The Third International Symposium on Manila (Asari) Clam-International Collaboration for Manila clam (Asari) Studies-

Ust-Tsu, Tsu, Mie, Japan,
June 1 – 2, 2015

Co-organized by
Fisheries Research Agency
Graduate School & Faculty of Bioresources, Mie University
Mie Prefectural Government

Programme
SymposiumJune 1, 2015 (Monday)
Venue: Ust-Tsu, Tsu, Mie, Japan
9:30 - 9:45: Registration
9:45 - 10:00: Welcome Remarks and Opening Addresses
Fuminari Ito (Executive Director, Fisheries Research Agency)
Yoshihiro Komada (President, Mie University)
Eikei Suzuki (Governor, Mie Prefecture)
10:00-10:10: Outline of the Symposium
10:10-12:00: Session I, Manila clam fisheries in Asian countries
1. Stocks and fisheries of asari in Japan. (Mitsuharu Toba, Tokyo University of Marine Scienceand Technology, Japan)
2. Perkinsus (Lester and Davis 1981) infection in the Manila clam (Ruditapes philippinarum) in
Korea; species identification, impacts and spatio-temporal distribution (Kwang-Sik Choi, Jeju
National University, Korea)
3. Development of Manila clam industry in China (Fang Jianguang, Yellow Sea Fisheries
Research Institute, China)
12:00-14:00: Lunch Break and Poster Session
14:00-15:45: Session II, Manila clam fisheries in Western countries
4. Asari clam in France: 1972 - 2015 (Xavier de Montaudouin, University of Bordeaux, France)
5. Manila clam introduction in the Sacca di Goro Lagoon (Northern Italy): ecological andeconomic implications (Marco Bartoli, Parma University, Italy)
6. Status of Manila clam, Ruditapes philippinarum, culture and fisheries on the West coast of
North America (Brian C. Kingzett, Vancouver Island University, Canada)
15:45-16:00: Coffee Break
16:00-17:10: Session III, Genetic diversity of Manila clam and fishery ground restoration
7. Mapping the stranger: genetic diversity of Manila clam in European coastal lagoons (Stefania
Chiesa, University of Aveiro, Portugal)
8. An a-priori evaluation model for restoration of fisheries population of the Mania clam and acountermeasure example (Hisami Kuwahara, Fisheries Research Agency, Japan)
17:10-18:00: General Discussion
19:00-21:00: Banquet (Restaurant Le Vert)
Field trip
June 2, 2015 (Tuesday)
Field trip to fishing ground, aquaculture site and spat collection site of the Manila clam in Matsusaka andToba, Mie.

Contents

Keynote Lectures
1: Stocks and fisheries of asari in Japan (Mitsuharu Toba)
2: Perkinsus (Lester and Davis 1981) infection in the Manila clam (Ruditapes philippinarum) in Korea;
species identification, impacts and spatio-temporal distribution (Kwang-Sik Choi)
3: Development of Manila clam industry in China (Fang Jianguang)
4. Asari clam in France: 1972 - 2015 (Xavier de Montaudouin)
5. Manila clam introduction in the Sacca di Goro Lagoon (Northern Italy): ecological and economic
implications (Marco Bartoli)
6. Status of Manila clam, Ruditapes philippinarum, culture and fisheries on the West coast of North
America (Brian C. Kingzett)
7. Mapping the stranger: genetic diversity of Manila clam in European coastal lagoons (S. Chiesa, L.
Lucentini, R. Freitas, F.N. Marzano, S. Breda, E. Figueira, N. Caill-Milly, R.J.H. Herbert, A.M.V.M.
Soares and E. Argese)
8. An a-priori evaluation model for restoration of fisheries population of the Mania clam and acountermeasure example (H. Kuwahara, R. Nambu, J. Higano, S. Watanabe, N. Hasegawa, Y.
Fujioka, Y. Ishihi, K. Hanyu, D. Miyawaki, Y. Tanaka, M. Saito, T. Kudo and H. Okamoto)

Poster Presentations
1: Marine microalga Rhodomonas sp. as a novel live food for bivalves (S. Yamamoto, M. Okauchi andT. Yoshimatsu)
2: Observation and monitoring of asari clam predators in a population-collapsed habitat using Field
Server (N. Tezuka, N. Kajihara, T. Fukatsu, K. Oguri and T. Yamakita)
3: Seasonal variations of carbon and nitrogen stable isotope ratios in Manila clam, Ruditapes
philippinarum, in Wajiro intertidal sand flat, Japan (M. Kodama, M. Yamada, S. Yamazaki and N.
Ikeda)
4: Predator-prey relationship among 3 species (Manila clam, kuruma prawn, tiger puffer) for stockenhancement program at tidal flat in Japan (A. Yoshida, H. Yamane, H. Yamazaki, A. Itou, K.
Sakiyama and Y. Sakakura)
5: Correlation between water nutrient level and catch of asari, Ruditapes philippinarum, in fishinggrounds in Japan (M. Uchida, M. Tsujino, N. Tezuka, T. Shigeta, Y. Takada, K. Niwa and Y. Ishihi)
6: Long-term fluctuations in stock abundance of the asari clam (Ruditapes philippinarum) in a
no-fishing area in the southern part of Ise Bay, Japan (K. Hanyu)
7: Effects of small clam abundance, rainfall and sediment on recruitment success of the asari clam
(Ruditapes philippinarum) in a no-fishing area in the southern part of Ise Bay, Japan (K. Hanyu)
8: Sampling design for abundance estimation of the asari clam (Ruditapes philippinarum) in Ise Bay,
Japan (K. Hanyu, H. Kokubu, N. Hata, T. Mizuno, T. Inoue, T. Kudo, N. Hasegawa, Y. Ishihi, S.
Watanabe, Y. Fujioka, J. Higano, R. Nambu and H. Kuwahara)
9: Discovery of a spawning ground of the asari clam (Ruditapes philippinarum) in Ise Bay, Japan (K.
Hanyu, H. Kokubu, N. Hata, T. Mizuno, T. Inoue, Y. Tanaka, T. Kudo, N. Hasegawa, Y. Ishihi, S.
Watanabe, Y. Fujioka, J. Higano, R. Nambu and H. Kuwahara)
10: Ontogenetic changes in ingestion and digestion abilities against diatom cells of the Manila clam (S.
Houki, T. Kawamura, N. Ogawa, N.I. Won and Y. Watanabe)
11: Reproductive biology of Manila clam Ruditapes philippinarum in the coastal waters along eastern
Hokkaido, Japan (Y. Konda and M. Sasaki)12: Food environment for bivalves around Zostera marina beds (H. Kokubu, H. Hanyu and N. Hata)
13: Manila clam, Ruditapes philippinarum, culture using Pyropia spheroplast in closed recirculation
system (N. Arisman, M. N. D. Khan, A. M. Shahabuddin, T. Yoshimatsu, T. Araki)
14: Comparison of types of cages and substrates in suspended culture of the Manila clam, Ruditapes
philippinarum (N. Hata, N. Hasegawa, T. Mizuno, Y. Fujioka, Y. Ishihi, S. Watanabe, D. Asao, M.
Yamaguchi, H. Imai, K. Morita and J. Higano)
15: Effects of feeding regimes on oocyte quality of Manila clam Ruditapes philippinarum (M. Awaji, T.
Matsumoto and J. Higano)
16: Low-salinity endurances of the penshell Atrina sp. and clam Trapezium liratum (T. Kurihara, S.
Nakano, Y. Matsuyama1, K. Hashimoto, A. Ito and M. Kanematsu)
17: Effect of salinity on the survival, growth and settlement of full-grown larvae of the Manila clam
Ruditapes philippinarum in rearing tanks (M. Kanematsu, N. Tezuka, H. Yamazaki, A. Itou, D.
Ojima and A. Nishimoto)
18: Effect of netting on survival of Manila clam Ruditapes philippinarum in an artificial tideland in
Okayama, Japan (K. Izumikawa, T. Mototani, F. Murayama, J. Sato, A. Nishimoto, H. Yazamazaki,
K. Sakiyama, and A. Ito)
19: Effects of water temperature on the expression of heat shock protein (HSP) 22, 40, and 70 genes in
Manila clam (Ruditapes philippinarum) larvae (D. Ojima, M. Kanematsu, A. Nishimoto, A. Ito, H.
Yamazaki, K. Asami and K. Sakiyama)
20: Spatiotemporal population structure of the asari clam Ruditapes philippinarum juvenile in Ise Bay
inferred by microsatellite marker analysis (N. Sano, N. Hasegawa, K. Hanyu, D. Miyawaki, A.
Komaru and H. Kuwahara)
21: Present situation of the asari clam Ruditapes philippinarum resources in Mikawa Bay, Japan (D.
Miyawaki, Y. Murauchi, M. Hibino and S. Okamoto)
22: Seasonal dynamics of the parasitic larvae and free-living adults of the sea spider Nymphonella
tapetis infecting the asari Ruditapes philippinarum in the eastern coast of Chita Peninsula (Y.
Murauchi, S. Okamoto, A. Hirai, D. Miyawaki, N. Yamamoto and M. Hibino)
23: Shellfish production and new approaches in Turkey (S. Sedar)
24: Variations of glycogen, protein and lipid contents depend on size of Ruditapes decussatus in
Bostanli Seashore Izmir Bay, Aegean Sea, Turkey (S. Serdar, H. Pulat and G. Gungor)
25: Use of Pyropia spheroplasts as a live food substitute for culturing Manila clam, Ruditapes
philippinarum (A.M. Shahabuddin, M.N.D. Khan, N. Arisman, D. Saha, T. Yoshimatsu and T.
Araki)
26: Main ecological processes for the determination of Ruditapes philippinarum population size on an
extensive intertidal sandflat in Ariake Sound, Kyushu, Japan (S. Takeuchi and A. Tamaki)
27: Age determination of Asari Ruditapes philippinarum using growth rings on shell surface andsection in Mutsu Bay, northern Japan (D. Sugiura and N. Kikuya)
28: Abundance of planktonic larvae of the asari clam Ruditapes philippinarum around fishing grounds
in Mikawa Bay (N. Kuroda, S. Okamoto, T. Matsumura and M. Hamaguchi)
29: Population status of Manila clam, Ruditapes philippinarum, and physical environmental conditionsin the Natori River estuary in northeastern Japan after the Great Tsunami (K. Ito, H. Yoshida, Y.
Morioka, A. Katayama, D. Takahashi, M. Shoji, K. Sasaki and S. Katayama)
30: Dynamics of the sea spider parasitism on asari in Matsukawaura Lagoon, Fukushima, Japan (T.
Tomiyama, T. Iwasaki, K. Wakui, K. Yamada, M. Tamaoki and K. Miyazaki)
31: Life history and distribution of a sea spider, Nymphonella tapetis, parasitic on the Manila clam,
Ruditapes philippinarum, in Tokyo Bay, Japan (K. Yamada, K. Miyazaki, S. Chow, T. Yamamoto,T. Tomiyama, T. Yoshinaga, Y. Miyama, M. Tamaoki and M. Toba)
32: Distribution, morphology and mode of life in the sea spider Nymphonella spp. (Arthropoda,
Pycnogonida): Potential harmful endoparasitism on asari outside Japan (K. Miyazaki, T. Tomiyama,
K. Yamada and M. Tamaoki)
33: Larval and juvenile dynamics of the Manila clam Ruditapes philippinarum in northeastern Japan (H.
Abe, M. Hamaguchi, N. Kajihara, Y. Taniai, A. Oshino, T. Iwasaki, T. Wada and T. Kamiyama)
34: Condition index and reproduction of the Manila clam Ruditapes philippinarum in suspended andbottom culture (T. Matsumoto, Y. Ishihi, M. Awaji and J. Higano)
35: Report of a novel flagellated parasite in the Manila clam Ruditapes philippinarum on the west coastof Korea (K.I. Park)
36: Geographical distribution of mitochondrial COII haplotypes in the brackish water clam, Corbicula
japonica (Yamato-Shijimi), around the Japanese archipelago (M. Yamada, R. Ishibashi, K. Toyoda,
K. Kawamura and A. Komaru)
37: Effect of different artificial sea waters on survival and growth of adult Manila clam, Ruditapes
philippinarum (M.N.D. Khan1, A.M. Shahabuddin1, N. Arisman, D. Saha, T. Araki and T.
Yoshimatsu)
38: Method for detection of colored sand using image analysis and its application to monitoring
sediment movement on a tidal flat (A. Kurosawa, T. Okabe, Y. Aoki and S. Kato)
39: Four-year investigations into asari clam and molluscan community in tidal flats after the 2011
Tohoku earthquake (K. Okoshi, W. Shinohara and S. Shimizu)
40: Effect of alien predator Euspira fortunei on the distribution and abundance of asari clam after the2011 Tohoku earthquake and tsunami (M. Suzuki and K. Okoshi)
41: Asari clam lived in new intertidal flat after subsidence of the 2011 Tohoku earthquake (T. Uemura
and K. Okoshi)
42: Development of in situ measurement of clearance rate of the Manila clam under suspended culture
conditions (S. Watanabe, N. Hasegawa and J. Higano)
43: Growth and food environment of the Manila clam in suspended culture (Y. Ishihi, S. Watanabe, T.
Matsumoto and J. Higano)
44: Relationship between abundance of planktonic larvae and benthic juveniles of asari Ruditapes
philippinarum in eastern Hokkaido, Japan (N. Hasegawa, T. Onituska, S. Ito and H. Abe)45: Energy budget and neuroenzymatic activity in asari, Ruditapes philippinarum, following short-term
exposure to the toxic alga, Heterocapsa circularisquama: implications for reproductive success (L.
Basti, S. Nagai, S. Segawa and Y. Tanaka)
46: Evaluating the growth and mortality of transplanted asari Ruditapes philippinarum juveniles in the
Matsusaka region, Mie prefecture, Japan (R. Nambu, Y. Fujioka, N. Hasegawa, T. Kudo and H.
Kuwahara)
47: Risk assessment on the mortality of asari clam under oxygen deficiency (J. Higano and T. Mizuno)

Keynote Lectures

Stocks and fisheries of asari in Japan
Mitsuharu Toba*
Tokyo University of Marine Science and Technology, Konan, Minato, Tokyo, Japan,*
Corresponding author: mtoba00@kaiyodai.ac.jp
Asari is one of the most important fishery resources in Japan. Populations of asari are naturally
maintained in the coastal bay areas throughout the country. They have been utilized not only as a foodbut also as a recreational harvest species at least since eighth century AD. Asari is popular among
Japanese people because it is a popular seafood, and is abundant in shallow sandy coasts near urbanizedareas and thus can be harvested easily.
Major harvested areas of asari are Tokyo Bay, Mikawa Bay, Ise Bay, Seto Inland Sea and Ariake
Bay in Japan. Habitats (harvested zone) of asari stretch from intertidal to shallow subtidal areas withmuddy or sandy bottoms. Fishermen harvest asari using a hand rake or a basket rake in tidal areas, anda long-handled basket rake, a vessel-trawled dredge or by helmet diving in deeper areas. Annual
production of asari in Japan been in decline since reaching its maximum of about 160,000 mt in the mid
1980’s, and the production has stayed below 40,000 mt after the 1990’s. The production decreased in
all major harvested areas mentioned except Mikawa Bay.
Stock decline of natural asari is remarkable and seriously problematic for coastal fisheries in Japan.
A number of factors are thought to be responsible for the clam decline, including a decrease of suitable
habitat areas, deterioration of water and substrate quality due to coastal development, physicaldestabilization of bottom substrate by strong wave disturbance, newly arrived invasive predators andparasites, oligotrophication of seawater with strict regulation of waste water quality control, andoverexploitation. The extent and intensity of these factors seem to differ among harvested areas basedon a number of field and laboratory investigations.
Various countermeasures have been taken to restore the natural stocks of asari, mainly
manipulations of habitat environment, including control of strong wave action or bottom substrate
movement by artificial structures, improvement of bottom substrate quality by spreading of sand or
cultivation, improvement of seawater exchange with training dikes or dredging of channels. While
positive results were obtained in some cases, particularly with spreading of sand, there were certain
cases that showed little or no effects.
Recently, challenges are being set to integrate several techniques into one; for example,
countermeasures for improvement of physical environment of habitat, control of predation andcompetition and transplantation of seed clams are to be performed in the same area at the same time.
While these subtechniques are not novel, integrated techniques are characterized by being planned andperformed under comprehensive investigation of the population ecology of asari in relation to theenvironmental conditions in the entire bay area. The investigation includes determination of possible
contribution of local asari populations to larval supply, locations of sources and sinks of clam larvae,
natural mortality and causative factors for juvenile mortality, and so on.
On the other hand, trials of asari culture using on-site facilities are being developed in many areas.
These operations do not focus mainly on restoration of asari stocks but on economic feasibility. One
successful example is suspended culture using oyster rafts and plastic containers. Although production
is limited, suspended culture has become important for local industry because the asari produced are ofhigh quality (more meat content), and thus fetch higher prices.
Recent topics in the related fields are extreme oligotrophication of water in some areas, mass

