Läänemere fütoplankton muutuste keerises

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Käesolev töö analüüsib Läänemere fütoplanktonikoosluse pika-ajalisi (1966-2008) ja ruumilisi mustreid. Aastakümneid väldanud vaatluste jooksul on fütoplanktoni suvised kooslused kõikjal Läänemeres pidevas muutumises. Järske muutusi, sama-aegselt teadaoleva rezhiiminihkega toiduahela tipus 1980ndail, fütoplanktonikoosluses ei toimu, mis annab aimu fütoplanktonikoosluse suhteliselt nõrkadest seostest toiduahela ülemiste astmetega ja pigem toiduvõrgustiku kui toiduahela tüüpi ökosüsteemist. Vaguviburvetikate osakaal kevadõitsenguis on kasvanud ränivetikate arvelt Läänemere keskosas ja põhjapoolsemates basseinides (Soome laht, Botnia meri). Nihe ränivetika-domineeritud õitsenguilt vaguviburvetikate ülekaalu suunas mõjutab kogu ökosüsteemi, läbi orgaanilise aine settimise ning hapnikutarbe setete pinnal. Analüüs põhineb Läänemere seire jooksul kogutud fütoplanktoni andmestikul. Kokku hõlmab andmestik ca 15000 kvantitatiivset fütoplanktoni proovi, ajavahemikust 1966-2008 ning ruumiliselt üle kogu Läänemere. Kirjeldatud on andmete ajaline ja ruumiline jaotus ning kvaliteet allikate kaupa. Analüüsitud on ka ajalise ja ruumilise autokorrelatsiooni tugevust ning ulatust fütoplanktoni vaatlusandmeis. Oluline positiivne autokorrelatsioon esines andmeis kuni 100 km kauguseni ja kuni 30 päevani. Seega, nimetatuist kõrgema ruumilise ja ajalise sagedusega kogutud fütoplanktoni vaatlusandmete analüüsil tuleb kindlasti arvestada ajalise ja ruumilise autokorrelatsiooniga.This thesis analyses long-term dynamics (1966–2008) and spatial patterns of the Baltic Sea phytoplankton. Over the four decades of observations, phytoplankton summer community composition has gone through a significant gradual change everywhere in the Baltic Sea. No abrupt or stepwise changes, in synchrony with the known regime shift at the top of the food web, could be detected. This implies relatively strong resistance of the phytoplankton community to the top down effect in the Baltic Sea food web. Proportion of spring bloom dinoflagellates has increased conspicuously over the decadal time scale to the disadvantage of diatoms in the central and northern Baltic Sea. Shifts in the diatom-to-dinoflagellate propotion can have ecosystem wide consequences, via the changes in sedimentation of organic material and benthic oxygen demand. Analysis was based on a phytoplankton data-set that was compiled from the data collected during routine monitoring programs of many countries around the Baltic Sea. The data-set contains records from ca 15 000 phytoplankton field samples, covers the time period of 1966–2008 and the whole Baltic Sea, including the Danish Straits. In the work, the spatio-temporal distribution of the data and the quality of the data between different data providers is described. It also touches upon the extent and strength of spatial and temporal autocorrelation in the phytoplankton data. Significant positive autocorrelation at the spatial scale of 100 km and temporal scale of 30 days implies the need to use appropriate autocorrelation structures in statistical models with phytoplankton field data

Editorial: Changing Plankton Communities : Causes, Effects and Consequences

Non peer reviewe

Decadal-Scale Changes of Dinoflagellates and Diatoms in the Anomalous Baltic Sea Spring Bloom

The algal spring bloom in the Baltic Sea represents an anomaly from the winter-spring bloom patterns worldwide in terms of frequent and recurring dominance of dinoflagellates over diatoms. Analysis of approximately 3500 spring bloom samples from the Baltic Sea monitoring programs revealed (i) that within the major basins the proportion of dinoflagellates varied from 0.1 (Kattegat) to >0.8 (central Baltic Proper), and (ii) substantial shifts (e.g. from 0.2 to 0.6 in the Gulf of Finland) in the dinoflagellate proportion over four decades. During a recent decade (1995–2004) the proportion of dinoflagellates increased relative to diatoms mostly in the northernmost basins (Gulf of Bothnia, from 0.1 to 0.4) and in the Gulf of Finland, (0.4 to 0.6) which are typically ice-covered areas. We hypothesize that in coastal areas a specific sequence of seasonal events, involving wintertime mixing and resuspension of benthic cysts, followed by proliferation in stratified thin layers under melting ice, favors successful seeding and accumulation of dense dinoflagellate populations over diatoms. This head-start of dinoflagellates by the onset of the spring bloom is decisive for successful competition with the faster growing diatoms. Massive cyst formation and spreading of cyst beds fuel the expanding and ever larger dinoflagellate blooms in the relatively shallow coastal waters. Shifts in the dominant spring bloom algal groups can have significant effects on major elemental fluxes and functioning of the Baltic Sea ecosystem, but also in the vast shelves and estuaries at high latitudes, where ice-associated cold-water dinoflagellates successfully compete with diatoms

