On the ecology of cold-water phytoplankton in the Baltic Sea

Increased anthropogenic loading of nitrogen (N) and phosphorus (P) has led to an eutrophication problem in the Baltic Sea, and the spring bloom is a key component in the biological uptake of increased nutrient concentrations. The spring bloom in the Baltic Sea is dominated by both diatoms and dinoflagellates. However, the sedimentation of these groups is different: diatoms tend to sink to the sea floor at the end of the bloom, while dinoflagellates to a large degree are been remineralized in the euphotic zone. Understanding phytoplankton competition and species specific ecological strategies is thus of importance for assessing indirect effects of phytoplankton community composition on eutrophication problems. The main objective of this thesis was to describe some basic physiological and ecological characteristics of the main cold-water diatoms and dinoflagellates in the Baltic Sea. This was achieved by specific studies of: (1) seasonal vertical positioning, (2) dinoflagellate life cycle, (3) mixotrophy, (4) primary production, respiration and growth and (5) diatom silicate uptake, using cultures of common cold-water diatoms: Chaetoceros wighamii, C. gracilis, Pauliella taeniata, Thalassiosira baltica, T. levanderi, Melosira arctica, Diatoma tenuis, Nitzschia frigida, and dinoflagellates: Peridiniella catenata, Woloszynskia halophila and Scrippsiella hangoei. The diatoms had higher primary production capacity and lower respiration rate compared with the dinoflagellates. This difference was reflected in the maximum growth rate, which for the examined diatoms range from 0.6 to 1.2 divisions d-1, compared with 0.2 to 0.3 divisions d-1 for the dinoflagellates. Among diatoms there were species specific differences in light utilization and uptake of silicate, and C. wighamii had the highest carbon assimilation capacity and maximum silicate uptake. The physiological properties of diatoms and dinoflagellates were used in a model of the onset of the spring bloom: for the diatoms the model could predict the initiation of the spring bloom; S. hangoei, on the other hand, could not compete successfully and did not obtain positive growth in the model. The other dinoflagellates did not have higher growth rates or carbon assimilation rates and would thus probably not perform better than S. hangoei in the model. The dinoflagellates do, however, have competitive advantages that were not included in the model: motility and mixotrophy. Previous investigations has revealed that the chain-forming P. catenata performs diurnal vertical migration (DVM), and the results presented here suggest that active positioning in the water column, in addition to DVM, is a key element in this species' life strategy. There was indication of mixotrophy in S. hangoei, as it produced and excreted the enzyme leucine aminopeptidase (LAP). Moreover, there was indirect evidence that W. halophila obtains carbon from other sources than photosynthesis when comparing increase in cell numbers with in situ carbon assimilation rates. The results indicate that mixotrophy is a part of the strategy of vernal dinoflagellates in the Baltic Sea. There were also indications that the seeding of the spring bloom is very important for the dinoflagellates to succeed. In mesocosm experiments dinoflagellates could not compete with diatoms when their initial numbers were low. In conclusion, this thesis has provided new information about the basic physiological and ecological properties of the main cold-water phytoplankton in the Baltic Sea. The main phytoplankton groups, diatoms and dinoflagellates, have different physiological properties, which clearly separate their life strategies. The information presented here could serve as further steps towards better prognostic models of the effects of eutrophication in the Baltic Sea.Övergödningen av Östersjön är ett välkänt problem som förorsakas av mänskligt utsläpp av kväve och fosfor. Många av dessa näringsämnen blir tagna upp av algerna under våren när ljusets ökade intensitet sätter igång en vårblomning hos algerna. Därför är kunskap om algernas växt under denna period viktig för förståelsen av eutrofieringsprocesser i Östersjön. Målsättningen av denna avhandling var att beskriva grundläggande fysiologiska och ekologiska egenskaper hos alger som är vanliga under vårblomningen i Östersjön. Detta mål uppnåddes genom specifika studier av (1) långskiktig vertikal placering (2) dinoflagellateers livscykler (3) mixotrofi (4) primärproduktion, respiration och tillväxt och (5) kiselalgers silikatupptag. Arbetet blev utfört i havet utanför Hangö och med laboratoriekulturer av kiselalgerna: Chaetoceros wighamii, C. gracilis, Pauliella taeniata, Thalassiosira baltica, T. levanderi, Melosira arctica, Diatoma tenuis, Nitzschia frigida, och dinoflagellaterna: Peridiniella catenata, Woloszynskia halophila and Scrippsiella hangoei. Kiselalgerna hade högre primär produktion och lägre respiration än dinoflagellaterna. Denna skillnad reflekterades också i den maximala tillväxthastigheten som för kiselalgerna var 0.6-1.2 delningar per dag och för dinoflagellaterna 0.2-0.3 delningar per dag. Bland kiselalgerna var det också arts specifika skillnader i användandet av ljus och upptagandet av silikat. C. wighamii hade den högsta primärproduktionen, silikatupptag och maximal tillväxthastighet. De fysiologiska egenskaperna hos kiselalgerna och dinoflagellaterna blev använda i en modell av tidpunkten för vårblomningen. För kiselalgerna kunde modellen förutspå vårblomingens början men dinoflagellaterna fick inte positiv växt i modellen. Dessa arter finns i Östersjön under våren och måste därför ha andra konkurrensegenskaper som inte var med i modellen så som mobilitet och mixotrofi (förmågan till att uppta näring i organisk form). Den kolonibildande dinoflagellaten P. catenata är en god simmare, och resultaten indikerar att aktiv positionering i vattenpelaren är viktigt för denna arts ekologiska strategi. Det var bevis för mixotrfi i S. hangoei eftersom arten producerar enzymet leucine aminopeptidase (LAP). Det var också resultat som indirekt pekade mot mixtotrofi hos W. halophila eftersom tillväxten var mycket högre än fixeringsraten av karbon indikerade. Det ursprungliga antal dinoflagellater verkar också vara mycket viktig för den biomassa som byggs upp under vårblomningen. Denna avhandling har beskrivit ny information om fysiologiska och ekologiska egenskaper hos algerna som är vanliga under vårblomningen i Östersjön. Detta är information som inte tidigare har funnits på artnivå

