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Selective retention of essential amino acids (AA) (A), major fatty acid (FA) groups (B) and the percentage of retained FA allocated to structural FA (C) in copepods grown on different food algae. Selective retention is expressed as the retention efficiency of a FA relative to the retention efficiency of bulk carbon. Values above 100% indicate positive and values below 100% negative selection in the retention of a given compound (n = 3).
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The flexible regulation of feeding behaviour and nutrient metabolism is a prerequisite for consumers to grow and survive under variable food conditions. Thus, it is essential to understand the ecological trade‐offs that restrict regulatory mechanisms in consumers to evaluate the consequences of nutrient limitations for trophic interactions.
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Context 1
... a 333 significantly higher relative allocation of different C20 PUFA to structural FA in the N -compared to the 334 replete treatment (ANOVA, F(2, 15) = 22, p < 0.001; Tukey Post-Hoc, p < 0.001). While in the replete 335 treatment copepods allocated 65% of retained C20 PUFA to structural FA, this number increased to 336 83% in N-limited copepods (Fig. ...
Context 2
... scarcity of EPA and especially DHA in copepods fed N -algae was also revealed by the isotopic 338 labelling experiment. The retention efficiencies of FA were in general lower than those of bulk C in 339 respective treatments (Fig. 5B). An exception to this trend were DHA and EPA under N-limitation, 340 which showed a positive and significantly higher selective retention than did other FA, reflecting the 341 physiological importance of these resources. 342 343 Discussion ...
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Fatty acids are widely used to study trophic interactions in food web assemblages. Generally, it is assumed that there is a very small modification of fatty acids from one trophic step to another, making them suitable as trophic biomarkers. However, recent literature provides evidence that many fishes possess genes encoding enzymes with a role in b...
Citations
... Aquatic consumers generally select high-quality resources (Marcarelli et al., 2011). Food quality depends on the elemental content of resources, such as the carbon (C):nitrogen (N) and C:phosphorus (P) ratios, and the biochemical composition, including the fatty acid (FA) profiles (Burian et al., 2018;Danger et al., 2022;Ruiz et al., 2021). In situations where only low-quality resources are available, consumers can compensate by increasing their feeding rate to maintain their fitness (e.g., Cruz-Rivera & Hay, 2000). ...
In streams, phototrophic biofilms are considered to be a good‐quality resource for consumers and are essential to support secondary production. However, with the increasing occurrence of flow intermittency as a consequence of global climate change, limited information exists regarding the impact of drying and rewetting events on biofilm nutritional quality indicators and their consequences for consumers. This study aims at understanding how river intermittency affects the nutritional quality of phototrophic biofilms. Specifically, we examine the effects of drying and rewetting events on their capacity to support secondary production.
Our hypothesis was that the capacity of biofilms to support secondary production relies on their nutritional quality: biofilms characterised by higher contents of long‐chain fatty acids, nitrogen and phosphorus are expected to provide a better‐quality resource for consumers. We also hypothesised that the nutritional quality of biofilms undergoes changes over time during drying events, and that these changes are influenced by their initial algal composition. This is because the algal composition within biofilms may shift in response to drying events, subsequently impacting the nutritional quality of the biofilms.
We grew four phototrophic biofilms in flowing water, each with a different nutritional quality, and then exposed them to a short (3 days) or a long dry period (14 days). Biofilms were sampled 3 days and 18 days after rewetting (post‐disturbance and post‐recovery) to assess alterations in nutritional indicators relative to their pre‐disturbance state through pigment, fatty acid and stoichiometric analyses. We fed these biofilms to Gammarids ( Gammarus fossarum ) for 29 days and measured individual growth, feeding rate and locomotor activity. We also calculated a secondary production index to assess the biofilms' capacity to support higher trophic levels.
