Seagrass is a type of flowering plant. It resides underwater, and is classified as one of four different plant families, which are Zosteraceae, Posidoniaceae, Cymodoceaceae and Hydrocharitaceae. They are part of the Alismatales order. Seagrass takes its name due to its slender, green and long leaves, and also because the plants tend to grow in vast meadows that resemble grasslands.
Seagrass needs to photosynthesize, which requires it to reside submerged within the photic zone (also known as the euphotic zone), which is an area of the ocean that receives enough sunlight to allow photosynthesis to occur. Seagrass tends to appear in sheltered and shallow waters off of coasts, deep in mud bottoms or sand. Its full life cycle is completed underwater.
Seagrass is commonly referred to as being an ecosystem engineer, due to the fact that it produces its own habitat. Leaves of seagrass work to slow water currents, which then raises sedimentation. The seabed is then balanced out by the rhizomes and roots of the seagrass. Seagrass provides a defense against coastal erosion.
Seagrass has also historically been used to fertilize sandy types of soils. In Portugal, collected seagrass plants were known as "molico." Apart from being used as fertilizer, seagrass was used by the French (in the 1900s) as mattress filler (known as paillasse). In more modern times, seagrass has been used to make furniture.
Bigger creatures such as manatees, turtles and fish often consume seagrass as food. The flowers and the seeds that are made during reproduction are eaten, as are the blades of the seagrass.
Many creatures use seagrass as a habitat. Bacteria and algae grow on the leaves of seagrass, and are considered to be epiphytes (plants that live on a surface). Some small animals, such as shrimp, amphipods and snails, also graze on the bacterial and algae growth and live on the seagrass blades. These are known as epifauna. Also, small fish such as pinfish consume amphipods and shrimp directly off of the seagrass.
Seagrass is suffering from global decline, mostly due to disturbances from humans, like eutrophication (increase in chemical concentration in the ecosystem) and overfishing. Excess amounts of nutrients (such as phosphorus and nitrogen) are toxic to seagrass.
Seagrass can be found in coastal areas all over the planet. It appears on all of the continents, except for Antarctica. All over the world, there are more than 50 different species of seagrass.