Full text of DOI:10.1007/BF02900472

scale of 1:1000000 by the Institute of Oceanology, the Chi-
nese Academy of Sciences in 1992 and 1994 respectively.
During the investigation cruises, numbers of Calyptogena sp.
cells were dredged at two sites (ES1 and ES2 in fig. 1) in the
north of the trough. Based on the fact that Calyptogena sp. is
only observed around the hydrothermal vents and lives on
hydrothermal activities, it is predicted that there is the possi-
bility of modern hydrothermal activities in the northern part
of the trough.
Two possible hydrothermal
vents in the northern
Okinawa Trough
ZHAI Shikui1, XU Shumei1, YU Zenghui1,
QIN Yunshan2 & ZHAO Yiyang2
1. Ocean University of Qingdao, Qingdao 266003, China;
2. Institute of Oceanology, Chinese Academy of Sciences, Qingdao
266071, China
1
Calyptogena sp. shells and sample locations
Calyptogena sp. shells were collected at two sites in
the north of the Okinawa Trough (fig. 1). Site ES1 is lo-
cated at 129q04.96cE, 30q19.82cN, with 521 m water depth,
the south side of a submarine volcano on the south of Ku-
sagaki. The water depth of the volcano summit is only 118
m. Site ES2 is located at 128q06.17cE, 28q48.82cN, with
779.2 m water depth, the south side of a small crater be-
tween two relatively large submarine volcanoes. The wa-
ter depth around the crater is about 1000 m. The seafloor
around site ES1 is covered by loose and sandy sediments
(sand: 93.1%, fine sand: 6.9%), with abundant volcanic
fragments and foraminiferal shells. Sediments on site ES2
are poorly graded and sandy (sand: 65.9%; fine sand:
10.2%; clay: 23.9%), mainly composed of volcanic glass
and foraminiferal shells, with some pumice fragments.
Calyptogena sp. shells collected from site ES1 are
about 11×6 cm in size, grey, with a few tawny spots on the
surface. The growth striations are very clear on the outer
surface of shells, while the muscle scars on the inner sur-
face are not clear. This kind of Calyptogena sp. was iden-
tified as Calyptogena soyoae (or Lucinoma spectabilis)
Abstract
As the Okinawa Trough is a back-arc basin in
early spreading, modern submarine hydrothermal activity
and minerallization have many characteristics which have
aroused wide attention. Up to now, three well-known hydro-
thermal venting areas are all located in the middle part of
the trough. During two cruise investigations to map and
sample the seafloor, numbers of Calyptogena sp. shells were
dredged at two sites in the northern trough with compara-
tively thicker crust and numerous submarine volcanoes.
Based on the fact that Calyptogena sp. is only observed
around the hydrothermal vents and lives on hydrothermal
activities, it is predicted that there is the possibility of mod-
ern hydrothermal activities in the northern part of the
trough. In this note, the shell is carefully characterized and
the sample locations with possible hydrothermal activity are
given. It is pointed out that the research of biogenic fossils to
trace hydrothermal activity changes in venting time, strength
fluctuations, evolution in chemical compositions and so on
should be stressed in the future in addition to the study of the
ecological characteristics of hydrothermal organisms.
Keywords: shells of Calyptogena sp., possible hydrothermal vents,
northern Okinawa Trough.
(Plate ĉ-1, 2). Calyptogena sp. shells collected from site
ES2 are similar to those from ES1 in size and color, with
more evident tawny spots. The muscle scars on the inner
surface and the growth striations of the outer surface are
both clear. This kind of clam shells was identified as Ca-
lyptogena sp. (Plate ĉ-3, 4). Xu Fengshan, the con-
chologist and professor in the Institute of Oceanology, the
Chinese Academy of Sciences, did all of the identification
work on the clam species.
Up to now, several active hydrothermal vents and de-
posit areas have been found in the Okinawa Trough, of which
three well-known hydrothermal vents are Minami-Ensei
knoll (28q23cN, 127q38cE) with the water depth of about 770
m and maximum hydrothermal fluid temperature of 270ć[1],
Izena cauldron (JADE Site, 27q16cN, 127q05cE) with 1300ü
1600 m water depth and maximum temperature of about 320
ć[2], Iheya ridge (CLAM Site, 27q33cN, 126q58cE) with
about 1400 m water depth and the maximum of 220ć[2]. All
of these hydrothermal vents are located in the middle part of
the trough (fig. 1).
2
Ecological habits of Calyptogena sp. in the Oki-
nawa Trough
The Calyptogena sp. in the Okinawa Trough mainly
In September 1984, Japan Marine Science and Tech-
nology Center first discovered hydrothermal deposits and
vent system of chimney in middle part of the Okinawa
Trough and observed a large amount of benthons[3]. As
known to all, Calyptogena sp. and Bathymodiolus are the
dominant clam species in the hydrothermal community and
the former is specially aboundant[4—6]. Up to now, two spe-
cies of Calyptogena sp. living in the hydrothermal venting
area have been observed in the trough. Two cruise investiga-
tions were carried out to map and sample the seafloor on the
lives in the seafloor covered by sediments, which is dif-
ferent from that in Galapagos, living in the fissures of
basalt[7]. On the sandy sediment-covered seafloor where
organisms cluster densely, the Calyptogena sp. is distrib-
uted as dense as up to 10 kg/m2, of which some large ones
are as long as 15 cm. They are half buried in sediments.
From the opening of the shells, pink mantle can be seen
venting gas with a poorly matured-siphon. The thickness
of sediments in the most areas where Calyptogena sp. is
distributed densely is about 10—15 cm, while that of am-
Chinese Science Bulletin Vol. 46 No. 11 June 2001
943

