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Reef Photosynthesis
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Productivity
• the production of organic compounds from inorganic atmospheric or aquatic carbon sources – mostly CO2
• principally through photosynthesis– chemosynthesis much less important.
• All life on earth is directly or indirectly dependant on primary production.
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gC/m2/d
TropicalCoral Reef 4.1 - 14.6
Tropical open ocean 0.06 - 0.27
Mangrove 2.46
Tropical Rain Forest 5.5
Oak Forest 3.6
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Productivity
• no single major contributor to primary production on the reef
• a mixture of photosynthetic organisms– can be different at different locations
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• net productivity values (varies with location):
gC/m2/d
Calcareous reds 1 - 6
Halimeda 2 -3
Seagrass 1 - 7
N.S. kelp 5
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• Overall productivity of the reef:
4.1 - 14.6 gC/m2/d
• from– epilithic algae, on rock, sand etc., – few phytoplankton– seagrasses– Zooxanthellae (in coral etc.)– Fleshy and calcareous macroalgae
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• One obvious differences between different algae is their colour
• Different colours due to the presence of different photosynthetic pigments
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Light
ReflectedLight
Chloroplast
Absorbedlight
Granum
Transmittedlight
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Light and Photosynthesis
• Air & water both absorb light– a plant at sea level receives 20% less light than
a plant on a mountain at 4,000m
– this reduction occurs faster in seawater – depends a lot on location
• get 20% light reduction in 2m of tropical seawater
• get 20% light reduction in 20cm of Maritime seawater
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• a very specific part of the EM spectrum
• PAR
• Photosynthetically Active Radiation
• 350-700 nm
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Gammarays X-rays UV Infrared
Micro-waves
Radiowaves
10–5 nm 10–3 nm 1 nm 103 nm 106 nm1 m
106 nm 103 m
380 450 500 550 600 650 700 750 nm
Visible light
Shorter wavelength
Higher energy
Longer wavelength
Lower energy
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• Measure it as IRRADIANCE– moles of photons per unit area per unit time– mol.m-2.s-1
– E = Einstein = 1 mole of photons
E.m-2.s-1
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• As light passes through seawater it gets ABSORBED & SCATTERED – = ATTENUATION (a reduction in irradiance)
• pure water– attenuation lowest at 465nm
– increases towards UV and IR ends of spectrum
• TRANSMITTANCE is highest at 465nm
• not dealing with pure water– Seawater has all kinds of dissolved salts, minerals,
suspended material etc.:
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• Attenuation is different in different locations - different light transmittance spectra:
To fully exploit a particular location, marine plants have a wide variety of PS pigments they can use.
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Chloroplast
Mesophyll
5 µm
Outermembrane
Intermembranespace
Innermembrane
Thylakoidspace
Thylakoid
GranumStroma
1 µm
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CO2
CALVINCYCLE
O2
[CH2O](sugar)
NADP
ADP+ P i
An overview of photosynthesis
H2O
Light
LIGHT REACTIONS
Chloroplast
ATP
NADPH
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Light Reactions
• In the thylakoid membrane,
– chlorophyll molecules, other small molecules & proteins, are organized into photosystems
– photosystems composed of a reaction center surrounded by a number of light-harvesting complexes (LHC)
• LHC = pigment molecules bound to proteins
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• LHC = pigment molecules bound to proteins
• funnel energy of photons to the reaction center
• reaction-center chlorophyll absorbs energy– One of its electrons gets bumped up to a primary
electron acceptor– electron transport– ATP & NADPH production
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Photosystems
Primary electionacceptor
Photon
Thylakoid
Light-harvestingcomplexes
Reactioncenter
Photosystem
STROMAT
hyla
koid
mem
bran
e
Transferof energy
Specialchlorophyll amolecules
Pigmentmolecules
THYLAKOID SPACE(INTERIOR OF THYLAKOID)
e–
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Light• The visible light spectrum includes
