Browsing by Subject "SPRING BLOOM"

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  • Milardi, Marco; Lappalainen, Jyrki; McGowan, Suzanne; Weckström, Jan (2017)
    The additional input and enhanced cycling of nutrients derived from introduced fish can be a significant factor altering nutrient dynamics in oligotrophic lakes. To test this, we used a bioenergetic model to estimate the fish-derived nutrient load in Lake Kuutsjurvi, a historically fishless boreal lake of northern Fennoscandia. The lake was selected because of the absence of other anthropogenic stressors, a known stocking history and the possibility of quantitatively estimating the size-structure and biomass of the fish population through a mass removal. Subsequently, we used a mass balance model to compare fish-derived nutrients with other nutrient load pathways. For comparison over longer timescales, we used lake sediment records of diatoms, chlorophyll and carotenoid pigments, C: N ratios and stable isotopes to infer whether fish introduction produced detectable changes in the lake trophic state, primary productivity and terrestrial nutrient input. Based on the nutrient mass balance model, we found that phosphorus and nitrogen derived from fish were 0.46% and 2.2%, respectively, of the total load to the lake, suggesting that fish introduction could not markedly increase the nutrient load. Accordingly, the palaeolimnological record indicated little increase in primary production but instead a shift from pelagic to benthic production after fish introduction.
  • Tallberg, Petra; Räike, Antti; Lukkari, Kaarina; Leivuori, Mirja; Lehtoranta, Jouni; Pitkänen, Heikki (2012)
  • 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
  • Jerney, Jacqueline; Rengefors, Karin; Nagai, Satoshi; Krock, Bernd; Sjöqvist, Conny; Suikkanen, Sanna; Kremp, Anke (2022)
    Genetic diversity is the basis for evolutionary adaptation and selection under changing environmental conditions. Phytoplankton populations are genotypically diverse, can become genetically differentiated within small spatiotemporal scales and many species form resting stages. Resting stage accumulations in sediments (seed banks) are expected to serve as reservoirs for genetic information, but so far their role in maintaining phytoplankton diversity and in evolution has remained unclear. In this study we used the toxic dinoflagellate Alexandrium ostenfeldii (Dinophyceae) as a model organism to investigate if (i) the benthic seed bank is more diverse than the pelagic population and (ii) the pelagic population is seasonally differentiated. Resting stages (benthic) and plankton (pelagic) samples were collected at a coastal bloom site in the Baltic Sea, followed by cell isolation and genotyping using microsatellite markers (MS) and restriction site associated DNA sequencing (RAD). High clonal diversity (98%-100%) combined with intermediate to low gene diversity (0.58-0.03, depending on the marker) was found. Surprisingly, the benthic and pelagic fractions of the population were equally diverse, and the pelagic fraction was temporally homogeneous, despite seasonal fluctuation of environmental selection pressures. The results of this study suggest that continuous benthic-pelagic coupling, combined with frequent sexual reproduction, as indicated by persistent linkage equilibrium, prevent the dominance of single clonal lineages in a dynamic environment. Both processes harmonize the pelagic with the benthic population and thus prevent seasonal population differentiation. At the same time, frequent sexual reproduction and benthic-pelagic coupling maintain high clonal diversity in both habitats.
  • Camarena-Gomez, Maria T.; Lipsewers, Tobias; Piiparinen, Jonna; Eronen-Rasimus, Eeva; Perez-Quemalinos, Daniel; Hoikkala, Laura; Sobrino, Cristina; Spilling, Kristian (2018)
    In recent decades, the phytoplankton community in parts of the Baltic Sea has shifted from diatom dominance to co-occurrence of diatoms and dinoflagellates during the spring bloom. We investigated whether this shift affects bacterial production (BP), abundance and community composition (BCC). Two mesocosm experiments were carried out with water from the SW coast of Finland during the winters of 2012 and 2013. The water was collected before the onset of the spring bloom. Natural seawater was used as a control, and various inocula of diatom and dino flagellate cultures were used as treatments. After the phytoplankton bloom development, BP (thymidine: BPT; leucine: BPL) was significantly higher in the diatom treatments than in the controls and dinoflagellate treatments (BPT and BPL in 2012 and BPL in 2013). In 2013, the BCC was significantly different between the diatom and dinoflagellate treatments and there was a temporal shift in both experiments. Alphaproteobacteria predominated in all treatments at the beginning of the experiments and shifted to flavobacterial (2012) and betaproteobacterial predominance (2013) during the chlorophyll a peak. Towards the end of the experiment, Actinobacteria and Betaproteo bacteria predominated in the diatom treatment in 2012, whereas in 2013 Flavobacteriia (all treatments) predominated together with Gammaproteobacteria and Cytophagia (diatom treatments). The results demonstrated that bacterial physiology and community structure are affected by relatively small changes in the phytoplankton community. Thus, the ongoing changes in the phytoplankton community resulting from co-occurrence of diatoms and dinoflagellates may decrease pelagic remineralization of carbon and reduce organic matter fluxes through the microbial loop.