Environmental/palaeoenvironmental studies on benthic assemblages from SE Asia: balances and perspectives after 20 years of research

The earliest research group on tropical benthic assemblages was composed in Somalia by the Milan-Catania-Padua Universities. Surveys in south eastern Asia (Vietnam, Indonesia, Thailand) followed this first experience. The first MIUR-funded national project dates back to 1989, and was aimed to export in these areas the bionomic model, well tested for the description of Mediterranean environments and paleoenvironments. Researches mostly dealt with systematics and palaeoecology/palaeoclimatology of Indonesian Coenozoic mollusk deposits from Bali, West Timor and Central Java (Sangiran Basin) and were performed with the partnership of colleagues from the Bandung University. Several surveys, which delivered a first copious inventory of Quaternary mollusk species from the Bangkok Clays, were undertaken in Thailand (Senanivate and Wat Tammakay: Bangkok Central Plain), opening the cooperation with the Dept. of Mineral Resources - Geological Survey of Bangkok (Dr P. Dheeradilok and subsequently Dr N. Chaimanee). From 1996 to 2003 a research program was exclusively focused on benthic mollusk associations and thanatocoenoses and related bottom sediments, from the Petchaburi coastal area in the Gulf of Thailand. This area was considered suitable for a pilot study of marine paleoecology applied to the Gulf of Thailand, since it undergoes increasing anthropogenic impact (domestic sewage, overfishing, mining, industrial pollution) and sediment load. The goal was to convey the Italian know-how on coastal zone management, particularly focusing, on Recent sedimentary dynamics, fish catching stress and environmental protection. The ongoing PRIN cooperative project on the impact of the December 26th 2004 tsunami along the Khao Lak coastal area (Andaman Sea, SW Thailand) was started in 2005 by the Milan, Catania and Turin Research Units, in collaboration with researchers from the Dept. of Geology, Chulalongkorn Bangkok University and the Phuket Marine Biological Center. The research program aims to detect and quantify the environmental changes caused by this catastrophic event, with emphasis on depositional and erosive processes and related impact on the benthos. Survey and sampling have been recently completed and data are presently in process: sedimentology and morphology of the soft bottoms, oceanographic data (T, S, pH, O2), geochemistry of the water-sediment interface and macro- and microbenthos analysis. Coastal and shallow bottom morphological analyses will be performed comparing the 1:20.000 bathymetric map newly acquired from upper-infralittoral bottoms, with historical data (aerial and satellite images, nautical and topographic maps). The final goal is to interpret the shoreline variation caused by the tsunami, in the framework of the present littoral dynamics, and to reconstruct the modality of the benthic re-colonization, in the scheme of a pre impact - impact - post impact sequence. Since historical faunistic data are lacking, thanaocoenoses, which testify the preexistent scenario, will be used for comparison with newly settled communities