Enhancement of rooted algae on the rocky shore is an overarching practice to
manage and promote wildstock enhancement and marine ranching for commodity production
and ecological sustainability. Recently, natural fisheries resources are decreasing
in the coastal waters due to various reasons coming mainly from industrialization
near the shores. Construction of artificial seaweed beds is presently looked
into as a necessary factor for the recovery of natural resources. Seaweed bed
is an important part of the marine food web. There are many kinds of seaweeds
growing on the coast, forming a marine forest in coastal waters where they make
a good habitat and spawning grounds for a number of fisheries resources. Of
them, marine forests of Sargassum and Laminaria are of interest
The coastal line of Jeju island is 253km long. The coast has played an important
role in the fisheries economy of the area, producing lots of valued marine products.
Recently, however, sea walls for the coastal protection of the reclaimed land
have been constructed from the sea bottom at depths of more than 17m. As a result,
many seaweed beds have been reduced in areas. Coastal pollution accumulated
in last decades also caused the reduced natural products in the area.
Table 1. Areas of barren ground in Jeju island of Korea
Cooperate fishing area (ha)
Barren ground area (ha)
The currents of Kuroshio Extension
characterized by higher temperature and
malnutrition near Cheju (Jeju) island
|Barren ground on Intertidal zone in Jeju island
||Barren ground on subtidal zone in Jeju island
||Barren ground on subtidal zone in Jeju island
Factors influencing seaweed bed
Factors affecting seaweed beds are climate, water
temperature, nutrients, and grazing. The monsoon-generated waves and storm affect
to some extent the seaweed bed. On the coastal areas which show barrens in Korea,
resulted in the decline of fisheries resources
in these areas. Barren grounds are mainly due to the warm water from Kuroshio
Extension which is characterized by malnutrition.
Effects of grazing in seaweed beds
The activities of grazers affect the distribution and abundance
of the rooted brown algae. The influence of grazing generally changes abruptly
at the boundary between the intertidal and subtidal zones. Even on shores where
the abundance of herbivorous gastropods (such as limpets and trochids) is high,
their distribution tends to end at the zone of dense algae (normally fucoids)
found in the immediate subtidal area. Herbivorous gastropods are normally the
major grazing invertebrate. Herbivorous fishes may also affect the subtidal
1. Invertebrate grazers
Some herbivorous invertebrate organisms can graze heavily
on new fronds and broken-ends of old fronds of brown algae. Abalone and sea-stars
may have some small-scale effects upon algal abundance in Laminaria forests.
Small crustaceans may be very abundant in algal turfs and may be major grazers of algal spores, thus influencing recruitment in
the seaweed bed.
Sea urchins may have dramatic effects on kelp assemblages,
on most temperate shores, in both hemispheres. In areas where sea urchins are
abundant, their effects have been generally documented in three categories:
(1) whole-scale removal of algae; (2) the alteration of species
diversity via feeding preferences and selective removal of algal species;
(3) the provision of cleared primary substratum suitable for kelp recruitment.
It is commonly observed worldwide that dense aggregations of sea urchins may
remove large tracts of algae, creating barren ground.
2. Effects of fish grazers
A recent study suggested that fishes, particularly
the halfmoon (Medialuma californiensis) and opaleye (Girella nigricans) can
be important grazers on small algal spores. These fishes seasonally appear in
seaweed beds. Opaleye are grazers on the fronds of Laminaria in autumm.
Rabbitfishes are notorious herbivores in the Eucheuma farming areas of the Philippines.
Methods for the construction of artificial seaweed beds
Techniques developed for the construction of artificial
seaweed beds can be classified into 2 general types: 1) a spore technique, and
2) a vegetative transplanting technique. The following techniques may fall under
either of the above classifications:
1. Spore dispersal technique as used for Macrocystis (North,
Techniques have been developed for raising Macrocystis
plants in mass cultures, from liberated zoospores, via the gametophyte, to the
embryonic sporophyte. The zoospores are allowed to settle on various substrata
which are then placed in flowing seawater under continuous
illumination. The gametophyte phase requires 10-20 days to reach sexual maturity
and another 5-20 days are allowed for development of embryonic sporophyte stages.
Cultures then are scraped·free from their substrata and dispersed close
to the bottom in coastal areas suitable for kelp growth. The embryonic, microscopic
plants are able to reattach at this stage, if the sites are fairly calm. Preliminary
estimates indicate that about 10s embryos must dispersed to yield a single,
attached, identifiable Macrocystis juvenile about 15 cm tall. Mass culture systems,
however, can produce very large numbers of embryos (upto 105-106 embryos.cm-2
of culture substratum). Consequently, the low survival rates following dispersal
do not preclude the practical application of this system as a means to enhance
the development of new stands of kelp in the sea.
