Welcome Photo An albino individual of Kita-murasaki sea urchin
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Site opening on 31 December 2023
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With this sea urchin content, we have almost completed the 20 contents of FoM that we originally planned to publish. We have several more in the planning stages, and we will continue to provide advanced marine biology topics as we release them and update existing content. We would like to thank not only the professors and researchers at Hokkaido University for providing us with much interesting scientific information, but also Hakodate Fisheries Experiment Station, Museum of Natural and Environmental History, Shizuoka, National Institute of Polar Research, Ashoro Museum of Paleontology, and Softbank Corp.
Above all, we would like to express our deepest gratitude to Toyo Suisan Kaisha, Ltd., Asahi Group Holdings, Ltd., and Yamasa Corp., for their support of FoM from the beginning. We would also like to extend our sincere thanks to Adobe Inc. for their technical support of the distribution tools.
Sea urchin were marine animals that had been thoroughly researched, but new studies have been developed on efficient seedling production and release, physiology of maturation, and the function of intestinal bacteria, and many interesting new scientific results continue to be obtained. It is no exaggeration to say that these studies have been conducted largely by people who work at or have graduated from the Faculty of Fisheries Sciences, Hokkaido University. We hope you enjoy our findings on sea urchins, which are an indispensable part of Hokkaido's oceans and a colorful addition to Japan's year-end and New Year's dishes. We wish you a happy and prosperous new year.
FoM Editorial
31 December 2023 posted
Seed Production
There are currently 830（重井 1974）to 850 （Harries & Eddy 2015）species of sea urchin in the world, of which about 17 species from the tropical and subarctic zones are edible（Harries & Eddy 2015）.
In Japan, sea urchin have been used as food since the Jomon period, and appear in the Yoro Code (718) compiled in the Nara period and the Engishiki (905) of the Heian period. The history of Hokkaido's fishing industry is much shorter, and it is said that salted roe of sea urchin was first manufactured in 1879 by settlers in Muroran from Fukui Prefecture, which is famous for Echizen sea urchin. Hokkaido was developed as a fishing center after the technology to manufacture the salted roe of sea urchin had developed, which allowed them to be transported from the remote Ezo region to the mainland, where they were consumed（北海道立網走水産試験場 1979）.
On the other hand, on Rishiri Island, fishing began in 1932, which had been exterminated as a predator of the valuable Saccharina kelp. After this, sea urchin was excluded item of Food Control Law enforced during the World war 2nd, catch of sea urchin began to dramatically increased and shipped to Honshu（北海道立網走水産試験場 1979）.
Mesocentrotus nudus and Strongylocentrotus intermedius are mainly fished in Hokkaido and the catch of sea urchins reached 1,606t in 1967. There after decreased to about 1/3 in 2022 (Fig 1). After this, artificial seed production and release begun in Hokkaido aimed to restock. The first attempt to produce sea urchin seeds was with the Red Sea Urchin Psuedocentrotus depressus in the 1960s. This was followed by the development of techniques using the Purple Sea Urchin Anthocidaris crassispina and the Bafun-uni Hemicentrotus pulcherrimus.
In Hokkaido, over grazing by Mesocentrotus nudus considered as the factor of distraction of Saccharina kelp bed called Isoyake, so Strongylocentrotus intermedius is mainly released. After observing that sea urchins settled on the scallop culturing facilities, post settled juveniles were collected from late 1970’s. However, the annual production of juveniles collected with this method fluctuated considerably. To achieve stable production of S. intermedius seeds, mass production methods to raise the juveniles from the artificially fertilized eggs was established in 1981.
Artificial seedling production begins by collecting the parents from the area where they are to be released and from which fertilized eggs are secured by egg collection and sperm sampling (Photo C). Next, the hatched larvae are fed with the floating diatom Chaetoceros gracilis, which has a length diameter of about 5 μm, and raised at a water temperature of 18°C for about three weeks (Photo A&D). When sufficiently mature, the larvae metamorphose (Photo F) by contact with discoid green alga Ulvella lenz (Photo H) and become juvenile sea urchin (Photo I) （Sakai et al. 2003）.
At the seed production facility, Ulvella lenz is grown on the surface of polycarbonate corrugated plates. The young sea urchin fed with Ulvella lenz and grow to a test diameter of 5 mm after about 4 months. In order to increase this discoid green alga, it is necessary to maintain the water temperature between 15°C and 20°C.
