Zooplankton Investigations in the Setonaikai (Inland Sea of Japan),IV.*

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1 Journal of the Oceanographical Society of Japan Vol.25, No.3, pp.145 to 150, June 1969 Zooplankton Investigations in the Setonaikai (Inland Sea of Japan),IV.* Occurrence of Zooplankton in the Sea Regions from Iyo-nada to Harima-nada in the Winter of 1966 Reiichiro HIROTA** Abstract: 22 species of zooplankton, including 2 species of Tunicata, 2 species of chaetognatha, 13 species of Copepoda, 1 species of Branchiopoda and 4 species of Ciliophora, were discriminated at 18 stations in the sea regions from Iyo-nada to Harima-nada, in the winter of From Iyo-nada to Bingo-nada, the representatives of the zooplankton communities changed successively as follows according as the hydrographical conditions became more and more embaymental: Oncaea media Paracalanus parvus Oikopleura dioica. But the species composition of the zooplankton communities in Bisan-seto and Harima-nada varied irregularly from station to station. 1. Introduction Continued from the previous three reports (HIROTA, '68a, b, '69), the description of the species composition and the regional variation of the zooplankton fauna in 7 sea regions of the Setonaikai in the winter, 1966, and the consideration on the zooplankton communities found in these sea regions were dealt in this paper. The samples were collected at 18 stations in Iyo-nada, Hiroshima Bay, Aki-nada, Hiuchinada, Bingo-nada, Bisan-seto and Harima-nada, from 28th of January to 3rd of February, 1966 (Fig. 1 and Table 1). The sampling and the quantitative measurement of zooplankton were made by the same methods as already employed in my previous investigations in the Setonaikai Fig. 1. Map showing the collecting stations. Received February 7, 1969 Contributions from the Aitsu Marine Biological Station, No.13 Contributions from the Mukaishima Marine Biological Station, No.96 Special Project Research supported by the Ministry of Education "Studies on the dynamic status of biosphere." This study was carried out as a part of JIBP Project. Aitsu Marine Biological Station, Faculty of Science, Kumamoto University (27)

2 146 Jour. Oceanogr. Soc. Japan, Vol.25, No.3 (1969) Table 1. Some hydrographical conditions observed at each collecting station. Table 1. Continued. Cl... Chlorinity. O2(cc/l)... Dissolved oxygen in volume as reduced to standard state.... Saturation percentage of dissolved oxygen. (28)

Zooplankton Investigations in the Setonaikai (HIROTA, '68a). Some hydrographical conditions observed at each station, during the survey, are shown in Table 1. 2.

3 Zooplankton Investigations in the Setonaikai (HIROTA, '68a). Some hydrographical conditions observed at each station, during the survey, are shown in Table Species composition and regional variation of zooplankton fauna The occurrence of the important zooplankton groups, except Dinoflagellata, is shown in Fig. 2. And the percentage composition of the dominant groups is as shown in Fig. 3. In this investigation, Copepoda was the most predominant component of zooplankton. And following 22 species of zooplankton, except Dinoflagellata, were discriminated: 2 species of Tunicata, 2 species of Chaetognatha, 13 species of Copepoda (Crustacea), 1 species of Branchiopoda (Crustacea) and 4 species of Ciliophora. The occurrence of these plankters at each station is shown in Table 2. And the general feature of the regional occurrence of them is mentioned in the following. Tunicata: Oikopleura dioica, the littoral appendicularian, occurred abundantly or commonly in all the surveyed regions. Doliolurn gegenbauri var. tritonis, the oceanic thaliacean, Fig. 2. Occurrence zooplankton Fig. 3. groups of the important per m3 at each Percentage composition of zooplankton collecting of the at each collecting groups of station. dominant station. (29) (Inland Sea of Japan), IV. 147 occurred only at St. C-4 (Harima-nada) and very rarely. Chaetognatha: In the species of Sagitta crassa, two forms have been known; one is a large form (S. crassa typica) and the other is a small form (S. crassa f. naikaiensis). And there are various intermediate forms between these two forms. In this investigation, S. crassa f. naikaiensis was collected commonly or rarely in all the surveyed regions. And a intermediate form, C form classified by HIROTA ('59), was collected very rarely in Hiuchi-nada, Bingo-nada and Harima-nada. Malacostraca: Some undetermined species of Mysidacea were collected very rarely in Iyo-nada and Bisan-seto. Copepoda: Of the littoral species, Paracalanus parvus, Oithona similis, Oncaea media and Microsetella norvegica were the important constituents. The major form of Paracalanus parvus was abundant in all the surveyed regions, but the minor form was common or rare. Oithona similis was abundant in Harima-nada, rare in Aki-nada, and common in the other regions. Oncaea media was generally abundant in most of the surveyed regions, but rare in the inner part of Hiroshima Bay. Microsetella norvegica was common at some stations from Hiroshima Bay to Hiuchi-nada, but abundant at the other stations. Of the other littoral species, Acartia clausi, Corycaeus affinis and C. andrewsi occurred commonly or rarely at all the surveyed stations. And Centropages abdominalis and Oithona nana occurred commonly or scantly at most of the surveyed stations. Calanus helgolandicus occurred scantly at most of the surveyed stations. Pseudodiaptomus marinus occurred scantly at some stations from Bingonada to Harima-nada. Calanopia thompsoni occurred only at St. C-1 in Bisan-seto and very rarely. Clitemnestra rostrata, the oceanic form, occurred very rarely at Sts. C-13 (Iyo-nada), C-7 (Hiuchi-nada) and C-2 (Harima-nada). Branchiopoda: Evadne nordmanni was collected only at St. C-14 in Hiroshima Bay and very rare. Hydrozoa: Some undetermined hydromedusae were collected rarely or very rarely in this survey. Ciliophora: Tintinnopsis beroidea, T. loh-