Phytoplankton species richness along coastal and estuarine salinity continua

Ligi 80 aastat on meie arusaama vee organismide liigirikkusest soolsusgradiendil kujundanud paradigmaks muutunud Remane kõver. Selle järgi on magevee liigirikkus suur, suur on liigirikkus ka ookeanis, kuid vahepealses riimveelises osas on tuntav liigirikkuse madalseis. Adolf Remane sedastas oma seaduspära uurides põhjaeluliste suurselgrootute liigirikkust Läänemeres. Kas ja millisel määral on seaduspära kehtiv teiste organismirühmade puhul, eriti vabalt hõljuvate plankterite puhul, ei ole teada. Me analüüsisime ligi 16,000 fütoplanktoni proovi liigirikkust kahe suure ökosüsteemi, Läänemere ja Chesapeake Lahe soolsusgradientidel. Proovide liigirikkus oli madalaim gradiendi mesohaliinses piirkonnas, soolsusel 7–9. Ka harvenduskõverad kitsastes soolsusvahemikes näitasid madalat liigirikkust mesohaliinses piirkonnas ja fütoplanktoni liigirikkus suurenemist nii magevee, kui ookeani soolsuse suunal. Liikide kumulatiivne esinemise tõenäosus soolsuse gradiendil näitas samuti liigirikkuse miinimumi riimveelises osas. Chesapeake Lahes muutub fütoplanktoni kooslus mageveelisest mereliseks sujuvalt kogu soolsusgradiendil. Kontrastina, Läänemere eripäraks on fütoplanktoni koosluse järsk muutus liigirikkuse miinimumi piirkonnas. Analüüsi tulemused näitavad, et Remane printsiip on täiel määral kehtiv ka fütoplanktoni puhul.The high number of freshwater species at low salinity and the correspondingly high number of marine species at high salinity enveloping a conspicuous richness minimum at intermediate salinities has shaped our basic understanding of biodiversity along a coastal salinity gradient for almost 80 years. Visualized as the Remane curve, this iconic concept was originally based on sedentary macroinvertebrates in the Baltic Sea. To what extent the concept can be generalized, particularly to free-drifting organisms, is currently debated. Here we use approximately 16,000 phytoplankton samples from two large coastal ecosystems—the Baltic Sea and Chesapeake Bay—to analyze the relationship between salinity and phytoplankton species richness. Alpha diversity showed a consistent variation along the salinity gradient, with a minimum at mesohaline salinities of around 7–9. Rarefied species pools at narrow salinity intervals also showed reduced diversity at intermediate salinities, surrounded by high richness toward both ends of the gradient. The cumulative likelihood of species presence validated the minimum at intermediate salinities. Community composition changed abruptly at the α diversity minimum in the Baltic Sea, while it changed gradually along the salinity gradient in Chesapeake Bay. We conclude that the Remane concept is in every respect valid for phytoplankton

Primary production, carbon release, and respiration during spring bloom in the Baltic Sea

We determined the gross and net primary production (GPP and NPP) for the total community and the < 10 μ m size fraction, the net release of dissolved organic carbon (DOC), and the microbial respiration in the Baltic Sea during the spring bloom. Samples ( n  = 126) were taken from the surface (3 m depth) covering most subbasins and different phases of the bloom, defined by the inorganic nutrient and Chlorophyll a (Chl a ) concentrations. During the course of the bloom, the NPP rate (i.e., growth rate) decreased from 0.34 d −1  ± 0.03 (SE) to 0.15 d −1  ± 0.02 (SE), the contribution of the < 10 μ m fraction increased from 14% ± 2.5 (SE) to 47% ± 4.0 (SE) and the percent extracellular release (PER) increased from 3.8% ± 0.7 (SE) to 8.9% ± 1.5 (SE). The assimilation number, was on average 0.13 mol C (g Chl a ) −1 h −1  ± 0.01 (SE), and the average GPP:NPP rate was 1.25. The respiration increased with growth rate and was 21% of the GPP rate. The net release of DOC was relatively constant over the bloom phases, with increasing PER compensating for the reduction in biomass, and estimated to 24–36  μ mol DOC L −1 during the whole spring bloom period in all subbasins except in the Bay of Bothnia where it was 75% lower. The assimilation number was surprisingly stable, suggesting it is uncoupled from the inorganic nutrient concentration, likely a reflection of physiological acclimation and changing phytoplankton community.Academy of Finland | Ref. 259164Walter ja Andrée de Nottbeckin Sääti

