Spatial and temporal zooplankton feeding dynamics across the water column of lakes are key for un... more Spatial and temporal zooplankton feeding dynamics across the water column of lakes are key for understanding site-specific acquisition of diet sources. During this 6-week lake study, we examined stable carbon (δ 13 C) and nitrogen (δ 15 N) isotopes and conducted compound-specific fatty acid (FA) stable isotope analysis (CSIA) of edible seston in the epi-, meta-, and hypolimnion, and zooplankton of Lake Lunz, Austria. We predicted that CSIA of essential FA can discern the foraging grounds of zooplankton more accurately than the commonly used bulk stable isotopes. The δ 13 C and δ 15 N values of seston from different lake strata were similar, whereas a dual CSIA approach using stable carbon and hydrogen isotopes of FA (δ 13 C FA and δ 2 H FA) provided sufficient isotopic difference in essential FA to discern different lake strata-specific diet sources throughout the study period. We present a CSIA model that suggests strata-specific foraging grounds for different zooplankton groups, indicating higher preference of cladocerans for feeding on epilimnetic diet sources, while calanoid copepods retained more hypolimnetic resources. The CSIA approach thus yields strata-specific information on foraging strategies of different zooplankton taxa and provides more details on the spatial and temporal trophodynamics of planktonic food webs than commonly used bulk stable isotopes.
Species invasions can lead to ecological regime shifts by altering food web structure and changin... more Species invasions can lead to ecological regime shifts by altering food web structure and changing nutrient cycling. Stable isotopes are a powerful tool to understand the potential and realized impacts of invasive species on food webs, especially when used in tandem with other dietary tracers. An invasion by one of the most notorious freshwater invaders in North America, the quagga mussel (Dreissena bugensis), is imminent in Lake Champlain, United States. An invasion by this filter feeder has the potential to drastically alter energy pathways and destabilize pelagic fisheries via bottom-up impacts. However, the extent and magnitude of these impacts depend on the current food web structure of the mid-trophic pelagic food web, which was previously not well described. We used Bayesian stable isotope mixing models informed by stomach content analysis to identify which energy pathways are currently most important to mid-trophic level fishes. We determined that in the Main Lake basin, the spring phytoplankton bloom and deep chlorophyll layer-the resources most vulnerable to quagga mussels-provide a disproportionate amount of support to the pelagic food web via zooplankton and the migrating macroinvertebrate Mysis. The food web in the Northeast Arm of Lake Champlain is supported by epilimnetic phytoplankton, which is more protected from the filtration effects of quagga mussels than the deep chlorophyll layer. However, the Northeast Arm will likely not provide a high-quality foraging refuge to coldwater pelagic fish due to unfavorable oxythermal conditions. The mid-trophic food web of Lake Champlain-and consequently piscivores who rely on these prey-may be vulnerable to the impending quagga mussel invasion if migratory Mysis are not able to shift their diet to benthic resources.
Much of our current knowledge about non-limiting dietary carbon supply for herbivorous zooplankto... more Much of our current knowledge about non-limiting dietary carbon supply for herbivorous zooplankton is based on experimental evidence and typically conducted at ~1 mg C L-1 and ~20°C. Here we ask how low supply of dietary carbon affects somatic growth, reproduction, and survival of Daphnia magna and test effects of higher water temperature (+3°C relative to ambient) and brownification (3X higher than natural water color; both predicted effects of climate change) during fall cooling. We predicted that even at very low carbon supply (~5µg C L-1), higher water temperature and brownification will allow D. magna to increase its fitness. Neonates (<24 h old) were incubated with lake seston for 4 weeks (October-November 2013) in experimental bottles submerged in outdoor mesocosms to explore effects of warmer and darker water. Higher temperature and brownification did not significantly affect food quality, as assessed by its fatty acid composition. Daphnia exposed to both increased temperature and brownification had highest somatic growth and were the only that reproduced, and higher temperature caused the highest Daphnia survival success. These results suggest that even under low temperature and thus lower physiological activity, low food quantity is more important than its quality for D. magna fitness.