2. The spore-bag technique
Mesh-bags ("spore-bags") packed with fertile,
adult plants have proven to be a successful method for the establishment of
Sargassum beds The spore-bags are usually suspended over rocky
substrata or artificial reefs during the reproductive season. During this time,
spores are released naturally and eventually settle on the hard bottom surface.
The distance of settlement and establishment, from the site of the spore bag
depends on prevailing water currents. From previous experience, this Is usually
less than 40 m. Young Sargassum plants become noticeable on the natural or artificial
substrata, as the case may be, after a few months.
The spore bag method of establishing a seaweed population.
3. Rope-seeding technique
Fertile thalli of
Laminaria may be allowed to sporulate in indoor tanks. Once ropes are seeded, the seeded ropes are then firmly attached to concrete blocks for growing.
4. Adult-plant transplantation method
The transplantation of adult plants of Ecklonia and
Laminaria has been undertaken by fishermen for many years. This practice was initiated when natural recruitment was poor as a result of the barren-grounds (caused by excessive sea urchin grazing). Recently, this method of algal transplantation was improved by fishery scientists in Korea, making the construction of seaweed beds a little easier. There are various modifications of this technique depending on the species.
Adult-plant transplantation of Laminaria and defence of herbivore.
5. Concrete blocks
Ecklonia can be carried out in September to December, at the time when seawater temperature is optimal for growth. One or two adult individuals can be attached to concrete blocks with strong rubber bands or ropes. In some cases, to increase the area of the attachment surface, the concrete blocks may be covered with coils of plastic material. Whichever case is used the plants are then covered with plastic sheets or placed in large cages for protection against fish grazing. The holdfasts of
Ecklonia were found to attach to the blocks after one month of growth.
New blades of adult plants of
Ecklonia appear in late December and become young plants in early January. In May, new beds of
Ecklonia will be formed around the blocks. A transplanted area of 9 m
3 can be expected to form a new
Ecklonia bed of about 3000 m2 area.
Although many plants may gradually disappear (due to grazing and wave action during summer), surviving plants begin to form spores until the end of August. Thereafter. a new community of
Ecklonia can be expected to become established on the same rocks. within an area of approximately 400 m
2, in March of the following year.
Transplantation, by attachment of adult plants on concrete blocks, has proven to be a most effective method of establishing new algal beds in Korea.
Various concrete blocks for construction of seaweed
6. The "threading technique" as used for
This method is used in California, USA. Several
Macrocystis plants can be threaded, at intervals by means of a rope passed through their holdfasts. After threading onto the rope, the plants can be moved to the site for transplantation by boat. The
plants can then be moored by means of anchors and buoys until they start to gain permanent hold on the substratum.
7 "Gravel-bag" technique used for Macrocystis transplantation
A more elaborate method of attaching
Macrocystis to an artificial substratum was devised by larger and Neushul (1983) . Nylon mesh-bags are filled with coarse gravel (3 cm diameter) and their rims are drawn around the holdfast of the plant. Once transplanted, the bags gradually accumulate sand and sediments thereby increasing stability. Eventually the kelp haptera grow out of the bag and down to the sandy bottom.
About 50 kg of coarse-gravel can be used for the anchor, which underwater, will weigh approximately 28 kg. Several plant bags can then be anchored to a grid of chain and rope to an optimum stocking density. Maximum stocking density of a
Macrocystis artificial bed was determined by larger and Neushul (1983) to produce a higher biomass if fertilized with ammonium sulphate (less than optimum density dissipates the fertilizer before it can be absorbed by the plants) .
8. Transplantation of young plants
Young plants, particularly of
Undaria, can be anchored using concrete blocks or ropes as substrata. The substrata with attached young plants are transplanted on the bottom of rocks or artificial reefs after they are seeded.
Young plants transplantation of Ecklonia.
Subjects for the future
The possibility of management-free seaweed bed restoration by reducing local limiting factors, e.g. by rasing bottom and improving substrata for seaweeds at actual sites, has been suggested.
In the future, it is supposed that the transparency in coastal water will decrease due to the continuous water pollution of coastal areas, and the distribution of new natural and artificial seaweed beds will be limited on many coasts by such factors. Therefore, it is indispensable to improve water quality to ensure the high transparency of coastal waters.
Marine forest enhancement on east coast of Korean Peninsula
1. Whitening area (barren area) on eastern coasts of Korean peninsula
2. Artificial reefs for rooted seaweed attachment
3. Slags and stones for the seaweed habitation
Laminaria japonica seeded on the artificial reefs
Costaria costata grown on the reefs
Undaria pinnatifida enhanced in the whitening area
Sargassum horneri forest enhanced in the previously whitened area
8. Eisenia bucyclis forest
9. Management of marine forest enhanced
10. Young seaweeds growing on the artificial reefs
11. Total recovery from the whitening