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アイテム
瀬戸内海産浮游性毛顎類に関する海洋生物学的研究
https://fra.repo.nii.ac.jp/records/2005092
https://fra.repo.nii.ac.jp/records/200509261e827cb-c88a-4f91-9a00-5478c7730a6e
| Item type | 紀要論文 / Departmental Bulletin Paper(1) | |||||
|---|---|---|---|---|---|---|
| 公開日 | 2024-05-17 | |||||
| タイトル | ||||||
| タイトル | 瀬戸内海産浮游性毛顎類に関する海洋生物学的研究 | |||||
| 言語 | ja | |||||
| タイトル | ||||||
| タイトル | Marine Biological Study on the planktonic Cheatognaths in the Seto Inland Sea. | |||||
| 言語 | en | |||||
| 言語 | ||||||
| 言語 | jpn | |||||
| 資源タイプ | ||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_6501 | |||||
| 資源タイプ | departmental bulletin paper | |||||
| アクセス権 | ||||||
| アクセス権 | metadata only access | |||||
| アクセス権URI | http://purl.org/coar/access_right/c_14cb | |||||
| 著者 |
村上, 彰男
× 村上, 彰男 |
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| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | Part I Studies on the occurrences and habits of chaetognaths. §1 Distribution and habit The material was collected during 1953~1957 at about 100 stations distributed over the Seto Inland Sea. By occupying these stations in different seasons of the year, a total of 940 tow-nettings were done. In each tow the plankton net was hauled vertically from a depth of 50m. or less up to the surface. The following 15 forms are represented in the collection: Sagitta enflata, S. bedoti, S, robusta, S. bipunctata, S. serratodentata pacifica, S. pulchra, S. ferox, S. ser. atlantica forma pseudoserratodentata, S. minima, S. regularis, S. neglecta, S. decipiens, S. crassa (including forma naikaiensis and the intermediate form), Pterosagitta draco and Krohnitta pacifica. Since this list includes almost all the chaetognaths known from the neighboring seas of Japan, it may be said that the chaetognath fauna characterizing the Kuroshio region around. Japan is represented within the small area of the Seto Inland Sea. Dominant species were S. crassa, S. enflata, S. bedoti and S. minima. On an average 9 individuals of chaetognaths were caught per m³ of the sea water filtered through the net, and the maximum density of 196 individuals per m³ was recorded in Osaka Bay in August, 1955. Seasonal changes in the abundance of chaetognaths were largely due to the changes in the abundance of S. enflata. Generally speaking, S. enflata was abundant in the years of high salinity. The Seto Inland Sea can be divided into the following. three regions on the basis of the chaetognath fauna: (1) the outer region (Kii and Bungo Straits), where only the oceanic species occur but the chaetognath fauna is richest in both variety and abundance; (2) the inner region (Suho Nada, Aki Nada and Bingo Nada, excluding the inlets located in the innermost part of this region), where only S. crassa and S. enflata occur and the chaetognath fauna is poorest in both variety and abundance; (3) the intermediate region (Izumi Nada, Harima Nada and Iyo Nada), where S. crassa, S. enflata and two sub-oceanic species(S. bedoti and S. minima) occur, The inlets located in the innermost part of the second region constitute another faunal region, which is referred to as the inlet region. The correlation between the occurrences of various species and the hydrographic conditions is discussed for each faunal region, and the data on abundance, population composition by body length and maturity, water temperature and chlorinity are shown on monthly basis. The habit of each species is also discussed. The lowest water temperature and chlorinity at which the oceanic speices occurred were 10°C and 17.5%. A half, of the oceanic species were found spawning in the Seto Inland Sea, S. enflata