This is an open access article under the terms of the Creat ive Commo ns Attri bution License, wh... more This is an open access article under the terms of the Creat ive Commo ns Attri bution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Comparative Biochemistry and Physiology B, Mar 1, 2015
The aim of this 14-month feeding study was to investigate the effects of dietary docosahexaenoic ... more The aim of this 14-month feeding study was to investigate the effects of dietary docosahexaenoic acid (DHA) on tissue fatty acid composition, DHA retention and DHA content per biomass accrual in muscle tissues of Arctic charr (Salvelinus alpinus). A control feed, formulated with a relatively high DHA inclusion level (F1), was compared with feeds containing gradually reduced amounts of DHA (Feeds F2, F3, and F4). Arctic charr were randomly distributed among 12 tanks and fed one of the feeds in triplicate. The DHA content within muscle tissues of fish fed diets F1 and F2 was generally higher compared to fish fed diets F3 and F4. However, there was an interaction between dietary DHA treatment and season, which resulted in fish muscle tissues having similar DHA contents irrespective of dietary supply during specific sampling periods. Although diets F3 and F4 contained ~4-fold less DHA compared to diets F1 and F2, retention of DHA in dorsal and ventral muscle tissue was up to 5-fold higher relative to the diet content in fish fed diets F3 and F4. However, the difference among treatments was dependent on the month sampled. In addition, younger fish retained DHA more efficiently compared to older fish. DHA (µg DHA/g/day) accrual in muscle tissue was independent of somatic growth, and there was no difference among treatments. The results suggested that dietary DHA may be essential throughout the lifecycle of Arctic charr and that the DHA content of muscle tissues was influenced by diet and metabolic/physiological factors, such as specific DHA retention during the entire growth cycle. Finally, this long-term feeding study in Arctic charr indicated a non-linear function in DHA retention in dorsal and ventral muscle tissues throughout the lifecycle, which varied in its relationship to dietary DHA.
IntroductionAmong long-distance migratory insects, the monarch butterfly (Danaus plexippus) is on... more IntroductionAmong long-distance migratory insects, the monarch butterfly (Danaus plexippus) is one of the most iconic, whose journey is fueled by nectar from flowering plants along the migratory route which may involve up to 3,500 km. Understanding how and where monarchs obtain their dietary resources to fuel migratory flight and ensure overwintering stores would provide new insights into the migratory strategy of this species and subsequently help focus conservation efforts.MethodsThis pilot study was designed as a first attempt to assess the composition, dynamics, and isotopic (δ2H, δ13C) composition of essential and non-essential fatty acids (FA) acquired or manufactured de novo from larval host milkweed (Asclepias spp.) by monarch butterflies and from adult emergence to overwintering.ResultsData from controlled laboratory isotopic tracer tests suggested that adult monarchs convert their dietary energy mainly into 16:0 and 18:1 fatty acids and store them as neutral lipids in thei...
Global warming enhances the dominance of poorly palatable PUFA-deprived bloom-forming cyanobacter... more Global warming enhances the dominance of poorly palatable PUFA-deprived bloom-forming cyanobacteria. Chytrid fungal parasites increase herbivory and dietary access to polyunsaturated fatty acids (PUFA) across the phytoplankton-zooplankton interface. Little is known however about the role chytrids may play in compensating for the decrease of algae-derived PUFA under global warming scenarios. We tested experimentally the combined effects of water temperature increase and the presence of chytrids withDaphnia magnaas the consumer and the cyanobacteriumPlanktothrix rubescensas the main diet. We hypothesised that the diet including chytrids would enhanceDaphniafitness due to increased PUFA transfer irrespective of water temperature. Chytrid-infected diet significantly increasedDaphniasurvival, somatic growth, and reproduction, irrespective of water temperature. The PUFA content ofDaphniafeeding on the chytrid-infected diet was unaffected by heat at the onset of the first successful reprod...
Emergent insects represent a key vector through which aquatic nutrients are transferred to adjace... more Emergent insects represent a key vector through which aquatic nutrients are transferred to adjacent terrestrial food webs. Aquatic fluxes of polyunsaturated fatty acids (PUFA) from emergent insects are particularly important subsidies for terrestrial ecosystems due to high PUFA contents in several aquatic insect taxa and their physiological importance for riparian predators. While recent meta-analyses have shown the general dichotomy in fatty acid profiles between aquatic and terrestrial ecosystems, differences in fatty acid profiles between aquatic and terrestrial insects have been insufficiently explored. We examined the differences in fatty acid profiles between aquatic and terrestrial insects at a single aquatic-terrestrial interface over an entire growing season to assess the strength and temporal consistency of the dichotomy in fatty acid profiles. Non-metric multidimensional scaling clearly separated aquatic and terrestrial insects based on their fatty acid profiles regardles...
We studied how physiologically important long‐chain polyunsaturated fatty acids (PUFA) in benthic... more 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 (δ13CFA) 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, chironomids, and oligo...
