Since the 1970s Japan has produced billions of nori sheets a year at a market value exceeding one billion dollars. The development of this technology stems from the work of Kathleen Drew-Backer, a British scientist who found a ‘missing link’ in the life cycle of nori, a red alga (Rhodophyta, Porphyra spp). She discovered the ‘conchocelis stage’, a filamentous diploid generation that grows on oyster shells (see Photo 1). It is the conchocelis stage that produces the spores (conchospores) that grow into nori.
The discovery of the conchocelis stage enabled nori farmers to culture this stage and use it to ‘seed’ their nets**. Nearly all the nori grown today in Japan is susabinori (Porphyra yezoensis); it tolerates warmer waters, and waters less than pristine. Additional advances in nori culture include the floating net system, freezing nets so that nori can be grown over a longer season, and the development of the ‘One Man’ machine to process nori into sheets.
To learn more about nori mariculture (sea farming), Reiko and I visited the nori farmers of Bouze Island last fall and winter to observe three main steps: ‘seeding’ the nori nets, first stage of cultivation in the ocean, and the eventual harvest. This May, we visited the Awaji Nori Center and its Nori Kenkyusho (nori research center). It is here where the conchocelis stage is cultured. This stock is used by the nori farmers of Hyogo Prefecture, including the farmers of Bouze Island. It is here that I will begin the modern story.
Culture of the Conchocelis-Stage
The Awaji Nori Center lies on the northwest cost of Awajishima (Awaji Island), on the eastern shore of the Seto Naikai (Japan’s Inland Sea). Yoshimi Konishi, Chief of Research at the center, oversees the production of the conchocelis stage. His facility has supplied the conchocelis stage to the farmers of Hyogo Prefecture for forty years. He continues to search for new varieties of nori while at the same time maintaining strains developed decades ago (see Photo 2).
The process begins with the collection of nori in February and March. Prior to this time, nori undergoes sexual reproduction to produce a microscopic carposporophyte generation. Carposporophytes develop within the sheets of living nori, the ‘gametophyte’ generation (see Life Cycle, Photo 1). The collected nori with carposporophytes is kept in glass jars. Carposporophytes release carpospores, which develop into the conchocelis stage: small filaments a few centimeters in length. The filaments are separated from the nori and carposporophytes, and stored in flasks under refrigeration (see Photo 3). As they grow, each culture will be split into two, to create clones. Each of these two cultures will be split into two, etc. to create large numbers of free-living conchocelis filaments. While new material is harvested every year, most of the conchocelis filaments used to make nori come from well-established clones; some are 20 years old. Farmers prefer known strains that grow well in their local waters.
In nature, the conchocelis stage attaches to oyster shells and other substrate. From December to March, the Awaji Nori Center inoculates oyster shells with the free-living conchocelis filaments. They buy oyster shells from Miyagi Prefecture, famous for the number and quality of its oysters. Only the lower shell is used; it is relatively flat, which provides an even exposure to sunlight. Two holes are drilled into each shell, and pairs of shells are tied back-to-back with their inner shells exposed. Five pairs of shells are then tied together, with a loop tied at each end of the string to suspend the shells in the water. Periodically, the oysters will be turned upside down to ensure each shell receives adequate light (see Photo 4).
Before inoculation, staff at the center use a blender to chop free-living filaments into 0.4 mm lengths. Next, they place oyster shells on the bottom of a tub, covered by approximately 15 cm (6 inches) of seawater, and spray the chopped filaments over the shells. Over the next few days, the shells will be examined to ensure that the filaments have attached to the oysters. This year, it took 9-10 days to verify successful inoculation (normal range 5-14 days). Rarely, they spray the shells a second time with more filaments. Finally, they suspend the strings of shells from rods that rest on the top of tubs, and fill the tubs with seawater to a depth of approximately 50 cm (1.5 feet; see Photos 5 & 6).
Each tub supports 20 bars, with 13 strings of oysters per bar, and ten oysters per string, a total of 2,600 oysters per tub. Currently, the facility has 325 tubs, for a grand total of 845,000 oysters (see Photo 7).