Our findings revealed that the nutritional quality of biofilms was significantly reduced during the post‐disturbance phase. The duration of the dry period had minimal effect on this decline. Subsequently, during the recovery phase, nutritional quality indicators improved for biofilms initially dominated by cyanobacteria, while they either remained unchanged or decreased for biofilms initially dominated by diatoms, in comparison to the pre‐disturbance state. As a result, biofilms that initially exhibited a high nutritional quality were disrupted by the dry period, depending on the duration. However, the overall effects of dry period on gammarid's response and on secondary production were less pronounced, which is likely to have resulted from changes in the quantity of available resources.
Our study demonstrates that a disturbance can modify the expected and effective qualities of biofilms. It highlights that biochemical parameters cannot reliably predict biofilm capacity to support secondary production. Biofilm history of disturbance, among other parameters, must be taken into account.
... In contrast to primary producers, consumers tend to be more stoichiometrically homeostatic (Persson et al., 2010;Kagata & Ohgushi, 2006), and consumer tissue C:N, C:P, as well as N:P ratios are generally lower than those of producers (Sardans, Rivas-Ubach & Peñuelas, 2012b;Fagan et al., 2002;Hessen et al., 2013;Sterner & Elser, 2002;Hessen, 2008;Elser et al., 2000a). High tissue C:N content often negatively influences herbivore performance, reproduction or density in terrestrial (Throop, 2005;Throop & Lerdau, 2004;Couture, Servi & Lindroth, 2010;Loaiza, Jonas & Joern, 2008, 2011Kagata & Ohgushi, 2006Lebigre et al., 2018;Hessen, 1992;White, 1993) and aquatic (Kiørboe, 1989;Burian et al., 2018;Thomas et al., 2022) ecosystems. Producers have also been shown to have a higher mean N:P ratio compared to consumers (Elser et al., 2000a), which may indicate that herbivores are often (co-)limited by P. Indeed, various studies have reported negative (Zhu et al., 2019;Zehnder & Hunter, 2009;Cease et al., 2012;Kay et al., 2007;Nijssen & Siepel, 2010;Pöyry et al., 2017;Fischer & Fiedler, 2000;Vogels et al., 2017Vogels et al., , 2021Kurze et al., 2018) or optimum (Joern & Behmer, 1997) herbivore responses to increased producer N content and/or N:P ratio. ...
Nitrogen (N) deposition has increased substantially since the second half of the 20th century due to human activities. This increase of reactive N into the biosphere has major implications for ecosystem functioning, including primary production, soil and water chemistry and producer community structure and diversity. Increased N deposition is also linked to the decline of insects observed over recent decades. However, we currently lack a mechanistic understanding of the effects of high N deposition on individual fitness, species richness and community structure of both invertebrate and vertebrate consumers. Here, we review the effects of N deposition on producer-consumer interactions, focusing on five existing ecological frameworks: C:N:P ecological stoichiometry, trace element ecological stoichiometry, nutritional geometry, essential micronutrients and allelochemicals. We link reported N deposition-mediated changes in producer quality to life-history strategies and traits of consumers, to gain a mechanistic understanding of the direction of response in consumers. We conclude that high N deposition influences producer quality via eutrophication and acidification pathways. This makes oligotrophic poorly buffered ecosystems most vulnerable to significant changes in producer quality. Changes in producer quality between the reviewed frameworks are often interlinked, complicating predictions of the effects of high N deposition on producer quality. The degree and direction of fitness responses of consumers to changes in producer quality varies among species but can be explained by differences in life-history traits and strategies, particularly those affecting species nutrient intake regulation, mobility, relative growth rate, host-plant specialisation, ontogeny and physiology. To increase our understanding of the effects of N deposition on these complex mechanisms, the inclusion of life-history traits of consumer species in future study designs is pivotal. Based on the reviewed literature, we formulate five hypotheses on the mechanisms underlying the effects of high N deposition on consumers, by linking effects of nutritional ecological frameworks to life-history strategies. Importantly, we expect that N-deposition-mediated changes in producer quality will result in a net decrease in consumer community as well as functional diversity. Moreover, we anticipate an increased risk of outbreak events of a small subset of generalist species, with concomitant declines in a multitude of specialist species. Overall, linking ecological frameworks with consumer life-history strategies provides a mechanistic understanding of the impacts of high N deposition on producer-consumer interactions, which can inform management towards more effective mitigation strategies.