Fatty acids (FA) are a major source of nutrients and energy in aquatic food webs, as well as serv... more Fatty acids (FA) are a major source of nutrients and energy in aquatic food webs, as well as serving as the main components of all cell membranes. Increasing anthropogenic impacts (e.g., climate change) are predicted to selectively alter the production of these critical compounds, with potential cascading effects reaching higher trophic level organisms, including humans. To provide a more comprehensive assessment of these potential effects, we synthesized and systematically explored differences in the abundance and distribution of FA in fish, due to their pivotal role in aquatic ecosystems and value to humans. An extensive data set consisting of 1382 fish FA profiles was analyzed to identify the main differences in FA composition of freshwater vs. marine fish, taking into account the effects of taxonomic, geographic (i.e., latitude zone), and functional (i.e., feeding mode) factors. Freshwater fish had relatively high contents of 18:2n-6 (linoleic acid, LNA) and 20:4n-6 (arachidonic...
The ecological role of emergent aquatic insects from lakes in exporting dietary polyunsaturated f... more The ecological role of emergent aquatic insects from lakes in exporting dietary polyunsaturated fatty acids (PUFA) across the freshwater‐land interface is still poorly understood. In this field study, we explored the seasonal biomass export of emergent insects from three subalpine lakes and investigated how lipids of emergent insects were related to lake bathymetry, lipids of organic matter in lake sediments (i.e., basal resources), and the taxonomic composition of insects. The total lipid and PUFA fluxes of emergent insects were strongly related to taxonomy and lake bathymetry, but weakly associated with the PUFA content of the uppermost lake sediment layers. PUFA flux estimates of the dominant taxon, Chironomidae, from the shallowest lake (3 m depth; 125 g PUFA m−2 season−1) were considerably higher than those from the deepest lake (33 m depth; 56 g PUFA m−2 season−1), due to the higher per area biomass of emergent insects from this shallow lake. Insect taxonomy also affected the ...
Across ecosystems, resources vary in their nutritional composition and thus their dietary value t... more Across ecosystems, resources vary in their nutritional composition and thus their dietary value to consumers. Animals can either access organic compounds, such as fatty acids, directly from diet or through internal biosynthesis, and the extent to which they use these two alternatives likely varies based on the availability of such compounds across the nutritional landscape. Cross-ecosystem subsidies of important dietary nutrients, like omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA), may provide consumers with the opportunity to relax the demands of synthesis and rely upon dietary flexibility rather than internal metabolic processes. Here, we examined how dietary flexibility and distance from a lake influenced the degree to which generalist insectivores relied upon dietary n-3 LC-PUFA from emergent aquatic insects versus n-3 LC-PUFA synthesized from precursor compounds found in terrestrial insects. We used bulk and compound-specific stable isotope analyses to understand...
The trophic fate of various food sources is of central interest for ecologists, yet not well unde... more The trophic fate of various food sources is of central interest for ecologists, yet not well understood in coastal lagoon food webs. In this field study, fatty acids (FA), stable isotopes (SI), and compound-specific isotopic analysis (CSIA) on FA were used to investigate how diets from oceanic and local sources are retained in a bivalve species (Spondylus crassisquama; Lamarck 1819) along a transect in the Ojo de Liebre lagoon (BCS, Mexico). Results from SI and FA indicated the contribution of oceanic diatoms at the entrance of the lagoon, through 15N enrichment, and higher proportions of 16:1n-7 and 20:5n-3 in digestive glands. In the inner bay, higher abundance of 18-carbon FA (18:1n-9, 18:3n-3, 18:4n-3) suggested a higher contribution of microheterotrophs, including (dino)flagellates and ciliates, to the diet of this bivalve derived from local production. Significant spatial differences for the δ13C of FA highlighted changes in the origin of food sources. Indeed, a 13C depletion was observed in the δ13C of heterotrophic flagellates biomarkers in individuals from the innermost station, revealing that their origin in the diet of bivalves differs within the lagoon, highlighting the importance of local processes (sediment resuspension, remineralization) in the trophic functioning of the lagoon. The δ13C values of FA considered as diatoms biomarkers (16:1n-7 and 20:5n-3) were consistent, which suggests that diatoms assimilated have very similar origins throughout the lagoon. The complementary of the tracers used here allowed for a better understanding of the trophic functioning of this coastal lagoon submitted to oceanic influences.
Polyunsaturated fatty acids (PUFA), especially long-chain (i.e., ≥20 carbons) polyunsaturated fat... more Polyunsaturated fatty acids (PUFA), especially long-chain (i.e., ≥20 carbons) polyunsaturated fatty acids (LC-PUFA), are fundamental to the health and survival of marine and terrestrial organisms. Therefore, it is imperative that we gain a better understanding of their origin, abundance, and transfer between and within these ecosystems. We evaluated the natural variation in PUFA distribution and abundance that exists between and within these ecosystems by amassing and analyzing, using multivariate and analysis of variance (ANOVA) methods, >3000 fatty acid (FA) profiles from marine and terrestrial organisms. There was a clear dichotomy in LC-PUFA abundance between organisms in marine and terrestrial ecosystems, mainly driven by the C18 PUFA in terrestrial organisms and omega-3 (n-3) LC-PUFA in marine organisms. The PUFA content of an organism depended on both its biome (marine vs terrestrial) and taxonomic group. Within the marine biome, the PUFA content varied among taxonomic gro...