– the colors of light we can see– the wavelengths that drive photosynthesis
• Photosymthetic pigments absorb light
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Gammarays X-rays UV Infrared
Micro-waves
Radiowaves
10–5 nm 10–3 nm 1 nm 103 nm 106 nm1 m
106 nm 103 m
380 450 500 550 600 650 700 750 nm
Visible light
Shorter wavelength
Higher energy
Longer wavelength
Lower energy
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Light
ReflectedLight
Chloroplast
Absorbedlight
Granum
Transmittedlight
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• different pigments have different absorption spectra
• combine in different amounts in different species to give each a unique absorption spectrum
• tells us which wavelengths of light are being absorbed (and thus it’s colour)
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Ab
sorp
tion
of
ligh
t b
ych
loro
pla
st p
igm
en
ts
Chlorophyll a
Wavelength of light (nm)
Chlorophyll b
Carotenoids
Absorption spectra of pigments
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• doesn’t tell us what the alga is doing with the light
• For this you need to look at the ACTION SPECTRUM– measures photosynthesis at different
wavelengths
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• The action spectrum of a pigment
– show relative effectiveness of different wavelengths of radiation in driving photosynthesis
• Plots rate of photosynthesis versus wavelength
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Marine PS pigments
• 3 major groups of PS pigments in marine organisms
– Chlorophylls– Phycobiliproteins– Carotenoids
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• Chlorophyll a is essential
– find it in all plants and algae
• the other pigments are accessory pigments
– in the antennae complexes – funnel electrons to chlorophyll a in the reaction
centres
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• 5 types of chlorophyll commonly found in marine organisms
• all are tetrapyrrole rings with Mg++ in the middle
• chlorophyll a, b, c1, c2 & d
• a all green plants and algae• b Chlorophyceae• c1 & c2 Phaeophyceae• d Rhodophyceae
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• Chlorophyll a– Is the main photosynthetic pigment
• Chlorophyll b– Is an accessory pigment
C
CH
CH2
CC
CC
C
CNNC
H3C
C
CC
C C
C
C
C
N
CC
C
C N
MgH
H3C
H
C CH2CH3
H
CH3C
HHCH2
CH2
CH2
H CH3
C O
O
O
O
O
CH3
CH3
CHO
in chlorophyll a
in chlorophyll b
Porphyrin ring:Light-absorbing“head” of moleculenote magnesiumatom at center
Hydrocarbon tail:interacts with hydrophobicregions of proteins insidethylakoid membranes ofchloroplasts: H atoms notshown
Accessory pigments absorb different wavelengths of light and pass the energy to chlorophyll a
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• Also a wide range of carotenoids– C40 TETRATERPENES– very hydrophobic– sit in membranes
• 2 types of carotenoids
– CAROTENES (hydrocarbons)– XANTHOPHYLLS (have 1 or 2 oxygens)
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-CAROTENE is the most common carotenoid in marine organisms
• often see a mixture of -CAROTENE & FUCOXANTHIN (another carotenoid) in the Phaeophyceae– gives the brown colour
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• PHYCOBILINS are linear tetrapyrroles attached to proteins– red pigments
– no ring, no chelation of a metal
• Only found in Rhodophyceae & Cyanophyceae– and a few species of Cryptophyceae
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• Algae from different locations will often have different absorption and action spectra
– CHROMATIC ADAPTATION
• difference in pigment composition due to a difference in light quality
• most pronounced when comparing algae grown at different depths
• Allows for optimal PS with the different wavelengths of light seen at different depths
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• occurs within and between species
• In general, less light means more pigment
• e.g. Sea Lettuce (Ulva spp)
• move from high to low light– 10x less: 300 to 30 E.m-2.s-1
• chl a,b & c go up 700%
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• One pigment doesn’t respond in this way
• FUCOXANTHIN– yellowish pigment found in brown algae
– probably because it performs 2 functions
• light harvesting
• protection from high light levels
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• Overall productivity of the reef:
4.1 - 14.6 gC/m2/d
• this is organic carbon production
• must also consider carbonate production (deposition of physical structure of the reef)
