Algae and Men
  Sources and Uses of Commercial Algae
    - Food
      - Cyanophyta
      - Rhodophyta 
      - Heterokontophyta
      - Chlorophyta
    - Extracts 
      - Agar
      - Alginate 
      - Carrageenan
    - Animal Feed
    - Fertilizers 
    - Cosmetics 
    - Therapeutic Supplements 
    - Toxin

Monostroma (Figure 7.9) and Enteromorpha (Figure 7.10) are the two green macroalgae genera cultivated in Japan, and known as aonori or green laver.

Frond of Monostroma latissimum
FIGURE 7.9 Frond of Monostroma latissimum.
Frond of Enteromorpha sp.
FIGURE 7.10 Frond of Enteromorpha sp.

Monostroma latissimum occurs naturally in the bays and gulfs of southern areas of Japan, usually in the upper eulittoral zone. The fronds are bright green in color, flat and leafy, consisting of a single cell layer. They are slender at the holdfast and growing wider toward the apex, often with a slight funnel shape that has splits down the side. Monostroma reproduces seasonally, usually during tropical dry season or temperate spring. It is found in shallow sea water usually less than 1 m in depth; generally grows on rocks, coral, mollusk shells, or other hard substrates, but also grows as an epiphyte on sea plants including crops such as Kappaphycus and Eucheuma. It averages 20% protein and has a useful vitamin and mineral content. It has a life cycle involving an alternation of generations, one generation being the familiar leafy plant, the other microscopic and approximately spherical. It is this latter generation that releases spores that germinate into the leafy frond. For cultivation, these spores are collected on rope nets by submerging the nets in areas where natural Monostroma populations grow. The seeded nets are then placed in the bay or estuary, fixed to poles so that they are under water at high tide and exposed for about 4 h at low tide, or using floating rafts in deeper water. The nets are harvested every 3–4 weeks and the growing season allows about three to four harvests. The harvested macroalga is washed well in seawater and freshwater. It can then either be processed into sheets and dried, for sale in shops, or dried, either outside or in dryers, and then boiled with sugar, soy sauce, and other ingredients to make “nori-jam.”

Enteromorpha prolifera and Enteromorpha intestinalis are found in bays and river mouths around Japan, and are also found in many other parts of the world, including Europe, North America, and Hawaii. Fronds usually flat, narrow, and bright green in color can be seen waving gently with water movement. They can be attached to firm substrate in clear, shallow waters, and also occur as epiphyte on cultured red seaweeds such as Kappaphycus, Eucheuma, Gracilaria, Gelidiella, and others.

It can thrive in both salt and brackish waters and is usually found at the top of the sublittoral zone. It contains about 20% protein, little fat, low sodium, and high iron and calcium. Its vitamin B-group content is generally higher than most vegetables, and while its vitamin A is high, it is only half of that found in spinach. Its life history involves an alternation of generations with the same appearance of long, tubular filaments. As for Monostroma, rope nets are seeded with spores by submerging them in areas where Enteromorpha is growing naturally.

In the Republic of Korea, seed collection is from June to August and the strings or ropes are taken to culture sites in September; in Japan, seeding is done in September, and by early November young plants are visible. The nets are placed in calm bays or estuaries using either fixed poles in shallow waters or floating rafts in deeper waters. Harvesting can be done two to three times during the growing period, either by hand picking from the nets or by machine. Harvested fronds are washed in freshwater and dried in large trays.

Ulva sp. is known as sea lettuce, as fronds may be convoluted and have an appearance rather like lettuce. It can be collected from the wild and added to Monostroma and Enteromorpha as part of aonori. It has a higher protein content than the other two, but much lower vitamin content, except for niacin, which is double that of Enteromorpha. Bright green in color, it has a double or multiple cell layer. Slender at the holdfast and growing wider toward the apex, it reproduces seasonally, usually during tropical dry season or temperate spring. It is naturally found in shallow sea water usually less than 1 m in depth, where it grows on rocks, coral, mollusk shells, or other hard substrate, but also as an epiphyte on other sea macroalgae. It was used as flavoring with other seaweed by Kashaya Pomo natives of northern California.

Caulerpa lentillifera (Figure 7.11) and Caulerpa racemosa are the two edible green algae used in fresh salads and known as sea grapes or green caviar. As the common name suggests, their appearance looks like bunches of green grapes. These algae often produce “runners” under the substrate, which can produce several vertical branches that extend above the substrate. They naturally grow on sandy or muddy bottom in shallow protected waters.

Frond of Caulerpa lentillifera.
FIGURE 7.11 Frond of Caulerpa lentillifera.

Caulerpa lentillifera has been very successfully cultivated in enclosures similar to prawn ponds in the central Philippines, where about 400 ha of ponds are under cultivation, producing 12–15 tons of fresh macroalgae per hectare per year. Water temperature can range between 25 and 30°C. Pond depth should be about 0.5 m and areas of about 0.5 ha are usual. Also some strains of C. racemosa give good yields under pond cultivation conditions.

Planting is done by hand; about 100 g lots are pushed into the soft bottom at 0.5–1 m intervals. Harvesting can commence about 2 months after the first planting; fronds are pulled out of the muddy bottom, but about 25% of the plants are left as seed for the next harvest. Depending on growth rates, harvesting can then be done every 2 weeks. The harvested plants are washed thoroughly in seawater to remove all sand and mud, then sorted and placed in 100–200 g packages; these will stay fresh for 7 days if chilled and kept moist.

Table 7.5 summarizes edible algae and the corresponding food item.