There are 355 species of seaweed found in Indonesia waters (Weber van Bosse, 1928). About 55 species of them have been utilized by Indonesia as food (salad, vegetable, and soup thickening) and medical treatments (Zeneveld, 1955). Some of them are high economic value as a source of agar such as Gracilaria, Gelidiella, and Gelidiopsis, and a source of carrageenan (Eucheuma and Hypnea) which required by modern food industries. The average seaweed production in Indonesia 1984 is about 9 644 mt (Table 8) which are mostly harvested from natural ground.
A suitable culture site for seaweed culture should be sheltered from prevailing wind or monsoonal strong weather conditions. Wave action can have a severe impact on seaweed culture operation not only removing significant amount of seaweed from culture facilities, but also damaging the culture facilities.
Ecological parameters used for assessment of the site are water movement, indicator species, substratum, depth, salinity, and light intensity.
4.1.1 Water movement
Water movement is a key factor that control or influence the growth of the seaweed. It plays an important role in preventing an increase in pH, caused by consumption of carbon dioxide and supply of salt-nutrient. It is also important in aeration of water, prevents the rise in water temperature. Water movement caused by current is considered a better form of water motion than wave. It is more predictable and less destructive. Matumoto (1950) suggested that in ordinary site, a current of about 20 cm/sec is considered suitable for seaweed culture. However, if the site is rich in salt-nutrients, the current can be as small as 10 cm/sec. On contrary if the sites is deficient in salt-nutrients, the current of a higher speed is required but should not exceed 30/sec.
4.1.2 Indicator species
The presence of wild stocks of the seaweed at the site or in nearby areas is not only a good indicator of ecological suitable of the site, but also eliminate the problem of seed acquisition when the operation is taken place. The present of some species of benthic coelenterate is also an indicator to support the suitability of the site for Eucheuma in terms of good water movement, high level of phosphate, silicate, salinity, dissolved oxygen and high transparency. The abundance of soft corals for instance is an indicator of good water movements. These animals are filter feeders and depend on food transported by currents.
4.1.3 Substratum
The substratum reflects the oceanographic conditions of the site and determine the degree of ease in constructions of the supporting culture facilities. Areas which are too rocky are generally wave exposed area while those characterized by fine sand and silt are generally protected. On the other hand, site with coarse sandy bottom mixed with coral fragments are generally current washed area. For Eucheuma, substratum of the site should be of sandy loam, or hard coral and covering the dead reef flats.
4.1.4 Depth
Generally, Eucheuma are found just below the lowest tide level or slightly below it. At this level the Eucheuma are exposed to air for an hour or so during extreme tides. Exposure to air appears to be an ecological advantage especially when grazing pressure in the area is high. Predators are limited only to periods of high tides. Under such conditions the seaweed generally form thick lumps on the surface of the substratum. Growth proceeds laterally instead of upwards. In contrast stocks found in areas which are never exposed even during average low tides form erect robust thalli where growth proceeds both seaward and upwards.
Water depth is an important factor to consider when selecting a site for the establishment of seaweed farms. Greater tidal ranges allow for less working time at a farm. Too high tides inhibit working at farm since diving is not every efficient. Low tides that consistently expose the reef should be avoid. However tidal ranges can also be associated with water motion. Therefore, a balance need to be found between suitable tidal range and water motion. Area where depth of the water is 0.3m to 0.6m. during extreme tides are most preferred. At this depth the farmer can stand or walk in knee to waist-deep water in stead of swimming and diving such as the case in deeper areas.
4.1.5 Salinity
Most seaweed species cannot withstand exposed to a wide variation in salinity regimes. Areas influenced by freshwater generally characterized by low species diversity compared to reef areas not influenced by low salinity. The low diversity may be mainly due to the fact that only few species can thrive in habitat with fluctuating salinity regimes. Species like Gracilaria verfrucosa thrives well in a salinity ranging from 8 to 25 ppt while Eucheuma spinosum and E. cottonii prefer higher salinity 30– 34 ppt with a narrow range of salinity fluctuation.
4.1.6 Light penetration
Seaweed require light as a source of energy for the synthesis of organic products necessary for their normal growth and development. The potential site should have water with good transparency. Water with high silt load is not good for seaweed growing. It is not only hindering light penetration, but silt also accumulate on the algal thalli which adversely effect growth and development of the plants. The site that suitability for seaweed culture should have the transparency value above 1.50 m for secchi disc measurement.
Potential areas for the seaweed culture are found in Merah Hajran, Danao, Ungas island, Penean Basar and Pancan Kercil in North Sumatra; Weh island, Sabang, Simeulu West Aceh in Aceh; Padang, carocko, Bangus in West Sumatra; Bengkulu in Bengkulu; Telang Besar, Pankil, Karas, Matak, and Beliba islands in Riau; Bangka, Belitung in South Sumatra; Ketapang Kalihada, Ketapang Padang Cermin in Lampung; Seribu island, Jakarta; Banten bay, Pelabuahan Ratu, Cimare, Cikelet, Cikalong, Cikangkung, Cidaun, Cipatujah and Pameungpeuk in West Java; Gunung Kidul, Cilacap and Jepara in Central Java; Pacitan, Banyuwangi and Sumenep in East Java, Serangan Island, Nusa Dua, Tj. Benoa, Ungasan Cekik, Nusa Penida, Nusa lembongan, Nusa Ceringan In Bali, Gili manuk, Banyuwedang, Sendang, Bondalem, Ujung, Padang bay, Sengkidu, Saleh bay and Waworada bay of Sumbawa, Maringgi, Kabing and Kera Islands, and Ekas bay of Lombok in West Nusatenggara; Tj. Karoso of West Sumba, Warambadi of East Sumba, Komodo Island, Besar Island, Maumere, and Tablolong, Timor in East Nusatenggara; North Maluku (Limbo Island in West Ialiabu, Doi and Ngelengele in North Halmahera and Jorongan in South Halmahera), Central Maluku (Geser, Seran Rei, Kefar, Kidang, Nukus and Grogus in East Seram, Tujuh Island in North Seram and Ose Island in West Seram), Southeast Maluku (Kg. Warilau, Krei Baru in Aru islands; Meti Rotan, Watidal, Nusa lima island and Kg. Nurkat of Maru island in North Tanimbarj; Kg Lat Dalaun, Namtabung, Adaut Nuyanat in South Tanimbar; Babar, Wetarin Babar islands; Marsela, Sermata, Luang and Meti Miarang in Semeta islands; Kisar, Wetar, Lirang, Romang and Damar in Leti islands) Maluku; Laut island in South Kalimantan ; Tarakan Berau, Bentang, Balikpapan, in East Kalimantan; Buton, Muna, Kendari and Kaledupa in Southeast Sulawesi; Pengkep, Jeneponto, Polmas, Mamuju, and Sinjai in South Sulawesi; Samaringa in Central Sulawesi; and Sorong in Irian Jaya. The total estimated is about 23 000 ha (Table 9).
The main area for Eucheuma are found in Riau, Lampung, Jakarta, Bali, West Nusatenggara, East Nusatenggara, Maluku, South Kalimantan, East Kalimantan, South Sulawesi, Central Sulawesi, Southeast Sulawesi and Irian Jaya (Table 10). Gelidium can be grown in West Sumatra, South Sumatra, Riau, West Java, Bali and West Nusatenggara while the potential area for culture of Gracilaria are found in Central Java, East Java, and Maluku. Hypnea can be grown in almost every seaweed producing area.
