Russian Journal of Marine Biology, Vol. 31, Suppl. 1, 2005, pp. S41–S48.
Original Russian Text Copyright © 2005 by Biologiya Morya, Latypov, Dautova.
1063-0740/05/3101-S © 2005 Pleiades Publishing, Inc.
The Gulf of Tonkin is located in northeastern Viet-
nam, close to the northern border of the Tropical Zone.
Water temperature in this area in winter can fall to
C; salinity in rainy seasons decreases to
31‰ [29, 31]. Fluvial waters cause desalination in
the western and northwestern parts of the bay and form
a steady drainage current with a salinity of 21–22‰,
directed southward along the western coast [2, 29]. A
signiﬁcant role is played by the considerable water run-
off from the mainland brought by numerous rivers that
enter the Gulf of Tonkin. For example, the Red River
alone brings every year 137 billion m
of fresh water
and 116 million tons of suspended matter . Every
day more than 180 g of argillaceous materials yields
onto 1 m
of the bottom. During typhoons these indices
increase signiﬁcantly [3, 6, 20, 26]. During periods of
wide-range tidal ﬂuctuations of sea level (up to 3.5–3.7 m
between the low and high tides), entire coral communi-
ties can be extinguished in large areas of drained reefs
due to heavy rainfall. The shallowness of the Gulf of
Tonkin and its peculiar bottom relief are of particular
signiﬁcance. In the northern part of the gulf, extensive
areas are occupied by shallows limited from the south
by a 50-m isobath. A wide band with depths shallower
than 50 m runs along the western coast of the gulf. The
bottom of the gulf is mostly smooth and covered with
soft grounds dominated by silts, silted sands with an
admixture of broken mollusk shells, and organogenic
materials. Silts and silted substrates ﬁll up the central
trench of the gulf, which is limited to 50- to 60-m iso-
baths. The lack of hard substrates provides additional
limitations for the development of reef structures.
Water temperature and salinity, the intensity of sedi-
mentation, and wave and tidal currents are major fac-
tors that determine the structure and composition of coral
communities in shallow waters [4, 15–17, 23, 24, 28]. In
different years, on certain reefs, the correlations were stud-
ied between the distribution of reef-building corals and
certain abiotic environmental factors [4, 5, 7, 26]. This
paper provides the results of studies on the structure
and composition of reef-building coral communities in
different reefs in the Gulf of Tonkin and describes pecu-
liarities of the sedimentation regime in the areas of
MATERIALS AND METHODS
The studies were performed in the northern part of
the Gulf of Tonkin during August–September 1997.
The distribution of scleractinians was studied with a
method of transects and frames  using SCUBA. In
each transect we estimated the degree of substrate cov-
erage by corals (and registered percentage ratios of dif-
ferent species), the quantity of colonies of different
shape, and their relative percentage proportions.
Altogether, 16 reefs were studied (Fig. 1). Relative
to their location against the coastline and geomorpho-
logical characteristics, we distinguished reefs of open
and closed bays, reefs located around capes, and reefs
located in straits. We analyzed species composition and
processes of sedimentation and water exchange in the
near-bottom water layer for each type of reef and one
coral bank. To study the transport of precipitating suspen-
sion and water exchange processes in the near-bottom
water layer, we used a method of sedimentation traps and
plaster balls [1, 27] modiﬁed by Moshchenko [8, 9].
Species Composition of Corals in Silty Shallows
of the Bai Thu Long Archipelago
(Gulf of Tonkin, South China Sea)
Yu. Ya. Latypov and T. N. Dautova
Institute of Marine Biology, Far Eastern Division, Russian Academy of Sciences, Vladivostok, 690041 Russia
Received September 27, 2004
—Coral communities were investigated on 16 reefs in open and closed bays, in straits, and around
capes of different islands of the Bai Thu Long Archipelago (Gulf of Tonkin, South China Sea). Variations
observed in the communities of
Goniopora columna, Goniopora stokesi
are caused by different
ecological conditions and may be linked with sedimentation ﬂux within the water column and near the bottom,
as well as with the rate of integral water exchange and resuspension above the coral settlements.
reefs, coral communities, sedimentation ﬂux, Gulf of Tonkin.