TY - JOUR A1 - Marzetz, Vanessa A1 - Spijkerman, Elly A1 - Striebel, Maren A1 - Wacker, Alexander T1 - Phytoplankton community responses to interactions between light intensity, light variations, and phosphorus supply JF - Frontiers in Environmental Science N2 - In a changing world, phytoplankton communities face a large variety of challenges including altered light regimes. These alterations are caused by more pronounced stratification due to rising temperatures, enhanced eutrophication, and browning of lakes. Community responses toward these effects can emerge as alterations in physiology, biomass, biochemical composition, or diversity. In this study, we addressed the combined effects of changes in light and nutrient conditions on community responses. In particular, we investigated how light intensity and variability under two nutrient conditions influence (1) fast responses such as adjustments in photosynthesis, (2) intermediate responses such as pigment adaptation and (3) slow responses such as changes in community biomass and species composition. Therefore, we exposed communities consisting of five phytoplankton species belonging to different taxonomic groups to two constant and two variable light intensity treatments combined with two levels of phosphorus supply. The tested phytoplankton communities exhibited increased fast reactions of photosynthetic processes to light variability and light intensity. The adjustment of their light harvesting mechanisms via community pigment composition was not affected by light intensity, variability, or nutrient supply. However, pigment specific effects of light intensity, light variability, and nutrient supply on the proportion of the respective pigments were detected. Biomass was positively affected by higher light intensity and nutrient concentrations while the direction of the effect of variability was modulated by light intensity. Light variability had a negative impact on biomass at low, but a positive impact at high light intensity. The effects on community composition were species specific. Generally, the proportion of green algae was higher under high light intensity, whereas the cyanobacterium performed better under low light conditions. In addition to that, the diatom and the cryptophyte performed better with high nutrient supply while the green algae as well as the cyanobacterium performed better at low nutrient conditions. This shows that light intensity, light variability, and nutrient supply interactively affect communities. Furthermore, the responses are highly species and pigment specific, thus to clarify the effects of climate change a deeper understanding of the effects of light variability and species interactions within communities is important. KW - phytoplankton communities KW - light variability KW - photosynthetic rate KW - climate change KW - resource competition KW - light intensity (irradiance) KW - pigment composition KW - nutrient supply Y1 - 2020 U6 - https://doi.org/10.3389/fenvs.2020.539733 SN - 2296-665X VL - 8 PB - Frontiers Media CY - Lausanne ER - TY - JOUR A1 - Wacker, Alexander A1 - Piepho, Maike A1 - Harwood, John L. A1 - Guschina, Irina A. A1 - Arts, Michael T. T1 - Light-Induced Changes in Fatty Acid Profiles of Specific Lipid Classes in Several Freshwater Phytoplankton Species JF - Frontiers in plant science : FPLS N2 - We tested the influence of two light intensities [40 and 300 μmol PAR / (m2s)] on the fatty acid composition of three distinct lipid classes in four freshwater phytoplankton species. We chose species of different taxonomic classes in order to detect potentially similar reaction characteristics that might also be present in natural phytoplankton communities. From samples of the bacillariophyte Asterionella formosa, the chrysophyte Chromulina sp., the cryptophyte Cryptomonas ovata and the zygnematophyte Cosmarium botrytis we first separated glycolipids (monogalactosyldiacylglycerol, digalactosyldiacylglycerol, and sulfoquinovosyldiacylglycerol), phospholipids (phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, and phosphatidylserine) as well as non-polar lipids (triacylglycerols), before analyzing the fatty acid composition of each lipid class. High variation in the fatty acid composition existed among different species. Individual fatty acid compositions differed in their reaction to changing light intensities in the four species. Although no generalizations could be made for species across taxonomic classes, individual species showed clear but small responses in their ecologically-relevant omega-3 and omega-6 polyunsaturated fatty acids (PUFA) in terms of proportions and of per tissue carbon quotas. Knowledge on how lipids like fatty acids change with environmental or culture conditions is of great interest in ecological food web studies, aquaculture, and biotechnology, since algal lipids are the most important sources of omega-3 long-chain PUFA for aquatic and terrestrial consumers, including humans. KW - freshwater algae KW - light adaptation KW - lipid classes KW - fatty acid changes Y1 - 2016 U6 - https://doi.org/10.3389/fpls.2016.00264 SN - 1664-462X VL - 7 SP - 1 EP - 13 PB - Frontiers Media CY - Lausanne ER - TY - JOUR A1 - Spijkerman, Elly A1 - Lukas, Marcus A1 - Wacker, Alexander T1 - Ecophysiological strategies for growth under varying light and organic carbon supply in two species of green microalgae differing in their motility JF - Phytochemistry : an international journal of plant biochemistry N2 - Mixing events in stratified lakes result in microalgae being exposed to varying conditions in light and organic carbon concentrations. Stratified lakes consist of an upper illuminated strata and a lower, darker strata where organic carbon accumulates. Therefore, in this contribution we explore the importance of dissolved organic carbon for growth under various light intensities by measuring some ecophysiological adaptations in two green microalgae. We compared the non-motile Chlorella vulgaris with the flagellated Chlamydomonas acidophila under auto-, mixo-, and heterotrophic growth conditions. In both algae the maximum photosynthetic and growth rates were highest under mixotrophy, and both algae appeared inhibited in their phosphorus acquisition under heterotrophy. Heterotrophic conditions provoked the largest differences as C. vulgaris produced chlorophyll a in darkness and grew as well as in autotrophic conditions, whereas Chl. acidophila bleached and could not grow heterotrophically. Although the fatty acid composition of both phytoplankton species differed, both species reacted in a similar way to changes in their growth conditions, mainly by a decrease of C18:3n-3 and an increase of C18:1n-9 from auto- to heterotrophic conditions. The two contrasting responses within the group of green microalgae suggest that dissolved organic carbon has a high deterministic potential to explain the survival and behaviour of green algae in the deeper strata of lakes. KW - Chlamydomonas acidophila KW - Chlorella vulgaris KW - Chlorophyceae KW - Ecophysiology on freshwater phytoplankton KW - Glucose KW - Mixotrophy KW - Osmotrophy KW - Heterotrophy KW - Photosynthesis KW - Fatty acids Y1 - 2017 U6 - https://doi.org/10.1016/j.phytochem.2017.08.018 SN - 0031-9422 SN - 1873-3700 VL - 144 SP - 43 EP - 51 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Colombo, Stefanie M. A1 - Wacker, Alexander A1 - Parrish, Christopher C. A1 - Kainz, Martin J. A1 - Arts, Michael T. T1 - A fundamental dichotomy in long-chain polyunsaturated fatty acid abundance between and within marine and terrestrial ecosystems JF - Environmental reviews = Dossiers environnement N2 - 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 C-18 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 groups. PUFA content of marine organisms was dependent on both geographic zone (i.e., latitude, and thus broadly related to temperature) and trophic level (a function of diet). The contents of n-3 LC-PUFA were higher in polar and temperate marine organisms than those from the tropics. Therefore, we conclude that, on a per capita basis, high latitude marine organisms provide a disproportionately large global share of these essential nutrients to consumers, including terrestrial predators. Our analysis also hints at how climate change, and other anthropogenic stressors, might act to negatively impact the global distribution and abundance of n-3 LC-PUFA within marine ecosystems and on the terrestrial consumers that depend on these subsidies. KW - climate change KW - food webs KW - omega-3 KW - polyunsaturated fatty acids KW - trophic ecology Y1 - 2017 U6 - https://doi.org/10.1139/er-2016-0062 SN - 1208-6053 SN - 1181-8700 VL - 25 SP - 163 EP - 174 PB - NRC Research Press CY - Ottawa ER - TY - JOUR A1 - Raatz, Michael A1 - Gaedke, Ursula A1 - Wacker, Alexander T1 - High food quality of prey lowers its risk of extinction JF - Oikos N2 - The mineral and biochemical food quality of prey may limit predator production. This well-studied direct bottom-up effect is especially prominent for herbivore-plant interactions. Low-quality prey species, particularly when defended, are generally considered to be less prone to predator-driven extinction. Undefended high-quality prey species sustain high predator production thereby potentially increasing their own extinction risk. The food quality of primary producers is highly species-specific. In communities of competing prey species, predators thus may supplement their diets of low-quality prey with high-quality prey, leading to indirect horizontal interactions between prey species of different food quality. We explore how these predator-mediated indirect interactions affect species coexistence in a general predator-prey model that is parametrized for an experimental algae-rotifer system. To cover a broad range of three essential functional traits that shape many plant-herbivore interactions we consider differences in 1) the food quality of the prey species, 2) their competitive ability for nutrient uptake and 3) their defence against predation. As expected, low food quality of prey can, similarly to defence, provide protection against extinction by predation. Counterintuitively, our simulations demonstrate that being of high food quality also prevents extinction of that prey species and additionally promotes coexistence with a competing, low-quality prey. The persistence