2.5.2.2 Sargassum
Sargassum is the most common brown macroalgae found in temperate, tropical,
and subtropical waters worldwide with more than 346 species (Guiry and Guiry
2015). Sargassum species have traditionally been utilized for food and medicine in
Asia. They continue to be wild harvested and cultivated in Japan, China and the
Republic of Korea, for human consumption as sea vegetables and for use as a
medicinal “seaweed herbs”. Locally known as the “black vegetable” in China,
Sargassum is valued for its high nutritional content and nutty flavor. It is added to
salads, soups or vegetable dishes (Xie et al. 2013). Sargassum is utilized in Chinese
medicine as an expectorant for bronchitis, and to treat laryngitis, hypertension,
infections, fever, and goiter (Hou and Jin 2005). Sargassum fusiforme (formally
“Hizikia fusiformis”) cultivation was initiated in the early 1980s. Thus, the production and economic value is still low, approximately 150,000 t of production
with an annual value of US $70 million in 2013 (FAO 2014). Nearly all Sargassum
production takes place in China, including several species such as S. thunbergii, S.
fulvellum, S. muticum, and S. horneri (Xie et al. 2013). In the Republic of Korea, S.
fusiforme and S. fulvellum are being cultured (Hwang et al. 2006).
Traditional culture methods initially relied on the use of wild seedlings collected
from natural beds. Groups of 3–4 seedlings, 5–10 cm in length, were inserted onto
seeding ropes at intervals of 5–10 cm. These smaller seeding lines were then
attached to a main longline placed at depths of 2–3 m, and cultivated from
November to May (Sohn 1998; Hwang et al. 2006; Redmond et al. 2014). This
dependency on wild seedlings resulted in the overharvesting of natural beds, so new
culture methods were developed. Holdfast-derived seeding was the first step
towards developing more efficient culture techniques for Sargassum. This type of
culture takes advantage of the perennial nature of the holdfast, allowing farmers to
reuse the holdfasts from the previous year’s crops (Hwang et al. 1998). While
plants may still be sourced from wild beds, the attached holdfasts can be re-used for
the next season’s crop by over-summering in the sea after harvest until the next
growing season. While this allows for reuse of existing cultured plants, the resulting
harvestable biomass tends to diminish after each year. Today, Sargassum lines are
seeded with juvenile plants obtained from reproductive adults. Obtaining seedlings
through sexual reproduction allows for mass production of new plants for seeding,
and results in higher biomass yields (Hwang et al. 2007; Peng et al. 2013; Redmond
et al. 2014). Fertilized eggs are gathered from mature fronds and “seeded” onto seed
string by allowing juveniles to attach to seed lines with newly forming rhizoids.
Once attached, seedlings are cultured in a nursery until ready for out-planting at sea,
where they are transferred to submerged long lines until harvest. The attached
holdfasts can also be re-used for multiple years without any further initiation of
culture ropes. This is an economically reasonable cultivation method, but there are
problems with fouling organisms. New technologies to reduce fouling problems are
in urgent need for the sustainability and growth of the Sargassum aquaculture
industry.
32
B.H. Buck et al.
Sargassum is the most common brown macroalgae found in temperate, tropical,
and subtropical waters worldwide with more than 346 species (Guiry and Guiry
2015). Sargassum species have traditionally been utilized for food and medicine in
Asia. They continue to be wild harvested and cultivated in Japan, China and the
Republic of Korea, for human consumption as sea vegetables and for use as a
medicinal “seaweed herbs”. Locally known as the “black vegetable” in China,
Sargassum is valued for its high nutritional content and nutty flavor. It is added to
salads, soups or vegetable dishes (Xie et al. 2013). Sargassum is utilized in Chinese
medicine as an expectorant for bronchitis, and to treat laryngitis, hypertension,
infections, fever, and goiter (Hou and Jin 2005). Sargassum fusiforme (formally
“Hizikia fusiformis”) cultivation was initiated in the early 1980s. Thus, the production and economic value is still low, approximately 150,000 t of production
with an annual value of US $70 million in 2013 (FAO 2014). Nearly all Sargassum
production takes place in China, including several species such as S. thunbergii, S.
fulvellum, S. muticum, and S. horneri (Xie et al. 2013). In the Republic of Korea, S.
fusiforme and S. fulvellum are being cultured (Hwang et al. 2006).
Traditional culture methods initially relied on the use of wild seedlings collected
from natural beds. Groups of 3–4 seedlings, 5–10 cm in length, were inserted onto
seeding ropes at intervals of 5–10 cm. These smaller seeding lines were then
attached to a main longline placed at depths of 2–3 m, and cultivated from
November to May (Sohn 1998; Hwang et al. 2006; Redmond et al. 2014). This
dependency on wild seedlings resulted in the overharvesting of natural beds, so new
culture methods were developed. Holdfast-derived seeding was the first step
towards developing more efficient culture techniques for Sargassum. This type of
culture takes advantage of the perennial nature of the holdfast, allowing farmers to
reuse the holdfasts from the previous year’s crops (Hwang et al. 1998). While
plants may still be sourced from wild beds, the attached holdfasts can be re-used for
the next season’s crop by over-summering in the sea after harvest until the next
growing season. While this allows for reuse of existing cultured plants, the resulting
harvestable biomass tends to diminish after each year. Today, Sargassum lines are
seeded with juvenile plants obtained from reproductive adults. Obtaining seedlings
through sexual reproduction allows for mass production of new plants for seeding,
and results in higher biomass yields (Hwang et al. 2007; Peng et al. 2013; Redmond
et al. 2014). Fertilized eggs are gathered from mature fronds and “seeded” onto seed
string by allowing juveniles to attach to seed lines with newly forming rhizoids.
Once attached, seedlings are cultured in a nursery until ready for out-planting at sea,
where they are transferred to submerged long lines until harvest. The attached
holdfasts can also be re-used for multiple years without any further initiation of
culture ropes. This is an economically reasonable cultivation method, but there are
problems with fouling organisms. New technologies to reduce fouling problems are
in urgent need for the sustainability and growth of the Sargassum aquaculture
industry.
32
B.H. Buck et al.