Algae photosynthetic product release

There are reports of algae releasing as much as 90t of their total photosynthetic product into the water (3-8). A great deal of energy is invested in those complex molecules. If these were of no value, such incredibly inefficient organisms could not dominate a community. Since they do, there is a value and the trait is fixed in evolutionary terms. This is the basis for primary allelochemical activity. 

The effect of irradiance on excretion was investigated by Smith et al. [88] but no changes in extracellular production were detected. Also Williams and Yentsch [87],Lancelot [89] and Karl et al. [90] apparently came to the same conclusion. This point thus seems to be fairly well established. The exception may be situations where surface photoinhibition takes place. In these cases the relative release may increase as a result of a reduced photosynthetic rate. There is convincing evidence, however, that phytoplankton algae exposed to direct sunlight have very high excretion rates [30]. 

The carbon cycle Oidy about 0.03 percent of Earth s atmosphere is carbon dioxide (CO2), yet CO2 is vital to life. During photosynthesis, plants, algae, and some bacteria convert CO2 from the atmosphere into carbohydrates. In turn, plants, animals, and other living things break down carbohydrates during cellular respiration and release CO2 as a waste product. The cycle continues as photosynthetic organisms take in the released CO2. 

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