Fluxes to coastal regions of phosphorus (P) and nitrogen (N) have worldwide more than doubled in the last decades, accompanied by decreases in dissolved silicate (DSi). These trends have been pronounced in the Baltic Sea, causing extensive eutrophication. Dissolved silicate is essential for siliceous phyto-plankton, the diatoms. One of the peculiarities of the Baltic Sea is the co-occurrence of dinoflagellates during the spring bloom. N limitation of the Baltic Sea could develop with eutrophication towards DSi limitation, leading to major shifts in the relative dominance of the 2 algal groups during the spring bloom. This would have a large effect on material fluxes, as dinoflagellates do not provide a pulse of organic matter to the bottom comparable to settling diatoms. Spring blooms in the Baltic Sea show high interannual variability of diatom and dinoflagellate domi-nance. Dinoflagellates are considered inferior competitors when nutrients are plenty, which indicates that they possess compensating means for competition. Motility and production and release of com-pounds that inhibit competitors (i.e. allelopathy) has been hypothesized to be important competitive strategies of dinoflagellates. This project addresses specifically the mechanisms behind the competitive success of diatoms and dinoflagellates, and the effects of the competition on major compartments of the planktonic community. We will test sets of hypotheses on species-level nutrient stoichiometry, allelochemical properties, and food web consequences of changing spring bloom phytoplankton. Experimentation is based on continu-ous culturing techniques (chemostats) developed in recent and ongoing projects. The hypotheses follow 3 general objectives: 1. Bottom-up: to study how nutrient stoichiometry, uptake properties and different nutritional demands (P, N, DSi) of the spring bloom diatoms and dinoflagellates are able to explain community succession 2. Allelopathy: to study competitive adaptations that explain the success of dinoflagellates in building up the blooms that frequently dominate the phytoplankton spring community in the Baltic Sea, despite the apparently superior ability of diatoms to compete for resources 3. Trophic transfer: to study negative or beneficial effects of changed spring phytoplankton community structure on zooplankton consumers It has been proposed that the Baltic Sea has passed a threshold in terms of nutrient loading, bringing about a regime shift that would lock the basin in a permanently deteriorated state. Increased spring blooms have led to a regime-shift-like development, as inorganic P pools remain at elevated levels after the bloom. This is an indication of ecosystem-wide consequences of the spring bloom competition and production dynamics. Experimental data emanating from the present project will be used for analyses of threshold phenomena of the system through networking with 2 major EU-funded projects with exten-sive participation from European institutes.
Vastaava tutkija
Tamminen Timo, Helsingin yliopisto, Tvärminnen eläintieteellinen asema Hankkeen kesto 2006 -
Asiasanat
Itämeri, kevätkukinta, rehevöityminen, kasviplankton, piilevät, panssarisiimalevät, allelopatia, ravinteet, silikatti, stökiömetria, hankajalkaiset
Hankkeen vaihe: päättynyt
HUOM! Tämä tutkimushankekuvaus on tuotettu Hankehaaviin Helsingin yliopiston TUHTI-tutkimustietojärjestelmästä, jota ei enää ylläpidetä. Tarkista ajantaiset tutkimushanketiedot Helsingin yliopiston TUHAT-järjestelmästä.
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