outbreaks of parasitic sea spiders (Nymphonella tapetis) and increasing production of the exotic hardclam (Mercenaria mercenaria) in Tokyo Bay. Dissolved inorganic nutrients (DIN and DIP) in the Seto
Inland Sea frequently decrease to levels below those in the open ocean from fall to winter. Low
nutrients directly affect the growth of the macroalgae nori (Porphyra) that is cultured widely in the area.
Decreased nutrient levels is reported to cause bay-wide depression of primary production, which in turnmay result in lower egg production and retarded growth of asari.
Mass mortality of asari by the parasitic infection of sea spiders has seriously hampered the asari
fishery in Tokyo Bay since 2007. The origin and cause of the sudden outbreak of the parasite are still
unknown. Measures attempted for controlling the parasite infection (e.g. extermination of free-living
adult sea spider by net trawling) had been ineffective. The asari production in Kisarazu area (Tokyo
Bay) has decreased by more than 90% due to the parasite outbreak.
Natural colonization of the hard clam was confirmed in 1998 in Tokyo Bay. The hard clam isconsidered to be introduced to Japan unintentionally with ballast water of ships from North America.
The hard clam production is increasing steadily, exceeding 1,000 mt in 2014, and has become an
important local fishery resource to substitute asari in Tokyo Bay. The hard clam, however, is classified
as an invasive alien species. Although there is no legal restriction, artificial enhancement or culture of
the hard clam should be avoided from the viewpoint of biodiversity conservation.
＜要約＞日本のアサリ資源と漁業（鳥羽光晴）	
 アサリは日本全国の内湾沿岸に自然分布する重要な水産資源である。レジャー対象種としても古くから利用されており、８世紀には潮干狩りの記録がある。アサリの主要生産海域は、
東京湾、伊勢・三河湾、瀬戸内海西部、有明海で、主な生息域は潮間帯から浅い潮下帯の砂泥域である。潮間帯では手掘りや鋤簾、潮下帯では大型の鋤簾、底引き、潜水器などで漁獲されている。日本のアサリ生産量は 80 年代に 16 万トンに達したが、三河湾を除く全ての主要海域
で生産は減少し、90 年代以降は 4 万トン以下にまで低下しており、近年の沿岸漁業の重要か
つ深刻な問題の一つである。減少原因とされる要因は数多く、沿岸開発による生息場の減少や水底質の悪化、貧酸素、強い波浪による底質の物理的な不安定化、新たな食害生物や病虫害、水質規制による海域の貧栄養化、過剰な漁獲などがある。各要因の影響の強さと広がりは海域によって異なっている。アサリの資源回復を図るために、さまざまな漁場環境の改善努力が行われてきた。構造物による海水の流動や底質の移動緩和、覆砂や耕耘による底質改善，導流堤や削澪による海水交換促進などである。これらの環境改善は一定の効果があり、とくに覆砂では稚貝の増加が認められる例が多いが、期待した効果が得られない場合もある。近年、生息場
所の物理環境の改善、食害生物や競合生物の除去、稚貝の移植などの技術を組み合わせた意欲的な手法が試みられている。個々の技術は以前からあるものであるが、対象海域全体のアサリの個体群生態と環境条件の網羅的な調査を行い、最も効果的な実施条件を判断した上で統合的な手法を適用している。一方、資源増殖策とは別に、全国的に試行例が増えているのは採算性を重視した施設養殖事業である。代表的なものは海面イカダでプラスチック容器に入れたアサリを垂下飼育する養殖事業である。生産量は少ないが、身入りが良く高品質のアサリが生産できることから高価格で取引され、地域の重要な産業になっている。アサリに関連する近年の話題として、海域の貧栄養化、カイヤドリウミグモの寄生による大量死、外来種ホンビノスガイの増加がある。近年は排水の水質規制が進んだために栄養塩（無機溶存態窒素、同リン）が減少している海域があり、特に瀬戸内海では冬季には栄養塩が外洋より低いレベルにまで減少す
ることがある。これは直接的には海藻（ノリ）の著しい生育不良を起こしてノリ養殖業にとって最大の問題になっている。さらに、栄養塩量の減少は海域全体の一次生産力の低下につながっており、アサリにおいても成貝の産卵量の低下、成長の悪化などとの関係が指摘されている。
東京湾では 2007 年に寄生性節足動物カイヤドリウミグモの大量発生があり、その寄生によってアサリが大量死亡した。カイヤドリウミグモの由来と発生原因は不明である。そりネットに
よる自由生活成体の除去など様々な防除対策が試みられたが十分な効果を上げていない。カイヤドリウミグモの寄生は続いており，木更津地区ではアサリの生産量は発生前の 1/10 以下まで低下している。1998 年以降、東京湾で外来種のホンビノスガイが自然発生している。由来は北米地域からの船舶のバラスト水などによる非意図的移入であると言われている。ホンビノ
スガイの漁獲量は年々増加し、2014 年には千トンを越えており、地域の重要な漁獲対象種となっている。一方でホンビノスガイは、侵略的外来種として区分されており、法的規制はない
ものの積極的な増殖や養殖は控えるべきとされている。	
 Perkinsus (Lester and Davis 1981) infection in the Manila clam (Ruditapes philippinarum) in
Korea: species identification, impacts and spatio-temporal distribution
Kwang-Sik Choi*
School of Marine Biomedical Science, Jeju National University, Jejudaehakno, Jeju, Republic of Korea*
Corresponding author: skchoi@jejunu.ac.kr
Asari or Manila clam Ruditapes philippinarum (=Venerupis philippinarum) is commonly
distributed on the west and south coast of Korea, supporting the local shellfisheries industry. Studies
examined Manila clams in Korean waters have reported Perkinsosis, a parasitic disease caused byprotozoan belonging to the Genus Perkinsus. PCR analysis of the Perkinsosis agent indicated that P.
olseni is the only Perkinsosis agent in Manila clam in Korea’s waters, while P. houshuensis, first
discovered in Japan from Japanese Manila clam, detected from R. variagata in coastal Jeju Island.
Several surveys carried out in Korea’s waters for the past decade revealed that infection intensity of
P. olseni over 1 × 106 cells/g tissue caused necrosis and lesion of the gills and the mantle tissues. Heavy
infection with P. olseni also retarded reproductive process of the clams, including slow gonad
maturation and decrease in the reproductive effort. Clams survived from mass mortality event occurred
during post-spawning period on the west coast also showed high infection prevalence and intensity of P.
olseni, suggested that P. olseni is closely linked to the mass mortality event.
Despite the high infection intensity, some clam populations on the coastal Yellow Sea where thephytoplankton biomass was relatively higher, showed relatively higher condition factor, suggested thathigh level of food supply may compensate the energetic loss caused by high load of the parasite in
Manila clam.
<要約>	
 韓国のアサリのパーキンサス病：種の同定と時空間分布と影響（崔光植）	
 アサリは韓国の西岸と南岸に広く分布しており地元の水産業を支えている。韓国水域のアサリには、Perkinsus 属の原虫寄生によるパーキンサス病が報告されている。PCR 法により、韓国
では P. olseni 一種のみが報告されていたが、日本で最初に発見された P. houshuensis が済州島沿岸で発見された。P. olseni の密度が組織 1g あたり百万細胞を超えると組織が壊死してエラや外套膜に障害が起きることが知られている。重篤の場合は、生殖腺発達異常など生殖に影響を及ぼす。韓国西岸で繁殖シーズン後に起きた大量斃死の際に P. olseni の感染が確認され、大量斃死の原因であると考えられた。アサリの餌となる植物プランクトンに富む黄海沿岸では、感染があってもアサリの栄養状態が良いことが知られており、感染症による栄養消費を豊富な餌の供給が助けている可能性がある。
	 	 Development of Manila clam industry in China
Fang Jianguang*
Yellow Sea fisheries Research Institute, CAFS. Qingdao, P. R. China*
Corresponding author: fangjg@ysfri.ac.cn
Over 2 million tons of Manila clams Ruditapes philippinarum (Adams et Reeve) were produced
each year on the coast of Yellow Sea, Bohai Sea and East China Sea of China. Most of this production
occurs in Liaoning, Shandong and Fujian Provinces. In addition, a significant Manila clam seedproduction industry has developed with pond production facilities in Fujian province. Before 1970’s, allfarmed seeds of Manila clam relied on natural. Farmers collected seeds of Manila clam from natural
inhabit. By the late of 1970’s, the seed production technology of Manila clam in ponds was developed
rapidly and achieved great success in Fujian Provinces because the natural seed was not enough to meetthe demand from farming.
Since 1990’s, the Manila clam industry has developed rapidly in China prompted by the demand
from domestic and abroad. In order to meet the increasing demand of seed from whole China, the seedproduction of Manila clam in reclamation areas became the major sources of seed of Manila clam forfarming in China. In 2013, the total seed production in Fujian province was 7952 tones with shell length
about 1 cm. Meanwhile, the Manila clam is also the major species farmed with shrimp, fish, crab inform of pond integrated multi-trophic aquaculture that is practiced in commercial scale in Zhejiang andFujian Provinces.
In history, the farming of Manila clam was mainly carried out in tidal zone and subtidal zone before
1980’s. An unfilled domestic and overseas demand was pushing attempts to increase production of thisclam from 1990’s. The farming areas of the clam has extended from intertidal zone to shallow sea withthe depth of about 10 m in Shandong and Liaoning provinces. Because of longer time immersing inwater and richer supply of phytoplankton, the growth rate and suitable harvest time of the clam
cultivated in deeper water is much higher and longer than that of clam growing in natural inhabits. The
main problems for such farming are the predation from crab, starfish and sea snails.
The farming space decreasing mainly due to sea reclamation along the coast, and the pollution fromlands are being the major threat to Manila clam industry in China. However, the impact of climatechange, such as acidification, sea storm and extreme weather on development of Manila clam should bestudied systematically in the world.
<要約>中国のアサリ産業の発展（方建光）
中国では黄海、渤海、東シナ海の沿岸、主に遼寧省、山東省、福建省でアサリが年間約２百万
トン以上生産されてきた。70 年代以前は天然種苗に依存してきたが、需要の増大のため 70 年
代以降養殖池での種苗生産技術が発達し、福建省で成功を収めた。90 年代以降国内外の需要の増加によりアサリ産業は急激に成長した。種苗需要の増大のために造成場での種苗生産が主な供給源となった。2013 年の福建省での種苗生産量は 7952 トンであった（殻長 1cm）
。福建省と浙江省では、養殖池でのアサリ、エビ、魚、カニの複合養殖が商業規模で行われている。
80 年代前のアサリ養殖は主に潮間帯と浅い潮下帯で行われたが、90 年代以降の需要増加のため山東省と遼寧省では、水深 10m にまでエリアが拡大した。深い水深帯では干出がなく餌となる植物プランクトンが豊富なためアサリの成長がよく収穫期も長いが、カニ、ヒトデ、巻き貝類による食害が問題となっている。漁場面積は沿岸の埋め立てにより減少し陸域からの環境汚染が問題となっている。温暖化や酸性化の影響に関してはさらに研究を進める必要がある。

	
 Asari clam in France: 1972 - 2015
Xavier de Montaudouin*
OASU, Station Marine d'Arcachon, Université de Bordeaux, 2 Rue du Professeur Jolyet, Arcachon,
Cedex, France*
Corresponding author: x.de-montaudouin@epoc.u-bordeaux1.fr
Asari clam was introduced to France in 1972 for aquaculture purpose. At this time, France
underwent an oyster crisis and urgently needed to diversify its aquaculture. All adults and spat
originated from the same area (Puget Sound, WA, USA). After a promising start, Asari clam culture
rapidly faced a series of concomitant handicaps: firstly, there was a lack of suitable ground availability
due to certain reluctance from oyster farmers to share their fields and/or diversify their activity. Indeed,
Asari clam introduction was concomitant with the introduction of Pacific oyster (Crassostrea gigas);secondly, economical competition with Italy rapidly became tough, exacerbated by the occurrence of
neonaturalized Asari clam populations. In this context, European regulation was unfavorable to France
due to contrasted rules between the Mediterranean Sea and the Atlantic Ocean; finally, several diseases
impacted clam populations. At the end of the 80’s, mass mortality occurred due to Brown Ring Disease
and related to a prokaryote (Vibrio tapetis).
Today, the French production remains low (2-3000 tons) and most of it is provided by harvesting
the neonaturalized populations in two sites (Arcachon lagoon and Morbihan Gulf). In Arcachon Bay, an
exhaustive population dynamics study highlighted the shared responsibility of fishing activity andenvironmental characteristics. A management model proposed different scenarios based on fishingeffort reduction (i.e. fishing area, and/or fishing licences number, and/or fishing period). The
implementation of these recommendations provided some encouraging results. However, Asari clamfitness remains poor. A genetic impoverishment due to population isolation was argued by fishermen,
but transplant experiment demonstrated that these bivalves kept their plasticity, at least in terms ofgrowth and condition index. Thus, several environmental factors were investigated as possible fey
factors explaining clams low performances. Again, pathologies were pointed out and in particular thehigh pressure exerted by the protist Perkinsus sp. (perkinsosis). Besides, in 2005 a new pathology was
discovered in Arcachon bay, the Brown Muscle Disease. The etiological factor is not yet discovered,although viral origin is suspected.
A meta-analysis comparing Asari clam characteristics in Arcachon Bay with the international
literature pointed out that one of the most important factor explaining their bad condition index in thisFrench lagoon was certainly a pool of unfavorable factors (diseases, trace elements, …). However, 30%of the differences of condition index among sites over the world were explained by chlorophyll aconcentration.
Finally, marine ecologists must deal with a conflictual goal: on the one hand Asari clam is an
important exploited bivalve in France, on the other hand it remains an exotic species which needs
careful attention (European regulations).
＜要約＞フランスのアサリ 1972-2015（グザビエ・デ・モントドゥアン）
アサリは 1972 年に養殖目的でアメリカ、ワシントン州のピュージェット湾からフランスに持ち込まれた。この時フランスではカキ養殖の不振のために養殖の多角化が求められていた。ア
サリ養殖は順調なスタートを切ったが、いくつもの問題に直面することとなった。まず、カキ

養殖業者が経営の多角化や養殖場の共有に積極的でなかったため、養殖場の不足が問題となった。実際にアサリの導入はマガキと同時に行われた。次に、アサリ販売はイタリアとの商業的競争が熾烈であったが、さらに天然繁殖アサリが増えるにつれて収益性が低下した。これに関連して、欧州での規制が大西洋と地中海で対照的であることがフランスにとって不都合であった。最後に、疾病がアサリに打撃を与えた。1980 年代の終わりにブラウンリング病またそれに関連したウイルス性疾病による大量斃死が問題となった。今日のフランスでのアサリ生産量
は低位水準（2000〜3000 トン）であり、ほとんどがアルカション湾とモルビアン湾の天然資源に依存している。アルカション湾では、徹底的な個体群動態に関する研究により、資源量に対する漁業と環境の両方の影響が指摘されている。異なる漁獲圧の低減方法（漁場面積、免許制限、漁期制限）を想定した管理モデルが提唱されており、これらの導入により良好な結果が得られている。しかし、アサリの生産力は低いままである。漁業者から、隔離による遺伝的脆
弱性の可能性が指摘されたが、移殖実験により少なくとも成長や肥満度に関しては多様性が保たれていることが示された。アサリの生産性に影響を与える環境要因に関して調査が行われ、寄生虫病、とくにパーキンサスの影響が取りざたされた。さらに 2005 年にアルカション湾で新しくブラウンリング病が発見され、ウイルス感染が疑われているが、まだ明らかとなっていない。アサリの様々な特性をアルカション湾での調査と文献値とで比較したメタアナリシスにより、フランスの低生産には、疾病や重金属などの複合的要因が考えられた。一方で、クロロ
フィル濃度（餌の量）は生産性の差の３０％しか説明しなかった。アサリがフランスにおいて重要な漁業対象二枚貝であると同時に、扱いに注意が必要な外来種（欧州規制）であるという対立する要素を持った生物であるという難しい問題と対峙する必要がある。
	 	 Manila clam introduction in the Sacca di Goro Lagoon (Northern Italy): ecological andeconomic implications
Marco Bartoli*
Department of Life Sciences, Parma University, Parma, Italy*
Corresponding author: marco.bartoli@unipr.it
Monitoring activities in the Sacca di Goro Lagoon (Po River Delta, northern Italy) started in 1988,
when summer dystrophic events associated to macroalgal bloom and collapse seriously impacted themost relevant local economic activity (clams farming). The manila clam was introduced a few years
before and represented an incredible economic success and somehow a paradox, as this species is
exotic.
From 1988 to 1994 an intensive, monthly-based monitoring plan of water column physio-chemicalparameters was performed, aiming at analyzing salinity, dissolved oxygen, chlorophyll a and nutrient
distribution in a grid of sampling stations, with respect to hydrodynamics and freshwater inputs.
Later on, monitoring of spatial distribution and biomass evolution of the dominant macroalgal
community was started (1990-1996), together with experiments focusing on primary production andnitrogen uptake by macroalgae and on the theoretical role of clams in coupling benthic and pelagic
processes. Regular monitoring was afterwards flanked by a more experimental approach aiming at moredetailed analyses of how clams affect benthic processes, in particular aerobic and anaerobic respiration,
the regulation of denitrification and the analysis of nitrogen cycling within farmed areas (1993-2005).
More recently different European projects focused on socio-economic aspects associated to clams
farming. In this review I summarize the main outcomes of these research activities with the overall aimof quantifying at the lagoon scale the role of farmed organisms, as regulators of some of the multiple
processes involved in N cycling. Special emphasis is given to how clams affect nitrogen uptake,dissipation and recycling pathways, with respect to external loads and net export to the adjacent coastal
area, and to how the introduction of this species altered and improved the local economy.
＜要約＞イタリア北部サッカディゴロ湾のアサリ導入（マルコ・バルトリ）
夏季の赤潮による栄養障害がイタリア北部ポ川の三角州サッカディゴロ湾のアサリ養殖産業に大打撃を与えた 1988 年にアサリのモニタリングが始まった。アサリはこの数年前に移殖され商業的に大成功を収めていたと同時に移入種であることが問題視されていた。1988 年から1994 年にかけて海水の塩分、溶存酸素、クロロフィル、栄養塩に関する物理化学的モニタリ
ングが海洋の動態と淡水流入との関係を調べるために毎月行われた。1990 年から 1996 年に優占海藻群落の空間分布と生物量の推移に関する調査が行われ、同時に海藻の生産量と栄養塩吸収およびアサリが水柱と底質との関わりに与える影響に関する実験が行われた。その後、1993
年から 2005 年まで、この定期調査は、アサリが底質の嫌気呼吸、好気呼吸、脱窒、窒素循環に与える影響に注目してより詳細に行われた。近年のヨーロッパでは、アサリ養殖の社会経済学的な要因に関するプロジェクトが行われている。本公演では、これらの調査の結果に関して、養殖が湾の窒素循環に与える影響を網羅的かつ定量的に評価することを目的としてまとめる。
とくに、アサリが窒素の吸収、消費、再利用の経路に与える影響のうち外部からの負荷と近隣の沿岸域への流出に関して、また、アサリがどのように地域経済を改善したかに関して紹介する。