of the high-quality prey enables a high conversion efficiency and control of the low-quality prey by the predator and allows for re-allocation of nutrients to the high-quality competitor. Our results show that high food quality is not necessarily detrimental for a prey species but instead can protect against extinction and promote species richness and functional biodiversity. Y1 - 2017 U6 - https://doi.org/10.1111/oik.03863 SN - 0030-1299 SN - 1600-0706 VL - 126 SP - 1501 EP - 1510 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Sperfeld, Erik A1 - Raubenheimer, David A1 - Wacker, Alexander T1 - Bridging factorial and gradient concepts of resource co-limitation: towards a general framework applied to consumers JF - Ecology letters N2 - Organism growth can be limited either by a single resource or by multiple resources simultaneously (co-limitation). Efforts to characterise co-limitation have generated two influential approaches. One approach uses limitation scenarios of factorial growth assays to distinguish specific types of co-limitation; the other uses growth responses spanned over a continuous, multi-dimensional resource space to characterise different types of response surfaces. Both approaches have been useful in investigating particular aspects of co-limitation, but a synthesis is needed to stimulate development of this recent research area. We address this gap by integrating the two approaches, thereby presenting a more general framework of co-limitation. We found that various factorial (co-)limitation scenarios can emerge in different response surface types based on continuous availabilities of essential or substitutable resources. We tested our conceptual co-limitation framework on data sets of published and unpublished studies examining the limitation of two herbivorous consumers in a two-dimensional resource space. The experimental data corroborate the predictions, suggesting a general applicability of our co-limitation framework to generalist consumers and potentially also to other organisms. The presented framework might give insight into mechanisms that underlie co-limitation responses and thus can be a seminal starting point for evaluating co-limitation patterns in experiments and nature. KW - Consumer KW - essential nutrient KW - factorial design KW - food quality KW - growth rate KW - multi-nutrient limitation KW - nutritional ecology KW - performance landscape KW - substitutable resource KW - synergistic effect Y1 - 2016 U6 - https://doi.org/10.1111/ele.12554 SN - 1461-023X SN - 1461-0248 VL - 19 SP - 201 EP - 215 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Koussoroplis, Apostolos-Manuel A1 - Pincebourde, Sylvain A1 - Wacker, Alexander T1 - Understanding and predicting physiological performance of organisms in fluctuating and multifactorial environments JF - Ecological monographs : a publication of the Ecological Society of America. N2 - Understanding how variance in environmental factors affects physiological performance, population growth, and persistence is central in ecology. Despite recent interest in the effects of variance in single biological drivers, such as temperature, we have lacked a comprehensive framework for predicting how the variances and covariances between multiple environmental factors will affect physiological rates. Here, we integrate current theory on variance effects with co-limitation theory into a single unified conceptual framework that has general applicability. We show how the framework can be applied (1) to generate mathematically tractable predictions of the physiological effects of multiple fluctuating co-limiting factors, (2) to understand how each co-limiting factor contributes to these effects, and (3) to detect mechanisms such as acclimation or physiological stress when they are at play. We show that the statistical covariance of co-limiting factors, which has not been considered before, can be a strong driver of physiological performance in various ecological contexts. Our framework can provide powerful insights on how the global change-induced shifts in multiple environmental factors affect the physiological performance of organisms. KW - co-limitation KW - covariance KW - eco-physiology KW - feeding rate KW - global change KW - multiple stressors KW - nonlinear averaging KW - nutrients KW - scale transition KW - temperature KW - temporal ecology KW - variance Y1 - 2017 U6 - https://doi.org/10.1002/ecm.1247 SN - 0012-9615 SN - 1557-7015 VL - 87 SP - 178 EP - 197 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Koussoroplis, Apostolos-Manuel A1 - Wacker, Alexander T1 - Covariance modulates the effect of joint temperature and food variance on ectotherm life-history traits JF - Ecology letters N2 - Understanding animal performance in heterogeneous or variable environments is a central question in ecology. We combine modelling and experiments to test how temperature and food availability variance jointly affect life-history traits of ectotherms. The model predicts that as mean temperatures move away from the ectotherm's thermal optimum, the effect size of joint thermal and food variance should become increasingly sensitive to their covariance. Below the thermal