... Essential fatty acids were highly retained in organisms at each trophic level up to zooplankton in all treatments, as found in lake studies (Kainz et al., 2004), whereas lower retention was found for essential amino acids. This suggests that dietary essential amino acids were sufficiently available as zooplankton can efficiently retain amino acids from diets (Burian et al., 2018). ...
Primary production is the basis for energy and biomolecule flow in food webs. Nutritional importance of terrestrial and plastic carbon via mixotrophic algae to upper trophic level is poorly studied. We explored this question by analysing the contribution of osmo‐ and phagomixotrophic species in boreal lakes and used ¹³C‐labelled materials and compound‐specific isotopes to determine biochemical fate of carbon backbone of leaves, lignin–hemicellulose and polystyrene at four‐trophic level experiment. Microbes prepared similar amounts of amino acids from leaves and lignin, but four times more membrane lipids from lignin than leaves, and much less from polystyrene. Mixotrophic algae (Cryptomonas sp.) upgraded simple fatty acids to essential omega‐3 and omega‐6 polyunsaturated fatty acids. Labelled amino and fatty acids became integral parts of cell membranes of zooplankton (Daphnia magna) and fish (Danio rerio). These results show that terrestrial and plastic carbon can provide backbones for essential biomolecules of mixotrophic algae and consumers at higher trophic levels.
... However, this pattern was not evident for the congeneric species Acartia tonsa; both species, nonetheless, showed higher egg production rates when fed the N-limited prey. In contrast, Burian et al. (2018) found that A. tonsa had enhanced ingestion, compared to the balanced diet, when offered P-limited prey, while when fed N-limited prey the ingestion rates were somewhat intermediate. These higher intakes, however, did not compensate for the nutrient lack, and egg production rates in the limited treatments declined. ...
... We chose R. salina as prey in the experiments, since it is well established that under balanced nutrient conditions this alga constitutes a prey of very good quality for copepods (Broglio et al., 2003;Vu et al., 2015), and it has been used in many previous stoichiometric studies (Bi and Sommer, 2020;Burian et al., 2018;Meunier et al., 2016). The general protocol followed was described in Isari et al. (2013). ...
... As expected, the different nutrient treatments resulted in changes in the stoichiometry of R. salina, particularly the higher C:N ratio in the N/ 20 treatment and the higher C:P and N:P ratios in the P-limited one. The molar ratios exhibited by R. salina in our experiments fell within the range of values reported for Rhodomonas spp. in similar stoichiometry experiments (e.g., Bi and Sommer, 2020;Burian et al., 2018; Suppl. Table A.1). Nutrient limitation, particularly N, reduces the protein content and increases the lipid content of R. salina, therefore explaining the increase in the C:N ratios we detected (Guevara et al., 2016). ...
We assessed the effects of nutrient imbalanced diets on the feeding, reproduction and gross-growth efficiency of egg production of the copepod Paracartia grani. The cryptophyte Rhodomonas salina, cultivated under balanced (f/2) and imbalanced growth conditions (N and P limitation), served as prey. Copepod C:N and C:P ratios increased in the imbalanced treatments, particularly under P limitation. Feeding and egg production rates did not differ between the balanced and N-limited treatments but decreased under P limitation. We found no evidence of compensatory feeding in P. grani. C gross-growth efficiency averaged 0.34 in the balanced treatment and declined to values of 0.23 and 0.14 for the N- and P-limited treatments, respectively. Under N limitation, N gross-growth efficiency increased significantly to a mean value of 0.69, likely as a result of increasing the nutrient absorption efficiency. P gross-growth efficiency reached values > 1 under P limitation, involving the depletion of body P. Hatching success was >80%, with no differences among diets. Hatched nauplii, however, had lower size and slower development when the progenitor was fed a P-limited diet. This study highlights the effects of P limitation in copepods, which are more constraining than N, and the presence of maternal effects driven by prey nutritional composition that ultimately may affect population fitness.
