Well-BeingSafeguarding the fine taste of nori (seaweed) produced in Ariake

Nori (seaweed) is one of Japan's signature foods. The most productive cultivation area is the Ariake Sea, in the country's southwest, famed for its umami-rich, melt-in-the-mouth nori. Fukuoka Fisheries and Marine Technology Research Center Ariake Regional Laboratory, which supports experiments, research and aquaculture activities throughout the Ariake Sea, uses Nikon's fluorescence microscopes to monitor nori growth and the surrounding environment.

Safeguarding the fine taste of nori (seaweed) produced in Ariakes
- Nikon's microscopes play a key role -

This movie features an interview with Yusuke Yasukouchi, Nori Aquaculture Chief Engineer, Ariake Sea Laboratory at the Fukuoka Fisheries and Marine Technology Research Center, explaining how the most delicious nori is cultured, and the role that Nikon microscopes play in helping to achieve this.

What makes Ariake nori so tasty?

Nori plays an essential role in Japanese cuisine, used for rice balls, sushi, rice cakes and more. It has been eaten since the Jomon period of Japanese prehistory, and was later listed as a taxable item in a law issued in AD 701.
People outside Japan used to turn their noses up at it, saying it looked like carbon paper sheets when dried. However, numbers of its fans have been increasing recently around the world, thanks to the growing popularity of Japanese food such as sushi. It probably helps that it is so good for you: healthily rich in protein, dietary fiber, vitamins, calcium, omega-3, amino acids, and much more besides.

But what exactly is nori? In a broad sense, the word refers to all mossy seaweeds that attach to surfaces such as rocks and trees in the water. Its name is said to come from the Japanese word nura, which means something slimy. The familiar thin, dried nori sheets are made from seaweeds such as Pyropia yezoensis and laver, which are filtered and dried much like paper. Most are currently produced through aquaculture, to the tune of approximately 8 billion sheets across Japan every year.
Nori is produced all over Japan, but more than half of it actually comes from the Ariake Sea (which encompasses Saga, Fukuoka and Kumamoto prefectures). What makes the Ariake Sea so special?

Average production from 2013-2017

The answer lies in its environmental features. The Ariake Sea is an elongated bag-shaped bay, covering approx. 1,738 km2, with a vast tideland that has developed in the shallow waters. Many rivers including the Chikugo River flow into it, bringing the rich nutrient salts (such as nitrogen and phosphorus) that are necessary for nori to grow. Moreover, since there is a difference of up to 6 meters between high and low tide, the tidal current is fast, which enables the seaweed to absorb nutrient salts more easily. These unique conditions in the Ariake Sea make this area particularly suitable for aquaculture.
As Yusuke Yasukouchi from the Fukuoka Fisheries and Marine Technology Research Center tells us, using aquaculture methods that utilize these tidelands helps nurture the delicious flavor of nori from the Ariake Sea.
"The taste of nori is determined not by the amount of amino acids it contains (the umami components), but by how much it releases when it is eaten. The melt-in-the-mouth quality of nori from the Ariake Sea means that it releases amino acids quickly when put on the tongue, and that's what makes it taste so immediately delicious. 'Pole-system aquaculture' is used in the shallow waters of the Ariake Sea, which involves stretching nets between poles planted in the seabed. This method leaves the nets exposed above water at low tide, when we say they are 'dried out,' and that's believed to be connected to the good mouthfeel of the nori."

Fukuoka Fisheries and Marine Technology Research Center Ariake Regional Laboratory, Nori Aquaculture Chief Engineer
Yusuke Yasukouchi
Pole-system aquaculture in the Ariake Sea, Fukuoka (at high tide)
The nori-laden nets are completely exposed at low tide (dried out)

Microscopes play an important role in keeping nori flavorful.

Mr. Yasukouchi belongs to the Nori Aquaculture Department at the Fukuoka Fisheries and Marine Technology Research Center Ariake Regional Laboratory. He and his colleagues regularly monitor the nutrient salts and diseases in aquaculture areas, and provide this information to nori cultivators. They also conduct experiments and research to ensure stable production, such as development of aquaculture techniques and varieties, countermeasures for disease, and research into cultivation environments. And it's in these key areas that Nikon's microscopes come into play.
Nori aquaculture processes can be broadly divided into two categories: what happens before seedings (attaching shell spores to nets), and what comes after. Nikon microscopes are used in both processes.

Fukuoka Fisheries and Marine Technology Research Center Ariake Regional Laboratory
Nori aquaculture in the Ariake Sea

In the pre-seeding process from spring to autumn, oyster shells are used to grow conchocelis filaments that bear conchospores, the seeds of nori. This involves shredding moss ball-like free-living filaments and seeding them in oyster shells placed in water tanks. They are kept in this condition during the summer, maturing until the day before seedings.

Free-living filaments (shown in microscopic close-up in the right-hand image)

"The first time I use a microscope is about two weeks after the free-living filaments are seeded, when I measure how many filaments are rooted into the oyster shells and what the density is. The second time is during the summer, when I observe the quantity of spores the concochelis have produced. Then in autumn, I use a microscope again to confirm the maturity of the spores."
Once the mature spores are seeded on nets, the focus of the action moves to the sea.
"After seedings, we cut a part of the seaweed net, and use microscopes to confirm how much the spores have actually settled. From September to March, seawater is also collected at 19 survey points and inspected for water quality, nutrient salt content, and for both the types and amount of phytoplanktons that compete with nori. We also check for diseases of nori during aquaculture, and fluorescence microscopes are essential during all of these processes. The research results are provided to fishing unions and nori cultivators via the Fukuoka Ariake Federations of Fishery Cooperatives."

Phytoplanktons that compete with nori

Phytoplanktons absorb nutrient salts, which has an effect on nori aquaculture.
Left: Coscinodiscus. Right: Eucampia.

Nori diseases

Red rot disease
Caused by fungal infection. The fungus is vulnerable to dryness, so it can be countered by drying out nori. Cultivators are instructed on the appropriate net height according to the tide level.
Chytridium fungi disease
Caused by chytridiomycete infestation. It can be countered by harvesting as soon as possible.

Ensuring consistent quality and stable production in the future.

Mr. Yasukouchi and his team do more than just provide information. Each fishery/aquaculture cooperative owns microscopes, as do individual nori cultivators. Every year, Mr. Yasukouchi and his team hold a two-day training workshop on microscope techniques, so that everyone can use them without problems.
"About ten people participate in the seminar every year and study the most effective ways to utilize microscopes, and we've had very positive feedback."
They have also been conducting research with the aim of increasing the number of asari clams, which are an important fishery target species in the Fukuoka area of the Ariake Sea. Asari clams also play an important role in the development of nori: they consume the phytoplanktons that compete with it, while excreting the nutrient salts that the seaweed requires.
"Nori aquaculture is highly weather dependent, so naturally we care about climate change. Utilizing microscopes, we are supporting aquaculture to ensure that nori can be stably cultivated into the future. Thanks to the recent Japanese food boom, nori is now also becoming better known around the world. I would like for as many people as possible, both inside and outside Japan, to experience the rich particularly flavor of Ariake nori."
Nikon's fluorescence microscopes support the ongoing research that is helping to ensure the high quality and stable production of nori. And Nikon will continue to contribute through its businesses to the various work that will keep nori tasting mouthwateringly delicious.