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Phytoplankton nutrient limitation in the Ria Formosa

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Phytoplankton nutrient limitation in the Ria Formosa

  1. 1. Phytoplankton nutrient limitation in the Ria Formosa: implications for eutrophication assessment Rita B. Domingues1,2, Cátia C. Guerra1, Ana B. Barbosa1, Helena M. Galvão1 1 Centro de Investigação Marinha e Ambiental, Universidade do Algarve 2 Centro de Oceanografia, Faculdade de Ciências, Universidade de Lisboa
  2. 2. What is phytoplankton? unicellular, photosynthetic prokaryotic and eukaryotic organisms whose powersof locomotion are such that they drift freely in the water column diatoms, dinoflagellates, coccolithophores, cyanobacteria, …Why is phytoplankton so important? phytoplankton is the main primary producer in most aquatic ecosystems phytoplankton is a fundamental player in many ecosystem processes phytoplankton is a gauge of ecological condition and change phytoplankton can be used to predict the functioning of aquatic ecosystems andecosystem responses to natural and anthropogenic perturbations
  3. 3. Studying phytoplankton is not straightforward… the ecological role played by different phytoplankton groups and species variessignificantly phytoplankton in coastal ecosystems is undergoing marked changes(biomass, composition, phenology) – linked to local anthropogenic influences andclimate change links between environmental and phytoplankton changes are difficult to establishImportance of nutrients Nutrient availability is a key driver of phytoplankton dynamics Nutrient limitation is a central question for eutrophication controlHow do nutrients affect phytoplankton growth, diversity and production?Assessment of the impact of nutrient enrichment (eutrophication) andsubsequent nutrient reduction strategies
  4. 4. Why the Ria Formosa coastal lagoon? multiple anthropogenic influences very vulnerable to climate changephytoplankton regulation is a critical aspectin a fast-changing ecosystem  lack of information on phytoplankton regulation in the Ria Formosa  studies are mostly descriptiveProject PHYTORIA – Environmental Regulation of Phytoplankton in theRia Formosa coastal lagoon (PTDC/MAR/114380/2009) Goals • to determine the limiting nutrients for phytoplankton growth and their seasonal variation in the Ria Formosa coastal lagoon • to understand the effects of potential anthropogenic nutrient enrichment on phytoplankton structure in the Ria Formosa
  5. 5. Approaches nutrient addition experiments in 2 L microcosms containing naturalphytoplankton assemblages from the Ria Formosa coastal lagoon autumn, winter, spring, summer addition of dissolved inorganic macronutrients, alone and in combinations, in asingle, saturating pulse control +NO3- +NH4+ +P +Si +NP +SiN +SiP +NPSi in situ incubation (under in situ T and light) phytoplankton growth (epifluorescence and inverted microscopy) nutrient consumption
  6. 6. Results – N consumption 25 13.5 Autumn 11.5 Spring N uptake (µM d-1) 20 9.5N uptake (µM d-1) 15 7.5 5.5 10 3.5 5 1.5 -0.5 0 -2.5 -5 35 30 Summer 30 25 Winter N uptake (µM d-1) 25N uptake (µM d-1) 20 20 15 15 10 10 5 5 0 0 -5 -5  higher N uptake in N-enriched treatments in relation to the control indicate N limitation phytoplankton in the Ria Formosa is N-limited throughout the year  NO3- concentrations up to 12 µM were limiting to phytoplankton growth
  7. 7. Results – Establishing nutrient criteriaApplication of nutrient limitation criteria based on Ks – problems… Ks obtained for unialgal cultures under equilibrium conditions Ks vary temporally, spatially, inter- and intraspecificallyEstablishment of nutrient criteria - should consider the seasonal variation of phytoplankton community (different spp. are limited in different ways by different nutrients) - should consider that limiting concentrations don’t have to be necessarily low concentrations (e.g., in the Guadiana estuary N is limiting up to 20 µM: Domingues et al., 2011) B 0,5 ** Community net growth rate (d -1) 0,45 spring ** Initial N = 22 µM 0,4 0,35 0,3 ** ** 0,25 0,2 0,15 0,1 0,05 0 control N P Si NP SiN SiP NPSi
  8. 8. Results – Phytoplankton net growth 1.1 Summer Community net growth rate (d-1) 0.9Increased nutrient uptake 0.7 0.5 0.3 phytoplankton growth 0.1 -0.1 -0.3 -0.5 control Nit Amm P Si NP SiN SiP NPSi 0.45 0.4 Winter luxury consumption 0.35 Net growth rate (d-1) 0.3 0.25 0.2 0.15 0.1 0.05 0 control Nit Amm P Si NP SiN SiP NPSi
  9. 9. Bottle effects on microcosm Effects of nutrient enrichment on Phytoplankton mortality in the experiments bacterioplankton in the RF Ria FormosaEffects of ultraviolet radiation and CO2 increase on winter phytoplanktonassemblages in a temperate coastal lagoon (Ria Formosa)Rita B. Domingues, Ana B. Barbosa, Vanda Brotas18h15
  10. 10. Thank You for Your Attention!AcknowledgementsFCT project Phytoria – Environmental regulation of phytoplankton in the Ria Formosacoastal lagoon (PTDC/MAR/114380/2009)Postdoctoral fellowship awarded to RBD (SFRH/BPD/68688/2010)

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