4 148 Jour. Oceanogr. Soc. Japan, Vol.25, No.3 (1969) (30)

Zooplankton Investigations in the Setonaikai (Inland Sea of Japan), IV. 149 manni, T. radix and T. tubulosa were collected commonly or rarely at several stations in all the surveyed regions.

5 Zooplankton Investigations in the Setonaikai (Inland Sea of Japan), IV. 149 manni, T. radix and T. tubulosa were collected commonly or rarely at several stations in all the surveyed regions. Codonellopsis nipponica was collected at all the surveyed stations and generally abundant or common. Larval form of benthos: Larval forms, including ascidian tadpole, ophiopluteus, bipinnaria, actinotrocha, cyphonautes, four stages (megalopa, mysis, zoea and nauplius) of Decapoda, cypris and nauplius stages of Cirripedia, Polychaeta larva, molluscan veliger and pilidium larva, occurred abundantly in all the surveyed regions, especially very abundantly at St. C-7 in Hitachinada. Among them, molluscan veliger was the most predominant ( %). Dinoflagellata and Diatom: Noctiluca scintillans (Dinoflagellata, Mastigophora) was collected abundantly or very abundantly in all the surveyed regions. The results of the quantitative and qualitative examinations of dinoflagellates (except Noctiluca) and diatoms at 10 stations (Sts. C-3, C-4, C-5, C-7, C-9, C-11, C-12, C-14, C-15 and BG-1) will be reported in the separate publication, together with the values of the chlorophyll a content and the photosynthesis. 3. Consideration on the zooplankton communities The most important component of the zooplankton communities in the sea regions from Iyo-nada to Harima-nada in the winter of 1966 was Copepoda (Fig. 3). And the nextly im - portant components were Tunicata, Ciliophora or benthos larvae. On Copepoda, the percentage composition of the important species at each station is shown in Fig. 4. In most of the surveyed regions, except Iyo-nada and Harimanada, Paracalanus parvus was the most dominant and Oncaea media was generally subdominant. But in Iyo-nada, Oncaea media was the most predominant and Paracalanus parvus was subdominant. In Harima-nada, Paracalanus parvus, Oithona similis, Oncaea media and Microsetella norvegica occurred as the important components, and their composition varied from station to station. On the other groups, the important components were Oikopleura dioica (Tunicata) and Codonellopsis nipponica (Ciliophora). Putting together these results, the important zooplankton organisms representing the community in each sea region are generalized as follows. Iyo-nada...Oncaea media, with Paracalanus parous Hiroshima Bay... Paracalanus parvus, with Oikopleura dioica Aki-nada...Paracalanus parvus, with Oncaea media Hiuchi-nada...Paracalanus parvus, with Oikopleura dioica Bingo-nada...Oikopleura dioica, with Paracalanus parvus Bisan-seto...Paracalanus parvus and Codonellopsis nipponica Harima-nada...Oncaea media, Microsetella norvegica and Oikopleura dioica (southwestern part), or Paracalanus parvus, with Oithona similis (central part) In this survey, the hydrographical conditions (water temperature, chlorinity and transparency) were the most oceanic in Iyo-nada and the most embaymental in the eastern part of Bisan-seto. From Iyo-nada to Bingo-nada, the representatives of the zooplankton communities change succes- sively as follows according as the hydrographical conditions became more and more embaymental. Oncaea media Paracalanus parvus Oikopleura dioica But in Bisan-seto and Harima-nada, the species composition of the zooplankton communities varied considerably from station to station. Accordingly, it was difficult to indicate the conspicuous interrelation between the distribution of the zooplankton communities and the environmental conditions. Fig. 4. Percentage composition of the dominant copepods at each collecting station. (31)

6 150 Jour. Oceanogr. Soc. Japan, Vol.25, No.3 (1969) Reference HIROTA, R. (1959): On the morphological variation of Sagitta crassa. Jour. Oceanogr. Soc. Japan, 15, (In Japanese with English abstract) HIROTA, R. (1968a): Zooplankton investigations in the Setonaikai (Inland Sea of Japan), I. Occurrence of zooplankton in the western half of the Setonaikai in June, Ibid., 24, HIROTA, R. (1968b): Idem, II. Occurrence of zooplankton in the eastern half of the Setonaikai in September, Ibid., 24, HIROTA, R. (1969): Idem, III. Occurrence of zooplankton in the sea regions from Iyo-nada to Harima-nada in the autumn of Ibid., 25,

아산만해역중형동물플랑크톤의시공간적변동

The Sea Journal of the Korean Society of Oceanography Vol. 11, No. 1, pp. 1 10, February 2006 아산만해역중형동물플랑크톤의시공간적변동 Á Á 1 Á 2 û w y w 1Ÿ w y œw 2 sw w w lœw Spatio-temporal Variation of Mesozooplankton