omega-3 PUFA may ultimately have profound impacts on trophic interactions leading to potential changes in community structure and ecosystem functioning that, in turn, may affect the supply of DHA within and across ecosystems, including the supply for human consumption.
... Therefore, they are responsible for half of the atmospheric oxygen. Zooplankton diet consists of various phytoplankton species, which differ in their grazing resistance (e.g., size, shape, and toxins) and nutritional quality (Taipale et al., 2013;Taipale et al., 2016) [1,2] . Zooplankton species have different types of life histories influenced by seasonal variations of biotic factors, feeding ecology and predation pressure. ...
... Therefore, they are responsible for half of the atmospheric oxygen. Zooplankton diet consists of various phytoplankton species, which differ in their grazing resistance (e.g., size, shape, and toxins) and nutritional quality (Taipale et al., 2013;Taipale et al., 2016) [1,2] . Zooplankton species have different types of life histories influenced by seasonal variations of biotic factors, feeding ecology and predation pressure. ...
... These browning-induced changes in temperature and oxygen regimes have far-reaching consequences on phytoplankton community composition, favouring taxa with buoyancy control mechanisms, while disproportionately suppressing diatoms with higher sedimentation rates. The consequences of declines in diatom production are not trivial as they are considered high-quality resources for consumers due to a high content in the omega-3 essential fatty acids, eicosapentaenoic acid and docosahexaenoic acid (Taipale et al. 2013;Taipale et al. 2016). ...
... Mixotrophs (e.g., dinoflagellates and raphidophytes) may be resistant to grazing due to size incompatibilities or defensive mechanisms, thus restricting nutrient transfer. Finally, DOM-rich environments have lower primary production, which further lower the phytoplankton resources supporting food webs (Taipale et al. 2016;Senar et al. 2019). ...
Article
Lake browning—the increase in catchment-derived (allochthonous) dissolved organic matter (DOM) to lakes—is altering lake physicochemical environments, with consequences for phytoplankton biomass and community composition. We hypothesized that as lakes brown, there will be an increase in phytoplankton biomass and a shift to cyanobacteria-dominated phytoplankton communities as a result of the reduced light availability and increased DOM-bound nutrients (e.g., nitrogen, phosphorus, iron). We tested this hypothesis by sampling temperate lakes in central Ontario (Canada) spanning DOM quantity and quality gradients. We found that lake browning results in larger concentrations of more refractory (i.e., aromatic, high molecular weight) DOM and greater concentrations of nutrients; however, internal nutrient loading was also an important nutrient source in these lakes. We also found that these changes were related to the predominant species in the phytoplankton community. Diatoms dominated in clear oligotrophic lakes. Low levels of lake browning, with concentrations of dissolved organic carbon (DOC) between 4 and 8 mg L− 1, resulted in a shift from diatoms to cyanobacteria. Higher levels of lake browning, with concentrations of DOC between 8 and 12 mg L− 1, resulted in a replacement of cyanobacteria with mixotrophic species. Lake browning appears to fuel phytoplankton chlorophyll-a concentrations while triggering shifts to phytoplankton able to survive if not thrive in progressively browner waters. Lake browning may therefore have consequences on energy transfer through the lower food web.
... Por outro lado, em ecossistemas oligotróficos, são relatadas menores concentrações de nutrientes e matéria orgânica, além de menores valores de turbidez e pH (Almeida et al., 2012). Com relação à comunidade fitoplanctônica, estudos têm mostrado que em ecossistemas eutróficos há predominância de cianobactérias (Taipale et al., 2016), clorofíceas (Pastich et al., 2016), euglenofíceas (Santana et al., 2016) e espécies de rotíferos (Browen et al., 2017), enquanto em ambientes oligotróficos, espécies de diatomáceas são mais abundantes (Taipale et al., 2016). Com relação à comunidade zooplanctônica, a dominância de copepodas calanoidas e ciclopoidas pode indicar baixos graus de trofia (Esteves, 2011). ...
... Por outro lado, em ecossistemas oligotróficos, são relatadas menores concentrações de nutrientes e matéria orgânica, além de menores valores de turbidez e pH (Almeida et al., 2012). Com relação à comunidade fitoplanctônica, estudos têm mostrado que em ecossistemas eutróficos há predominância de cianobactérias (Taipale et al., 2016), clorofíceas (Pastich et al., 2016), euglenofíceas (Santana et al., 2016) e espécies de rotíferos (Browen et al., 2017), enquanto em ambientes oligotróficos, espécies de diatomáceas são mais abundantes (Taipale et al., 2016). Com relação à comunidade zooplanctônica, a dominância de copepodas calanoidas e ciclopoidas pode indicar baixos graus de trofia (Esteves, 2011). ...
... Chrysophyceae occur in a wide range of habitats, yet the largest abundance of chrysophytes are in low nutrient lakes, oligo-or mesotrophic, with low to moderate productivity (Wetzel 2001, Holopainen et al. 2003, Reynolds 2006, Taipale et al. 2016) () (Nicholls and Wujek 2015). Chrysophyceae are reported as common both in highly colored, humic waters, and in clear waters (Olrik 1998, Holopainen et al. 2003, Nicholls and Wujek 2015. ...
... ,Klug and Cottingham 2001, Weyhenmeyer et al. 2004, Urrutia- Cordero et al. 2017, Kankaala et al. 2019). However, a large-scale survey of Finnish lakes found that chrysophytes were actually less abundant in brown water lakes, and their abundance decreased with browning ((Taipale et al. 2016) and references therein). This indicates that even though chrysophytes are often present, and occasionally dominating humic lakes, they might be more abundant in clear lakes. ...
... Dissolved organic carbon levels are increasing owing to climate change and land use (peat mining and forestry), an issue that has been neglected in water management until recently (Kritzberg et al., 2020). The lake water colour also affects the critical phosphorus threshold that triggers the growth of bloom-forming Cyanobacteria (Vuorio et al., 2020) and decreases the nutritional quality of fish for human consumers (Taipale et al., 2016). ...
Article
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Aim We use lake phytoplankton community data to quantify the spatio-temporal and scale-dependent impacts of eutrophication, land-use and climate change on species niches and community assembly processes while accounting for species traits and phylogenetic constraints. Location Finland. Time period 1977–2017. Major taxa Phytoplankton. Methods We use hierarchical modelling of species communities (HMSC) to model metacommunity trajectories at 853 lakes over four decades of environmental change, including a hierarchical spatial structure to account for scale-dependent processes. Using a “region of common profile” approach, we evaluate compositional changes of species communities and trait profiles and investigate their temporal development. Results We demonstrate the emergence of novel and widespread community composition clusters in previously more compositionally homogeneous communities, with cluster-specific community trait profiles, indicating functional differences. A strong phylogenetic signal of species responses to the environment implies similar responses among closely related taxa. Community cluster-specific species prevalence indicates lower taxonomic dispersion within the current dominant clusters compared with the historically dominant cluster and an overall higher prevalence of smaller species sizes within communities. Our findings denote profound spatio-temporal structuring of species co-occurrence patterns and highlight functional differences of lake phytoplankton communities. Main conclusions Diverging community trajectories have led to a nationwide reshuffling of lake phytoplankton communities. At regional and national scales, lakes are not single entities but metacommunity hubs in an interconnected waterscape. The assembly mechanisms of phytoplankton communities are strongly structured by spatio-temporal dynamics, which have led to novel community types, but only a minor part of this reshuffling could be linked to temporal environmental change.
... A higher NOM content negatively influences the process of disinfection with ultraviolet light and promotes microbiological regrowth in the distribution system (Hem et al. 2015). Moreover, brownification results in challenges for the ecosystem, for example, increased surface water temperatures due to higher energy dissipation of solar radiation induced by a darker water surface, could disturb the fish community (Taipale et al. 2016;Hedström et al. 2017;Creed et al. 2018;Van Dorst 2020). Changing light transmission because of coloring may affect lake stratification, resulting in different oxygen levels in the water column, which in turn influence the food web structures of the ecosystem (Williamson et al. 2015;Pilla et al. 2018). ...