... It is increasingly recognized that zooplankton rely on a variety of prey sources and that this diversity may offer nutritional advantages (e. g., Kleppel, 1993;El-Sabaawi et al. 2009b). Rather than optimizing for a single nutritional factor, zooplankton productivity is usually highest with a varied diet, pointing to the importance of complicating factors such as co-limitation (Burian et al., 2018) or variable nutritional needs over the lifecycle (Leiknes et al. 2016). Flexible feeding strategies with prey switching can allow zooplankton to persist through changing prey fields (Zamora-Terol et al. 2020;El-Sabaawi et al. 2009b;Landry, 1981) and may also provide a more nutritionally complete diet. ...
Particulate organic matter (POM) forms the base of the pelagic food web, but is a complex category of material that undergoes substantial changes in quantity and quality across different time scales. As the primary consumers of POM, zooplankton are influenced by these fluctuations, resulting in shifts in the food web pathways that contribute to the production of higher trophic levels. We measured POM fatty acids, which are critical nutritional components in marine food webs, along with a suite of associated biotic and abiotic environmental conditions at a temperate coastal site over four years. Using these data, we investigated the co-occurring patterns of prey quality, quantity, and size, to develop a holistic understanding of how the prey field for zooplankton varies over the seasonal cycle and inter-annually. The seasonal pattern of POM fatty acids corresponded to the succession of phytoplankton taxa, but displayed stronger relationships to size-fractionated Chl a than taxonomic observations. Times with high micro-Chl biomass (spring and fall blooms) had the greatest concentrations of high quality food, but fatty acid levels remained high throughout the summer when Chl a concentrations dropped and the size distribution shifted towards pico-Chl. The 18-carbon polyunsaturated fatty acids 18:3ω3 (α-linolenic acid) and 18:4ω3 (stearidonic acid) increased during this time and were correlated with pico-Chl. In addition, the important nutritional factor for zooplankton and fish, the fatty acid ratio DHA:EPA (22:6ω3/20:5ω3), peaked during the middle of summer separately from the peak in Chl a. These seasonal patterns resulted in tradeoffs among the abundance, size, and nutritional quality of prey for zooplankton. We validated the basal sources of several fatty acids used as trophic markers within food web studies and in particular note their power for resolving size-based trophic connections. Interannual variability, e.g., the occurrence of fall diatom blooms and the timing of community shifts, is also discussed. This work lays the foundation for future studies of the zooplankton community at this location and the incorporation of realistic prey conditions into zooplankton studies.
... , T. weissflogii (Saiz et al. 1992) and O. marina (Calbet et al. 2007b), and for the closely-related Acartia tonsa on similarly-sized prey (Saiz et al. 1992;Saiz and Kiørboe 1995;Besiktepe and Dam 2002). Regarding stoichiometric ratios as proxy of food quality, we found a relationship between copepod ingestion rate and prey N:P ratio ( Fig. 3.2 b), indicating that P-poor prey were ingested at higher rate, probably as a means to compensate for the lack of the specific nutrient (Burian et al. 2018), although copepod response to nutrient deficient-prey may also be unaffected as previously demonstrated ). However, the amount of variance in ingestion rates explained by prey N:P ratio was rather modest (30%), and was basically driven by the data on M. rubrum and T. weissflogii. ...
... Concerning low nutritional quality arguments (stoichiometric constraints), one would expect some compensatory feeding as demonstrated to occur in A. tonsa fed nutrient-deficient algae (Burian et al. 2018). In our study, high N:P prey such as M. rubrum were ingested at higher rates ( Fig. 3.2 b). ...