Status of Manila Clam, Ruditapes philippinarum, culture and fisheries on
the West coast of North America
Brian C. Kingzett*Centre for Shellfish Research, Vancouver Island University, Nanaimo, British Columbia, Canada*
Corresponding author: brian.kingzett@viu.ca
The Manila clam Ruditapes philippinarum was inadvertently introduced into the Northeast Pacific
Coast in the early 1900’s with seed shipments of Pacific oysters (Crassostrea gigas). The species was firstdetected on the east coast of Vancouver Island in 1930 and spread rapidly. It is now found from theCentral Coast of British Columbia to California. Production from aquaculture and commercial fisheries isapproximately 5938 tonnes from British Columbia, Washington and California.
Commercial fisheries for Manila clams began in Washington State in the 1940’s and the 1960’s in
British Columbia. Aquaculture of Manila clams supplemented by hatchery produced seed began in 1972
in Washington State; clam aquaculture was permitted since 1981 in California and 1985 in British
Columbia. Washington State is unique in that tidelands may be privately held and this has promoted thedevelopment of intertidal shellfish aquaculture. Tidelands are leased from the State and the Provincial
governments in California and British Columbia respectively.
Aboriginal groups in British Columbia and Washington State have differential access to wild stocks ofManila clams. Under federal treaties of 1854 and 1855, Washington tribes reserved the right to harvest
fish and shellfish at all usual grounds and stations. Recent court decisions have upheld the Puget Soundtribes’ rights to up to 50 percent of the sustainable yield from natural shellfish beds which exclude
aquaculture sites. In British Columbia there are 597 Aboriginal Commercial Fishery licenses which areheld by various First Nations (aboriginal communities) which subsequently distribute them to members.
British Columbia First Nations’ traditional harvest for Food Social and Ceremonial purposes may occur
coast-wide where areas are open for harvest. In both Canada and the USA aboriginal groups who
previously had strong cultural ties to shellfish are exploring or becoming increasing involved in clam
aquaculture.
Clam aquaculture in North America utilizes conventional techniques included the use of hatcheryproduced seed to augment natural recruitment and predator netting to protect seeded stocks. Most
harvesting is conducted by hand raking although the adaption of mechanical digging machines is being
used at certain sites in Washington State and tested in British Columbia.
Social conflicts with clam aquaculture are increasing within the Strait of Georgia (British Columbia)
and Puget Sound (Washington State) where upland urbanization is increasing. Controversy includes theconcerns over the use of intertidal areas for shellfish cultivation, and licensing of new farms. These
include increasing opposition to the use of predation netting which is believed to cause negative effects on
wildlife, benthic ecosystems, increasing mechanization in the marine environment and public use andenjoyment of the marine areas. Non-point source pollution in these areas as a result of population increase
have resulted in downgraded water quality and increased restrictions on harvesting in certain areas.
Depuration of clams harvested from areas with decreased water quality is practiced in British Columbia
only. Social conflicts are one of the drivers of research examining ecosystem interactions of clam
aquaculture. Recent research projects have examined the ecological impacts that clam aquaculture may
have in the marine environment as well as the ecosystem services that it may provide.
	 ＜要約＞北米西海岸のアサリ漁業と養殖（ブライアン・キンゼット）	
 アサリは 1900 年代にマガキ種苗に混入して北米に移植された。1930 年にバンクーバー島東岸
で発見され、その後急速に分布を拡大した。現在ではブリティッシュコロンビア州中部からカ
リフォルニア州にまで分布している。ブリティッシュコロンビア州、カリフォルニア州、ワシントン州の養殖と漁業生産は合計で 5938 トンである。アサリ漁業はワシントン州で 1940 年代に始まりブリティッシュコロンビア州では 1960 年代に始まった。人工種苗による養殖は 1972
年にワシントン州で始まり、カリフォルニア州では 1981 年、ブリティッシュコロンビア州では 1985 年に養殖が許可された。ワシントン州では個人所有の干潟が多いために養殖の開始が早かった。ブリティッシュコロンビア州とカリフォルニア州の干潟は州からの借地である。ブ
リティッシュコロンビア州とワシントン州の先住民には特別許可が与えられている。ワシントン州では、1954 年と 1955 年の国との協定によりワシントン州の先住民には全ての場所で魚類と二枚貝類の採捕が認められている。近年の裁判では、ピュージェット湾の、養殖場を除く持続可能な二枚貝資源の 50%を先住民が採補する権利を認めた。ブリティッシュコロンビア州では先住民グループが 597 の先住民漁業許可を有しており、それぞれ所属メンバーに配付している。ブリティッシュコロンビア州の「先住民グループ食用および儀式のための伝統的採捕」は、漁業が許されている全ての地域に広がっている。カナダとアメリカの両方で採貝と文化的に強いつながりも持ってきた先住民グループによる養殖が増えている。北米の二枚貝養殖は、人工種苗を用いた種苗数の補強と被覆網による食害防除を組み合わせた手法で従来行われている。
収穫は手堀が主だが、ワシントン州の一部では機械堀りを用いており、ブリティッシュコロン
ビア州でも試験的に導入されている。ジョージア海峡とピュージェット湾では、無計画な都市化が進んでいる地域で養殖と住民との間に社会葛藤が生じており、潮間帯での二枚貝養殖や新規養殖場の許可が問題となっている。被覆網が自然生物や底生生態系へ与える悪影響、機械化の促進、海の娯楽利用などが問題点となっている。人口増加による非特定汚染源負荷が水質悪化を招き、採貝が禁止されている場所もある。水質が悪化した地域での貝の浄化処理は、ブリティッシュコロンビア州でのみ行われている。社会葛藤のために養殖と環境との関係に関する研究が求められている。近年の研究プロジェクトでは、二枚貝養殖が環境へ与える影響や生態系サービスへの役割が調べられている。	
 Mapping the stranger: genetic diversity of Manila clam in European coastal lagoons
Stefania Chiesa1*, Livia Lucentini2, Rosa Freitas1, Francesco Nonnis Marzano3, Silvia Breda4, Etelvina
Figueira1, Nathalie Caill-Milly5, Roger J.H. Herbert6, Amadeu M.V.M. Soares1 and Emanuele Argese4.
1

Department of Biology & CESAM, University of Aveiro, Campus de Santiago, Aveiro, Portugal;
Department of Chemistry, Biology and Biotechnologies, University of Perugia, Via Elce di Sotto,
Perugia, Italy; 3Department of Life Sciences, University of Parma, Viale delle Scienze, Parma, Italy;
4
Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Dorsoduro,
Venice, Italy; 5Ifremer, Laboratory Halieutic Resources from Aquitaine, UFR Sciences and Technics, 1
allée du Parc Montaury, Anglet, France; 6Centre for Conservation Ecology and Environmental Sciences,
Faculty of Science and Technology, Bournemouth University, Christchurch House, Fern Barrow, Poole,
Dorset, United Kingdom.
*
Corresponding author: stefania.chiesa@ua.pt
2

Manila clam Ruditapes philippinarum - synonym Venerupis philippinarum (Adams and Reeve, 1850)
is one of the most successful marine invaders worldwide and represents almost 20% of worldwide
mollusc total production. Originally distributed in the Indo-Pacific region, the species was introduced foraquaculture and fisheries in North America, Polynesia, the US Virgin Islands, as well as in Atlantic andMediterranean coasts of Europe. Due to the commercial value of the species, population genetics andstock composition are of primary importance both in natural and invaded environments. Moreover,molecular genetics can provide valuable data in invasion biology, as, for example, the structure of the
exploited populations, the origin of source populations and the routes of invasions. Furthermore,
molecular data might be useful for the tracking of seafood products, as requested by the European
Commission for European seafood products (see EC laws n°178/2002, 509/2006, 510/2006 and theirimprovements). Despite all these considerations genetic data are lacking, especially for introduced
populations, and should be urgently provided.
In a framework of an European network of researchers involved in Manila clam studies, clams werecollected in coastal lagoons and estuaries in both Mediterranean (Northern Adriatic Sea, Italy) andAtlantic (England, France, Spain and Portugal) coasts of Europe. Both mitochondrial and nuclear
molecular markers were applied to investigate the genetic structure of populations, specifically by the
direct sequencing of 16S rDNA and COI gene fragments and by the genotyping of 7 microsatellite
markers previously used in native populations. Results demonstrated the occurrence of multiple
haplotypes for both mtDNA markers. Singletons were occurring, but most of the samples were grouped
into 1-3 main haplotypes (depending on the mtgene) with high frequencies. Regarding 16S rDNA, one
main haplotype was identified in the European analyzed populations, but few sequences were available
in Genbank to make comparisons with native populations. As for COI, even if new haplotypes were
described for Europe, the main frequent haplotypes identified in European samples were alreadydescribed in native Japanese and Chinese populations, allowing the identification of source and possible
routes of invasion. Concerning the microsatellite data, the genotyping of Manila clam populations
showed low genetic diversity among them, considering the Fst values, and a lack of genetic structuringwhen analysed by Structure software. Both these data suggest the absence of geographic differentiation
among the introduced populations of Manila clam, as a result of introgression due to translocations andother human activities. The levels of genetic diversity within introduced populations were comparable
to those described from native regions, suggesting that multiple introduction events and mixed source
populations can counterbalance the loss of genetic diversity caused by the founder effect. However, itmust be remarked that microsatellites showed a strong occurrence of null alleles when tested byMicro-checker, as previously observed in other bivalves, suggesting that the problem is differently
distributed among Manila clam populations or specific loci, thus microsatellites should be carefully
checked before used in extensive population studies. In the near future, population genetics and stock
identification of this species on a large scale should be assessed using new powerful markers such as
those obtained by NGS (Next Generation Sequencing) methods. In conclusion, this research represents
the very first extensive genetic investigation on Manila clam’s European populations, confirming theusefulness of molecular studies for comparing native and introduced populations, defining the levels ofgenetic diversity that will help to inform management practices.
＜要約＞	
 ヨーロッパ沿岸のアサリの遺伝的多様性（ステファニア・チエサ）	
 アサリは世界的に最も成功した移入種のひとつであり、世界の貝類生産の 20%を占める。原産
地はインド太平洋で、北米、ポリネシア、バージン諸島、ヨーロッパの大西洋と地中海沿岸に養殖目的で移殖された。商業価値が高いため原産地と移殖先の両方において、集団遺伝と資源組成の解明は重要である。また分子生物学的手法は、移入元、移殖経路、資源構成に関して重
要な情報を与え、欧州委員会の欧州水産物のトレーサビリティーにも有用である。しかし、移殖種に関するこのような情報は少なく、緊急に入手すべきである。欧州でのアサリ研究ネット
ワークでは、地中海沿岸（北アドリア海、イタリア）と大西洋沿岸（イギリス、フランス、スペイン、ポルトガル）でアサリを採集している。ミトコンドリアと染色体マーカー、特に
16SrDNA と COI 遺伝子とマクロサテライトを用いた資源の集団遺伝構造が調査された。これらの結果から、16SrDNA と COI 遺伝子の両方で、遺伝子多型が認められた。単一遺伝子も出現したが、ほとんどは 1 から 3 のハプロタイプにグルーピングされた。16SrDNA に関しては、一つの大きなハプロタイプが認められたが、比較するための原産地からの遺伝子情報が少ない。COI に関しては、欧州で確認された主なハプロタイプが日本や中国から報告されており、移殖経路を知るために利用できる。マイクロサテライトからは、遺伝的多様性が少ない
ことが示され、人的に移殖されたアサリには地理的隔離が起こっていないことが考えられる。
集団内での多様性に関しては、原産地と同様に豊かで、移殖が複数回にわたって行われたこと、複数の原産地が混ざっていることなどが創始者効果を打ち消していると思われる。マイクロサ
テライトに関しては他の二枚貝同様に無効対立遺伝子の出現が強く、使用には注意が必要である。今後アサリの大規模な集団遺伝と資源判別を次世代シーケンサー等強力なツールを用いて行われるべきである。

An a-priori evaluation model for restoration of fisheries population of the Manila clam
and a countermeasure example
Hisami Kuwahara1*, Ryogen Nambu2, Junya Higano3, Satoshi Watanabe3, Natsuki Hasegawa3, Yoshimi
Fujioka3, Yuka Ishihi3, Kazuhiro Hanyu4, Dai Miyawaki5, Yoshio Tanaka6, Masayuki Saito6, Tomoaki
Kudo7 and Hiroshi Okamoto8
1

Fisheries Research Agency, Yokohama, Kanagawa, Japan; 2National Research Institute of Fisheries
Engineering, Fisheries Research Agency, Kamisu, Ibaraki, Japan; 3Natioanl Research Institute of
Aquaculture, Fisheries Research Agency, Minamiise, Mie, Japan; 4Mie Prefectural Fisheries Institute,Suzuka, Mie, Japan; 5Aichi Fisheries Research Institute, Minamichita, Aichi, Japan; 6Tokyo Kyuei,
Kwaguchi, Sitama, Japan; 7Kaiyo Engineering, Suzuka, Mie, Japan; 8Nippon Aspi, Kashiwa, Chiba,
Japan.
*

Corresponding author: kwhr@affrc.go.jp

The national production of the Manila clam, Ruditapes philippinarum, fishery has been continuously
declining since the mid 1980s in Japan. The production of the clam in Ise Bay has also been declining,which was around 10,000 t per year from 1980 to 1995 and then sharply dropped to the current level ofless than 5,000 t per year. Fisheries Agency of Japan has been implementing stock enhancement
programs, including fisheries management, fishing ground development and reseeding as
countermeasures for the production decline. In order to attain successful stock enhancement, it is first of
all necessary to elucidate the causes of stock depletion in different stages in life cycle of the clam. Then,
one must make a plan to remove or reduce the effects of the elucidated causes taking into account what
measures should be applied to what location to what extent. In the present study, we introduce an a-priori
evaluation model for stock restoration of the clam, which we developed under a Fisheries Agency project
conducted in Ise Bay. An example of a countermeasure is also introduced.
The a-priori evaluation model takes into account the life cycle characteristics of the clam anddescribes broad area larval network, juvenile mortality to the instability of the sediment due to wave
action, fishing mortality, and so on. In addition, the model makes it possible to evaluate the efficacy ofnursery ground and spawning ground for stock restoration. The model estimated clam catch well agreed
with the actual catch in Ise Bay. It was also predicted that spawning grounds should be developed in
inner parts of the bay and nursery grounds in middle parts of the bay or near the bay mouth.
The population level of the clam juvenile is relatively stable in Ise Bay every year; however, theyoften fail to recruit into marketable size due to adverse effects of wave actions and strong river runoffs.
In order to cope with this problem, we have established an effective collection method of juveniles from
unfavorable habitats, and we are trying to develop a nursery ground where the collected juveniles can bereleased and grow up to marketable size with high growth and low mortality. We have succeeded incollecting 3.8 million juveniles by using developed device in only four days and 5 workers at Kushida
estuary, Mie prefecture. Nursery grounds were developed by capping on the seabed within a radius of
50m using river sand (median grain size: 0.75mm) and gravel (median grain size: 5mm), respectively, in
October 2016 in cooperation with Mie prefectural government. Their attempts were expected efficiency
to improve sediment without silt ratio and stability for wave action on seabed, and their efficacy has been
investigated.
	 ＜要約＞アサリ資源回復のための事前評価モデルと対策事例の紹介	
 （桑原久実）	
 我が国のアサリ漁獲量は、1980年の後半から減少傾向にあり、回復の兆しが見えない状況にある。伊勢湾のアサリ漁獲量も同じ傾向にあり、1980年～1995年は、おおよそ1万トン程度であったが、その後急激に減少し、現在は、半分より少ない状況が続いている。このため、水産庁は、資源管理、漁場造成および種苗放流などの資源回復の取り組みが実施している。このような対策の成果をあげるためには、まず生活史のどの段階で何が制限になり資源が回復しないのか明らかにする必要がある。次に、その制限要因を除去や緩和するために、どのような対策をどの場所でどの規模で実施すべきか明らかにする必要がある。本発表は、筆者らが水産庁事業において伊勢湾のアサリを対象に実施している調査研究の中から、１．アサリ資源回復にための事
前評価モデル、２．対策事例について紹介する。１．アサリ資源回復にための事前評価モデル：	
 本モデルは、アサリの生活史を考慮し、広域な幼生ネットワーク、波浪による底質の安定性か
らみた稚貝の死亡、漁獲の影響などを表現したものとなっている。また、資源回復のために実施する成育場、母貝場などの対策がこのモデルに組み込まれ、これらの効果を事前に評価できるようになっている。母貝場造成は、母貝を増やしてアサリ漁場への幼生の供給量を増加させる場をつくること、成育場造成は、アサリ幼生が着底した後、稚貝の死亡が少なく成長が早く
数多くの成貝が成育する場をつくることが目的である。漁獲量の計算結果は、実際の漁獲量と良好な一致を示した。資源の回復には、湾奥部で母貝場、湾中央部～湾口部で成育場の設置が効果的であることが示された。２．具体的な対策事例：	
  伊勢湾のアサリは、毎年、比較的安定して稚貝は発生するが、その後、波浪や河川出水によって、漁獲サイズまで成長できずに死亡する場合が多い。このため対策としては、放置しておけば死んでしまうアサリ稚貝を効率よく回収すること、回収したアサリ稚貝を放流して成貝まで安定して成長できる成育場をつくることが重要で、これらの技術開発について取り組んでいる。前者については、アサリ稚貝回収装置を開発し、三重県松阪海域で現地実用試験を実施した。2013年5月27日～31日(29日のぞく)の4日間で380万個体の稚貝回収に成功した。後者については、三重県庁の協力を得て、川砂覆砂（シルト含有率の少ない）と砕石覆砂（中央粒径=5mm）共に50m×50mを2014年10月に施工し、成育場としての機能を調査中である。川砂覆砂は、アサリが生息する底質環境の改善、砕石覆
砂は波浪に対する底質の安定性の増加しアサリが定着できる環境に改善する効果を期待している。	
 Poster Presentations

1
Marine microalga Rhodomonas sp. as a novel live food for bivalves
Satoshi Yamamoto1, Masanori Okauchi2 and Takao Yoshimatsu1*
1

Graduate School of Bioresources, Mie University, Tsu, Mie, Japan; 2National Research Institute of
Aquaculture, Fisheries Research Agency, Minamiise, Mie, Japan*
Corresponding author: takaoyos@bio.mie-u.ac.jp
Recently, many species of bivalves, including the asari clam have become more popular as seafood
all-over the world. In spite of the increasing demands of bivalves, the natural resources are becoming
scarce year by year. Therefore, stable aquaculture production of bivalves is highly required to substitutethe natural resources. Marine microalga Rhodomonas sp. is widely distributed in Japan’s coastal waters.
This species has a high content of highly unsaturated fatty acids (HUFAs) that enhance the survival andgrowth of bivalves. For this reason, Rhodomonas sp. is expected to play an important role as feed forbivalve aquaculture. In this study, suitable conditions for mass culture of Rhodomonas sp. in terms oftemperature, salinity and light intensity were investigated. A series of rearing experiments was
conducted with one of the three factors altered at a time. In temperature, higher cell increase rate wasobserved between 16 and 24°C, and the maximum cell density (435.8 × 104 cells ml-1) was observed at
24°C. In salinity, higher cell increase rate was observed between 14 and 35 psu, and the maximum celldensity (373.9 × 104 cells ml-1) was observed at 21 psu. In light intensity, higher cell increase rate wasobserved between 35 and 80 µmol m-2 s-1, and the maximum cell density (360.1 × 104 cells ml-1) was
observed at 80 µmol m-2 s-1.