Article
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Increases in organic content and the resulting browning of freshwater are a current and growing challenge for the ecology of these waters, leading to the need for more efforts in drinking water production. This study investigated the implications of short-term changes in the water quality from Lake Bolmen on the treatment process at the downstream located at the Ringsjö water treatment plant. The main objective was to understand short-term organic matter fluctuations to efficiently manage drinking water treatment. The ability to make predictions about expected raw water quality based on variations in the watershed and upstream waters facilitates optimal adjustment of drinking water treatment processes. Key elements in the water supply system studied included a tunnel and pipeline system and a sub-basin of Lake Bolmen. A wealth of data were available for the analysis to establish temporal and spatial properties of the water quality in the system and its dependence on the governing factors. The main factors controlling water quality were identified, both regarding the transport in the tunnel and through the sub-basin, including surface runoff, hydrodynamic properties, sedimentation, resuspension, and biomass availability. Although a particular case was investigated, the study has implications for improving drinking water treatment. HIGHLIGHTS Analysis of unique long-term hourly data set on water quality in a lake and drinking water system.; Coupling of short-term organic matter fluctuations and catchment processes.; Influence of wind induced waves on the water color and organic mater content.;
... First, human impacts such as enhanced nutrient loads can reduce EPA content at the base of aquatic food chains; e.g., by altering periphyton assemblages to those containing less EPA (Cashman et al., 2013). Lower EPA production at the base of the food chain is transferred to higher trophic levels (consumers), causing aquatic organisms including emergent insects to contain less EPA (Müller-Navarra et al., 2004;Taipale et al., 2016;Scharnweber et al., 2019). Second, the abundance of some stream invertebrates also can be reduced in degraded streams through negative impacts of high nutrient or fine sediment loads; e.g., aquatic invertebrates that emerge from the stream during their lifecycle seem to be particularly susceptible to environmental stressors (Manning and Sullivan, 2021). ...
Article
Freshwater systems have undergone drastic alterations during the last century, potentially affecting cross-boundary resource transfers between aquatic and terrestrial ecosystems. One important connection is the export of biomass by emergent aquatic insects containing omega-3 polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic acid (EPA), that is scarce in terrestrial systems. Because of taxon-specific differences in PUFA content and functional traits, the contribution of different insect groups should be considered, in addition to total biomass export. In this context, one important trait is the emergence mode. Stoneflies, in contrast to other aquatic insects, crawl to land to emerge instead of flying directly from the water surface, making them accessible to ground-dwelling predators. Because stoneflies are especially susceptible to environmental change, stream degradation might cause a mismatch of available and required nutrients, particularly for ground-dwelling predators. In this study, we estimated emergent biomass and EPA export along two streams with different levels of habitat degradation. The EPA content in aquatic insects did not differ with different degrees of habitat degradation and total biomass export in spring was with 7.9 ± 9.6 mg m⁻² day⁻¹ in the degraded and 7.3 ± 8.5 mg m⁻² day⁻¹ in the natural system, also unaffected. However, habitat degradation substantially altered the contribution of crawling emergence to the total export in spring, with no biomass export by stoneflies at the most degraded sites. The EPA content in ground-dwelling spiders was correlated with emergent stonefly biomass, making up only 16.0 ± 6.2 % of total fatty acids at sites with no stonefly emergence, but 27.3 ± 3.0 % at sites with highest stonefly emergence. Because immune function in ground-dwelling spiders has been connected to EPA levels, reduced crawling emergence might impact spider fitness. Functional traits, like emergence mode as well as nutritional quality, should be considered when assessing the effects of stream degradation on adjacent terrestrial ecosystems.
... The availability and quality of FAs and sterols in phytoplankton have been repeatedly demonstrated as necessary for the growth and reproduction of zooplankton (Brett & Müller-Navarra, 1997;Martin-Creuzburg et al., 2009;Peltomaa et al., 2017). This has great ecological importance since zooplankton have a key position in aquatic food webs, linking the flow of dietary energy and essential biomolecules from phytoplankton to fish (Taipale et al., 2016). ...
Article
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Light availability is the main regulator of primary production, shaping photosynthetic communities and their production of ecologically important biomolecules. In freshwater ecosystems, increasing dissolved organic carbon concentrations, commonly known as browning, leads to lower light availability and the proliferation of mixotrophic phytoplankton. Here, a mixotrophic algal species (Cryptomonas sp.) was grown under five increasing dissolved organic carbon concentrations to uncover the plastic responses behind the success of mixotrophs in browning environments and their effect in the availability of nutritionally important biomolecules. In addition to the browning treatments, phototrophic, heterotrophic and mixotrophic growth conditions were used as controls. Despite reduced light availability, browning did not impair algal growth compared to phototrophic conditions. Comparative transcriptomics showed that genes related to photosynthesis were down‐regulated, whereas phagotrophy gene categories (phagosome, lysosome, and endocytosis) were up‐regulated along the browning gradient. Stable isotope analysis of phospholipid fractions validated these results, highlighting that the studied mixotroph increases its reliance on heterotrophic processes with browning. Metabolic pathway reconstruction using transcriptomic data suggests that organic carbon is acquired through phagotrophy and used to provide energy in conjunction with photosynthesis. Although metabolic responses to browning were observed, essential fatty acid content was similar between treatments while sterol content was slightly higher upon browning. Altogether, our results provide a mechanistic model of how a mixotrophic algae responds to browning and how such responses affect the availability of nutritionally essential biomolecules for higher trophic levels.
... These factors have the potential to alter the plankton community composition due to loss of phytoplankton biodiversity and shifts towards more mixotrophic species (Urrutia-Cordero et al., 2017). The shifts in light spectrum by brownification can also affect the phytoplankton community composition (Hintz et al., 2021;Senar et al., 2021), and higher trophic levels may be affected by less and/or lower quality food caused by increasing brownification (Taipale et al., 2016;Paczkowska et al., 2020). ...
Article
Climate change is projected to cause brownification of some coastal seas due to increased runoff of terrestrially derived organic matter. We carried out a mesocosm experiment (15 d) to test the effect of this on the planktonic ecosystem expecting reduced primary production and shifts in the phytoplankton community composition. The experiment was set up in 2.2 m³ mesocosm bags using four treatments, each with three replicates: control (Contr) without any manipulation, organic carbon additive HuminFeed (Hum; 2 mg L⁻¹), inorganic nutrients (Nutr; 5.7 μM NH4 and 0.65 μM PO4), and combined Nutr and Hum (Nutr + Hum) additions. Measured variables included organic and inorganic nutrient pools, chlorophyll a (Chla), primary and bacterial production and particle counts by flow cytometry. The bags with added inorganic nutrients developed a phytoplankton bloom that depleted inorganic N at day 6, followed by a rapid decline in Chla. Brownification did not reduce primary production at the tested concentration. Bacterial production was lowest in the Contr, but similar in the three treatments receiving additions likely due to increased carbon available for heterotrophic bacteria. Picoeukaryotes clearly benefited by brownification after inorganic N depletion, which could be due to more effective nutrient recycling, nutrient affinity, light absorption, or alternatively lower grazing pressure. In conclusion, brownification shifted the phytoplankton community composition towards smaller species with potential effects on carbon fluxes, such as sinking rates and export to the sea floor.
... Dissolved 401 organic carbon levels are increasing due to climate change and land-use (peat mining and 402 forestry), an issue that has been neglected in water management until recently (Kritzberg et 403 al. 2020). The lake water colour also affects the critical phosphorus thresholds that triggers 404 the growth of bloom-forming cyanobacteria (Vuorio et al. 2020) and decreases the nutritional 405 quality of fish for human consumers (Taipale et al. 2016). 406 407 When considering the historically vastly dominating community type of RCP 1 as a baseline, 408 we show that environmental filtering and species sorting have resulted in a macrosystem-409 wide restructuring of Finnish lake phytoplankton communities over the past four decades. ...
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The combined effects of eutrophication, land-use and climate change are major threats to aquatic ecosystems, their biodiversity and integrity in sustaining ecosystem functions. Disentangling the mechanisms by which environmental change contributes to community assembly processes and species niches remains challenging, especially at macro-ecological scales. Here, we collated phytoplankton community data including 853 lakes along a 1200km latitudinal gradient, monitored over four decades, to quantify the spatio-temporal and scale-dependent environmental impacts on species niches and assembly processes while accounting for species traits and phylogenetic constraints. Our results demonstrate the emergence of novel and widespread community composition clusters in previously more uniform communities. While total species richness remained relatively stable, changes in community weighted mean traits of the clusters indicate functional differences. A robust phylogenetic signal of species responses to the environment indicates strong niche conservatism and low taxonomic dispersion. Our findings imply profound spatio-temporal structuring of species co-occurrence patterns and highlight emerging functional differences of lake phytoplankton communities to environmental change over space and time.