Until now, it was believed that young sea urchin could not eat seaweed until grow to 5 mm in test diameter, which requires a very large number of corrugated plates and efforts to support the growth of the sea urchin, thus requiring a large expenditure.
The author has shown that by changing the rearing conditions, it is possible to grow the juveniles even in 2 mm in its test diameter by feeding seaweed and/or dried sea weed (Table 1). It is expected that low-cost seed production without the corrugated plates mentioned above will be possible in the future.
SAKAI Yuichi・Chief Researcher・ Hakodate Fisheries Experiment Station (Master's degree from the Graduate School of Fisheries Science, Hokkaido University)
References
重井陸夫 (1974) ウニ（海胆）類 動物系統分類学8巻8（中） 棘皮動物、中山書店、208－332．
Harries LG and Eddy SD. (2015) Sea urchin ecology and biology 3-24. Echinoderm Aquaculture, Edited by Nicholas P. Brown and Stephen D. Eddy.
北海道立網走水産試験場 (1979)ウニ（海胆）の加工.
Sakai, Y., Tajima, K. and Agatsuma, Y., (2003) Mass production of seed of the Japanese edible sea urchins Strongylocentrotus intermedius and S. nudus. Proceedings of the international conference on Sea-Urchins: Fisheries and Ecology 287-298.
酒井勇一 (2023)多段式育成手法を活用した道産エゾバフンウニの効率的な種苗生産体系の開発 令和3年度 道総研 函館水産試験場事業報告書5－8.
31 December 2023 posted
Releasing Seedlings
In 2003, the 22nd year since Hokkaido began releasing artificial seedlings of Ezo-Bafun Sea Urchin Strongylocentrotus intermedius, I compiled a list of 59 releases that had taken place in various locations in Hokkaido up to that year. The average percentage of released seedlings caught by fishing was 25.8%. Since the catch size differs between the Sea of Japan side (45 mm or larger) and the Pacific side (55 mm or larger), the investment efficiency (catch revenue divided by released seedling cost) was calculated based on the fish price (1,638 yen/kg in whole weight) at the time of compilation of the cases in each area: 3.13 in the Sea of Japan side and 5.58 in the Pacific coastal area (酒井 2003).
The lower the unit cost of seed production, the greater the investment efficiency. However, the smaller the seedlings are, the more likely they are to be victims of predators after release (宮本ら 1985), and it was believed that large seedlings (15 mm or larger) would be suitable for release. On the other hand, the rearing period is limited to eight months from April to December due to the low water temperatures, and it is difficult to grow large-sized seeds in a land-based facility in the Pacific coast in Hokkaido.
Furthermore, sea urchin is considered ‘pests’ that eat kelp, and their release into kelp grounds has been avoided, so the release sites are limited. It has been difficult to release artificial seeds in the waters of East Hokkaido, where many fishermen are engaged in kelp harvesting.
In the Eastern Hokkaido coast, a rock throwing test (throwing in land stones or concrete blocks with no marinealgae zoospore on the surface) confirmed that Saccharina kelp zoospore settle on the sea bottom from November to May of the following year, while the perennial Uganomoke Cystoseria hakodatensis, which competes with Saccharina kelp, settle from July to September. In addition, a rearing test using Strongylocentrotus intermedius juveniles with a test diameter of 5 mm confirmed that they feed on Cystoseria hakodatensis as well as Saccharina kelps (酒井 2003). Therefore, we conducted a double gain release test: (1) we destroyed the Cystoseria hakodatensis colony by feeding pressure of released juveniles and caught the grown individuals between November and May of the following year to make profits, and (2) we created a Saccharina kelp bed by creating bare ground on the bottom of the fishing ground where Saccharina kelp zoospore can settle (Sakai 2004).
We will release 495,000 artificial seeds with an average test diameter of 5.9 mm at a high density of 190 seeds/m2 in a Cystoseria hakodatensis dominant area (60 x 43 m) and destroy this community. A 4 m2 permanent quadrat was set up in this release site and the adjacent non release site (control site), and plastic ties were attached to the holdfast of the Saccharina coriacea and Cystoseria hakodatensis that were growing in this area. The plastic ties were attached to the newly released individuals every year for three years to examine the growth of the seaweed community. The results showed that, unlike in the control area, in the released area, the number of new sprout was not observed in the year following the release of the artificial seeds. The algal standing crop at the reseeding site decreased to 10% of that at the control site 3 years after reseeding.
