Phytoplankton and Primary Production (www.microbiological garden) Marine habitats High tide Supralitoral Low tide Pelagic zone neritic Epipelagic oceanic Litoral Mesopelagic Sublitoral Bathyal Bathypelagic Abyssal Abyssopelagic Benthic habitats pelagic Hadal Hadal (Lalli & Parsons 1995) Communities of the marine pelagic zone Plankton: Organisms buoyant and passively drifting in the water, unable to actively move against the water currents. - Virioplankton - Bacterioplankton - Mycoplankton - Phytoplankton - Protozooplankton / Metazooplankton Nekton: Actively moving and migrating organisms Benthos: Organisms living in benthic habitats. Viriobenthos, Bacteriobenthos, Mycobenthos, Phytobenthos, Zoobenthos. Neuston: Organisms living at the air-sea interface. Producers Consumers Decomposers Plankton size classes Size (m) Size Body weight (Sieburth 1978) Primary Production – light as a resource De novo synthesis of organic matter from inorganic constituents by autotrophic organisms. If the energy source is light: photoautotrophic → 6 H2O + 6 CO2 C6H12O6 + 6 O2 Light reaction (absorption by light-harvesting pigments and chlorophyll a) + → + H2O + NADP + Pi + ADP ½O2 + NADPH + H + ATP Dark reaction (Calvin-Benzon Cycle) + → + CO2 + NADPH + H + ATP CH2O + NADP + ADP + Pi Light harvesting pigments of phytoplankton (http://www.uic.edu/classes/bios/bios100/lecturesf04am/absorption-spectrum.jpg) Light harvesting pigments of phytoplankton (Lalli & Parsons 1995) Primary Production Controlling factors of primary production: · Light (ressource and environmental factor!) photosynthetic active radiation (PAR): 400 – 700 nm · Temperature · Hydrography, Stratification · Nutrients Primary Production – Light (P vs I curve) Photosynthetic rate mg C (mg Chl x l x h)-1 Pmax α -2 -1 Ic Ii: I (µE m s ) Irradiance Controlled by: light reaction dark reaction α: slope Ic: light saturation Ii: light inhibition Light adaptation of phytoplankton groups low light-adapted high light-adapted Vertical attenuation of light in the water column • Exponential attenuation with depth (absorption by pigments and dissolved organic substances and scattering by ions and particles) • Attenuation is wave length-specific • Euphotic depth: photosynthesis = respiration (0.1-1% of surface light intensity) (Lalli & Parsons 1995) Vertical zonation of light in the water column (Lalli & Parsons 1995) Controlling factors for the light climate in the euphotic zone (Lalli & Parsons 1995) Temperature as controlling factor • Direct control of primary production of minor importance. Light reaction of photosynthesis little controlled by temperature. • Indirect control by hydrographic conditions (blooms only develop when euphotic depth exceeds critical depth) Temperature as controlling factor Sverdrup's Model of Critical Depth • Photosynthesis decreases exponentially with depth due to decrease in light availability. • Respiration is unaffected by light and remains constant with depth. • Phytoplankton is mixed by turbulence and experiences different light intensities over time, sometimes above and sometimes below compensation point. • Critical depth = depth at which photosynthesis of the total water column phytoplankton population equals their total respiration. A phytoplankton population can only proliferate if mixing is shallower than the critical depth. Only then is the population net production >0 (Lalli & Parsons 1995) Nutrients • Macro-Nutrients: C, N, P, Si, S, K, Ca, Mg. • Micro-Nutrients: Fe, Zn, Mb, Cl- • Vitamins Available form of macro-nutrients (C, N, P, Si, S)? Nutrient uptake Uptake rate Concentration Michaelis-Menten Kinetics: V = Vmax x [S] / (Ks + [S]) Nutrient requirements and limitation • Phytoplankton biomass - C : N : P = 106 : 16 : 1 (Redfield-ratio) • In most cases N or P are limiting (sometimes Fe). N : P > 16 b P-limitation N : P < 16 b N-limitation Nitrate : phosphate ratio in the eastern tropical Pacific (Fiedler et al. 1991) Nitrate : phosphate ratio in the eastern Mediterranean Sea (Krom et al. 1991) Nitrogen and phosphorus in the open and coastal North Sea 1980-2002 Coastal North Sea: PPR P-limited open North Sea: PPR N-limited (McQuatters et al. 2007) HNLC-regions (High Nutrient Low Chlorophyll) Fe