Journal of The School of Marine Science and Technology,Vol.4 No.2
Seasonal Occurrence of Chaetognaths off Miho Key, Suruga Bay, Central Japan in
Addition to Seasonal Succession of Zooplankton Assemblage in Inner Part of Suruga Bay
Hiroshi ITOH, Takeshi MIZUSHIMA and Tadashi KUBOTA
Abstract
Seasonal occurrence of chaetognaths was investigated on the basis of47samples 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 a Norpac net.
A total of 15species, representing eight genera of three families were identified. The chaetognath assemblage
was characterized by the high abundance of a single neritic species from spring to summer and the high species
diversity from summer to autumn.
Among them, 11species occurred in more than 10% frequency and were grouped into the following four types
on the basis of their seasonal occurrence:
(1)Summer-Autumn Type:relatively abundant from summer to early autumn and mostly disappeared in December.
The abundance positively correlated with water temperature in all species. Inlet water species:Aidanosagitta
crassa f. naikaiensis. Oceanic species:A. neglecta, Ferosagitta ferox.
(2)Summer-Winter Type:relatively abundant from summer to winter and occurred until early in January. The
abundance positively correlated with water temperature in all species. All species were oceanic forms:
Aidanosagitta regularis, Ferosagitta robusta, Flaccisagitta enflata, Zonosagitta pulchra.
(3)Autum-Spring Type:relatively abundant from late autumn to spring.The abundance negatively correlated with
water temperature in one species and positively correlated with salinity in two species. All species were oceanic
forms:Serratosagitta pacifica, Pterosagitta draco, Mesosagitta minima.
(4)Spring-Summer Type:relatively abundant from May to July. The abundance positively correlated with water
temperature and negatively correlated with salinity. A single neritic species:Zonosagitta nagae.
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,the high abundance of the neritic species,
Z. nagae from May to July can be explained by the seasonal abundance of prey, calanoid copepod.
Also,the seasonal succession of zooplankton assemblage in the inner part of Suruga Bay was summarized on the
basis of the present result and previous reports dealt with copepods and appendicularians collected by a same Norpac
net.