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  • 1. Andriukonis, Eivydas
    et al.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Kinetic N-15-isotope effects on algal growth2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 44181Article in journal (Refereed)
    Abstract [en]

    Stable isotope labeling is a standard technique for tracing material transfer in molecular, ecological and biogeochemical studies. The main assumption in this approach is that the enrichment with a heavy isotope has no effect on the organism metabolism and growth, which is not consistent with current theoretical and empirical knowledge on kinetic isotope effects. Here, we demonstrate profound changes in growth dynamics of the green alga Raphidocelis subcapitata grown in N-15-enriched media. With increasing N-15 concentration (0.37 to 50 at%), the lag phase increased, whereas maximal growth rate and total yield decreased; moreover, there was a negative relationship between the growth and the lag phase across the treatments. The latter suggests that a trade-off between growth rate and the ability to adapt to the high N-15 environment may exist. Remarkably, the lag-phase response at 3.5 at% N-15 was the shortest and deviated from the overall trend, thus providing partial support to the recently proposed Isotopic Resonance hypothesis, which predicts that certain isotopic composition is particularly favorable for living organisms. These findings confirm the occurrence of KIE in isotopically enriched algae and underline the importance of considering these effects when using stable isotope labeling in field and experimental studies.

  • 2.
    Bighiu, Maria Alexandra
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Carney Almroth, Bethanie
    Eriksson Wiklund, Ann-Kristin
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Metal contamination in harbours impacts life-history traits and metallothionein levels in snails2017In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 12, no 7, article id e0180157Article in journal (Refereed)
    Abstract [en]

    Harbours with limited water exchange are hotspots of contaminant accumulation. Antifouling paints (AF) contribute to this accumulation by leaching biocides that may affect non-target species. In several leisure boat harbours and reference areas in the Baltic Sea, chronic exposure effects were evaluated using caging experiments with the snail Theodoxus fluviatilis. We analysed variations in ecologically relevant endpoints (mortality, growth and reproduction) in concert with variation in metallothionein-like proteins (MTLP) levels. The latter is a biomarker of exposure to metals, such as copper (Cu) and zinc (Zn), which are used in AF paints as active ingredient and stabilizer, respectively. In addition, environmental samples (water, sediment) were analysed for metal (Cu and Zn) and nutrient (total phosphorous and nitrogen) concentrations. All life-history endpoints were negatively affected by the exposure, with higher mortality, reduced growth and lower fecundity in the harbours compared to the reference sites. Metal concentrations were the key explanatory variables for all observed adverse effects, suggesting that metal-driven toxicity, which is likely to stem from AF paints, is a source of anthropogenic stress for biota in the harbours.

  • 3.
    Bighiu, Maria
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Carney Almroth, Bethanie
    Eriksson-Wiklund, Ann-Kristin
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Metal contamination in harbours impacts life-history traits and metallothionein levels in snailsManuscript (preprint) (Other academic)
  • 4. Brutemark, Andreas
    et al.
    Engström-Öst, Jonna
    Vehmaa, Anu
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Growth, toxicity and oxidative stress of a cultured cyanobacterium (Dolichospermum sp.) under different CO2/pH and temperature conditions2015In: Phycological Research, ISSN 1322-0829, E-ISSN 1440-1835, Vol. 63, no 1, p. 56-63Article in journal (Refereed)
    Abstract [en]

    Cyanobacteria blooms are a worldwide nuisance in fresh, brackish and marine waters. Changing environmental conditions due to upwelling, changed mixing conditions or climate change are likely to influence cyanobacteria growth and toxicity. In this study, the response of the toxic cyanobacterium Dolichospermum sp. to lowered pH (-0.4 units by adding CO2) and elevated temperature (+4 degrees C) in an experimental set-up was examined. Growth rate, microcystin concentration and oxidative stress were measured. The growth rate and intracellular toxin concentration increased significantly as a response to temperature. When Dolichospermum was exposed to the combination of elevated temperature and high CO2/low pH, lipid peroxidation increased and antioxidant levels decreased. Microcystin concentrations were significantly correlated with growth rates. Our results show, although oxidative stress increases when exposed to a combination of high CO2/low pH and high temperature, that growth and toxicity increase at high temperature, suggesting that the cyanobacterium in general seems to be fairly tolerant to changes in pH and temperature. Further progress in identifying biological responses and predicting climate change consequences in estuaries experiencing cyanobacteria blooms requires a better understanding of the interplay between stressors such as pH and temperature.

  • 5. Calliari, Danilo
    et al.
    Andersen Borg, Marc
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Thor, Peter
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Tiselius, Peter
    Instantaneous salinity reductions affect the survival and feeding rates of the co-occuring copepods Acartia tonsa Dana and A. clausi Giesbrecht differently2008In: Journal of experimental marine biology and ecology, ISSN 0022-0981, Vol. 362, no 1, p. 18-25Article in journal (Refereed)
    Abstract [en]

    Salinity variability at short time scales constitutes a severe restriction to marine life in coastal and estuarine ecosystems. In these environments zooplankters may experience rapid salinity variations due to diverse processes, yet lethal or sub-lethal responses to such changes have been scarcely studied. We assessed short-term (12 h) survival and time-integrated clearance (F; mL ind(-1) h(-1)) and ingestion rates (1, mu gC ind(-1) h(-1)) after 1, 2, 4, 8 and 12 h of two widespread and abundant coastal copepods, Acartia tonsa and A. clausi, subjected to instant salinity changes from 32 PSU to 26, 20,14, 8 and 4 PSU (A. tonsa) and from 32 to 26, 20 and 14 PSU (A. clausi). We expected that A. tonsa, which occur naturally in environments where sharp salinity gradients are common would tolerate wider salinity changes than A. clausi, which less frequently encounter sharp gradients in nature. For A. tonsa mortality for the extreme haline shock (change from 32 to 4 PSU) was 31%, whereas A. clausi reached 22% Mortality already at a change from 32 to 14 PSU; in comparison, mortality for A. tonsa at the 32/14 PSU treatment was only 3%. F and I decreased significantly at extreme treatments, and the total clearance in experimental bottles with salinity shocked animals (F-tot, mL h(-1)) was only 5% of rates measured in non-shocked control bottles for A. tonsa (32/4 PSU change) and 20% for A. clausi (32/14 PSU change); corresponding total ingestion (I-tot, mu gC h(-1)) represented 9.5% of that in control bottles for A. tonsa and 24% for A. clausi. In comparison, the 32/14 PSU treatment did not affect either clearance or ingestion rates in A. tonsa. Results suggest that in the field A. tonsa is not likely to suffer significant mortalities due to sudden salinity reductions in the Surrounding medium - except under extreme circumstances- while A. clausi cannot tolerate changes > 18 PSU. However, in both species feeding activity could be severely compromised by salinity reductions. The decreased feeding rate may have direct implications for processes ranging from energy acquisition at individual level to organic matter transfers at ecosystem level and thus deserves more attention in experimental studies and population modelling.

  • 6.
    Dahl, Ulrika
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Lind, Charlotta Rubio
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Eklund, Britta
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Breitholtz, Magnus
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Food quality effects on copepod growth and development: Implications for bioassays in ecotoxicological testing2009In: Ecotoxicology and Environmental Safety, ISSN 0147-6513, E-ISSN 1090-2414, Vol. 72, no 2, p. 351-357Article in journal (Refereed)
    Abstract [en]

    We evaluated effects of six algal species in 25 combinations on growth and reproduction of the harpacticoid copepod Nitocra spinipes. In the first lifecycle test, Rhodomonas salina, Phaeodactylum tricornutum, and Dunaliella tertiolecta were used. The results showed that R. salina was the best food, whereas P. tricornutum (0% development success) and D. tertiolecta (41.7% malformations) were poor food items. In the second lifecycle test, a mixture of R. salina, Tetraselmis suecica, and Thalassiosira weisflogii (selected from screening tests) was tested together with a mono-diet of R. salina. Also in this test, copepods fed R. salina performed better (i.e. had higher survival and reproductive success) compared with the other treatment. We conclude that R. salina is appropriate to use as food in toxicity testing with N. spinipes, whereas some of the algae commonly used as feed in ecotoxicological tests with other copepods had detrimental effects on the development, reproduction, and survival of N. spinipes.

