The cultivation method and farm design – which are highly influenced by the individual site conditions – determine what type of equipment is needed on the seaweed farm. Anchors, ropes, culture lines and floats are essential equipment for all cultivation taking place at sea.The material the farmer chooses for each will not only depend on the site conditions, but also on the price and availability of equipment.
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The speed and direction of the ocean current at the farm site tends to determine the type of farm structure (rig) and direction it faces.
The farm design differs between countries and regions and can generally be categorised in floating raft type or single or double long line systems.
Within these, cultivation lines are either set up in a vertical or horizontal rope method. The benefits of using the horizontal rope method are that the seaweed can receive light evenly and can utilise space efficiently, resulting in higher yields.
In the vertical rope method, a seeded rope will hang vertically from the floating rope. The advantage of this method is the utilisation of vertical space. The disadvantages are that it is more work intensive and that the seaweed at the bottom receives hardly any light. Depending on the turbidity of a site the main ropes are installed up to 2 m beneath the water surface and will be adjusted during the grow out cycle, depending on the intensity of sunlight.
Undaria farms in Japan use the horizontal longline method, often with double long lines per anchor. In Sanriku, a line length of 100 – 150 metres is most common. In South Korea, horizontal raft type method is more common, however single lone line systems are used in some region like Gijang, where open ocean conditions prevail.
In Dalian, the main Undaria producing region in China, pretty much all farms use the horizontal raft type method. Each raft consists of 50 culture lines that are 8 m long and installed horizontally with 1.8 m intervals in between. Thus, each raft holds 400 m of culture lines in total.
In general the raft style methods, compared to the long lines, can achieve highest densities but are not very suitable for highly exposed locations.
Different anchors and floats
Since the substrate beneath the farms varies substantially from farm site to farm site, different types of anchors are used. In Dalian, China, wooden stakes are commonly used as anchors, since the substrate beneath the farms is mainly mud.
In South Korea, the government is trying to promote more environmentally friendly farm equipment. Especially the floats should all be replaced with proper buoys instead of styrofoam.