SUBMARINE PHOTOSYNTHESIS

By Katie-Marie Brown and Colin Bursey

Submarine Photosynthesis

Photosynthesis is the process by which plants, algae and photosynthetic bacteria use light energy to drive the synthesis of organic compounds.

The organic molecules created by this process are an important energy source for many small organisms that are the base of the entire marine food chain.

Photosynthesis works by fixing atmospheric carbon:

CO2 + 2H2O + light (CH2O)n + O2 + H2O

Photic zone

The euphotic (photic) zone includes the surface waters down to a depth of 200 meters.

200 meters is the maximum depth of light for photosynthesis (in clear water). Anything deeper gets very little sunlight, preventing photosynthesis.

The upper most part of the photic zone contains 70% of the worlds photosynthesis.

The depth of the photic zone can be affected greatly by water turbidity and the angle of the sun to the sea surface.

The photic zone does not necessarily mean that photosynthesis can occur (other factors involved).

Photic zone

Plankton and Photosynthesis

Phytoplankton uses the power of the sun for photosynthesis (producers), while Zooplankton only feed upon Phytoplankton for energy (consumers).

Many fish, whales and crustaceans feed upon these plankton. Therefore nothing could survive without the sun’s energy.

Phytoplankton

Diatoms form a shell of silica, large amount of variance in

structure between species contribute ~45% of all ocean primary productionharvest light energy by using chlorophyll a and c as

well as fucoxanthin

Dinoflagellatesuse chlorophylls a and c and either peridinin or

fucoxanthin cause “red tides” – harmful algal blooms zooanthellae which are associated with corals are

dinoflagellates

Photosynthetic pigments

Most land plants are green and flowering but marine plants come in a more wide variety of color.

The characteristic colors of the different algal groups are caused by different combinations of photosynthetic pigments.

Over 98% of land and freshwater plants contain the pigment chlorophyll b but only 13% of marine plants contain it.

Green algae contains chlorophyll b and chlorophyll a, kelps and diatoms contain chlorophyll c instead of b, red algae contains only chlorophyll a.

Chlorophyll allows plants to obtain energy from the sun.

Pigments continued

Chlorophyll a is in every photosynthetic plant and is the most common.

The reason that there are so many pigments is that each absorbs light more efficiently in a different part of the spectrum.

Chlorophyll a absorbs well at a wavelength of about 400-450 nm and at 650-700 nm; chlorophyll b at 450-500 nm and at 600-650 nm.

In low light conditions, such as in deeper parts of the photic zone, plants produce a greater ratio of chlorophyll b to chlorophyll a. This increases the photosynthetic yield.

Algae

Note: All contain chlorophyll a

Cyanobacteria

Also referred to as blue-green algae

Account for 20-30% of Earth’s photosynthetic productivity

Use the phycocyanin pigment to capture light

oxygenic photosynthesis

can also fix atmospheric nitrogen

are hypothesized to be the evolutionary precursor to eukaryotic chloroplasts (Endosymbiotic theory)

are also hypothesized to have caused the conversion of the Earth’s atmosphere from a reducing to an oxidizing one

Bacterial Photosynthesis

Purple and Green sulphur bacteriaobligate anaerobesuse the bacteriochlorophyll pigment to harvest light

energy which they use to break down sulphur-containing compounds water is not the reducing agent; does not produce

oxygen

Important things Bob said

Some animals may be able to detect light at greater depths because they have very specialized organs.

Photosynthetic efficiency is more important in sea plants than in land plants due to the lack of light.

Seaweed with high efficiency will not release any photons. Therefore, it will appear black when you take a picture of it.

The Calvin cycle in photosynthesis uses photons at 680nm.

Step Down Florescence: Chlorophyll a and the other accessory pigments can absorb

photons greater than 680nm and will release them with less energy (until they reach 680nm and can be useful in the Calvin cycle).

References

Dring, M. J. The biology of Marine Plants. (1992) Cambridge University Press.

Pinet, P. Invitation to Oceanography. (2009). Jones and Bartlett Publishers

Owens, T.G., J.C. Gallagher, and R.S. Alberte. 1987. Photosynthetic light-harvesting function of violaxanthin in Nannochloropsis spp. (Eustimatophyceae). J. Phycol. 23:79-85.