  • 7.
    Edlund, Anna
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Ek, Karin
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Breitholtz, Magnus
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Antibiotic-Induced Change of Bacterial Communities Associated with the Copepod Nitocra spinipes2012In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 7, no 3, p. e33107-Article in journal (Refereed)
    Abstract [en]

    Environmental pressures, such as physical factors, diet and contaminants may affect interactions between microbial symbionts and their multicellular hosts. Despite obvious relevance, effects of antimicrobial contaminants on host-symbiont relations in non-target aquatic organisms are largely unknown. We show that exposure to antibiotics had negative effects on survival and juvenile development of the copepod Nitocra spinipes and caused significant alterations in copepod-associated bacterial communities. The significant positive correlations between indices of copepod development and bacterial diversity indicate that disruption of the microflora was likely to be an important factor behind retarded juvenile development in the experimental animals. Moreover, as evidenced by ribotype distribution in the bacterial clone libraries, the exposure to antibiotics caused a shift in dominance from Betaproteobacteria to Cardinium bacteria; the latter have been shown to cause reproductive manipulations in various terrestrial arthropods. Thus, in addition to providing evidence that the antibiotic-induced perturbation of the microbial community associates with reductions in fitness-related traits of the host, this study is the first record of a copepod serving as a host for endosymbiotic Cardinium. Taken together, our results suggest that (1) antimicrobial substances and possibly other stressors can affect micobiome and symbiont-mediated interactions in copepods and other hosts, and (2) Cardinium endosymbionts may occur in other copepods and affect reproduction of their hosts.

  • 8.
    Ek, Caroline
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Garbaras, Andrius
    Yu, Zhenyang
    Oskarsson, Hanna
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Eriksson Wiklund, Ann-Kristin
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Kumblad, Linda
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Increase in stable isotope ratios driven by metabolic alterations in amphipods exposed to the beta-blocker propranolol2019In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 14, no 5, article id e0211304Article in journal (Refereed)
    Abstract [en]

    Anthropogenic pressures, such as contaminant exposure, may affect stable isotope ratios in biota. These changes are driven by alterations in the nutrient allocation and metabolic pathways induced by specific stressors. In a controlled microcosm study with the amphipod Gammarus spp., we studied effects of the beta-blocker propranolol on stable isotope signatures (delta N-15 and delta C-13), elemental composition (%C and %N), and growth (protein content and body size) as well as biomarkers of oxidative status (antioxidant capacity, ORAC; lipid peroxidation, TBARS) and neurological activity (acetylcholinesterase, AChE). Based on the known effects of propranolol exposure on cellular functions, i.e., its mode of action (MOA), we expected to observe a lower scope for growth, accompanied by a decrease in protein deposition, oxidative processes and AChE inhibition, with a resulting increase in the isotopic signatures. The observed responses in growth, biochemical and elemental variables supported most of these predictions. In particular, an increase in %N was observed in the propranolol exposures, whereas both protein allocation and body size declined. Moreover, both ORAC and TBARS levels decreased with increasing propranolol concentration, with the decrease being more pronounced for TBARS, which indicates the prevalence of the antioxidative processes. These changes resulted in a significant increase of the delta N-15 and delta C-13 values in the propranolol-exposed animals compared to the control. These findings suggest that MOA of beta-blockers may be used to predict sublethal effects in non-target species, including inhibited AChE activity, improved oxidative balance, and elevated stable isotope ratios. The latter also indicates that metabolism-driven responses to environmental contaminants can alter stable isotope signatures, which should be taken into account when interpreting trophic interactions in the food webs.

  • 9.
    Ek, Caroline
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Gerdes, Zandra
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Garbaras, Andrius
    Adolfsson-Erici, Margaretha
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Growth Retardation and Altered Isotope Composition As Delayed Effects of PCB Exposure in Daphnia magna2016In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 50, no 15, p. 8296-8304Article in journal (Refereed)
    Abstract [en]

    Trophic magnification factor (TMF) analysis employs stable isotope signatures to derive biomagnification potential for environmental contaminants. This approach relies on species delta N-15 values aligning with their trophic position (TP). This, however, may not always be true, because toxic exposure can alter growth and isotope allocation patterns. Here, effects of PCB exposure (mixture of PCB18, PCB40, PCB128, and PCB209) on delta N-15 and delta C-13 as well as processes driving these effects were explored using the cladoceran Daphnia magna. A two-part experiment assessed effects of toxic exposure during and after exposure; juvenile daphnids were exposed during 3 days (accumulation phase) and then allowed to depurate for 4 days (depuration phase). No effects on survival, growth, carbon and nitrogen content, and stable isotope composition were observed after the accumulation phase, whereas significant changes were detected in adults after the depuration phase. In particular, a significantly lower nitrogen content and a growth inhibition were observed, with a concomitant increase in delta N-15 (+0.1 parts per thousand) and decrease in delta C-13 (-0.1 parts per thousand). Although of low magnitude, these changes followed the predicted direction indicating that sublethal effects of contaminant exposure can lead to overestimation of TP and hence underestimated TMF.

  • 10.
    Ek, Caroline
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Holmstrand, Henry
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mustajärvi, Lukas
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Garbaras, Andrius
    Bariseviciute, Ruta
    Sapolaite, Justina
    Sobek, Anna
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Karlson, Agnes M. L.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Using Compound-Specific and Bulk Stable Isotope Analysis for Trophic Positioning of Bivalves in Contaminated Baltic Sea Sediments2018In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 52, no 8, p. 4861-4868Article in journal (Refereed)
    Abstract [en]

    Stable nitrogen isotopes (delta N-15) are used as indicators of trophic position (TP) of consumers. Deriving TP from delta N-15 of individual amino acids (AAs) is becoming popular in ecological studies, because of lower uncertainty than TP based on bulk delta N-15 (TPbulk). This method would also facilitate biomagnification studies provided that isotope fractionation is unaffected by toxic exposure. We compared TPAA and TPbulk estimates for a sediment-dwelling bivalve from two coastal sites, a pristine and a contaminated. Chemical analysis of PCB levels in mussels, sediments, and pore water confirmed the expected difference between sites. Both methods, but in particular the TPAA underestimated the actual TP of bivalves. Using error propagation, the total uncertainty related to the analytical precision and assumptions in the TP calculations was found to be similar between the two methods. Interestingly, the significantly higher intercept for the regression between T-AA, and TPbulk in the contaminated site compared to the pristine site indicates a higher deamination rate due to detoxification as a result of chronic exposure and a higher N-15 fractionation. Hence, there is a need for controlled experiments on assumptions underlying amino acid-specific stable isotope methods in food web and bimagnification studies.

  • 11.
    Ek, Caroline
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Holmstrand, Henry
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mustajärvi, Lukas
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Garbaras, Andrius
    Bariseviciute, Ruta
    Sapolaite, Justina
    Sobek, Anna
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Karlson, Agnes M. L.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Using compound-specific and bulk stable isotope analysis for trophic positioning of bivalves in contaminated Baltic sediments: a field evaluationManuscript (preprint) (Other academic)
  • 12.
    Ek, Caroline
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Karlson, Agnes M. L.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Garbaras, Andrius
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Stable Isotope Composition in Daphnia Is Modulated by Growth, Temperature, and Toxic Exposure: Implications for Trophic Magnification Factor Assessment2015In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 49, no 11, p. 6934-6942Article in journal (Refereed)
    Abstract [en]

    The potential for using stable isotope analysis in risk assessment of environmental contaminants is crucially dependent on the predictability of the trophic transfer of isotopes in food webs. The relationship between contaminant levels and trophic position of consumers is widely used to assess biomagnification properties of various pollutants by establishing trophic magnification factors (TMF). However, contaminant-induced variability of the isotopic composition in biota is poorly understood. Here, we investigated effects of toxic exposure on delta N-15 and delta C-13 values in a consumer, with a main hypothesis that these effects would be largely mediated via growth rate and metabolic turnover of the test animals. The cladoceran Daphnia magna was used in two experiments that were conducted to manipulate growth and body condition (assayed as C:N ratio) by food availability and temperature (Experiment 1) and by toxic exposure to the pesticide lindane (Experiment 2). We found a significant negative effect of growth rate and a positive effect of temperature on the consumer-diet discrimination factor for delta N-15 and delta C-13, with no effects on the C:N ratio (Experiment 1). In lindane-exposed daphnids, a significant growth inhibition was observed, with concomitant increase in metabolic costs and significantly elevated size-specific delta N-15 and delta C-13 values. Moreover, a significantly higher incorporation of carbon relative to nitrogen, yet a concomitant decrease in C:N ratio was observed in the exposed animals. Together, these results have methodological implications for determining trophic positions and TMF in polluted environments, where elevated delta N-15 values would translate into overestimated trophic positions and underestimated TMF. Furthermore, altered delta C-13 values may lead to erroneous food-chain assignment of the consumer in question.