The center uses water from the Seto Naikai (Inland Sea), passed through a sand filter and treated with chlorine, to grow the conchocelis stage. They add nutrients to the water as well: sodium, phosphorous, iron and magnesium. Despite the many oyster shells, the conchocelis filaments themselves are quite small, and do not need much care. An air stone is turned on for only 10-30 minutes per day in each tub and the water is changed only twice until September, when they are ready for sale. Sunlight comes through the roof of corrugated fiberglass, regulated by a mechanized system of curtains (see Photo 8).
Temperatures in the summer reach 27-28oC (80.6-82.4oF). The conchocelis filaments grow well in these conditions. However, the purpose of raising these filaments is for their conchospores, the ‘seeds’ that will grow into nori. To stimulate the release of conchospores in September, they reduce the temperature to 17oC (62.6oF).
The Awaji Nori Center is owned by the Hyogo-ken Gyogyou Kyoudou Kumiai Rengoukai (Hyogo Prefecture Fisheries Co-operative). Hyogo has the second highest production of nori in Japan (Ariake Prefecture, on Kyuushuu Island, is the leading producer). Many of the oysters remain on Awajishima to seed the nets of local nori farmers (see Photo 9). Other farmers buy the oysters and bring them to their home facility before they ‘shock’ the oysters to seed their nets. Last September, we watched the seeding of nets in Bouze Island.
‘Seeding’ Nori Nets
Bouze Island lies in the Seto Naikai, a 25-minute boat ride from the Port of Himeji. Bouze Island and its three neighbor islands are included within Himeji City (Phoenix’s sister city). Bouze Island’s Fishermen’s Association separated from the other islands in 1989. It is the largest association in Hyogo Prefecture with 500 members, and one of the most productive. They have owned their own nori seeding facility for 30 years: Saibyojyo (collecting seed place); it was upgraded with the latest equipment 10 years ago (Photo 10).
We visited the facility on the afternoon of September 26, 2011, the second day of seeding. Seeding was already done for the day, but Mr. Katsura, Director of Saibyojyo, gave us a tour of his facility. He was very gracious, especially considering that his crew started work at dawn and seeded 2,800 nets that day. As we toured the facility, he described the main steps in the seeding process (see Photo 11).
In Hyogo Prefecture, nori is grown on standard-sized nets, approximately 1.6 m wide x 20 m long (5’2.5” x 67’; the actual measures are in traditional Japanese units). They store hundreds of these nets in a shed (Photo 12). Each nori farmer is responsible for cleaning the nets they use. The association has a machine to clean them, available to each of the farmers. Nets can be used a second year; older nets are re-purposed (e.g. to protect crops from birds).
Mr. Katsura took his boat to the Awaji Nori Center the previous week to pick up their order of 50,000 oysters covered in conchocelis-stage nori. They use a special strain, Kousuion (‘high water temperature’) that grows well in warmer waters and allows for growth earlier in the fall (see Photo 13). They chill the conchocelis-stage nori to 19.5OC (67.1OF) to stimulate sporulation, the release of conchospores (the ‘seed’). By comparison, the ocean surrounding Bouze was 24-25OC that day (75.2-77OF).
Mr. Katsura told us we could not really understand tanesuke (the process of seeding), until we saw it the next morning (we had to see it to believe it). Briefly, a few rods of oyster shells with conchocelis-stage filaments are placed into a tub below a large roller. Women wrap 16 sets of five (5) nets each (a total of 80 nets) around the roller, and spin it in the tub with oysters. The spinning agitates the water, which stimulates sporulation – the release of conchospores; the spores become attached to the net (i.e. the nets become ‘seeded’). After a few minutes of spinning, runners cut a sample from the outer net. The sample is brought to Mr. Katsura’s office, where he and his colleague inspect samples for spores (Photos 14-16). If enough spores are found, he will order the removal of the outer layer of nets.
Once the nets have been seeded, they are pulled off the wheel into long receiving tubs. They will remain there through the early morning, allowing the spores to become well attached. Later, the nets are hung on racks for drying. Finally, the nets are placed in plastic bags and boxed up for the freezer. Seeded nets will kept frozen (-30OC) for the next month before being placed into the sea (Photos 17-19). Freezing preserves the spores for at least two years, and inhibits other organisms from growing on the nets. We thanked him and prepared for our return at dawn (Photo 20).
