Abunda nce of C. serrulat a at South Bar Ensuring seagrass ecosystem values are incorporated with coastal area planning in Sri Lanka LK5 Seagrasses serve as a source of energy for complex food webs; provide habitats for aquatic organisms as well as important threatened organisms, such as dugongs. Although data are available on the seagrasses in the western and North western coastal coastal water bodies in Sri Lanka, there is a scarcity in availability of data in the intertidal areas of northern part as well as sub tidal areas of the country. Most of the shallow coastal habitats are located in the Gulf of Mannar, Palk Bay and Palk Strait in the northern coastal line where high dugong incidence are recorded. The project was carried out with the aim of influence decision making and coastal planning in Sri Lanka with the increased knowledge on the seagrass habitats in Palk Bay, Gulf of Mannar with a prime objective of conservation of dugongs. The National Aquatic Resources Research and Development Agency(NARA) is the apex body vested with the responsibility of carrying out and coordinating research, development and management activities on the subject of aquatic resources in Sri Lanka. The NARA is a statutory body duly established by Parliament Act of No.54 of 1981. During the past 35 years NARA conducted numerous scientific studies in the field of fisheries and aquatic resources. NARA also provides services for development and sustainable utilization of living and non-living aquatic resources. plc Ten species of seagrasses were documented out of 15 species recorded in Sri Lanka in the present study. Highest species diversity was recorded at Mandathivu (Shannon index) while that around Nagadeepa islands was the least in the Palk Strait. Among the all sub tidal areas, Shannon Wiener diversity indices were higher in the seagrasses habitats of Gulf Mannar than that of the Palk Bay and were in descending order of Vidathalthivu> South Bar> Vankale= Thalpadu > Walepadu. Enhalus acoroides was dominant up to 2Km from the shore at Palk Bay and Palk Strait making high densities. In general stand density has clear inverse relationship with the biomass in all the study locations Although the biomass was less, stand density was higher in smaller stature species such as Halophila and Halodule tending to distribute considerably large extent in Gulf of Mannar and this has made a common phenomena in the sub tidal areas in Palk Bay and Gulf of Mannar. Halophila species was the major constituent of feed of stranded dugongs in Gulf of Mannar (Pahalawattaarachchi and Pushpakumara, 2012). This may conclude that this opportunistic pioneer seagrass species may has an ability to recover from disturbances and play a crucial role in providing constant food source for the dugongs around Gulf of Mannar and Palk Bay in Sri Lanka. Sub tidal seagrass stands in Gulf of Mannar and Palk Bay are extensive and excellent feeding niches for dugongs. Owing the specific adaptations, the genera Halophila has been found at shallow to 7-10m deep areas while E. acoroides has a limited distribution to intertidal and shallow water, also often found near fringing mangroves. Outcome of stomach content analysis were useful in surveying seagrass areas for Dugong as feeding habitats. South Bar and associated areas such as Thalpadu and Vankale comprised of high biomass of favorable species for dugongs, protection could be suggested as most important habitats. Even though seagrass habitats at Vedithathivu is most significant, the area is already declared as a nature reserve by the Department of Wild Life Conservation. Abunda nce of C. serrulat a at South Bar Extensi vely distribu ted H.ovali s at Thalpa du Long term monitoring plan should be established for the seagrass areas and habitat assessment indicators should be developed. NARA annual research funds will be utilized for continuation of habitat assessment project The data gathered will be used as a data base in the future management practices Variatio n of Shanno n Wiener Diversit y Index at surveye d sub tidal stands Compar ison of total biomass at sub tidal stands   V.Pahalawattaarachchi and D.D.G. L.Dahanayaka