Relationships between stock of clam Cyclina sinesis and environmental factors in the estuary of Cigu River in southwestern Taiwan
Date Issued
2009
Date
2009
Author(s)
Lin, Ching-Cheng
Abstract
The study mangrove area, which was located in the estuary of Cigu River in southwestern Taiwan has abundant biological resources. The clam Cyclina sinesis was one of the most common economical bivalve in the estuary. The data sampling was carried out from July, 2008 to June, 2008. The transect sampling was used to collect the clam stock and environmental factors. Clam’s morphology such as shell length, height, width, weight, age and density were investigated in the survey. The environmental factors, such as pH, salinity, temperature, dissolved oxygen, water content, organic matter, grain size and the proportion of mud/sand were also investigated. The results indicated that the clam was mainly concentrated in the Cigu River sector, which consisted of clam less than 3 cm shell length and 2 years old. The clam mainly distributed in the low and mid tidal zone. The aerial root zone of mangrove in high tidal zone became a boundary of the clam distribution. The density of the clam increased in March because of recruitment of juveniles which shell length less than 2 cm and age about 1 year old, and decreased in June because of fishing. The Cigu estuary could be divided into three sectors, such as Cigu River sector, small water channel sector, Sangu River which was composed of different water and sediment factors. PCA also indicated that the main variation of Cigu estuary and Cigu River sector were from sediment factors. In conclusion, Cigu River sector of Cigu estuary became the only habitat of the clam Cyclina sinesis because it possessed the environmental factors they preferred, especially in the fine sand sedimental environment with less mud, which could provide juvenile clam’s successful settlement and better growth and survival rate for adult clam. According to the clam’s morphological composition and density variation, the clam Cyclina sinesis in Cigu estuary had faced heavy fishing pressure.
Subjects
clam Cyclina sinesis
environmental factors
Cigu River
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