  • 13.
    Ek, Caroline
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Yu, Zhenyang
    Garbaras, Andrius
    Oskarsson, Hanna
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Eriksson Wiklund, Ann-Kristin
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Kumblad, Linda
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Metabolic alterations in Gammarus spp. exposed to the beta-blocker propranolol: what causes the increase in stable isotope ratios?Manuscript (preprint) (Other academic)
  • 14. El-Shehawy, Rehab
    et al.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Fernandez-Pinas, Francisca
    del Campo, Francisca F.
    Global warming and hepatotoxin production by cyanobacteria: What can we learn from experiments?2012In: Water Research, ISSN 0043-1354, E-ISSN 1879-2448, Vol. 46, no 5, p. 1420-1429Article in journal (Refereed)
    Abstract [en]

    Global temperature is expected to rise throughout this century, and blooms of cyanobacteria in lakes and estuaries are predicted to increase with the current level of global warming. The potential environmental, economic and sanitation repercussions of these blooms have attracted considerable attention among the world's scientific communities, water management agencies and general public. Of particular concern is the worldwide occurrence of hepatotoxic cyanobacteria posing a serious threat to global public health. Here, we highlight plausible effects of global warming on physiological and molecular changes in these cyanobacteria and resulting effects on hepatotoxin production. We also emphasize the importance of understanding the natural biological function(s) of hepatotoxins, various mechanisms governing their synthesis, and climate-driven changes in food-web interactions, if we are to predict consequences of the current and projected levels of global warming for production and accumulation of hepatotoxins in aquatic ecosystems.

  • 15. Engstrom-Öst, Jonna
    et al.
    Holmborn, Towe
    Brutemark, Andreas
    Hogfors, Hedvig
    Vehmaa, Anu
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    The effects of short-term pH decrease on the reproductive output of the copepod Acartia bifilosa - a laboratory study2014In: Marine and Freshwater Behaviour & Physiology, ISSN 1023-6244, E-ISSN 1029-0362, Vol. 47, no 3, p. 173-183Article in journal (Refereed)
    Abstract [en]

    This laboratory study reports some reproductive responses of the copepod Acartia bifilosa to rapid variations in pH. The imposed changes mimic those that copepods could experience due to coastal upwelling, changed mixing conditions or vertical migration. We measured effects of low pH on egg production, hatching and early nauplii development (H-0: no effects on response variables between low and ambient pH). On treatment with low pH, we found positive effects on egg production rate and nauplii development time. The positive response to low pH could be an initial stress response or show that A. bifilosa is tolerant to the experimental pH values. The result suggests that A. bifilosa is adapted to pH changes as it performs daily migrations between the depths with differing pH. It could also be advantageous for population development if eggs hatch at high speed and so reduce the possibility that they will sink into anoxic and low pH waters.

  • 16. Engström-Öst, Jonna
    et al.
    Hogfors, Hedvig
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    El-Shehawy, Rehab
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    De Stasio, Bart
    Vehmaa, Anu
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Toxin-producing cyanobacterium Nodularia spumigena, potential competitors and grazers: testing mechanisms of reciprocal interactions2011In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 62, no 1, p. 39-48Article in journal (Refereed)
    Abstract [en]

    Interactions among toxic cyanobacteria, sympatric algae and planktivorous grazers are key processes governing plankton dynamics and cyanobacterial blooms. We studied interactions between the cyanobacterium Nodularia spumigena and microalgae (Rhodomonas salina and Tetraselmis suecica) as well as effects of zooplankton (copepod Eurytemora affinis) grazing on these interactions. N. spumigena was incubated without algae or with algae at different concentrations and with or without copepods. Following similar to 24 h incubation, we assayed changes in N. spumigena and algae abundance, concentration of intracellular (IC) and dissolved nodularin (toxin produced by N. spumigena) and quantity of Nodularia DNA in copepod guts (as a proxy for grazing pressure on the cyanobacterium). In the presence of algae, IC nodularin levels increased in a concentration-dependent manner; however, when copepods were present in the mixtures of algae and cyanobacterium, this increase was significantly less. The presence of T. suecica negatively affected the growth rate of N. spumigena, whereas the presence of the cyanobacterium strongly impeded growth of R. salina, but not of T. suecica. The IC nodularin quota correlated negatively with growth of R. salina, implicating the toxin's involvement in the observed growth suppression of the eukaryotic alga. Copepods actively ingested N. spumigena, even when the alternative food was plentiful, and neither N. spumigena quantity nor its toxin concentrations influenced copepod feeding rates and survival. These findings suggest complex allelopathic interactions between the autotrophs, whereas mesozooplankton grazers have an indirect negative effect on the nodularin concentrations by suppressing the competitors. These findings underscore the need to study ecologically important interactions among toxic cyanobacteria, sympatric algae and grazers, if we are to understand mechanisms regulating cyanobacterial blooms.

  • 17.
    Furuhagen, Sara
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Fuchs, Anne
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Lundström Belleza, Elin
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Breitholtz, Magnus
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Are Pharmaceuticals with Evolutionary Conserved Molecular Drug Targets More Potent to Cause Toxic Effects in Non-Target Organisms?2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 8, article id e105028Article in journal (Refereed)
    Abstract [en]

    The ubiquitous use of pharmaceuticals has resulted in a continuous discharge into wastewater and pharmaceuticals and their metabolites are found in the environment. Due to their design towards specific drug targets, pharmaceuticals may be therapeutically active already at low environmental concentrations. Several human drug targets are evolutionary conserved in aquatic organisms, raising concerns about effects of these pharmaceuticals in non-target organisms. In this study, we hypothesized that the toxicity of a pharmaceutical towards a non-target invertebrate depends on the presence of the human drug target orthologs in this species. This was tested by assessing toxicity of pharmaceuticals with (miconazole and promethazine) and without (levonorgestrel) identified drug target orthologs in the cladoceran Daphnia magna. The toxicity was evaluated using general toxicity endpoints at individual (immobility, reproduction and development), biochemical (RNA and DNA content) and molecular (gene expression) levels. The results provide evidence for higher toxicity of miconazole and promethazine, i.e. the drugs with identified drug target orthologs. At the individual level, miconazole had the lowest effect concentrations for immobility and reproduction (0.3 and 0.022 mg L-1, respectively) followed by promethazine (1.6 and 0.18 mg L-1, respectively). At the biochemical level, individual RNA content was affected by miconazole and promethazine already at 0.0023 and 0.059 mg L-1, respectively. At the molecular level, gene expression for cuticle protein was significantly suppressed by exposure to both miconazole and promethazine; moreover, daphnids exposed to miconazole had significantly lower vitellogenin expression. Levonorgestrel did not have any effects on any endpoints in the concentrations tested. These results highlight the importance of considering drug target conservation in environmental risk assessments of pharmaceuticals.

  • 18.
    Furuhagen, Sara
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Fuchs, Anne
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Lundström, Elin
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Breitholtz, Magnus
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Do pharmaceuticals with evolutionary conserved molecular drug targets pose a greater environmental risk?Manuscript (preprint) (Other academic)
  • 19.
    Furuhagen, Sara
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Liewenborg, Birgitta
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Breitholtz, Magnus
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Feeding Activity and Xenobiotics Modulate Oxidative Status in Daphnia magna: Implications for Ecotoxicological Testing2014In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 48, no 21, p. 12886-12892Article in journal (Refereed)
    Abstract [en]

    To apply biomarkers of oxidative stress in laboratory and field settings, an understanding of their responses to changes in physiological rates is important. The evidence is accumulating that caloric intake can increase production of reactive oxygen species and thus affect background variability of oxidative stress biomarkers in ecotoxicological testing. This study aimed to delineate effects of food intake and xenobiotics on oxidative biomarkes in Daphnia magna. Antioxidant capacity measured as oxygen radical absorbance capacity (ORAC) and lipid peroxidation assayed as thiobarbituric acid reactive substances (TBARS) were measured. Food intake was manipulated by varying food densities or by exposing the animals to chemicals inhibiting feeding rate (pharmaceutical haloperidol and pesticide lindane). Feeding rate proved to affect both protein, ORAC, and TBARS in unexposed daphnids. However, there was no significant effect of feeding rate on the protein-specific ORAC values. Both substances affected individual protein and ORAC levels and changed their relationship to feeding rate. Our results show that inhibition of feeding rate influenced the interpretation of biomarker response and further emphasize the importance of understanding (1) baseline variability in potential biomarkers due to variations in metabolic state and (2) the contribution of feeding rate on toxic response of biomarkers.