Spring bloom community change modifies carbon pathways and C : N : P : Chl a stoichiometry of coastal material fluxes

Peer reviewe

Functional shifts in estuarine zooplankton in response to climate variability

Functional traits are becoming more common in the analysis of marine zooplankton community dynamics associated with environmental change. We used zooplankton groups with common functional properties to assess long-term trends in the zooplankton caused by certain environmental conditions in a highly eutrophicated gulf. Time series of zooplankton traits have been collected since the 1960s in the Gulf of Riga, Baltic Sea, and were analyzed using a combination of multivariate methods (principal coordinate analysis) and generalized additive models. One of the most significant changes was the considerable increase in the amount of the zooplankton functional groups (FGR) in coastal springtime communities, and dominance shifts from more complex to simpler organism groups-cladocerans and rotifers. The results also show that functional trait organism complexity (body size) decreased considerably due to cladoceran and rotifer increase following elevated water temperature. Salinity and oxygen had negligible effects on the zooplankton community.Peer reviewe

Primary production, carbon release, and respiration during spring bloom in the Baltic Sea

We determined the gross and net primary production (GPP and NPP) for the total community and the <10 mu m size fraction, the net release of dissolved organic carbon (DOC), and the microbial respiration in the Baltic Sea during the spring bloom. Samples (n = 126) were taken from the surface (3 m depth) covering most subbasins and different phases of the bloom, defined by the inorganic nutrient and Chlorophyll a (Chl a) concentrations. During the course of the bloom, the NPP rate (i.e., growth rate) decreased from 0.34 d(-1) +/- 0.03 (SE) to 0.15 d(-1) +/- 0.02 (SE), the contribution of the <10 mu m fraction increased from 14% +/- 2.5 (SE) to 47% +/- 4.0 (SE) and the percent extracellular release (PER) increased from 3.8% +/- 0.7 (SE) to 8.9% +/- 1.5 (SE). The assimilation number, was on average 0.13 mol C (g Chl a)(-1) h(-1) +/- 0.01 (SE), and the average GPP:NPP rate was 1.25. The respiration increased with growth rate and was 21% of the GPP rate. The net release of DOC was relatively constant over the bloom phases, with increasing PER compensating for the reduction in biomass, and estimated to 24-36 mu mol DOC L-1 during the whole spring bloom period in all subbasins except in the Bay of Bothnia where it was 75% lower. The assimilation number was surprisingly stable, suggesting it is uncoupled from the inorganic nutrient concentration, likely a reflection of physiological acclimation and changing phytoplankton community.peerReviewe

Patterns of vertical cyst distribution and survival in 100-year-old sediment archives of three spring dinoflagellate species from the Northern Baltic Sea

The history of expansion of bloom-forming cold water dinoflagellates in the Northern Baltic Sea was studied using 100-year-old sediment archives of their resting cysts. Vertical cyst distributions of Biecheleria baltica and Apocalathium malmogiense, two dinoflagellates indistinguishable by light microscopy and not recognized as distinct species in monitoring, and chain-forming Peridiniella catenata were analysed in Pb210 and Cs137 dated layers of a sediment core from deep, hypoxic accumulation bottoms of the Gulf of Finland. Cyst profiles showed that B. baltica and A. malmogiense were already present in the Baltic spring phytoplankton community at the beginning of the 20th century. This confirms that B. baltica, which was only recognized in the late 1980s, is a native species in the area. A drastic increase in B. baltica cyst concentrations in the 1930s to 1960s coincided with the acceleration of anthropogenic eutrophication. Large cyst deposits accumulated over several decades in the sediment which, by the 1980s, amounted to the seed stock necessary to inoculate dominant blooms. In the cyst records A. malmogiense always contributed a minor fraction of the two species. P. catenata had a relatively short cyst record in Gulf of Finland sediments despite demonstrated long-term presence in the plankton, which emphasizes that cyst-based historic surveys are not suitable for all cyst-forming dinoflagellates. This was corroborated by correspondence analyses of long-term plankton and cyst records which validated the trends from the sediment archive for B. baltica and A. malmogiense, but failed to do so for P. catenata. Germination experiments with 100-year-old cysts revealed a remarkable long-term survival capacity of A. malmogiense, making this species a suitable model for resurrection studies testing adaptation in heavily impacted systems such as the Baltic Sea