Nitrogen is one of the main elements making up the cell organism that is in the process of formation of protoplasm. Nitrogen often in limited quantities in the waters, especially tropical areas. Shortage of nitrate in the water can inhibit the growth of aquatic plants, although other nutrients are in abundant quantities (Hunter, 1970 in Patadjal, 1993). Nitrogen in the waters mostly in the form of nitrite ions and nitrate ions, then with the help of bacteria that have the ability to change nitrites and then to ammonia nitrate widened through the reduction process, so that the process of assimilation of ammonia by aquatic plants can take place.
Nitrate and nitrite first reduced before it is used by the cells of algae. While ammonia is usually used directly for the synthesis of amino acids through a process transamilasi (Coolos and Slawyk, 1980 in Patadjal, 1993). Nitrates are also a type of nitrogen that is very soluble in water and are stable resulting from the complete oxidation of nitrogen compounds in the water. Increased levels of nitrates in the sea due to the influx of domestic or agricultural waste generally contains a lot of nitrate.
According to Morris (1974) in Patadjal (1993) algae have a tendency to first use the N-inorganic and urea, and dissolved organic N will only be used if the source or form another nitrogen konsentasinya already very low. Nitrate is used for metabolism by the enzyme nitrate reductase produces. The formation of the enzyme nitric requires a long time, so that the rate of nitrate-making is very slow compared to the rate of ammonia retrieval that does not require enzymes in utilization.
Nitrate reductase enzyme levels are very low in algae that live in waters with low nitrate concentrations. High ammonia concentrations in the water will cause the formation of the enzyme nitrate reductase inhibition on algae. In addition to nitrate and ammonia, algae can also use nitrites and hydroxyl amine to the process of metabolism. Nitrite compounds contained in sea water is the result of the reduction or oxidation of ammonia nitrate compounds by microorganisms.
Nitrite is usually found in very small quantities of natural waters, the levels are smaller than the nitrates because it is unstable. This concentration can increase towards the coastal waters and estuaries. Increased levels of nitrite at sea is closely related to the influx of organic material that easily explained (both of which contain nitrogen and nitrate). Thus the nitrite compound is one indicator of pollution (Hutagalung et al., 1997). Research Dawes et al., (1974) showed a high carrageenan content value in the summer, when the rate of photosynthesis is high and low nitrogen levels. Instead, in the spring of carrageenan levels low, while the optimal environmental conditions for growth and higher nutrient supply.