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Abstract |
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Seasonal occurrence of calanoid copepods was investigated on the basis of48samples taken from April 1979to
June 1980at a station off Miho Key in Suruga Bay,central Honshu,Japan.Samples were obtained by vertical hauls
from 30-m depth to the surface with the Norpac net.
A total of 109calanoid species, including 21species newly recorded from the bay, representing to 41genera of
19families were identified.The copepod assemblage was characterized by the high abundance of cold-water neritic
species from winter to spring,the occurrence of warm-water neritic species in summer,and the occurrence of many
oceanic species and high species diversity in autumn.
Among them, 40species were sampled abundantly and frequently and were grouped into the following 4types
on the basis of their seasonal occurrence by cluster analysis excluding an outlier, Eucalanus subtenuis:
(1) Autumn type (14 oceanic and 1 neritic species): relatively abundant from September to November and the
abundance positively correlated with water temperature. Oceanic species:Clausocalanus minor, Nannocalanus
minor, Eucalanus pileatus, E. subcrassus, Paracalanus aculeatus, Candacia catula, Acrocalanus gracilis, Undinula
vulgaris, Calocalanus plumulosus, C. pavo, Temora discaudata, Calanopia minor, Canthocalanus pauper and
Euchaeta rimana. Neritic species:Temora turbinata.
(2) Autumn-Winter Type (10 oceanic species): relatively abundant not only in autumn but also in winter (from
December to February). All species are oceanic form. Acartia danae, Paracalanus denudatus, Clausocalanus
furcatus, C. mastigophorus, Scolecithrix danae, Cosmocalanus darwini, Paraeuchaeta russelli, Lucicutia flavicornis,
Pleuromamma gracilis and P. piseki.
(3)Winter-Spring Type (6 oceanic and 5 neritic species): relatively abundant from December to May and the
abundance negatively correlated with water temperature in most species. Oceanic species: Calanus jashnovi,
Clausocalanus arcuicornis, C. parapergens, C. pergens, Ctenocalanus vanus and Candacia bipinnata.Neritic species:
Centropages abdominalis, Paracalanus parvus s. l., Acartia omorii, A. steueri and Calanus sinicus.
(4)Summer Type (1 oceanic and 2 neritic species): Relatively abundant from June to August and abundance
positively correlated with water temperature in all species.Oceanic species:Centropages bradyi. Neritic species:
Labidocera japonica and Centropages tenuiremis.
The differences in the seasonal occurrence among the oceanic species can be explained by the optimum
temperature and the vertical distribution of each species. On the other hand, that of the neritic species can be
explained by their resting-egg formation depending on the temperature or by the seasonal abundance of food
organisms and predators, as suggested by previous studies.
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