We arrived at the seeding facility just after 6:00 AM. A crew of 34 women had nearly finished stringing nets onto ten rollers. While the last few nets were being added, the crew moved drying racks out of the way and prepared nets for the second round of seeding. By 6:15, the rollers had begun to spin their nets into the tub below. A few bars of oysters with conchocelis-stage nori were suspended within each tub. The spinning of the roller agitated the water, which stimulated the release of the conchospores (‘seeds’; see Photos 21-26). Three runners stood by ready to sample the nets.
Mr. Katsura, the Director, called out to his runners, ‘‘Jyuu ban, kyuu ban” (‘number 10, number 9’) telling his runners to sample the outer net of these rollers. The runners ran to the rollers, cut a sample, and ran it back to the office (see Photo 27). Mr. Katsura and his colleague took the net samples, twisted them to separate the fibers, and inspected them under their microscopes (Photo 28).
Katsura-san quickly called out, “Kyuu ban, jyuu ban, jyuu mai” (‘number nine and number ten, 10 nets’), telling his crew to remove the outer ten nets from rollers 9 and 10. It took 50 seconds from the time he requested the sample to his order to pull the nets. Women ran to the rollers, untied the nets, turned on the roller again to unspool them, and pulled the nets into their receiving tub. The first set of nets had been seeded and removed from the rollers after 35 minutes (see Photos 29-31 and Video 1).
As each wheel was emptied, two-woman teams rapidly reloaded it (about 10 minutes) and started it spinning (see Photo 32). Whereas the first batch of nets took 30-35 minutes for seeding, subsequent nets seeded more rapidly (10-15 minutes). The first nets had to stimulate the process of sporulation. Once started, sporulation continued as long as the rollers were spinning.
The oysters/conchocelis-stage nori that had been in use from the first day of seeding was still in use this morning. Shortly after 7:00 AM, however, the runners began to add new oysters/conchocelis-stage nori to the tubs (Photo 33). They left the older material in the tubs; it can be used for up to five days.
The crew works from 6:00 AM to noon. By 7:15 AM, the third round of nets were being seeded. Having seen the main steps of seeding, we returned to Minshuku Yamamoto for breakfast. Our host, Yamamoto-san, had gone fishing while we were out. He showed us his catch of aori ika (Sepioteuthis lessoniana, bigfin reef squid) and served us some for breakfast (Photo 34).
Seeding takes place 20 days each fall, within a four-week period. The seeded nets would wait in the freezer until late October, when they would finally go into the sea. We made plans to return. Yamamoto-san sent us home with some of Bouze Island’s seasoned nori from the last harvest (early 2011; Photo 35). The Kousuion strain they prefer in Bouze grows well. It produces a relatively thick and durable nori, good for seasoned nori and foods like onigiri (rice balls).
Initial Growth of Nori: First Ocean Phase
Whereas Bouze Island’s seeding facility and freezer are owned by the Fishermen’s Association, individual farmers grow nori on their own. Each farm gets a share of the seeded nets, approximately 900 nets per farm. Growing areas in the sea are assigned by lottery. All farmers must have gyo-ken (fishing rights) and be members of the fishermen’s association, but not all members of the association choose to farm. Thirty-one farms grew nori around Bouze this season (2011-2012). Most nori farms have four to five people (often family members) to work the farm.
On October 20, 2011, Bouze’s nori farmers began to put their nets into the sea. Nets were still tied together in sets of five. They were suspended from a complex of floats and lines. It took several days prior to October 20th to create this complex, and three days to complete the placement of all the nets. Nets would remain in the sea for 3-4 weeks, and then be returned to the freezer. During this initial phase in the sea, the single-celled conchospores grow into the multicellular gametophyte, the form know as nori (see Photo 1).
Yamamoto-san picked us up in his boat at the Port of Himeji on the afternoon of October 23rd. Nori work was already completed for the day. We walked around the island, stopped by the fishermen’s association, and enjoyed the views. Some of the nori nets were visible from shore (Photos 36 & 37). Yamamoto-san made arrangements for us to visit his nephew’s farm in the morning.