  • 20.
    Furuhagen, Sara
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Liewenborg, Birgitta
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Breitholtz, Magnus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Oxidative biomarkers as indicators of reproductive effects in Daphnia magnaManuscript (preprint) (Other academic)
    Abstract [en]

    Oxidative stress can be induced by various stressors, and oxidative biomarkers are commonly used as indicators of xenobiotic exposure. However, the capacity of oxidative biomarkers to predict pro-oxidative exposure or indicate reproductive effects has not been evaluated. In this study, we hypothesized that biomarkers of oxidative stress (catalase, antioxidant capacity, and lipid peroxidation) can be used to diagnose pro-oxidative exposure, with concomitant reproductive penalties. We exposed Daphnia magna to UVB irradiation, a known agent inducing pro-oxidative processes in various organisms, from birth to adult stage. The biomarker responses were followed in different life-stages in concert with reproductive success and individual growth rate. The UVB exposure induced alterations in antioxidant capacity (measured as oxygen radical absorbance capacity, ORAC) in both juvenile and adult daphnids. Moreover, these effects were age-specific, with decreased and increased ORAC in juveniles and adults, respectively. These changes were associated with reproductive success, as increased number of offspring was negatively associated with antioxidant capacity. Also, a trans-generational effect was observed as exposed females allocated less antioxidants to their offspring. ORAC normalized to protein content (ORACp) was identified as a suitable biomarker of pro-oxidative exposure. For diagnostics of oxidative stress in field and laboratory settings, two logistic models employing ORACp in juvenile and adult D. magna were proposed; the classification accuracy of the models was about 80%. None of the other biomarkers contributed significantly to the models.

  • 21.
    Furuhagen, Sara
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Liewenborg, Birgitta
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Breitholtz, Magnus
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    The effects of feeding and xenobiotics on oxidative stress in Daphnia magna: implications for ecotoxicological testingManuscript (preprint) (Other academic)
  • 22.
    Gerdes, Zandra
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Hermann, Markus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ogonowski, Martin
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    A novel method for assessing microplastic effect in suspension through mixing test and reference materials2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 10695Article in journal (Refereed)
    Abstract [en]

    The occurrence of microplastic in the environment is of global concern. However, the microplastic hazard assessment is hampered by a lack of adequate ecotoxicological methods because of conceptual and practical problems with particle exposure. In the environment, suspended solids (e.g., clay and cellulose) in the same size range as microplastic, are ubiquitous. Therefore, it must be established whether the addition of microplastic to these background levels of particulate material represents a hazard. We present a novel approach employing a serial dilution of microplastic and reference particles, in mixtures, which allows disentangling the effect of the microplastic from that of the other particulates. We demonstrate the applicability of the method using an immobilization test with Daphnia magna exposed to polyethylene terephthalate (test microplastic; median particle diameter similar to 5 mu m) and kaolin clay (reference material; similar to 3 mu m). In the range of the suspended solids test concentrations (0-10 000 mg L-1), with microplastic contributing 0-100% of total mass, the Lc(50) values for the plastic mixtures were significantly lower compared to the kaolin exposure. Hence, the exposure to polyethylene terephthalate was more harmful to the daphnids than to the reference material alone. The estimated threshold for the relative contribution of the test microplastic to suspended matter above which significantly higher mortality was observed was 2.4% at 32 mg of the solids L-1. This approach has a potential for standardization of ecotoxicological testing of particulates, including microplastic.

  • 23.
    Gerdes, Zandra
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ogonowski, Martin
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Aquabiota Water Research AB, Sweden; Swedish University of Agricultural Sciences, Sweden.
    Nybom, Inna
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ek, Caroline
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Adolfsson-Erici, Margaretha
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Barth, Andreas
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Microplastic-mediated transport of PCBs? A depuration study with Daphnia magna2019In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 14, no 2, article id e0205378Article in journal (Refereed)
    Abstract [en]

    The role of microplastic (MP) as a carrier of persistent organic pollutants (POPs) to aquatic organisms has been a topic of debate. However, the reverse POP transport can occur if relative contaminant concentrations are higher in the organism than in the microplastic. We evaluated the effect of microplastic on the PCB removal in planktonic animals by exposing the cladoceran Daphnia magna with a high body burden of polychlorinated biphenyls (PCB 18, 40, 128 and 209) to a mixture of microplastic and algae; daphnids exposed to only algae served as the control. As the endpoints, we used PCB body burden, growth, fecundity and elemental composition (%C and %N) of the daphnids. In the daphnids fed with microplastic, PCB 209 was removed more efficiently, while there was no difference for any other congeners and Sigma PCBs between the microplastic-exposed and control animals. Also, higher size-specific egg production in the animals carrying PCB and receiving food mixed with micro-plastics was observed. However, the effects of the microplastic exposure on fecundity were of low biological significance, because the PCB body burden and the microplastic exposure concentrations were greatly exceeding environmentally relevant concentrations.

  • 24.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    A single-step staining method to evaluate egg viability in zooplankton2010In: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, Vol. 8, p. 414-423Article in journal (Refereed)
    Abstract [en]

    A simplified method for viability analysis of zooplankton eggs by staining of nonviable eggs with a fluorescent nucleic acid stain TO-PRO-1 iodide is proposed here as a further development of fluorescence-based egg viability assays. This is one-step analysis with no intermediate steps for chorion removal. The method was calibrated using predetermined mixtures of viable and nonviable eggs (rotifers and copepods), and validated using hatching experiments (copepods) and egg development assay (cladocerans) as reference measurements. In these tests, eggs of several zooplankton species, Brachionus plicatilis (Rotatoria), Daphnia magna (Cladocera), Nitocra spinipes (Harpacticoida), Acartia tonsa (Calanoida), were used. Moreover, staining efficiency was not affected by storage of samples for up to 1 month in -80 degrees C, making the assay suitable for egg viability assessment in field and laboratory studies. To illustrate usefulness of the method, it was applied to evaluate how absence of re-mating affects production of viable eggs in females of A. bifilosa (Calanoida). In females separated from males, proportion of sterile eggs increased in 3 d after the separation and no viable eggs were produced after 5 d. The effects of mating frequency on egg viability are important to understand when designing egg production experiments and interpreting field data on egg viability in populations with skewed sex ratios.

  • 25.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Individual growth as a non-dietary determinant of the isotopic niche metrics2018In: Methods in Ecology and Evolution, ISSN 2041-210X, E-ISSN 2041-210X, Vol. 9, no 2, p. 269-277Article in journal (Refereed)
    Abstract [en]

    1. Quantitative analytical approaches for isotopic niche analysis in the trophic diversity studies are proliferating rapidly; however, the assumptions behind the isotopic niche applications are rarely tested. One of the main assumptions is independence of the niche metrics and physiological status of the animals. The aim of this experimental study was to test the relationship between growth and Layman's metrics of isotopic niche in consumers eating the same food but in different quantities and growing at different rates.

    2. Based on research indicating that individual variability in isotopic fractionation increases under suboptimal conditions, I hypothesized that a group of consumers originating from the same population and exposed to food limitation would have greater estimates of the niche breadth and diversity as a result of higher inter-individual variability in growth rate and stable isotope signatures than in non-limiting feeding conditions. This hypothesis was tested using Baltic mysids Neomysis integer fed isotopically uniform diet under laboratory conditions and analysing individual growth and stable isotope signature in concert.

    3. As hypothesized, mysid growth rate was a significant negative predictor of most niche metrics. These effects were related to both increased inter-individual variability and higher trophic fractionation in malnourished animals, whereas in actively growing mysids, lower fractionation was observed together with lower values for niche size, isotopic range and trophic diversity.

    4. These findings challenge how we interpret the intrapopulation isotopic variance and evaluate isotopic evidence of individual specialization and call for integrated approaches for isotopic niche and growth assessment.

