Direct effects of increased CO2 concentrations in seawater on the net primary production of charophytes in a shallow, coastal, brackish-water ecosystem

Charophytes are found in fresh and brackish waters across the globe and play key roles in coastal ecosystems. However, their response to increasing CO2 is not well understood. The aim of the study was to detect the effects of elevated CO2 on the physiology of charophyte species growing in the brackish Baltic Sea by measuring net primary production. Mesocosm experiments were conducted in the Kõiguste Bay (N Gulf of Riga) during the field season of 2012. Separate mesocosms were maintained at different pCO2 levels: 2000, 1000 and 200 µatm. The experiments were carried out with three species of charophytes: Chara aspera, C. tomentosa and C. horrida. The short-term photosynthetic responses of charophytes to different treatments were measured by the oxygen method. The results show that elevated CO2 levels in brackish water may enhance the photosynthetic activity of charophyte species and suggest that increasing CO2 in the Baltic Sea could have implications for interspecific competition and community structure in a future high CO2 world

Temporal development of coastal ecosystems in the Baltic Sea over the past two decades

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Kohalike ja invasiivsete zooplanktoni liikide ajalis-ruumiline varieeruvus muutuvates kliima- ja eutrofeerumistingimustes

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Eutrofeerumist, kliimamuutusi ja bioinvasioone peetakse olulisteks teguriteks, mis võivad tõsiselt ohustada rannikumere koosluste stabiilsust. Samas pole olemas ühte kindlat ruumiskaalat, millel nende muutuste mõju elusloodusele uurida. Üheaegselt mõjutavad ökosüsteemi nii laial skaalal toimuvad protsessid kui ka vaid kohalikul tasandil toimunud muutused. Käesolevas töös hinnati, kuidas erinevatel ruumiskaaladel toimivad troofsuse- ja kliimamuutujad mõjutavad Soome lahe zooplanktoni biomassi, seda nii kohalike kui võõrliikide puhul. Samuti kirjeldati nelja Läänemerre elama asunud võõrliigi Balanus improvisus, Marenzelleria neglecta Cercopagis pengoi ja Evadne anonyx populatsioonide dünaamikat ja ökoloogilist mõju Eesti vetes. Zooplanktoni koosluse dünaamika oli mõjutatud nii klimaatiliste tingimuste kui ka eutrofeerumise teguritest ja seda kõikidel uuritud ruumiskaaladel. Enamike liikide puhul olid kõige vähem mõjuvateks, kuid siiski olulisteks teguriteks just väikseima ehk lokaalse skaala keskkonnatingimused. Samas ei olnud kliima ja eutrofeerumise muutujate koosmõju zooplanktoni liikidele oluliselt suurem kui nende mõju eraldi võetuna. Käsitletud võõrliikide vaatlused näitavad, et nende biomass on viimastel aastatel näidanud tõusutrendi. Võõrliigi Cercopagis pengoi tihedus oli korrelatsioonis nii klimaatiliste tingimustega kui ka näiteks teiste vesikirpude liikidega, kuid olulist seost eutrofeerumisega selle liigi puhul ei leitud. Röövtoidulise Cercopagis pengoi mõju oma potensiaalsele saakloomale avaldus peamiselt saaklooma populatsiooni paiknemisena sügavamates veekihtides nendes jaamades, kus röövloom esines suure arvukusega. Värskeima võõrliigi Evadne anonyx arvukus on seni jäänud madalaks.Eutrophication, climate change and bioinvasions are ranked among the major threats to the stability of the marine coastal environment and can have severe impacts on near-shore biodiversity and functioning, but there is no single natural scale at which the effects of eutrophication and climate should be studied. The contribution of eutrophication and climate variables estimated at local, gulf and regional scales to the biomass of native and invasive zooplankton species in a shallow brackish water ecosystem of the Baltic Sea was evaluated in this thesis. Population dynamics and ecological impacts in north-eastern Baltic Sea of four established alien species: Balanus improvisus, Marenzelleria neglecta, Cercopagis pengoi and Evadne anonyx, was described in this thesis. The study demonstrated that eutrophication and climate variables largely explained the observed patterns in zooplankton communities and most species were affected by environmental variability at all spatial scales. Both eutrophication and climate variables describe a substantial amount of the variability in the models of mesozooplankton species. On the other hand, the interactive effect of eutrophication and climate variables on mesozooplankton was not significant. The abundance of Cercopagis pengoi was best explained by climate variables and the densities of selected cladocerans while eutrophication had no significant effect on it within a broad range of spatial and temporal variability. The effect of predatory Cercopagis pengoi on the potential prey species Bosmina coregoni maritima was revealed as changed vertical distribution of the pray species by the presence of the predator. Although it still has low densities, Evadne anonyx will most likely further increase in abundance and colonize new areas in the Baltic Sea

Factors describing the distribution of the zooplankton community in the Gulf of Finland in the context of interactions between native and introduced predatory cladocerans

