Protecting the Naruto Wakame Brand by Developing a Variety Resistant to High Water Temperatures
Naruto Wakame is a brand of seaweed from Tokushima prefecture, which boasts the third highest wakame seaweed production in Japan. This wakame has a supple, chewy texture and excellent taste, and is recognized as high quality, especially in the Kansai market. In response to a recent drop in production volume, the prefecture is taking ongoing measures to maintain and expand the brand name. In 2015, we interviewed Norio Tanada with the Marine Research Department of the Tokushima Agriculture, Forestry, and Fisheries Technology Support Center, which has developed a new variety of wakame that grows well in high water temperatures.
Production Volume Drops to 40% of the Peak from Rising Seawater Temperature
Temporary offshoring, the process of moving seeds offshore, will start at Naruto Wakame farms at the end of October. When seeds grow to be about 1 centimeter, they are attached to ropes for seed culture and returned to the water to be nurtured until they grow larger. More fishers have recently been saying that fall temporary offshoring or seed culture is happening later in the season than in the past or that the wakame doesn’t grow sufficiently large during the winter growing period. The reason for these changes is the rise in seawater temperatures. Annual average water temperature in the Kii Channel, where many wakame fields are located, has risen by approximately 1.5˚C in the past 40 years. The temperature increase is particularly conspicuous during the wakame growing period from mid October to early November and during the harvesting period from February to March. These months are most important for wakame growth.
Wakame is a type of seaweed that grows during the cold season. That’s why fishers wait for the seawater temperature to drop to 23˚C before temporary offshoring. Over the last 20 years, this temperature drop has been delayed by two or so weeks. A delay in starting means reducing the culture period, which results in a production volume drop. High water temperatures negatively impact the quality of the wakame in that they can create more wrinkles in the leaves or cause discoloration. The percentage of salable wakame eventually drops dramatically. Wakame production volume in Tokushima prefecture fell from 15,000 tons* in 2016 to 5,900 tons, down almost 40%, as compared with the past record high in 1991. Although other factors, such as more producers retiring from business, are relevant, the impact of rising water temperatures is apparent.
If we continue to use the same seeds, we cannot to maintain the production volume of Naruto Wakame. Out of this sense of urgency, our Research Department in 2012 started to work on developing a new type of wakame variety adapted to climate change.
New Early Variety Generated From Free Gametophytes
The wakame generally eaten in Japan is mainly the leafy part of the seaweed. Wakame takes this form for only a few months in the spring but is almost too small for the naked eye to see at other times. Sprouts in the spring grow large at the foot of mature wakame plants, and these sprouts discharge numerous swarm spores. These spores in time are transformed into gametophytes, and divide into female or male. One parent gives birth to swarm spores, which produce female and male gametophytes. Wild wakame has plentiful gametophytes on rocks underwater. As the gametophytes are fertilized, a new cycle begins. Our department manually gathers wakame at the gametophyte stage, chooses one female and one male gametophyte, and then cultures and stores them. These are free gametophytes.
Using this approach, we tried mating our wakame with southern varieties, such as the wakame produced in Kagoshima and Nagasaki prefectures. We tried different combinations of female and male gametophytes, as well as various patterns. Simply reversing the female and male gametophytes resulted in totally useless wakame. Through trial and error, we discovered that the male gametophyte has a very strong impact on the growth of wakame. When we use southern male gametophytes, the resulting wakame exhibits rapid growth and strong resistance to high water temperatures. This kind of wakame resulting from such a combination was wrinkled, which did not meet the quality standards of Naruto Wakame.
A new type of wild wakame, which was thick with robust color, was found in Tsubakidomari, Anan City, in southern Tokushima prefecture along the warm waters of the Pacific Ocean in 2013. We produced a very good specimen in the first test stage and thought, “This is it!” This was an unusual stroke of luck, but there was probably excellent chemistry between the female and the male gametophytes.
The next year, we asked fishers to try culturing our specimen. We succeeded in producing satisfactory wakame that was almost equivalent to the traditional Naruto Wakame in taste and quality. The new variety was much heavier than usual; the weight of the leaves, which is the edible part, was 1.2 to 1.9 times greater. Another great advantage of this new variety is its early growth. Culture starts at the end of October, and early growth becomes visible soon after that, which means we can harvest the wakame about half a month earlier than usual. The new variety is shipped to market in January, which in the past was a period of short supply, and marketed as freshly harvested wakame, with high added value. The new variety of wakame is now distributed mainly in salted form.
