Saving Nori

scientist Drew-Baker reads a book by her microscope

Kathleen Drew-Baker discovered a new lifestage of Porphyra algae, saving the nori industry.

(Smithsonian Institution)

As an island nation, Japan and its culture are heavily influenced by the sea. It comes as no surprise that their cuisine is famous for incorporating fish and shellfish, and that many recipes rely on the savory umami taste of seaweed. Wakame is slivered and marinated into a crunchy salad and kombu boiled to flavor the warming dashi broths of ramen soup. But no seaweed has reached the international fame and popularity of nori.  

Today, nori is unmistakable as a deep green sheet wrapped around rolls of sticky rice and raw fish. The sheets are made by chopping nori algae into a slurry and then pouring that slurry over a woven mat to dry. It was the popularity of sushi that brought nori into American and European kitchens, first in trendy urban restaurants and then to the shelves of small-town grocery stores. But were it not for a timely scientific discovery, nori would likely never have graced our dinner plates around the world.  

Preview three pieces of sushi with chopsticks
Nori is a seaweed used to wrap the inner contents of sushi rolls.  (Pixabay)


Nori’s Story 

Records indicate that people in Japan have been collecting seaweed since ancient times. Shinto traditions dating from the 700s show people offered seaweed at shrines and in the 800s official reports list nori among acceptable payment methods for taxation.

Human cultivation of nori, however, didn’t begin until the late 1600s when Tokugawa leyasu came to power and moved the capital of Japan from Kyoto to Edo (now known as Tokyo). This new leader, called a shogun, ordered fresh fish every day, which put pressure on local fishermen to have a steady supply. To address the new demand, fishermen built holding pens for fish and soon noticed that seaweed readily grew around the stakes that held their nets in place. They began to purposefully drive bamboo stakes into the ground to promote algae growth and later built a more efficient horizontal net system along the sea surface. Nori became a stable source of income in its own right as well as a staple in people’s diets. By the 1800s nori was dried in sheets using a method borrowed from Japanese paper making. 

Preview a frond of red algae
Nori grows as paper thin fronds. (Flickr user holdfast...)

Then in 1948 the nori disappeared. Previous years had occasionally seen low yields that resulted in lean winters, but the nori had always bounced back. A series of severe typhoons combined with pollution from growing industrialization finally decimated the nori crop for good. The timing was terrible. World War II soldiers were returning to a country ravaged by the war and food was in short supply. With the majority of the fishing fleet bombed and food imports cut off, the loss of the nori crop was an especially hard hit.   

The “Mother of the Sea” 

On the other side of the world in England Dr. Kathleen Mary Drew-Baker had recently become enthralled by a mysterious pink algae scum that grew along the shores of Manchester, the city where she lived in England. A scientist at the University of Manchester, Drew-Baker had spent years diligently studying red algae, and despite sexist workplace norms she became an expert on algae.  

From her seaside laboratory, Drew-Baker set to work studying Porphyra umbilicalis, a nori relative known by English bakers as laver—an algae baked in traditional English bread recipes. During the summer months this algae would mysteriously disappear, and Drew-Baker was determined to figure out why. For nine years she attempted to grow the leafy fronds of Porphyra from spores, but nothing seemed to work. It wasn’t until she added oyster shells as substrate that the puzzle seemed to resolve. Fuzzy, pink filaments of a species known as Conchocelis rosea covered the old oyster shells placed in the tanks. But Drew-Baker quickly realized Conchocelis rosea wasn’t a species at all—it was another phase in Porphyra’s life cycle. When the summer heat and storms arrive, Porphyra algae release spores that then settle in deeper, cooler water where they ride out the turbulent weather as a pink filamentous algae. Drew-Baker named this life stage conchocelis in recognition of the false species previously named. In a short letter published in the October 1949 edition of Nature, Drew-Baker outlined her discovery of the new algae life stage. 

Back in Japan, Drew-Baker’s discovery would have immense implications. Upon learning of Drew-Baker’s findings, Dr. Sokichi Segawa of Kyushu University realized that the issues surrounding the nori crop had everything to do with this previously unknown life stage of the Porphyra genus—both the nori of Japan’s shores and the laver of the United Kingdom were Porphyra species. During World War II the U.S. armed forces set underwater mines that exploded in almost every one of Japan’s ports. Not only did the explosions decimate Japan’s shipping fleet, they destroyed the shellfish beds needed for completion of the nori lifecycle. Combined with the unusually volatile typhoon seasons, this devastation meant nori spores had nowhere to settle in the summer months. 

With the help of other scientists and fishermen, Segawa initiated research into a tank-based system for the production of nori. Through temperature control, scientists figured out how to spur the Porphyra spores from one life stage to the other. Once the conchocelis stage released spores (called conchospores to distinguish from the earlier spore stage) they were reintroduced to the sea for growth into the leafy stage, or the stage that is eventually harvested. Today seaweed growers from Japan across to China and other Southeast Asian nations use this method to successfully grow and harvest nori. 

Without knowing it, Drew-Baker saved the nori industry and allowed it to expand into a multi-billion-dollar industry that supports countless families in Southeast Asia. Her discovery about nori’s lifecycle is so essential to coastal Japan’s financial wellbeing that in the town of Uto people erected a shrine in her honor and celebrate her research every year on April 14. Now, every time you bite into a piece of sushi you too can marvel at the role a dedicated scientist and a little bit of luck played in the rescue of an especially delicious, and economically important, seaweed.

April 2021
Tags: Aquaculture