photosynthetic plankton (phytoplankton)

Photosynthetic Plankton Photosynthetic Plankton (Phytoplankton)(Phytoplankton)

Roadmap for this class session:

1. Recap lecture 3 (modeling).

Then phytoplankton:

2. What are the main groups? How did they arise?

3. Where are they found? Where do different types dominate?

4. How do we identify, enumerate, & count phytoplankton?

5. How do we describe their growth as a function of resources?

Phyto (plants) + Plankton (“wandering”)

“wandering plants” (Ehrenberg 1897; Hensen 1887)

- the opposite of sessile (attached) plants –

Encompasses a wide range of organisms, all photosynthetic

Images: CCMP, MBL, Wikipedia

Phytoplankton: an ecological term, not taxonomic

The fundamental importance of phytoplankton

Marine phytoplankton produce 50% of the planet’s oxygen Responsible for our oxidizing atmosphere in the first place Plays a (major ?) role in global carbon cycle / climate (Martin) The main energy input for pelagic food webs (including us)

(also material input, e.g. N from N2 & C from CO2) It’s the fundamental “physical-biological” interaction in ocean.

Also, societal import: it’s in the news as of late… The ocean’s role in absorbing anthropogenic CO2

“Fertilizing” the ocean – 2007 & 2010 workshops @ WHOI Funding cuts to NASA, NOAA ocean satellite programs Changes to the Arctic ocean & Arctic pelagic ecosystems At the movies: An Inconvenient Truth

1 µm

Madigan, 2002

Phytoplankton are cells (or groups of cells)

Considerable diversity within the phytoplankton

Falkowski et al. 2004

Some groups with few (no) marine species.

Other groups with mostly marine species.

Far fewer photosynthetic species in the ocean than on land.

Why?

The “phytoplankton” are an assemblage of taxa

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Guinardia spp.


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Chaetoceros spp.


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Guinardia flaccida


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Leptocylindrus spp.


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Thalassiosira spp.


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Thalassionema spp.

Time (January July) Time (January July)

6 diatom species that dominate winter “bloom” off Martha’s Vineyard

• Each diatom exhibits bursts of increased abundance lasting <1 -2 weeks

• Generally a mixture of many species: i.e., the phytoplankton assemblage

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Data: H. Sosik & R. Olson, Imaging FlowCytobot

The “phytoplankton” are an assemblage of taxa

• Many phytoplankton species compete for same basic resources, e.g.,:– Light– Nutrients

• How does the seemingly uniform ocean environment support high phytoplankton diversity?• Is it paradoxical or not?

So-called “Paradox of the Plankton”. Hutchinson, 1961

Miller Ch 2

How do we treat the phytoplankton taxonomically?

Logistic model(“Verhuslt equation”):

Numerous types of eukaryotic phytoplankton (microalgae)

Diatoms

Coccolithophores

Dinoflagellates


Prasinophyte

• Size: usually nano- to micro- (5s to 100 m). Many species form chains.• Siliceous exterior frustule: an absolute requirement for Si at 4 to 50% dry weight • Pigments: chl a, c, fucoxanthin, diatoxanthin and diadinoxanthin• Not motile, except in male gametes. Possible adjustments to buoyancy.• Representative taxa: Thalassiosira, Chaetoceros, Coscinodiscus, Nitzschia, Ditylum• “Pennate” and “centric” forms, some produce toxins (domoic acid)• Ecologically: relatively fast-sinking, prey for copepods, spring blooms, large cells

thrive in coastal environments, r-selected.

Bacillariophyceae (common name “diatoms”)

• Silica shells of diatoms appear to have evolved to reduce mortality due to grazing, e.g., by copepods.

• Arms race: what do copepods evolve?

• Some predators use alternate feeding mechanisms get around silica shell -> certain dinoflagellates

Nature, Vol. 421, 2003

Why a heavy glass shell in a planktonic organism?

We have 2 diatom genomes: a centric & a pennate

• Size: usually nano- to micro-• Pigments: chl a, c, peridinin• Motility: Yes, biflagellate. Vertical migrators. • Naked & armored forms (cellulose “theca” - plates)• Representative taxa: Alexandrium, Ceratium, Prorocentrum, Pfisteria• Distinguishing feature: Red tides, toxins, bioluminescence, kleptochloroplasts• Mixotrophs: predatory, with unusual feeding mechanisms• Commonly coastal, or estuarine, but also found in oligotrophic waters• Ecologically: some are predators, mixotrophs, red tides,

Dinophyceae (common name dinoflagellates)

• Size: usually nano-• Pigments: chl a, c, beta-carotene • Motility: Yes, some genera are biflagellate, others non-motile • Representative taxa: Emiliania huxleyi, Isochrysis, Phaeocystis (colonial)• Coccolithophorid taxa form CaCO3 coccoliths (“liths”)• Distinguishing feature: coccoliths CaCO3, effect on ocean color• Ecological: sensitive to pH (ocean acidification), DMS production,

Phaeocystis & Antarctic pelagic ecosystems

Haptophyceae / Prymnesiophyceae (incl. coccolithophorids)

A mechanism for climate feedback?

