Browsing by Subject "MARINE-PHYTOPLANKTON"

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  • Bermúdez, Rafael; Winder, Monika; Stuhr, Annegret; Almén, Anna-Karin; Engström-Öst, Jonna; Riebesell, Ulf (2016)
    Increasing atmospheric carbon dioxide (CO2) is changing seawater chemistry towards reduced pH, which affects various properties of marine organisms. Coastal and brackish water communities are expected to be less affected by ocean acidification (OA) as these communities are typically adapted to high fluctuations in CO2 and pH. Here we investigate the response of a coastal brackish water plankton community to increasing CO2 levels as projected for the coming decades and the end of this century in terms of community and biochemical fatty acid (FA) composition. A Baltic Sea plankton community was enclosed in a set of offshore mesocosms and subjected to a CO2 gradient ranging from natural concentrations (similar to 347 mu atm fCO(2)) up to values projected for the year 2100 (similar to 1333 mu atm fCO(2)). We show that the phytoplankton community composition was resilient to CO2 and did not diverge between the treatments. Seston FA composition was influenced by community composition, which in turn was driven by silicate and phosphate limitation in the mesocosms and showed no difference between the CO2 treatments. These results suggest that CO2 effects are dampened in coastal communities that already experience high natural fluctuations in pCO(2). Although this coastal plankton community was tolerant of high pCO(2) levels, hypoxia and CO2 uptake by the sea can aggravate acidification and may lead to pH changes outside the currently experienced range for coastal organisms.
  • Bach, Lennart T.; Taucher, Jan; Boxhammer, Tim; Ludwig, Andrea; Achterberg, Eric P.; Alguero-Muniz, Maria; Anderson, Leif G.; Bellworthy, Jessica; Buedenbender, Jan; Czerny, Jan; Ericson, Ylva; Esposito, Mario; Fischer, Matthias; Haunost, Mathias; Hellemann, Dana; Horn, Henriette G.; Hornick, Thomas; Meyer, Jana; Sswat, Michael; Zark, Maren; Riebesell, Ulf; Kristineberg KOSMOS Consortium (2016)
    Every year, the oceans absorb about 30% of anthropogenic carbon dioxide (CO2) leading to a re-equilibration of the marine carbonate system and decreasing seawater pH. Today, there is increasing awareness that these changes-summarized by the term ocean acidification (OA)-could differentially affect the competitive ability of marine organisms, thereby provoking a restructuring of marine ecosystems and biogeochemical element cycles. In winter 2013, we deployed ten pelagic mesocosms in the Gullmar Fjord at the Swedish west coast in order to study the effect of OA on plankton ecology and biogeochemistry under close to natural conditions. Five of the ten mesocosms were left unperturbed and served as controls (similar to 380 mu atm pCO(2)), whereas the others were enriched with CO2-saturated water to simulate realistic end-of-the-century carbonate chemistry conditions (mu 760 mu atm pCO(2)). We ran the experiment for 113 days which allowed us to study the influence of high CO2 on an entire winter-to-summer plankton succession and to investigate the potential of some plankton organisms for evolutionary adaptation to OA in their natural environment. This paper is the first in a PLOS collection and provides a detailed overview on the experimental design, important events, and the key complexities of such a "long-term mesocosm" approach. Furthermore, we analyzed whether simulated end-of-the-century carbonate chemistry conditions could lead to a significant restructuring of the plankton community in the course of the succession. At the level of detail analyzed in this overview paper we found that CO2-induced differences in plankton community composition were non-detectable during most of the succession except for a period where a phytoplankton bloom was fueled by remineralized nutrients. These results indicate: (1) Long-term studies with pelagic ecosystems are necessary to uncover OA-sensitive stages of succession. (2) Plankton communities fueled by regenerated nutrients may be more responsive to changing carbonate chemistry than those having access to high inorganic nutrient concentrations and may deserve particular attention in future studies.