Since Naruto Wakame is an established brand, wakame can only be shipped under the brand name when it meets a certain standard. The fishers themselves say they don’t want to grow substandard wakame. This feeling is quite natural, as they take pride in being established brand wakame producers. We believe that this new variety of wakame is resistant to high water temperatures and consistent with marketable quality.
Searching for All Potential Uses for Free Gametophytes
Our department has a set of wakame free gametophytes from various locations in Japan. We can preserve the wakame in its original condition for 10 years. My predecessor’s predecessor recognized the importance of free gametophytes. He thought that if he could preserve the gametophytes and separate them by gender, he would find unlimited potential to improve the Naruto Wakame breed. He began gathering wakame free gametophytes from all over Japan about 15 years ago.
Following the Great East Japan Earthquake in 2011, wakame was in short supply in Miyagi prefecture. That was when a use was found for Kesennuma’s free gametophytes, which had been preserved for seven years. We can produce wakame any time we want, which is the advantage of preserving wakame in gametophytes. With more people now developing business continuity plans for disaster management, a system that can meet its obligations even in the event of a major earthquake or power failure systems is crucial. Important gametophytes were brought last April to our department’s new facility in Hiwasa, Minami Town, to diversify against risks.
Ongoing R&D, 10 Years and 20 Years into the Future
Climate change is causing many anomalies in fishing grounds. One example is the period after November when wakame culture begins. This period generally has a relatively serene sea, but recently, unseasonable rainstorms have occurred and devastated culture rafts. The numbers of adhesives, which can be microorganisms, seashells and sea anemones, that adhere to the wakame are increasing in quantity. While some of these adhesives are harmless, others eat wakame. The expectation is that these adhesives will increase as the water temperature increases. I’ve heard that in some situations, fishers have to cut out about half the wakame to make it shippable.
Wakame damage from fish has also become serious since fall 2011. The rabbitfish is a herbivorous fish that eats seaweed. As these rabbitfish are a southerly fish, they tend to stop eating when temperatures fall below 15˚C and die when below 10˚C. The seawater of Naruto at the coldest period is just below 10˚C. Warmer water now means that rabbitfish have been eating more wakame and eating throughout December.
Land temperatures have also been rising over the past two or three years. Since wakame is cultured near the water surface, atmospheric temperature has a direct impact on wakame culture. Although fishers and fishing personnel are still clinging to the hope that the situation will improve, they have braced themselves for the reality of climate change. They have said that "Years with higher water temperature will follow" and "We should not expect a temperature drop as it used to be."
Considering this changing new reality, the current breed resistant to high water temperature may not be able to adapt 10 or 20 years from now. Unless we continue to improve and develop breeds, we may not be able to keep up with the progress of climate change. I am now working on developing a new variety using parents in areas of the prefecture farther south than Tsubakidomari. We are working on the production of a variety of seeds given the assumption that water temperatures will continue to rise.
Great variation from inland sea to ocean water is the most positive quality of the sea in Tokushima prefecture. The three kinds of seas have quite different physical characteristics: the Sea of Harima, an inland sea with rich nutrients; the Pacific Ocean, a pelagic sea affected by the Kuroshio Current (Japan Current); and the Kii Channel, a sea with characteristics between the Sea of Harima and the Pacific Ocean. The scenery, water temperatures, nutrient salts, and wave environments are all different. We need different approaches tuned to the different conditions. This situation is difficult and fascinating at the same time. My original work was seaweed bed research. I have been conducting submersible studies all over the prefecture, from Naruto to Shishikui. My discovery of the wakame at Tsubakidomari that was used to develop a new variety was just by chance. I had been doing a submersible survey for an unrelated purpose.。
We have become aware of the significant potential that waits for us to discover in the sea of Tokushima.
Related Sites
- (＊)Source: Statistics on Fisheries and Aquaculture Production 2016
- National Fisheries Experiment Station Directors' Association 2015 National Water Experiment Station Chairman's Award
- Tokushima Agriculture,Forestry,and Fisheries Technology Support Center
- Foods of Tokushima (Public interest group Tokushima Prefecture Bureau of Association)
(Published on November 27, 2017）