Mesozooplankton communities were studied monthlyat six sites in the Gulf of Finland during six ice-free seasons.The abundances of different zooplankton taxa were related totemperature, salinity, eutrophication level (total nitrogen andphosphorus), phytoplankton <i>Chl a</i> and density of predatorycladocerans, including the non-indigenous <i>Cercopagis pengoi</i>and the native <i>Leptodora kindtii</i>. The results indicated thatvariability in the zooplankton communities was correlated notonly with predation by mesozooplankton but also with bottom-upeffects. Predation by the non-indigenous <i>C. pengoi</i> may significantlyaffect the dynamics of Cladocera and Rotatoria in the Gulf ofFinland during the summer season

Seawater carbonate chemistry and net photosynthesis of seagrass Zostera marina in a brackish water environment

Seagrasses are distributed across the globe and their communities may play key roles in the coastal ecosystems. Seagrass meadows are expected to benefit from the increased carbon availability which might be used in photosynthesis in a future high CO2 world. The main aim of this study was to examine the effect of elevated pCO2 on the net photosynthesis of seagrass Zostera marina in a brackish water environment. The short-term mesocosm experiments were conducted in Kõiguste Bay (northern part of Gulf of Riga, the Baltic Sea) in June-July 2013 and 2014. As the levels of pCO2 naturally range from ca. 150 µatm to well above 1000 µatm under summer conditions in Kõiguste Bay we chose to operate in mesocosms with the pCO2 levels of ca. 2000, ca. 1000, and ca. 200 µatm. Additionally, in 2014 the photosynthesis of Z. marina was measured outside of the mesocosm in the natural conditions. In the shallow coastal Baltic Sea seagrass Z. marina lives in a highly variable environment due to seasonality and rapid changes in meteorological conditions. This was demonstrated by the remarkable differences in water temperatures between experimental years of ca. 8°C. Thus, the current study also investigated the effect of elevated pCO2 in combination with short-term natural fluctuations of environmental factors, i.e., temperature and PAR on the photosynthesis of Z. marina. Our results show that elevated pCO2 alone did not enhance the photosynthesis of the seagrass. The photosynthetic response of Z. marina to CO2 enrichment was affected by changes in water temperature and light availability

The effect of CO2 enrichment on net photosynthesis of the red alga Furcellaria lumbricalis in a brackish water environment

Anthropogenic carbon dioxide (CO2) emissions to the atmosphere are causing reduction in the global ocean pH, also known as ocean acidification. This change alters the equilibrium of different forms of dissolved inorganic carbon in seawater that macroalgae use for their photosynthesis. In the Baltic Sea, benthic macroalgae live in a highly variable environment caused by seasonality and rapid changes in meteorological conditions. The effect of increasing water CO2 concentration on the net photosynthesis of the red macroalgae Furcellaria lumbricalis (Hudson) Lamouroux was tested in short-term mesocosm experiments conducted in Kõiguste Bay (N Gulf of Riga) in June-July 2012 and 2013. Separate mesocosms were maintained at different pCO2 levels: ca. 2,000, ca. 1,000 and ca. 200 µatm. In parallel, different environmental factors were measured such as nutrients, light and water temperature. Thus, the current study also investigated whether elevated pCO2 and different environmental factors exerted interactive effects on the photosynthetic rate of F. lumbricalis. In addition, laboratory experiments were carried out to determine the optimal temperature for photosynthesis of F. lumbricalis. The results of our field experiments demonstrated that elevated pCO2 levels may remarkably enhance the photosynthetic rate of F. lumbricalis. However, the magnitude of this effect is altered by different environmental factors, mainly by changes in water temperature

The influence of CO2 enrichment on net photosynthesis of seagrass Zostera marina in a brackish water environment

Seagrasses are distributed across the globe and their communities may play key roles in the coastal ecosystems. Seagrass meadows are expected to benefit from the increased carbon availability which might be used in photosynthesis in a future high CO2 world. The main aim of this study was to examine the effect of elevated pCO2 on the net photosynthesis of seagrass Zostera marina in a brackish water environment. The short-term mesocosm experiments were conducted in Kõiguste Bay (northern part of Gulf of Riga, the Baltic Sea) in June-July 2013 and 2014. As the levels of pCO2 naturally range from ca. 150 μatm to well above 1000 μatm under summer conditions in Kõiguste Bay we chose to operate in mesocosms with the pCO2 levels of ca. 2000, ca. 1000 and ca. 200 μatm. Additionally, in 2014 the photosynthesis of Z. marina was measured outside of the mesocosm in the natural conditions. In the shallow coastal Baltic Sea seagrass Z. marina lives in a highly variable environment due to seasonality and rapid changes in meteorological conditions. This was demonstrated by the remarkable differences in water temperatures between experimental years of ca. 8°C. Thus, the current study also investigated the effect of elevated pCO2 in combination with short-term natural fluctuations of environmental factors, i.e. temperature and PAR on the photosynthesis of Z. marina. Our results show that elevated pCO2 alone did not enhance the photosynthesis of the seagrass. The photosynthetic response of Z. marina to CO2 enrichment was affected by changes in water temperature and light availability