158
E. Flach and A. Tamaki
presence of epibenthic predators also lowered the survival rate of Corophium
(Flach and De Bruin 1994).
7.5 Ghost Shrimps in the Ariake Sound Estuarine
System in Japan
The study area is an estuarine system located in the middle part of western
Kyushu, Japan (around 130 0 E and 32SN), spanning from Ariake Sound
(l700km 2 estuary) through Tachibana Bay (700km 2 ) to the coastal waters of
the East China Sea (open sea) (Fig. 7.5). There are two major water masses in
Tachibana Bay, the northern lower-salinity one and the southern highersalinity one, which are originally derived from the Ariake Sound waters and
the East China Sea waters, respectively, with their time-averaged current
directions being opposite (westward and eastward) (Matsuno et ai. 1999). For
20 years, since 1979, Tamaki and colleagues have studied macrobenthic community dynamics on the intertidal sand flat in Tomioka Bay on the northwestern corner of Amakusa-Shimoshima Island; Tomioka Bay is a small part
of Tachibana Bay, situated in the southwestern portion of the estuarine
system. As the sand flat faces Ariake Sound, it is washed by much weaker
waves than the exposed sandy beaches facing the East China Sea.
Until recently, it was believed that two species of Callianassa commonly
occurred in Japan: C. japonica Ortmann, inhabiting bare intertidal sand flats,
and C. petalura Stimpson, inhabiting boulder beaches (see Sakai 1969). However, in their taxonomic revision of the Japanese species, Manning and
Tamaki (l998) revealed that Sakai's 'c. japonica' was in fact a mixture of C.
japonica and C. harmandi Bouvier. They also proposed a new genus, Nihonotrypaea, to include the three Japanese species. All the material studied by
Tamaki and colleagues, so far described as C. japonica, has now proven to be
N. harmandi, exclusively occurring on the Tomioka Bay sand flat; the distributions of N. harmandi and N. japonica are well separated around the
boundary between the outer one-third and the inner two-thirds of Ariake
Sound (Tamaki et ai. 1999; Fig. 7.5). Of the local populations of N. harmandi,
that on the Tomioka Bay sand flat is the largest in terms of both the density
and the area occupied (Tamaki et aI.1997, 1999; Tamaki et aI., in preparation).
The study site for the benthic community is situated in a moderately
sheltered section of the Tomioka Bay sand flat (the black-coloured area in the
inset in Fig. 7.5, about 300m wide along shore and exposed for 310-32Sm
from the shoreline). The surface sediment consisted of well to moderately
sorted, fine sand with 0.4 %-2.6 % silt-clay content. The first survey conducted in July 1979 revealed that the macrobenthic community in the study site
E. Flach and A. Tamaki
presence of epibenthic predators also lowered the survival rate of Corophium
(Flach and De Bruin 1994).
7.5 Ghost Shrimps in the Ariake Sound Estuarine
System in Japan
The study area is an estuarine system located in the middle part of western
Kyushu, Japan (around 130 0 E and 32SN), spanning from Ariake Sound
(l700km 2 estuary) through Tachibana Bay (700km 2 ) to the coastal waters of
the East China Sea (open sea) (Fig. 7.5). There are two major water masses in
Tachibana Bay, the northern lower-salinity one and the southern highersalinity one, which are originally derived from the Ariake Sound waters and
the East China Sea waters, respectively, with their time-averaged current
directions being opposite (westward and eastward) (Matsuno et ai. 1999). For
20 years, since 1979, Tamaki and colleagues have studied macrobenthic community dynamics on the intertidal sand flat in Tomioka Bay on the northwestern corner of Amakusa-Shimoshima Island; Tomioka Bay is a small part
of Tachibana Bay, situated in the southwestern portion of the estuarine
system. As the sand flat faces Ariake Sound, it is washed by much weaker
waves than the exposed sandy beaches facing the East China Sea.
Until recently, it was believed that two species of Callianassa commonly
occurred in Japan: C. japonica Ortmann, inhabiting bare intertidal sand flats,
and C. petalura Stimpson, inhabiting boulder beaches (see Sakai 1969). However, in their taxonomic revision of the Japanese species, Manning and
Tamaki (l998) revealed that Sakai's 'c. japonica' was in fact a mixture of C.
japonica and C. harmandi Bouvier. They also proposed a new genus, Nihonotrypaea, to include the three Japanese species. All the material studied by
Tamaki and colleagues, so far described as C. japonica, has now proven to be
N. harmandi, exclusively occurring on the Tomioka Bay sand flat; the distributions of N. harmandi and N. japonica are well separated around the
boundary between the outer one-third and the inner two-thirds of Ariake
Sound (Tamaki et ai. 1999; Fig. 7.5). Of the local populations of N. harmandi,
that on the Tomioka Bay sand flat is the largest in terms of both the density
and the area occupied (Tamaki et aI.1997, 1999; Tamaki et aI., in preparation).
The study site for the benthic community is situated in a moderately
sheltered section of the Tomioka Bay sand flat (the black-coloured area in the
inset in Fig. 7.5, about 300m wide along shore and exposed for 310-32Sm
from the shoreline). The surface sediment consisted of well to moderately
sorted, fine sand with 0.4 %-2.6 % silt-clay content. The first survey conducted in July 1979 revealed that the macrobenthic community in the study site