Just as the land has grass so does the sea. Although the seagrass is related to the land-based grass it only returned to the sea in recent evolutionary history.
Seagrasses are flowering plants that grow along the coast in well-lit quiet waters sheltered by bays and inlets. They form into lush grass meadows and are a hiding ground for small crustaceans, fish, and anything wanting to hide from a predator. These are also feeding grounds for dugongs (manatees) and green turtles. Black swans also like to feed on the seagrass. Australian waters have the world’s highest diversity of seagrass species:
- 22 species found in temperate (cold) waters
- 15 species found in tropical waters.
Australia has about 51 000 sq. km. of seagrass meadows. The largest of these are in Western Australia and Queensland. Western Australia is home to the most diverse number of seagrass species in Australia. One square meter of seagrass can generate up to 10 liters of oxygen per day. Seagrass meadows capture and store carbon at a rate forty times faster than a tropical rainforest – and they can store that carbon for thousands of years. On the other hand when the seagrass is destroyed the carbon is released back into the atmosphere. Cyclones are responsible for some of this destruction as well as loss of light due to sedimentation and algae growth due to increased nutrient levels in the water. These plants flower in autumn or summer and their roots absorb nutrients but unlike land plants do not take up water. They are more closely related to terrestrial lilies and gingers than to true grasses, they grow in sediment on the sea floor with erect, elongated leaves a buried root-like structure (rhizome).