Surveying of biodiversity of coral, mollusk, crustacean, marine fish and bird at Nom Sao Island, Chanthaburi Province was conducted on February, May, September, November 2017 and February 2017. Sampling design was devided to four ecosystems; sand beach, rocky shore, coral reef and bareground. Specimens were collected by using drift net, free hand, scuba diving and collapsible crab trap. The result found that diversity of the coral was belonged to 11 family 18 genera and 23 species. Porites lutea, Favia sp. and Platygyra daedalea were the most dominant species in the coral reef ecosystem. Diversity of mollusk was belonged to 29 Family, 39 genera and 47 species. Gastropod was 32 species and bivalve was 15 species. Family Muricidae was the most dominant (4 genera and 4 species). Moreover, rocky shore had the highest diversity of mollusk (20 species). Shannon–Wiener index, evenness index and species richness were 1.5931, 0.5838 and 2.1284, respectively. Abundance of mollusk was most found in rocky shore (397 individual) and was found in dry season (58%) higher than wet season (42%). Species diversity of crustacea was belonged to 19 family, 28 genera and 37species. Anomuran was 7species where as brachyuran was 37 species. Family Portunide had the highest diversity (6species). Rocky shore ecosystem was found highest diversity of crustacea (30 species). Species diversity index, evenness index and species richness were 2.1150, 0.6347 and 3.9608, respectively. Abundance of crustacea was found the highest in rocky shore ecosystem in dry season (63%) higher than wet season (37%). Species diversity of marine fish was belonged to 10 family 12 genera and 13 species. Family Serranidae was the most dominant (2 species). The highest diversity of marine fish was found in coral reef ecosystem (7species). Diversity index, evenness index and species richness were 1.8065, 0.7846 and 2.2358, respectively. Abundance of marine fish was most found in coral reef ecosystem and was found in dry season (77%) higher than wet season (23%). The result also found that a total of 96 birds were recorded and identified to 17 species. Thirteen species were considered as resident to Thailand such as Spotted Dove (Spilopelia chinensis), Mangrove Whistler (Pachycephala cinereal), Stork-billed Kingfisher (Pelargopsis capensis), Asian Koel (Eudynamys scolopaceus), Oriental Magpie Robin (Copsychus saularis), Brown-throated Sunbird (Anthreptes malacensis), Olive-backed Sunbird (Cinnyris jugularis), Streak-eared Bulbul (Pycnonotus blanfordi), Yellow-vented Bulbul (Pycnonotus goiavier), Pacific Reef Egret (Egretta sacra), Heart-spotted Woodpecker (Hemicircus canente), Malaysian Pied Fantail (Rhipidura javanica) and Eastern Jungle Crow (Corvus levaillantii), and 4 as winter visitor namely Yellow-browed Leaf Warbler (Phylloscopus inornatus), Taiga Flycatcher (Ficedula albicilla), Asian Brown Flycatcher (Muscicapa dauurica) and Whiskered Tern (Chlidonias hybrida). The first trail, coastal ecosystem, 47 birds of 15 species were recorded. The second trail, forest ecosystem, 49 birds were found belonging 14 species. The Shannon-Wiener diversity index (H’) of the island was 2.4500, and the Pielou’s evenness index (J’) was 0.8600. The species diversity index and evenness index of the first trail were higher than the second trail (H’= 2.4200 and 2.2100, and J’= 0.8900 and 0.8400, respectively). There were 12 species of birds found in both trails. Sorensen index showed high similarity (83%). The most relative abundance species was Streak-eared Bulbul (Pycnonotus blanfordi) with 13.51%, followed by Malaysian Pied Fantail (Rhipidura javanica) and Eastern Jungle Crow (Corvus levaillantii) with 10.81%.