Coccolithophore blooms in ocean color images

CaCO3 liths strongly scatter light“milky” appearance to seawater

Dimethylsulfoniopropionate

Normal CO2

High CO2 Fig. 3 in Riebesell et al. (2000)

Emiliana huxleyi Gephyrocapsa oceanica

A “few” ecologically important prokaryotic phytoplankton

Prochlorophytes, e.g., Prochlorococcus

Cyanobacteria, e.g., Synechococcus

Colonial cyanobacteria, e.g., Trichodesmium spp.

“tuft”

“puff”

ProchlorococcusProchlorococcus• small unicellular (0.5 x 0.8 µm)

• temperature range (20-30°C)

• extremely abundant (up to 4x105 cells/ml)

• Contains divinyl chlorophyll a (chl a2) and divinyl chlorophyll b(chl b2) as its major photosynthetic pigments

• small unicellular (0.6 to 0.8 small unicellular (0.6 to 0.8 µµm)m)

• Ubiquitous in the worlds oceans in temperatures >5Ubiquitous in the worlds oceans in temperatures >5ooCC

•• Present in high concentrations within the euphotic zonePresent in high concentrations within the euphotic zone

•• Contain phycobilisomes with phycoerythrin as primaryContain phycobilisomes with phycoerythrin as primarylight harvesting pigmentlight harvesting pigment

SynechococcusSynechococcus

Unicellular picoplankton: “cyanos”

Prochlorococcus rangeSynechococcus range

Adapted from Partensky et al, 1999

Distribution of Synechococcus & Prochlorococcus

Rocap et al Nature 2003

Niches set by vertical gradients of light

Moore et al 2002 LOMoore et al 2002 LO

High light:only NH4

+,Specialist

low light: NH4+, NO2

-

low light: NH4+, NO2

-, NO3-,

Generalist

Niches also set by vertical gradients of nutrients

Crocosphaera 1. Unicellular, 2 to 5 m2. Isolated from the tropical and south

Atlantic and Hawaii3. Temperature range 24 to 32oC4. Fixes N2 maximally at night

Trichodesmium1. Filamentous, 5 to 40 m2. Ubiquitous, significant source of

“new” nitrogen in tropic to subtropicalregions

3. Temperature range 20 to 30oC4. Fixes N2 at maximally at midpoint of

light period

T. thiebautii

T. erythraeum

Diazotrophic (or N2-fixing) cyanobacteria in the ocean

This is the presumed structure in Trichodesmium and Synechococcus

Many of the components have not been biochemically characterized

outside

inside

Photosynthesis in cyanobacteria

Phycobilisome

outside

inside

Prochlorococcus does not have phycobilisomes

Photosynthesis in Prochlorococcus

Short life spans 1 - few days when active

Little control over the environment they experience

Diverse photosynthetic physiologies & strategies

Marine photosynth. microbes

Many aspects of phytoplankton ecology have nothing to do with being planktonic.

(not really “plants”)

(ephemeral)(planktonic)

• Cell counts (light microscopy)

• Chl a (fluorometry)

• Pigments (HPLC)

• Flow cytometry

• Ocean color remote sensing

• Molecular assays– Whole cell techniques (molecular probes)

– PCR (quantitative PCR)

How do we enumerate and identify phytoplankton?

Microscopy: “traditional”

Microscopy: automated, e.g. Video Plankton Recorder


10

20

30

40

Guinardia spp.


2

4

6

8

10

Chaetoceros spp.


2

4

6

8

Guinardia flaccida


10

20

30

40

50

Carb

on (

g L -1

)

Leptocylindrus spp.


10

20

30

40

50

Carb

on (

g L -1

)

Thalassiosira spp.


5

10

15

20

Carb

on (

g L -1

)

Thalassionema spp.

Seeing smaller cells by automation: Imaging FlowCytobot

IFCB underwater

at 4 m depth

ASIT

12 m

Olson et al. 2003 Olson & Sosik 2007 Sosik & Olson 2007

Chlorophyll fluorometry: bulk biomass estimates

Bellingham et al. (2007) Science

23 m

6.5 km

Spatial mapping

High performance (pressure) liquid chromatography– Run samples on HPLC– Use program like CHEMTAX to perform matrix factorization program to

derive taxonomic structure of assemblage from pigment ratios

www.sb-roscoff.fr/Phyto/PICODIV/Workshop_2001/Mackey_Chemtax_Barcelona.ppt Havskum et al. (2004) MEPS

By pigments signatures: HPLC analysis

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HPLC signature of Dunaliella

Flow cytometry of phytoplankton cells

Orient cells in single-file streamLaser in stream scatters off cell & stimulates chlorophyll fluorescence

“Cytograms” of fluorescence vs. scatter indicate populations of cells of different sizes (species).Primary way of counting solitary prokaryotes (Syn & Pro), & picoeuks.

http://earthobservatory.nasa.gov/Observatory/Datasets/chloro.ocean.html

Data from the MODIS instrument on NASA’s AQUA spacecraft,Global [chl a], averaged 1 July 2002 – 31 Dec. 2004

Ocean color remote sensing

• Physiological responses to resources (light, nutrients) and environment (temperature) that affect phytoplankton photosynthesis & growth.

• How photosynthesis & growth translate into primary production.

• Patterns & characteristics of primary production in the ocean (new production, regenerated production, f-ratio, biological pump, etc.)

From taxonomy physiology ecology

photosynthetic plankton (phytoplankton)

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