2
Observation and monitoring of asari clam predators in a population-collapsed habitat
using Field Server
Naoaki Tezuka1*, Naoto Kajihara1, Tokihiro Fukatsu2, Kazumasa Oguri3 and Takehisa Yamakita3
1

National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency,
Hatsukaichi, Hiroshima, Japan; 2National Agriculture and Food Research Organization Agricultural
Research Center, Tsukuba, Japan; 3Japan Agency for Marine-Earth Science and Technology, Yokosuka,
Kanagawa, Japan*
Corresponding author: tezukan9@fra.affrc.go.jp
The Nakatsu tidal flat, located in western Seto Inland Sea, Japan, is known as an asari clam,
Ruditapes philippinarum, population-collapsed habitat. A recent study observed low clam survival rates,< 15%/yr, from post-settlement until fishable size in this flat. Based on previous netting/caging
experiments, predation has been suggested as a major cause of clam mortality. However, we do nothave enough information on predator species composition or when and how often the predators appear
on the flat. We employed the Field Server, originally developed for agricultural field monitoring
equipped with a web-camera and sensors, to observe the asari clam predators on the Nakatsu tidal flat.
Field Server observations, comprised web-camera images retrieved every 30 min via the internet,
revealed that ducks (Anas acuta) often appear on the monitoring site during low tide in winter. These
results suggest that predation by ducks may be a significant cause of asari clam mortality during winterin the Nakatsu tidal flat.
This study was supported by the Ministry of Agriculture, Forestry and Fisheries of Japan.

3
Seasonal variations of carbon and nitrogen stable isotope ratios in Manila clam, Ruditapes
philippinarum, in Wajiro intertidal sand flat, Japan
Masashi Kodama1*, Machiko Yamada2, Sayaka Yamazaki2 and Norihiro Ikeda2
1

Japan International Research Center for Agricultural Sciences, Tsukuba Japan; 2Fukuoka Women’s
University, Fukuoka Japan*
Corresponding author: mkodama@affrc.go.jp
Seasonal variations of carbon and nitrogen stable isotope ratios, δ13C and δ15N, in soft body tissue ofthe Manila clam, Ruditapes philippinarum, and their potential food sources were investigated in the
Wajiro intertidal sand flat, Fukuoka, Japan. The δ13C and δ15N of R. philippinarum varied between-15.0‰ and -19.1‰ and between 10.2‰ and 14.0‰, respectively, and they showed a seasonal cyclethat was higher from summer to autumn and lower from winter to spring. Carbon to nitrogen (C/N)
ratio of the soft body tissue, which is related to glycogen content, also showed a seasonal cycle whichbecame higher in spring and lower in winter, and C/N ratio exhibited a significant negative correlation
with δ13C. Comparison of the yearly mean stable isotopic signatures of R. philippinarum and those of
potential food sources indicates that R. philippinarum utilize particulate organic matter in the watercolumn and benthic micro algae as main food sources. These results suggest that the stable isotopic
signatures of R. philippinarum reflect not only the isotopic signature of assimilated food but also thefluctuation of their body condition related to seasonal storage cycle of glycogen.

4
Predator-prey relationship among 3 species (Manila clam, kuruma prawn, tiger puffer) for
stock enhancement program at tidal flat in Japan
Ayumi Yoshida1, Hikaru Yamane1, Hideki Yamazaki2, Atsushi Itou2, Kazutaka Sakiyama3 andYoshitaka Sakakura1*
1

Graduate School of Fisheries Science & Environmental Studies, Nagasaki University, Nagasaki,
Japan; 2National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research
Agency, Hiroshima, Japan; 3Japan Sea National Research Institute, Fisheries Research Agency, Kyoto,
Japan*
Corresponding author: sakakura@nagasaki-u.ac.jp
Hatchery-reared Manila clam (Ruditapes philippinarum), kuruma prawn (Marsupenaeus japonicus)
and tiger puffer juveniles (Takifugu rubripes) are released into the same tidal flat, however, they can bein predator-prey relationship at the nursery area. If this is the case, we need to reconsider a releasing
strategy. However, it is unclear whether predator-prey relationship occurs among these seedlings. We
examined Exp.1) size-related predator-prey relationship between kuruma prawn and Manila clam,
Exp.2) size-related predator-prey relationship between tiger puffer and kuruma prawn and Exp.3)
predator-prey relationships among 3 species. Exp.1) One kuruma prawn and 5 - 10 Manila clams wereplaced into a container. We identified shell-length of Manila clam ingested by kuruma prawn aftercollecting Manila clam survivors after 24 hours. Kuruma prawn (23.1 - 141.2 mm BL) preyed on
Manila clam (1.6 - 10.4 mm shell length). Size ratio between prey and predator ranged 1.3 - 9.5%. The
size of second maxilliped of kuruma prawn coincided with the maximum size of ingested clam. Exp.2)
One tiger puffer and 10 kuruma prawns were placed into a tank (43 cm diameter, 30 cm water depth).
After 24 hours, we identified BL of kuruma prawn ingested by tiger puffer after collecting survivors ofkuruma prawn. Tiger puffer juvenile (25.7 - 100.3 mm SL) preyed on kuruma prawn (18.6 - 52.2 mm
BL). Size ratio between prey and predator was 20.7 - 118.4%. Tiger puffer preyed on kuruma prawn 25
individuals at maximum in 24 hours. Exp.3) Tiger puffer, kuruma prawn and 2 size classes of Manila
clam (9.0 cm and 3.2 cm shell length) were placed into a tank (167 × 75 cm, 30 cm water depth) and we
counted survival individuals twice a day for 5 days. Next, we set 5 partition nets (4 × 4 m) in amesocosm, and 3 species were transferred into 3 compartments, and 3 species and black seabream(Acanthopagrus schlegeli) were transferred into 2 other compartments. We counted survived
individuals 5 days later. Kuruma prawn and Manila clam survived at 43% and 69.5% in theexperimental tanks, respectively. In the mesocosm, Manila clam (3.2 mm shell length) greatly
decreased in the 3 species mixed experiment. On the other hand, kuruma prawn greatly decreased andManila clam (3.2 mm shell length) survived when 3 species and black seabream coexisted.

5
Correlation between water nutrient level and catch of asari, Ruditapes philippinarum,in fishing grounds in Japan
Motoharu Uchida1*, Mutsumi Tsujino1, Naoaki Tezuka1, Toshihiro Shigeta1, Yoshitake Takada2,
Kentaro Niwa3 and Yuka Ishihi41National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency,
Hatsukaichi, Hiroshima, Japan; 3Japan Sea National Research Institute, Fisheries Research Agency,
Chuo-ku, Niigata, Japan; 3Yokosuka Station, National Research Institute of Aquaculture, Fisheries
Research Agency, Yokosuka, Kanagawa, Japan; 4National Research Institute of Aquaculture, Fisheries
Research Agency, Minamiise, Mie, Japan*
Corresponding author: uchida@affrc.go.jp
Catastrophic decrease of catch of the asari clam, Ruditapes philippinarum, has been observed forthe last three decades in Japan’s coastal waters. Many factors including overfishing, disease, habitat loss,
competition with invasive species, global warming, and altered trophic cascade are suggested to be
involved. However, major factor is still not well characterized to explain the widespread and long-term
decrease of the catch. We conducted comprehensive comparison of environmental and biologicalcharacteristics among 17 asari fishing grounds. Significant relationship was observed between water
nutrient level (i.e., total nitrogen and chlorophyll a) and the asari catch. Significant relationship was
also observed between the benthos biomass (macrobenthos, meiobentos, and nematodes) and the asari
catch. Stable carbon isotope ratio of asari was found to be a useful indicator representing not only the
primary production but also the asari catch per unit area.

6Long-term fluctuations in stock abundance of the asari clam (Ruditapes philippinarum)in a no-fishing area in the southern part of Ise Bay, Japan
Kazuhiro Hanyu*
Mie Prefecture Fisheries Research Institute, Suzuka, Mie, Japan*
Corresponding author: hanyuk00@pref.mie.jp
Commercial catch of the asari clam (Ruditapes philippinarum) decreased markedly in Japan after
the 1980’s, and catch in Mie prefecture decreased after the 1990’s. In addition, catch in Ise region,
southern part of Ise Bay, Mie prefecture, decreased after the 1990’s. Mie Prefecture Fisheries ResearchInstitute conducted a survey on the abundance of R. philippinarum in a no-fishing area in the southernpart of Ise Bay from 1954 to 2000 by direct estimation. The present study identified cohorts of R.
philippinarum and analyzed long-term fluctuations in the abundance of clams in two size classes (small,shell length of 2 – 7 mm and large, shell length of ≥20 mm) in each cohort in the no-fishing area from1957 to 2000 based on the data collected by Mie Prefecture Fisheries Research Institute. Forty cohorts
were identified in the no-fishing area during the period. The maximum density of small clam in cohorts
in the 1950’s, 1960’s, 1970’s, 1980’s, 1990’s, and 2000’s were 6408, 1120, 644, 514, 332 and 331
individuals/m2, respectively, showing a gradually decreasing decadal trend. The maximum density oflarge clam in the 1950’s, 1960’s, 1970’s, 1980’s, 1990’s, and 2000’s were 2.8, 5.0, 6.5, 2.7, 3.3 and 2.0
kg/m2, respectively. The density of large clam decreased markedly after the late 1970’s. Therefore, thedecreasing trend in the no-fishing area did not synchronize with those in Ise region and Mie prefecture(i.e., 1990’s). These results indicate that fishery catch data may not correctly predict actual fluctuation
pattern of stock abundance.

7
Effects of small clam abundance, rainfall and sediment on recruitment success of the asari clam
(Ruditapes philippinarum) in a no-fishing area in the southern part of Ise Bay, Japan
Kazuhiro Hanyu*
Mie Prefecture Fisheries Research Institute, Suzuka, Mie, Japan*
Corresponding author: hanyuk00@pref.mie.jp
The abundance of large (shell length of ≥ 20 mm) asari clam (Ruditapes philippinarum) in a no-fishingarea in the southern part of Ise Bay, Japan decreased markedly after the 1970’s. The present study
examined effects of small clam (shell length of 2 – 7 mm) abundance, rainfall pattern and sediment on
the recruitment success of the cohorts in the no-fishing area from 1957 to 2000 by using logistic
regression analysis. The recruitment success was defined as large clam abundance being higher than the
median of the entire set of data (355 individuals/m2). Small clam abundance and rainfall significantly
influenced the recruitment success of the cohort, whereas the effect of sediment (i.e. ratio of very finesilt, silt and clay to total weight) was not significant. The logistic regression analysis revealed that therecruitment success was most strongly affected by the maximum monthly rainfall within three monthsof the peak occurrence of the small clams. The heavy rainfall and consequent river flood seemed todecrease the recruitment success of the clam to the no-fishing area. However, heavy rainfall and riverflood (e.g. maximum monthly precipitation of over 500 mm) were often observed not only after the
1970’s but also before the 1970’s, and the maximum small clam abundance showed a decreasing
decadal trend from the 1960’s to 2000’s, so the decline in stock abundance after the 1970’s wasconsidered to be primarily caused by a decrease in abundance of small clams after the 1960’s. The very
high abundance of small clams in Shitomo River in the western part of Ise Bay during the 1990’s wasdetermined to be a result of abundant larval supply (Miyawaki and Sekiguchi 1999, 2000). Therefore,
larval supply from spawning grounds to the western and southern part of Ise Bay may have decreased
since the 1960’s, and this may have contributed to the decline in stock in the no-fishing area and theentire Ise Bay after the 1970’s.

8Sampling design for abundance estimation of the asari clam (Ruditapes philippinarum)in Ise Bay, Japan
Kazuhiro Hanyu1*, Hideki Kokubu1, Naotsugu Hata1, Tomomi Mizuno1, Takahiko Inoue2, Tomoaki
Kudo3, Natsuki Hasegawa4, Yuka Ishihi4, Satoshi Watanabe4, Yoshimi Fujioka4, Junya Higano4,
Ryogen Nambu5, and Hisami Kuwahara6
1

Mie Prefecture Fisheries Research Institute, Suzuka, Mie, Japan; 2Tokyo Kyuei, Kawaguchi, Saitama,
Japan; 3Kaiyo Engineering, Suzuka, Mie, Japan; 4National Research Institute of Aquaculture, Fisheries
Research Agency, Minamiise, Mie, Japan; 5National Research Institute of Fisheries Engineering,
Fisheries Research Agency, Kamisu, Ibaraki, Japan; 6Fisheries Research Agency, Yokohama,
Kanagawa, Japan*
Corresponding author: hanyuk00@pref.mie.jp
To elucidate the formation process and to develop maintenance techniques of populations of theasari clam (Ruditapes philippinarum) in Ise Bay, Japan, large-scale surveys were undertaken to estimate
the abundance of large and small clams in many local populations in the bay. In order to design anadequate sampling technique for estimating the clam abundance on a large scale, we conducted surveys
in 7 fishing grounds in Ise Bay and analyzed the data by using a two-stage sampling technique, which is
a common method used for estimating the mean, standard deviation and standard error of fishery andecological data. In the present study, the standard deviations positively correlated with the means bothin primary units (sampling points randomly selected in a given fishing ground) and in secondary units(replicates of each sampling point). In addition, the standard deviations in the primary units were larger
than those in the secondary units. If we diminish the ratios of the standard error to the mean (i.e.,
coefficient of variation of the abundance, which is one of the precision index), a sample size of 2 in thesecondary units may be sufficient and an as-large-as-possible sample size in the primary units may beadequate. In practice, in the present surveys with a sample size of > 0.18 points per hectare in the
primary units and a sample size of 2 replicates per point in secondary units, the coefficient of variations
were not small (i.e., 0.2 – 0.8), but we were able to discriminate the fishing grounds and seasons withlarge abundance from those with small abundance.
This study was supported in part by the Ministry of Agriculture, Forestry, and Fisheries of Japan.

9Discovery of a spawning ground of the asari clam (Ruditapes philippinarum)in Ise Bay, Japan
Kazuhiro Hanyu1*, Hideki Kokubu1, Naotsugu Hata1, Tomomi Mizuno1, Takahiko Inoue2, Yoshio
Tanaka2, Tomoaki Kudo3, Natsuki Hasegawa4, Yuka Ishihi4, Satoshi Watanabe4, Yoshimi Fujioka4,
Junya Higano4, Ryogen Nambu5 and Hisami Kuwahara6
1

Mie Prefecture Fisheries Research Institute, Suzuka, Mie, Japan; 2Tokyo Kyuei, Kawaguchi, Saitama,
Japan; 3Kaiyo Engineering, Suzuka, Mie, Japan; 4National Research Institute of Aquaculture, Fisheries
Research Agency, Minamiise, Mie, Japan; 5National Research Institute of Fisheries Engineering,
Fisheries Research Agency, Kamisu, Ibaraki, Japan; 6Fisheries Research Agency, Yokohama,
Kanagawa, Japan*
Corresponding author: hanyuk00@pref.mie.jp
Abundance of small (shell length of 2 - 7 mm) asari clam (Ruditapes philippinarum) in the southernpart of Ise Bay, Japan, explosively increases once in several years. However, the location of thespawning grounds, as well as the reason for the large fluctuation in abundance is yet to be discovered.
In order to locate the spawning grounds and elucidate the mechanisms of the fluctuations, we conductedsurveys of the clam abundance in several regions of Ise Bay, Japan from November 2012 to November
2014. We discovered a high abundance of large clams (shell length of ≥ 15 mm) at a water depth of 5 –10 m in a non-fishing ground, offshore of Suzuka region, northern part of Ise Bay in November 2013.
We subsequently observed a high abundance of small clams inshore of Matsusaka region, southern partof Ise Bay in May 2014. Therefore, this ground may be a spawning ground for the populations in thesouthern part. The occurrence of such ground with high abundance in the northern part was negatively
correlated with the occurrence of inflow of hypoxic water masses during the survey period. The inflow
of hypoxic water masses to the ground was often observed by Mie Prefecture Fisheries ResearchInstitute from 2002 to 2009, during which the occurrence of inflow negatively correlated withcommercial catch of the clam (shell length of ≥ 32 mm) in the southern part two years later. This
supports the hypothesis that the ground discovered in the northern region may be a spawning ground forthe populations in the southern part, and the occurrence pattern of hypoxic water masses in the northern
region may help understand the population dynamics of the clam in the southern part of Ise Bay.
This study was supported in part by the Ministry of Agriculture, Forestry, and Fisheries of Japan.

10
Ontogenetic changes in ingestion and digestion abilities against diatom cellsof the Manila clam
Shouji Houki1*, Tomohiko Kawamura1, Nobuhiro Ogawa1, Nam-Il Won2 and Yoshiro Watanabe1
1

Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Chiba, Japan; 2KWI, Korea
Water Resources Corporation, Jeonmindong, Yuseonggu, Daejeon, Korea*
Corresponding author: houki@aori.u-tokyo.ac.jp
Planktonic diatoms have long been considered as one of the main food sources for the Manila clam.
Whereas, recent studies using stable isotope analyses suggested that benthic diatoms, which often growat high densities on the tidal flat and are suspended by waves or tidal currents into the water column,
were mainly assimilated by the clams. To assimilate the diatom cell contents, clams need to physicallybreak the silica cell walls of diatoms. In the preceding studies on the feeding of abalone species, thephysical strength of the cell walls is an important factor determining the dietary value of diatoms forjuvenile abalone. Diatom cells cannot be efficiently broken in the abalone gut, and only highly
breakable diatoms when they are eaten, such as those with structurally weak cell walls, have highdietary values for abalone. For the Manila clam, detailed mechanisms in the ingestion and digestion of
diatoms have never been investigated, and whether the clam can break the diatom cells in the gut is still
totally unknown. In the present study, ontogenetic changes in the ingestion and digestion abilities
against diatoms of the Manila clam were examined using several diatom species with different hardness
and size of cells. Two planktonic and three benthic diatom species were isolated and cultured from atidal flat in Tokyo Bay, and the physical strength of their cell walls was measured using the
PicoIndenter® (Hysitron). Each diatom species was fed to newly settled (200 - 300 µm) and juvenile
clams of 3, 5 and 10 mm shell length (SL) respectively, and the cell walls of diatoms in the tissue
section of the digestive tract and feces of the clams were observed using a SEM or TEM. To evaluate
the dietary value of each diatom species for newly settled juvenile clams, growth rates of juveniles were
measured for a month. The percentage of crushed diatom cells in the ingested cells was measured. The
physical strength of cell walls was significantly different among the diatom species, for example, that ofthe pelagic Chaetoceros species was low, and that of the benthic Navicula species was high. The newly
settled juvenile clams did not crush the benthic diatoms with hard cell walls, and did not ingest large
diatoms. Consequently, small pelagic diatoms with fragile cell walls were considered to be suitable
foods for the newly settled juveniles. The clams of 3 - 5 mm SL partly crushed the benthic diatoms withhard cell walls. Clams of 10 mm SL ingested large diatoms, and crushed over 90% of ingested diatom
cells regardless of the physical strength of the cells.