NOTES
Fig. 1. Distribution of active hydrothermal vents and deposit areas in the Okinawa Trough. Ŷ, Confirmed hydrothermal vents and de-
posit areas; Ƒ, possible hydrothermal vents.
bient sediments is only 5 cm. In addition, all of the Ca-
lyptogena sp. in the trough have plenty of blood, retro-
gressive digestive tubes and mast gills, which are similar
to Calyptogena magnifica living on the base rocks in the
ture on land. Macroorganism communities thrive sur-
rounding hydrothermal vents, strongly depending on the
venting of hydrothermal fluid. Therefore, the study of the
origin, distribution, ecological characters and the relations
with hydrothermal activities of these creatures will be of
great benefit not only to the study of the regularities in the
submarine hydrothermal activity and the mechanism of
hydrothermal mineralizations but also to the research of
the origin and evolution of species on the Earth.
At present, the study of submarine hydrothermal
activities and mineralizations has been the international
multi-interdisciplinary frontier field. The study on the
hydrothermal biology, one of hot research points, mainly
includes two aspects. One is the study of origin, growth
process, ecological characters, feeding habit and reliance
on hydrothermal activities of hydrothermal organisms; the
other is the research of biogenic fossils to trace hydro-
thermal activities. Information recorded in the fossils can
be used to seek for the regularity of hydrothermal activi-
ties in venting time, strength fluctuations, evolution in
chemical compositions of the venting fluid, etc. Organ-
isms are generally sensitive to the environment. A little
change of hydrothermal activities in venting strength,
dormant period, and other physical-chemical indexes can
affect the ambient seawater. Then, the change can be pre-
cisely impressed on the texture, chemical compositions
(especially the trace element compositions) and the iso-
topic compositions of shells. Based on this fact, the
East Pacific Rise hydrothermal field[8,9]
.
3
Significance of further investigation and research
In 1977, macroorganism communities around the
hydrothermal vents were first discovered in Galapagos
Rift at water depth of 2500 m[5,10]. Till 1986, the hydro-
thermal communities had also been found in the
Mid-Atlantic Ridge and East Pacific Rise hydrothermal
fields by American famous submersible “ALVIN”[7,11]
.
The whole scientific circles, especially the life science and
environmental science realms, were shocked by all of
these discoveries because these creatures can survive in
the deep-sea environment, even on the new-formed
mid-ocean ridge crust, far away from the land and without
photosynthesis. In a word, these organisms survive de-
pending on the hydrothermal activity and play an impor-
tant role in the hydrothermal mineralization process at the
same time. Up to now, the research on modern submarine
hydrothermal biology has made great progress. It has been
found that most of hydrothermal organisms around the
vents are new species. They can survive healthily in a
comparatively high temperature environment near the
vents[7] and rely on the chemosynthesis to sustain the
ecosystem development and basic reproduction, having
nothing to do with photosynthesis necessary for the crea-
944
Chinese Science Bulletin Vol. 46 No. 11 June 2001

4. Somero, G. N., Siebenaller, J. F., Hochachka, P. W., Biochemical
and physiological adaptations of deep-sea animals, “Deep-Sea Bi-
ology”, The Sea, Vol. 8. (ed. Powe, G. Y.), New York: Wiley, 1983,
261—330.
regularities of hydrothermal activities especially in short
time scale can be systematically studied with fossils of
hydrothermal creatures.
5. Hessler, R. R., Smithey, W. M. Jr., The distribution and commu-
nity structure of megafauna at the Galapagos Rift hydrothermal
vents (eds. Rona, P. A., Bostrom, K., Laubier, L.), Hydrothermal
Process at Seafloor Spreading Centers, NATO Conference Series
IV, New York: Plenum, 1983, 735—770.
6. Laubier, L., Desbruyeres, D., Les oasis du fond des oceans, La
Recherche, 1984, 15: 1506.
7. Hessler, R. R., Smithey, W. M. Jr., Keller, C. H., Spatial and temporal
variation of giant clams, tube worms and mussels at deep-sea
hydrothermal vents, Bulletin of the Biological Society of Wash-
ington, 1985, 6: 411.
8. Suguru, O. H. T. A., Deep-sea submersible survey of the hydro-
thermal vent community on the northeastern slope of the Iheya
ridge, the Okinawa Trough, Proceedings of JAMSTEC Sympo-
sium on Deep Sea Research, No. 6, Japan Marine Science and
Technology Center, 1990, 145.
9. Dong Sung Kim, Suguru, O. H. T. A., Submersibles observations
and composition of the biological communities of the two hydro-
thermal vents on the Iheya Ridge of the Mid-Okinawa, Trough,
JAMSTECTR Deep Sea Research, 1991(7): 221.
It is well known that modern submarine hydrother-
mal activities are generally associated with submarine
volcano eruptions or magmatic activities. In the Okinawa
Trough, the magmatic activities and volcanic rocks are
mainly distributed in the middle and north part, especially
in the northern trough[12]. A lot of hydrothermal vents have
been found in the middle of the trough and a few also in
the south of the trough[2]. Modern hot springs are also
found in the Wakamiko caldera at the north end of the
trough and on the Taiwan and Iriomotejima islands at the
south end[13]. However, no report on hydrothermal vent in
the northern trough has been published, which needs to be
in detail investigated in the future.
Acknowledgements This work was supported by the National Natural
Science Foundation of China (Grant Nos. 49625609 and 49421007).
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(Received December 4, 2000)
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