We departed at 5:10 AM in Yamamoto-san’s skiff and met his nephew and crew at their dock. Similar to other fishers, whalers and Ama divers in Japan, they started the day around an open fire, chatting and getting warm. After a few minutes, we went together on Kobayashi-san’s boat to the farm. Along the way, Reiko explained our interest in nori, and asked Kobayashi-san about his farm. He was born and raised on Bouze Island, although he went away to college and knew the story of Dr. Drew-Baker. His father established the farm over 30 years ago. He has worked the farm for 20 years, and took over when his father became ill. Growing nori is still a good business, but the price has declined over the last decade. He had two younger relatives working with him, and a more experienced farmer (another Katsura-san, not related to the other two Katsura-sans).
It was a 20-minute ride in the dark. We could barely see the nets when we arrived. Kobayashi-san still had his nets tied into sets of five (from the seeding factory), but now two sets of five were tied together (10 nets total, Photo 38). Five sets of these pairs were lined up end to end in a row (50 total). Kobayashi-san had 19 rows for a total of 950 nets (Photo 39).
The job this morning, and throughout this phase of mariculture, is to raise the nets out of the water. Wild nori grows in the intertidal zone of the ocean, that part of the ocean that is periodically immersed (covered) and emersed (uncovered) by the tides. Lifting the nets out of the water mimics the natural tidal cycle. For the first few days of this phase, the nets were kept out of the water for one hour per day. Today, they expected to keep the nets raised for two hours. In the last two weeks they would typically keep the nets out of the ocean for 4-5 hours, depending on the weather. Their goal is to dry out the nets enough to kill other marine organisms that might grow on the nets. However, they don’t want the nets to completely dry out (e.g. if windy), nor do they want the nets exposed in the rain. Experience with how long to leave nori emersed is critical at this phase, and will determine the future success of the crop.
To raise the nets, each of the workers moved into small boats. The nets were supported by a system of buoys and poles. Rings attached to the nets were placed over the poles. When we arrived, the rings rested around the bottom of the poles and the nets were immersed (in the sea). One-by-one, each ring was lifted up and attached to a notch near the top of the pole, approximately one meter above the surface. Next, the boat was pulled by hand along the ropes to the next float, and the process was repeated. After completing one side of a row, the boats were swung around the end, or pulled under the nets to work on the other side (see Photos 40-43 and Video 2).
All of the nets were raised by 6:30 AM. One by one, we emerged from the nets. The three smaller boats were tied off to the net system, ready to lower the nets in a couple hours. The larger skiff picked up all the farm hands and brought them back to the boat (see Photos 44-47). They would take a break and then lower the nets back into sea.
Yamamoto-san showed up just in time to pick us up. He had gone fishing and brought back squid for the crew to thank them for letting us ride along (Photo 48).
Once back on shore, we visited Kobayashi-san’s processing facility and new ‘One Man’ machine. The government was currently providing 65% of the cost of new equipment for nori farmers. Kobayashi-san and ten others had taken advantage of this offer and installed brand new gear; full price: 100 million yen (about $1.25 million, see Photos 49 & 50). We would later see this machine in action (see below).
The initial phase of growth with daily emersion continued for the next three weeks, until the nori had grown 1-2 cm in length. Starting November 11th, the nets were brought back to the freezer, a process that took nearly a week. Nori would remain in the freezer for a minimum of three days to kill unwanted bacteria and other microorganisms on the nets, while the nori lies dormant. It would be put back out to grow when waters cooled later in November.
Nori Growth and Harvest
This year, the nori farmers of Bouze Island began to put their nets back in the water around November 20. It took several days to put out the nets. Each farmer had multiple growing sites, and sites were set up to facilitate harvest. It takes about two weeks of growth for the nori to reach harvestable size. It can then be cut every 9-10 days, although the first cuttings are best (many seaweeds and plants respond to grazing by producing noxious compounds that deter grazers).