11
Reproductive biology of Manila clam Ruditapes philippinarum
in the coastal waters along eastern Hokkaido, Japan
Yasuko Konda1* and Masayoshi Sasaki2
1

Kushiro Fisheries Research Institute, Hokkaido Research Organization; 2Mariculture Fisheries
Research Institute, Hokkaido Research Organization*
Corresponding author: konda-yasuko@hro.or.jp
In eastern Hokkaido, there is a potential for a further increase in production of Manila clam,
Ruditapes philippinarum, but there is insufficient information about the reproductive biology of theclam necessary for appropriate resource management. Therefore the reproductive biology was studied
from June to September 2011 in the coastal waters off Takase, Nemuro in eastern Hokkaido. The
condition factor increased during June, and the population maturity rate increased from late June to
mid-July. Both variables maintained high value until late August to early September and decreased
thereafter. Gonads in active stage and/or partially spawned stage of both females and males were
histologically observed in late June, and gonads in these stages were continuously observed during the
spawning peak from late August to early September. These results indicate that the spawning of theManila clam starts before late June and peaks in late August in eastern Hokkaido. Shell length at which
50% of individuals mature was estimated to be 23.6 mm by visual observation of the molluscous part,and to be 20.2 mm for females and 16.3 mm for males by histological observation. Female fecundity
was estimated by counting the number of eggs under the microscope, and it was positively correlated tothe shell length. The fecundity was also positively correlated to the condition factor. The maximum
fecundity estimated in this study was 107 eggs for a female with the shell length of 50.9 mm. The
current findings will be used to implement resource management proposal in eastern Hokkaido.

12
Food environment for bivalves around Zostera marina beds
Hideki Kokubu*, Hirokazu Hanyu and Naotsugu Hata
Mie Prefecture Fisheries Research Institute, Suzuka, Mie, Japan.
*
Corresponding author: kokubh00@pref.mie.jp
Zostera marina is a common seagrass that can be observed in Ise Bay, Japan. Zostera beds haveimportant functions as spawning and nursery grounds for valuable marine resources. However, the areaof Zostera beds in bay area drastically decreased from about 10,000 ha in 1955 to 100 ha in 2000 (onehundredth of 1945) by reclamation for industrial ground and devastation by fisheries trolling device. At
the same time the catch of fisheries in Ise Bay has been decreased by about half for 50 years. For thisreason, restorations of Zostera beds have recently been conducted in coastal environment in Ise Bay.
However, few studies have focused on the function of fish-gathering around Zostera beds. In this study,
we studied the food environment for bivalves around Zostera beds at Gotenba and Matsunase beach in
Ise Bay. Particulate matter suspended in the water of Zostera beds was collected in a sediment trap, andthe amount of bivalves was measured in both beaches every season in 2013. Around the margin of theZostera beds, high amount of bivalves were found, and they decreased with the increasing distancefrom Zostera beds. The chlorophyll-a level in the particulate matter was the highest at the center ofZostera beds and also decreased with the increasing distance from Zostera beds. The results suggestthat the deposition of particulate matter was increased by buffering of waves and currents by Zostera
beds. Thus, the food environment for bivalves was improved toward the Zostera beds, resulting inincreased amount and condition factor of bivalves around the Zostera beds.

13
Manila clam, Ruditapes philippinarum, culture using Pyropia spheroplastin closed recirculation system
Novi Arisman*, Mohammad Nakib Dad Khan, A.M. Shahabuddin, Takao Yoshimatsu, Toshiyoshi
Araki
Graduate School of Bioresources, Mie University, Tsu, Mie, Japan*
Corresponding author: novi.arisman@gmail.com
The Manila clam, Ruditapes philippinarum, were reared in an indoor closed recirculation system,
using Pyropia spheroplast feed products, freeze dried spheroplast (FDS), spray dried spheroplast (SDS),
and enzyme treated nori (ETN). The study aimed to investigate the compatibility of the recirculation
system in order to sustain the Manila clam culture using Pyropia spheroplast. Water quality parameters
and biological performances were evaluated within thirty days. Experimental results showed that there
were no statistical differences among all treatments in water quality parameters of ammonia, nitrite,
nitrate and phosphorus concentrations. Water quality on each dietary treatment was under the ambient
water quality criteria for the Manila clam. On the biological performance, there were no significant
different on survival, feed consumption and growth among the Manila clam feed FDS, SDS and ETN.
This result shows that the recirculation system is adequate in sustaining the Manila clam culture inindoor tank.

14
Comparison of types of cages and substrates in suspended culture of
the Manila clam, Ruditapes philippinarum
Naotsugu Hata1*, Natsuki Hasegawa2, Tomomi Mizuno1, Yoshimi Fujioka2, Yuka Ishihi2, Satoshi
Watanabe2, Daisuke Asao3, Megumu Yamaguchi4, Hotaka Imai4, Kazuhide Morita5 and Junya Higano2
1

Mie Prefecture Fisheries Research Institute, Suzuka, Mie, Japan; 2National Research Institute of
Aquaculture, Fisheries Research Agency, Minamiise, Mie, Japan; 3Uramura Asari Study Group,
Uramura Branch Office, Toba and Isobe Fisheries Association, Toba, Mie, Japan; 4Carshell Co., Ltd.,
Toba, Mie Japan; 5Mie Prefectural Government Office in Ise, Ise, Mie, Japan*
Corresponding author: hatan00@pref.mie.jp
A series of experiments was conducted to determine optimal rearing conditions for suspended
culture of the Manila clam, Ruditapes philippinarum, in Ounoura Bay, Mie prefecture, Japan.
Comparisons of four types of cages (plastic container, cylindrical net cage, small mesh cage, curing
cage used for pearl oyster) and two types of substrates (gravel and pumice) showed that the
combination of plastic container with gravel and the combination of cylindrical net cage with pumice
had the fastest growth rate of the clam. In terms of handling, however, cylindrical net cage with pumice
was considered superior due to its lighter weight. A rearing experiment with different amount of theclam and pumice in the cylindrical net cage (45 cm diameter) showed that installing two mesh bags
each containing 0.5 kg of the clam and 5 L of pumice had the best growth rate. The growth of the clam
was faster in inner part of the bay than in the bay mouth at the depth of 4 m among the three culturing
depths (1 m, 2 m and 4 m), and chlorophyll a level seemed to be one of the factors affecting the growthrate. The condition factor (CF, soft tissue weight / shell volume) of the clam cultured in cylindrical net
cages ranged from 18.0 to 22.9 from December to March, which increased from 16.5 at the initiation of
the experiment in October.

15
Effects of feeding regimes on oocyte quality of Manila clam Ruditapes philippinarum
Masahiko Awaji*, Toshie Matsumoto and Junya Higano
National Research Institute of Aquaculture, Fisheries Research Agency, Minamiise, Mie, Japan*
Corresponding author: awajim@affrc.go.jp
In the seed production of Manila clam, Ruditapes philippinarum, low survival and retarded growthof the larvae sometimes occur. One of the possible causes for these troubles is the inferior quality ofmature oocytes (eggs) spawned to be fertilized. Insufficient feeding of the female brood stocks is
expected to deteriorate the oocyte quality, but experimental studies to clarify the effects of feeding on
the oocyte quality are scarce. In this study, we examined effects of three different feeding regimes on
the quality of mature oocytes in Manila clam. Two hundred Manila clams (mean shell length 30 ± 1.7mm) in the spawning season (October) were divided into three groups (group H, M and L) and reared intanks at 22oC for 37 days. They were continuously fed with Chaetoceros neogracile at 6.0 x 104
cells/ml for the first 7 days. On day 8, the feed concentration was changed into three different levels (H,8.0; M, 1.6; L, 0.3 x 104 cells/ml) and the rearing was continued for the rest of the experiment period.
On days 28 and 37, a part of the clams from three groups were induced to spawn by an exposure toincreasing water temperature. Females and males that started gamete release were immediatelytransferred to a small container individually. The eggs collected from each female were inseminatedwith the pooled sperm obtained from three males, and the total number of eggs from each female wascounted. Then a part of the fertilized eggs from each female was transferred to 3 wells of a 24-well
microplate at 60-100 eggs/well and to 24 wells of a 48-well microplate at 3-4 eggs/well, and kept at
25oC. At 4-6 hours after the insemination, eggs in the 24-well plate were fixed with 5%
formalin/seawater to obtain the fertilization rate. At 22-23 hours after the insemination, larvae in the
48-well plate were fixed in the same way, and the number of veliger larvae was counted to obtain themetamorphosis rate. In addition, hinge length of the fixed larvae was measured. Average feed
concentration in the waste water (H, 1.7; M, 0.5; L, 0.17x104 cells/ml) confirmed difference in feedavailability among the experimental groups. The difference in the feeding regimes, however, did notshow significant effects on the number of the spawned eggs, the fertilization rate, the metamorphosisrate, or the hinge length of the veliger larvae. These results indicate that limited feeding (i.e. group L inthis study) for about one month during spawning season does not deteriorate the oocyte quality in
Manila clam. Large variation of the observed parameters within each group suggests presence of otherfactors that affect the oocyte quality.

16
Low-salinity endurances of the penshell Atrina sp. and clam Trapezium liratum
Takeo Kurihara1*, Shoji Nakano1, Yukihiko Matsuyama1, Kazumasa Hashimoto1, Atsushi Ito2 andMasaei Kanematsu2
1

Seikai National Fisheries Research Institute, Fisheries Research Agency, Tairamachi, Nagasaki, Japan;
National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency,
Momoshima, Onomichi, Hiroshima, Japan*
Corresponding author: takeo@affrc.go.jp
2

Species-specific and temperature-dependent endurances against low salinity were revealed for thebivalves Atrina sp. and Trapezium liratum in a 4-day consecutive laboratory experiment with an
orthogonal design: 12 levels of salinity ranging from 0 to 100 psu × 2 bivalve species × 2 temperatures,
12 and 24ºC. [Result 1] Atrina sp. was highly vulnerable to low salinities compared to T. liratum (meansurvival rate in salinities ≤ 20 psu: 11% and 94%, respectively). This conforms to the interspecificdifference such that, of the two species, Atrina sp. inhabits deeper water where abrupt decrease insalinity is relatively rare. [Result 2] Both species showed decreased survival rate and/or survival time ata higher temperature. This accords with the results of additional experiments that both species increased
clearance rate at higher temperatures owing presumably to increased respiration and were likely to
expose their fragile soft tissue to more low-salinity water.

17
Effect of salinity on the survival, growth and settlement of full-grown larvae ofthe Manila clam Ruditapes philippinarum in rearing tanks
Masaei Kanematsu1*, Naoaki Tezuka1, Hideki Yamazaki1, Atsushi Itou1, Daisuke Ojima1 and Atsushi
Nishimoto2
1

National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency,
Onomichi, Hiroshima, Japan; 2National Research Institute of Fisheries Science, Fisheries Research
Agency, Yokohama, Kanagawa, Japan*
Corresponding author: kanematu@fra.affrc.go.jp
The effect of salinity on the survival, growth and settlement of full-grown larvae of the Manila clam
Ruditapes philippinarum was examined in rearing tanks. Salinities were set at 12, 21 and 30 inquadruplicate (total 12 tanks), and we repeated experiments twice. The survival rate, growth in shelllength and settlement rate were measured at the end of the experimental period on day of culture 15(exp.1), and same measurements as experiment 1 were carried out on days of culture 3, 6, 9 and 12(exp.2). Exp.1: the highest survival rate (89.2%) and the settlement rate (84.9%) were obtained atsalinity 12. Higher larval growths were observed at lower salinity. The maximum growth in shell length(32.5 µm/day) were obtained at salinity 12. Exp.2: higher larval settlement rates were obtained at lower
salinities through the duration. On day 12, settlement rates were significantly different among thesalinity levels. The settlement rates were 67.5%, 16.7% and 4.6% at salinity 12, 21 and 30, respectively.
Salinity 12 was demonstrated to be suitable for full-grown larvae rearing of the Manila clam.

18
Effect of netting on survival of Manila clam Ruditapes philippinarum
in an artificial tideland in Okayama, Japan
Koichi Izumikawa1, Tsuyoshi Mototani1, Fumiyasu Murayama1, Jiro Sato1, Atsushi Nishimoto2,3,
Hideki Yazamazaki2, Kazutaka Sakiyama2,4 and Atsushi Ito2*
1

Research Institute for Fisheries Science, Okayama Prefectural Technology Center for Agriculture,
Forestry, and Fisheries, Setouchi, Okayama, Japan; 2National Research Institute of Fisheries andEnvironment of Inland Sea, Fisheries Research Agency, Onomichi, Hiroshima, Japan; 3Present address:
National Research Institute of Fisheries Science, Fisheries Research Agency, Yokohama, Kanagawa,Japan; 4Present address: Japan Sea National Fisheries Research Institute, Fisheries Research Agency,
Miyazu, Kyoto, Japan.
*
Corresponding author: itoa@affrc.go.jp
In Yorishima artificial tideland located in Seto Inland Sea, small Manila clams (Ruditapes
philippinarum) tend to be found in spring but disappear by autumn. Therefore, these clams might sufferhigh mortality during summer. In this study, the effect of netting of their habitat on survival of Manila
clam was examined in Yorishima artificial tideland. Prior to netting treatments, spatial distribution of
Manila clam in Yorishima artificial tideland was surveyed with line transect sampling. A core sampler(10 cm in diameter and 8 cm in depth) was used to measure the density of clams. A total of 160 plots
were surveyed and clam density ranged from 0 to 4318 clams/m2. Five plots with high clam densities(2159 to 4318 clams /m2) were assigned as netting treatment plots and covered with nets (2.5 × 2.5 m, 4
mm mesh openings) in May 2014. Net edges were buried 20 cm deep. A no-net control plot was placed
adjacently to each netting treatment plot. In October 2014, the clam densities in three netting treatment
plots were higher than those in no-net control plots. These results suggested that the netting treatment
was effective to protect the clams from waves and/or predators in Yorishima artificial tideland.
This study was supported by the Ministry of Agriculture, Forestry and Fisheries of Japan.

19
Effects of water temperature on the expression of heat shock protein (HSP)
22, 40, and 70 genes in Manila clam (Ruditapes philippinarum) larvae
Daisuke Ojima1*, Masaei Kanematsu1, Atsushi Nishimoto1,2, Atsushi Ito1, Hideki Yamazaki1, Kimio
Asami1,3 and Kazutaka Sakiyama1,41National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency,
Onomichi, Hiroshima, Japan; 2Present address: National Research Institute of Fisheries Science,
Fisheries Research Agency, Yokohama, Kanagawa, Japan; 3Present address: Seikai National Fisheries
Research Institute, Fisheries Research Agency, Ishigaki, Okinawa, Japan; 4Present address: Japan Sea
National Fisheries Research Institute, Fisheries Research Agency, Miyazu, Kyoto, Japan*
Corresponding author: ojidai@affrc.go.jp
Biomarkers are powerful tools to understand optimal environmental conditions for the rearing oftarget animals. The heat shock protein (HSP) family is one of the biomarkers, which responds tovarious stress factors. We examined HSP 22-1, 22-2, 40, and 70 expressions in the Manila clam
(Ruditapes philippinarum) larvae in different thermal conditions. In experiment (Exp.) 1 (short-term
stimulation), the fertilized eggs were collected by thermal spawning induction and were hatched at
23°C. D-shaped larvae [1 day after fertilization (DAF)] were transferred into 3 tanks at 20–22, 25, or
30°C, and were sampled after 24 h. In Exp. 2 (long-term stimulation), D-shaped larvae were reared in
the same thermal conditions as described for Exp. 1, and sampled at the ambo (5–7 DAF) and
full-grown stages (9–12 DAF). All samples were soaked in RNA preservative solution and stored at-80°C. Expressions of HSPs were quantified by real-time PCR. In Exp. 1, HSP 22-1 and 22-2
expressions significantly increased at 25 and 30°C. HSP 40 expression significantly decreased at 30°C,
and HSP 70 expression showed no significant changes. In Exp. 2, HSP 22-1 expression in full-grownlarvae at 25 and 30°C, and HSP 22-2 expression in the ambo and full-grown larvae at 25 and 30°C
increased significantly. HSP 40 expression in ambo and full-grown larvae in all temperature regimes
decreased significantly, and HSP 70 expression in ambo larvae in all temperature regimes increased
significantly. These results suggest that HSP 22-1 and 22-2 are suitable biomarkers of thermal stress in
Manila clam larvae.

20
Spatiotemporal population structure of the asari clam Ruditapes philippinarum juvenile
in Ise Bay inferred by microsatellite marker analysis
Natsumi Sano1*, Natsuki Hasegawa2, Kazuhiro Hanyu3, Dai Miyawaki4, Akira Komaru1 and Hisami
Kuwahara5
1

Graduate School of Bioresources, Mie University, Tsu, Mie, Japan; 2National Research Institute of
Aquaculture, Fisheries Research Agency, Minamiise, Mie, Japan; 3Mie Prefecture Fisheries ResearchInstitute, Suzuka, Mie, Japan; 4Marine Resources Research Center, Aichi Fisheries Research Institute,
Minamichita, Aichi, Japan; 5Headquarters, Fisheries Research Agency, Yokohama, Kanagawa, Japan.
*
Corresponding author: natsumi5@bio.mie-u.ac.jp
The production of asari clam Ruditapes philippinarum fishery has decreased severely in Ise Bay. To
distinguish the spatiotemporal population structure of the clam for the better resource management, we
sampled juvenile clams (shell length < 10 mm) in May and November 2013 and May 2014 at 6 to 7
sites in Ise Bay. For microsatellite analysis, total DNA was extracted from 23 to 32 individuals fromeach sampling location at each sampling period. The microsatellite analysis was performed on six loci
(Asari 16, Asari 43, Asari 62, Asari 64, KTp8 and KTp31-1) to reveal the genetical population structureof the clam in Ise Bay. Calculations of molecular variance and pairwise FST test were done using thesoftware ARLEQUIN. No significant population subdivision was detected between the May 2013 andMay 2014 specimens in all of 49 pairs by pairwise FST test. However, significant pairwise FST
differences were observed in 25 of 42 (0.015 - 0.048, p < 0.01) pairs between May 2013 and November
2013 and 26 of 42 (0.015 - 0.055, p < 0.01) pairs between November 2013 and May 2014. Assignment
analyses using the software STRUCTURE identified K = 1 as the most probable number of population.
Genetic relationship among the samples collected from different locations at each sampling period was
also estimated with the software PHYLIP using the neighbor-joining method. The samples weredivided into 2 clusters comprising 4 groups from November 2013 specimens and the other 17 groups
while the Bootstrap value was 56. These results suggested the main sources of the juvenile clams may
differ between May and November in Ise Bay.
This study was supported in part by the Ministry of Agriculture, Forestry, and Fisheries of Japan.