limits primary production. Dugdale & Wilkerson 1991 Annual vertical pattern of primary production and nutrients (Lalli & Parsons 1995) Saisonal pattern of primary production in various climatic regions (Lalli & Parsons 1995) Phytoplankton (Lalli & Parsons 1995) Cyanobacteria • prokaryotes • appr. 150 genera and >2000 species • single cells or colonies • pigments: chlorophyll a (and b) phycocyanin, phycoerythrin • asexual cell division • most important marine genera: • Syneccococcus (single cell) • Prochlorococcus (single cell, chlorophyll a+b) • Crocosphaera (N2-fixation) • Trichodesmium (colonies, bundles, N2-fixation) • Nodularia (colonies, N2-fixation, Baltic Sea) • Richelia intracellularis (colony, diatom symbiont, N2-fixation) Phylogenetic tree of cyanobacterial DNA polymerase I protein sequences showing genetic diversity among Prochlorococcus and Synechococcus strains compared with gene conservation in Crocosphaera strains high light adapted low light adapted Zehr J P et al. PNAS 2007;104:17807-17812 ©2007 by National Academy of Sciences Phylogenetic tree of Synechococcus and Prochlorococcus (16S rRNA gene) Low light High light Low light (West et al., Microbiology 147: 1731, 2001) Trichodesmium Satellite image of a Trichodesmium surface bloom Richelia intracellularis in a diatom cell (Bar Zeev et al., ISME J 2: 911, 2008) Cyanobacteria • important components of the phytoplankton in oligotrophic subtropical and tropical oceans. • constitute populations at the lower end of the euphotic zone (deep chlorophyll maximum) in stratified seas. • important sources of new nitrogen in N-limited regions (oligotrophic subtropical and tropical oceans). This source has been seriously underestimated in the past. Diatoms • 250 genera with appr. 100.000 species. • chloroplasts with chlorophyll a and fucoxanthin. • single cells or colony-forming, silicate frustule with epy- and hypotheca. • suborders Biddulphiales (Centrales) and Bacillariales (Pennales). • asexual reproduction usual, but sexual reproduction and formation of auxospores possible. Diatoms Diatoms (Sommer 2005) (Lalli & Parsons 1995) Diatoms Asterionellopsis glacialis Corethron sp Chaetoceros convolutus Chaetoceros debilis Annual production of particulate biogenic silikate (Bishop 1989) Diatoms • a dominant phytoplankton component in nutrient-rich marine regions (temperate, subpolar, upwelling). • important component of the sinking flux. Dinoflagellates • 130 genera with appr. 2000 species. • single cells with two flagella, one embedded in the sulcus as part of the cingulum. • cell surface covered with a layer of polygonal vesicles (theka). • vesicles can be empty (naked dinoflagellates) or filled with cellulose plates. • can be autotrophic or heterotrophic (Noctiluca scintillans). • asexual and sexual reproduction usual, formation of resting cysts. Dinoflagellates Dinoflagellates (Sommer 2005) (Lalli & Parsons 1995) Dinoflagellates Ceratium horridum C. fusus C. tripos C. furca Red Tide (Noctiluca scintillans) www.ecodivecenter.com/ecofact_otm-php?id=22) Dinoflagellates • important components of the phytoplankton in tropical to temperate seas. • can form toxic blooms (red tides). Prymnesiophytes / Haptophytes • 75 genera with appr. 500 species. •singlecellswithtwoflagellaorcolonies(Phaeocystis). • one important order includes the genus Phaeocystis, forming colonies with mucus and foam as decomposition product. • one important order has calcified scales: Coccolithophores. • important components of the oceanic phytoplankton globally. Various haptophytes (Sommer 2005) Coccolithophores Emiliana huxleyi 10 µm Global distribution of Emiliana spp Phaeocystis pouchetii (www.microbiological garden) Foam of Phaeocystis Global distribution of the major phytoplankton groups Diatoms: Polar-, subpolar regions, temperate zone and upwelling regions. Dinoflagellates: Tropical, subtropical and temperate zone, in summer and fall after disappearance of diatoms (depletion of silicate). Coccolithophores: Tropical, subtropical, temperate and subpolar (global). Synecchococcus: Tropical, subtropical, temperate and subpolar (deep chlorophyll maximum). Prochlorococcus: Tropical and subtropical stratified regions (surface and deep populations) .