... diatoms, cryptophytes and dinoflagellates) reduces the transfer of n3 PUFAs to higher trophic levels (e.g. Taipale et al., 2016). Additionally, as animals cannot synthesize n3 and n6 PUFAs, which are biochemical compounds essential for their survival, fitness and reproduction, fatty acids provide useful markers to assess nutritional quality in aquatic organisms (Arts and Kohler, 2009;Tocher, 2010;Meyer et al., 2019;Rangel et al., 2020). ...
Article
The synergistic effects of coastal urbanization have dramatically impacted biological communities. Yet, few studies have investigated how urbanization can influence the diet quality and trophic ecology of coastal sharks. In a preliminary study, we examined for spatial variation in the nutritional ecology of a highly active marine predator, the blacktip sharks (Carcharhinus limbatus) exposed to regional differences in coastal urbanization in southeast Florida. We used medium-term nutritional indicators (i.e., body condition; whole blood stable isotopes [δ¹⁵N and δ¹³C]) and short-term dietary markers (i.e., plasma fatty acid profiles) to test the hypothesis that the nutritional ecology of marine predators would differ in areas exposed to increased urbanization. Our initial results showed that blacktip sharks sampled in high urbanized area (hereafter, ‘urban sharks’) exhibited relatively higher body condition, blood δ¹⁵N levels, and percentages of saturated fatty acids compared to sharks sampled in low urbanized area (hereafter ‘non-urban sharks’). Collectively, these results suggest a possible positive alteration in the amount of food consumed by sharks and/or in the caloric value of their prey. We also found lower percentages of bacterial markers and higher values of dinoflagellate markers in urban sharks. Compared to more resident species evaluated in the region, we did not detect a reduction in diet quality (in terms of essential fatty acids) in this highly active species exposed to urbanization. Therefore, it is possible that the lifestyle and feeding behavior have an influence on the quality of food consumed by urban sharks, and maybe the impacts of urbanization are more pronounced in resident, sedentary and benthic species.
... All studied lakes were oligotrophic and unpolluted, except the nearly mesotrophic Lake Ladoga, which is subjected to an anthropogenic pollution [44]. Indeed, mesotrophic conditions and anthropogenic pollution could decrease LC-PUFA contents in fish biomass (e.g., [31,55]). However, in the present study S. alpinus from Lake Ladoga had EPA and DHA contents similar to those of fish from oligotrophic and unpolluted lakes. ...
Article
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Fatty acids (FA) of muscle tissue of Salvelinus species and its forms, S. alpinus, S. boganidae, S. drjagini, and S. fontinalis, from six Russian lakes and two aquacultures, were analyzed. Considerable variations in FA compositions and contents were found, including contents of eicosapentaenoic and docosahexaenoic acids (EPA and DHA), which are important indicators of fish nutritive value for humans. As found, contents of EPA+DHA (mg·g−1 wet weight) in muscle tissue of Salvelinus species and forms varied more than tenfold. These differences were supposed to be primarily determined by phylogenetic factors, rather than ecological factors, including food. Two species, S. boganidae and S. drjagini, had the highest EPA+DHA contents in their biomass and thereby could be recommended as promising species for aquaculture to obtain production with especially high nutritive value. Basing on revealed differences in FA composition of wild and farmed fish, levels of 15-17-BFA (branched fatty acids), 18:2NMI (non-methylene interrupted), 20:2NMI, 20:4n-3, and 22:4n-3 fatty acids were recommended for verifying trade label information of fish products on shelves, as the biomarkers to differentiate wild and farmed charr.
... The freshwater crustacean Daphnia occupies a keystone position in pelagic food webs by being the primary conveyor of energy and biomass as well as limiting biochemicals from primary producers, the phytoplankton, to higher trophic levels of consumers like planktivorous fish (Gaedke & Straile, 1998;Taipale et al., 2016). ...
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Fluidity of a given membrane decreases at lower ambient temperatures, whereas it rises at increasing temperatures, which is achieved through changes in membrane lipid composition. In consistence with homeoviscous adaptation theory, lower temperatures result in increased tissue concentrations of polyunsaturated fatty acids (PUFAs) in Daphnia magna, suggesting a higher PUFA requirement at lower temperatures. However, so far homeoviscous adaptation has been suggested for single or geographically separated Daphnia genotypes only. Here, we investigated changes in relative fatty acid (FA) tissue concentrations in response to a lower temperature (15°C) within a D. magna population. We determined juvenile growth rates (JGR) and FA patterns of 14 genotypes that were grown on Chlamydomonas klinobasis at 15°C and 20°C. We report significant differences of JGR and the relative body content of various FAs between genotypes at either temperature and between temperatures. Based on slopes of reaction norms, we found genotype‐specific changes in FA profiles between temperatures suggesting that genotypes have different strategies to cope with changing temperatures. In a hierarchical clustering analysis, we grouped genotypes according to differences in direction and magnitude of changes in relative FA content, which resulted in three clusters of genotypes following different patterns of changes in FA composition. These patterns suggest a lower importance of the PUFA eicosapentaenoic acid (EPA, C20:5ω3) than previously assumed. We calculated an unsaturation index (UI) as a proxy for membrane fluidity at 15°C, and we neither found significant differences for this UI nor for fitness, measured as JGR, between the three genotype clusters. We conclude that these three genotype clusters represent different physiological solutions to temperature changes by altering the relative share of different FAs, but that their phenotypes converge with respect to membrane fluidity and JGR. These clusters will be subjected to different degrees of PUFA limitation when sharing the same diet. In consistence with the homeoviscous adaptation theory, the concept of maintaining a constant membrane fluidity at changing temperatures, it has been shown for single D. magna, genotypes that lower temperatures result in increased tissue concentrations of PUFAs, suggesting a higher PUFA requirement at lower temperatures. Here, we investigated homeoviscous adaptation to a lower temperature (15°C) within a D. magna population by calculating the change of the relative content of individual fatty acids between 15°C and 20°C for 14 genotypes of a natural D. magna population. We applied a hierarchical clustering analysis that grouped genotypes according to differences in their fatty acid alteration profiles, which resulted in three different clusters of genotypes, that differ in terms of changes in their fatty acid content but whose phenotypes converge in terms of an unsaturation index and juvenile somatic growth, which were determined for each genotype as well.
... Research has shown that a higher color content can have negative effect on the live expectations of specific fish species (Hedström et al., 2017), which can change an ecosystem markedly. Thus, the productivity and composition of the community in such ecosystems can be negatively influenced and lead to long-term changes (Creed et al., 2018), eventually causing drastic alterations inside the food web systems of affected surface waters (Taipale et al., 2016). ...
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Study region This study focuses on the twelfth largest lake in Sweden, Lake Bolmen and its catchment. Study focus During the last decades the process of brownification has resulted in water with browner color, affecting water quality and ecosystems. The occurrence of brownification and its governing factors, especially with regard to the interaction with the environment, is not yet fully understood. This study therefore performed different statistical analysis to detect spatial and temporal patterns in brown color and associated forcing factors. In addition, models were developed to describe the water flows in the lake and their influence on the water color. New hydrological insights for the region Seasonal variations in color are dominated by meteorological parameters such as precipitation and temperature, whereas long-term (decadal) variations are functions of trends in these parameters as well as changes in land use, primarily related to forestry. Modeling the water flows yielded the residence time for different sub-basins in the lake, indicating the effects of travel time on the color. Calculated wind-generated surface waves and their effects on resuspension showed that such events may occur on a limited event and time scale.
... In general, the EPA þ DHA contents in farmed fish in the eutrophic WJD Reservoir were higher than that of the wild planktivorous fish in eutrophic Taihu (1.1 ± 0.4 mg/g w.w.) and lower than that of wild planktivorous fish from oligotrophic lakes in Canada (13.6 ± 4.8 mg/g d.w.) and Italian (12.2 mg/g d.w.) (Kainz et al., 2004;Vasconi et al., 2015). This might be explained by the fact that eutrophication could decrease the essential EPA and DHA contents accumulated in fish due to the increasing biomasses of chlorophyta and cyanobacteria (Razavi et al., 2014;Taipale et al., 2016). ...
... For instance, urban individuals have a higher body condition and more energetic reserves (especially lipids) than their rural counterparts, possibly linked to differences in food quality (Brans et al., 2017;Meillère et al., 2015). In eutrophic sites, growth patterns and energetic reserves are also altered, probably due to increased turbidity and changes in prey availability (Ahigren et al., 1996;Frisch et al., 2014;Leach et al., 1977;Pinto-Coelho et al., 2005;Razavi et al., 2014;Taipale et al., 2016). Moreover, some biotic factors such as parasitism can be strongly modified by changes in water quality, especially eutrophication, because nutrient pollution can alter the prevalence and intensity of some parasites (Maceda-Veiga et al., 2019;Smallbone et al., 2016). ...
