Sea grasses are flowering plants with roots, leaves and stems that distribute pollen in sea water currents. There are approximately 50 species of sea grasses which are found throughout coastal margins of temperate and tropical zones in mud or muddy sands.These sea grasses often form beds or meadows
Sea grass beds and the individual plants in them are important marine habitats. Sea grass is a major contributor to local food resources for grazing animals.Sea grasses are grazed on by many animals ranging from sea turtles, manatees and birds to sea urchins and starfish. Dead sea-grass material also becomes food for many animals such as worms and snails that live in the mud around the plants.
It also has extremely valuable microhabitats:
The leaves of the sea grasses are covered in the film of single-celled algae, mostly diatoms, that increase the overall primary production in the seagrass bed.
The leaves also carry blue-green algae that release nitrogen-rich nutrients that are essential for healthy plant growth.
In temperate zones the principle seagrass species are eel grasses. Eel grasses are sometimes found exposed on the lower shore and can grow as deep as 30 metres.
The turtle and manatee grasses are the principal sea grasses in tropical and subtropical areas. They are found from the edge of the shore down to 10 m, dependent on conditions.
Green surf-grass plants are the biggest and most vividly coloured of sea grass species. Their root system is very extensive and extremely tenacious. They anchor the long, flexible, tough stems into the substrate. The tightly packed stems dissipate wave energy which enables the plants to survive in the turbulent intertidal zones of temperate east Asia and northwest America.