  • 26.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Screening for microplastic particles in plankton samples: How to integrate marine litter assessment into existing monitoring programs?2015In: Marine Pollution Bulletin, ISSN 0025-326X, E-ISSN 1879-3363, Vol. 99, no 1-2, p. 271-275Article in journal (Refereed)
    Abstract [en]

    Microplastics (MPs) are a newly recognized type of environmental pollution in aquatic systems; however no monitoring of these contaminants is conducted, mostly due to the lack of routine quantification. In the net samples collected with a 90-mu m WP2 net, pelagic MP abundance was quantified by light microscopy and evaluated as a function of inshore-offshore gradient, depth, and season; the same samples were used for zooplankton analysis. The MP abundance was similar to 10(2)-10(4) particles m(-3), with no significant inshore-offshore gradient during summer but increasing offshore in winter. MP abundance in deeper layers was positively affected by zooplankton abundance in the upper layers and significantly lower during winter compared to summer. These findings indicate heterogeneity of MP distribution due to biotic and abiotic factors and suggest that samples collected for other purposes can be used for quantification of MPs in the Baltic Sea, thus facilitating integration of MP assessment into existing monitoring schemes.

  • 27.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Shifts in rotifer life history in response to stable isotope enrichment: testing theories of isotope effects on organismal growth2017In: Royal Society Open Science, E-ISSN 2054-5703, Vol. 4, no 3, article id 160810Article in journal (Refereed)
    Abstract [en]

    In ecology, stable isotope labelling is commonly used for tracing material transfer in trophic interactions, nutrient budgets and biogeochemical processes. The main assumption in this approach is that the enrichment with a heavy isotope has no effect on the organism growth and metabolism. This assumption is, however, challenged by theoretical considerations and experimental studies on kinetic isotope effects in vivo. Here, I demonstrate profound changes in life histories of the rotifer Brachionus plicatilis fed N-15-enriched algae (0.4-5.0 at%); i.e. at the enrichment levels commonly used in ecological studies. These findings support theoretically predicted effects of heavy isotope enrichment on growth, metabolism and ageing in biological systems and underline the importance of accounting for such effects when using stable isotope labelling in experimental studies.

  • 28.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Toxic cyanobacteria Nodularia spumigena in the diet of Baltic mysids: evidence from molecular diet analysis.2009In: Harmful Algae, ISSN 1568-9883, E-ISSN 1878-1470, Vol. 8, p. 264-272Article in journal (Refereed)
    Abstract [en]

    A PCR-based method was used to detect toxic cyanobacteria Nodularia spumigena in the diet of Baltic mysids, Mysis mixta and Mysis relicta. The decay in detectability of Nodularia DNA in mysid stomachs and feces following the cyanobacterium consumption was examined in laboratory with special references to (1) marker size (780 by vs. 200 bp), (2) mysid developmental stage (juveniles vs. subadults), and (3) feeding regime after consuming the cyanobacteria (continuous vs. interrupted feeding). The Nodularia DNA could be reliably detected in mysid stomachs and feces by PCR technique. In the mysid with interrupted feeding, the calculated half-lives of N. spumigena DNA in the mysid stomachs were 1.2 and 6.1 h for 780 and 200 by fragments, respectively. Continuous feeding, however, facilitated decay in the detectability, most likely due to increased gut evacuation rate. In stomachs of the field-collected mysids, the Nodularia DNA was detected with high frequencies, 60% in M. mixta and 51 % in M. relicta. Moreover, it was higher in immature mysids than in adults and correlated with stomach fullness in age-specific manner: in juveniles and subadults, stomachs containing Nodularia were significantly fuller, while in adults, the presence of the cyanobacteria was associated with empty stomachs. This suggests greater habitat overlap for juvenile mysids and N. spumigena and thus higher encounter and consumption rates. These findings contribute to a growing body of evidence that cyanobacteria in the Baltic Sea are important food for grazers.

  • 29.
    Gorokhova, Elena
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology. Marin ekologi.
    Edlund, Anna
    Hajdu, Susanna
    Stockholm University, Faculty of Science, Department of Systems Ecology. Marin ekologi.
    Zhivotova, E
    Nucleic acid levels in copepods: dynamic response to the phytoplankton bloom in the northern Baltic proper2007In: Marine Ecology Progress Series, Vol. 349, p. 213-225Article in journal (Refereed)
  • 30.
    Gorokhova, Elena
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Fagerberg, Towe
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Predation by herring (Clupea harengus) and sprat (Sprattus sprattus) on Cercopagis pengoi in a wastern Baltic Sea bay2004In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 61, no 6, p. 959-965Article in journal (Refereed)
  • 31.
    Gorokhova, Elena
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hajdu, Susanna
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Larsson, Ulf
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Responses of Phyto- and Zooplankton Communities to Prymnesium polylepis (Prymnesiales) Bloom in the Baltic Sea2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 11, article id e112985Article in journal (Refereed)
    Abstract [en]

    A large bloom of Prymnesium polylepis occurred in the Baltic Sea during the winter 2007 - spring 2008. Based on numerous reports of strong allelopathic effects on phytoplankton exerted by P. polylepis and its toxicity to grazers, we hypothesized that during this period negative correlations will be observed between P. polylepis and (1) main phytoplankton groups contributing to the spring bloom (i.e., diatoms and dinoflagellates), and (2) zooplankton growth and abundance. To test these hypotheses, we analyzed inter-annual variability in phytoplankton and zooplankton dynamics as well as growth indices (RNA: DNA ratio) in dominant zooplankton in relation to the Prymnesium abundance and biomass. Contrary to the hypothesized relationships, no measurable negative responses to P. polylepis were observed for either the total phytoplankton stocks or the zooplankton community. The only negative response, possibly associated with P. polylepis occurrence, was significantly lower abundance of dinoflagellates both during and after the bloom in 2008. Moreover, contrary to the expected negative effects, there were significantly higher total phytoplankton abundance as well as significantly higher winter abundance and winter-spring RNA: DNA ratio in dominant zooplankton species in 2008, indicating that P. polylepis bloom coincided with favourable feeding conditions for zooplankton. Thus, primary consumers, and consequently also zooplanktivores (e.g., larval fish and mysids), may benefit from haptophyte blooms, particularly in winter, when phytoplankton is scarce.

  • 32.
    Gorokhova, Elena
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Höglander, Helena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Andersen, Christian Marc
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Stable isotopes show food web changes after invasion by the predatory cladoceran Cercopagis pengoi in a Baltic Sea bay2005In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 143, no 2, p. 251-259Article in journal (Refereed)
    Abstract [en]

    Cercopagis pengoi, a recent invader to the Baltic Sea and the Laurentian Great Lakes, is a potential competitor with fish for zooplankton prey. We used stable C and N isotope ratios to elucidate trophic relationships between C. pengoi, zooplankton (microzooplankton, 90–200 m, mostly copepod nauplii and rotifers; mesozooplankton, >200 m, mostly copepods), and zooplanktivorous fish (herring, size range 5–15 cm and sprat, 9–11 cm) in a coastal area of the northern Baltic Sea. The isotope ratios in C. pengoi and fish were much higher than those of zooplankton, showing general trends of enrichment with trophic level. Young-of-the-year (YOY) herring had a significantly higher 15N/14N ratio than C. pengoi, suggesting of a trophic linkage between the two species. To evaluate the possible relative importance of different food sources for C. pengoi and YOY herring, two-source isotope-mixing models for N were used, with micro- and mesozooplankton as prey for C. pengoi and mesozooplankton and C. pengoi as prey for YOY herring. These models indicate that mesozooplankton was the major food source of both species. However, microzooplankton may be important prey for young stages of C. pengoi. Comparative analyses of the herring trophic position before and after the invasion by C. pengoi showed a trophic level shift from 2.6 to 3.4, indicating substantial alterations in the food web structure. Our findings contribute to a growing body of evidence, showing that C. pengoi can modify food webs and trophic interactions in invaded ecosystems.

