Seagrasses are flowering plants that live completely underwater. This type of underwater vegetation starts with small patches that grow into large meadows. Like terrestrial plants that grow on land, seagrasses produce oxygen and have leaves, veins and roots. They reproduce by seeds and flowers just as land plants do. These underwater plants produce a tough fiber which has been used for centuries in various industries for making products, including thatched roofs and home furnishings like seagrass rugs.
Seagrasses live in lagoons, protected bays and coastal waters on most of the world's continents. A wide range of sea creatures, such as crabs, shrimps, snails, worms and fish, spend their entire lifetimes within the underwater meadows of seagrass. China is the world's largest producer of the highest quality seagrass, which is grown in flooded rice paddies.
As the leaves of seagrasses decay, significant amounts of dissolved organic chemicals are released into the water and used as nutrients and for energy by bacteria and other microbes. The underwater grasses are extremely productive, regularly growing and shedding leaves, causing large amounts of decaying seagrass leaves and nutrients to be released. Seagrasses increase water quality while decreasing the amount of floating sediment that destroys coral reefs in neighboring areas. They also serve as protective nurseries for various endangered species.
According to the Nature Foundation St. Maarten website, there are seven types of seagrasses. Turtle grass has a deeper root structure than other types of seagrasses. Manatee grass is easy to recognize, as it has cylindrical leaves. Shoal grass, which typically grows in water that's too shallow for other seagrasses, colonizes disturbed areas. Widegon grass grows in both salt water and fresh water. Other species include Johnson's seagrass, star grass and paddle grass.
To survive, seagrass needs good water quality and clarity. It also needs sunlight to infiltrate the water so it can perform photosynthesis. Inadequate sunlight can lead to a depletion of seagrass.
Seagrasses can be threatened by natural disturbances such as floods, storms and turbidity, which cause haziness or cloudiness in a fluid because of individual particles usually hidden from the naked eye. They can also be destroyed by anthropogenic, or manmade, disturbances, including dredging, shipping and boating traffic and by propeller scarring and washing. Other factors that threaten seagrasses are shading from docks or boathouses and storm water runoff.