Abstract

In this study, the diversity index and relationships of water bugs (Hemiptera) and water beetles (Coleoptera) in ecosystem of agroforestry-aquaculture in the buffer zone in U Minh Thuong and Phu Quoc National Parks (EAAB), ecosystem of melaleuca swamp forest on peat layer at U Minh Thượng National Park (EMSF), and ecosystem of acid-sulphate water forest at Phu Quoc National Park (EAWF) were studied and evaluated. From 12 sampling sites of three ecosystems in U Minh Thuong and Phu Quoc National Parks were collected 577 individuals of the water bugs and water beetles representing 40 species of 27 genera of 11 families. 
The number of species in the family Nepidae, Naucoridae, Gerridae (Hemiptera), Dytiscidae, Hydrophilidae (Coleoptera) were highest in ecosystem of agroforestry-aquaculture in the buffer zone in U Minh Thuong and Phu Quoc National Parks. The diversity index (Dominance_D, Simpson_1-D, Shannon_H, Evenness_e^H/S, Brillouin, Menhinick, Margalef, Equitability_J, Fisher_alpha, Berger-Parker, Chao-1) and species richness have value in EAAB > EMSF > EAWF. EAAB showed the highest alpha diversity, EMSF moderate, and EAWF the lowest. Community similarity was highest between EAAB and EMSF, and much lower between EAAB–EAWF and EMSF–EAWF. Evenness analysis separated EAAB into its own cluster, while EMSF and EAWF grouped together. Synchrony between water bugs and water beetles was strongest in the more stable EAAB–EMSF ecosystems and weakest in the environmentally stressed EAAB–EAWF and EMSF–EAWF pairs.