Seagrass communities at Koh Samui, Surat Thani Province

Seagrass communities at Koh Samui, Surat Thani Province was investigated by the techniques used in the ASEAN-Australia : Coastal Living Resources Project, From April 1986 – January 1989. Five species of seagrasses were found among the four study sites. At Yai Point, on the west coast of Koh Samui, 3 species of seagrasses, Halodule uninervis (widesand substrates at the depth of 4 – 7 meters. H. uninervis (wide and narrow varieties). H. ovalis and H. ovate occurred at Chon Khram Point with H. uninervis (wide – leaved form) as the dominant seagrass growing on medium to coarse sand at 2.5 – 3.2 meters depth. The Halophilid seagrass, H. ovalis, H. decipiens and H. ovate were found at Hin Com Point, growing on medium sand at 4.2 – 4.5 meters depth. Enhalus acoroides, the large seagrass species, dominated the seagrass bed at Chaweng Beach locating on the east coast of Koh Samui. The seagrass biomass estimated was in the range of 0.004 – 1111.53 g dry wt/m2. Different plant structures such as shoot, root and rhizome play the major roles in the seagrass biomass of each species. Seasonal variations in seagrass biomass were observed. The major environmental factors determining the seagrass distribution in this area were substrate types, water depth in relation to turbidity and competition among seagrass species. It can be concluded from this study that the seagrass beds at Koh Samui play several important ecological roles in the marine ecosystem as food sources, habitat and shelter and nursery ground for numerous associated faunas. Copepod, mysidacea, ostracod, tanaidacea and brachyuran zoea were the dominant groups in the zooplankton community in the seagrass beds. Amphipods, polychaetes and mollusks were the three major groups of benthic fauna associated in the seagrass beds. The benthic fauna were most diverse in the E. acoroides bed at Chaweng Beach. Nekton in the seagrass beds can be divided into two groups : permanent resident; such as, caridean shrimps and small fishes, Favonigobius sp., Palates quadrilineatus and Arceochthys hajam, and seasonal resident; such as, brachyuran zoea and economically important fishes, Siganus spp., Epinephelus tauvina, Psammoperca waigiensis and Gerres sp.