Climate change scenarios predict increases in temperature and organic matter supply from land to ... more Climate change scenarios predict increases in temperature and organic matter supply from land to water, which affect trophic transfer of nutrients and contaminants in aquatic food webs. How essential nutrients, such as polyunsaturated fatty acids (PUFA), and potentially toxic contaminants, such as methylmercury (MeHg), at the base of aquatic food webs will be affected under climate change scenarios, remains unclear. The objective of this outdoor mesocosm study was to examine how increased water temperature and terrestrially-derived dissolved organic matter supply (tDOM; i.e., lake browning), and the interaction of both, will influence MeHg and PUFA in organisms at the base of food webs (i.e. seston; the most edible plankton size for zooplankton) in subalpine lake ecosystems. The interaction of higher temperature and tDOM increased the burden of MeHg in seston (< 40 μm) and larger sized plankton (microplankton; 40–200 μm), while the MeHg content per unit biomass remained stable. H...
In this fish‐feeding study, we tested similarity patterns between fatty acids (FA) in diets and c... more In this fish‐feeding study, we tested similarity patterns between fatty acids (FA) in diets and common carp (Cyprinus carpio) of fish ponds used for semi‐intensive aquaculture, containing naturally occurring pond zooplankton and different feeds (marine or terrestrial feeds) until carp reached market size. We evaluated if and how total lipid contents in dorsal fillets can reflect dietary FA compositions in farm‐raised common carp and hypothesized that increasing total lipid contents in dorsal fillets significantly increase the similarity between dietary and dorsal fillets’ FA compositions. Results of this study showed that carps had higher total lipids when supplied with marine feeds and dietary FA compositions were indeed more strongly reflected in fatty (i.e. high total lipid contents) than in leaner dorsal fillets (low total lipid contents). Increasing total lipid contents in dorsal fillets significantly increased the similarity between the dietary and dorsal fillets’ FA compositi...
Freshwater salmonids gain increasing popularity as diet fish and are an important dietary source ... more Freshwater salmonids gain increasing popularity as diet fish and are an important dietary source of omega-3 polyunsaturated fatty acids (PUFA) for humans. The aim of this study was to investigate effects of alternative feeds from domestic sources on fish growth and lipid composition of the sparctic Alsatian charr (Salvelinus alpinus X fontinalis), commonly used in freshwater aquaculture in Europe. In this fish feeding experiment, we used a control feed (32% fish meal; feed F1) and experimental diets containing generally only half the amount of fish meal, which was replaced in equal parts by poultry (F2), two different pork by-product meals (F3 and F4), plant-based feeds (F5), or by a feed containing 25% fish and 15% poultry meal (F6) that had a similar caloric value compared to the other feeds. Six hundred charrs of similar initial weight (ca. 90 g) were randomly distributed into 12 tanks (50/tank) of 1.4 m 3 , supplied with subalpine spring water, and fed one of the feeds. Fish biomass development was the highest in fish fed diet F6, followed by F1, F2, and F5. Pork by-product meals as partial replacement of fish meal resulted on average in a 25% lower biomass gain compared to charr feeding on poultry by-product meal (F6). The use of poultry or pork by-product meals as partial fish meal replacements did not significantly change the total lipids or fatty acids retained in these fish. This study shows that these alternative feeds, with similar lipid sources, had no significant effect on the fatty acid composition in Alsatian charr, however, poultry by-product meal as partial replacement of marine fish meal clearly enhanced charr biomass by 15% relative to conventional fish meals.
Coastal wetlands are increasingly recognised for their pivotal role in mitigating the growing thr... more Coastal wetlands are increasingly recognised for their pivotal role in mitigating the growing threats from cyclones (including hurricanes) in a changing climate. There is, however, insufficient information about the economic value of coastal wetlands for cyclone mitigation, particularly at regional scales. Analysis of data from 1990–2012 shows that the variation of cyclone frequencies is related to EI Niño strength in the Pacific Ocean adjacent to Australia, but not China. Among the cyclones hitting the two countries, there are significant relationships between the ratio of total economic damage to gross domestic production (TD/GDP) and wetland area within cyclone swaths in Australia, and wetland area plus minimum cyclone pressure despite a weak relationship in China. The TD/GDP ratio is significantly higher in China than in Australia. Despite their extensive and growing occurrence, seawalls in China appear not to play a critical role in cyclone mitigation, and cannot replace coasta...
