Traditional seaweed farming uses lines, ropes, nets or rafts, floating or suspended in the sea.   Young seaweed are seeded or attached to the substrate and left to grow for 6 to 8 weeks, depending on the species and location.   Generally seaweeds species grow very fast and can be cropped within a few months.

Line Culture

The shallow coral lagoons off the coast of East Africa and Zanzibar are host to multiple seaweed farms.  Traditionally this work is carried out by the women with their children swimming around them as they sit chest high in the sea, tying juvenile Euchema thallus to thin ropes supported at each end by small mangrove poles.   (The use of mangrove poles is known to put environmental pressure on mangroves near to seaweed farms)  

The alternative method used floats the seaweed just beneath the surface, allowing the farms to be in deeper water.   Although the seaweed seems to grow faster with this method the rope is thicker and more expensive and the seaweed cannot be harvest and cultivated on the beach.   These fast growing, carrageenan rich, seaweeds are cropped in 6 to 8 weeds, dried in the sun and then collected by the seaweed agent for either processing or shipping to a global market.   The main species cultivated are Eucheuma denticulatum (industrial name “Spinosum” and a source of iota carrageenan) and Kappaphycus alvarezii and K. striatum (industrial name “Cottonii” and a source of kappa carrageenan).   There is concern at present that the increase in temperature of the surrounding lagoon will slow growth rates and reduce crops.

Rope and Raft Cultures

Seaweed are also grown on vertical ropes and rafts, see the diagram below.   Because of the complex sexual behaviour of seaweeds the rearing of seedlings is a separate stage and involves complex processes.

Seedling Production - Laminaria Japonica

All seaweed cultivation relies on a source of seedling, and modern methods used in Japan and China can produce 800 million seedlings annually. After collecting the zoospores, the substrates with the attached spores are arranged in the greenhouse (hatchery). Because the gametophytes are autophytes, the breeding regime involves:

• Light intensity control and light periodicity adjustment by means of black and white roof-curtains.

• Seawater temperature control, adjusted by coolers.

• Fertilization with chemicals, normally nitrate and phosphate.

• Removal of miscellaneous algae.

• Strengthening the settling capacity of sporelings (young sporophytes).

• Controlling sporeling growth rate by temperature control.

All of this routine management is practiced in greenhouses from July to the end of October. When the seawater temperature in the farming site declines to 20 °C, the young seedlings, attached to substrates will be moved to nursing sites for further rearing into large seedlings for transplantation.

The rope length of each sporeling-curtain/substrate is about 50 m; there are about 8-10 seedlings per cm of rope. Hence, each sporeling-curtain has approximately 40 000-50 000 seedlings. Farmers estimate the quantity of the seedlings by the length of rope of each sporeling-curtain. The sporelings are reared in the nursing site until they reach 10-15 cm, when they are transplanted onto culture ropes. Farmers buy seedlings from seedling rearing stations/companies and nurse them to the size for transplantation. This is an Extract from the FAO Report Cited below.

Young seedlings attached to substrates (palm-fibre ropes

    Seaweed Farmers in Zanzibar

Ref:  Seaweed and monsoon rains: The Seaweed Africa workshop in Zanzibar  (Robert J. Anderson Seaweed Unit, Marine & Coastal Management, Dept. of Environmental Affairs & Tourism)



Floating Rope Culture in the Philippines SEAFDEC/AQD
(http://www.seafdec.org.ph/commodities/seaweed_farming.html)

Off bottom, Line Cultivation

Floating Line Cultivation

Handbook on Euchema Cultivation Methods in Fiji FAO South Pacific Aquaculture Development Project, Roberto Foscarini and Javant Prakash 1990

The production cycle used in China is shown in the figure below




FAO. © 2005-2009. - . Cultured Aquatic Species Information Programme. Text by Chen, J. In: FAO Fisheries and Aquaculture Department [online]. Rome. Updated 1 January 2004. [Cited 6 December 2009]
http://www.fao.org/fishery/culturedspecies/Laminaria_japonica/en


 

CRM - Costal Resource Management -Germany

Research and Marketing

A pilot plant for cultivation macro algae was build. Young brown algae of the species Laminaria saccharina nursed in the laboratory were cultivated in the Baltic Sea.

In parallel a market analysis analysed the potentials of Laminaria in different branches of production. A profile of market chances and patterns of utilisation was developed.

http://www.crm-online.de/crm_mambo_english/index.php/content/view/19/47/1/4/