ความหลากชนิดและความหนาแน่นของหอยทะเลบริเวณอ่าวบุญคง อำเภอสิเกา จังหวัดตรัง

Abstract

Species diversity and density of marine molluscs at Boonkong Bay, Sikao district, Trang Province was studied. The samples were collected bimonthly during February to December 2017, at three different areas near mangrove, seagrass bed and non- seagrass bed, using sampling technique on quadrats of 3 x 3 m. (10 points, 9 replicated per point). The results of water quality showed that salinity was value between 27.4 and 33.3, dissolved oxygen was value between 4.3 and 6.6 mg/l, pH was value between 7.7 and 8.4, temperature was value between 28.1 and 29.3°C, turbidity was value between 3.3 and 30.5 NTU and depth was value between 1.6 and 1.8 m. The percentage similarity of water quality in each month of sub area was rather high (93.0%). The area of nearby mangrove forest, sandy loam seafloor, was found the highest percentage of organic content at 5.1 ± 2.4%. However, seagrass and non- seagrass areas were different from near mangrove forest area which are loamy sand. The results of the percentage similarity of soil quality in each month of sub areas were 88.7%. From survey, three species of seagrass were recorded. Halophila ovalis was dominant and had the highest percent coverage (63.3 ± 6.1%), followed by Thalassia hemprichii (35.8 ± 3.8%) and Cymodocea rotundata (7.5 ± 2.7%). Fifteen families of marine mollusk were recorded including 9 families (14 species) of gastropods and 6 families (11 species) of bivalves. The near mangrove area was the highest density of molluscs, the seagrass bed area and outside seagrass bed, respectively. The cluster analysis of marine mollusk in each sub area (42.0%) was lower than in each month (72.0%). The diversity index (H), the richness index (D) and the evenness index (J) were the highest value in the seagrass areas and non-seagrass area (1.8, 2.9, 0.7 and 1.8, 2.7,0.7 respectively), followed by nearby mangrove area (0.8, 1.3 and 0.4 respectively). Canonical correspondence analysis showed that the Cum. Percentage is 80.263 and Eigenvalues of the axis 1 is equal to 0.418. Moreover, the distribution of marine molluscs was related to the amount of clay. This study can be concluded that the species, density of marine molluscs and the percent coverage of seagrass slightly decreased during monsoon season. The soil quality and water quality were rather high similarity level because all study areas were located in close and continuous areas. As the result can assume that the amount of clay was the most environmental factor associated with species and density of marine molluscs. Therefore, the information of species and density of marine molluscs in this study can be applied for preliminary assessment of the economy, such as the specie was important for economy, the suitable distribution of marine molluscs species in this area and basic information for research in the future study.