It was still dark at 6 a.m. on December 22(the longest night of the year) as we boarded a brand new nori harvesting boat. It was pitch black. A two-man crew of Maeda-san (42 years old, an experienced nori farmer) and Maeda-san (unrelated, 23 years old, his first nori season) took us out for the morning’s harvest at Yamaiwa Suisan (Mountain Boulder Marine Farm). This farm is owned by Mr. Koichi Uemura, head of the Bouze Island Fishermen’s Association. We were fortunate to be invited out on this new boat (part of the government subsidized program). The boat has a cabin and is much larger than the typical harvester – small, open boats similar to those used to raise the nets. More importantly, the new boat will quickly and efficiently cut nori from the nets (see Photo 51).
The experienced Maeda-san drove us through the dark for forty minutes, mostly navigating on instruments, until we reached a 120-net site due for harvest. Yamaiwa Suisan has its nets set up in three distinct regions around Bouze Island. This site was situated in 30-meter deep water, and was relatively far from Bouze Island, hence the long drive (see Photo 52). It would be the third cutting of these nets. They are cut about every ten days.
Initially, it was so dark that we could be barely see the nets, much less the nori. However, the boat and its crew performed well. The forward metal tubes were deployed off the bow of the boat, something like a cowcatcher on a train. This device lifted up the nets so they passed overhead. As the dangling nori hit the chopper, it sprayed everywhere. Most of it ended up somewhere on the boat, and all surfaces acted together as a single collector (see Photo 53).
As the sun finally came up, we could see that the 120 nets were laid out in long, paired rows; the 20-meter long axis of neighboring rows aligned. This arrangement was designed to allow the harvest of two nets at a time, one from each row. After each pair of nets was cut, the boat turned around and began to harvest another pair of nets (see Photo 54 and Video 3).
As we cut nori from one net, nets on either side would be lifted from the water. From the cabin, it was easy to see the uncut nori on these adjacent nets, approximately 30-40 cm long (Photo 55), whereas the nori on nets after cutting was 5-10 cm long (Photo 56).
By 8:20 a.m. the crew had trimmed 80 of the 120 nets and the boat was loaded with nori. We were met by another Katsura-san (unrelated, age 26) on a transport boat. He helped the crew transfer nori from the harvester onto his boat. They washed loose nori into the hold of the harvester, and then pumped nori from the hold into the transport boat. They also washed down the roof and other surfaces (see Photo 57). As soon as the nori had been transferred, the transport boat departed for port, and we went with it. As we departed, we were able to see the harvester boat with its ‘cowcatcher’ deployed (Photo 58).
We passed several other farms on the way back to port. Most were set up with the same system of floats, ropes and nets, and they harvested nori by passing each net over a harvester boat. However, the boats were much smaller, with no cabins. The two-man crew pulled the boat along by the ropes, similar to the style we observed when raising nets. Also, many farms ‘fertilized’ the nets after cutting with a low pH solution that inhibited other organisms from growing on the nori (see Photos 59 and 60).
Nori Processing: ‘One Man’ Machine
Back at the dock, nori from the boat was pumped into holding siloes at the processing facility (Photo 60). Processing continues 24 hours a day early in the season. The first cuttings produce higher quality nori and like all farmers, the nori farmers of Bouze are anxious to bring in their crop. It was a cold morning, the first day of winter. Fortunately for us, Mrs. Uemera invited us in for coffee break in their processing facility. She also roasted some fresh nori for us to sample and take home (Photos 61-63).
We actually arrived on Bouze Island the day before, December 21st, to visit the processing facility of Mr. Katsura (unrelated to the many others we met with that name). Mr. Katsura is a nori farmer with 35 years of experience. He drove us around the island on our earlier visits, and invited us to his farm in October. However, he had strained his back in the net-raising phase of growth (described above, see Photo 64).
Katsura-san bought a new ‘One Man’ machine this year, the same type as Kobayashi-san, made by Nishihatsu Company (priced at 100 million yen, about $1.25 million). This machine revolutionized nori processing, although it actually consists of several machines working together. ‘One man’ can put freshly cut nori into the machine; the machine spits out dried sheets of nori at the other end. It performs all the traditional steps of nori processing (and more). It washes with saltwater, minces, washes again with freshwater, mixes minced nori with freshwater to the desired consistency, deposits the correct amount of nori ‘slurry’ into frames onto mats (to form the basic sheet), sucks out extra water, presses out extra water, dries the nori (the dryer is the largest part of the machine), and dumps the dried sheets of nori onto a conveyor belt that delivers it to an inspection room (see Photos 65-73).