Spatial and temporal zooplankton feeding dynamics across the water column of lakes are key for un... more Spatial and temporal zooplankton feeding dynamics across the water column of lakes are key for understanding site-specific acquisition of diet sources. During this 6-week lake study, we examined stable carbon (δ 13 C) and nitrogen (δ 15 N) isotopes and conducted compound-specific fatty acid (FA) stable isotope analysis (CSIA) of edible seston in the epi-, meta-, and hypolimnion, and zooplankton of Lake Lunz, Austria. We predicted that CSIA of essential FA can discern the foraging grounds of zooplankton more accurately than the commonly used bulk stable isotopes. The δ 13 C and δ 15 N values of seston from different lake strata were similar, whereas a dual CSIA approach using stable carbon and hydrogen isotopes of FA (δ 13 C FA and δ 2 H FA) provided sufficient isotopic difference in essential FA to discern different lake strata-specific diet sources throughout the study period. We present a CSIA model that suggests strata-specific foraging grounds for different zooplankton groups, indicating higher preference of cladocerans for feeding on epilimnetic diet sources, while calanoid copepods retained more hypolimnetic resources. The CSIA approach thus yields strata-specific information on foraging strategies of different zooplankton taxa and provides more details on the spatial and temporal trophodynamics of planktonic food webs than commonly used bulk stable isotopes.
Species invasions can lead to ecological regime shifts by altering food web structure and changin... more Species invasions can lead to ecological regime shifts by altering food web structure and changing nutrient cycling. Stable isotopes are a powerful tool to understand the potential and realized impacts of invasive species on food webs, especially when used in tandem with other dietary tracers. An invasion by one of the most notorious freshwater invaders in North America, the quagga mussel (Dreissena bugensis), is imminent in Lake Champlain, United States. An invasion by this filter feeder has the potential to drastically alter energy pathways and destabilize pelagic fisheries via bottom-up impacts. However, the extent and magnitude of these impacts depend on the current food web structure of the mid-trophic pelagic food web, which was previously not well described. We used Bayesian stable isotope mixing models informed by stomach content analysis to identify which energy pathways are currently most important to mid-trophic level fishes. We determined that in the Main Lake basin, the spring phytoplankton bloom and deep chlorophyll layer-the resources most vulnerable to quagga mussels-provide a disproportionate amount of support to the pelagic food web via zooplankton and the migrating macroinvertebrate Mysis. The food web in the Northeast Arm of Lake Champlain is supported by epilimnetic phytoplankton, which is more protected from the filtration effects of quagga mussels than the deep chlorophyll layer. However, the Northeast Arm will likely not provide a high-quality foraging refuge to coldwater pelagic fish due to unfavorable oxythermal conditions. The mid-trophic food web of Lake Champlain-and consequently piscivores who rely on these prey-may be vulnerable to the impending quagga mussel invasion if migratory Mysis are not able to shift their diet to benthic resources.
Much of our current knowledge about non-limiting dietary carbon supply for herbivorous zooplankto... more Much of our current knowledge about non-limiting dietary carbon supply for herbivorous zooplankton is based on experimental evidence and typically conducted at ~1 mg C L-1 and ~20°C. Here we ask how low supply of dietary carbon affects somatic growth, reproduction, and survival of Daphnia magna and test effects of higher water temperature (+3°C relative to ambient) and brownification (3X higher than natural water color; both predicted effects of climate change) during fall cooling. We predicted that even at very low carbon supply (~5µg C L-1), higher water temperature and brownification will allow D. magna to increase its fitness. Neonates (<24 h old) were incubated with lake seston for 4 weeks (October-November 2013) in experimental bottles submerged in outdoor mesocosms to explore effects of warmer and darker water. Higher temperature and brownification did not significantly affect food quality, as assessed by its fatty acid composition. Daphnia exposed to both increased temperature and brownification had highest somatic growth and were the only that reproduced, and higher temperature caused the highest Daphnia survival success. These results suggest that even under low temperature and thus lower physiological activity, low food quantity is more important than its quality for D. magna fitness.
