Salinity is the amount (grams) of substances soluble kilogram of sea water which is considered all carbonates have been converted to oxide, bromine, and the ions replaced by Clor and all organic material has been oxidized completely. Salinity waters for marine organisms is an important environmental factor. Each marine organisms have different tolerance to salinity for survival.
Beveridre (1987) in Iksan (2005) states salinity is closely related to the osmotic pressure that affects the body’s balance of aquatic organisms. Also stated that the higher the levels of salt (salinity), the greater the osmotic pressure of the water. Salinity is also associated with the process of osmoregulation in the body of an organism. In seaweed Eucheuma sp grow well in high salinity.
A decrease in salinity due to the influx of fresh water from rivers can lead to the growth of seaweeds Eucheuma sp decreased. According to Dawes (1981), a good salinity range for growth is 30-35 ppt Eucheuma sp. According Zatnika and Space (1994) states that the salinity of the waters for the cultivation of seaweed Eucheuma sp., Ranging between 28-34 ppt. Meanwhile, according Soegiarto et al., (1978) good salinity range for Eucheuma sp is 32-35 ppt. If the salinity is below 30 ppt it will damage the seaweed which is marked by the emergence of white tip-end of the plant (Collina, 1976 in Iksan, 2005).
In general, the salinity of sea water 35 ‰ achieve maximum growth of seaweed are in the range of 15-38 ‰ salinity in sea water salinity is 35 ‰ maximum growth of seaweed found on the salinity range of 15-38 ‰ with optimum salinity of 25 ‰. Type gracillaria live well within the range of 15-22 ‰ salinity while Fucus vesiculosus types 8-34 ‰ salinity tolerant. Deployment of sea grass in an area is also determined by the mixing of fresh water from the river (Luning, 1990).
Seaweed can be abundant in waters with high salinity, but there are also abundant in low salinity because of the influence of freshwater input. Getting to the eastern waters of Indonesia, the higher the diversity of sea grass because of the structure and the better the condition of coral, the high water clarity, free of sedimentation and high salinity is 30 ‰ (Mubarak et al., 1990). Eucheuma genera requires moderate environmental requirements requires a substrate that is not soft but not too hard, which is sand and rubble, require moderate water motion, strong water movement can cause thallusnya fractures and stagnant water can cause death, salinity between 29-34 ‰ (Mubarak et al., 1990).
Gracillaria clan living on the range of environmental conditions is wider than the Eucheuma apart in coral reef ecosystems it can also live in estuarine ecosystems, it can stick to the mud, sand and coral or shells, he can live in water that is stagnant water movement is moderate , salinity between 15-34 ‰, because it can be cultivated in the sea or in ponds. Gelidium genera require a narrow range of environmental conditions which, requires a very strong water movement and attached to the substrate which is very hard because it is found in the Indian Ocean coast, this type has not been cultivated (Mubarak et al., 1990).
Sargassum including cosmopolitan genera of plants that live on the reef flats to the edge of the reef flat area, is able to grow well attached to a hard substrate, spreading very widely in the waters of Indonesia (Mubarak et al., 1990).