The Front Line of Seaweed Bed Formation, Nagasaki Prefecture Iki Sea Farming Center

Date of interview	July 5, 2021
Targets	Atsushi Yamamichi, Section Chief, Fishing Grounds and Environmental Planning Team, Fishing Harbors & Grounds Division, Fisheries Department, Nagasaki Prefectural Government Hiroki Yamanaka, Director, Iki Sea Farming Center

Development of a new seedling production technique for gulfweed

Please tell us about the current situation of rocky shore denudation in seaweed beds of Nagasaki Prefecture.

Mr. Yamamichi：In the past, Nagasaki Prefecture established two types of fishing grounds, which are “fish reefs” to gather fish and efficiently catch them, and “nurseries” to increase the fishery resources. On the other hand, “rocky shore denudation,” a phenomenon in which the seaweed bed declines, advanced in the coastal waters of Nagasaki Prefecture and became a serious problem. We therefore established a facility called the “seaweed bank” to transfer the seaweed from seaweed beds where rocky shore denudation had not advanced in the beginning of the Heisei era, and began our efforts to help seaweed beds recover. While this was a facility established in seaweed beds for the purpose of stopping the decline of seaweed beds by removing the seaweeds that naturally attached from the spores supplied from the seaweeds on the seaweed beds and transferring them to the areas where rocky shore denudation is occurring, it became difficult for seaweeds to attach to the seaweed bank itself due to the increase in seawater temperature and feeding damage by fish and sea urchins.
To solve this issue, we began the establishment of a nursery with added functions of seaweed bed in 2012. By protecting the area with protective nets to prevent feeding by fish and placing the materials attached with seaweed seeds, it has a structure in which seaweed growth is facilitated. We used seaweed species that abalone and turban shell favor as feed such as Eisenia bicyclis, Ecklonia cava, and Ecklonia kurome as the seedlings of the nursery. However, there was a problem in which they suffered feeding damages by fish, sea urchins, etc. and could not spread the seaweed bed beyond the nets. Last fiscal year, we started developing the seedling production technique for gulfweed and asked the Iki Sea Farming Center, which had delivered results in seaweed bed production, to take over the operations. That’s how it started.
Since Eisenia bicyclis and Ecklonia cava can be used to make “seed yarn,” which is a thread with seedlings attached, there was an advantage that this could be wound around various materials. However, gulfweed has larger seeds and is difficult to make seedlings in the form of seed yarn. We therefore adopted a new seedling production method to directly plant the seeds on concrete materials.

Mr. Yamanaka：In the coastal waters of Iki, Eisenia bicyclis and Ecklonia cava, which are component species of four-season seaweed beds, started decreasing first. Since we had experience of seedling production for only Eisenia bicyclis, Ecklonia cava, wakame seaweed, etc., last year was our first try in seedling production of gulfweed. Since the growth varies depending on the light, nutrition, illuminance, flow rate, etc. to help the growth in addition to seeding, we had a very hard time until this technique was developed. However, it has finally come into shape over the last year, and we are feeling the new possibilities for gulfweed seedling production.

Mr. Yamamichi：One of the causes of rocky shore denudation is that the period during which the organisms that cause feeding damage can be active has become longer, in addition to the growth of Eisenia bicyclis and Ecklonia cava being suppressed due to the increasing seawater temperature. Surveys revealed that the total area of seaweed beds in Nagasaki Prefecture decreased to 8,200 hectares in 2013 to 2014, which corresponded to a 40% decrease compared to approximately 13,000 hectares in 1989. While there were many “four-season seaweed beds,” which had seaweeds throughout the year, in 1989, most of them had disappeared in the survey of 2013 to 2014. The percentage of “spring seaweed beds,” which mainly consisted of gulfweed, etc., had increased instead.
Since gulfweed is a type of seaweed that grows rapidly in a short period from spring to early summer and that is relatively more resistant to feeding damages as well as high water temperatures, it can form seaweed beds in a short period and is easier to form the beds even under the current environment with higher seawater temperatures.

We also removed the organisms that caused feeding damages at the same time we established the nursery with added functions of seaweed bed to prevent feeding damages to the seaweed. We remove some fish species, such as rabbitfish, Japanese parrotfish, and large-tailed drummers, diadema urchins, sea urchins, small snails, etc. At present, recovery of spring seaweed beds has been observed in many areas where we removed these organisms.

What is the situation of fish catch in recent years?

