Productivity and the Coral Symbiosis:

Reef Photosynthesis II

Marine PS pigments

• 3 major groups of PS pigments in marine organisms

– Chlorophylls

– Phycobiliproteins

– Carotenoids

• 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

• 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

C

CH

CH2

CC

CC

C

CNNC

H3C

C

C

C

C C

C

C

C

N

CC

C

C N

MgH

H3C

H

C CH2CH3

H

CH3C

HH

CH2

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

• Chlorophyll a– Is the main photosynthetic pigment

• Chlorophyll b, c, d– Are accessory pigments

• 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)

-CAROTENE is the most common carotenoid in marine organisms

• often see a mixture of -CAROTENE & FUCOXANTHIN in the Phaeophyceae– gives the brown colour

• 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

• 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 amount & wavelengths of light seen at different depths

• 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%

• 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

• 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:

• Dinoflagellates - the zooxanthellae• Green algae - the zoochlorellae• Blue-green algae - the zoocyanellae

in a variety of:• Sea anemones• Sea slugs• Bivalves• Jellyfish• Ciliates• Radiolarians• Foraminifera

• 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

• e.g. Elysia viridis

• lettuce sea slug Elysia 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

• 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

• symbiotic algae in some anemones

Aiptasia pallida

• symbiotic algae in some anemones

Anthopleura elegantissima

Symbiodinium muscatinei

S. californium