180Vol 36 (suppl 4) 2005
BRACKISH-WATER MOLLUSKS OF SURAT THANI PROVINCE,
Pusadee Sri-aroon1, Chantima Lohachit1 and Masakazu Harada2
1Department of Social and Environmental Medicine, Faculty of Tropical Medicine,
Mahidol University, Bangkok, Thailand; 2Department of International Medical Zoology, Kagawa Medical
University, Kagawa, Japan
Abstract. Brackish-water mollusks inhabiting the mangrove areas along the Gulf of Thailand of Surat Thani
Province were investigated for distribution, abundance and natural infections. Nine families and 32 species of
brackish-water snails were recovered from 14 sampling stations. Species belonging to the genus Ceritidea of the
family Potamididae were mainly examined and Cerithidea (Cerithideopsilla) Cingulata, C. (C.) djadjariensis,
and C. (Cerithidea) charbonnieri were naturally infected with 2 types of trematode cercariae, and one which was
undetermined. C. (C.) cingulata had the highest infection rate (38.5%). Viewing two snail communities, the
first community on the mainland and the second on Samui Island in Surat Thani Province, 28 brackish-water
mollusk species were present on the mainland, 15 species were evident on Samui Island, and 11 snail species
were common to both the mainland and Samui Island. Measurement of community similarity based on species
presence revealed an index of similarity of 0.51. Concerning land use by the local people in the station areas
investigated, brackish-water snails in Surat Thani Province are facing habitat degradation by human use.
inhabiting mangrove areas along the Gulf of Thailand
may be dispersed or extinct because of land development.
MATERIALS AND METHODS
The 14 sampling stations in Surat Thani Province
were located along the Gulf of Thailand (Fig 1). Eight
stations (Nos.1, 2,3,10,11,12,13, and 14) were on the
mainland, while the remaining 6 stations (Nos. 4, 5, 6,
7, 8, and 9) were on Samui Island. The variety of
environments of stations is presented in Table 1.
Sampling was conducted from 2 to 4 February 2004.
This study was in accord with the study of brackish-
water mollusks in the south of Thailand.
The brackish-water snails were collected by a one
hour search of a station area of 100 m2 for snails that
characteristically occur in low densities in the
environment (Lohachit, 2001). Each of 6 experienced
persons searched for snails in each station. All likely
habitats, including between Nipa palm leaves, were
examined for snails. Environmental observation of
the station area, such as snail habitats and human use,
were also recorded. All of the snails collected were
packed in an ice box for transportation to Bangkok, as
described by Sri-aroon et al (2003), in order to examine
them for trematode infection and to identify species.
Snails were identified with the aid of the Identi-
fication Key for Fresh-and Brackish-Water Snails of
Thailand (Upatham et al, 1983), The Non-Marine
Aquatic Mollusca of Thailand (Brandt, 1974),
Systematic Studies on the Non-Marine Mollusca of
the Indo-Australian Archipelago (Van Benthum Jutting,
Correspondence: Pusadee Sri-aroon, Department of
Social and Environmental Medicine, Faculty of
Tropical Medicine, Mahidol University, 420/6 Rajvithi
Road, Bangkok 10400, Thailand.
Tel: 66 (0) 2354-9100-19 ext 1563, 2106
Surat Thani is the largest of the southern provinces
of Thailand, and is popular for both Thai and foreign
tourists for its beautiful islands, beaches, and submarine
fauna and flora. This includes Samui Island, a large
island in the Gulf of Thailand, which is 84 km east of
Surat Thani Province. Land development can be found
at many areas around the island.
Brandt (1974) reported that 43 common species
of brackish-water mollusks inhabit Thailand. Another
11 snail species can be found in Surat Thani Province,
of which 2 species of Cerithidea (Cerithidea)
charbonnieri and Morrisonietta bandonensis, are
present only in Surat Thani Province.