... Out of the whole constituents that compose the prey biomass, zooplankton can maximise the intake of the limiting nutrient by retaining the nutrient present in the least amount and by discarding the excess nutrient (Mayzaud et al. 1998;Mitra and Flynn 2005). This form of stoichiometric modulation can be obtained by a combination of active compensatory or selective feeding behaviour (Sailley et al. 2014;Burian et al. 2018) and passive internal homeostatic processes such as regulation of gut transit time, ultimately influencing the nutrient assimilation efficiency (Tirelli and Mayzaud 2005;Mitra and Flynn 2005). On the contrary, autotrophic growth in K. veneficum, and low inorganic N:P ratio are conditions that lower the TTE as they imply a reduced nutrient utilization by protists and transfer to copepods and possibly to higher trophic levels (Bi and Sommer 2020). ...
The classical dichotomy poses strict autotrophic (phytoplankton) and heterotrophic
(zooplankton) protists as the only “engines” at the base of marine food webs. This
paradigm has been challenged by the existence of unicellular mixoplankton, able to
photosynthesize and predate simultaneously. Due to only recently appraisal, our
knowledge on the role of mixoplankton in food webs is still very limited. By laboratory
and in silico approaches, this Thesis addressed the effect of protistan mixotrophy on
copepods, ubiquitous crustacean zooplankton that act as consumers of protists and as
prey for larger predators. The ecophysiological response of the calanoid copepod
Paracartia grani to several autotrophic, mixotrophic and heterotrophic diets was
examined. In most cases no substantial differences in the copepod vital rates emerged
on the basis of the nutrition type, as differences were mainly due to species-specific
traits of the prey. Nevertheless, when feeding on the dinoflagellate Karlodinium
veneficum grown under contrasting trophic modes (auto- vs mixotrophic), copepod
egestion rate and gross-growth efficiency varied significantly. This indicates that
mixotrophy in certain protists has the potential to influence nutrient transfer, export and
recruitment of next copepod generation. As interesting results had emerged from the
species K. veneficum, this dinoflagellate was tested as prey for the calanoid copepods
P. grani and Centropages typicus with the aim to investigate the effect of inorganic
nutrient limitation (N and P) on the food quality of K. veneficum and to ascertain how
these abiotic conditions might influence copepod ecophysiological response. Results
show that nutrient-limited mixotrophic K. veneficum had more stable stoichiometric ratios
in comparison to autotrophs. Both copepod species ingested and reproduced more
when fed nutrient-depleted mixotrophic K. veneficum compared to autotrophic
counterparts. In the light of this, it can be concluded that this mixoplankter can buffer
inorganic nutrient shortage by feeding on a prey, increasing the nutrient transfer to
copepods contrarily to autotrophs. Through in-silico experiments, the effect of future
environmental changes on the dynamics of a food web was simulated. The model
encompassed three plankton functional types (phyto-, mixo- and zooplankton) and three
trophic strategies (auto-, mixo- and heterotrophy). Blooms of K. veneficum were
simulated under autotrophic and mixotrophic strategies (feeding on cryptophytes) and
copepods of the species P. grani were allowed to feed on both protists. The
dinoflagellate growth was enhanced when supplied with phagotrophy, promoting more
nutritious and abundant food landscape for copepods. Bottom-up restrictions such as
low inorganic nutrients and low cryptophytes availability decreased K. veneficum
biomass with consequent limitation of zooplankton production. Copepods improved
protist food quality via nutrient regeneration, but young and high-biomass populations
attenuated the dinoflagellate bloom. The trophic transfer efficiency from prey to
predators increased in presence of mixotrophy, especially in oligotrophic condition. By
virtue of expected changes in the abiotic and biotic landscape, these simulations
pinpoint the need of addressing the mixoplankton-copepod link when describing foodweb
dynamics.
... Only 11 studies have been published to date which use CSIA to quantify trophodynamics in copepods. Of these, they address: benthic copepods (De Troch et longicornis (Grice et al., 1998;Klein Breteler et al., 2002), and other non-Temora small, lipid-poor copepods (Boissonnot et al., 2016;Burian et al., 2018;Helenius et al., 2020a). Our results are discussed below in light of relevant published data for pelagic copepods. ...
