Seagrass is a general term for marine submerged monocotyledonous flowering plants, which have roots, stems, leaves, flowers, fruits, and seeds. Sea grass can use vascular bundles to transport gases and nutrients, while conducting sexual reproduction. Thus, sea grasses differ from seaweeds.
 
  According to the categorization framework of Tomlinson (1982), seagrass can be divided into 4 families: the Hydrocharitaceae, Posidoniaceae, Cymodoceaceae, and Zosteraceae, with a total of 13 genera and 66 species.
 
  In Taiwan’s marine territory, Taiwan Island, the Pratas Island, and neighboring islands (Penghu, Xiaoliuqiu, Green Island, and Kinmen) all have seagrass distribution. Currently, Taiwan has 12 types of seagrass recorded, which accounts for 1/6 of the world’s total (Ko, 2004; Lin et al., 2005). Seagrass types recorded in Taiwan include: Halophila beccarii, Halophila depcipiens, Halophila ovalis, Thalassia hemprichii, Cymodocea rotundata, Cymodocea serrulate, Syringodium isoetifolium, Thalassiodendron ciliatum, Halodule pinifolia, Halodule uninervis, Zostera japonica,  Halophila major. Currently, many samples are being identified, waiting to be published. 
 
  Seagrass beds are important coastal ecosystems in shallow tropical and temperate marine areas across the globe. They have high productivity and biodiversity because they can provide food (Lanyon et al., 1989; Lee et al., 2001), habitats, sanctuary (Fong et al., 2000; Hindell et al., 2000), and incubation places (Bell & Pollard, 1989) for many fish and shrimps, large vertebrates (such as sea turtles and sharks), and benthic invertebrates. Seagrass beds can also protect the coast by settling silt, stabilizing the seabed, preventing coastal erosion, purifying water quality, and improving the visibility of the water. Because seagrass beds can resist waves and tides, they are great natural barriers for protecting the coast, while serving an important ecological function and having economic value.