The Story of Nori, Part II: Modern Mariculture and Processing*

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.

Life Cycle of Nori

Photo 1: Life cycle of nori (Porphyra spp). The GAMETOPHYTE generation produces the familiar leaf-like ‘body’ (thallus) harvested for nori. A microscopic CARPOSPOROPHYTE generation develops on the GAMETOPHYTE generation and produces carpospores. Carpospores settle onto oyster shells (and similar substrate) where they develop into a small, filamentous ‘Conchocelis’ stage (generation). The conchocelis stage produces the conchospores that settle onto shorelines, bamboo poles and nets to produce the GAMETOPHYTE generation, i.e. nori. The conchocelis stage was originally considered a completely separate species, Conchocelis rosea, until Dr. Kathleen Drew-Baker discovered it was part of the Porphyra life cycle. Photo copyrighted and used by permission, with thanks to its creator: Lisa Chen, and the Monterey Bay Aquarium Research Institute.

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).


Photo 2: Yoshimi Konishi, Chief of Research at the Awaji Nori Center, and I holding up oyster shells covered with the conchocelis stage of nori. The conchocelis stage appears as dark purple to brown patches on the white oysters. Note the upper rows of oysters tend to have more conchocelis growth, due to their greater exposure to sunlight.

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.


Photo 3a: Flasks of free-living conchocelis filaments are kept under refrigeration at the Awaji Nori Center. Rows of flasks in the refrigerator; labels indicate the strain.

Flask Close-up

Photo 3b: A close up of one flask of conchocelis filaments.

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).

Oyster Shell Holes

Photo 4a: The conchocelis stage of nori is grown on oyster shells; shells from Miyagi Prefecture are preferred. Two holes are drilled into each shell.

Strining Shells

Photo 4b: Pairs of shells are sown together, back-to-back with the inner surface of each shell facing out. The conchocelis face will grow on this inner surface.

Oyster String

Photo 4c: Five pairs of shells are tied together, for a total of 10 shells per string. A loop is added to each end of the string to suspend the shells in water.

Oyster Stringers

Photo 4d: A group of five women work seven hours each day creating strings of oysters. They typically process 11,000 shells per day. These women laughed when informed they will be stars on an American blog (thanks!).

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).

Oyster in Water

Photo 5: Oyster shells covered in conchocelis stage nori (purple/brown patches) submerged in seawater. The smaller green spots are an unknown alga that compete for space on the oyster shells, but usually disappear over the summer.


Photo 6: Thirteen (13) strings of oysters, with 10 oysters per string, are suspended from a single bar that rests on the edges of a culture tub. These shells are well covered with conchocelis stage filaments of nori.

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).

All Tubs

Photo 7: The Awaji Nori Center cultures the conchocelis stage of nori on a total of 845,000 oyster shells in 325 tubs. The center has been producing conchocelis stage nori for 40 years.

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).


Photo 8: Clear fiberglass panels in the roof allow sunlight into the Awaji Nori Center’s culture tubs. Mechanized curtains regulate the amount of sunlight.

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.

Wheels Awajishima

Photo 9: The Awaji Nori Center has a seeding facility outside and next to the conchocelis stage facility. Tubs of sporulating conchocelis stage nori will be placed under the large rollers. Nets placed on the rollers will move through the tubs picking up conchospores (‘seed’).

‘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).

Photo 10: Inside Saibyojyo, Bouze’s nori seeding facility, after a morning of seeding nets. Nets are spun on large rollers (background) for ‘seeding’. Seeded nets are pulled from the rollers into the long receiving tubs, and later onto drying racks. Compare to Photos 9 and 17.

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).


Photo 11: Mr. Katsura, Director of Saibyojyo, shows us some nets. Sets of 5 nets are tied together and will remain together through the first two months of nori culture.

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).

Net Piles

Photo 12: Piles of nets ready for seeding at Saibyojyo.

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).