– Get about half of this from the coral symbiosis
– the rest from the calcareous green & reds algae
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• a major source of calcium deposition on the reef
– the coral symbiosis
• However, CALCAREOUS ALGAE (greens & reds) also major contributors
– the more flexible magnesian calcite
• last 20 years - role of these algae receive more attention– play a much bigger role in calcium deposition than previously
thought
• 10% of all algae CALCIFY (about 100 genera)
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• Most calcareous algae in the Phyla: – RHODOPHYTA (REDS) & CHLOROPHYTA (greens)
– 1 genus in PHAEOPHYTA (brown - Padina)
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• Many not considered to be “plants” until 19C
– referred to as “corallines”
– calcareous horny sea organisms
• 3 genera particularly important in creating reef structure:
1. Halimeda (global)
2. Penicillus (Caribean)
3. Tydemania (Indo-pacific)
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Halimeda• variety of substrates from sand to rock
• different species adapted to specific substrates
– lagoon - large holdfast (1-5cm) deep into the sand
– on rock - small (1cm) in crevices
– sprawl across coral debris - attached by threadlike filaments
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• variety allows Halimeda to colonize all zones of the reef– except very high energy areas like reef crest, (find
calcareous reds here)
• Halimeda particularly abundant in lagoon and the back- and fore-reef areas– so not much in Bonaire
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• Halimeda grows quickly
• Can produce a new segment overnight
– a whitish mass– turns green in the morning– induction of chlorophyll synthesis by light
– after greening, it lays down the magnesian calcite and stiffens up
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• Estimates from Great Barrier Reef
– Halimeda doubles its biomass every 15d.– equates to 7g dry wt. per day per sq m.
• Segments get broken off– settle on lagoon floor– in sand grooves– adding solid material
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• Halimeda grows down to 150m
– light intensity is 0.05% of surface– grows slowly here, uses different pigments– limit for the Chlorophyta– algae growing deeper are Rhodophyta
• Texts often say euphotic zone ends at 1% surface light– No – Halimeda down to 0.05% – reds can be found as deep as 268m (0.01%)
• San Salvador Island in the Bahamas
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Tropical Marine Plants
• looked at zooxanthellae, now some of the other plants associated with the coral reef & tropical shoreline.
• 2 groups:– 1. SUBMERGED (mostly) (reef coral book pp 188 - 239)
– 2. SHORELINE - coastal plants that usually have “wet feet”
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1. SUBMERGED
• the primary producers of the reef – in the tropics, very few of the photosynthetic organisms
are in the water column – mostly benthic
– light penetrates deeper
– find photosynthetic organisms at far greater depths than in our local waters
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• much primary production comes from the coral symbiosis– other symbioses also contribute– other mutualistic plant-animal relationships
• algal partners in these are termed “ENDOZOIC” algae– found within animals– includes:
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• Dinoflagellates - the zooxanthellae
• Green algae - the zoochlorellae
• Blue-green algae - the zoocyanellae
• in a variety of sea anemones and sea slugs
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• Some sea slugs show an extreme variation on this theme
– do not live in a symbiosis with the algae– steal their chloroplasts– “kleptoplasty”– alga ingested by slug, but only partly digested– chloroplasts remain intact in the gut cells– continue to photosynthesize
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• e.g. Elysia viridis
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• lettuce sea slug Elysia (Tridachia) crispata
– gets quite green when feeding on Caulerpa spp
(sea grape). – unlike many other sea slugs, it spends a lot of
time during the day in the open– catching rays for photosynthesis
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• Also find symbiotic algae in some sponges
– e.g. Haliclona (red algae e.g. Ceratodictyon)
• Also find some green algae living mutualistically with some encrusting sponges