Reef Photosynthesis

Productivity the production of organic compounds from inorganic atmospheric or aquatic carbon sources – mostly CO 2 principally through photosynthesis –chemosynthesis much less important. All life on earth is directly or indirectly dependant on primary production.

gC/m 2 /d TropicalCoral Reef Tropical open ocean Mangrove2.46 Tropical Rain Forest5.5 Oak Forest3.6

Productivity no single major contributor to primary production on the reef a mixture of photosynthetic organisms –can be different at different locations

net productivity values (varies with location): gC/m 2 /d Calcareous reds1 - 6 Halimeda2 -3 Seagrass1 - 7 N.S. kelp5

Overall productivity of the reef: gC/m 2 /d from –epilithic algae, on rock, sand etc., –few phytoplankton –seagrasses –Zooxanthellae (in coral etc.) –Fleshy and calcareous macroalgae

One obvious differences between different algae is their colour Different colours due to the presence of different photosynthetic pigments

Light Reflected Light Chloroplast Absorbed light Granum Transmitted light

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

a very specific part of the EM spectrum PAR Photosynthetically Active Radiation nm

Gamma rays X-raysUVInfrared Micro- waves Radio waves 10 –5 nm 10 –3 nm 1 nm 10 3 nm 10 6 nm 1 m 10 6 nm 10 3 m nm Visible light Shorter wavelength Higher energy Longer wavelength Lower energy

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

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.:

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.

Chloroplast Mesophyll 5 µm Outer membrane Intermembrane space Inner membrane Thylakoid space Thylakoid Granum Stroma 1 µm

CO 2 CALVIN CYCLE O2O2 [CH 2 O] (sugar) NADP  ADP + P i An overview of photosynthesis H2OH2O Light LIGHT REACTIONS Chloroplast ATP NADPH

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

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

Photosystems Primary election acceptor Photon Thylakoid Light-harvesting complexes Reaction center Photosystem STROMA Thylakoid membrane Transfer of energy Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) e–e–

Light The visible light spectrum includes –the colors of light we can see –the wavelengths that drive photosynthesis Photosymthetic pigments absorb light

Gamma rays X-raysUVInfrared Micro- waves Radio waves 10 –5 nm 10 –3 nm 1 nm 10 3 nm 10 6 nm 1 m 10 6 nm 10 3 m nm Visible light Shorter wavelength Higher energy Longer wavelength Lower energy

Light Reflected Light Chloroplast Absorbed light Granum Transmitted light

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)

Absorption of light by chloroplast pigments Chlorophyll a Wavelength of light (nm) Chlorophyll b Carotenoids Absorption spectra of pigments

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

The action spectrum of a pigment –show relative effectiveness of different wavelengths of radiation in driving photosynthesis Plots rate of photosynthesis versus wavelength

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

Chlorophyll a –Is the main photosynthetic pigment Chlorophyll b –Is an accessory pigment 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

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 (another carotenoid) 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 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

Overall productivity of the reef: gC/m 2 /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

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)

Most calcareous algae in the Phyla: –RHODOPHYTA (REDS) & CHLOROPHYTA (greens) –1 genus in PHAEOPHYTA (brown - Padina)

Many not considered to be “plants” until 19 C –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)

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

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

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

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

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

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 ) –2. SHORELINE - coastal plants that usually have “wet feet”

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

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 and sea slugs

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 (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

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