Phytoplankton and Primary Production

Phytoplankton and Primary Production

(www.microbiological garden)

Marine habitats

Pelagic zone

oceanic

SupralitoralHigh tide

Low tide

Litoral

Sublitoral

Abyssal

Hadal

Bathyal

Benthichabitats

Epipelagic

Mesopelagic

Bathypelagic

Abyssopelagic

pelagic Hadal

neritic

(Lalli & Parsons 1995)

Communities of the marine pelagic zone

Plankton: Organisms buoyant and passively drifting in the water, unable to activelymove 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

(Sieburth 1978)

Size (m)

Body weightSize

Primary Production – light as a resource

De novo synthesis of organic matter from inorganic constituentsby 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 → ½ O2 + NADPH + H+ + ATP

Dark reaction (Calvin-Benzon Cycle)

CO2 + NADPH + H+ + ATP → CH2O + NADP+ + ADP + Pi

Light harvesting pigmentsof phytoplankton

(http://www.uic.edu/classes/bios/bios100/lecturesf04am/absorption-spectrum.jpg)

Light harvesting pigmentsof phytoplankton


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 ratemg C (mg Chl x l x h)-1

Pmax

α Ic Ii: I (µE m-2 s-1)Irradiance

α: slopeIc: light saturationIi: light inhibition

Controlled by: light reaction dark reaction

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 dissolvedorganic substances and scattering byions and particles)

• Attenuation is wave length-specific

• Euphotic depth: photosynthesis = respiration(0.1-1% of surface light intensity)

Vertical zonation of light in the watercolumn


Controlling factors for the light climate in the euphotic zone


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 exceedscritical depth)

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 overtime, sometimes above and sometimes belowcompensation point.

• Critical depth = depth at which photosynthesisof the total water column phytoplanktonpopulation equals their total respiration.

Temperature as controlling factor

A phytoplankton population can onlyproliferate if mixing is shallower thanthe critical depth. Only then is the population net production >0


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

Concentration

Uptake rate

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 � P-limitationN : P < 16 � 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)

(McQuatters et al. 2007)

Nitrogen and phosphorusin the open and coastal North Sea 1980-2002

Coastal North Sea: PPR P-limitedopen North Sea: PPR N-limited

HNLC-regions(High Nutrient Low Chlorophyll)

Dugdale & Wilkerson 1991Fe limits primary production.

Annual vertical pattern of primary production and nutrients


Saisonal pattern of primary production in various climatic regions


Phytoplankton


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

Zehr J P et al. PNAS 2007;104:17807-17812

©2007 by National Academy of Sciences

low light adaptedhigh light adapted

Phylogenetic tree of Synechococcus and Prochlorococcus (16S rRNA gene)

(West et al., Microbiology 147: 1731, 2001)

Low light

High light

Low light

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 oligotrophicsubtropical 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 withepy- and hypotheca.

• suborders Biddulphiales (Centrales) and Bacillariales(Pennales).

• asexual reproduction usual, but sexual reproductionand formation of auxospores possible.

Diatoms

(Lalli & Parsons 1995)(Sommer 2005)

Diatoms

Diatoms

Corethron spAsterionellopsis glacialis

Chaetoceros convolutus Chaetoceros debilis

Annual production of particulate biogenic silikate

(Bishop 1989)

Diatoms

• a dominant phytoplankton component in nutrient-richmarine 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 sulcusas part of the cingulum.

• cell surface covered with a layer of polygonal vesicles (theka).

• vesicles can be empty (naked dinoflagellates) or filledwith cellulose plates.

• can be autotrophic or heterotrophic (Noctiluca scintillans).

• asexual and sexual reproduction usual, formation of resting cysts.

Dinoflagellates

Dinoflagellates

(Lalli & Parsons 1995)(Sommer 2005)

Dinoflagellates

Ceratium horridum

C. fusus

C. furcaC. tripos

Red Tide (Noctiluca scintillans)

www.ecodivecenter.com/ecofact_otm-php?id=22)

Dinoflagellates

• important components of the phytoplankton in tropical totemperate seas.

• can form toxic blooms (red tides).

Prymnesiophytes / Haptophytes

• 75 genera with appr. 500 species.

• single cells with two flagella or colonies (Phaeocystis).

• one important order includes the genus Phaeocystis,forming colonies with mucus and foam as decompositionproduct.

• 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 fallafter 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 subtropicalstratified regions(surface and deep populations)

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Phytoplankton and Primary Production