ISSN 10630740, Russian Journal of Marine Biology, 2011, Vol. 37, No. 2, pp. 111–122. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © E.A. Petrova, T.N. Dautova, L.S. Shkoldina, 2011, published in Biologiya Morya.
Despite its wide distribution and important role in
biocenoses, the hydroid medusae (Cnidaria: Hydro
zoa) rarely dominate planktonic samples. For this rea
son and due to the difficulties of species identification,
in many zooplankton studies this group of organisms
has been entirely ignored and no species lists have
been presented. To date almost no information is
available concerning the density of hydroid medusae
and schedules of their appearance in the plankton of
the northwestern Sea of Japan, with the exception of
certain isolated water areas, such as the Tatarsky Strait
 and Kievka Bay .
The target of this project was to study species com
position, seasonal density dynamics, and spatial distri
bution of hydromedusas in the Vostok Bay of the Sea of
MATERIAL AND METHODS
The planktonic samples were collected in Vostok
Bay (Peter the Great Bay, Sea of Japan), at nine per
manent stations; from May to November in 2002, in
April and June of 2003 and in May and November of
2004 (Fig. 1, Table 1).
Vostok Bay is located in the southeastern part of
Peter the Great Bay and faces the open sea. The deep
est depths in the bay reach 25–28 m . The deepest
sampling depth equaled 22 m (Stn. 6, Srednyaya
Bight). The subsurface water circulation in the bay
demonstrates a cyclonic pattern. The speed of subsur
face water currents ranges from 0.1 to 0.24 m/s [2, 4].
Surface water currents are chaotically arranged
depending upon wind conditions, but cyclonic water
turnover pattern still prevails .
The sampling stations were located in Tikhaya
Zavod’ Bight (Stn. 1, 2 m deep; Stn. 8, 13 m and
Stn. 9, 10 m deep); Vostok (Stn. 2, 7.6 m); Litovka
(Stn. 3, 3.7 m and Stn. 4, 6.8 m); and Srednyaya
(Stn. 6, 22 m and Stn. 7, 16.5 m deep) bights and at
Podosenova Cape (Stn. 5, 9.5 m deep). For the sake of
convenience, each the examined plankton sample
received a particular reference designation (Table 1).
The samples were collected along a vertical line
from the bottom to the surface using a Juday net with
a mouth 35.7 cm in diameter and a filtering cone made
of no. 59 mesh. At each the station two samples were
collected and fixed with 4% formalin. Hydroid medu
sae were counted either throughout the entire sample
or in a certain proportion of the latter (1/5 or 1/10 of
the entire sample volume). The density of hydromedu
sae for each sample was counted proceeding from their
number in the sample, taking the mouth diameter of
the planktonic net and the distance covered by the net
during the sampling into consideration. For each sur
Species Composition, Seasonal Dynamics of Quantities and Spatial
Distribution of Hydromedusae (Cnidaria: Hydrozoa) in Vostok Bay
of the Sea of Japan
E. A. Petrova
, T. N. Dautova
, and L. S. Shkoldina
Far Eastern Federal University, Vladivostok, 690950 Russia
Institute of Marine Biology, Far Eastern Branch, Russian Academy of Sciences, Vladivostok, 690041 Russia
Received September 25, 2010
—Hydromedusae (Cnidaria: Hydrozoa) are one of the most common and widely spread plankton
organisms. Due to their low quantities in the plankton and complicated species identification, they are poorly
observed in zooplankton research works, especially in the Northwestern part of the Sea of Japan. The subjects
of the present work are the seasonal dynamics of the spatial distribution and abundance of hydromedusae that
inhabit Vostok bay (Peter the Great bay of the Sea of Japan), which were observed from April to November in
2002–2004. The timing of mature specimens was studied for different species. Eighteen species were found.
(Sars, 1835) and
(Murbach et Shearer, 1903)
are the first records for Peter the Great Bay; the last two species are the first records for the Northwestern part
of the Sea of Japan.
: hydromedusa, Hydrozoa, Cnidaria, distribution, Vostok Bay, Sea of Japan, abundance, seasonal