was found to be euryhaline. In September it begins spreading toward the inner region, where it remains in abundance until December. Two types, namely, the large and the small type, were distinguished in this species; the former type occurs only in the waters of high salinity. The two sub-oceanic species showed similar distributions to each other. S. crassa (as including forma naikaiensis and the intermediate form) is adapted to relatively low salinities and its abundance reached maxima in April, August and November. §2 Indicator species Many examples are related regarding how chaetognaths can be used as the indicator of hydrographic conditions. For instance, in Kii Strait S, bipunctata, S. minima and S. crassa have proved to be of practical value as the indicator species of three waters of different origins. The three species respectively indicate the highly saline water that flows into the strait from the ocean along the bottom, the water of neritic origin which overlies the former water and is lower in salinity, and another water of lower salinity which is the outflow from the inner part of, the Seto Inland Sea subsequently diluted by the river drainage. When the ratio of the combined abundance of S. enflata, S. bedoti and S. minima to the abundance of S. crassa is computed for each season of each year, its value is highly correlated to the seasonal shifting of the iso-halines in the Seto Inland Sea; as a result, the seasonal change in the abundance of S. enflata indicates the seasonal change in the influence of the Kuroshio Current to the Seto Inland Sea. It is also found that the abundance of S. enflata in the whole Seto Inland Sea in a given year is correlated positively to the same year's commercial catch of the fishes preferring high salinities, and negatively to the same of the fishes preferring low salinities. Furthermore, when the abundance of S. enflata is computed for the whole, western and eastern part of the Seto Inland Sea, for each year, its value is negatively correlated to the same year's catch of Engraulis japonicus in the respective sea region. It therefore follows that chaetognaths are useful not only as the indicator of hydrographic conditions but also as the indicator of the fluctuation of fisheries. §3 Other results The importance of using a plankton net of suitable mesh-size is emphasized by showing that the species, body length and maturity compositions of captured chaetognaths differ very considerably according to the mesh-size of the net. Pre-spawning stage (the stage at which the fully ripen eggs have just entered the oviduct) is described in various species. A pair of S. crassa which were presumably in copulation were observed. The two individuals oriented themselves in reciprocal directions, contrary to what had generally been believed. Part II Studies on Sagitta crassa. §1 Life history Intensive collection of field samples was continued in Kasaoka Bay of the Seto Inland Sea throughout 1954~1958 by the following methods: surface tow and set-netting in the upper, middle and bottom layers at the mouth of the bay (once a week); surface tow in Yokoshima Strait leading to the eastern part of the bay (two to six times a week); collection at closely spaced stations distributed all over the bay and continuous collection at fix stations for 13 hours (several times). In the laboratory various rearing experiments were done and the development of spawned eggs was studied. S, crassa is distinguished into eleven types on the basis of the position of the collarette: C-and C'-types correspond to the form which has hitherto been known as S. crassa, O-and N-types to S, crassa forma naikaiensis, and I₁-through