Photo 13a: The Bouze Fishermen’s Association buy conchocelis-stage nori from the Awaji Nori Center. Mr. Katsura took a boat to Awajishima the week before to bring back 50,000 oysters coated with conchocelis-stage nori. Mr. Katsura holds up a rod with strings of oysters.

Oysters Close-up

Photo 13b: Close-up of the conchocelis-stage nori and oyster shells. Compare the amount of nori on these shells (September 2011) to those in May 2012 (at the Awajishima Nori Center, Photos 2 & 6).

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.

Net Pieces

Photo 14: Samples from nets are cut out during seeding and inspected for the presence of conchospores.


Photo 15: Mr. Katsura in his office inspecting pieces of net for conchospores at 100x magnification. From his ‘command center’ he can observe the entire facility and direct the efforts of his crew. Seeding was finished for the day; his office was set up for the following morning. On his left are 10 petri dishes, each with a number corresponding to the 10 rollers used to seed the nets. Pairs of scissors rest below the window, ready for the runners that sample the nets.


Photo 16: Reiko examines conchospores on a sample of net left over from earlier that day. Mr. Katsura can view samples from either inside his office, or through this window. A second microscope is set up to his left and used by his colleague.

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).

Bag & Box

Photo 17: Dried nets are placed in plastic bags and cardboard boxes, and then taken to the freezer.

Truck Freezer

Photo 18: Boxes full of seeded nets are driven to the Bouze Fishermen’s Association freezer.


Photo 19: The seeded nori nets will be kept inside the freezer at -30OC for one month.


Photo 20: Reiko with a hearty fisherman’s dinner at Minshuku Yamamoto (Yamamoto-san’s motel). Yamamoto-san has been our host on each of our visits. His minshuku sits across the street from the docks. Every morning we hear the boats as they head out before dawn.

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.

Spinning Wheel

Photo 21a: A spinning roller covered with 80-90 nets. The lower part of the roller spins through a tub. Conchocelis-stage nori on oyster shells is suspended from bars at either end of the tub.

Oysters in Wheel

Photo 21b: The spinning of the wheel agitates the water and stimulates release of conchospores into the water. Conchospores (‘seeds’) attach to the net.

Carrying Rack

Photo 22: A group of women pick up a drying rack and will move it out of the way. It will be brought back later to dry the nori nets. Six rollers are visible in the background.

Carrying Rack

Photo 23: The drying rack is turned upside down to move it.

More Nets

Photo 24: Preparing more nets for seeding. Sets of five nets each are tied together. Two-woman teams position fresh nets by the rollers.

More Nets

Photo 25: Carrying nets to a roller.

More Nets

Photo 26: Positioning nets by a roller.

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).

Runner Cutting

Photo 27a: Three runners were responsible for taking samples and rushing them back to the office for inspection. A runner cuts a sample from the outer net.


Photo 27b: Running with the sample back to the office (caution: do not try this at home. Running with scissors can be hazardous).

Runner & Sample

Photo 27c: Delivering the sample.

Petri Dishes

Photo 27d: Samples are placed into numbered petri dishes (numbers refer to the roller that was sampled).


Photo 28a: Samples from the nets are twisted to separate the fibers, and then inspected under the microscope for the presence of conchospores. Katsura-san reads a sample.

Sharing Inspection

Photo 28b: Katsura-san shares inspections with his colleague.

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).


Photo 29a: When the nets have been adequately seeded, Mr. Katsura announces the removal of the top set of nets. Roller 4 is turned off.


Photo 29b: The lines of the top set of five nets are untied from either side of the wheel.


Photo 29c: The nets are pulled into the receiving tub with the help of the roller. Note the tub is empty; these nets are the first of the day.


Photo 30: Unspooling nets from roller 6. Note the ropes tied together (foreground). Nets are arranged in sets of five, but two sets of five nets are tied together for seeding. In the center a runner (red shirt) samples the next layer of nets from roller 4. This picture was taken four and a half minutes after the first nets were removed (see Photo 29c).


Photo 31: Removing the final set of nets from roller 7 (round one). A pair of women will immediately reload the roller with another 80 nets.

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.