Depending on the model, it may also inspect the sheets for any defects (e.g. holes or frayed edges), bundle sheets in tens, fold them in half, combine these into hundreds, band them with appropriate labels and organize them in rows of 600 (see Photos 74-79 and Video 4). Katsura-san’s machine does all of the above at the rate of 16,800 sheets every 3 hours (5,600 sheets/hour). The nori produced on Bouze Island will be sent to the association for grading. Most of it will then be sent to Awajishima, where it will be roasted and packaged, or otherwise prepared for sale.
Katsura-san still needs helpers to handle the nori after it has been bundled He hires three women that rotate in shifts; the factory runs 24 hours a day in December. These women are responsible for inspecting the nori rejected by the machine and bundling it by hand. It will be sold at a lower price. They also box the bundled nori and look after the office (see Photo 80). He also hires workers to care for the nori on the farm. He estimated his annual costs of running the factory and boats (gas, electricity, etc.) at 5 million yen (about $65,000). He expects the machine will be profitable in a few years, especially given the government subsidy. However, nori farming has experienced some recent problems.
The discovery of conchocelis-stage nori by Dr. Drew-Baker enabled the modern mariculture of nori. In 1965, the floating net system was developed, with the raising and lowering of nori to mimic the tides. At the same time, farmers started freezing nets to inhibit organisms and extend the growing season began. Nori production in Hyogo Prefecture went up ten-fold by 1972, to over 500 million sheets. The ‘One Man’ machine debuted in 1975. Production in 1978 exceeded 1 billion sheets; in 1983 Hyogo produced more than 1.5 billion sheets of nori.
As production increased, more people were able to eat nori on a regular basis and demand grew. The price went up initially, from about 5 yen per sheet (less than 4 cents at that time, 1965) to over 20 yen per sheet in 1977. The higher prices attracted more farmers and more investment; Katsura-san started farming at this time. Over the next decade the price varied around 15 yen per sheet, but by 1988-2002 nori sold for 9-12 yen per sheets.
The last decade has been less successful for nori farmers. The price per sheet has declined since 2004 to approximately 8 yen per sheet (about 8 cents). In 2003, production dropped 25% with the first ‘iroochi’ (yellow nori) event. Yellow nori grows when blooms of diatoms remove too many nutrients from the water (diatoms are single-celled algae; common problem species are Eucampia zodiacus and Coscinodiscus wailesii, and last year Chaetoceros socialis). Without these nutrients, nori cannot produce their phycobili proteins, the photosynthetic pigments that give nori its red color. Yellow nori lacks flavor and earns little money for nori farmers. The problem develops during the coldest months (January and February). Bouze Island experienced yellow nori last winter (February 2011).
Rising sea temperatures pose another problem for nori farmers. Warmer temperatures in the fall restrict the growing season, and reduce production. Temperatures were above average through November this fall (2011), and all the nori farmers said it was a bad year.
Despite these problems, Bouze Island farmers may benefit this year from reduced production in other areas, particularly in Kyuushuu Prefecture, the largest producer. Kyuushuu is further south and experienced greater warming, with more significant consequences. A smaller crop tends to raise prices, and there is still strong demand for nori in Japan. Nori today accounts for more than 75% of Japan’s seaweed consumption.
Special thanks to Yamamoto-san, our host on many visits to Bouze Island. Thanks also to Mr. Katsura, Director of Saibyojyo, Bouze Island’s nori seeding facility, and Mr. Yoshimi Konishi, Chief of Research, Nori Kenkyusho, Awaji Nori Center. Many thanks to the nori farmers on Bouze Island, especially Katsura-san, Kobayashi-san, and Mr. and Mrs. Uemura for letting us intrude on their during their busiest times of the year. They were more than hospitable and we enjoyed every scrap of nori!
** Seaweeds (e.g. nori) produce single-celled spores rather than seeds for reproduction. The term ‘seed’ and ‘seeding’ are commonly used because of the more familiar seeds of plants used in agriculture.