PHYTOPLANKTON PIGMENT
COMPOSITION
Importance
•
•
•
•
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Phytoplankton composition
Light absorption
Primary production
Light penetration in the ocean
Remote sensing of phytoplankton biomass
and primary production
• Mixed-layer dynamics
Influence of absorption on the
attenuation of light in the ocean
Kd ≈
a + bb
µ
ƒ a: total absorption coefficient (m-1)
ƒ bb: backscattering coefficient (m-1)
ƒ µ: average cosine of light field
Influence of phytoplankton absorption
on reflectance
bb (λ )
R (λ ) = f
a (λ )
R(λ): reflectance at wavelength λ
bb(λ): backscattering coefficient at λ
a(λ): absorption coefficient at λ
Components of absorption in the ocean
a (λ ) = aw (λ ) + Ca (λ ) + Da (λ ) + Ya (λ )
*
ph
*
d
*
y
a (λ ) : total absorption coefficient of seawater (m-1)
aw (λ ) : absorption coefficient of pure seawater (m-1)
C : concentration of chlorophyll-a (mg m-3)
*
a ph (λ ) : specific absorption coefficient of phytoplankton
[m-1 (mg m-3)-1]
Y : concentration of yellow substances (expressed in absorption m-1)
a *y (λ ) : specific absorption coefficient of yellow substances
(dimensionless)
D : concentration of detritus (mg m-3)
*
ad (λ ) : specific absorption coefficient of detritus [m-1 (mg m-3)-1]
Chemotaxonomic markers
• Advantages
Chemotaxonomic markers
• Disadvantages
Phytoplankton pigments
• Chlorophyll-a (or its substitutes bacteriochlorophyll-a
or divinyl-chlorophyll-a) is located in the RCs of all
photosynthetic organisms.
• Three main types of accessory pigments:
chlorophylls, carotenoids and biliproteins are
located in the subantennae and LHCs of different
taxonomic groups of algae.
Chlorophylls
• Green coloured pigments.
• Absorb light energy in the blue
and red regions of the spectrum.
• Porphyrin ring – conjugated
double bonds, magnesium ion,
nonpolar phytol tail.
• Three main types: a, b, and c
(divinyl-chl-a, -b, chl-c1, -c2, c3).
• Fluoresce (máximum 680 nm).
• Photochemistry, and lightharvesting.
Carotenoids
• Red, orange or yellow
pigments.
• Absorb light in the blue-green
region.
• Conjugated hydrocarbons.
• Two main groups: carotenes
(e.g., β-carotene) and
xanthophylls (e.g.,
fucoxanthin).
• Do not fluoresce per se.
• Some light-harvesting, some
photoprotective.
Phycobilins
• Brightly coloured pigments (red,
orange, pink).
• Absorb light in the green-yellow
region.
• Linear tetrapyrroles (water soluble).
• Four major types: phycocyanin,
phycoerythrin, allophycocyanin,
phyoerythrocyanin.
• Fluoresce (máximum 570 nm).
• Light-harvesting.
Pigment composition in phytoplankton taxa
Algal Division/Class
Common Name
Genera
Golden-brown algae (chl-a and c)
Bacillariophyta
Dinophyta
Chrysophyta
Chrysophyceae
Raphydophyceae
Haptophyta
Prymnesiophyceace
Xanthophyta
Cryptophyta*
Eustigmatophyta
diatoms
dinoflagellates
Golden-brown flagellates
chrysophytes,silicoflagellates
chloromonads
Golden-brown flagellates
coccolithophorids
Yellow-green algae
cryptomonads
Yellow-green algae
210
550
120
4
50
600
8
6
Green algae (chl-a and –b)
Chlorophyta
Chlorophyceae
Prasinophyeceae
Euglenophyta
green algae
green flagellates
euglenoids
350
13
43
Rhodophyta (chl-a and biliproteins)
Rhodophyta
red algae
3
Blue-green algae (chl-a and biliproteins)
Cyanophyta
cyanobacteria
prochlorophytes
??
3
Pigment composition in phytoplankton
taxa
Absorption spectra of
pigment-protein-complexes
(from Barrett and Anderson, 1980)
Absorption spectra of different algae
(from Kirk, 1994)
Response to the light field
• Different algae have pigment composition
suitable for growth under their typical natural
light environments.
• Intracellular pigment concentration is also
variable with the intensity of the light field.
• Both pigment composition and intracellular
pigment concentration influence the absorption
characteristics of the phytoplankton.