21
Present situation of the asari clam Ruditapes philippinarum resources in Mikawa Bay, Japan
Dai Miyawaki1*, Yoshiki Murauchi1, Manabu Hibino2 and Shunji Okamoto2
1

Marine Resources Research Center, Aichi Fisheries Research Institute, Minamichita, Aichi, Japan;
Fisheries Administration Division, Department of Agriculture, Forestry and Fisheries, Aichi
Governmental Office, Nagoya, Aichi, Japan*
Corresponding author: dai_miyawaki@pref.aichi.lg.jp
2

The annual catch of the asari clam in Aichi prefecture amounted approximately to 16,000 tons,
occupying about 70% of the national catch of Japan in 2013. The national catch of Japan has decreased
by 80% in 30 years, whereas the catch in Aichi has been maintained above 10,000 tons annually for thelast 30 years. We suggest the following factors contribute to the stable asari clam resources in Aichi. (1)Wider tidal flat and shallow areas for the asari clam habitats. Fishing grounds of the asari clam arereported in depths shallower than 10 m close to the flats. (2) Availability of seeds on the tidal flatsaround river mouths. (3) Transplantation of juvenile clams for stocking from the seed areas into various
areas within the bay. (4) Planktonic larvae with high density from spring to early winter. (5) Fishery
managements by the local fishery associations, including the transplantation, restriction on the shell size
and amount of commercial catches, setting of no-fishing periods and areas, removal of predatory andcompetitive organisms, tilling of the fishing grounds, and also prohibition of stocking juveniles fromthe above areas. In particular, factors (1) to (4) are important for the formation, maintenance, andenhancement of the asari clam resources to maintain population network of the asari clam within thebay thorough the life cycle. The asari clam spends most of its lifecycle on tidal flats and the neighboring
shallow areas, so we need to keep environmental conditions suitable for the asari clam. Currently, thesupply of juvenile clams for the transplantation is dependent upon limited seed areas. We assume thatjuvenile clam aggregations in the seed areas are generated largely by the characteristic bottom waterflow patterns at river mouth areas.

22
Seasonal dynamics of the parasitic larvae and free-living adults of the sea spider Nymphonella
tapetis infecting the asari Ruditapes philippinarum in the eastern coast of Chita Peninsula.
Yoshiki Murauchi1*, Shunji Okamoto2, Akira Hirai2, Dai Miyawaki1, Naoki Yamamoto3 and Manabu
Hibino2
1

Marine Resources Research Center, Aichi Fisheries Research Institute, Minamichita, Aichi, Japan;
Fisheries Division, Aichi Prefectural Office, Nagoya, Aichi, Japan; 3Chita Agriculture, Forestry and
Fisheries Office, Handa, Aichi, Japan*
Corresponding author: yoshiki_murauchi@pref.aichi.lg.jp
2

We investigated infection of the Manila clam Ruditapes philippinarum with larvae of the sea spider
Nymphonella tapetis and distribution density of free-living adults of N. tapetis on the eastern coast of
the Chita Peninsula, Japan. The prevalence of infection and mean abundance of parasitic larvae per hostdecreased in May or June when many adults were released from the host and peaked in June or Julywhen many young larvae had parasitized R. philippinarum. Subsequently, the prevalence of infection
and mean abundance of parasitic larvae per host decreased sharply between August and October. After
October, only a few larvae of N. tapetis invaded R. philippinarum. Invasion after October wasconsidered to contribute to the main reproductive cycle that occurred from May onward. The
prevalence of infection and mean abundance of parasitic larvae per host fluctuated each year. Highsurvival rate of larvae in summer 2009, which was caused by lower water temperature than in otheryears, was considered to be the factor of the increase in N. tapetis larval numbers from October 2009 to
March 2010.

23
Shellfish production and new approaches in Turkey
Serpil Serdar*
Faculty of Fisheries, Ege University, Bornova-Izmir, Turkey*
Corresponding author: serpil.serdar@ege.edu.tr, serdarserpil@yahoo.com
Turkey is a large, roughly rectangular peninsular country bridging Europe and Asia. This peninsula
is surrounded by the Mediterranean Sea (south part), the Black Sea (north part) and the Aegean Sea(west part). The Sea of Marmara, the Bosphorus and the Dardanelles which are the Turkish Straits
demarcate the boundary between Thrace and Anatolia. Turkey has 8333 km of coastline with different
ecological properties, so it is one of the best countries having suitable conditions for aquaculture andfisheries. Fishery production consists of marine fisheries (56%), marine and freshwater aquaculture(26%), inland fisheries (11%) and other marine species fisheries (7%) such as crustaceans and molluscs.
Aquaculture is a relatively new industry in Turkey. While the total fisheries production has remained
stable over the last decade, aquaculture production has been increasing rapidly. Rainbow trout(Oncorhynchus mykiss), seabass (Dicentrarchus labrax), gilthead seabream, (Sparus aurata) and carp
(Cyprinus carpio) are the main aquacultured fish species. Shellfish production is mainly from capture
fisheries except mussel production in a few amounts within a short period. An economical species are
Venus gallina, Ruditapes decussatus, Mytilus galloprovincialis, Ostrea edulis, Venus verrucosa, Donax
trunculus, and Chlamys glabra. Moreover Ruditapes philippinarum was recorded from Turkish waters
in 2003. This species is collected irregularly from Çardak Lagoon-Çanakkale, and the catch statistics is
combined with that of Ruditapes decussatus. Republic of Turkey Ministry of Agriculture and Rural
Affairs arranges some legislations and guidelines for safety and sustainable bivalve production in
Turkey. Also regulation and control cover from harvest to process (process techniques), as well astransport and marketing. Totally, 32 regions are monitored regularly for bivalve production, and 8
regions have been investigating in order to start bivalve production in Turkish coastline. There are 12commercial companies with a depuration plant that export shellfish. Recently, several enterprises havestarted to culture mussel and also some official permission has been completed for the production
especially along the coast of the Marmara Sea. Clam and oyster cultures are expected to be accelerated
in Turkey.

24
Variations of glycogen, protein and lipid contents depend on size of
Ruditapes decussatus in Bostanli Seashore Izmir Bay, Aegean Sea, Turkey
Serpil Serdar*, Hazal Pulat and Gulcin Gungor
Faculty of Fisheries, Ege University, Bornova-Izmer, Turkey*
Corresponding author: serpil.serdar@ege.edu.tr, serdarserpil@yahoo.com
Biochemical composition of bivalves is important factor for understanding physiological activities
such as feeding, growth and reproduction. Energy is stored prior to gametogenesis in the form of
glycogen, lipid and protein. Furthermore, environmental factors particularly food availability play adominant role in the level of biochemical components. The aim of this study was to compare
biochemical contents of the Carpet shell clam, Ruditapes decussatus, among different sizes. Carpet
shell clam samples were collected monthly between May 2013 and April 2014 from Bostanli seashore,
Izmir Bay in Turkey. The samples were divided into three size groups; Group I from 20.0 to 25.0 mm,
Group II from 30.0 mm to 33.0 mm and Group III from 45.0 mm to 51.0 mm. At the same time,
temperature, salinity, chlorophyll a, total particulate matter were measured each month. Temperature
ranged between 11.0°C (in December) and 26.0°C (in June and August) during the study. Salinity wasmeasured between 35.68‰ and 37.44‰ in the study area. Total particulate matter and chlorophyll aconcentration changed from 1.7 mg/l to 8.4 mg/l and from 0.21 µg/l to 19.68 µg/l, respectively. The
maximum glycogen value was determined in all groups in September: 18.36% (Group I), 18.86%(Group II) and 20.81% (Group III). Protein and lipid contents in Group I had the highest value in May
71.66% and 8.21%. The maximum lipid level in Group II and Group III was found to be 6.74% and5.98% in April. The highest protein content in Group II and Group III was 61.67% in April and 63.01%
in March, respectively. The results of this study showed that the size and glycogen ratio increased
synchronously, whereas protein and lipid contents decreased to relatively larger extents within sampling
period. It is thought that this situation is closely related to not only water temperature and foodavailability but also reproduction and spawning period.

25
Use of Pyropia spheroplasts as a live food substitute for culturing
Manila clam, Ruditapes philippinarum
A.M. Shahabuddin1, Mohammad Nakib Dad Khan1, Novi Arisman1, Debasish Saha1, Takao
Yoshimatsu1* and Toshiyoshi Araki2
1

Graduate School of Bioresources, Mie University, Tsu, Mie, Japan;
Community-based Research Institute, Iga, Mie, Japan.
*
Corresponding author: takaoyos@bio.mie-u.ac.jp

2

Mie University Iga

An experiment was conducted to assess the Pyropia spheroplasts as a live food substitute forculturing Manila clam in indoor flow through system. Pyropia yezoensis (red algae) is one of the mostimportant aquaculture species that contains a higher percentage of protein, as well as minerals andvitamins. Spheroplast is a cell from which cell wall is removed by enzymatic treatments. Threedifferent kinds of cell wall degrading enzymes (i.e., agarose, β-1-3 mannan agar and β-1-3 xylanase)were used to breakdown the cell wall. Four diets (PS inclusion levels of 1%, 2% and 3% body weightbasis, and live diatom Chaetoceros calcitrans) were fed to the three replicate groups of clams for 9
weeks. Significantly higher survival was obtained in the PS diets than the diatom group (P < 0.05).
Manila clam cultured with PS level 2% diet showed higher carcass weight (soft tissue) compared to theother PS diets and was not different than diatom (P > 0.05). Results of the experiment indicated that PS
is a good candidate for a substitute to live diatom for culturing Manila clam.

26
Main ecological processes for the determination of Ruditapes philippinarum population size on an
extensive intertidal sandflat in Ariake Sound, Kyushu, Japan
Seiji Takeuchi1a* and Akio Tamaki1
Graduate School of Fisheries and Environmental Sciences, Nagasaki University, Nagasaki, Japan;
aPresent address: Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan*Corresponding author: stakeuchi@jamstec.go.jp
For the sustainable use of fishery resources under a proper ecosystem management program, it isnecessary to understand the role of main ecological processes in community organization in which thetarget species population is involved. These include predation, competition, adaptation and limitationby habitat carrying capacity. In the present study, by combining field monitoring with field andlaboratory experiments, we attempted to extract several ecological processes that can primarily
determine the population size of the Manila clam, Ruditapes philippinarum, on an extensive intertidal
sandflat in Ariake Sound, western Kyushu. In 2004, the macrobenthic community on the sandflat was
mainly composed of five phytoplankton-feeders, two powerful bioturbating shrimps, Nihonotrypaea
japonica and Upogebia major, and three veneroid clams, Ruditapes philippinarum, Mactra
veneriformis and Meretrix lusoria. The results of the field survey suggested that the five species
competed for space, with superiorities exerted by shrimps to clams through the former's intense
bioturbating activities and by one or two species of clams to the other in specific tide zones, and forfood to the limit of the carrying capacity provided by the sound. The two shrimp species populations,which predominated over the high- and mid-tide zone, considerably declined almost to the extirpation
during 2004 to 2008. This event was followed by the higher recruitment and biomass increment of thethree clam species populations than before, most probably owing to competitive release from theshrimp. Thereafter, only Me. lusoria and Ma. veneriformis were successful in establishing their adult
populations in the newly vacated habitat (i.e., with no shrimps). The sediments there were moreunstable than that of the low-tide zone where R. philippinarum population persisted. We hypothesizedthat some high burrowing ability of juvenile clams is required for their persistence in the unstablesediment, especially in the wintertime. The results of the field and laboratory experiments suggested
that burrowing ability can be one key trait for success/failure in the population establishment of clam
species in the newly vacated habitat. These findings could be used as a basis for the ecosystem-based
management of Manila clam populations in well-mixed shallow estuaries.

27
Age determination of asari Ruditapes philippinarum using growth rings on shell surface andsection in Mutsu Bay, northern Japan
Daisuke Sugiura1,2*and Naohisa Kikuya2
1

Fisheries Research Institute, Aomori Prefectural Industrial Technology Center, Hiranai, Aomori,Japan; 2The Headquarters, Aomori Prefectural Industrial Technology Center, Kuroishi, Aomori, Japan*Corresponding author: daisuke_sugiura@aomori-itc.or.jp
Asari has scarcely been caught for commercial aim in Mutsu Bay, northern Japan. Hence,
productivity of asari in the bay is largely unknown. In the recent summers, Mutsu Bay has sometimes
encountered higher water temperatures than observed in the past. To enhance fisheries production insuch environmental condition, the species tolerant for the warm water should be efficiently used. As thefirst step for stock assessment of asari in Mutsu Bay, we explored the age characteristics on its shellsurface and section. The specimens were collected between April 2014 and March 2015 from two
locales in Mutsu Bay: Ashizaki Bay and Noheji. First, we observed the shell outer surface and founddark-olive colored bands accompanied by notches. Second, the shell was embedded in epoxy resin, andthen sectioned into ca. 300 µm thick along its axis of maximum growth. When the thin section wasobserved under a light microscope, translucent lines started from umbo and passed through middle layerof shell. Each line finally reached a notch on shell outer surface. Thus, the dark-olive colored bands
with notches on shell surface were assumed to be “outer growth rings”. However, seasonal changes inthe structures of the ventral margins of shell sections suggested that the translucent line was mainly
formed in August (summer) and also in December (winter). Some translucent lines on shell sections
branched off in middle layer of shell and reached nearby the shell outer surface. We used only theventral one of those as “inner growth rings” to avoid overestimating age. The mean shell lengths (SLs)at the first, second and third growth rings were estimated to be 10, 22, 30 mm based on the outer growth
ring and to be 14, 27, 32 mm based on the inner one, respectively. The observed maximum ages were 7
years old based on the outer growth ring and 5 years old based on the inner one. The results suggest
asari reach SL 30 mm (commercial size) in around 3 years in Mutsu Bay, although further evidence
should be collected to establish the criterion of outer and inner “growth rings” as age characteristics.

28
Abundance of planktonic larvae of the asari clam Ruditapes philippinarum
around fishing grounds in Mikawa Bay
Nobuo Kuroda1*, Shunji Okamoto2, Takaharu Matsumura1 and Masami Hamaguchi3
1

Marine Resources Research Center, Aichi Fisheries Research Institute, Minamichita, Aichi, Japan;
Fishery Division, Aichi Prefectural Government, Nagoya, Aichi, Japan; 3National Research Institute ofFisheries and Environment of Inland Sea, Hatsukaichi, Hiroshima, Japan*
Corresponding author: nobuo_kuroda@pref.aichi.lg.jp
2

Densities of planktonic larvae of the asari clam were monitored by fluorescent antibody method in
Mikawa Bay, which has the largest asari clam resource in Japan, from 1999 to 2008. Monitoring
stations were set in 4 areas near Isshiki tidal flat, Fukue Bay, Toyogawa river mouth and Yahagi rivermouth; the exact location of the stations differed from year to year. Former 2 sites are the main fishinggrounds in Mikawa Bay and latter 2 sites are known as high level juvenile occurring areas. The larvae
occurred between spring and autumn every year with varying densities from 102 to 104 individuals per
m3. The occurrence peaks were found in different time from year to year and area to area. The years andareas with apparently two occurrence peaks in spring and autumn were not common. The D-shaped
stage larvae occurred at density of 103 individuals per m3 on the average, whereas full grown stage
larvae at 102, and thus the survival rate during planktonic stage was estimated to be about 10%.
Significant correlation in D-shaped larvae densities was not found among stations except for between
Isshiki tidal flat and the neighboring Yahagi river mouth. This fact indicates that the spawning periodsof the clam are different among different habitats in Mikawa Bay. It was considered that the high levelof juvenile occurrence in Toyogawa river mouth is attributable to the high survival rate after settlingrather than high larval supply because abundance of the full grown stage larvae in this area were notparticularly higher than in other areas.

29
Population status of Manila clam, Ruditapes philippinarum, and physical environmental
conditions in the Natori River estuary in northeastern Japan after the Great Tsunami
Kinuko Ito*, Hirofumi Yoshida, Yoshiaki Morioka, Ayu Katayama, Daisuke Takahashi, Michihiro
Shoji, Koichi Sasaki and Satoshi Katayama
Graduate School of Agricultural Science, Tohoku University, Sendai, Miyagi, Japan*
Corresponding author: itokn@bios.tohoku.ac.jp
The Great East Japan Earthquake and tsunami in March, 2011, resulted in ground subsidence,
deposition of rubble and mud. Severe morphological changes occurred in the Natori River estuary innortheastern Japan, damaging bivalve fishing grounds. To clarify the population status of the manila
clam, Ruditapes philippinarum, and physical environmental conditions, surveys have been proceeding
regularly since the tsunami. Population density was estimated based on a quadrat method. Water
temperature and salinity were measured in the field whenever sampling was conducted. To obtainaccurate diurnal changes in salinity, data-loggers have been installed since 2011. Bottom sediments arealso collected and analyzed at regular intervals. Two years after the tsunami, the manila clam
population in the Natori River recovered temporarily: many juveniles were collected during the period
from autumn, 2012, to the spring of 2013. However, a marked reduction in the population was recorded
after heavy rainfall in the summer of 2013. Manila clam recruitment has not yet occurred successfully
since the tsunami. It is suggested that low salinity has induced the damage to the manila clam
population. The data logger recorded salinity as low as 0 psu during flood tides. Heavy rain and dam
discharge to relieve high reservoir levels have induced longer periods of fresh water detention in thispart of the river. Topographical changes, especially the formation of sand spit intrusions into the river,
have reduced the width of the river mouth. The destruction of a training wall at the river mouth appears
to be the cause of sedimentation. In contrast, the abundance of another clam species, Nuttallia olivacea,
has returned to approximately the same level as before the tsunami. This bivalve is a euryhaline species,
which inhabited the same region in the Natori River estuary as R. philippinarum before the tsunami.

