Depending on the type of seaweed, the reproduction process differs and therefore the complexity of obtaining seed material does as well. The seeding method is the process of bringing the seed material on to the line used for grow out. The method for attaching these seeded lines to the farm site is called deploying.
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The introduction of artificial seeding methods based on the cultivation of spores (seeds) in a land-based tank allowed for large scale production of seed material and thus the scaling of commercial Pyropia farming.
Compared to other commercially cultivated seaweed species, the lifecycle of Pyropia is fairly complex. The seed production stage is a complex process with several steps that are carried out in land-based hatcheries, where from February till September the conchocelis stage takes place and conchospores are produced.
In South Korea there are more than 160 specialised companies producing the material for Pyropia seeding (data from the Korea Maritime Institute, 2019). This is made up of oyster shell bearing conchocelis and sold in boxes to the farmers.
In Japan, this process is either done by government run regional seed centres or the farmers’ cooperatives themselves.
In China, (Jiantsu and Shandong region) large farming companies typically operate their own hatcheries. In the South, Fujian, where smaller farms dominate, this process is done by external seed companies.
The actual seeding of Pyropia takes place between September and October, where the artificially cultivated Pyropia spores are attached to the cultivation nets using different methods, either indoors or outdoors.
The indoor seeding method uses a large wheel that rotates cultivation nets through the spore tank, so the spores can attach on the net substrate.
In the outdoor method, the nets together with the seed material are placed in large plastic bags and moved out to sea. This method is much more weather dependent and uncontrolled, however it requires much less land-based infrastructure and is therefore more widely practiced.
In a nursery location at sea, the grow out nets will be placed for 2-3 weeks to grow the Pyropia ‘leaves’ up to 5 mm and then relocated to the dedicated farm site. A similar nursery stage can also be carried out on land in a concrete basin with seawater, which requires a lot of space.
Another common method is to freeze the seeded nets at -20°C to deploy them at sea again at a later stage (even after several months). This not only extends the season, but also reduces the risk of diseases and is said to improve the quality of the final product.