  • 33.
    Gorokhova, Elena
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology. Marin ekologi.
    Lehtiniemi, M
    A combined approach to understand trophic interactions between Cercopagis pengoi (Cladocera: Onychopoda) and mysids in the Gulf of Finland2007In: Limnology and Oceanography, Vol. 52, no 2, p. 822-835Article in journal (Refereed)
  • 34.
    Gorokhova, Elena
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lehtiniemi, Maiju
    Motwani, Nisha H.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Trade-Offs between Predation Risk and Growth Benefits in the Copepod Eurytemora affinis with Contrasting Pigmentation2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 8, article id e71385Article in journal (Refereed)
    Abstract [en]

    Intraspecific variation in body pigmentation is an ecologically and evolutionary important trait; however, the pigmentation related trade-offs in marine zooplankton are poorly understood. We tested the effects of intrapopulation phenotypic variation in the pigmentation of the copepod Eurytemora affinis on predation risk, foraging, growth, metabolic activity and antioxidant capacity. Using pigmented and unpigmented specimens, we compared (1) predation and selectivity by the invertebrate predator Cercopagis pengoi, (2) feeding activity of the copepods measured as grazing rate in experiments and gut fluorescence in situ, (3) metabolic activity assayed as RNA: DNA ratio in both experimental and field-collected copepods, (4) reproductive output estimated as egg ratio in the population, and (5) total antioxidant capacity. Moreover, mitochondrial DNA (mtDNA) COI gene variation was analysed. The pigmented individuals were at higher predation risk as evidenced by significantly higher predation rate by C. pengoi on pigmented individuals and positive selection by the predator fed pigmented and unpigmented copepods in a mixture. However, the antioxidant capacity, RNA: DNA and egg ratio values were significantly higher in the pigmented copepods, whereas neither feeding rate nor gut fluorescence differed between the pigmented and unpigmented copepods. The phenotypic variation in pigmentation was not associated with any specific mtDNA genotype. Together, these results support the metabolic stimulation hypothesis to explain variation in E. affinis pigmentation, which translates into beneficial increase in growth via enhanced metabolism and antioxidant protective capacity, together with disadvantageous increase in predation risk. We also suggest an alternative mechanism for the metabolic stimulation via elevated antioxidant levels as a primary means of increasing metabolism without the increase in heat absorbance. The observed trade-offs are relevant to evolutionary mechanisms underlying plasticity and adaptation and have the capacity to modify strength of complex trophic interactions.

  • 35.
    Gorokhova, Elena
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Lehtiniemi, Maiju
    Postel, Lutz
    Rubene, Gunta
    Amid, Callis
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Lesutiene, Jurate
    Uusitalo, Laura
    Strake, Solvita
    Demereckiene, Natalja
    Indicator Properties of Baltic Zooplankton for Classification of Environmental Status within Marine Strategy Framework Directive2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 7, article id e0158326Article in journal (Refereed)
    Abstract [en]

    The European Marine Strategy Framework Directive requires the EU Member States to estimate the level of anthropogenic impacts on their marine systems using 11 Descriptors. Assessing food web response to altered habitats is addressed by Descriptor 4 and its indicators, which are being developed for regional seas. However, the development of simple foodweb indicators able to assess the health of ecologically diverse, spatially variable and complex interactions is challenging. Zooplankton is a key element in marine foodwebs and thus comprise an important part of overall ecosystem health. Here, we review work on zooplankton indicator development using long-term data sets across the Baltic Sea and report the main findings. A suite of zooplankton community metrics were evaluated as putative ecological indicators that track community state in relation to Good Environmental Status (GES) criteria with regard to eutrophication and fish feeding conditions in the Baltic Sea. On the basis of an operational definition of GES, we propose mean body mass of zooplankton in the community in combination with zooplankton stock measured as either abundance or biomass to be applicable as an integrated indicator that could be used within the Descriptor 4 in the Baltic Sea. These metrics performed best in predicting zooplankton being in-GES when considering all datasets evaluated. However, some other metrics, such as copepod biomass, the contribution of copepods to the total zooplankton biomass or biomass-based Cladocera: Copepoda ratio, were equally reliable or even superior in certain basin-specific assessments. Our evaluation suggests that in several basins of the Baltic Sea, zooplankton communities currently appear to be out-of-GES, being comprised by smaller zooplankters and having lower total abundance or biomass compared to the communities during the reference conditions; however, the changes in the taxonomic structure underlying these trends vary widely across the sea basins due to the estuarine character of the Baltic Sea.

  • 36.
    Gorokhova, Elena
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Löf, Marie
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Halldorsson, Halldor Palmar
    Tjärnlund, Ulla
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Lindström, Magnus
    Elfwing, Tina
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Sundelin, Brita
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Single and combined effects of hypoxia and contaminated sediments on the amphipod Monoporeia affinis in laboratory toxicity bioassays based on multiple biomarkers2010In: Aquatic Toxicology, ISSN 0166-445X, E-ISSN 1879-1514, Vol. 99, no 2, p. 263-274Article in journal (Refereed)
    Abstract [en]

    In estuaries, hypoxic conditions and pollution are among the major factors responsible for the declines in habitat quality, yet little is known about their combined effects on estuarine organisms. In this study, to investigate single and combined effects of hypoxia and contaminated sediment, the Baltic amphipod Monoporeia affinis was exposed for 5-9 days to four different combinations of oxygen conditions (moderate hypoxia vs. normoxia) and contamination (polluted vs. unpolluted sediments) at environmentally realistic levels. To detect oxidative stress, a suite of biomarkers was used - antioxidant enzymes [superoxide dismutases (SOD), catalase (CAT), and glutathione S-transferases (GST)], acetylcholinesterase (AChE), lipid peroxidation status (TBARS concentration), protein carbonyl content (PCC), and DNA strand breakage (DNA-SB). To assay effects at the organism level, we used RNA:DNA ratio as a proxy for growth and metabolic rate and mortality. There were significant increases in CAT and SOD activities and TBARS levels in response to both moderate hypoxia and contaminated sediment, while GST increased and AChE decreased in response to the contamination only. Significant positive correlations were observed among the antioxidant enzymes and between the enzyme activities and TBARS concentration, suggesting a complex response to the oxidative stress. No significant changes in PCC were recorded in any of the treatments. Furthermore, the negative effect of hypoxia on DNA integrity was significant; with frequency of DNA-SB increasing in animals exposed to hypoxia in contaminated sediment. Despite clear effect at the cellular and biochemical levels, no responses at the organism level were observed. Multivariate analyses of the dataset have allowed us to link exposure factors to individual biomarker responses. Of the potential biomarkers assessed in this study, CAT activity was found to be associated with hypoxia, while SOD, GST and AChE activities appear to predict best the effects of exposure to sediments containing several contaminants (e.g. heavy metals, PCBs and PAHs), and TBARS concentration is particularly indicative of combined effects of hypoxia and contamination. In addition to providing new knowledge on the combined effects of multiple stressors on estuarine organisms, the findings of the present study are also important to understand data from biomonitoring studies in the Baltic Sea and in other regions where multiple stress factors co-occur.

  • 37.
    Gorokhova, Elena
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Löf, Marie
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Reutgard, Martin
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Lindström, Magnus
    Sundelin, Brita
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Exposure to contaminants exacerbates oxidative stress in amphipod Monoporeia affinis subjected to fluctuating hypoxia2013In: Aquatic Toxicology, ISSN 0166-445X, E-ISSN 1879-1514, Vol. 127, p. 46-53Article in journal (Refereed)
    Abstract [en]

    Fitness and survival of an organism depend on its ability to mount a successful stress response when challenged by exposure to damaging agents. We hypothesized that co-exposure to contaminants may exacerbate oxidative stress in hypoxia-challenged benthic animals compromising their ability to recover upon reoxygenation. This was tested using the amphipod Monoporeia affinis exposed to hypoxia followed by reoxygenation in sediments collected in polluted and pristine areas. In both sediment types, oxygen radical absorbance capacity (ORAC) and antioxidant enzyme activities [superoxide dismutase (SOD) and catalase (CAT)] increased during hypoxia, suggesting that M. affinis has a strategy of preparation for oxidative stress that facilitates recovery after a hypoxic episode. Exposure to contaminants altered this anticipatory response as indicated by higher baselines of ORAC and SOD during hypoxia and no response upon reoxygenation. This coincided with significantly elevated oxidative damage evidenced by a marked reduction in glutathione redox status (ratio of reduced GSH/oxidized GSSG) and an increase in lipid peroxidation (TSARS levels). Moreover, RNA:DNA ratio, a proxy for protein synthetic activity, decreased in concert with increased TBARS, indicating a linkage between oxidative damage and fitness. Finally, inhibited acetylcholinesterase (AChE) activity in animals exposed to contaminated sediments suggested a neurotoxic impact, whereas significant correlations between AChE and oxidative biomarkers may indicate connections with redox state regulation. The oxidative responses in pristine sediments suggested a typical scenario of ROS production and removal, with no apparent oxidative damage. By contrast, co-exposure to contaminants caused greater increase in antioxidants, lipid peroxidation, and slowed recovery from hypoxia as indicated by CAT, GSH/GSSG, TBARS and AChE responses. These results support the hypothesized potential of xenobiotics to hamper ability of animals to cope with fluctuating hypoxia. They also emphasize the importance of understanding interactions between antioxidant responses to different stressors and physiological mechanisms of oxidative damage.

