Common Structures and Properties of Seagrass Beds Fringing the Coasts of the World

Seagrasses are aquatic angiosperms which are completely confined to the marine environment. The name refers to a superficial resemblance to grasses, because of the linear leaves of most of the approximate 60 species (Den Hartog 1970). They are of paramount importance in the coastal environment as, when they occur, they generally form dense beds that may cover extensive areas. One of the most conspicuous ecological functions of the seagrass beds is their capacity to stabilize and to modify the unconsolidated substrates in which they are rooted. By their dense growth, they protect the substrate to considerable extent from erosion, but they also trap floating coarse and suspended fine materials. Further, they produce litter. The accompanying organisms contribute to the alteration of the substrate by contributing fecal material, shells or other protective structures. Part of this material leaves the system, and may be washed up onto the beach, or may be deposited on the bottom of adjacent systems in deeper waters. There are even records of seagrass remains from depths of thousands of metres (Wolff 1976). Another function is that the seagrass beds offer a substrate to many algae and animals which otherwise could not establish themselves on the sandy and muddy bottoms. Furthermore, the seagrass beds serve as a nursery for many fish, crustaceans, and other invertebrates, providing food not only for these animals, but also for a considerable number of migrating birds, sirenians, turtles, and many organisms from neighbouring habitats.