The average depth of the water required for the growth of seaweed depending on the amount of sunlight intensity. According Soegianto and Sulistijo (1985) in Syahputra (2005), the depth of which is ideal for the growth of seaweed in the Thousand Islands with basic methods in the 0.3 to 0.6 m at its lowest ebb. Such circumstances can prevent drought to plants. The depth of the water also affects the seaweed cultivation methods that will be used for the cultivation of seaweed.
Waters with a depth <3 m can use basic methods or freelance basis, but the waters that have a depth of> 3 meters should use the floating method. It also affects the construction costs to be incurred by seaweed farmers.
Figure 11. Use of the method freelance basis for the cultivation of seaweed at a depth waters still get enough sunlight