Consumer regulation of lipid composition during assimilation of dietary items is related to their ecology, habitat, and life cycle, and may lead to extra energetic costs associated with the conversion of dietary material into the fatty acids (FAs) necessary to meet metabolic requirements. For example, lipid-rich copepods from temperate and polar latitudes must convert assimilated dietary FAs into wax esters, an efficient type of energy storage which enables them to cope with seasonal food shortages and buoyancy requirements. Lipid-poor copepods, however, tend to not be as constrained by food availability as their lipid-rich counterparts and, thus, should have no need for modifying dietary FAs. Our objective was to test the assumption that Temora longicornis, a proxy species for lipid-poor copepods, does not regulate its lipid composition. Isotopically-enriched (¹³C) diatoms were fed to copepods during a 5-day laboratory experiment. Compound-specific stable isotope analysis of algae and copepod samples was performed in order to calculate dietary FA assimilation, turnover, and assimilation efficiency into copepod FAs. Approximately 65% of the total dietary lipid carbon (C) assimilated (913 ± 68 ng C ind⁻¹ at the end of the experiment) was recorded as polyunsaturated FAs, with 20 and 15% recorded as saturated and monounsaturated FAs, respectively. As expected, T. longicornis assimilated dietary FAs in an unregulated, non-homeostatic manner, as evidenced by the changes in its FA profile, which became more similar to that of their diet. Copepods assimilated 11% of the total dietary C (or 40% of the dietary lipid C) ingested in the first two days of the experiment. In addition, 34% of their somatic growth (in C) after two days was due to the assimilation of dietary C in FAs. Global warming may lead to increased proportions of smaller copepods in the oceans, and to a lower availability of algae-produced essential FAs. In order for changes in the energy transfer in marine food webs to be better understood, it is important that future investigations assess a broader range of diets as well as lipid-poor zooplankton from oceanographic areas throughout the world’s oceans.
... On other hand, the recorded total fatty acids (six major one) were ranged between 64.75 ± 1.14% and 78.44 ± 1.18%, respectively, during all nitrogen and phosphorus deficient experimental conditions. Some fatty acids are exempted from own synthesis due to their insensitivity under nutrient deficiency conditions as early examined and agreed byBurian et al. (2018) in Rhodomonas salina. Moreover, the limitation of nitrogen and phosphorus algal culture medium may influence the reproduction rate of the copepod, P. annandalei when fed with the nutrient limited medium cultured algae. ...
Algal lipids are considered to be good raw materials towards aqua feed formulation and biofuels production, and hence, they have been investigated for decades. Using external carbon source, microalgal cultivation has been getting attention due to high biomass productivity and lipid content with flexible cultivation of algae. In this present study, a marine microalga, Tetraselmis suecica was cultivated by combined method with sodium acetate as carbon source and reciprocal nutrients concentration. The reciprocal concentration of nitrogen and phosphorus with sodium acetate supply towards lipid and fatty acid methyl esters (FAME) synthesis in terms of live feed efficiency was attempted. The highest FAME content (78.44 ± 1.18% of DW) of alga was obtained in nil nitrogen condition with limited phosphate concentration (N0‐PL) followed by N0‐P (77.31 ± 2.5% of DW) combination. Limitation of phosphate with combination of nil nitrogen (N0‐PL) showed slight increment of total FAME accumulation and its higher increments resulted in mono‐unsaturated fatty acids (MUFA) accumulation, indicating nitrogen starvation was a real FAME trigger under heterotrophic cultivation. Effect of heterotrophic cultivated T. suecica feeding on marine copepod Pseudodiaptomus annandalei produced higher population density (119 ± 15 ind. L−1) in N0‐P combination and high rate (71.98%) of nauplii production was obtained in N0‐PL combination. These findings suggested that the heterotrophic microalgae cultivation can be practiced for aqua feed (especially for copepod cultivations) formulation as well as to phosphorous removal from wastewaters.
