Seagrasses are found across the world, from the tropics (hot) to the arctic (freezing). Australia has approximately 51,000 km2 of seagrass meadows and Antarctica is the only continent without seagrasses. Segrasses inhabit bays, estuaries and coastal waters from the shallow intertidal areas to 60m, however most species are found in the inshore areas between 0 – 25m.
Shades of green on this map indicate the number of species reported for a given area. The darker shades of green indicate more species are present. While most coastal regions are dominated by one or a few seagrass species, regions in the tropical waters of the Indian and western Pacific oceans have the highest seagrass diversity, with as many as 15 species growing together. As you can see from the red circle, Australia has some of the highest diversity in the world, with large areas along Queensland’s coastline.
Seagrasses are widespread in the Broadwater and estuarine areas around the Gold Coast, and their growth depends on a combination of natural and human factors. Natural factors include water movement, wind, light, overall water quality, and grazing by dugongs and turtles. Human disturbances such as boat moorings, anchorages, and damage from boat propellers can also affect patterns of seagrass distribution. Slow growing seagrass species are found in areas with relatively low disturbance, while species that grow rapidly and produce large numbers of seed are more often found in highly disturbed areas.
Almost all species of seagrass reproduce completely underwater, making them unique among the angiosperms.
Seagrass can reproduce sexually or asexually:
Sexual Reproduction: They are flowering plants that produce seeds. Pollen is carried through the water to fertilise female flowers. Once seeds are set they are dispersed from the plant by water movements or animals where they can recruit to new areas many kilometres away, much like wind carried seeds of terrestrial grasses. Depending on many biophysical factors such as currents, winds and temperature, dispersal can range from 10 to 30 days.
Asexual reproduction: Seagrass can also send out rhizome roots that can sprout new growth, so a single plant is capable of producing an entire underwater meadow.
Local seagrass flowering generally takes place in winter or early spring. However, this is not common for most tropical species and the spread of seagrasses is largely through the growth and branching of rhizomes.