Photo 32a: A pair of women rapidly reload a roller with another 80 nets. A set of five nets is spread out.


Photo 32b: One end of the nets is hooked around the roller, but not tied; the nets will come off easily after seeding.


Photo 32c: The roller is turned on to spool the nets.

Respool End

Photo 32d: The other end of the nets is tied to a spoke of the roller. These ropes will be untied and used to pull nets off the roller after seeding (e.g. Photos 29-31).

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.

Fresh Kaki

Photo 33a: A pair of runners carry fresh conchocelis-stage nori from the storage tub to a roller.

Fresh Kaki

Photo 33b: And place it into the roller tub.

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).


Photo 34a: Yamamoto-san loves to go fishing for his guests, his own family and just for the sake of fishing. Live aori ika (Sepioteuthis lessoniana, bigfin reef squid) caught this morning by Yamamoto-san, while we were watching nori seeding.


Photo 34b: Yamamoto-san returning after fishing and a swim, in his undies.

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).


Photo 35: Reiko stands in front of Minshuku Yamamoto with a package of seasoned nori from Bouze Island, Hyogo Prefecture.

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.

Fishermen's Association

Photo 36: Bouze Island Fishermen’s Association office. The association has 500 members, the largest of Hyogo Prefecture. Within Japan, Hyogo Prefecture ranks second in nori production.

Nets From Shore

Photo 37: A view of a nori farm from the shore of Bouze Island.

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).

Big View Later

Photo 39: A larger view of Kobayashi-san’s nori farm. By 6:30 AM most of the nets have been raised.

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).

Raising Nets

Photo 40: Raising nets just before dawn. A row of nets on the right side of the picture is still immersed (in the sea). Note the buoy and poles that support the nets, and the orange ring that attaches the nets to the poles. A boat on the other side of these nets is moving toward me and raising that side of the nets. A row of nets on the left have already been raised.

Raising Nets

Photo 41a: Raising the nori nets. This farm worker has just pulled up the net by the orange ring in the center of the picture and attached it into a groove near the top of the pole. He pulls himself along by the rope system. Note the boat is shallow and rectangular. A single oar is the only other means of locomotion.

Raising Nets

Photo 41b: The next ring has been raised. Note the other side of these nets is being raised simultaneously by the boat carrying Reiko and myself.

Ring System

Photo 42a: Closer up view of the buoy, pole and ring system.

Ring Close-up

Photo 42b: A ring in the upper notch of the pole.

Under Net

Photo 43a: Moving under the nets. It was often more direct to travel under the nets, rather than go around them. Having completed one row, this farm worker lies on his back and pulls himself under the nets.

Under Net

Photo 43b: He emerges on the other side.

Under Net

Photo 43c: He begins work on the next row of nets.

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.

Large Skiff

Photo 44: Katsura-san took us into the nori nets with the larger skiff. We finished first and picked up the other farm hands.

Small Boat

Photo 45: Another farm worker finishes his nets. He ties off his boat to the float system. It will be used again in about two hours to lower the nets.

Small Boat

Photo 46: The farm owner, Kobayashi-san (orange shirt) is the last one to be picked up.

Raised Nets

Photo 47a: Views of the raised nets.

Raised Nets

Photo 47b: Views of the raised nets.

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).

Morning Fishing

Photo 48: Yamamoto-san describes the morning’s fishing as he takes us back to Bouze Island.

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).

Kobayashi-sans Facility

Photo 49: The front of Kobayashi-san’s nori processing facility.

One Man

Photo 50a: One of the most significant technologies of modern nori culture is the ‘One Man Machine’. It takes fresh cut nori and creates dried nori sheets: 5,600 sheets per hour. A view down the side of the machine.

One Man Machine

Photo 50b: The One Man Machine has many mats to make many sheets of nori. Compare to Photo 17, Part I.

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).


Photo 51a: A new-generation nori harvester unloading on December 21, 2011. 51a. The boat carries a system of metal tubes that will lift nori nets over the boat and direct the nori into the chopper. Note the dark red water; run off from the nori processing facilities along the waterfront.