30
Dynamics of the sea spider parasitism on asari in Matsukawaura Lagoon, Fukushima, Japan
Takeshi Tomiyama1*, Takashi Iwasaki2, Kunihiro Wakui2, Katsumasa Yamada3, Masanori Tamaoki4
and Katsumi Miyazaki5
1Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Japan; 2Fukushima
Prefectural Fisheries Office, Iwaki, Japan; 3Seikai National Fisheries Research Institute, Fisheries
Research Agency, Taira, Nagasaki, Japan; 4Center for Environmental Biology and Ecosystem Studies,
National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan; 5Seto Marine Biological
Laboratory, Field Science Education and Research Center, Kyoto University, Shirahama, Wakayama,Japan*
Corresponding author: tomiyama@hiroshima-u.ac.jp
The parasitic sea spider Nymphonella tapetis is recognized as one of the harmful organisms for
Manila clam (asari) Ruditapes philippinarum in Japan. In 2007, sudden outbreak of N. tapatis occurredand probably caused mass mortality of Manila clam in Tokyo Bay. Then, only three locations in Japan(Tokyo, Aichi, and Fukushima) have been found as the habitat of N. tapatis during 2007 - 2011. In
Matsukawaura Lagoon, Fukushima, N. tapatis was first found in 2009 from wild Manila clam, andthereafter rapidly spread into almost entire lagoon. On 11 March 2011, a huge tsunami caused by the
Tohoku-Pacific Earthquake hit the lagoon and greatly altered its environment and landscape. After thatincident, the prevalence of N. tapatis greatly reduced from 2011 - 2012, and finally N. tapatis
disappeared from the lagoon in 2013 whereas the Manila clam density has greatly increased. This result
implies that N. tapatis population may collapse when environmental condition greatly changes despite
host clams densely inhabit.

31Life history and distribution of a sea spider, Nymphonella tapetis, parasitic on the Manila clam,
Ruditapes philippinarum, in Tokyo Bay, Japan
Katsumasa Yamada1*, Katsumi Miyazaki2, Seinen Chow3, Toshihiro Yamamoto4, Takeshi Tomiyama5,
Tomoyoshi Yoshinaga6, Yoshifumi Miyama7, Masanori Tamaoki8 and Mitsuharu Toba91

Seikai National Fisheries Research Institute, Fisheries Research Agency, Taira Nagasaki, Japan; 2Seto
Marine Biological Laboratory, Field Science Education and Research Center, Kyoto University,
Shirahama, Wakayama, Japan; 3National Research Institute of Fisheries Science, Fisheries Research
Agency, Yokohama, Kanagawa, Japan; 4National Research Institute of Aquaculture, Fisheries Research
Agency, Yokosuka, Kanagawa, Japan; 5Graduate School of Biosphere Science, Hiroshima University,
Kagamiyama, Higashi-Hiroshima, Japan; 6Graduate School of Agricultural and Life Sciences,
University of Tokyo, Bunkyo, Tokyo, Japan; 7Tokyo Bay Fisheries Laboratory, Chiba Prefectural
Fisheries Research Center, Futtsu, Chiba, Japan; 8National Institute for Environmental Studies, Tsukuba,
Ibaraki, Japan; 9Tokyo University of Marine Science and Technology, Shinagawa, Tokyo, Japan.
*
Corresponding author: k.yamada@affrc.go.jp
Nymphonella tapetis is a sea spider that is endoparasitic on bivalves including the commercially
important Manila clam Ruditapes philippinarum. In 2007, it showed a sudden outbreak in a narrow areaof Tokyo Bay and brought serious fishery damage. Because the occurrence of this parasitic sea spider
from the shallow coastal areas of Japan had scarcely been reported, knowledge on its fundamental
ecological characteristics was limited. Under such circumstances, we first established the monitoring
methods for quantitative capture, length measurement and identification of developmental stages. In
order to reveal the life history and distribution pattern, monthly monitoring using these methods was
conducted on the Manila clams and parasitic sea spiders in Banzu and Futtsu tidal flat of Tokyo Bay
from 2010 to 2011. The seasonal occurrence pattern of the parasitic sea spider showed a clear tendency,
i.e., higher in summer and lower in other seasons. Based on the monthly changes in the composition of
growth stages of the parasite, its primary reproductive season was considered to be in early summer. On
the other hand, low recruitment of larvae in hosts was observed almost throughout the year, except forMay. We suggest that this year-round continuous recruitment may contribute to a massive increase of
the parasite densities in Tokyo Bay and the other regions (e.g., Mikawa Bay).

32
Distribution, morphology and mode of life in the sea spider Nymphonella spp. (Arthropoda,
Pycnogonida): potential harmful endoparasitism on asari outside Japan
Katsumi Miyazaki1*, Takeshi Tomiyama2, Katsumasa Yamada3 and Masanori Tamaoki4
1

Seto Marine Biological Laboratory, Field Science Education and Research Center, Kyoto University,
Japan; 2Graduate School of Biosphere Science, Hiroshima University, Japan; 3Seikai National Fisheries
Research Institute, Fisheries Research Agency, Japan; 4Center for Environmental Biology andEcosystem Studies, National Institute for Environmental Studies, Japan*
Corresponding author: miyazaki.katsumi.7e@kyoto-u.ac.jp
Sea spiders or pycnogonids are a distinct monophyletic group of exclusively marine arthropods,
consisting of about 1,300 described species (ca. 160 species are recorded from Japan’s waters). The
taxonomic position of sea spiders has been controversial for a long period, but most recent phylogenetic
analyses support their class status in the subphylum Chelicerata. Although the information on theirmode of life is still insufficient, some species show a close association with soft-bodied invertebrates
such as sponges, cnidarians, annelids and molluscs including apparent cases of parasitism. Nymphonella
is a curious form of sea spider genus composed of the following three (or two) species: N. tapetis
Ohshima, 1927 recorded from Japan, N. lambertensis Stock, 1959 from southern Africa, and N.
lecalvezi Guille and Soyer, 1967 (often synonymized to N. tapetis) from the Mediterranean andNamibia. The adult morphology is very similar among these species, but the parasitism is known onlyin Japanese N. tapetis, which caused serious fishery damage on asari in recent years. In this species,
larvae show endoparasitism on bivalves whereas adults live freely on or just under the surface of sandy
bottoms. Although the mode of life in other species is not yet fully studied, the sharing of some distinct
apomorphies such as the markedly modified second head appendages (palps) and first walking legs
raises a possibility of endoparasitism on bivalves, and thus a potential harmful nature of Nymphonella
species outside Japan. Accordingly, we would like to point out the possibility of prospective fisherydamage on asari and other commercial bivalves by means of the endoparasitic Nymphonella larvae
especially in the eastern Asian and the Mediterranean coastal countries where the aquaculture ofbivalves is highly active.

33
Larval and juvenile dynamics of the Manila clam Ruditapes philippinarum in northeastern Japan
Hirokazu Abe1*, Masami Hamaguchi2, Naoto Kajihara2, Yuichi Taniai3, Akio Oshino3, Takashi
Iwasaki4, Toshihiro Wada4 and Takashi Kamiyama1
1

Tohoku National Fisheries Research Institute, Fisheries Research Agency, Shiogama, Miyagi, Japan;
National Research Institute of Fisheries and Environment of Inland Sea, Hatsukaichi, Hiroshima,
Japan; 3Miyagi Prefecture Fisheries Technology Institute, Ishinomaki, Miyagi, Japan; 4Soma Branch,
Fukushima Prefectural Fisheries Experimental Station, Soma, Fukushima, Japan*
Corresponding author: hirokazuabe@affrc.go.jp
2

Investigations of the larval manila clam Ruditapes philippinarum were conducted weekly or
fortnightly in Matsushima Bay from 2012 to 2014 and Mangoku-ura Inlet from 2013 to 2014. Monthly
field investigations of the juveniles were conducted at 13 stations in Matsukawa-ura Lagoon from June
2011 to December 2014. Results of larval investigations showed considerable short-term variability oflarval densities from June to October. The peak of larval density was observed usually from mid-July toearly-August and the second peak occasionally occurred in September. The highest larval density
observed in the present study was comparable to that of other major clam habitats in Japan. Therefore,
reproductive potential of the clam populations in Matsushima Bay and Mangoku-ura Inlet wasconsidered to be high. Recruitment of juvenile clam (>1 mm SL) was observed in Matsukawa-ura Inlet
in December 2011 and from August to February in 2012 and 2013. Early juveniles grew slowly withdecreasing their density in winter season and their growth rate rose sharply from spring. Mortality ofjuvenile clam was observed in summer in 2012 and 2013. Although mortality was not observed in 2014,
the growth of juveniles was very slow from August to December. The juveniles which settled inprevious year reached almost 20 mm in December 2014. Larval supply and the recruitment of the clam
seemed to be basically favorable in the clam habitats in northeastern Japan. However, substantial annual
variability in juvenile survival in summer would be critical for the dynamics of the clam populations innortheastern Japan.

34
Condition index and reproduction of the Manila clam Ruditapes philippinarum
in suspended and bottom culture
Toshie Matsumoto*, Yuka Ishihi, Masahiko Awaji and Junya Higano
National Research Institute of Aquaculture, Fisheries Research Agency, Minamiise, Mie, Japan*
Corresponding author: mtosie@affrc.go.jp
Bivalve suspended culture offers a number of advantages over bottom culture. In this study, we
compared the condition index and gametogenesis of the Manila clam Ruditapes philippinarum between
suspend and bottom culture. We suspended the clam in a plastic container with gravel at a depth of 2 mfrom a raft in Gokasho Bay, Mie and cultured the clam in a mesh bag containing gravel placed in a tidal
flat adjacent to the raft. Samples from each culture were collected monthly from September 2012 to
May 2013. The soft tissues were removed from their shells and fixed for histology in Davidson fluid.
The tissue samples were embedded in paraffin wax and 5 µm sections were stained with hematoxylin
and eosin. The prepared microscope slides were examined to determine sex and stage of reproductive
development. Clam reproductive maturity was categorized into six stages: undifferentiated, early
developing, late developing, ripe, spawning, and spent. At the start of the study, in September 2012
when clams reached shell length of 15.9 mm (mean, n = 15), most individuals were in a gonadal resting
period. There was an increase of the condition index from February to May 2013 in suspended culture,
while the index of clams on bottom culture reached the highest value in March and decreased in April
and May 2013. Spawning on bottom culture appears to have occurred by May 2013 as suggested by thepresence of spent individuals in the May sample. However, spawning in suspended culture appeared tocontinue from March to May 2013. By May 2013, the majority of samples was in the ripe and spawningstages. It appears from these observations that the spawning period was extended in suspended culture.

35
Report of a novel flagellated parasite in the Manila clam Ruditapes philippinarum
on the west coast of Korea
Kyung-Il Park*
Department of Aquatic Life Medicine, Kunsan National University, Korea*
Corresponding author: pk1469@hanmail.net
The Manila clam Ruditapes philippinarum is endemic to the Yellow Sea of Korea and China andcommercially important in this region. Mass mortality of the Manila clam has occurred since mid 1990s,
and the protozoan parasite Perkinsus olseni has been regarded as one of the causative agents for the
mortality due to its rapid infection and severe pathogenicity. In the present study, I report anunidentified protozoan parasite (MPX) in the Manila clam collected from west coast of Korea. Because
MPX was morphologically similar to P. olseni and co-parasitizing Manila clam with P. olseni, MPX
was isolated and diagnostic methods for P. olseni were applied to distinguish MPX from P. olseni.
When trophozoite of MPX were incubated in Ray’s fluid thioglycollate medium (RFTM) for 2 weeks
and staining with Lugol’s iodine, cell enlargement and dark brown spheres were observed as like P.
olseni but lysed with 2M NaOH, suggesting that cell-wall composition of MPX is different from P.
olseni. The zoospore of MPX observed by SEM averaged 2.38 µm in body length with 6.03 µm ofanterior flagellum and 4.37 µm of posterior flagellum. Mastigonemes were found on the anterior
flagellum with bilateral array. In PCR diagnosis, MPX was found to spread in the Manila clams
collected from the south and west coasts of Korea but not found in the clams from east coast. Clams
injected with MPX trophozoites showed 50% of mortality within a week, suggesting that MPX has highpathogenecity in the Manila clam.

36
Geographical distribution of mitochondrial COII haplotypes in the brackish water clam,
Corbicula japonica (Yamato-shijimi), around the Japanese archipelago
Mitsuya Yamada1*, Ryo Ishibashi2, Kei Toyoda1, Kouichi Kawamura1 and Akira Komaru1
1

Graduate School of Bioresources, Mie University, Tsu, Mie, Japan; 2Aquatic Life Conservation
Research Center, Research Institute of Environment, Agriculture and Fisheries, Neyagawa, Osaka,Japan*
Corresponding author: hemigramms26@hotmail.co.jp
Genetic structure of the brackish water clam, Corbicula japonica, around the Japanese archipelago
and adjacent areas were investigated using partial mitochondrial COII (990 bp) gene sequences. 142
haplotypes were detected among 283 individuals collected from 52 sites (260 individuals) in Japan, one
site (eight individuals) in Sakhalin Island and three sites (15 individuals) in South Korea. Both ofneighbor-joining and maximum likelihood phylogenetic trees revealed the presence of two majorgroups (Group I and II). Group I was monophyletic, and comprising five monophyletic lineages(Lineages A-E) of C. japonica, while Group II including Corbicula sp. was paraphyletic. Mean
pairwise genetic distance between Group I and II was 1.9%, and they were conspicuously distinct inshell coloration. Lineages A-C were recognized in Japan and Sakhalin Island, while Lineages D, E andCorbicula sp. were found in the Korean peninsula. Lineage A was dominant in Japan. Nested clade
analysis (NCA) revealed three sublineages in Lineage A, which were distributed in Pacific Ocean,
northern and southern regions of Japan Sea, respectively. In sublineages, ancestral haplotype wascommonly observed throughout their entire distribution, with 110 haplotypes unique to single localities
in Japan and Sakhalin Island. Mismatch distribution of Lineage A showed the population expansion in
the near past. Lineage B was restricted to a single locality on the western coast of Kyushu. Lineage C
was mainly observed at the areas between Sendai and Tokyo Bays. Lineages D and E were distributedin the eastern and southern coasts of the Korean peninsula, respectively. Geographical distribution ofthese lineages appears to have been influenced by major ocean currents around the Japanesearchipelago. The ubiquity of ancestral haplotypes and the pattern of mismatch distribution indicate thatearly stages of range formation of C. japonica were characterized by rapid dispersal influenced byocean currents. In contrast, the presence of many haplotypes specific to single locality suggests thatcurrent gene flow among extant populations is rather limited.

37
Effect of different artificial sea waters on survival and growth of adult Manila clam, Ruditapes
philippinarum
Mohammad Nakib Dad Khan, A.M. Shahabuddin, Novi Arisman, Debasish Saha, Toshiyoshi Araki and
Takao Yoshimatsu*
Graduate School of Bioresources, Mie University, Tsu, Mie, Japan; 2Iga Community-based ResearchInstitute, Mie University, Iga, Mie, Japan*
Corresponding author: takaoyos@bio.mie-u.ac.jp
We investigated the influence of water-types (T1: Sea water, T2: Distilled water with 3% NaCl, T3:
Deionized water with 3% NaCl, T4: Deionized water containing 3% natural sea salt and T5: Tap water
mixed with 3% NaCl) on survival of adult Manila clam, R. philippinarum in a twenty-day experiment.
The adult clams were reared in plastic mesh cages at 6 individuals per cage with three replicates. One
diet (PS: Pyropia spheroplasts) was fed to the test clams two times a day (10:00 and 15:00) at the rate of
0.25% body weight per day in a closed water system. Survival and growth of shell size were taken into
consideration for evaluating dietary performance. A significantly (P < 0.05) higher survival was obtainedin T1 followed by T4, T5, T3 and T2, indicating the superiority of natural sea water over other forms ofwater in spite of having the same basic nutritional value and exhibiting the deficiencies of certain salts
considered to be indispensable for clams` life and survival.

38
Method for detection of colored sand using image analysis and its application to monitoring
sediment movement on a tidal flat
Aiko Kurosawa*, Takumi Okabe, Yusuke Aoki and Shigeru Kato
Toyohashi University of Technology, Toyohashi, Aichi, Japan*
Corresponding author: a-kurosawa@umi.ace.tut.ac.jp
Field investigation of sediment movement in estuarine area is necessary to elucidate not only the
sediment dynamics and tidal-flat geomorphology but relation between estuarine morphology andecological environment. In coastal areas, there are sand transport studies and observations by use ofcolored and/or fluorescent sand as a tracer. For detecting the colored tracer from sediment samples,
human visual inspection has been conventionally used, thereby a huge cost is required to the tracer
survey. Frequent and multipoint tracer surveys to understand coastal and estuarine morphodynamics
need a low-cost method for detection having satisfactory the accuracy. In this study, we developed amethod of colored sand detection using computer-assisted digital image analysis technique and humanvisual inspection. These digital images of sediment samples were taken by flatbed scanner from papers
which were pasted the sand. The colored sand detection was carried out by image analysis. In the final
stage of this procedure, check of trimmed-image outputs as the results of image analysis by humanvisual inspection was employed to eliminate the erroneous detection and to increase its accuracy. Thismethod was time-saving in the tracer detection from a large number of the samples, therefore it was
suitable for the multipoint tracer survey. In addition, we applied this method to field observation in a
tidal flat of the Toyo River estuarine (Rokujo-gata), Aichi, Japan. This observation was carried out for 9
months, from September 14, 2012 to June 18, 2013 to grasp characteristics of sediment movement in
the tidal flat. The sediment samples were collected at 18 points within a spatial coverage extended 1 km
alongshore and 800 m cross-shore direction on the tidal flat and once a month during the observation
period. The analysis results from the 156 samples using the method indicated that colored sand tracers
were detected from samples of the primary observation in the range of up to distance of about 500 m
from the location of the tracer injection. After 6 months passed, the tracer had been distributed
throughout the survey area. Therefore, the sediment in the tidal flat was estimated to move widely but
to remain in the tidal flat.

39
Four-year investigations into asari clam and molluscan community in tidal flats
after the 2011 Tohoku earthquake
Kenji Okoshi*, Wataru Shinohara and Saki Shimizu
Laboratory of Marine Ecology, Department of Environmental Science, Graduate School of Science,
Toho University, Chiba, Japan*
Corresponding author: kenji.okoshi@env.sci.toho-u.ac.jp
The 2011 Tohoku earthquake and tsunami caused a lot of damage to the Tohoku region including
marine life and fisheries industry. Bivalves like Mya arenaria oonogai normally distributed in deep andasari clam Ruditapes philippinarum were dug out to surface by liquefaction and by strong wave actionof massive tsunami. The “tsunami break” was observed almost all shell surface of asari clam collectedin May 2011. The earthquake caused sudden land subsidence of about 1m in maximum where intertidal
zone became subtidal zone. Spat of oyster Crassostrea gigas was observed to attach to new hardsubstances after summer 2011. Littorina brevicula and Batillaria cumingi were found at shores thatwere land before the earthquake. What creatures advanced to new environment and disappeared withinfour years after the tsunami? The result suggests that sort of disturbance was different by place. The
species richness decreased significantly at Matsukawa-ura Inlet, Fukushima, in comparison to other twosites investigated in this study. Larval recruitment of asari clam was found every year after the tsunami,
and they are surviving and growing. Reed field were rushed by the tsunami, and mollusks that dependon reed also disappeared. Juveniles of deep burrowing bivalve Macoma contacrata have not developed
after the earthquake. In Matsushima, Miyagi, juveniles and adults of mollusks were found just after thetsunami at the same place. The community structures have not changed since the earthquake.
Musculista senhousia dominated in the place of subsidence in Mangoku-ura Inlet after the earthquake.
From the result of nMDS analysis, molluscan community gradually changed in Mangoku-ura Inlet.
Dominant species changed from species live in sandy bottom (asari clam) to those live in muddy
bottom (M. incongrua and C. angustus). We have to clarify not only short-term effect which may
explain an initial recovery of intertidal and subtidal animals but also a long-term effect which may
explain continuous changes in population with land subsidence.