Photoadaptation & Photoacclimation
• The pigment characteristics of a species reflects
adaptation at evolutionary time scales to their
environment (Photoadaptation).
• The response of phytoplankton to the light field
may also be temporary (Photoacclimation).
Photoacclimation
• Short-term changes.
• Long-term changes:
–Changes in the number of PSUs.
–Changes in the size of the PSUs.
–Changes in the proportion of
photosynthetic (PS) and photoprotective
(PP)pigments.
Short-term photoacclimation
Xanthophyll cycle
Long-term photoacclimation:
Changes in the size of the PSU
(from Falkowski, 1983)
Effect of temperature on pigment composition
(Maxwell et al. 1995)
Changes in intracellular pigment concentrations in
different species of phytoplankton under HL and LL
(Lutz et al. 2001)
Variations in optical properties with changes in pigment
composition due to photoacclimation
Changes in pigment composition
Lutz et al., 1998)
Pigment indeces (Vidussi et al. 2001)
Pigment sum
Formula
TChla
Total chlorophyll a
Chla + Chlidea
DP
Diagnostic pigments
All + But + Chlb + Fuc +
Hex + Per + Zea
Pigment index
Formula
Diatom proportion of DP
Fuc/DP
PerDP
Dinoflagellate proportion of DP
Per/DP
FlagDP
Flagellate proportion of DP
ZeaDP
Prokaryote proportion of DP
(All + But + Chlb +
Hex)/DP
Zea/DP
FucDP
Pigment indeces
mg m -3
mg m -3
0 2 4 6 8 10 12 14 16 18 20
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
0
0
5
20
15
Depth (m)
Depth (m)
10
20
25
30
35
40
Stn100
45
0.0
TChla
FucDP
FlagDP
0.2 0.4 0.6 0.8 1.0
Diagnostic Index
40
60
80
100
Stn93
120
TChla
FucDP
PerDP
FlagDP
ZeaDP
0.0 0.2 0.4 0.6 0.8 1.0
Diagnostic Index
(Barlow et al., in press)
Modelling of phytoplankton absorption:
“Multi pigment” method
a ph (λ ) = ∑ a (λ )C i
n *
i i
• aph(λ): absorption coefficient of phytoplankton at
wavelength λ, (m-1)
• a*i(λ): specific absorption coefficient of the i-th
pigment at λ, (m-1(mg pigment m-3)-1)
• Ci: concentration of the i-th pigment, (mg m-3)
Decomposition of the in vivo absorption
spectrum of phytoplankton: pigments
and chromoproteins
(from Johnsen and Sakshaug, 1996)
Decomposition of the in vivo absorption
spectrum of phytoplankton: Gaussian curves
(from Hoepffner and Sathyendranath, 1991)
Field sampling
• Collection:
– Surface: bucket; on-line system
– Depth: Niskin bottles (~ 40 min)
• Put in black-covered carboys
• Filter immediately:
–
–
–
–
Onto GF/F filters
Low vacumm (< 35 kPa)
Dim light
Volume depending on the amount of phytoplankton in the
water; no more than 40 min.
– Suck dry, remove the filter, place on blotting paper, folded
once (algae inside!) and dry 3 times.
• Put dry filter in cryovial, rotulate twice.
• Put cryovials in liquid nitrogen, or deep-freezer.
Message from Simon Wright (December 2005)
• Regarding the filtration volumes, we use variable volumes. We are
normally limited in the amount of water we can get, typically 2L max
from a 10L Niskin bottle after the oceanographers have finished
sampling. Our samples range from very oligotrophic (<0.05 ug chla/L) to
moderately eutrophic (4 ug/L, max). We use 13mm dia GF/F filters so
that we can extract in a small volume (1.5 ml methanol, by sonication).
In oligotrophic water, we can filter 2L, but when there's more
phytoplankton in the water, the filter starts to clog. We set an arbitrary
time limit of 20 min for filtration.
• Clearly the sample size is important in integrating the variation due to
phytoplankton patchiness. A bigger sample will give a better average.
Also when you have huge cells like Coscinodiscus, that may be present
at only a few cells per litre, getting a bigger volume would be better.
Having said that, if (as satellite images suggest) the distribution of
phytoplankton is fractal, you would need an ocean-sized sample to get a
proper average. Also a lot of the small scale patchiness due to marine
snow particles is lost because the particles break up and disperse during
sampling with a Niskin bottle, so small samples are probably OK. But in
our case, it's a decision based on how much water we can get.
• The only real choice we have is in not filtering for too long - activates
chlorophyllases and leaves pigments vulnerable to breakdown.