Seaweed Aquaculture Methods and Strategies for Cultivation

Seaweed has been cultivated for thousands of years especially among Asian countries. Seaweed is mostly used for food but surprisingly has more uses than just sustenance. Large-scale seaweed productions range depending on the type of seaweed; both extensive and intensive methods can be used. There are both positives and negatives to large-scale seaweed cultivations. Positive being seaweed had to ability to essentially act as a biological filter; getting rid of inorganic and organic molecules. On the other hand, large amounts of seaweed can affect the overall quality of water. This includes the light intensity and slow water turbidity. Disease, like many other aquatic productions, is prevalent within the seaweed community but there are ways to combat that. In this essay on aquaculture the topic of Seaweed cultivation, goals, methods and other details are explored. 

Seaweed has been cultivated for thousands of years all across the world. In the past four hundred years, seaweed has been an important part of Asian cuisine more than any other country. Mariculture in Asian countries, such as Japan, China, Korea, and Vietnam, has reached the largest scale of production contributing 80% of the world seaweed biomass production. China is the largest producer with 60% of global seaweed production. There are several types of seaweeds produced in marine cultures. As reported by the Food and Agriculture Organization of the United Nations (FAO) in 2018, the most important farmed seaweed species is Eucheuma, followed by Japanese kelp.

Goals and Management Strategies

Seaweeds are mostly valued for food in mostly Asia which a growing demand in the Western countries like the United States of America. Seaweeds are cultivated extensively to aim for large yields with definite properties such as high content of polysaccharides and/or good taste. Seaweeds can also be used to produce animal feed, chemicals, paper, fertilizer, biofuel and other renewable products. A goal, like many aquaculture productions, is to develop improved sustainable methods to make commercial aquaculture, like large-scale seaweed, has minimal effects on the environment.

Because of the growing market of seaweed aquaculture, people have become more aware of the effects of such systems. Aquaculture productions have the potential to be a sustainable development. Ways to manage a sustainable development can include careful site selection, maintaining long-term health of coastal environment, and control of the species and density. With maintaining the coastal environment, the highest priority is to rebuild depleted resources and habitats. Policies and laws can easily ensure the restoration of such. To control seaweeds and the density of stock, a site in Hong Kong that good flushing and low initial stocking can be highly beneficial.

Culture Systems, Its Sources and Stages

The method to seaweed cultivated is species specific and is chosen according to the location of the farm and cultivation facilities. Most seaweed productions are grown extensively in natural waters using only natural light. Although, there are areas which culture seaweed intensively. For this paper, I will focus on large-scale commercial mariculture of seaweed.

Extensive Methods

Seabeds. Species of seaweed such as Gracilaria spp. are grown in seabeds in mostly Chile and Vietnam. In this way of cultivation, pieces of seaweed are anchored to the bottom for several months before the formation of reproduction organs. Seabed seaweed is usually cultivated in shallow bays that are protected from winds on sandy or muddy sand bottoms. In temperate waters, the algae grow most intensely in the spring and summer due to the dependency on temperature and concentration of nutrients.

Ropes. Seaweed can be cultivated on lines or ropes suspended from the surface of water. Plantlets are fixed onto the ropes which are tied to buoys or rafts. The duration of growth and harvesting is dependent on the species of seaweed. For example, U. pinnatifida in Japan is harvested after 3 months compared to S. japonica in China which is harvested after 10-20 months. Seaweed grown on ropes and lines depends on many factors, mostly on the hydrological and chemical conditions of the growing site. There must be a balanced ratio of nitrogen to phosphorus along with moderate currents and wave action.

Nets. Cultivation in nets are usually used on the species of Porphyra and Cladosiphon. Mesh size of nets are important to the culture of seaweed and can be adjusted depending on the external morphology of plants. The cultivations starts with the spore collection and then the spores are moved to nets. Which the spores grow, the nets are changed to a larger size until harvesting. Species cultivated in nets are usually harvested approximately three to four times a year.

Intensive Methods

Tanks. Started in the 1970s, tank cultivation produces a high yield compared to other methods. Seaweed grown in tanks are cultivated in order to purify effluents from cultivated animals. Tank cultivation requires high power inputs and use of expensive materials; it is usually too expensive for commercial-scale production. Amount yield is dependent on many factors such as the irradiation, light intensity, depth of tanks The density of seaweed grown within a tank can also affect the product yield.

Ponds. Species of seaweed can be cultivated on the bottom of ponds or suspended on ropes within a pond. Ponds can be supplied with seawater or a mix of seawater and river water. If nutrient content is low within a pond, fertilizers can be used. Gracilaria is largely cultivated in ponds in China and Vietnam. In these ponds, the depth ranges from 20-30 cm. Usually the product is harvested after 30-45 days.

Integrated Farming with Marine Organisms. Integrated farming implies the combined culturing of marine organisms along with seaweed. There are three methods within integrated farming: seaweeds are cultivated in ponds/tanks and received effluents from fish or invertebrates and seaweeds are grown in ponds together with fish, crustacean, and mollusks and seaweeds are cultivated near sea cages with animals. Using seaweed in polyculture is becoming more popular due to the seaweed’s ability to assimilate inorganic and organic nutrients in animals waste.

Environmental Issues and Related Diseases

Like all large-scale productions, many challenges are faced. First, seed quality is a large issue in the seaweed industry due to propagation techniques from a limited gene pool. To combat this, there has been talks about introducing non-native species, also known as invasive species, to mix up the gene pool. Invasive species can always have the potential to damage environments massively. Due to the possibly negative impacts, policies limit or completely resitch the use of non-native genotypes in seaweed aquaculture. On the other hand, seaweed culture has been shown to prove positive effects on the surround environment due to its ability to remove organic and inorganic wastes from the water, decreasing eutrophication. Although, large commercial cultures of seaweed can definitely cause harm to the surrounding environment. The greatest damage is done to shallow-water lagoons and small bays. Because of the shallow environment which lagoons and bays tend to be, large amounts of seaweed can decrease the light intensity, increase sedimentation, and even slower the water motion.

Disease always seems to find a way into production. Due to the result of farming intensification, there has been an increase in laver red rot and “chytrid” diseases. There has also been a decline in production of many carrageenophytes which is accredited to rising sea temperatures. The rising temperatures can cause the dreaded bleaching of the thallus which makes the seaweed more susceptible to disease. To treat this, chemical treatments may be used but can cause possible side effects on the product. Another disease that is somewhat common among seaweed farms is known as “ice-ice”. This affects seaweeds when they are in low light, slow water motion, or low concentrations of nutrients. The best way to resolve this disease is to simply move the seaweeds to another place with an optimal environment.

Conclusion

In conclusion, seaweed cultivation takes place in over 50 countries with the top producers being China, Indonesia, Japan, and the Republic of Korea. Importing seaweed is extremely important to these seaweed productions with China being the most important partner in international trade. Both edible and non-edible seaweed is exported from China with a value of more than $200 million USD in 2016. While China is the most important in trade, Japan produces essential seaweed to cuisine. Japanese wakame, nori, and kombu are heavily used in Japanese cuisine and are exported globally. Annual exports of seaweed from Japan have been valued at $200 million USD.

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