Sunlight needed by the seaweed to the process of photosynthesis, where the result is CO2 fixation. Besides ultraviolet also needed for growth itself. The ability of light to penetrate the waters will decrease with increasing with depth. This zone is called the photic zone. Changes in the intensity and quality of light that penetrates the water with increasing depth illustrates the ability of seaweed to grow.
Eucheuma sp. included in the class Rhodophyceae that can live in waters deeper than class Chlorophyceae and Phaeophyceae (Dawes, 1981). Brightness waters of determining the amount of the intensity of sunlight or the light that comes into the waters. Brightness waters can also be seen from the color of the waters, the content of organic materials and inorganic suspended in water, the density of plankton, micro-organisms and detritus can affect the brightness waters.
Turbidity is a limiting factor for photosynthesis and primary production waters because it affects the penetration of sunlight. In addition, turbidity is a picture of a water optical properties are determined based on the amount of light (light) is emitted and absorbed by the particles present in water (Boyd, 1988 in Apriyana 2006). According Soemarwono (1984) in Masrawati (1999) states that one of the causes of turbidity is the presence of organic substances are decomposed, microorganisms, silt and clay or colloidal substances are substances that easily settles floating.
All types of seaweed contain a variety of pigments. The ability of the pigment in assisting this growth is strongly influenced by sunlight. Kappaphycus are marine plants that have chlorophyll derivatives that require sunlight for survival (Doty, 1987). The synthesis of chlorophyll was strongly influenced by light. If the plants irradiated with sufficient light so it would be perfect formation of chlorophyll (Sallisbury and Ross, 1969).
According Dwijoseputro (1989), the formation of chlorophyll starts from protoklorofil which was reduced to the chlorophyll-a, if there is sunlight. Sunlight is absorbed by protoklorofil and converted into chlorophyll-a. This event is referred to as autotransformasi.
Figure 10. pigments contained in seaweed which helps the process of photosynthesis
According to Kimball (1990), fikoeritrin a complementary pigment that helps chlorophyll-a in absorbing light in the process of photosynthesis. The amount of chlorophyll-a low insufficient in absorption of light for photosynthesis, thus spurring the formation fikoeritrin more. According Saffo (1987) in Veronika and Izzati (2009), fikoeritrin able to absorb green light efficiently.
Meanwhile, fikoeritrin and fikobilin pigment capable of absorbing light green and blue (Dawes, 1987). It is the cause of the change in the pigment composition Eucheuma planted in deeper ocean waters. Nybakken (1988) states, after the light waves penetrate the surface of the sea, purple and red components are quickly absorbed by the water. Green and blue components are absorbed more slowly and can penetrate deeper water. Saffo (1987) in Veronika and Izzati (2009) and Dawes (1981) also explains that the light can penetrate deep water is light with a wavelength being. Green light is the light that corrugated medium because it has a wavelength of 525 nm.
Quality and quality of light influence on spore production and growth of seaweed. High light intensity stimulate persporaan Porphyra but inhibits persporaan Eucheuma sp. Needs light in red seaweed lower than the brown algae. For example persporaan gracillaria verrucosa developing well in light intensity of 400 lux, whereas Ectocarpus in light intensity between 6500-7500 lux (Aslan, 1998).