Determining inorganic and organic nitrogen

Correction: Methods in Molecular Biology Volume1980 Page 243-243 Article Number107968 DOI 10.1007/7651_2019_252 Published 2020Nitrogen (N) is one of the key nutrients for algal growth and is an integral part of many cellular components, for example in proteins. Being able to determine the inorganic and organic pools of N is consequently critical for algal cultivation. In this chapter we present the methods we use for determining dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and particulate organic nitrogen (PON). The methods presented here for DIN rely on colorimetric methods and those of DON and PON on filtration and high temperature catalytic oxidation.Peer reviewe

Determining inorganic and organic carbon

Carbon is the element which makes up the major fraction of lipids and carbohydrates, which could be used for making biofuel. It is therefore important to provide enough carbon and also follow the flow into particulate organic and potential loss to dissolved organic forms of carbon. Here we present methods for determining dissolved inorganic carbon, dissolved organic and particulate organic carbon.Peer reviewe

Determining dissolved and biogenic silica

Most algae do not use silicon in any form with one notable exception, diatoms. Silicon is a major constituents of diatoms. Diatoms are characterized by high growth rates and are often one of the key groups in forming algal blooms in natural waters, and as such it is an interesting group for cultivation. In this chapter we present methods for determining dissolved silica (DSi) and biogenic silica (BSi), oxide forms of silicon, based on colorimetric methods. BSi is determined after filtration and alkaline digestion.Peer reviewe

Determining inorganic and organic phosphorus

The original version of this chapter was revised. The correction to this chapter is available at https://doi.org/10.1007/7651_2019_253Phosphorus (P) is a macronutrient for all microalgal species, and the main form of uptake is as orthophosphate (PO4). In this chapter we present a colorimetric method for determining the PO4 concentration and dissolved organic phosphorus (DOP) based on total phosphorus (TP) measurements. We also describe a method for determining particulate organic phosphorus (POP) based on the same principles.Peer reviewe

Total nitrogen determination by a spectrophotometric method

Being able to measure total nitrogen (TN) is important for following the nitrogen budget. In this chapter, we present the spectrophotometric method we use for determining TN. The method relies on oxidation and reduction steps, involving persulfate digestion of nitrogen compounds into nitrate followed by spectrophotometric determination.Peer reviewe

Editorial: Changing Plankton Communities : Causes, Effects and Consequences

Non peer reviewe

Shifting diatom—dinoflagellate dominance during spring bloom in the Baltic Sea and its potential effects on biogeochemical cycling

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

Viability of pico- and nanophytoplankton in the Baltic Sea during spring

Phytoplankton cell death is an important process in marine food webs, but the viability of natural phytoplankton communities remains unexplored in many ecosystems. In this study, we measured the viability of natural pico- and nanophytoplankton communities in the central and southern parts of the Baltic Sea (55°21′ N, 17°06′ E–60°18′ N, 19°14′ E) during spring (4th–15th April 2016) to assess differences among phytoplankton groups and the potential relationship between cell death and temperature, and inorganic nutrient availability. Cell viability was determined by SYTOX Green cell staining and flow cytometry at a total of 27 stations representing differing hydrographic regimes. Three general groups of phytoplankton (picocyanobacteria, picoeukaryotes, and nanophytoplankton) were identified by cytometry using pigment fluorescence and light scatter characteristics. The picocyanobacteria and picoeukaryotes had significantly higher cell viability than the nanophytoplankton population at all depths throughout the study area. Viability correlated positively with the photosynthetic efficiency (Fv/Fm, maximum quantum yield of photosystem II) as measured on the total phytoplankton community. However, an anticipated correlation with dissolved organic carbon was not observed. We found that the abiotic factors suggested to affect phytoplankton viability in other marine ecosystems were not as important in the Baltic Sea, and other biotic processes, e.g. processes related to species succession could have a more pronounced role.peerReviewe