Mr. Yamanaka：Although the Iki Sea Farming Center grows and releases seedlings and young fish for abalone, red sea urchins, scorpion fish, etc., some of the fishermen say “they will not grow even if you release them, unless there is enough feed.” The amount of abalone catch in this area has shown a tendency to decrease these few years. Since the spawning period for abalone is around November, they do not have enough nutrition unless they have the seaweed to feed on at that time of the year, indicating that they will proliferate only in four-season seaweed beds. I have worked here for many years, and the state of seaweed beds is changing constantly year by year. Even though there were some beds where Eisenia bicyclis and Ecklonia cava barely survived until around 2018, they have all but disappeared after that.

On the other hand, turban shell catches are somehow maintaining. Since turban shells spawn in spring, they are less susceptible to rocky shore denudation than abalone. They can survive if there are small seaweeds, and they can spawn if there is a small spring seaweed bed in the spring. The current situation is that some fishermen are barely making a living with turban shells. To start working on a completely new fishing method requires initial investment to establish the facilities, and only a limited number of fishermen can do this. It is also an issue that the vast majority of the fishermen are not capable of starting new fishing methods.

Mr. Yamamichi：While we do not know the causal relationship with the water temperature since fish catches have relatively large variations by the year, yellowtail catch has been increasing in Nagasaki Prefecture in recent years. This is not limited to Iki, but happening for the entire prefecture.

Mr. Yamanaka：When we focus on Iki, most of the fish species show tendencies to decrease. However, longtooth groupers and groupers are showing tendencies to increase. The catch for longtooth grouper in particular nearly tripled in the last 5 to 6 years. Although the percentage of large longtooth groupers that weighed 5 K or more had been higher before, that of small fish has increased, with the amount that corresponds to the increase in catch being the smaller ones that weigh less than 5 K. It gives me the impression that the resource distribution of longtooth groupers moved slightly north, even though we used to catch large ones that grew in the south before.

To expand spring seaweed beds and increase the fish catch in the prefecture

What measures is Nagasaki Prefecture considering against the future impacts of climate change that are of concern?

Mr. Yamamichi：It is expected that the four-season seaweed beds consisting of Eisenia bicyclis and Ecklonia cava may shift to the southern gulfweed, and eventually convert to coral reef like those in southern seas due to the increase in seawater temperature. Nagasaki Prefecture needs to continue establishing seaweed beds in the future for those who harvest abalone and turban shells. More specifically, I assume that the assessment of sea areas will be extremely important in order to form seaweed beds in areas that are suitable for seaweed growth in the future, since there are opinions that rocky shore denudation is advancing along the coast where the warm current directly hits. Another possible measure is to change the subject species for seaweed bed formation, as the seaweed species suited to living in the area will also change in the future.
We transmit the technique that was developed at Iki to the other farming centers in the 5 regions of the prefecture starting in this fiscal year, and take measures to establish the seedling production system for seaweed beds for the entire prefecture. Since the facility structure, scale, etc. vary by each center, it will not be completely identical. But the Iki Sea Farming Center has been providing support, and they have consented to taking on everything up to preparation of the seedling production manual.

Mr. Yamanaka：It has become a serious matter for the entire prefecture that seaweeds are decreasing every year. I fear that this phenomenon will keep moving gradually north along the Japanese islands in the future. Since we are beginning to see southern species of gulfweed as well, it may be a good idea to adopt a policy to add as many southern species as possible. In addition, in the field, I hope to keep forming spring seaweed beds in the sea off Iki first by gradually expanding gulfweed that we are currently working on.

Finally, what gives you the sense of satisfaction in your current work? And what are your future prospects?

Mr. Yamamichi：I create nurseries as a part of fishing ground development. We are better able to protect the young fish by adding the seaweed bed functions. Nurseries can function as the core and expand seaweed beds around them as seeds spread. Then effects can multiply as seaweeds protect the young fish outside the nurseries. If it works well, we can expand the spring seaweed beds, which will lead to increased fish catch in Nagasaki. I hope to achieve such a good circulation. That my efforts will lead to fish catch for fishermen in the future gives me the sense of satisfaction more than anything else.

Mr. Yamanaka：I work closely with fishermen, and see their lives with my own eyes. The circumstances are extremely difficult especially for fishermen who make a living by catching abalone and turban shells. Increasing the resources by increasing seaweeds, which hopefully will stabilize the lives of fishermen. I work hard for this purpose. The Iki Sea Farming Center also has fisheries classes, which elementary school children often come to attend. I take the opportunity to try to transmit what is happening with rocky shore denudation so that they understand the current situation, and say “please go home and tell your parents.” I hope that the children will be interested in environmental issues of the sea even when they grow up.