I₇-types to the intermediate form. The changes in the abundance and the size, maturity and type compositions of the field population are examined in great details, From the results, it is deduced that the annual cycle of this species is constituted by the following three generations: the spring-summer generation, which is born in spring and spawns in summer; the summer-autumn short-period generation, which has the life span of three and a half months; and the autumn-winter generation, whose life span is five months. And it is presumed that this annual cycle is augmented by the fourth generation, namely, the summer-winter long-period generation, which is born in summer and spawns in winter, The seasonal changes in the abundances of larvae, adults and spawning individuals as were observed in the sea are explained adequatley by introducing the concept of the last-named generation. The individuals belonging to the summer-winter long-period and autumn-winter generations assume I₁-type in late November at water temperatures 12~14°C. In about a month those inhabiting the regions where the water temperature drops below 8 or 9°C assume C-type, while those in the other regions remain as various I-types. In the warm period the individuals of these generations spawn and die before attaining large sizes, but they grow to large sizes in the cold period. §2 Life history in different sea regions Even within such a small sea like the Seto Inland Sea the annual life cycle of S. crassa somewhat differs by regions. For instance, spawning takes place earliest in the innermost region and is delayed toward the outer region. In one region a particular generation is numerically strongest in the annual cycle, while another generation is the strongest in another region. Judging from the manner in which this species occurs in various sea regions and from the results of rearing experiments, S. crassa is presumed to be adapted essentially to warm neritic waters of relatively low salinity, Of the various types of this species, N-type (forma naikaiensis) is distributed most extensively and occurs for the longest period of time. Accordingly, it is presumed that this type is the typical form of this species. In neritic waters, which is the typical habitat of N-type, the spring-summer generation is numerically . much stronger than the other generations. As one moves toward the inlet region, C- and I-types (which are regarded as low-temperature types) account for increasingly larger portions of the population and the autmn-winter generation becomes the most productive generation. The main habitat of C-type is the shallow neritic waters where the water temperature falls markedly in winter. In the Seto Inland Sea such waters are located in the western part of Suho Nada, the northern parts of Bingo Nada and Harima Nada and along the coast of Osaka Bay. When reared, C-type survives until early May (water temperature 17°C). I-type occurs in all regions of the Seto Inland Sea in colder seasons, but its occurrence is rather exceptional in warmer seasons. In the Kuroshio region, however, it presumably survives temperatures upto about 20°C, In the Seto Inland Sea, the most favorable habitats of this species are such parts of the inlet region where the water temperature does not drop so much as to induce the appearance of C-type; in such habitats this species flourishes in both summer and winter. Another suitable habitat of this species is the intermediate region, where population increases greatly in summer. In the inner region the population remains at low levels throughout the year; this region and the outer region are unfavorable to the propagation of this species. In