This is an open access article under the terms of the Creat ive Commo ns Attri bution License, wh... more This is an open access article under the terms of the Creat ive Commo ns Attri bution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Comparative Biochemistry and Physiology B, Mar 1, 2015
The aim of this 14-month feeding study was to investigate the effects of dietary docosahexaenoic ... more The aim of this 14-month feeding study was to investigate the effects of dietary docosahexaenoic acid (DHA) on tissue fatty acid composition, DHA retention and DHA content per biomass accrual in muscle tissues of Arctic charr (Salvelinus alpinus). A control feed, formulated with a relatively high DHA inclusion level (F1), was compared with feeds containing gradually reduced amounts of DHA (Feeds F2, F3, and F4). Arctic charr were randomly distributed among 12 tanks and fed one of the feeds in triplicate. The DHA content within muscle tissues of fish fed diets F1 and F2 was generally higher compared to fish fed diets F3 and F4. However, there was an interaction between dietary DHA treatment and season, which resulted in fish muscle tissues having similar DHA contents irrespective of dietary supply during specific sampling periods. Although diets F3 and F4 contained ~4-fold less DHA compared to diets F1 and F2, retention of DHA in dorsal and ventral muscle tissue was up to 5-fold higher relative to the diet content in fish fed diets F3 and F4. However, the difference among treatments was dependent on the month sampled. In addition, younger fish retained DHA more efficiently compared to older fish. DHA (µg DHA/g/day) accrual in muscle tissue was independent of somatic growth, and there was no difference among treatments. The results suggested that dietary DHA may be essential throughout the lifecycle of Arctic charr and that the DHA content of muscle tissues was influenced by diet and metabolic/physiological factors, such as specific DHA retention during the entire growth cycle. Finally, this long-term feeding study in Arctic charr indicated a non-linear function in DHA retention in dorsal and ventral muscle tissues throughout the lifecycle, which varied in its relationship to dietary DHA.
IntroductionAmong long-distance migratory insects, the monarch butterfly (Danaus plexippus) is on... more IntroductionAmong long-distance migratory insects, the monarch butterfly (Danaus plexippus) is one of the most iconic, whose journey is fueled by nectar from flowering plants along the migratory route which may involve up to 3,500 km. Understanding how and where monarchs obtain their dietary resources to fuel migratory flight and ensure overwintering stores would provide new insights into the migratory strategy of this species and subsequently help focus conservation efforts.MethodsThis pilot study was designed as a first attempt to assess the composition, dynamics, and isotopic (δ2H, δ13C) composition of essential and non-essential fatty acids (FA) acquired or manufactured de novo from larval host milkweed (Asclepias spp.) by monarch butterflies and from adult emergence to overwintering.ResultsData from controlled laboratory isotopic tracer tests suggested that adult monarchs convert their dietary energy mainly into 16:0 and 18:1 fatty acids and store them as neutral lipids in thei...
Global warming enhances the dominance of poorly palatable PUFA-deprived bloom-forming cyanobacter... more Global warming enhances the dominance of poorly palatable PUFA-deprived bloom-forming cyanobacteria. Chytrid fungal parasites increase herbivory and dietary access to polyunsaturated fatty acids (PUFA) across the phytoplankton-zooplankton interface. Little is known however about the role chytrids may play in compensating for the decrease of algae-derived PUFA under global warming scenarios. We tested experimentally the combined effects of water temperature increase and the presence of chytrids withDaphnia magnaas the consumer and the cyanobacteriumPlanktothrix rubescensas the main diet. We hypothesised that the diet including chytrids would enhanceDaphniafitness due to increased PUFA transfer irrespective of water temperature. Chytrid-infected diet significantly increasedDaphniasurvival, somatic growth, and reproduction, irrespective of water temperature. The PUFA content ofDaphniafeeding on the chytrid-infected diet was unaffected by heat at the onset of the first successful reprod...
Emergent insects represent a key vector through which aquatic nutrients are transferred to adjace... more Emergent insects represent a key vector through which aquatic nutrients are transferred to adjacent terrestrial food webs. Aquatic fluxes of polyunsaturated fatty acids (PUFA) from emergent insects are particularly important subsidies for terrestrial ecosystems due to high PUFA contents in several aquatic insect taxa and their physiological importance for riparian predators. While recent meta-analyses have shown the general dichotomy in fatty acid profiles between aquatic and terrestrial ecosystems, differences in fatty acid profiles between aquatic and terrestrial insects have been insufficiently explored. We examined the differences in fatty acid profiles between aquatic and terrestrial insects at a single aquatic-terrestrial interface over an entire growing season to assess the strength and temporal consistency of the dichotomy in fatty acid profiles. Non-metric multidimensional scaling clearly separated aquatic and terrestrial insects based on their fatty acid profiles regardles...
We studied how physiologically important long‐chain polyunsaturated fatty acids (PUFA) in benthic... more 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 (δ13CFA) 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, chironomids, and oligo...
