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, c 1, c 2 & d a all green plants and algae b Chlorophyceae c 1 & c 2 Phaeophyceae dRhodophyceae

C CH CH 2 C C C C C CN N C H3CH3C C C C C C C C C N C C C C N Mg H H3CH3C H C CH 2 CH 3 H C H H CH 2 H CH 3 C O O O O O CHO in chlorophyll a in chlorophyll b Porphyrin ring: Light-absorbing “head” of molecule note magnesium atom at center Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts: H atoms not shown 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