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International Journal of Marine Science 2013, Vol.3, No.4, 23-32
http://ijms.sophiapublisher.com
30
At 2.5 m depth, a reef crest (breakwater) exists. This
is a coralogenic-algal ridge 3~4 m wide, with
individual colonies of scleractinian and alcyonarian
and single bush of macrophytes. At a depth of 2 m, the
reef crest gives way to a reef flat. A reefogenous
plateau stretches for up to 1.5 km and is cut with
longitudinal sand channels running from southwest to
northeast. Throughout the reef flat zone, diverse
scleractinian-alcyonarian or alcyonarian-scleractinian
assemblages observed. In the former assemblages,
Acropora cytherea
,
A. hyacinthus
,
A. florida
,
A.
robusta
, and
Montipora verrucosa
predominated in
terms of substrate cover and frequency of occurrence;
Alcyonaria, Lobophytum
and
Sarcophyton
dominated
in the latter. Everywhere on the reef flat, large
colonies occurred as patches of a single species such
as
Acropora valenciennesi
,
A. cytherea
,
A. florida
,
A.
spicifera
,
A. millepora
,
A. humilis
,
M. aequituberculata
,
M. danae
,
M. undata
,
P. lobata
,
Cyphastrea
microphthalma
,
Lobophytum sarcophyloides
,
Sarcophyton
glaucum
and
Sinularia flexibilis
.
At these sites,
scleractinian and alcyonarian covered the substrate
completely. Of the accompanying macrobenthos, the
sea urchins
E. molaris
,
D. setosum
and
E. diadema
,
starfishes
L. laevigata
,
A. planci
and
C. novaeguineae
,
and the holothurian
H. atra
found most frequently.
The sand paving the bottom of channels and refuges
under the corals was inhabited by fairly numerous
(0.5~2.0 ind./m
2
) gastropods
Terebra
sp.,
T. maculatus
,
Turbo argyrostoma
,
Drupa ricinus
and
Vasum
turbinellum
, as well as the bivalves
P. margaritifera
and
Cardita variegata.
On the northwestern side of the
reef crest, at a depth of 4~16 m, is an outer reef slope
with a system of spurs and grooves. It extends for
250~750 m and characterized by a high species
richness of the coral community.
Acropora
and
Montipora
formed an upper reef slope community
with the predominance of
A. cytherea
,
A. formosa
,
A.
grandis
,
A. millepora
,
A. spicifera
,
M. hispida
,
M.
aequituberculata
,
M. vietnamensis
,
P. verrucosa
and
S.
hystrix.
As a rule, these were large colonies of corals
that entirely covered the substrate over tens of square
meters (Figure 9). The highest species diversity of
scleractinian (more than 160 species) was observed in
the spurs and grooves zone. In addition to acroporids
and pocilloporids, numerous faviids, euphyllids,
poritids, mussids, and dendrophylliids (5~7 species of
each family) were widespread here, as well as
individual colonies of alcyonarian and single bushes
of algae.
The accompanying fauna on the northwestern part of
the reef was comprised of the same set of species as in
the corresponding zones on the northeastern reef side.
However, a greater number of mollusks, holothurians,
sea urchins, and other organisms found here.
With regard to its geomorphological profiles, coral
species diversity and zonal distribution, the reef of
Jiang Bo, Re Island and Bach Long Vi Island are
comparable to the ribbon reefs of the Great Barrier
Reef in Australia (Veron and Hodgson, 1989) and to
the barrier reefs of the Philippines (Pichon, 1977) and
Indian Ocean (Picard, 1967; Pichon, 1974; Bouchon,
1981). Based on its geomorphological characteristic,
the presence of a large elongate and wide reef flat with
distinctive flora and fauna, as well as a small lagoon,
the investigated reef can be classified accordingly as
the barrier reefs and the platform reef type.
Figure 9 Colonies of corals covered the substrate over tens of
square meters on the reef Bath Long Vi (depth 8 m)
The Bach Long Vi reef exhibits a pronounced axial
zoning. Its central part (reef flat) characterized by a
homogenous coral community distinctly dominated by
branching and plate-like
Acropora
and
Montipora
,
which form extensive fields. The periphery of the reef
plateau consists of an extensive zone of accumulation