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• Freshwater ecosystems are highly impacted by human activities, but the effects of human‐induced perturbations on fish phenotypic divergence remain poorly understood, especially in riverine systems. • In this study, we tested the effects of urbanisation and eutrophication on several morphological and physiological traits in 17 gudgeon populations of Gobio occitaniae from South of France. • We first demonstrated that eutrophication gradient was associated with changes in morphology and energy reserves, while urbanisation was associated with changes in body condition. More specifically, fish from highly eutrophic sites had deeper bodies and larger jaws, and a higher lipid content in their muscles. • Urban fish had a higher body condition compared to their rural counterparts. The phenotypic divergence (Pst) among sites was significantly higher than the neutral genetic differentiation (Fst), suggesting that these morphological and physiological differences cannot be explained by neutral genetic drift alone. • This study thus suggests that eutrophication and urbanisation are major drivers of phenotypic divergence in riverine fish populations, and calls for further experimental studies investigating the ecological and evolutionary effects of human activities on riverine fish populations.
... Factors that limit the development of large Cladocera in dystrophic (humic) lakes, despite low fish pressure and a large amount of food resources are still discussed [14]. Among the factors limiting the development of zooplankton are humic stress connected to the high concentrations of humic substances and DOC [90,91], low food quality [92], low pH [49], UV radiation [93,94], sharp temperature, and oxygen gradients from the surface [95]. We suggest that zooplankton in humic lakes are strongly limited by all of the above factors and only a few species could thrive under such conditions. ...
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This study presents the diversity and structure of pelagic zooplankton in north-eastern Poland. The research was conducted in 47 lakes with different trophic conditions in the middle of summer. Samples were collected close to the deepest part of the lakes to avoid the diverse benthic and littoral zones. We found 119 zooplankton species of which 32 were Cladocera, 16 were Cyclopoida, 4 were Calanoida, and 67 were Rotifera. We determined which species occurred most frequently in the region, as well as the species that were characteristic of different trophic conditions. We also recorded the presence of eight cold-adapted species which some of them are considered as glacial relicts (e.g., Eurytemora lacustris, Heterocope appendiculata, Cyclops lacustris). Our research revealed potential glacial refugia for planktonic species in 14 lakes of NE Poland. Our study suggests that the presence of stenotherm species may be an excellent indicator of the ecological status of deep lakes and could be considered in lake monitoring programs. Furthermore, we did not find Bythotrephes longimanus which has been reported from Poland. Instead, we found that B. brevimanus was the most common representative of the genus in the study area.
... In general, the EPA þ DHA contents in farmed fish in the eutrophic WJD Reservoir were higher than that of the wild planktivorous fish in eutrophic Taihu (1.1 ± 0.4 mg/g w.w.) and lower than that of wild planktivorous fish from oligotrophic lakes in Canada (13.6 ± 4.8 mg/g d.w.) and Italian (12.2 mg/g d.w.) (Kainz et al., 2004;Vasconi et al., 2015). This might be explained by the fact that eutrophication could decrease the essential EPA and DHA contents accumulated in fish due to the increasing biomasses of chlorophyta and cyanobacteria (Razavi et al., 2014;Taipale et al., 2016). ...
... In general, the EPA þ DHA contents in farmed fish in the eutrophic WJD Reservoir were higher than that of the wild planktivorous fish in eutrophic Taihu (1.1 ± 0.4 mg/g w.w.) and lower than that of wild planktivorous fish from oligotrophic lakes in Canada (13.6 ± 4.8 mg/g d.w.) and Italian (12.2 mg/g d.w.) (Kainz et al., 2004;Vasconi et al., 2015). This might be explained by the fact that eutrophication could decrease the essential EPA and DHA contents accumulated in fish due to the increasing biomasses of chlorophyta and cyanobacteria (Razavi et al., 2014;Taipale et al., 2016). ...
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Fish is an important source of nutritional omega-3 (n-3) polyunsaturated fatty acids, but it also readily accumulates toxic mercury (Hg) and microcystins (MC) in eutrophic aquatic systems. In China, farmed fish was widely consumed, and aquaculture has caused pervasive eutrophication of freshwater lakes, resulting in the increasing accumulation of MC in fish tissue. To assess the risk-benefit of consuming farmed fish, 205 fish samples of 10 primary species were collected from the eutrophic Wujiangdu (WJD) Reservoir, SW China. The contents of Hg, microcystin-RR (MC-RR), microcystin-LR (MC-LR), and polyunsaturated fatty acids (PUFA) in fish were analyzed. The results showed that THg and MeHg concentrations in all fish sampls were well below the safety limit (500 ng/g w.w) established by the Standardization Administration of China, with average values of 22.9 ± 22.8 and 6.0 ± 6.6 ng/g wet weight (w.w.), respectively. Average concentrations of MC-RR and MC-LR were 40 ± 80 and 50 ± 80 ng/g w.w., respectively. MC-RR and MC-LR concentrations in fish were significantly higher in silver carp and black carp than in perch and catfish (p < 0.05). In nutritional terms, average concentrations of n-3 PUFA and the eicosapentaenoic (EPA) + docosahexaenoic acids (DHA) of fish were 2.0 ± 2.5 and 1.4 ± 0.5 mg/g w.w., respectively. The risk-benefit assessment suggests that the n-3 PUFA benefits from consuming all farmed fish species in the WJD Reservoir outweigh the adverse effects of MeHg. However, except for perch, most fish species still pose a high MC-LR exposure risk that created a requirement for fish consumption advisories and monitoring. Consequently, more attention should be paid on the health risk of combined exposure to pollutants by aquatic product consumption.
... [ Managing aquatic ecosystems and water resources under multiple stresses (MARS: www.marsproject.eu) [10,11]. ...
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To assess if environmental differences other than water quality may affect the outcome of the Benthic Quality Index, a comparison of the application of four different methods (Benthic Quality Index—BQIES, Lake Habitat Modification Score—LHMS, Lake Habitat Quality Assessment—LHQA and Organisation for Economic Co-operation and Development—OECD) used to classify the lake ecological and hydro-morphological status of 10 Italian lakes was performed. Five lakes were natural and five were reservoirs belonging to both Alpine and Mediterranean Ecoregions. The 10 lakes were sampled using the Water Framework Directive compliant standardized national protocol, which includes sampling soft sediment in the littoral, sublittoral and deep layers along transects with a grab of 225 cm2 during spring and autumn. The application of Generalised Linear Mixed Effect Models both at the lake level and at the single station of each lake highlighted that, at the lake level, no significant correlations existed between any couple of hydro-morphological, ecological and trophic status assessments, with each metric representing a different facet of human impact on the environment. At the single site level, we found significant effects of depth on the metrics of biodiversity. The best approximation of single-site macroinvertebrates diversity among the metrics of overall lake quality was with the LHMS, but not with the BQIES. Our hypotheses that lake macroinvertebrates assemblages depend also on other potential confounding variables of habitat degradation and intrinsic differences between lakes were confirmed, with depth playing a major role. Therefore, the assessment of lakes with different depths may produce different whole-lake BQIES values, only because of the effect of depth gradient and not because of differences in lake quality.
... Lake phosphorus concentrations are negatively correlated with the availability of essential PUFAs in the seston, resulting in reduced growth rates and reproduction of zooplankton in eutrophic lakes (Müller-Navarra et al., 2004). Furthermore, increased abundance of cyanobacteria restricts energy and PUFA transfer in the food web and ultimately results in fish being lower quality resources for human nutrition (Taipale et al., 2016b). In contrast to cyanobacteria, diatoms and cryptophytes have abundant long-chain PUFAs and sterols to support high growth rates in zooplankton (Galloway and Winder, 2015;Taipale et al., 2016a;Peltomaa et al., 2017). ...
