Phosphorus is an essential element for all aspects of life, especially work for the transformation of metabolic energy that role can not be replaced by another element (Kuhl, 1974). Phosphorus is a constituent element of pyrophosphate bond of adenosine triphosphate (ATP), which is rich in energy and the fuel for all activities in all living cells and is an important constituent cells. Phosphate compound is a phospholipid constituent important as a constituent of membrane and present in large quantities.
The energy released from hidrosis pyrophosphate and various organic phosphate bond is used to control a variety of chemical reactions (Noggle and Fritz, 1986 in Patadjal, 1993). The content of phosphorus in the algae cells affect the rate of uptake of phosphate, which decreases with increasing phosphorus content in the cell. Some types of algae are able to absorb phosphate at very low concentrations and has the enzyme alkaline.
It can be said that the shortage of phosphate will be critical for aquatic plants including algae plant, as opposed to when a shortage of nitrate in water. On the other hand despite the availability of phosphorus in waters often abundant in the form of various phosphate compounds, but only in the form of orthophosphate (PO42-) which can be used directly by aquatic plants (Fritz, 1986). Phosphate needs for optimum growth of algae is affected by nitrogen compounds.
The highest limit phosphate concentrations will be lower if the nitrogen is in the form of ammonium salt. Conversely, if the nitrogen in the form of nitrate, phosphate highest concentration required will be higher. Lower limit concentration for optimum growth of marine algae ranging from 0.018 to 0.090 ppm of P-PO4 when nitrogen in nitrate form, whereas when nitrogen in the ammonium form the highest limit of 1.78 ppm range in P-PO4 (Fritz, 1986).
Phosphate in the water either dissolved or suspended, shaped both inorganic and organic. Organic phosphates in the sea is generally in the form of ions (ortho) phosphoric acid H3PO4 which around 10% is in the form of inorganic phosphate PO43- and 90% in the form of HPO42-. Natural sources of phosphate in the waters originating from soil erosion, sewage effluent animals, lapukan plants, industrial waste, fertilizer drift, domestic waste, destruction of organic matter and minerals phosphate (Susana, 1989).
Based on the levels of orthophosphate, the waters are classified into three, namely waters oligotrofik who possess the levels of orthophosphate from 0.003 to 0.01 mg / l, water mesotrofik orthophosphate levels from 0.011 to 0.03 mg / l and eutrophic waters have high levels of orthophosphate from 0.031 to 0.1 mg / l (Iksan 2005). Phosphate compounds in water comes from natural sources such as soil erosion, effluent lapukan animals and plants as well as from the sea itself. Phosphate absorbed by phytoplankton and so enter into the food chain. In seawater, the average levels of phosphate is about 2ug at PO4-p / l.