The total amount of sea urchins harvested 4 years after releasing was 5.8 metric tons as whole weight, which corresponded to a revenue of 6.7 million yen. Since 72,800 reseeded sea urchins were harvested, the recapture rate was about 14.8%. The cost of the reseeding was 5 million yen, and therefore the profit amounted to 1.7 million yen. The investment efficiency was reached 1.35.
From the survey after the harvest, it is estimated that about 7.4 tons of the sea urchins, corresponding to a revenue of more than 11.08 million yen, remained. 5 mm juveniles, the more likely to be victims of predators after release, was enough for restock at least in Pacific area in Hokkaido.
The standing crop of S. coriacea at the reseeding site was about 6 times greater than that at the control site. In contrast, the standing crop of C. hakodatensis was 2/5 times less than that at the control site, confirming that a Saccharina kelp bed could be formed as intended (background photo).
In kelp producing areas in Hokkaido, bare land is created by using heavy machinery and underwater blasting to create communities (known as "miscellaneous seaweed removal"), but the method using Sea Urchin Strongylocentrotus intermedius, as in this study, is also effective.
However, in areas with high densities of leftover sea urchin, the upper part of blades of Saccharina kelp colony were already grazed by sea urchin at the releasing area.
As people working in the ocean, it is essential to balance biological conservation and economic activities such as fishing.
SAKAI Yuichi・Chief Researcher・ Hakodate Fisheries Experiment Station (Master's degree from the Graduate School of Fisheries Science, Hokkaido University)
References
酒井勇一 (2003) エゾバフンウニ漁業を取り巻く現状と人工種苗放流について 北水試だより（59）1-8.
宮本建樹・伊藤雅一・水鳥純雄 (1985) 天然採苗したエゾバフンウニ稚仔の種苗性について 北水試月報42．203－221.
Sakai, Y., Tajima，K. and Agatsuma Y. (2004) Stock enhancement of the short-spined sea urchin Strongylocentrotus intermedius in Hokkaido, Japan. Stock Enhancement and Sea Ranching developments, pitfalls and opportunities Second Edition 465-476. Ed.K.M. Leber, S. Kitada, H. L. Blankenship, T. Svasand.
Backgroud photo: A&C Kelp community formed after harvested the sea urchin in released area, B Kelp blade grazeing by sea urchin wich left behind in this area, D Kelp bed begining to break by over grazing of the sea urchin which left behind in this area.
31 December 2023 posted
The Sea Urchin Microbiome
Sea urchin are important model organisms, commonly used in science experiments to observe developmental processes. The physiological and developmental biology, and molecular biology of the host are highly advanced. In contrast, studies on the function of its gut microbiome has been lagging behind since the existence of nitrogen-fixing bacteria was found in the 1980s. The idea is that nitrogen-fixing bacteria supplement the nitrogen source that is lacking in the sea urchin's food supply.
As was mentioned in the sea cucumber article, sea urchin, like sea cucumber, are echinoderms. Echinoderms, like humans, are a type of metazoan, which means that they have a simpler digestive tract structure than humans, but their digestive tract development process is similar to that of humans in some respects. Increasing our knowledge of the structure and function of the echinoderm gastrointestinal microbiome and the dynamics of its formation process will help us understand the similarities and differences between the microbiomes of the human and fish gastrointestinal tracts. It is also expected this will help the development of prebiotics and probiotics that promote a healthy gut environment in terms of food and substance production.
In humans, the microbial community structure of the digestive tract is known to be affected by the food consumed. Therefore, we moved two different species of sea urchin (Ezo-bafun Sea Urchin and Northern Sea Urchin) that had been reared in different seed production facilities in Hokkaido, Japan, to the same experimental facility, fed the same diet in the same environment, and reared them to observe changes in the community structure of digestive tract microbes. The results revealed that feeding the same diet, rather than different species of sea urchin or rearing environments, was a factor in defining the gastrointestinal bacterial community structure of the sea urchin. We have also discovered the presence of a new microbial community associated with sea urchin growth. A variety of nitrogen-fixing bacteria, previously unknown in sea urchin, have been detected in the gut contents of some individuals (Haditomo et al. 2021).
SAWABE Tomoo・Faculty of Fisheries Sciences・Professor
References
31 December 2023 posted
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