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The effects of multiple stressors are difficult to separate in field studies, and their interactions may be hard to predict if studied in isolation. We studied the effects of decreasing food quality (increase in cyanobacteria from 5 to 95% simulating eutrophication), temperature increase (by 3°C), and microplastic exposure (1% of the diet) on survival, size, reproduction, and fatty acid composition of the model freshwater cladoceran Daphnia magna. We found that food quality was the major driver of Daphnia responses. When the amount of cyanobacteria increased from 5 to 95% of the diet, there was a drastic decrease in Daphnia survival (from 81 ± 15% to 24 ± 21%), juvenile size (from 1.8 ± 0.2 mm to 1.0 ± 0.1 mm), adult size (from 2.7 ± 0.1 mm to 1.1 ± 0.1 mm), and reproduction (from 13 ± 5 neonates per surviving adult to 0), but the decrease was not always linear. This was most likely due to lower availability of lipids, eicosapentaenoic acid (EPA), and sterols from the diet. Micro-plastic exposure did not affect Daphnia survival, size, or reproduction. Food quality had an interactive effect with temperature on fatty acid content of Daphnia. Total fatty acid content of Daphnia was almost 2-fold higher at 20 °C than at 23 °C when fed 50% cyanobacteria. This may have implications for higher trophic level consumers, such as fish, that depend on zooplankton for energy and essential lipids. Our findings suggest that as proportions of cyanobacteria increase, in tandem with water temperatures due to climate change, fish may encounter fewer and smaller Daphnia with lower lipid and EPA content.
... It has been demonstrated that eutrophication in lake systems can reduce the proportion of EPA and DHA transferred to higher organisms from primary producers (Strandberg et al., 2015;Taipale et al., 2016). Furthermore, it is known that cyanobacteria and chlorophytes often dominate the phytoplankton in eutrophic waters (Scheffer and Van Nes, 2007;Berthold et al., 2018) which contain different FA biomarkers. ...
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Benthic diatoms are a high-quality food resource providing essential fatty acids to benthic grazers. Different stressors may alter the proportion of diatoms and other microalgae and thus can affect the quality as well as quantity of food available to benthic consumers. Microphytobenthos (MPB) lipid biomarkers were assessed in a field experiment to elucidate changes to the biosynthesis of fatty acids (FA) under nitrogen (N) enrichment (three levels) at eight intertidal sites that spanned a turbidity gradient. Influences on the flow of carbon and energy were determined using FA biomarkers of a functionally important deposit-feeding tellinid bivalve (Macomona liliana). Site-specific effects of N enrichment were detected in MPB quantity and quality measurements. Enrichment generally increased MPB biomass (chl a) across all sites, while the proportion of diatom associated fatty acid biomarkers was more variable at some sites. Analysis of sediment FA biomarkers and environmental variables suggested that changes to the microbial community composition and quality were related to water clarity and mud content of the bed. The ability of the MPB to utilize the increased nitrogen, as indicated by the resource use efficiency index, was also important. Despite the increase in MPB biomass, lipid reserves in the tissue of M. liliana, a primary consumer of MPB, were reduced (by up to 6 orders of magnitude) in medium and high N addition plots compared to control plots. Further, the nutritional quality of the bivalves to higher trophic levels [indicated by a lower ratio of essential FAs (ω3:ω6)] was reduced in high treatment plots compared to control plots suggesting the bivalves were adversely affected by nutrient enrichment but not due to a reduction in food availability. This study suggests anthropogenic nutrient enrichment and turbidity may indirectly alter the structure and function of the benthic food web, in terms of carbon flow and ecosystem productivity. This may indirectly change the interactions between MPB and key bivalves as suspended sediment concentrations and nutrient enrichment continue to increase globally. This has implications for various ecosystem functions that are mediated by these interactions, such as nutrient cycling as well as primary and secondary production.
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The land-affected signal in remotely sensed radiance from nearshore waters is a common problem for remote sensing, introducing uncertainty in atmospheric correction and subsequent water quality constituent concentration estimates. This study proposes a new method for identifying effects of land on satellite remote sensing of water quality. The new optical water types (OWT) containing the land-affected signal were derived from POLYMER-corrected imagery of the Medium Resolution Imaging Spectrometer in reduced resolution (MERIS RR) and Sentinel-3 Ocean and Land Colour Instrument (OLCI). These were then applied, as part of a larger set of existing OWTs corresponding to the variability observed in natural waters, to satellite images. The ability to identify pixels containing both water and land, and those contaminated with radiance from adjacent land, was evaluated. Our test sites include dark lakes of varying size in Sweden (Lakes Rusken, Bolmen, Ringsjön, and Ivösjön) where the classification showed high sensitivity to land near the lake shore. The land-affected signal is shown to lead to underestimations of chlorophyll-a concentration and Forel-Ule colour indices, and overestimations of turbidity in these lakes, which can be corrected after masking out the land-affected pixels. The land-affected signal is strongest in summer, both NDVI and sun zenith angle covaried with the seasonal variation of land-affected signal. Further, the results confirmed that satellite images with coarser spatial resolution are more prone to land-affected signal compared to images with finer spatial resolution, for small inland water bodies. We propose a data-driven approach for water quality processing with ‘land-affected water types’ as an effective way to improve the lake optical water quality monitoring from water colour sensors.
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The effects of lake browning on trophic functioning of planktonic food webs are not fully understood. We studied the effects of browning on the response patterns of polyunsaturated fatty acids and n −3/ n −6 ratio in seston and compared them between boreal and temperate lakes. We also compared the regional differences and the effects of lake browning on the reliance of zooplankton on heterotrophic microbial pathways and the mass fractions of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in zooplankton. Lake browning was associated with increasing phytoplankton biomass and concentrations of EPA and DHA in both temperate and boreal lakes, but the seston n −3/ n −6 ratio was lower in temperate than boreal lakes, most likely due the differences in phytoplankton community composition. The browning-induced increase in phytoplankton biomass was associated with increased reliance of zooplankton on a heterotrophic microbial pathway for both cladocerans and copepods in boreal and temperate lakes. This increased reliance on the heterotrophic microbial diet was correlated with a decrease in the EPA and DHA mass fractions in temperate copepods and a decrease in the n −3/ n −6 ratio in boreal cladocerans and copepods. Our results indicate that although phytoplankton responses to lake browning were similar across regions, this did not directly cascade to the next trophic level, where zooplankton responses were highly taxa- and region-specific. These results indicate that lake browning should be considered as an overarching moderator that is linked to, e.g., nutrient increases, which have more immediate consequences on trophic interactions at the phytoplankton–zooplankton interface.
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Concentrations of terrestrial‐derived dissolved organic carbon (DOC) in freshwater ecosystems have increased consistently, causing freshwater browning. The mechanisms behind browning are complex, but in forestry‐intensive regions browning is accelerated by land drainage. Forestry actions in streamside riparian forests alter canopy shading, which together with browning is expected to exert a complex and largely unpredictable control over key ecosystem functions. We conducted a stream mesocosm experiment with three levels of browning (ambient vs. moderate vs. high, with 2.7 and 5.5‐fold increase, respectively, in absorbance) crossed with two levels of riparian shading (70% light reduction vs. open canopy) to explore the individual and combined effects of browning and loss of shading on the quantity (algal biomass) and nutritional quality (polyunsaturated fatty acid and sterol content) of the periphytic biofilm. We also conducted a field survey of differently colored (4.7 to 26.2 mg DOC L‐1) streams to provide a ‘reality check’ for our experimental findings. Browning reduced greatly the algal biomass, suppressed the availability of essential polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA), and sterols, but increased the availability of terrestrial‐derived long‐chain saturated fatty acids (LSAFA). In contrast, loss of shading increased primary productivity, which resulted in elevated sterol and EPA content of the biofilm. The field survey largely repeated the same pattern: biofilm nutritional quality decreased significantly with increasing DOC, as indicated particularly by a decrease of the ω‐3:ω‐6 ratio and increase in LSAFA content. Algal biomass, in contrast, was mainly controlled by dissolved inorganic nitrogen (DIN) concentration, while DOC concentration was of minor importance. The ongoing browning process is inducing a dramatic reduction in the nutritional quality of the stream biofilm. Such degradation of the major high‐quality food source available for stream consumers may reduce the trophic transfer efficiency in stream ecosystems, potentially extending across the stream‐forest ecotone.