The major intent of this study was to investigate the
distribution of species of brackish-water mollusks
(hereafter referred to as snails) in Surat Thani Province,
southern Thailand. The secondary purpose was to
determine the common trematode infections in snails and
the abundance of snail species in the localities. Surat
Thani Province was chosen because land development is
continuously expanding for residences, agriculture,
fisheries, water resource development, recreation, and
tourism. Hence, some of the brackish-water snails
Vol 36 (suppl 4) 2005181
1965), and with a collection of species of snails at the
Museum of Mollusks, Faculty of Tropical Medicine,
The trematode infection was examined by crushing
the snails. Trematode cercariae obtained were
measured and their morphology was recorded for
idetification. Analysis of the relative abundance of
each identified species was performed based on the
total number of snails collected (Coney et al, 1982).
In order to demonstrate the geographical distribution
relationship to various species, analysis of the nature
of the community were performed on the mainland
and on Samui Island, using the index of similarity
described by Sorensen (1948). In two communities,
one with [a] number of species on the mainland of
Surat Thani Province and another with [b] number of
species on Samui Island, and [c] species occurring in
both communities, we defined: Index of similarity =
2c / a + b. This index ranges from 0 to 1.0, to quantify
the range from no similarity to complete similarity.
Nine families and 32 species of brackish-water
snails were recovered from Surat Thani Province. The
number of snails collected by each station is given for
each species in Table 2. Also shown in this table is the
number of species (S), number of individuals (N), and
most abundant species (Nmax) of each identified
brackish-water snail in the station. Moreover, some
descriptions of snail habitats are described in detail
(Table 1). Table 3 demonstrates the relative abundance
of each brackish-water snail species as percent
composition, based upon the total number of snails
collected (9,718). In addition, the total number of
stations is given for each species and is referred to as
Of Cerithidea species examined, three species,
Cerithidea (Cerithideopsilla) cingulata, C. (C.)
djadjariensis, and C. (Ceritidea) charbonnieri, were
naturally infected with trematode cercariae (Table 4)
were found from them although another one type was
undetermined. The first type of cercariae had the
cystogenous gland cells but neither eyespot nor collar
spines. The second type had two eyespots, 4 and 3
penetration gland cells forming two rows, and a tail
with a fin. The number of snails infected with each
type of trematode varied markedly among species and
localities (Table 4).
Viewing two snail communities, the first
BRACKISH-WATER MOLLUSKS IN SOUTHERN THAILAND
Fig 1- Location of 14 investigated stations along the Gulf of Thailand, Surat Thani Province, southern Thailand.
SOUTHEAST ASIAN J TROP MED PUBLIC HEALTH
188 Vol 36 (suppl 4) 2005
Pongponratn for their valuable encouragement. This
study was supported by the Faculty of Tropical
Medicine, Mahidol University, Bangkok, Thailand, and
partly supported by a Grant-in-Aid for Scientific
Research (No. 15510192) from the Ministry of
Education, Culture, Sports, Science and Technology,
Brandt RAM. The non-marine aquatic Mollusc of
Thailand. Arch Molluskenkund 1974;105:1-423.
Coney CC, Tarpley WA, Warden JC, Nagal JW.
Ecological studies of land snails in the Hiwassee
River basin of Tennessee, USA. Malacol Rev
Lohachit C. Ecological studies of Bithynia siamensis
goniomphalos, a small Intermediate host of
Opisthorchis viverri, in Khon Kaen Province,
Northeast Thailand. Bangkok: Mahidol University,
Thailand 2001. PhD Thesis.
Sri-aroon P, Lohachit C, Masakazu Harada. Survey
of brackish-water snails in eastern Thailand.
Proceedings of the 4th Seminar on Food and Water-
Borne Parasitic Zoonoses and 2nd International
Meeting on Gnathostomiasis. Southeast Asian J
Trop Med Public Health 2004;35 (suppl 1):150-5.
Sorensen T. A method of establishing groups of equal
amplitude in plant sociology based on similararity
of species content and its application to analyses
of the vegetation on Danish commouns. D Kgl
Danske Vidensk Selskab Biol Skrifter 1948;4:1-34.
Upatham ES, Sornmani S. Kittikoon V, Lohachit C,
Burch JB. Identification key for fresh-brackish-
water snails of Thailand. Malacol Rev 1983;16:
Van Benthum Jutting WS. Systematic studies on the
non-marine Mollusca of the Indo-Australian