1063-0740/04/3004- © 2004
Russian Journal of Marine Biology, Vol. 30, No. 4, 2004, pp. 223–230.
Original Russian Text Copyright © 2004 by Biologiya Morya, Nadtochy.
The southern Kurils area is a part of the Paciﬁc sub-
region of the Arctic-boreal region , and its inhabitants
exhibit a pronounced seasonal succession connected
with regular change in the dominant groups of plankton
and variations in their abundance and character of func-
tioning [5, 13, 21]. The seasonal processes are also man-
ifested in summer–fall mass migrations into these waters
of certain ﬁshes (saury, sardine, scomber, and anchovy)
and squids, whose behavior and distribution of shoals are
related to the composition, biomass, and development
terms and dynamics of plankton.
The investigated area is situated on the northwest-
ern periphery of the Subarctic front and is character-
ized by high dynamic activity of the water. The hydro-
logical regime is affected by a system of currents
(Fig. 1). The major currents are the Oyashio, Kuro-
shio, and Soya [3, 29, 32].
The authors of early publications concerned with
plankton of the southern Kurils region (SKR) [14, 21,
23] recognized two types of water thermal structures
(subarctic and subtropical) and analyzed the seasonal
dynamics of plankton according to this discrete repre-
sentation. Comprehensive investigations in the south-
ern Kurils region begun by the Paciﬁc Institute of Fish-
eries and Oceanography (TINRO) in 1979–1980 pro-
vided the basis for a number of publications on the
distribution, seasonal development, and dynamics of
the trophic structure of plankton [1, 6–8, 17, 18, 24].
The results from these studies suggest that the consis-
tent local distribution patterns of plankton off the south-
ern Kuril Islands are primarily due to the thermal struc-
ture of the water, which determines the composition of
planktonic communities and their seasonal develop-
ment rates. The present work is a continuation of these
studies. Based on a detailed classiﬁcation of biotopes,
the seasonal dynamics of plankton is examined within
natural environmental areas, each being characterized
by a speciﬁc thermal structure of the water and more-
or-less uniform oceanological conditions.
MATERIALS AND METHODS
Material was sampled from November 1979
through October 1980 on a uniﬁed grid of stations
called the “Polygon,” which covers the area from Hok-
kaido Island to Urup Island and extends from the Kuril
arc into the ocean over 120–150 miles. The distance
between stations was 15–20 miles and that between
transects, 20–22 miles. Plankton samples were col-
lected every ten days during summer (Fig. 2) and every
month during winter but over a looser grid of stations.
Plankton was sampled using a Juday net (mouth
diameter 37 cm, capron sieve no. 49) in 100–0 m depths
and in shallow water bottom–0 m. At each station, the
water temperature was measured with a bathithermo-
graph on standard horizons. Thus, the following zones
with a characteristic thermal structure of the water were
singled out: the Kuril, Oyashio, subarctic, Soya, and
transformed subtropical zones . The borders of
these zones were thermal fronts. The position of zones
within the investigated region was preserved through-
out the summer–fall period; however, their size and out-
lines of borders changed as the seasonal development
of plankton proceeded (Fig. 1).
Seasonal Dynamics of Plankton in Zones with Different Thermal
Structures of Water off the Southern Kuril Islands
V. V. Nadtochy
Paciﬁc Fisheries Research Center, Vladivostok, 690950 Russia
Received December 9, 2003
—Based on plankton samples collected from 100–0 m depths in the years 1979–1980, the duration of
biological seasons was determined and the seasonal succession of plankton was followed in ﬁve surface water
modiﬁcation zones: Kuril, Subarctic, Subtropical transformed, Oyashio (cold), and Soya (warm). The “bloom”
of phytoplankton off the southern Kuril Islands begins in the months March–May and continues until June in
waters of warm currents and until September in cold waters. Succession rates vary among the zones. In cold-
water zones, the change in the plankton community from the spring to the summer state occurs about half a
month later than in warm waters. The reason for this lag is the slower sea surface heating and the later stratiﬁ-
cation in cold-water zones.
southern Kurils region, vertical structure of water, succession, biological season, phytoplankton
“bloom,” zooplankton species composition, dominant species, biomass, abundance.