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We analyzed the taxonomic and fatty-acid (FA) composition of phytoplankton and zooplankton, and the environmental conditions at three coastal and offshore stations of the northern Baltic Sea. Plankton samples for FA analyses were collected under the framework of sampling campaigns of the Swedish National Marine Monitoring program in September 2017. Monitoring data of phytoplankton and zooplankton biomass, and environmental variables at each station were extracted from the Swedish Meteorological and Hydrological Institute database (https://sharkweb.smhi.se/). Monthly phytoplankton biomass at each station in July-September 2017 was aggregated by class (i.e., chyrsophytes, cryptophytes, dinoflagellates, diatoms, euglenophytes, cyanobacteria, etc.). Zooplankton biomass in September 2017 was aggregated by major taxa (i.e., Acartia sp. [Calanoida], Eurytemora affinis [Calanoida], Cladocera, Limnocalanus macrurus and other copepods (i.e. excluding Eurytemora and Acartia)). Environmental variables monthly monitored in January-October 2017 included salinity, concentrations of dissolved organic carbon, humic substances, total nitrogen and total phosphorus. These variables were measured from 0 to 10 m depth below water surface, and the depth-integrated averages were used for data analyses. Seston and zooplankton (Eurytemora affinis, Acartia sp. and Cladocera) FA composition was analyzed using gas chromatography and mass spectroscopy (GC-MS). Our dataset could provide new insights into how taxonomic composition and biochemical quality of the planktonic food chains change with the environmental conditions in subarctic marine ecosystems.
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Eutrophication and rising water temperature in freshwaters may increase the total production of a lake while simultaneously reducing the nutritional quality of food web components. We evaluated how cyanobacteria blooms, driven by agricultural eutrophication (in eutrophic Lake Köyliöjärvi) or global warming (in mesotrophic Lake Pyhäjärvi), influence the biomass and structure of phytoplankton, zooplankton, and fish communities. In terms of the nutritional value of food web components, we evaluated changes in the ω‐3 and ω‐6 polyunsaturated fatty acids (PUFA) of phytoplankton and consumers at different trophic levels. Meanwhile, the lakes did not differ in their biomasses of phytoplankton, zooplankton, and fish communities, lake trophic status greatly influenced the community structures. The eutrophic lake, with agricultural eutrophication, had cyanobacteria bloom throughout the summer months whereas cyanobacteria were abundant only occasionally in the mesotrophic lake, mainly in early summer. Phytoplankton community differences at genus level resulted in higher arachidonic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) content of seston in the mesotrophic than in the eutrophic lake. This was also reflected in the EPA and DHA content of herbivorous zooplankton (Daphnia and Bosmina) despite more efficient trophic retention of these biomolecules in a eutrophic lake than in the mesotrophic lake zooplankton. Planktivorous juvenile fish (perch and roach) in a eutrophic lake overcame the lower availability of DHA in their prey by more efficient trophic retention and biosynthesis from the precursors. However, the most efficient trophic retention of DHA was found with benthivorous perch which prey contained only a low amount of DHA. Long‐term cyanobacterial blooming decreased the nutritional quality of piscivorous perch; however, the difference was much less than previously anticipated. Our result shows that long‐term cyanobacteria blooming impacts the structure of plankton and fish communities and lowers the nutritional quality of seston and zooplankton, which, however, is mitigated at upper trophic levels. We evaluated how cyanobacteria blooms driven by agricultural eutrophication and global warming influence on the biomass and structure of phytoplankton, zooplankton, and fish communities and nutritional value of different food web components. Our result showed that lower availability of physiologically important long‐chain PUFA by primary producers and at lower trophic levels is mitigated by efficient trophic retention and biosynthesis at upper trophic levels.
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Inflows of colored terrestrial organic matter cause seawater browning and reduced phytoplankton production in sub-Arctic coastal ecosystems, potentially deteriorating the nutritional quality of marine food webs. We analyzed the fatty-acid (FA) composition of seston and the zooplankton taxa Eurytemora affinis and cladocerans at three locations of the northern Baltic Sea. At the coastal and northerly locations, salinity and phosphorus concentrations were low, while concentrations of humic substances, i.e. terrestrial organic matter, were high. The southerly location showed the opposite trend. The ratio between alga-specific ω-3 polyunsaturated FA and terrigenous monounsaturated FA (MUFA) in Eurytemora decreased from south to north, as did the ratio between the alga-specific docosahexaenoic acid (DHA) and terrigenous MUFA in cladocerans. With increasing humic substances, the biomass of DHA-rich phytoplankton decreased and the zooplankton MUFA content increased. Our results indicate that colored terrestrial organic matter alters the phytoplankton composition, consequently affecting the zooplankton nutritional quality.
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Organisms at the base of aquatic food webs synthesize essential nutrients, such as omega‐3 polyunsaturated fatty acids (n‐3 PUFA), which are transferred to consumers at higher trophic levels. Many consumers, requiring n‐3 long‐chain (LC) PUFA, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have limited ability to biosynthesize them from the essential dietary precursor α‐linolenic acid (ALA) and thus rely on dietary provision of LC‐PUFA. We investigated LC‐PUFA metabolism in freshwater zooplankton using stable hydrogen isotopes (δ2H) of fatty acids as tracers. We conducted feeding experiments with the freshwater keystone grazer Daphnia to quantify changes in the δ2H value of body FA in response to the FA composition of their food and the δ2H value of the ambient water. The isotopic composition of LC‐PUFA changed in Daphnia, depending on the integration of 2H from ambient water during de novo synthesis or bioconversion from dietary precursors, allowing us to distinguish dietary from bioconverted EPA in body tissue. We tested the applicability of these laboratory findings in a field setting by analyzing δ2H values of PUFA in primary producers and consumers in eutrophic ponds to track EPA sources of zooplankton. Multilinear regression models that included conversion of ALA to EPA correlated better with zooplankton δ2HEPA than seston δ2HEPA at low dietary EPA supply. This study provides evidence that zooplankton can compensate for low dietary EPA supply by activating LC‐PUFA biosynthesis and shows that herbivorous zooplankton play a crucial role in upgrading FA for higher trophic levels during low dietary EPA supply.
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Many lakes in the northern hemisphere are browning due to increasing concentrations of terrestrial dissolved organic carbon (DOC). The consequences of lake browning to littoral invertebrates, however, are not fully understood. We analyzed community structure and fatty acid (FA) profiles of littoral invertebrates in humic (DOC-rich) and clear-water lakes in Eastern Finland. We found higher abundance of chironomids (Diptera: Chironomidae) in humic compared to clear-water lakes, whereas stoneflies (Plecoptera) and mayflies (Ephemeroptera: Baetidae) were more abundant in clear-water lakes. Taxon explained 65% of the differences in the FA composition of littoral invertebrates. However, the proportion and content of polyunsaturated FAs of several taxa were significantly higher in clear-water lakes compared to humic lakes. Our results reveal differences in both community structure and nutritional quality of littoral invertebrates for fish between humic and clear-water lakes.
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Gammarid amphipods are a crucial link connecting primary producers with secondary consumers, but little is known about their nutritional ecology. Here we asked how starvation and subsequent feeding on different nutritional quality algae influences fatty acid retention, compound-specific isotopic carbon fractionation, and biosynthesis of ω-3 and ω-6 polyunsaturated fatty acids (PUFA) in the relict gammarid amphipod Pallaseopsis quadrispinosa. The fatty acid profiles of P. quadrispinosa closely matched with those of the dietary green algae after only seven days of refeeding, whereas fatty acid patterns of P. quadrispinosa were less consistent with those of the diatom diet. This was mainly due to P. quadrispinosa suffering energy limitation in the diatom treatment which initiated the metabolization of 16:1ω7 and partly 18:1ω9 for energy, but retained high levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) similar to those found in wild-caught organisms. Moreover, α-linolenic acid (ALA) from green algae was mainly stored and not allocated to membranes at high levels nor biosynthesized to EPA. The arachidonic acid (ARA) content in membrane was much lower than EPA and P. quadrispinosa was able to biosynthesize long-chain ω-6 PUFA from linoleic acid (LA). Our experiment revealed that diet quality has a great impact on fatty acid biosynthesis, retention and turnover in this consumer.
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It has been postulated that eutrophication causes replacement of n3 highly unsaturated fatty acids (n3 HUFA) rich taxa, such as Bacillariophyta, Cryptophyta and Dinophyta, with taxa poor in these fatty acids (FA), such as Chlorophyta and Cyanobacteria. Such a change in community composition at the basis of the food web may alter the FA composition of consumer tissues. Here, we investigated the effects of eutrophication on phytoplankton composition and FA profiles of seston and muscle of two omnivorous fish species (Astyanax fasciatus and Astyanax altiparanae) from reservoirs of different trophic status in Southeast Brazil. The phytoplankton composition and seston FA profiles reflected the degree of eutrophication at most of the studied sites. Three of the five most eutrophic sites were dominated by cyanobacteria and had the highest saturated fatty acid (SFA) and lowest polyunsaturated fatty acid (PUFA) relative contents among all sites. In contrast, the remaining two sites presented a higher phytoplankton diversity and higher relative contribution of sestonic PUFAs with 18 carbons (C18) and HUFAs than less eutrophic systems. However, there were no clear effects of sestonic FA profiles on the FA profiles of muscle of both fish species. A higher percentage of n3 HUFAs was found in the fish samples from a hypereutrophic and cyanobacteria dominated reservoir than in those from sites with a more diverse phytoplankton community in which fish mainly showed higher percentages of C18 PUFA. These results suggest a lack of a direct relationship between the degree of eutrophication and the percentage of n3 HUFAs in both fish species, which can be caused by specific characteristics of the reservoirs that may modulate eutrophication effects. Therefore, consumer FA biochemistry seemed to be dictated by their ability to select, accumulate, and modify dietary FAs, rather than by the eutrophication degree of the studied tropical reservoirs.