... 38 , T. weissflogii 39 and O. marina 40 , and for the closely-related Acartia tonsa on similarly-sized prey 39,41,42 . Regarding stoichiometric ratios as proxy of food quality, we found a relationship between copepod ingestion rate and prey N:P ratio (Fig. 2b), indicating that P-poor prey were ingested at higher rate, probably as a means to compensate for the lack of the specific nutrient 43 , although copepod response to nutrient deficient-prey may also be unaffected as previously demonstrated 38 . However, the amount of variance in ingestion rates explained by prey N:P ratio was rather modest (30%), and was basically driven by the data relative to M. rubrum and T. weissflogii. ...
... Alternatively, we may suggest toxicity (as observed in some diatom species 58 ) or deficient food quality in these prey 7,30,56 . Concerning low nutritional quality arguments (stoichiometric constraints), one would expect some compensatory feeding as demonstrated to occur in A. tonsa fed nutrient-deficient algae 43 . In our study, high N:P prey such as M. rubrum were ingested at higher rates (Fig. 2b). ...
Copepod reproductive success largely depends on food quality, which also reflects the prey trophic mode. As such, modelling simulations postulate a trophic enhancement to higher trophic levels when mixotrophy is accounted in planktonic trophodynamics. Here, we tested whether photo-phagotrophic protists (mixoplankton) could enhance copepod gross-growth efficiency by nutrient upgrading mechanisms compared to obligate autotrophs and heterotrophs. To validate the hypothesis, we compared physiological rates of the copepod Paracartia grani under the three functional nutrition types. Ingestion and egg production rates varied depending on prey size and species, regardless of the diet. The gross-growth efficiency was variable and not significantly different across nutritional treatments, ranging from 3 to 25% in the mixoplanktonic diet compared to autotrophic (11-36%) and heterotrophic (8-38%) nutrition. Egg hatching and egestion rates were generally unaffected by diet. Overall, P. grani physiological rates did not differ under the tested nutrition types due to the large species-specific variation within trophic mode. However, when we focused on a single species, Karlodinium veneficum, tested as prey under contrasting trophic modes, the actively feeding dinoflagellate boosted the egestion rate and decreased the copepod gross-growth efficiency compared to the autotrophic ones, suggesting possible involvement of toxins in modulating trophodynamics other than stoichiometric constraints.
... biomass fraction respired/bioconverted) determine the magnitude of isotopic fractionation. Consistent low fractionation of 20-C PUFA could therefore be explained by high absorption efficiencies [70] and limited use for respiration. (Online version in colour.) ...
Compound-specific isotope analyses (CSIA) of fatty acids (FA) constitute a promising tool for tracing energy flows in food-webs. However, past applications of FA-specific carbon isotope analyses have been restricted to a relatively coarse food-source separation and mainly quantified dietary contributions from different habitats. Our aim was to evaluate the potential of FA-CSIA to provide high-resolution data on within-system energy flows using algae and zooplankton as model organisms. First, we investigated the power of FA-CSIA to distinguish among four different algae groups, namely cyanobacteria, chlorophytes, haptophytes and diatoms. We found substantial within-group variation but also demonstrated that δ ¹³ C of several FA (e.g. 18:3 ω 3 or 18:4 ω 3) differed among taxa, resulting in group-specific isotopic fingerprints. Second, we assessed changes in FA isotope ratios with trophic transfer. Isotope fractionation was highly variable in daphnids and rotifers exposed to different food sources. Only δ ¹³ C of nutritionally valuable poly-unsaturated FA remained relatively constant, highlighting their potential as dietary tracers. The variability in fractionation was partly driven by the identity of food sources. Such systematic effects likely reflect the impact of dietary quality on consumers' metabolism and suggest that FA isotopes could be useful nutritional indicators in the field. Overall, our results reveal that the variability of FA isotope ratios provides a substantial challenge, but that FA-CSIA nevertheless have several promising applications in food-web ecology.
This article is part of the theme issue ‘The next horizons for lipids as ‘trophic biomarkers’: evidence and significance of consumer modification of dietary fatty acids’.