40
Effect of alien predator Euspira fortunei on the distribution and abundance ofasari clam after the 2011 Tohoku earthquake and tsunami
Masahiro Suzuki* and Kenji Okoshi
Laboratory of Marine Ecology, Department of Environmental Science, Graduate School of Science,
Toho University, Chiba, Japan*
Corresponding author: 7615001s@nc.toho-u.ac.jp
On 11 March 2011, the great earthquake occurred in Japan. It caused huge damage to the asari clam
Ruditapes philippinarum along the Pacific coast of northern Japan. The alien naticid gastropod Euspira
fortune, which was introduced with imported asari clams from China and Korea, prey on asari clam andother mollusks, has been found living after the earthquake. The purpose of this study is to examine the
distribution and abundance of asari clam and E. fortunei after the earthquake. Quantitative andqualitative samplings were conducted in the tidal flats at Mangoku-ura Inlet and Matsushima Bay in
Miyagi Prefecture and Matsukawa-ura Inlet in Fukushima Prefecture from May 2011 to November
2014. The size and weight were measured in all individuals collected. Population density of E. fortunei
dramatically decreased after the earthquake but many juveniles have collected in 2012. However, it has
been decreased since 2013. Over 500 dead shells including about 150 shells with drill hole werecollected from a quadrat of Matsukawa-ura Inlet in July 2011. E. fortunei ate at least 15 species ofmollusks and diets of the snail were heavily dominated by the infaunal bivalves mainly of Asari clam.
Therefore, E. fortunei has given multiple effects on asari clam stocks after the earthquake.

41
Asari clam lived in new intertidal flat after subsidence of the 2011 Tohoku earthquake
Teppei Uemura* and Kenji Okoshi
Laboratory of Marine Ecology, Department of Environmental Science, Graduate School of Science,
Toho University, Chiba, Japan*
Corresponding author: 6614005u@nc.toho-u.ac.jp
Mangoku-ura Inlet in Miyagi Prefecture, northern Japan had a great catch of asari clam and had
great fields of shell gathering. Our study area “Ohama” in Mangoku-ura Inlet was one of the famous
fields of shell gathering. The earthquake on March 11, 2011 caused land subsidence, and the land has
sunk by about 78 cm at this location where the intertidal zone became subtidal zone. After that event,the mussel Musculista senhousia has increased dramatically and formed mats over the sediment surface.
The presence of these mats has altered the benthic habitat. The mats have led to siltation of the sedimentand have resulted in hypoxia of water just above the seabed. The mussel mats have reduced thedensities of asari clam, which suggested that Ohama has become unsuitable for habitation of asari clam.
Parts of the land became intertidal zone. In May 2013, habitat of asari clam has been confirmed in the
new tidal flats where the land sank after the earthquake. It indicated asari clam changed their habitat tothe new tidal flats. This examination proceeded by quadrat method to find creatures and measured
distance from the shoreline. Finally, what creatures advanced to the new environment, focusing on asari
clams inhabit conditions and growth condition were discussed. It was found asari clam lives in landside
up to 8 m from the shoreline at greater ebb. Although the sexual maturation and reproduction was also
observed, almost all the asari clams in new tidal flat had rounded shell morphology, indicating thatgrowth was bad. In addition, the spats (shell length: 1 - 2 mm) have been collected through the year andfew middle-sized individuals (shell length: 10 - 20 mm). The recruitment and growth of asari clams
were not constant by 2014. These suggested the new environment was not suitable for clam growth andsurvival. Since 2015, the number of spats and middle-sized individuals has increased. It suggested thisnew tidal flat is changing continuously.

42
Development of in situ measurement of clearance rate of the Manila clam
under suspended culture conditions
Satoshi Watanabe*, Natsuki Hasegawa and Junya Higano
National Research Institute of Aquaculture, Fisheries Research Agency, Minamiise, Mie, Japan*
Corresponding author: swat@affrc.go.jp
Due to drastically declining production of the Manila clam (Ruditapes philippinarum) fisherycaused by environmental degradation and other anthropogenic effects, suspended culture of theManila clam has recently been receiving much attention in Japan. Research institutes are trying to
improve the efficiency of suspended culture to promote commercialization of this technique. Bivalve
suspended cultures are commonly operated on sessile or epibenthic species, such as oysters andscallops that do not require sediments. In the case of the bottom burrowing Manila clam, however, thesuspended culture is done in a container (e.g. plastic container or net cage) with substrate (e.g. sand,gravel or pumice) hanging in the water column. Manila clams in suspended culture thus faceenvironmental conditions quite different from those in their natural habitat. In this study, a method forin situ water clearance measurement was developed for monitoring physiological conditions of theManila clam under suspended culture conditions. The device consisted of a semi-translucent plastic
chamber (55 L capacity) with two smaller plastic boxes attached to both lateral sides. The smaller
boxes were equipped with optical chlorophyll/turbidity loggers (Compact-CLW, JFE Advantech Co.
Ltd.), and the inside of each box was painted a non-reflective matte black. One of the boxes had asubmersible water pump, which pumped water out at a rate of 240 L/hr to the water surface via a tube,
drawing in water from the other smaller box though the main chamber containing Manila clams.
Preliminary test runs with (600 pieces of Manila clams, approx. 3 cm shell length) and without Mania
clams in the chamber were carried out at a depth of 2 m, suspended from a pier at the National
Research Institute of Aquaculture in Mie, Japan. Inflow and outflow chlorophyll a (chl a)concentrations were simultaneously measured every 15 minutes (i.e. complete water replacement in
the chamber occurred in about 15 minutes). Water clearance rate (CR) was calculated as CR = F [(Ci C0) / C0], where F is flow rate, Ci is inflow chl a concentration and Co is outflow chl a concentration.
The mean Ci and Co did not differ significantly without Manila clams (p = 0.24). The mean Co (2.13µg/L) was significantly lower than the mean Ci (3.04 µg/L) with Manila clams (p < 0.001). With
Manila clams, the CR greatly fluctuated ranging from 0 to 616 mL/hr/ind, and the mean CR (178.1 ±103.7 mL/hr/ind) was 10 to 20 times lower than previously reported values measured for similar sizedclams at similar temperatures in the laboratory (i.e. in beakers). The CR changed gradually, and it
seemed all the clams in the chamber were acting similarly. However, the pattern in the CR change wasirregular and did not correlate with tidal height, water temperature or time of the day. The CR was
positively correlated with Ci (p < 0.001).

43
Growth and food environment of the Manila clam in suspended culture
Yuka Ishihi*, Satoshi Watanabe, Toshie Matsumoto and Junya Higano
National Research Institute of Aquaculture, Fisheries Research Agency, Minamiise, Mie, Japan*
Corresponding author: ishihi@fra.affrc.go.jp
Suspended culture of the Manila clam (Ruditapes philippinarum) has recently been developed due
to drastic decline of the fishery production. In this study, we compered the growth of the clam between
suspend culture in a plastic container in the water column and bottom culture in a mesh bag in a tidal
flat. We also determined the relationship between the growth of the clam and food environment byanalyzing chlorophyll a level and carbon and nitrogen stable isotope ratios (δ13C and δ15N) of the clamand particulate organic matter in water column and sediment. We conducted an experimental suspended
culture of the clam at rafts in Gokasho Bay and Ounoura Bay in Mie from September 2012 to May
2013 and from March to September 2013. We suspended the clam in a plastic container with gravel at a
depth of 2 m from the rafts, and cultured the clam in a mesh bag containing gravel placed in a tidal flatadjacent to the rafts. We measured the size, total wet weight and stable isotope ratios of the clam every
one to four weeks, and also monitored the chlorophyll a level continuously using a logger. The fastest
growth was observed in the suspended culture in Gokasho Bay, where the clam grew from 12.8 mm
shell length (0.3 g) to 34.5 mm (8.2 g) in 8 months. The growth was faster in suspended culture thanbottom culture by 2 to 4 times in shell length and 2 to 6 times in wet weight. The maximum mean
growth rate was 0.26 mm/day (0.055 g/day) in suspended culture, and there was a significant positive
correlation between the mean growth rate and chlorophyll a level. The stable isotopic signature
indicated that the clam with faster growth mainly assimilated organic matter in the water column rather
than those in the sediment.

44
Relationship between abundance of planktonic larvae and benthic juveniles ofasari Ruditapes philippinarum in eastern Hokkaido, Japan
Natsuki Hasegawa1*, Toshihiro Onituska2, Sayaka Ito2 and Hiroya Abe3
1

National Research Institute of Aquaculture, Fisheries Research Agency, Minamiise, Mie, Japan;
Hokkaido National Fisheries Research Institute, Fisheries Research Agency, Kushiro, Hokkaido,
Japan; 3Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido, Japan*
Corresponding author: hasena@fra.affrc.go.jp
2

The larval recruitment process has been focused as a key aspect for understanding the population
dynamics of asari and improving stock enhancement strategies of this symbolic fishery species incoastal areas of Japan. In southern parts of Japan, such as Honshu and Kyusyu islands, asari usuallyspawn intermittently from spring to autumn, and thus multiple cohorts occur in the same year. In
eastern Hokkaido contrastingly, asari show a single synchronized spawning event during summer
because of a slow maturation process associated with low-temperature water from the cold Oyashio
current. Additionally, they are distributed in semi-closed estuaries with minor larval exchanges among
one another. Therefore, the population structures are simple, and this makes it suitable to trace each
population and evaluate the dynamics during the early life stages including planktonic larvae andbenthic juveniles. A research (2012 - 2015) on the planktonic larvae and benthic juveniles of asari in
Akkeshi area consisting of estuary and bay, which is one of the main asari production area in eastern
Hokkaido, showed that abundance and the appearance frequency of planktonic larvae did not have aclear relationship with the magnitude of recruitment of benthic juveniles to the intertidal fishinggrounds in the estuary. Moreover, high level of settlement of benthic juveniles was observed at thefishing grounds only in 2012, wherein planktonic larvae were collected only once during the 7
sampling days only in the bay area. These results showed that a large number of the planktonic larvaein the estuary drifted to the bay and then succeeded in returning to the benthic habitats in the estuary
only in 2012. This may explain the highly variable year class strength of asari in eastern Hokkaido.
This study was supported by the Ministry of Education, Culture, Sports, Science, and Technology ofJapan (Coastal Ecosystem Complex Project).

45
Energy budget and neuroenzymatic activity in asari, Ruditapes philippinarum, following
short-term exposure to the toxic alga, Heterocapsa circularisquama: implications for reproductive
success
Leila Basti1*, Satoshi Nagai2, Susumu Segawa3 and Yuji Tanaka1
1
Tokyo University of Marine Science and Technology, Minato, Tokyo, Japan; 2National ResearchInstitute of Fisheries Science, Fisheries Research Agency, Yokohama, Kanagawa, Japan; 3Faculty of
Bio-Industry, Tokyo University of Agriculture, Abashiri, Hokkaido, Japan*
Corresponding author: lbasti1@kaiyodai.ac.jp
The Manila (asari) clam, Ruditapes philippinarum, is an important fishery resource in Japan;
however, several factors have contributed to the decline of its commercial fishery production over the
past two decades. Reclamation of tidal flats, overfishing, hypoxic coastal waters and diminished foodsupply as a result of eutrophication, heavy metal pollution, outbreaks of flood events, strong winds, theintroduction of alien species including predators, and inadequate fishery management practices have all
been identified as playing a major or a synergistic role in the decrease of Manila clam stocks. Pathogens,mainly bacterial and protozoans are also responsible for mass mortalities or the reduction of fitness ofManila clams so should do harmful algal blooms (HAB). Among the HAB occurring in Japan,
Heterocapsa circularisquama is by far the most toxic to Manila clams, and to shellfish in general. Massmortalities caused by this HAB are well-documented, recurrent, and geographically-expanding events
around Japan. In spite of the relative decrease in the frequency and intensity of its blooms after 2000, H.
circularisquama is highly lethal and/or detrimental even at low cell-density, and has been going
through a revival period since 2008. The mortalities of Manila clams in fishing grounds have beenreported when H. circularisquama blooms at several hundred cells per ml. Nonetheless, the impacts ofbackground exposures to H. circularisquama on Manila clams, and bivalves in general, have so far
been overlooked. Therefore, we assessed the energy budget and neuroenzymatic activity of adult
Manila clams following short-term exposures to several realistic cell densities of H. circularisquama, at
two incubation temperatures which are lower than the ones at which H. circularisquama causes thereported mortality in Asari. The Energy budget (J h-1 g-1) was significantly affected following a 2-h
exposure to 50 and 5 cells ml-1 H. circularisquama at 15 and 20°C, respectively. The
Acetylcholinesterase activity (nmol min-1 mg total protein-1) was also decreased following 3 – 48 h of
exposure to 5 cells ml-1. The results of this study demonstrate that even short exposures to low celldensities of H. circularisquama could affect the key neuroenzymatic activity acetylcholine and theenergetic performance of Manila clams without necessarily causing mortalities. These findings imply
that H. circularisquama may play a role not only in the survivability of Manila clam fishing grounds
but also on the reproductive success of Manila clam in Japan. The management and restoration ofsustainable fishing grounds of Manila clam would reply on proper understanding of the environmental
factors that contribute the most to stock depletion, which should include HAB as background negative
effectors.

46
Evaluating the growth and mortality of transplanted asari Ruditapes philippinarum juveniles
in the Matsusaka region, Mie prefecture, Japan
Ryogen Nambu1*, Yoshimi Fujioka2, Natsuki Hasegawa2, Tomoaki Kudo3 and Hisami Kuwahara1
1

National Research Institute of Fisheries Engineering, Fisheries Research Agency, Kamisu, Ibaraki,
Japan; 2National Research Institute of Aquaculture, Fisheries Research Agency, Minamiise, Mie, Japan;
3
Kaiyo Engineering Co., Ltd., Tokyo, Japan*
Corresponding author: cjapo@affrc.go.jp
Asari juveniles settle in estuary and often die out due to freshwater discharges, resulting in failed
recruitment into commercial size (> 20 mm) in the Matsunase area Mie, Japan. In this study, we
examined the growth and mortality of asari juveniles transplanted to two subtidal areas (Matsunase
area: M1, Miwatari area: M2) with environments different from those in the nearby estuary areas tosimultaneously monitor physical environments (i.e., wave-current flow, salinity, temperature, dissolved
oxygen and turbidity) above the bottom sediment. Initial density of transplanted asari juveniles wasapproximately 1200 ind/m2 in both areas on 31 May 2013. The density of transplanted asari juveniles at
M1 drastically decreased during the first two months to 35 ind/m2 on 8 July and then to 2 ind/m2 on 19
August 2013. In contrast, the density at M2 was 534 ind/m2 on 8 July, 262 ind/m2 on 10 September and
120 ind/m2 on 2 October 2013. We also examined the characteristics of mortality of transplanted asari
juveniles in relation to physical environments, using generalized liner model (GLM). A best-fitted
model selected the maximum wave-current velocity during the survey period as the positive
explanatory variable for the juvenile growth although the velocity at M1 tended to be higher than at M2
that had higher juvenile survival than at M1. Thus, growth and survival are in trade-off relationship, andin order to maximize the efficiency of transplantation, a habitat with lower wave current velocity suchas M2 should be selected.
This study was supported in part by the Ministry of Agriculture, Forestry, and Fisheries of Japan.

47
Risk assessment on the mortality of asari clam under oxygen deficiency
Junya Higano1* and Tomomi Mizuno2
1
National Research Institute of Aquaculture, Fisheries Research Agency, Minamiise, Mie, Japan; 2Mie
Prefecture Fisheries Research Institute, Shima, Mie, Japan*
Corresponding author: higa@affrc.go.jp
Oxygen deficiency has often occurred in major habitats of asari clam in Japan, such as Tokyo Bay,
Mikawa Bay, Ise Bay, and Isahaya Bay. It has been considered that prolonged oxygen deficiency
brought about the mass mortality of the clam. On the other hands, most bivalves can switch toanaerobiosis to maintain their metabolism and survive several days in anoxic conditions. Asari clam
also has tolerance for anoxic and hypoxic conditions through the anaerobic biosis. Since the impact ofanoxia on the clam population is poorly understood, it is necessary to quantitatively assess the risk ofoxygen deficiency for survival of the clam. In order to evaluate the effect of low oxygen concentrationon the survival of asari clam, exposure experiments at different oxygen concentrations (1.0 mg/l, 0.5
mg/l, 0 mg/l and 0mg/l with 10 mg-S/l sodium sulfide) were conducted in 700 ml volume containers.
Ten clams were placed in each container and water temperature was set at 20, 25 and 30°C. The results
showed that mortality was higher at lower oxygen levels and with the presence of sulfide. We obtained
the following linear regression curves to express the median lethal time (LT50, h) as a function of watertemperature (WT, °C). Oxygen concentration of 1.0 mg/l: LT50 = -17.7 WT + 582.7 (R² = 1), 0.5 mg/l:
LT50 = -15.7 WT + 523.9 (R² = 1), Anoxic: LT50 = -9.4 WT + 318.4 (R² = 0.98), Anoxic + Na2S: LT50 =-3.2 WT + 129.2 (R² = 0.72). Particularly, the mortality rate (Mo, %) in the anoxic condition was
expressed as a multiple regression equation with WT and duration of anoxia (D). Mo = 26.3 WT + 2.6 D- 828.6. We further conducted experiments for evaluating the long-term influence of experienced
anoxia on the survival of the clams. Asari clams were exposed to anoxic water for 24, 48, and 72 h at 20
and 25°C. After the exposure, the clams were placed in oxygen-saturated water, and the survival of theclams was subsequently monitored for two weeks. The mortality rate in two weeks (Mo’) was
expressed as the following equation. Mo’ = 6.0 WT + 1.9 D - 167.6. The results implied that anoxia
caused not only acute but more seriously prolonged mortality. The equations would be useful for
predicting the mortality in combination with the in situ measurement of oxygen deficiency.