JAPANESE STYLE NORI
a new plant for aquaculture?
BY DR MICHAEL MORRIS
Nori is sold in sheets, typically 10 to a pack
Source: Copyright Michael Morris
Fig. 1: The life
cycle of Porphyra species
Source: Copyright Michael Morris
he Japanese have a culinary tradition of edible seaweeds
dating back hundreds of years. One of the more
ubiquitous of these is the dried sheets of nori made
from the red algae Porphyra yezonensis or P. tenera. Nori is
a common sight in Japanese bento lunch boxes, wrapped
around sushi or onigiri – filled rice balls. With the increasing
popularity of Japanese food worldwide, the demand for nori
is growing.
The lifecycle of nori, like that of most algae, is incredibly
complex and involves alternation of generations.
The seaweed actually exists as two separate forms. The
part that is harvested, dried and eaten is a long thin leaf-like
structure called the thallus and typical of most seaweeds. It
produces the gametes (sperm and egg cells) in specialised
parts of the thallus, the spermatia and carpogonia respectively.
The sperm cells are released and drift to the carpogonia, where
they are fertilised. Once fertilisation has taken place, special
spores called carpospores are released from the carpogonia.
The carpospores do not grow directly into a new thallus, but
into a microscopic filamentous plant called the conchocelis,
that grows by boring inside shells. The conchocelis filaments
produce visible conchosporangia on the shell surface and
these release conchospores, which grow into a new thallus.
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The thallus can also grow asexually through a different type
of spore, a monospore, that grows directly into a new thallus.
Until 1949 it was thought that the filamentous conchocelis
was a totally different species. Once it became known
that this was part of the Porphyra life cycle, commercial
production of nori became easier, because the conchocelis
could be grown in the laboratory on crushed shells and the
conchospores could be seeded onto nets when they were
released. These nets are then placed in the open ocean to
grow the thallus forms, which are then harvested.
In Japan, nori is produced by fisheries co-operatives
under licence from prefectural governors, who in turn
have delegated authority from the Ministry of Agriculture,
Forestry and Fisheries. It is an unusual arrangement in that
no commercial companies are involved.
Nori would lend itself well to production in New
Zealand for several reasons. Firstly, there are a number of
Porphyra species native to New Zealand. These are called
kerengo in Maori and have traditionally been harvested
by southern iwi. The life cycle and taxonomy of New
Zealand kerengo is still not known with any certainty, but
research is underway at the National Institute of Water and
Atmospheric Research to clarify the life cycle and to find
culture methods.
Porphyra grows well in
nutrient rich (eutrophic)
water, so it would be
suitable in New Zealand
where some coastal areas
have become polluted
from effluent and farm
waste running from fresh
water bodies into harbours
and estuaries. Porphyra
cultures could even help
to clean up the waterways
by absorbing the nutrients.
Since the conchocelis is
grown indoors on crushed
Vegetarian sushi, wrapped
shell, this could provide
in nori. Source: Wikicommons