  • 38.
    Gorokhova, Elena
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Faculty of Science, Department of Systems Ecology.
    Mattsson, Lisa
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Sundström, Annica M.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    A comparison of TO-PRO-1 iodide and 5-CFDA-AM staining methods for assessing viability of planktonic algae with epifluorescence microscopy2012In: Journal of Microbiological Methods, ISSN 0167-7012, E-ISSN 1872-8359, Vol. 89, no 3, p. 216-221Article in journal (Refereed)
    Abstract [en]

    Two fluorescent dyes, TO-PRO-1 iodide and 5-CFDA-AM, were evaluated for LIVE/DEAD assessment of unicellular marine algae Brachiomonas submarina and Tetraselmis suecica. Epifluorescence microscopy was used to estimate cell viability in predetermined mixtures of viable and non-viable algal cells and validated using microplate growth assay as reference measurements. On average, 5-CFDA-AM underestimated live cell abundance by similar to 25% compared with viability estimated by the growth assay, whereas TO-PRO-1 iodide provided accurate viability estimates. Furthermore, viability estimates based on staining with TO-PRO-1 iodide were not affected by a storage period of up to one month in -80 degrees C, making the assay a good candidate for routine assessment of phytoplankton populations in field and laboratory studies.

  • 39.
    Gorokhova, Elena
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Rivetti, Claudia
    Furuhagen, Sara
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Edlund, Anna
    Ek, Karin
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Breitholtz, Magnus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Bacteria-Mediated Effects of Antibiotics on Daphnia Nutrition2015In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 49, no 9, p. 5779-5787Article in journal (Refereed)
    Abstract [en]

    In polluted environments, contaminant effects may be manifested via both direct toxicity to the host and changes in its microbiota, affecting bacteria host interactions. In this context, particularly relevant is exposure to antibiotics released into environment. We examined effects of the antibiotic trimethoprim on microbiota of Daphnia magna and concomitant changes in the host feeding. In daphnids exposed to 0.25 mg L-1 trimethoprim for 24 h, the microbiota was strongly affected, with (1) up to 21-fold decrease in 16S rRNA gene abundance and (2) a shift from balanced communities dominated by Curvibacter, Aquabacterium, and Limnohabitans in controls to significantly lower diversity under dominance of Pelomonas in the exposed animals. Moreover, decreased feeding and digestion was observed in the animals exposed to 0.25-2 mg L-1 trimethoprim for 48 h and then fed C-14-labeled algae. Whereas the proportion of intact algal cells in the guts increased with increased trimethoprim concentration, ingestion and incorporation rates as well as digestion and incorporation efficiencies decreased significantly. Thus, antibiotics may impact nontarget species via changes in their microbiota leading to compromised nutrition and, ultimately, growth. These bacteria-mediated effects in nontarget organisms may not be unique for antibiotics, but also relevant for environmental pollutants of various nature.

  • 40. Griniene, Evelina
    et al.
    Lesutiene, Jurate
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Zemlys, Petras
    Gasiunaite, Zita R.
    Lack of ciliate community integrity in transitional waters: A case study from the Baltic Sea2019In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 226, article id UNSP 106259Article in journal (Refereed)
    Abstract [en]

    The Baltic Sea, one of the world's largest brackish water environments, is particularly suitable for studies aiming to understand biodiversity in saltwater-freshwater mixing zones, i.e., transitional waters at different spatial and temporal scales. To evaluate diversity fluctuations in the pelagic microbial communities experiencing frequent brackish water intrusions, we analyzed seasonal dynamics of ciliates inhabiting transitional waters of the Curonian Lagoon. During the intrusion periods, the community presented a mixture of fresh- and brackish taxa, with no specific autochthonous component unique to the transitional waters. In the plume area, outside of the lagoon, we found that (i) high biodiversity was due to mixing of two distinct assemblages, and (ii) freshwater taxa are rather resistant to salinity change, their abundance decreases almost linearly with the increasing salinity, following conservative mixing model. Small unidentified Lohmanniella occurring exclusively in the plume zone during our survey possibly presents an autochthonous component based on locally available resource. Also mixed assemblage of the plume is characterised by absence of large predatory ciliate species.

  • 41.
    Hajdu, Susanna
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Larsson, Ulf
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    In-depth analysis of an alternate-stage Prymnesium polylepis (Haptophyta) bloom and long-term trends in abundance of Prymnesiales species in the Baltic Sea2015In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 526, p. 55-66Article in journal (Refereed)
    Abstract [en]

    In late autumn/winter 2007, high abundances of the alternate-stage Prymnesium polylepis were observed in many Baltic Sea areas, attaining bloom concentrations in spring 2008. To understand long-term variability in Prymnesiales density, we analysed changes in the abundance of different size classes of Prymnesiales using a long-term time series (1985-2008) for an inshore-offshore gradient in the northern Baltic proper. Further, to understand environmental conditions contributing to the P. polylepis bloom, we examined environmental factors associated with the increase in Prymnesiales abundances by placing the bloom dynamics within the context of temporal and spatial environmental variability over the last decades in the Baltic Sea. Significantly increasing abundances were found for larger size classes of Prymnesiales (6-10 mu m and >10 mu m) but not for the smaller species (Prymnesiales < 6 mu m). Our analyses indicate that high spring sea surface temperatures favor development of larger Prymnesiales (6-10 mu m and > 10 mu m) that tolerate low annual NO2+NO3 concentrations. Thus, long-term trends in increase in abundance, as well as changes in the relative contributions of species within these potentially toxic haptophytes, are likely to be the result of interacting changes in temperature and nutrient conditions since the late 1980s.

  • 42.
    Hogfors, Hedvig
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Holmborn, Towe
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hajdu, Susanna
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Does female RNA content reflect viable egg production in copepods?: A test with the Baltic copepod Acartia tonsa2011In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 33, no 9, p. 1460-1463Article in journal (Refereed)
    Abstract [en]

    Biomarkers are very useful for in situ assessments of zooplankton growth. In particular, RNA-based methods have been developed to estimate egg production in copepods. However, RNA-growth relationships can potentially depend on a variety of factors, such as egg quality. This study shows that in Acartia tonsa, female RNA-content reflects egg production irrespective of egg viability, implying that this growth proxy is not applicable for recruitment studies if the proportion of viable eggs fluctuates widely.

  • 43.
    Hogfors, Hedvig
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Motwani, Nisha H.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hajdu, Susanna
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    El-Shehawy, Rehab
    Holmborn, Towe
    Vehmaa, Anu
    Engström-Öst, Jonna
    Brutemark, Andreas
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Bloom-Forming Cyanobacteria Support Copepod Reproduction and Development in the Baltic Sea2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 11, article id e112692Article in journal (Refereed)
    Abstract [en]

    It is commonly accepted that summer cyanobacterial blooms cannot be efficiently utilized by grazers due to low nutritional quality and production of toxins; however the evidence for such effects in situ is often contradictory. Using field and experimental observations on Baltic copepods and bloom-forming diazotrophic filamentous cyanobacteria, we show that cyanobacteria may in fact support zooplankton production during summer. To highlight this side of zooplankton-cyanobacteria interactions, we conducted: (1) a field survey investigating linkages between cyanobacteria, reproduction and growth indices in the copepod Acartia tonsa; (2) an experiment testing relationships between ingestion of the cyanobacterium Nodularia spumigena (measured by molecular diet analysis) and organismal responses (oxidative balance, reproduction and development) in the copepod A. bifilosa; and (3) an analysis of long term (1999-2009) data testing relationships between cyanobacteria and growth indices in nauplii of the copepods, Acartia spp. and Eurytemora affinis, in a coastal area of the northern Baltic proper. In the field survey, N. spumigena had positive effects on copepod egg production and egg viability, effectively increasing their viable egg production. By contrast, Aphanizomenon sp. showed a negative relationship with egg viability yet no significant effect on the viable egg production. In the experiment, ingestion of N. spumigena mixed with green algae Brachiomonas submarina had significant positive effects on copepod oxidative balance, egg viability and development of early nauplial stages, whereas egg production was negatively affected. Finally, the long term data analysis identified cyanobacteria as a significant positive predictor for the nauplial growth in Acartia spp. and E. affinis. Taken together, these results suggest that bloom forming diazotrophic cyanobacteria contribute to feeding and reproduction of zooplankton during summer and create a favorable growth environment for the copepod nauplii.