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Thesis
Agriculture puts major strains on Germany’s aquatic ecosystems because intensive livestock farming and overfertilization contaminate surface and groundwater bodies with nitrates. In order to address this environmental problem, Germany is obliged to implement the Nitrates Directive, a central water protection directive of the European Union. But ever since the adoption of this directive at the Euro-pean level in 1991, German policy-makers have struggled to properly implement it, both time- and content-wise. In June 2018, the European Court of Justice convicted the German government for the second time due to its non-compliance with the Nitrates Directive. This empirical observation forms the starting point of my research. The following thesis investigates why the German political decision-makers have repeatedly failed to produce timely and sufficient pol-icy outputs to comply with the European Nitrates Directives. Existing scientific literature points to the importance of party politics for policy responses to aquatic nitrate contamination. On that account, my thesis traces the German transposition of the Nitrates Directive between 1991 and 2018 with a focus on the policy process within the formal decision-making bodies of the national state, and the political parties operating within these decision-making bodies. In terms of theoretical framework, this research combines insights from cleavage theory, the Punctu-ated Equilibrium Framework and the EU implementation literature. Methodologically, it consists of a case study and analyses a variety of official documents (inter alia accounts of legislative debates, mo-tions, interpellations, bills and court judgments) with the aid of both qualitative and quantitative tech-niques of data analysis. The empirical findings confirm that party politics is key to understanding the policy process underlying the German transposition of the Nitrates Directive. Coupled with European pressure for policy reform, party-political cleavages helped put the nitrate issue onto the political agenda. However, the distribu-tion of policy-making competencies across decision-making bodies and the prevalence of coalition gov-ernments provided both proponents and opponents of strict nitrate policies among the political parties with possibilities to further their preferences. Besides, dissent between different state governments of the German bundesländer, and between environmental and agricultural policy-makers materialized. The policy process was therefore characterized by lengthy and controversial negotiations and trans-lated into policy compromises which fell short of the provisions of the Nitrates Directive.
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This text examines the impact of climate change on freshwater ecosystems, past, present and future. It especially considers the interactions between climate change and other drivers of change including hydromorphological modification, nutrient loading, acid deposition and contamination by toxic substances using evidence from palaeolimnology, time-series analysis, space-for-time substitution, laboratory and field experiments and process modelling. The book evaluates these processes in relation to extreme events, seasonal changes in ecosystems, trends over decadal-scale time periods, mitigation strategies and ecosystem recovery. The book is also concerned with how aspects of hydrophysical, hydrochemical and ecological change can be used as early indicators of climate change in aquatic ecosystems and it addresses the implications of future climate change for freshwater ecosystem management at the catchment scale. This is an ideal book for the scientific research community, but is also accessible to Masters and senior undergraduate students.
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We investigated the effects of temperature (4°C, 8°C, and 12°C) on structural and storage dynamics, as measured by changes in fatty acids (FA) associated with cell membrane phospholipids (PL) and triacylglycerols (TAG), respectively, as well as on body weight and survival of a freshwater calanoid copepod (Eudiaptomus gracilis) during fasting (10 d) and refeeding (10 d) with two algae of differing nutritional quality (Cryptomonas ozolinii and Scenedesmus obliquus). Fasting led to 50% loss in body weight, a near total depletion of TAG, and a drastic decrease of the polyunsaturated FA (PUFA) in TAG and PL, indicating their preferential utilization and alterations in membrane function, respectively. Higher temperatures accelerated the decrease of body weight and of PUFA in PL and TAG, and decreased survival. After 10 d of refeeding, copepods partially recovered their initial lipid stores and cell membrane composition. The effects of food quality were temperature dependent: Cryptomonas promoted better recovery (i.e., return to or close to the levels at the beginning of the experiment) of both body weight and TAG at only the two higher temperatures (8°C and 12°C), whereas no recovery was observed at 4°C. Higher temperatures and refeeding on Cryptomonas also had a positive, but minor, influence on the recovery of membrane FA composition. Survival differed among treatments but was lowest at the intermediate temperature (8°C) for both diets. We conclude that temperature changes on the order of 4–8°C significantly influence TAG and PL during fasting periods and interact with food quality to determine the extent of recovery in copepod lipids.
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Climate change is increasing ambient temperatures in Arctic and subarctic regions, facilitating latitudinal range expansions of freshwater fishes adapted to warmer water temperatures. The relative roles of resource availability and interspecific interactions between resident and invading species in determining the outcomes of such expansions has not been adequately evaluated. Ecological interactions between a cool-water adapted fish, the perch (Perca fluviatilis), and the cold-water adapted European whitefish (Coregonus lavaretus), were studied in both shallow and deep lakes with fish communities dominated by (1) monomorphic whitefish, (2) monomorphic whitefish and perch, and (3) polymorphic whitefish and perch. A combination of stomach content, stable-isotope, and invertebrate prey availability data were used to identify resource use and niche overlap among perch, the trophic generalist large sparsely rakered (LSR) whitefish morph, and the pelagic specialist densely rakered (DR) whitefish morph in 10 subarctic lakes at the contemporary distribution limit of perch in northern Scandinavia. Perch utilized its putative preferred littoral niche in all lakes. LSR whitefish utilized both littoral and pelagic resources in monomorphic whitefish-dominated lakes. When found in sympatry with perch, LSR whitefish exclusively utilized pelagic prey in deep lakes, but displayed niche overlap with perch in shallow littoral lakes. DR whitefish was a specialist zooplanktivore, relegating LSR whitefish from pelagic habitats, leading to an increase in niche overlap between LSR whitefish and perch in deep lakes. Our results highlight how resource availability (lake depth and fish community) governs ecological interactions between native and invading species, leading to different outcomes even at the same latitudes. These findings suggest that lake morphometry and fish community structure data should be included in bioclimate envelope-based models of species distribution shifts following predicted climate change.
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There is considerable interest in the pathways by which carbon and growth-limiting elemental and biochemical nutrients are supplied to upper trophic levels. Fatty acids and sterols are among the most important molecules transferred across the plant-animal interface of food webs. In lake ecosystems, in addition to phytoplankton, bacteria and terrestrial organic matter are potential trophic resources for zooplankton, especially in those receiving high terrestrial organic matter inputs. We therefore tested carbon, nitrogen, and fatty acid assimilation by the crustacean Daphnia magna when consuming these resources. We fed Daphnia with monospecific diets of high-quality (Cryptomonas marssonii) and intermediate-quality (Chlamydomonas sp. and Scenedesmus gracilis) phytoplankton species, two heterotrophic bacterial strains, and particles from the globally dispersed riparian grass, Phragmites australis, representing terrestrial particulate organic carbon (t-POC). We also fed Daphnia with various mixed diets, and compared Daphnia fatty acid, carbon, and nitrogen assimilation across treatments. Our results suggest that bacteria were nutritionally inadequate diets because they lacked sterols and polyunsaturated omega-3 and omega-6 (omega-3 and omega-6) fatty acids (PUFAs). However, Daphnia were able to effectively use carbon and nitrogen from Actinobacteria, if their basal needs for essential fatty acids and sterols were met by phytoplankton. In contrast to bacteria, t-POC contained sterols and omega-6 and omega-3 fatty acids, but only at 22%, 1.4%, and 0.2% of phytoplankton levels, respectively, which indicated that t-POC food quality was especially restricted with regard to omega-3 PUFAs. Our results also showed higher assimilation of carbon than fatty acids from t-POC and bacteria into Daphnia, based on stable-isotope and fatty acids analysis, respectively. A relatively high (>20%) assimilation of carbon and fatty acids from t-POC was observed only when the proportion of t-POC was >60%, but due to low PUFA to carbon ratio, these conditions yielded poor Daphnia growth. Because of lower assimilation for carbon, nitrogen, and fatty acids from t-POC relative to diets of bacteria mixed with phytoplankton, we conclude that the microbial food web, supported by phytoplankton, and not direct t-POC consumption, may support zooplankton production. Our results suggest that terrestrial particulate organic carbon poorly supports upper trophic levels of the lakes.