Fatty acids (FA) are a major source of nutrients and energy in aquatic food webs, as well as serv... more Fatty acids (FA) are a major source of nutrients and energy in aquatic food webs, as well as serving as the main components of all cell membranes. Increasing anthropogenic impacts (e.g., climate change) are predicted to selectively alter the production of these critical compounds, with potential cascading effects reaching higher trophic level organisms, including humans. To provide a more comprehensive assessment of these potential effects, we synthesized and systematically explored differences in the abundance and distribution of FA in fish, due to their pivotal role in aquatic ecosystems and value to humans. An extensive data set consisting of 1382 fish FA profiles was analyzed to identify the main differences in FA composition of freshwater vs. marine fish, taking into account the effects of taxonomic, geographic (i.e., latitude zone), and functional (i.e., feeding mode) factors. Freshwater fish had relatively high contents of 18:2n-6 (linoleic acid, LNA) and 20:4n-6 (arachidonic...
The ecological role of emergent aquatic insects from lakes in exporting dietary polyunsaturated f... more The ecological role of emergent aquatic insects from lakes in exporting dietary polyunsaturated fatty acids (PUFA) across the freshwater‐land interface is still poorly understood. In this field study, we explored the seasonal biomass export of emergent insects from three subalpine lakes and investigated how lipids of emergent insects were related to lake bathymetry, lipids of organic matter in lake sediments (i.e., basal resources), and the taxonomic composition of insects. The total lipid and PUFA fluxes of emergent insects were strongly related to taxonomy and lake bathymetry, but weakly associated with the PUFA content of the uppermost lake sediment layers. PUFA flux estimates of the dominant taxon, Chironomidae, from the shallowest lake (3 m depth; 125 g PUFA m−2 season−1) were considerably higher than those from the deepest lake (33 m depth; 56 g PUFA m−2 season−1), due to the higher per area biomass of emergent insects from this shallow lake. Insect taxonomy also affected the ...
Across ecosystems, resources vary in their nutritional composition and thus their dietary value t... more Across ecosystems, resources vary in their nutritional composition and thus their dietary value to consumers. Animals can either access organic compounds, such as fatty acids, directly from diet or through internal biosynthesis, and the extent to which they use these two alternatives likely varies based on the availability of such compounds across the nutritional landscape. Cross-ecosystem subsidies of important dietary nutrients, like omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA), may provide consumers with the opportunity to relax the demands of synthesis and rely upon dietary flexibility rather than internal metabolic processes. Here, we examined how dietary flexibility and distance from a lake influenced the degree to which generalist insectivores relied upon dietary n-3 LC-PUFA from emergent aquatic insects versus n-3 LC-PUFA synthesized from precursor compounds found in terrestrial insects. We used bulk and compound-specific stable isotope analyses to understand...
The trophic fate of various food sources is of central interest for ecologists, yet not well unde... more The trophic fate of various food sources is of central interest for ecologists, yet not well understood in coastal lagoon food webs. In this field study, fatty acids (FA), stable isotopes (SI), and compound-specific isotopic analysis (CSIA) on FA were used to investigate how diets from oceanic and local sources are retained in a bivalve species (Spondylus crassisquama; Lamarck 1819) along a transect in the Ojo de Liebre lagoon (BCS, Mexico). Results from SI and FA indicated the contribution of oceanic diatoms at the entrance of the lagoon, through 15N enrichment, and higher proportions of 16:1n-7 and 20:5n-3 in digestive glands. In the inner bay, higher abundance of 18-carbon FA (18:1n-9, 18:3n-3, 18:4n-3) suggested a higher contribution of microheterotrophs, including (dino)flagellates and ciliates, to the diet of this bivalve derived from local production. Significant spatial differences for the δ13C of FA highlighted changes in the origin of food sources. Indeed, a 13C depletion was observed in the δ13C of heterotrophic flagellates biomarkers in individuals from the innermost station, revealing that their origin in the diet of bivalves differs within the lagoon, highlighting the importance of local processes (sediment resuspension, remineralization) in the trophic functioning of the lagoon. The δ13C values of FA considered as diatoms biomarkers (16:1n-7 and 20:5n-3) were consistent, which suggests that diatoms assimilated have very similar origins throughout the lagoon. The complementary of the tracers used here allowed for a better understanding of the trophic functioning of this coastal lagoon submitted to oceanic influences.
Polyunsaturated fatty acids (PUFA), especially long-chain (i.e., ≥20 carbons) polyunsaturated fat... more Polyunsaturated fatty acids (PUFA), especially long-chain (i.e., ≥20 carbons) polyunsaturated fatty acids (LC-PUFA), are fundamental to the health and survival of marine and terrestrial organisms. Therefore, it is imperative that we gain a better understanding of their origin, abundance, and transfer between and within these ecosystems. We evaluated the natural variation in PUFA distribution and abundance that exists between and within these ecosystems by amassing and analyzing, using multivariate and analysis of variance (ANOVA) methods, >3000 fatty acid (FA) profiles from marine and terrestrial organisms. There was a clear dichotomy in LC-PUFA abundance between organisms in marine and terrestrial ecosystems, mainly driven by the C18 PUFA in terrestrial organisms and omega-3 (n-3) LC-PUFA in marine organisms. The PUFA content of an organism depended on both its biome (marine vs terrestrial) and taxonomic group. Within the marine biome, the PUFA content varied among taxonomic gro...
