BIODIVERSITAS ISSN: 1412-033X Volume 18, Number 2, April 2017 E-ISSN: 2085-4722 Pages: 788-794 DOI: 10.13057/biodiv/d180250 Seagrass community structure of Tayando-Tam Island, Southeast Moluccas, Indonesia TYANI FITRIAN 1,♥ , AGUS KUSNADI 2 , ROSMI NUSLAH PERSILETTE 3 Tual Technical Management Unit for Marine Life Conservation, Research Center for Oceanography, Indonesian Institute of Sciences. Jl. Merdeka, Watdek, Kota Tual 97611, Maluku, Indonesia. Tel.: +62-916-23839, Fax.: +62-916-23873, ♥ email: tyanifitrian09@gmail.com Manuscript received: 21 April 2016. Revision accepted: 24 April 2017. Abstract. Fitrian T, Kusnadi A, Persilette RN. 2017. Seagrass community structure of Tayando-Tam Island, Southeast Moluccas, Indonesia. Biodiversitas 18: 788-794. Seagrass bed is one of the marine ecosystem that having the highest productivity that could sustain coastal resources. The research purposes of this paper is to determine the community structure of seagrass at Tayando-Tam Island, Southeast Moluccas, Indonesia. The method of observation of seagrass bed using a line transect, transect ran perpendicular to the shore line for 100 meters. The field of observations include identification of seagrass species, counting the number of shoots and percentage (%) of seagrass cover. Seven species of seagrass had been found in Tayando-Tam island, i.e. Enhalus acoroides, Thalassia hemprichii, Cymodocea serrulata, Cymodocea rotundata, Halodule pinifolia, Halophila ovalis, Syringodium isoetifolium. Halodule pinifolia had the highest density in Tam Island with the number of 684.18 shoots/m 2 . The coverage in this area was between 4.64-43.1 %. Based on the number of species, diversity index and dominance index Tam Island had the most stable seagrass communities, with moderate value of diversity index (H'=1.26), high evenness Index (E=1.63), and low value of dominance index (D=0.34). Seagrass resources in the Tayando-Tam islands is good and the potential for biota the association, which is supported by the quality of water is good for the growth of seagrass. Keywords: Community structure, seagrass bed, Tayando-Tam waters INTRODUCTION Seagrasses are the specialized marine flowering plants (Angiospermae) which have the ability to adapt fully in waters that have high salinity fluctuations, live submerged in the water and have rhizomes, leaves and true roots (Nontji 1987). Seagrasses mostly grow in mud or sand, the only significant exception to this being Phyllospadix, which can cling to rocky shelves (Hemminga and Duarte 2000). Worldwide seagrasses do not comprise a large number of species: 58 or so species in 12 genera. Seagrasses are not restricted to tropical or subtropical latitudes, and extend into high northern and southern latitudes, although there is a tendency for more species to be present in the tropics. These marine plants usually dominate shallow coastal waters around the world. The distribution of seagrass species can be defined as the range over which a species occurs or the area within a location where a particular species is located (Short and Coles 2001). Globally, seagrass distributions suggest six regional floras as Temperate North Atlantic, Tropical Atlantic, Mediterranean, Temperate North Pacific, Tropical Indo- Pacific, Temperate Southern Ocean (Short et al. 2007). Seagrass meadows generally comprise very few species. In the Indo-West Pacific region, up to seven species may be found in the same meadow, with Thalassia hemprichii often the most abundant (Duarte 2001). Indonesia has around 12 species of seagrasses, i.e. Syringodium isoetifolium, Halophila ovalis, Halophila spinulosa, Halophila minor, Halophila decipiens, Halodule pinifolia, Halodule uninervis, Thalassodendron ciliatum, Cymodocea rotundata, Cymodocea serrulata, T. hemprichii and Enhalus acoroides. Seagrass beds are one of the most productive marine ecosystems so as to support the potential of coastal resources (Azkab 2001). Seagrass beds have long been recognized as critical coastal nursery habitat for estuarine fisheries and wildlife (Bell et al. 1989). They function as direct food sources for fish, water flow, dugongs, manatees and sea turtles. They are also participants in nutrient cycling processes and are stabilizing agents in coastal sedimentation and erosion processes and they have received attention as biological indicators of estuarine water quality and ecosystem health as a result of their sensitivity to nutrient enrichment and eutrophication (Dennison et al. 1993). The structural function of seagrasses is a result of the morphology of seagrass plants. The seagrass plants possess an extensive underground rhizome/root system with erect shoots with bundles of leaves, which extend into the water column. As a result, they create a highly structured ecosystem from a relatively unstructured one (Philips and Milchakova 2003). When the seagrass ecosystem is intact, the seagrass beds serve as nursery grounds, places of both food and shelter for juveniles of a variety of finfish and shellfish of commercial and sports fishing importance. Healthy intact seagrass ecosystem provides services since they related to the health, stability and being of the environment in which they live, and also for human populations. Seagrasses provide physical structure on otherwise largely featureless sediment