Photo 51b: A closer view of the chopper that runs from starboard to port. As nori nets pass over the metal tubing, the nori hangs down where it meets the chopper.


Photo 51c: View from the port side into the hold full of fresh nori. The orange hoses suck up the nori and deliver it to storage siloes. Most of the driving and chopping can be conducted from the covered cabin of the boat.

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.

Inside Early

Photo 52a: Inside the cabin on our ride to the nori farm. It was still night at 6:00 AM on December 22, 2011. Maeda-san navigated with the use of instruments and buoy lights.

Inside Cabin

Photo 52b: Reiko was thankful to be inside a cabin, rather than an open boat.

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).

Dark Cut

Photo 53: Cutting nori in the dark (6:55 AM). A structure of metal tubes placed off the bow of the boat guides nori nets over the top of the boat. Nori dangling from the net is cut off as it hits the chopper, which was operated from within the cabin. Note the adjacent net on the side of the boat.

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).

Big Cut

Photo 54a: A 120-net section of Yamaiwa Suisan (Mountain Boulder Marine Farm). Floats in the foreground are placed on the periphery of the site. Ropes attached to the floats hold the nori nets.

Big Cut

Photo 54b: The boat runs between a pair of floats.

Big Cut

Photo 54c: As the boat engages the rope system, it lifts the nets. The adjacent rows of nets can be seen as they are pulled from the water.

Main Cut

Photo 54d: The targeted net comes over the boat, and nori enters the chopper.

Big Cut

Photo 54e: The cut nori falls onto the bow and is washed into the hold.

Big Cut

Photo 54f: Close up of the nori as it falls into the hold.

Big Cut

Photo 54g: Maeda-san simultaneously operates the chopper and drives the boat from inside the cabin.

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).

Side Nori

Photo 55a: Nori on the nets adjacent to those being cut passed close to the cabin and provided the best views of uncut nori. The strands of uncut nori hanging from the adjacent net, approximately 30-40 cm long.

Nori Close-up

Photo 55b: Close-up of uncut nori.

Net Stern

Photo 56: The trimmed net passes over the stern of the boat. Compare nori on the trimmed net to the uncut nori on the adjacent net.

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).


Photo 57a: The morning’s harvest was too large to be carried by the harvester boat. A transport arrived to carry the cut nori back to port.


Photo 57b: Nori was pumped from the hold while the bow was hosed down.


Photo 57c: Nori from the roof of the cabin drained into buckets.


Photo 57d: Nori carried onto the transport boat.


Photo 58: The harvester boat with ‘cowcatcher’ deployed.

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).

Fertilizer & Small Harvester

Photo 59a: Other farms used small boats to harvest nori and many added a ‘fertilizer’ after cutting. The long yellow boat carries a solution in its bow that is applied to the freshly trimmed nets. Nets are passed over the bow and dip into the solution. A small harvester boat with two-man crew is just behind the fertilizer.


Photo 59b: Close-up of small harvester. Note the net passing over the boat; the same general method used at Yamaiwa Suisan (Mountain Boulder Marine Farm).


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).

Dock Boats

Photo 60: The transporter boat returned us back to the dock in front of Yamaiwa Suisan, where its cargo of nori would be unloaded. A fertilizer boat was tied up at the same dock.

Roasting Nori

Photo 61: Mrs. Uemura roasts fresh nori for Reiko and explains nori processing, in the office of Yamaiwa Suisan’s facility.


Photo 62: Most of the nori grown on Bouze Island will be sent to a large processor on Awajishima. However, Yamaiwa Suisan packages a small amount of their highest quality nori from a favorite growing area. Reiko holds a package given to us by Mrs. Uemura.

Eating Nori

Photo 63: Early season nori, cut yesterday and fresh roasted, tastes good.

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).

Nori Processing Facility

Photo 64: Reiko with Katsura-san and Yamamoto-san outside Katsura-san’s nori processing facility.

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).

First Washer

Photo 65a: The ‘One Man’ machine actually begins with the ‘Catch Cleaner’.