such parts of the inlet region where the water temperature falls so much in winter as to cause the appearance of C-type (e. g., Kasaoka Bay), the propagation of I-type is not very vigorous in summer. §3 Rearing and development Adults of S. crassa were successfully reared in the laboratory for three months in the case of C-type and for a month in the case of N-type, Special care was taken to keep the rearing water clean. Light intensity was controlled to a low level, and fresh copepods were used as food. For the purpose of stirring and aeration, air bubbles about 5 m.m. in diameter were released from the bottom of the rearing vessel at a rate of 1 to 2 per second, The results of the rearing experiments were advantageously utilized in interpreting the results of the examination of field samples. The adult of S. crassa dies in about ten minutes in distilled water. The lower limit of chlorinity that it can tolerate is 5%. It tolerates a temperature changes of more than 10°C if the change is gradual, but hardly tolerates any sudden change in temperature. Generally speaking, S. crassa is adapted to wide ranges of water temperature and chlorinity, and can be reared rather easily. Therefore, it can be used as a testing animal. Once an adult S. crassa is exposed to a temperature below the threshold of about 7°C, its collarette continues to increase gradually, but the rate of the increase is slowed down if temperature is raised subsequently. It is thus proved, at least partially, that the three types of S. crassa are the polytypes due to the temperature effect. Both spawning and the release of the sperm lump are repeated more than twice at intervals of several days. The development of the fertilized egg was traced and described in the three types, and the time required to attain various developmental stages is determined. The period from spawning to hatching changes with water temperature and chlorinity, and a minimum of fifteen hours was recorded at a temperature above 27°C. It is presumed that eggs of S. crassa spawned in the sea hatch in one day in summer and in two to four days in winter. Spawned eggs measure about 350μ in diameter, and the larvae measure about 800μ in body length immediately after hatching. At 20°C the tail septum appears on the third day and the anus opens in four days. Hatching and growth of the larva advance normally at chlorinities 13~20‰. From this result and the aforementioned salinity tolerance of the adult, it can be said that the optimum chlorinity range for S. crassa is 17~18‰. Laboratory-hatched larvae were successfully reared for a maximum period of three weeks, but none of them could be raised to an adult because suitalbe food was not found. §4 Morphology and ecology In every generation, the numbers of hooks anterior and posterior teeth change as the body length increases. The number of posterior teeth increases suddenly when the food habit changes. The number of teeth varies markedly with seasons and body lengths. Data on the body lengths of spawning individuals , the relative length of ovary to body length and the number of eggs in oviducts are presented. The major factor controlling the vertical distribution of S. crassa in inlet waters in the day-time is the photo-sensitivity of the animal, which differs according to growth stages, rather than the sea condition. Various responses of this animal to the light are described. Many chaetognaths including S. crassa have such great swimming abilities that it seems appropriate to call them "nekto-plankton" rather than "plankton". §5 Values as the indicator species and the food for fishes The author discussed the conditions that should be satisfied in