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Algae and Men 267

sporophyte. Spores collected from the sporophytes are stored during the summer and used for
seeding nets in fall. When young sporophytes have grown to 2–5 cm, the nets are moved to the
main cultivation sites. The fronds are harvested after about 90 days, when they have grown to
50 cm. Harvesting is done by divers using a suction pump that draws the macroalgae up and
into a floating basket besides the attending boat. The harvested macroalgae are washed, salted
with 20–25% salt, and let to dehydrate for about 15 days. Drained fronds are sold in wet, salted
form in packages.

Chlorophyta
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.
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 approxi-
mately 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

FIGURE 7.9 Frond of Monostroma latissimum.