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The color of freshwaters, often measured as absorbance, influences a number of ecosystem services including biodiversity, fish production, and drinking water quality. Many countries have recently reported on increasing trends of water color in freshwaters, for which drivers are still not fully understood. We show here with more than 58000 water samples from the boreal and hemiboreal region of Sweden and Canada that absorbance of filtered water (a420) co-varied with dissolved organic carbon (DOC) concentrations (R(2) = 0.85, P<0.0001), but that a420 relative to DOC is increased by the presence of iron (Fe). We found that concentrations of Fe significantly declined with increasing water retention in the landscape, resulting in significantly lower Fe concentrations in lakes compared to running waters. The Fe loss along the aquatic continuum corresponded to a proportional loss in a420, suggesting a tight biogeochemical coupling between colored dissolved organic matter and Fe. Since water is being flushed at increasing rates due to enhanced runoff in the studied regions, diminished loss of Fe along the aquatic continuum may be one reason for observed trends in a420, and in particular in a420/DOC increases. If trends of increased Fe concentrations in freshwaters continue, water color will further increase with various effects on ecosystem services and biogeochemical cycles.
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Algal fatty acid (FA) composition is an important determinant of their food quality for consumers. FA can also be used as biomarkers for biochemical and energetic pathways in food webs. FA analyses of seven freshwater algal classes and 37 strains showed clear similarity within classes and strong differences amongst classes. The algal class was dominant factor (66.4%) explaining variation in FA signatures of microalgae. Seven algal classes created four separate groups according to their FA profiles: 1) Chlorophyceae and Trebouxiophyceae 2) Bacillariophyceae, 3) Cryptophyceae, Chrysophyceae, and Raphidophyceae, and 4) Euglenophyceae. Each group has a characteristic FA composition although the proportional abundance of individual FA also differs between species and with environmental conditions. The FA which were found to be particularly representative for each group (i.e., diagnostic biomarkers) are: 16:4ω3 and 16:3ω3 for Chlorophyceae and Trebouxiophyceae; 16:2ω7, 16:2ω4, 16:3ω4, 16:4ω1 and 18:4ω4 for Bacillariophyceae; 22:5ω6 and 18:4ω3 for Cryptophyceae and Chrysophyceae (Synurales), 16:3ω1 for Chrysophyceae (Ochromonadales), 16:2ω4, 16:3ω4, 16:3ω1 and 20:3ω3 for Raphidophyceae; and 15:4ω2, 20:4ω3, 20:2ω6, 20:3ω6 and 22:4ω6 for Euglenophyceae. FA thus offer a powerful tool for lacustrine food web studies to track different consumer diets in a food web. Based on the 20:5ω3 (eicosapentaenoic acid) and 22:6ω3 (docosahexaenoic acid) content among the investigated freshwater algal classes, Chlorophyceae, Trebouxiophyceae and Chrysophyceae, are intermediate food quality for zooplankton and Cryptophyceae, Bacillariophyceae, Euglenophyceae and Raphidophyceae should be excellent resources for zooplankton.
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Few studies have examined multiple life-history traits across a latitudinal gradient to test whether variation in growth rate and mortality schedules induces trends predicted by life-history theory. We collected data for the following life-history traits for 75 Eurasian perch (Perca fluviatilis) populations: growth coefficient (K) and asymptotic body length (L') from the von Bertalanffy growth model, size at ages one and two years, specific juvenile growth rate, instantaneous adult and juvenile mortality rates, life span, age and length at maturity, and reproductive life span and investment. All life-history traits except L' were significantly correlated with latitude. In general, growth rates, mortality rates, and reproductive investment decreased with latitude, whereas age at maturity, size at maturity, and life span increased with latitude. Populations could be grouped into two categories based on variation in L': stunted (small sized) vs. piscivorous (large sized). Four trait-latitude relationships differed between these two types: the growth coefficient (K) and the juvenile growth rate were larger, and age and length at maturity were lower in the stunted populations compared with piscivorous populations. Perch from southern popula- tions tend to grow fast and experience high juvenile and adult mortality rates. As predicted from life-history theory, this selects for an early age and small size at maturity and relatively large investment in reproduction. The opposite pattern was found for northern populations.
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We used stable carbon (δ 13C) and nitrogen (δ 15N) isotopes to assess the energy sources supporting the top consumer (Arctic char, Salvelinus alpinus) in nine subarctic lakes in northern Sweden. The δ 13C of littoral (epipelic algae) and pelagic (bacterioplankton and phytoplankton) energy sources were clearly separated in the lakes, as reflected in habitat-specific consumers (zoobenthos, zooplankton). Char were enriched in 13C compared with pelagic energy sources and prey and isotopically more similar to littoral energy sources and prey. The contribution of littoral energy sources to char body carbon was estimated to range between 62% and 94% among the lakes. The reliance on littoral energy sources was independent of char size and did not change when char coexisted with a small-sized prey fish (nine-spined stickleback, Pungitus pungitus). The strong reliance of top consumers in subarctic lakes on littoral energy sources may be due to the higher energy mobilization and larger sizes of primary consumers in littoral than in pelagic habitats. © 2005, by the American Society of Limnology and Oceanography, Inc.
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Analysis of phytoplankton data from about 1,500 lakes in 20 European countries has revealed that two-thirds of the species that dominate lakes during the summer are dominant right across Europe. Using Canonical Correspondence Analyses, we have examined how both habitat conditions within lakes and environmental factors over broad geographical scales explained the distribution of the 151 most common summer dominant species. The distributions of these species were best explained by water colour and latitude, although alkalinity and total phosphorus also appeared to be important explanatory factors. Contrary to our original hypothesis, summer water temperatures had a negligible impact on the distribution of dominants, although, due to the restricted summer season we examined, only a limited temperature gradient was present in the dataset. Cryptophytes occurred more frequently among dominants in Northern Europe whereas cyanobacteria and dinophytes dominated more in Central and Southern Europe. Our analyses suggest that besides nutrient concentrations, other water chemistry variables, such as alkalinity and the content of humic substances, have at least as important a role in determining the distribution of the dominant phytoplankton species in European lakes.
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1. A safe, clean water supply is critical for sustaining many important ecosystem services provided by freshwaters. The development of cyanobacterial blooms in lakes and reservoirs has a major impact on the provision of these services, particularly limiting their use for recre-ation and water supply for drinking and spray irrigation. Nutrient enrichment is thought to be the most important pressure responsible for the widespread increase in cyanobacterial blooms in recent decades. Quantifying how nutrients limit cyanobacterial abundance in lakes is, therefore, a key need for setting robust targets for the management of freshwaters. 2. Using a data set from over 800 European lakes, we highlight the use of quantile regression modelling for understanding the maximum potential capacity of cyanobacteria in relation to total phosphorus (TP) and the use of a range of quantile responses, alongside World Health Organisation (WHO) health alert thresholds for recreational waters, for setting robust phos-phorus targets for lake management in relation to water use. 3. The analysis shows that cyanobacteria exhibit a nonlinear response to phosphorus with the sharpest increase in cyanobacterial abundance occurring in the TP range from about 20 lg L À1 up to about 100 lg L À1 . 4. The likelihood of exceeding the World Health Organisation (WHO) 'low health alert' threshold increases from about 5% exceedance at 16 lg L À1 to 40% exceedance at 54 lg L À1 . About 50% of the studied lakes remain below this WHO health alert threshold, irrespec-tive of high summer TP concentrations, highlighting the importance of other factors affecting cyanobacteria population growth and loss processes, such as high flushing rate. 5. Synthesis and applications. Developing a more quantitative understanding of the effect of nutrients on cyanobacterial abundance in freshwater lakes provides important knowledge for restoring and sustaining a safe, clean water supply for multiple uses. Our models can be used to set nutrient targets to sustain recreational services and provide different levels of precau-tion that can be chosen dependent on the importance of the service provision.
Book
Preface.- Introduction.- Algal Lipids and Effect of the Environment on their Biochemistry.- Formation and transfer of fatty acids in aquatic microbial food webs - role of heterotrophic protists.- Ecological significance of sterols in aquatic food webs.- Fatty acids and oxylipins as semiochemicals.- Integrating lipids and contaminants in aquatic ecology and ec