  • Spilling, Kristian; Ylöstalo, Pasi; Simis, Stefan; Seppälä, Jukka (2015)
    Light (20-450 mu mol photons m(-2) s(-1)), temperature (3-11 degrees C) and inorganic nutrient composition (nutrient replete and N, P and Si limitation) were manipulated to study their combined influence on growth, stoichiometry (C:N:P:Chl a) and primary production of the cold water diatom Chaetoceros wighamii. During exponential growth, the maximum growth rate (similar to 0.8 d(-1)) was observed at high temperture and light; at 3 degrees C the growth rate was similar to 30% lower under similar light conditions. The interaction effect of light and temperature were clearly visible from growth and cellular stoichiometry. The average C:N:P molar ratio was 80:13:1 during exponential growth, but the range, due to different light acclimation, was widest at the lowest temperature, reaching very low C:P (similar to 50) and N:P ratios (similar to 8) at low light and temperature. The C:Chl a ratio had also a wider range at the lowest temperature during exponential growth, ranging 16-48 (weight ratio) at 3 degrees C compared with 17-33 at 11 degrees C. During exponential growth, there was no clear trend in the Chl a normalized, initial slope (alpha*) of the photosynthesis-irradiance (PE) curve, but the maximum photosynthetic production (P-m) was highest for cultures acclimated to the highest light and temperature. During the stationary growth phase, the stoichiometric relationship depended on the limiting nutrient, but with generally increasing C:N:P ratio. The average photosynthetic quotient (PQ) during exponential growth was 1.26 but decreased to
  • Taipale, Sami J.; Vuorio, Kristiina; Brett, Michael T.; Peltomaa, Elina; Hiltunen, Minna; Kankaala, Paula (2016)
    Analyses of carbon stable isotopes are often used to estimate the contributions of allochthonous and autochthonous dietary resources to aquatic consumers. Most pelagic food web studies assume that all phytoplankton taxa have a similar delta C-13 value. We studied pelagic food web compartments (dissolved inorganic carbon [DIC], phytoplankton, bacteria, seston, cladoceran zooplankton) in 12 small (<0.1 km(2)) lakes in southern Finland. These lakes were classified as oligotrophic, mesotrophic, eutrophic, and dystrophic based on their concentrations of total phosphorus and dissolved organic carbon. Additionally, we studied phytoplankton photosynthetic carbon fractionation (epsilon(p)) in laboratory conditions. The photosynthetic fractionation in 28 phytoplankton cultures from nine different phytoplankton classes varied significantly at the class level, and fractionation correlated significantly with the DIC concentration of the growth media. In small boreal lakes, the delta C-13 values of different phytoplankton taxa, as directly measured or estimated from the delta C-13 values of biomarker fatty acids, varied greatly (-18 parts per thousand to - 44.5 parts per thousand). Phytoplankton delta C-13 values varied significantly by lake type and were most depleted in dystrophic lakes even though the delta C-13 values of the DIC was similar to mesotrophic lakes. Further within-taxa variation was found between lakes and between different depths within a lake. Vertical samples from dystrophic lakes also showed lower ep in the phytoplankton from meta-and hypolimnion, possibly as a result of reduced light intensity. Altogether, in nine of the 10 sampled lakes, the delta C-13 values of cladoceran zooplankton were between the minimum and the maximum phytoplankton delta C-13 value of each lake, and thus, phytoplankton alone could explain zooplankton delta C-13 values. We conclude that stable isotope mixing models should take into account carbon variation among different phytoplankton taxa.
  • Spilling, Kristian; Paul, Allanah J.; Virkkala, Niklas; Hastings, Tom; Lischka, Silke; Stuhr, Annegret; Bermudez, Rafael; Czerny, Jan; Boxhammer, Tim; Schulz, Kai G.; Ludwig, Andrea; Riebesell, Ulf (2016)
    Anthropogenic carbon dioxide (CO2) emissions are reducing the pH in the world's oceans. The plankton community is a key component driving biogeochemical fluxes, and the effect of increased CO2 on plankton is critical for understanding the ramifications of ocean acidification on global carbon fluxes. We determined the plankton community composition and measured primary production, respiration rates and carbon export (defined here as carbon sinking out of a shallow, coastal area) during an ocean acidification experiment. Mesocosms (similar to 55 m(3)) were set up in the Baltic Sea with a gradient of CO2 levels initially ranging from ambient (similar to 240 mu atm), used as control, to high CO2 (up to similar to 1330 mu atm). The phytoplankton community was dominated by dinoflagellates, diatoms, cyanobacteria and chlorophytes, and the zooplankton community by protozoans, heterotrophic dinoflagellates and cladocerans. The plankton community composition was relatively homogenous between treatments. Community respiration rates were lower at high CO2 levels. The carbon-normalized respiration was approximately 40% lower in the high-CO2 environment compared with the controls during the latter phase of the experiment. We did not, however, detect any effect of increased CO2 on primary production. This could be due to measurement uncertainty, as the measured total particular carbon (TPC) and combined results presented in this special issue suggest that the reduced respiration rate translated into higher net carbon fixation. The percent carbon derived from microscopy counts (both phyto- and zooplankton), of the measured total particular carbon (TPC), decreased from similar to 26% at t0 to similar to 8% at t31, probably driven by a shift towards smaller plankton (<4 mu m) not enumerated by microscopy. Our results suggest that reduced respiration leads to increased net carbon fixation at high CO2. However, the increased primary production did not translate into increased carbon export, and consequently did not work as a negative feedback mechanism for increasing atmospheric CO2 concentration.
  • Glippa, Olivier; Engström-Öst, Jonna; Kanerva, Mirella; Rein, Anni; Vuori, Kristiina (2018)
    On a daily basis, planktonic organisms migrate vertically and thus experience widely varying conditions in their physico-chemical environment. In the Gulf of Finland, these changes are larger than values predicted by climate change scenarios predicted for the next century (up to 0.5 units in pH and 5 degrees C in temperature). In this work, we are interested in how temporal variations in physico-chemical characteristics of the water column on a daily and weekly scale influence oxidative stress level and antioxidant responses in the planktonic copepod of the genus Acartia. Responses were determined from samples collected during a two-week field survey in the western Gulf of Finland, Baltic Sea. Our results showed that GST (Glutathione-S-transferase) enzyme activity increased in the surface waters between Weeks I and II, indicating antioxidant defense mechanism activation. This is most likely due to elevating temperature, pH, and dissolved oxygen observed between these two weeks. During Week II also GSSG (oxidized glutathione) was detected, indicating that copepods responded to stressor(s) in the environment. Our results suggest that Acartia copepods seem fairly tolerant to weekly fluctuations in environmental conditions in coastal and estuarine areas, in terms of antioxidant defense and oxidative stress. This could be directly connected to a very efficient glutathione cycling system acting as antioxidant defense system for neutralizing ROS and avoiding elevated levels of LPX.