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  • 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. 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. 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. 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. 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. 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. 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. 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. 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. 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)