Climate change scenarios predict increases in temperature and organic matter supply from land to ... more Climate change scenarios predict increases in temperature and organic matter supply from land to water, which affect trophic transfer of nutrients and contaminants in aquatic food webs. How essential nutrients, such as polyunsaturated fatty acids (PUFA), and potentially toxic contaminants, such as methylmercury (MeHg), at the base of aquatic food webs will be affected under climate change scenarios, remains unclear. The objective of this outdoor mesocosm study was to examine how increased water temperature and terrestrially-derived dissolved organic matter supply (tDOM; i.e., lake browning), and the interaction of both, will influence MeHg and PUFA in organisms at the base of food webs (i.e. seston; the most edible plankton size for zooplankton) in subalpine lake ecosystems. The interaction of higher temperature and tDOM increased the burden of MeHg in seston (< 40 μm) and larger sized plankton (microplankton; 40–200 μm), while the MeHg content per unit biomass remained stable. H...
In this fish‐feeding study, we tested similarity patterns between fatty acids (FA) in diets and c... more In this fish‐feeding study, we tested similarity patterns between fatty acids (FA) in diets and common carp (Cyprinus carpio) of fish ponds used for semi‐intensive aquaculture, containing naturally occurring pond zooplankton and different feeds (marine or terrestrial feeds) until carp reached market size. We evaluated if and how total lipid contents in dorsal fillets can reflect dietary FA compositions in farm‐raised common carp and hypothesized that increasing total lipid contents in dorsal fillets significantly increase the similarity between dietary and dorsal fillets’ FA compositions. Results of this study showed that carps had higher total lipids when supplied with marine feeds and dietary FA compositions were indeed more strongly reflected in fatty (i.e. high total lipid contents) than in leaner dorsal fillets (low total lipid contents). Increasing total lipid contents in dorsal fillets significantly increased the similarity between the dietary and dorsal fillets’ FA compositi...
Freshwater salmonids gain increasing popularity as diet fish and are an important dietary source ... more Freshwater salmonids gain increasing popularity as diet fish and are an important dietary source of omega-3 polyunsaturated fatty acids (PUFA) for humans. The aim of this study was to investigate effects of alternative feeds from domestic sources on fish growth and lipid composition of the sparctic Alsatian charr (Salvelinus alpinus X fontinalis), commonly used in freshwater aquaculture in Europe. In this fish feeding experiment, we used a control feed (32% fish meal; feed F1) and experimental diets containing generally only half the amount of fish meal, which was replaced in equal parts by poultry (F2), two different pork by-product meals (F3 and F4), plant-based feeds (F5), or by a feed containing 25% fish and 15% poultry meal (F6) that had a similar caloric value compared to the other feeds. Six hundred charrs of similar initial weight (ca. 90 g) were randomly distributed into 12 tanks (50/tank) of 1.4 m 3 , supplied with subalpine spring water, and fed one of the feeds. Fish biomass development was the highest in fish fed diet F6, followed by F1, F2, and F5. Pork by-product meals as partial replacement of fish meal resulted on average in a 25% lower biomass gain compared to charr feeding on poultry by-product meal (F6). The use of poultry or pork by-product meals as partial fish meal replacements did not significantly change the total lipids or fatty acids retained in these fish. This study shows that these alternative feeds, with similar lipid sources, had no significant effect on the fatty acid composition in Alsatian charr, however, poultry by-product meal as partial replacement of marine fish meal clearly enhanced charr biomass by 15% relative to conventional fish meals.
Coastal wetlands are increasingly recognised for their pivotal role in mitigating the growing thr... more Coastal wetlands are increasingly recognised for their pivotal role in mitigating the growing threats from cyclones (including hurricanes) in a changing climate. There is, however, insufficient information about the economic value of coastal wetlands for cyclone mitigation, particularly at regional scales. Analysis of data from 1990–2012 shows that the variation of cyclone frequencies is related to EI Niño strength in the Pacific Ocean adjacent to Australia, but not China. Among the cyclones hitting the two countries, there are significant relationships between the ratio of total economic damage to gross domestic production (TD/GDP) and wetland area within cyclone swaths in Australia, and wetland area plus minimum cyclone pressure despite a weak relationship in China. The TD/GDP ratio is significantly higher in China than in Australia. Despite their extensive and growing occurrence, seawalls in China appear not to play a critical role in cyclone mitigation, and cannot replace coasta...
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Papers by Martin Kainz