First Washer

Photo 65b: The ‘Catch Cleaner’ washes the freshly cut nori in seawater.


Photo 66: Washed nori enters the mincer and to be cut.

Second Washer

Photo 67: Minced nori is washed in fresh water.


Photo 68: Minced nori in fresh water enters the ‘Density Controller’ which adjusts the specific gravity of the solution. The slurry produced here enters the actual ‘One Man’ machine.

One Man

Photo 69: The ‘One Man’ machine turns the slurried nori into dried sheets.


Photo 70: Above the front end of the ‘One Man’ machine. Here, two rows of eight (8) sheets are placed on mats. Each row of 8 mats will travel together through this machine.


Photo 71: The new sheets are moved over a vacuum that will suck out excess water (exposed sheets), and moved to the right to be squeezed (under the white covers).


Photo 72a: The largest part of the ‘One Man’ machine is the dryer. View of the mats as the enter the dryer.

Big Dryer

Photo 72b: The dryer is contained in this section, covered by blue panels.


Photo 72c: Nearly dried nori about to be released from the dryer.

Conveyor Belt

Photo 73: Each row of mats with their sheets of nori will eventually be turned upside down. The sheets fall onto a conveyor belt, which moves them into a separate room. The ‘One Man’ machine is done with these sheets of nori. Note the empty mats above the conveyor belt. They will move to the front of the machine to accept more nori.

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.

Conveyor Belt

Photo 74: Sheets of nori from the ‘One Man’ machine enter an inspection room by conveyor belt. These sheets enter a small inspecting machine (foreground, bottom of picture) and are redirected to a second, larger inspector (right). Through the glass can be seen the empty mats that just released their nori.

Bad Nori

Photo 75: Imperfect sheets of nori that were pulled aside by the larger inspecting machine.


Photo 76: Nori that passed inspection was grouped into stacks of ten (10) sheets by the larger inspecting machine and moves to a folding machine.


Photo 77: The folding machine folds the stacks of ten sheets once (in half) and pushes ten stacks together into a bundle (total, 100 sheets).


Photo 78: Bundles enter the binding machine, which binds 100 sheets together. The label includes the farms name and specific region where it was grown.

Final Shelf

Photo 79: Bundles are pushed onto a shelf. Each shelf holds six bundles (600 sheets of nori). Full shelves are moved upward to accommodate more bundles. The inspection room houses the inspecting, folding, and binding machines. It also provides a warm place to rest for visitors and farmers.

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.

Bad Nori Wrap

Photo 80: Imperfect nori sheets will be inspected in more detail and bundled by hand.

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.

This entry was posted in Japan Sabbatical by Robert Reavis. Bookmark the permalink.

About Robert Reavis

I study fish behavior and marine ecology through direct observation while diving. I also teach General Biology, Marine Biology, SCUBA and Scientific Diving at Glendale Community College. This year (2011-2012) I will be in Japan to study Traditional Fisheries and Modern Environmentalism.

2 thoughts on “The Story of Nori, Part II: Modern Mariculture and Processing*

  1. My names is James C. Bergdahl and I help develop the first successful commercial nori farm in the western Hemisphere [in the San Juan (WA) and Gulf (BC) islands in the Pacific Northwest]. The farm operated for a few years (1987-1990). As far as I known there are still no sushi-nori farms outside of Asia even though there are about 15 native Porphyra species in the Pacific Northwest. I published a fairly detailed article about our experience. If you Google my name with nori the citation will usually come up in the more accessible literature. Your report is great, especially all the wonderful photos – I have never been to Japan. I make very simple sushi a couple times each week and love it.

    James Bergdahl
    Spokane, WA, USA

  2. Do the male/male and/or female/female “pairs” form permanent pair bonds? If not, under what conditions do they select another “partner?” Do these pairs indulge in homosexual behavior? If their same-sex partner dies or is removed will the remaining partner select a new partner of the same sex? If so, is this behavior fixed–that is, do they seem to select partners of the same sex when only birds of the opposite sex are available?

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