optimum, performance should be positively correlated with food–temperature covariance and the opposite is predicted above it. At lower temperatures, covariance should determine whether food and temperature variance increases or decreases performance compared to constant conditions. Somewhat stronger than predicted, the covariance effect below the thermal optimum was confirmed experimentally on an aquatic ectotherm (Daphnia magna) exposed to diurnal food and temperature variance with different amounts of covariance. Our findings have important implications for understanding ectotherm responses to climate-driven alterations of thermal mean and variance. KW - Biotic interactions KW - co-limitation KW - Daphnia KW - environmental fluctuations KW - heterogeneity KW - variability KW - vertical migration KW - zooplankton Y1 - 2016 U6 - https://doi.org/10.1111/ele.12546 SN - 1461-023X SN - 1461-0248 VL - 19 SP - 143 EP - 152 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Grzesiuk, Malgorzata A1 - Spijkerman, Elly A1 - Lachmann, Sabrina C. A1 - Wacker, Alexander T1 - Environmental concentrations of pharmaceuticals directly affect phytoplankton and effects propagate through trophic interactions JF - Ecotoxicology and Environmental Safety N2 - Pharmaceuticals are found in freshwater ecosystems where even low concentrations in the range of ng L−1 may affect aquatic organisms. In the current study, we investigated the effects of chronic exposure to three pharmaceuticals on two microalgae, a potential modulation of the effects by additional inorganic phosphorus (Pi) limitation, and a potential propagation of the pharmaceuticals’ effect across a trophic interaction. The latter considers that pharmaceuticals are bioaccumulated by algae, potentially metabolized into more (or less) toxic derivates and consequently consumed by zooplankton. We cultured Acutodesmus obliquus and Nannochloropsis limnetica in Pi-replete and Pi-limited medium contaminated with one of three commonly human used pharmaceuticals: fluoxetine, ibuprofen, and propranolol. Secondly, we tested to what extent first level consumers (Daphnia magna) were affected when fed with pharmaceutical-grown algae. Chronic exposure, covering 30 generations, led to (i) decreased cell numbers of A. obliquus in the presence of fluoxetine (under Pi-replete conditions) (ii) increased carotenoid to chlorophyll ratios in N. limnetica (under Pi-limited conditions), and (iii) increased photosynthetic yields in A. obliquus (in both Pi-conditions). In addition, ibuprofen affected both algae and their consumer: Feeding ibuprofen-contaminated algae to Pi-stressed D. magna improved their survival. We demonstrate, that even very low concentrations of pharmaceuticals present in freshwater ecosystems can significantly affect aquatic organisms when chronically exposed. Our study indicates that pharmaceutical effects can cross trophic levels and travel up the food chain. KW - Freshwater microalgae KW - Cellular phosphorus KW - Daphnia KW - Human used-drugs KW - Chronic exposure KW - Environmental risk KW - Fatty acids Y1 - 2018 U6 - https://doi.org/10.1016/j.ecoenv.2018.03.019 SN - 0147-6513 SN - 1090-2414 VL - 156 SP - 271 EP - 278 PB - Elsevier CY - San Diego ER - TY - JOUR A1 - Gall, Andrea A1 - Uebel, Udo A1 - Ebensen, Uwe A1 - Hillebrand, Helmut A1 - Meier, Sandra A1 - Singer, Gabriel A1 - Wacker, Alexander A1 - Striebel, Maren T1 - Planktotrons BT - a novel indoor mesocosm facility for aquatic biodiversity and food web research JF - Limnology and oceanography-methods N2 - We established a new indoor mesocosm facility, 12 fully controlled Planktotrons, designed to conduct marine and freshwater experiments for biodiversity and food web approaches using natural or artificial, benthic or planktonic communities. The Planktotrons are a unique and custom-tailored facility allowing long-term experiments. Wall growth can be inhibited by a rotating gate paddle with silicone lips. Additionally, temperature and light intensity are individually controllable for each Planktotron and the large volume (600 L) enables high-frequency or volume-intense measurements. In a pilot freshwater experiment various trophic levels of a pelagic food web were maintained for up to 90 d. First, an artificially assembled phytoplankton community of 11 species was inoculated in all Planktotrons. After 22 d, two ciliates were added to all, and three Daphnia species were added to six Planktotrons. After 72 d, dissolved organic matter (DOM, an alkaline soil extract) was added as an external disturbance to six of the 12 Planktotrons, involving three Planktotrons stocked with Daphnia and three without, respectively. We demonstrate the suitability of the Planktotrons for food web and biodiversity research. Variation among replicated Planktotrons (n=3 minimum) did not differ from other laboratory systems and field experiments. We investigated population dynamics and interactions among the different trophic levels, and found them affected by the sequence of ciliate and Daphnia addition and the disturbance caused by addition of DOM. Y1 - 2017 U6 - https://doi.org/10.1002/lom3.10196 SN - 1541-5856 VL - 15 SP - 663 EP - 677 PB - Wiley CY - Hoboken ER -