  • 44. Holeton, Claire
    et al.
    Lindell, Kristin
    Holmborn, Towe
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hogfors, Hedvig
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Decreased astaxanthin at high feeding rates in the calanoid copepod Acartia bifilosa2009In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 31, no 6, p. 661-668Article in journal (Refereed)
    Abstract [en]

    In marine food webs, copepods are the major producers of a carotenoid pigment astaxanthin, which is an important antioxidant. The availability of astaxanthin for higher trophic levels can be affected by changes in phytoplankton stocks and copepod feeding; however, the functional relationship between food availability and astaxanthin production is poorly understood. We hypothesized that with a given food type and quality, astaxanthin content in copepods is positively related to feeding and egg production rates. The hypothesis was tested by measuring astaxanthin accumulation in concert with ingestion and egg production rates in the copepod Acartia bifilosa exposed to different algal concentrations (Tetraselmis suecica; 0 to 1200 μg C L−1). Egg production and ingestion rates increased with increasing food availability and reached a plateau at ≥400–600 μg C L−1. In contrast, increasing accumulation of astaxanthin with increasing food availability was observed only at concentrations ≤150 μg C L−1. Contrary to our hypothesis, at 600–1200 μg C L−1 copepods had maximal ingestion and egg production rates, but low astaxanthin contents. It is suggested that this low accumulation of astaxanthin at high food concentrations results from a food-dependant decrease in assimilation efficiency. These findings are important for the understanding of astaxanthin dynamics within marine food webs, where increases in phytoplankton biomass may translate to a trade-off between zooplankton quantity and its nutritional quality for zooplanktivores.

  • 45.
    Holliland, Per B.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Holmborn, Towe
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Assessing diet of the non-indigenous predatory cladoceran Cercopagis pengoi using stable isotopes2012In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 34, no 5, p. 376-387Article in journal (Refereed)
    Abstract [en]

    In the Baltic Sea, the predatory cladoceran Cercopagis pengoi is a non-indigenous species that has potential to compete for mesozooplankton with pelagic zooplanktivorous fish. To understand the extent of diet overlap with these fishes in a coastal area of the northern Baltic proper, we studied the feeding of C. pengoi using stable C-13 and N-15 isotope signatures of the predator and possible prey. Feasible combinations of sources were estimated in two ways: (i) with the IsoSource mixing model, and (ii) temporal-tracking analysis. Further, contribution of different prey was related to ambient zooplankton composition to gauge selectivity. The modelling results indicate that C. pengoi is an opportunistic generalist predator with a positive selection towards older copepodites (CIVVI) of Acartia spp. and Eurytemora affinis, which also have the greatest contribution to its diet. Positive selection towards podonid Cladocera is also likely. In contrast, evidence for extensive feeding on microzooplankton was inconclusive, and bosminids were not found to be an important prey in the zooplankton assemblages studied. As the derived diet of C. pengoi overlaps greatly with that of zooplanktivorous fish, food competition between these zooplanktivores is possible.

  • 46.
    Holliland, Per
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Motwani, Nisha
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Ogonowski, Martin
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Growth, reproduction and genetic variation : testing causes of variable diel vertical migration in the copepod Eurytemora affinisManuscript (preprint) (Other academic)
  • 47.
    Holmborn, Towe
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Dahlgren, Kristin
    Holeton, Claire
    Hogfors, Hedvig
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Biochemical proxies for growth and metabolism in Acartia bifilosa (Copepoda, Calanoida)2009In: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, Vol. 7, p. 785-794Article in journal (Refereed)
    Abstract [en]

    Biochemical proxies are becoming increasingly common for growth assessment in zooplankton. Their suitability is often unknown, however, and proper calibration is lacking. We investigated correlations between physiological variables (ingestion, egg production, and respiration rates) and biochemical indices related to protein synthesis (RNA content, RNA:DNA ratio, RNA:protein ratio, and protein specific aminoacyl-tRNA synthetases [spAARS] activity) in copepods Acartia bifilosa exposed to different algal concentrations (0–1200 µg C L–1). All variables assayed increased with increasing food concentration either linearly (spAARS) or nonlinearly (all other variables). Egg production and ingestion rates were significantly and positively correlated with RNA content and RNA:protein ratio, whereas correlations with spAARS and RNA:DNA ratio were weaker or nonsignificant. However, when RNA:DNA ratio and spAARS activity were used as predictors of ingestion, together they had higher explanatory value than did either variable separately. As there were substantial differences in saturating food concentrations among the assayed variables, applicability of biomarkers as proxies of physiological rates will be more reliable if restricted to the nonsaturated phase of the functional response of either variable, unless both variables saturate simultaneously. These findings contribute to methodology of zooplankton growth assessment and to our understanding of biochemical processes underlying growth and metabolism in copepods.

  • 48.
    Holmborn, Towe
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Erratum to: Relationships between RNA content and egg production rate in Acartia bifilosa (Copepoda, Calanoida) of different spatial and temporal origin2008In: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 153, no 5, p. 1007-1008Article in journal (Refereed)
  • 49.
    Holmborn, Towe
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Relationships between RNA content and egg production rate in Acartia bifilosa (Copepoda, Calanoida) of different spatial and temporal origin2008In: MARINE BIOLOGY, ISSN 0025-3162, Vol. 153, no 3, p. 483-491Article in journal (Refereed)
    Abstract [en]

    To evaluate factors regulating RNA content (RNA, mu g RNA female(-1)) -egg production rate (EPR, eggs female(-1) day(-1)) relationship and to develop a model for in situ egg production rate estimates for Acartia bifilosa, we (1) measured EPR and RNA in females sampled at geographically distant areas at varying temperature (T, degrees C), (2) determined environmental (station, season, and T), endogenous (prosome length (PL), mm and EPR) variables that influence RNA levels, and (3) explored a set of multiple regression models to predict EPR from RNA, PL, station, season, and T. Egg production experiments were carried out in spring and summer 2005 in the Gulf of Finland and in the western part of the northern Baltic proper. We found that up to 88% of the RNA variation could be explained by variations in PL, EPR, and season/T. In explaining the RNA variability, PL played a major role followed in order of importance by EPR and season/T. Further, PL, RNA, and season/T explained up to 53% of the variation in EPR, nearly half of which is explained by RNA alone. The effect of spatial origin was never significant, suggesting that the derived relationships are general for A. bifilosa inhabiting northern Baltic proper.

  • 50. Holopainen, Reetta
    et al.
    Lehtiniemi, Maiju
    Meier, H. E. Markus
    Albertsson, Jan
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Kotta, Jonne
    Viitasalo, Markku
    Impacts of changing climate on the non-indigenous invertebrates in the northern Baltic Sea by end of the twenty-first century2016In: Biological Invasions, ISSN 1387-3547, E-ISSN 1573-1464, Vol. 18, no 10, p. 3015-3032Article in journal (Refereed)
    Abstract [en]

    Biological invasions coupled with climate change drive changes in marine biodiversity. Warming climate and changes in hydrology may either enable or hinder the spread of non-indigenous species (NIS) and little is known about how climate change modifies the richness and impacts of NIS in specific sea areas. We calculated from climate change simulations (RCO-SCOBI model) the changes in summer time conditions which northern Baltic Sea may to go through by the end of the twenty-first century, e.g., 2-5 A degrees C sea surface temperature rise and even up to 1.75 unit decrease in salinity. We reviewed the temperature and salinity tolerances (i.e., physiological tolerances and occurrence ranges in the field) of pelagic and benthic NIS established in-or with dispersal potential to-the northern Baltic Sea, and assessed how climate change will likely affect them. Our findings suggest a future decrease in barnacle larvae and an increase in Ponto-Caspian cladocerans in the pelagic community. In benthos, polychaetes, gastropods and decapods may become less abundant. By contrast, dreissenid bivalves, amphipods and mysids are expected to widen their distribution and increase in abundance in the coastal areas of the northern Baltic Sea. Potential salinity decrease acts as a major driver for NIS biogeography in the northern Baltic Sea, but temperature increase and extended summer season allow higher reproduction success in bivalves, zooplankton, amphipods and mysids. Successful NIS, i.e., coastal crustacean and bivalve species, pose a risk to native biota, as many of them have already demonstrated harmful effects in the Baltic Sea.

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