using S. crassa as an indicator species in inlet waters by referring to many examples, and showed how this species is used as the indicator for the inside and outside waters of Kasaoka Bay in various seasons. For example, in winter, the occurrence of many large-sized and fully grown specimens of C-type and I-types nearly resembling C-type can be used as an indicator for the inside water, and the occurrence of a few small-sized specimens of N-type and I-types nearly resembling N-type, as an indicator for the out-side water. In the inlet waters where various water masses move around in complicated manners, the origin of a given water mass can be identified by examining the size, maturity and type compositions of the S. crassa population inhabiting it, because the origin water mass of this particular water mass in question is inhabited by the S. crassa population of the identical compositions. It therefore follows that this species can be used also as an indicator for the movement of water masses, In Kasaoka Bay S. crassa is of more practical value as an indicator species than copepods, S. crassa is found in great numbers in the digestive tract of Ammodytes personatas and other fishes. Many hooks found in the digestive tract of Engraulis japonicus are identified as belonging to the individuals of N-type on the basis of their shape and the region and season in which the fish were taken. S. crassa is an important food for those larval fishes which occur in the Zostera zone in spring, and various other fishes also depend on it for nutrition from spring until summer. §6 Other results S. crassa specimens fixed and stored in formalin solution do not shrink by more than 0. 4m.m. in body length for a month, and such small shrinkage can be regarded as negligible when the body length is measured to the nearest m.m. In Kasaoka Bay S. crassa feed on such large copepods as Centropages and Calanus and small copepods such as Acartia clausii and Paracalanus in winter, and on the copepods of medium size (e. g. A. erythraea and Tortanus) in summer. In Kasaoka Bay there occur S. neglecta and S. minima in small numbers and S. enflata in great abundance, in addition to S. crassa. The last-named species occur only in the autumn, and the population consists exclusively of the individuals of the small type. This species also can be used as an indicator species in the inlet waters. | |||||
| 言語 | en | |||||
| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | 第Ⅰ部 出現及び生態に関する研究 1. 分布及び生態 1953~57年に瀬戸内海の約100測点で50m層以浅を総計940例垂直採集した。出現種は Sagitta enf., S. bed., S. rob., S. bip., S. ser., S. pul., S. frx., S. p-ser., S. min., S. reg. , S. neg. , S. dec., S. crassa (f.naikaiensis 及び両者の中間型をふくむ),Pterosagitta draco, Krohnitta pacifica で,本邦近海の出現種の大部分を含み本海域は本邦黒潮流域の縮図的組成を有している。優占種はS.crassa, S.enf.,S.bed., S.min.である。量的には採集例の総平均は9尾/m³で最大密度は'55年8月大阪湾の196尾/m³である。出現量の年変化は主として S.enf. 量に左右され一般に高塩分年ほど本種の増殖が盛んである。出現状況から瀬戸内海を外洋性種のみで種類·最共最大の紀伊·豊後両水道(外部区)と,S. crassa, S.enf. のみで量的にも最小の周防·安芸·備後灘(内部区 ……… 内湾部を除く)と,これに亜外洋性種のS.min.,S.bed. の加わった和泉·揺磨·伊予灘(中間区)の3つに分けられる。各海域毎に海況と出現状況との関係を論じ,海域別·月別の数量,体長·熟度組成と出現時の水温·塩素量を示した。各種類毎の生態を述べたが、外洋性種出現の水温·塩素量下限は10℃,17.5‰でありこの内半数の種類は内海でも産卵する。S. enf. は広塩分性で9月になると順次内海内部にも出現し増殖期は9~12月で,大小2型があり大型種は高塩分海域のみに棲息する。亚外洋性2種はよく似た分布を示し,低塩分性の S.crassa は3types を併せて考えると内海全域としては4,8,11月に量的な山がある。2. 指標生物 指標としての使用例を示したが,例えば紀伊水道では S.bip.は底層を通って外洋から侵入する高塩分水系に,S. min. はその上に存在する低塩分の沿岸水系に、S. crassa は内海内部から流入してくるものと河川水の混合した低塩分水系に対し指標生物として実用的に勝れた価値を有する。高塩分性の S. enf.,S.bed.,S.min. の合計と低塩分性の S.crassa の数量比の年変化は等塩素量線分布の年変化とよく対応し,瀬戸内海に及ぼす黒潮勢力の年変化は S.enf. の出現量の年変化を以て指標しうる。また瀬戸内海における S. enf. 出現量の年変動は高低両塩分性魚種の年間漁獲量の年変動とそれぞれ正·逆の相関を有し,内海全域及び東西両半分のそれぞれについてカタクチイワシ漁獲量の年変動と逆相関を有している。従って Chaetognatha は海況のみならず、漁況の指標生物としても有効である。3.,その他 使用した net の網目の大きさにより採集物の種類·体長·熟度組成に大きな差を生ずることを例示した。各種類について完熟卵が輪卵管内に入り込んだ排卵直前状態を示した。S.crassa の交尾個体と思われるものを示したが,その相互位置は従来の説と異り頭尾の方向を逆にしていると考えられる。第Ⅱ部 Sagitta crassa に関する研究 1. 生活史 1954~58年に備後灘北岸の笠岡々口で週1回の表面曳網及び表·中·底3層別定置採集,湾東小開口部たる横島水道で週2~6回の表面曳網,数回の湾内外及び定点潮間採集と飼育発生実験を行った。泡状組織の存在部位により11ヶの typeに別けたが,この内 C, C'-typesは S.crassa に,O, N-types はそのf. naikaiensis に, I₁~I₇-types は両者の中間型に当る。数量,体長·熟度·type 組成の変化等を詳細に調べると,内湾海域での生活史は春産れて夏産卵する寿命5カ月の春夏世代と,3.5カ月の夏秋短期世代と,5ヶ月の秋冬世代の3者が年間の cycle を形成し,これに夏産れたものの一部が越年して冬産卵する寿命7ヶ月の夏冬長期世代が加わることになる。また幼体の出現状況に長期世代の考えを導入して幼体·成体·産卵群の数量変化を説明した。type の変避は夏冬長期及び秋冬世代のものが11月下旬 12~14°Cで I₁-typeとなり,最低水温が8~9°C以下となる海域では約1カ月後 C-typeとなりその他の海域では I-typeの各段階に止まる。高温期は小型の内に産卵死亡し低温期には長大個体が現われる。2. 海域差 瀬戸内海の如き小海域内でも各海域により生活史は多少時期的にづれ,例えば内湾から外部区に向うにつれて産卵期が選れまた生活史中で占める各世代の比重が異る。各海域の出現状況と飼育実験結果とによれば本種は元来温暖でやや低塩分の近海産のものであり,出現期間·海域の規模からみて従来 forma とされていた naikaiensis 即ち N-type が種の type でありその本来の棲息海城である沿岸部では春夏世代の増殖力が最大で年間 cycle の主体をなすが、内湾部に近づくにつれ低温期型の C, I·types の比重が大きくなり秋冬世代の増殖力が最大となる。C-type の主産地は低塩分の沿岸浅海部の内冬季水温低下の著しい海域で,瀬戸内海では周防灘西部·備後灘北部·播磨灘北部及び大阪湾沿岸等である。飼育すれば·C-type は5月初旬(17°C)まで生存しうる。I-typeは低温期には内海全域に出現するが高温期でも例外的に出現し,黒湖海域では20℃前後までは存在しうると考えられる。内海における本種の接息域としては冬季の降温程度が著しくなく従って C-typeが出現しない内湾部では夏冬共増殖が盛んであり,夏季大増殖する中間区がこれに次ぎ、内部区はいづれの世代も増殖力が弱く外部区と共に最も不適である。内湾部でも笠岡湾のように降温が著しくて C-typeが出現する処では夏季の増殖カが比較的弱い。3. 飼育及び発生 飼育水の清澄,低照度,新鮮な Copepoda 給餌及び器底より径5m.m.位の気泡を毎秒1~2ヶ宛放出させて攪拌通気を行う方法等により,成体で C-type 3ヶ月,N-type 1ヶ月に及ぶ長期飼育に成功し,種々の飼育実験結果をえて採集結果の解釈を裏付けた。成体は蒸溜水中では約10分で死亡し,生存の塩素最下限は5%で,水温は徐々に変化させれば10℃以上の温度差にも耐えるが急激な上昇には弱い。一般に水温·塩分の変化には適応力が強く飼育も比較的容易であるから験体生物としても充分使用にたえうる。水湿と泡状組織増大の関係は一旦限界温度(約7°C)以下の低温に遭選すると以後次第に増大するが,加温すればその速度が抑制される。これにより3つの typeが水湿による多型であるととを或程度証明しえた。排卵放精とも数日おいて2度以上繰返えされる。各 typeの発生を追跡し各 stage に到るまでの所要時間を求めその stage の状態を図示した。孵化所要時間の水温·塩分による変化は最短は15時間(>27℃)であった。海中では夏季1日,冬季2~4日で孵化するものと思われる。卵径は350μ前後,孵化直後の幼体体長は800μ前後で,20°Cで3日目に尾部横隔膜を生じ4日後肛門が開く。13~20‰では孵化発育は順調に行われる。成体の耐塩分性実験結果と併せて考えると本種の最適塩素量は17~18‰である。幼体銅育の最長期間は化後3週間で餌料の点から完全飼育には成功しなかった。4. 形態及び生態 各世代を通じて顎毛·前後歯数の体長による変化を示したが、食性転換期には後歯数が急増する。歯の数は季節·体長による変異が著しい,その他産卵群体長·卵巣長比·朶卵数の変化を示した。浅海では日中の上下分布を支配するのは海況よりも成長度による光に対する感受性の差であることを初め光に対する種々の反応を示した。plankton としては最大に属する自主的移動力をもっておりむしろ nekto-plankton とでも称すべきであると考えられる。5. 指標及び餌料価値 内湾海域の指標生物使用の条件を例証し,笠岡湾の湾内外水系に対し各季毎に本種を指標として使用する方法を述べた。例えば冬季では湾内水には多数のC及びCに近いI-typeの大型完熱個体、湾外水には少数のN及びNに近いI-typeの小型個体の存在を指標としうる。水塊流動の烈しい内湾諸地点での本種の組成は採集時の地点にあった水塊の根源水塊のもつ組成に一致し水塊流動の生物指際としても使用しうる。指標生物としては Copepoda にくらべて遥かに実用的価値に富む。本種はイカナゴを初め各種魚類の消化管内容物中に多数発見され,特にカタクチイワシの消化管内に残留した多数の顎毛はその形態,捕食魚の出現した海域,季節からみてN-typeのものと断定しえた。本種は春には藻場稚魚の,夏にかけては各種魚類の重要な餌料である。6. その他 formalin 固定による体長縮少は1ヶ月間に最大0.4m.m.にすぎずm.m.単位の体長測定値としては持に考慮の必要はない。笠岡湾では冬季群は Centropages,Calanus 等の大型種と Acartia clausi, Paracalanus 等の小型種を,夏季群は A.erythraea,Tortanus 等の中型 Copepoda を餌料としている。笠岡湾には S.crassa 以外に少数の S.neg., S.min,S.bed. と多数の S.enf. が出現するが,S.enf. は秋~冬に限られ,小型種のみで,内湾海域の水系の指標として使用しうる。 | |||||
| 言語 | ja | |||||
| bibliographic_information |
ja : 内海区水産研究所研究報告 en : Bulletin of Naikai Regional Fisheries Research Laboratory 巻 12, p. 1-186, ページ数 186, 発行日 1959-03 |
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| 出版者 | ||||||
| 出版者 | 内海区水産研究所 | |||||
| 言語 | ja | |||||
| 出版者 | ||||||
| 出版者 | Naikai Regional Fisheries Research Laboratory | |||||
| 言語 | en | |||||
| item_10002_source_id_9 | ||||||
| 収録物識別子タイプ | PISSN | |||||
| 収録物識別子 | 0497-5022 | |||||
| item_10002_source_id_11 | ||||||
| 収録物識別子タイプ | NCID | |||||
| 収録物識別子 | AN00176718 | |||||
| 情報源 | ||||||
| 識別子タイプ | Local | |||||
| 関連識別子 | nai_k_1201 | |||||
| 関連サイト | ||||||
| 識別子タイプ | URI | |||||
| 関連識別子 | https://agriknowledge.affrc.go.jp/RN/2010841476 | |||||
| 言語 | ja | |||||
| 関連名称 | 日本農学文献記事索引(agriknowledge) | |||||
