Despite its name, seagrass is not actually a grass, it is an aquatic angiosperm (flowering plant) more closely related to terrestrial lily’s and ginger than grass as we know it. Around 100mya seagrass colonised the oceans and they are the only flowering plants that can live underwater.
There are 58 species of seagrass worldwide
Seagrass meadows may be monospecific or may consist of multispecies communities, sometimes with up to 15 species present within one location. Seagrass in Australia is particularly diverse with 30 species in Queensland, and 8 species right here in South East Queensland (Queensland Government, 2019)
Many different growth forms
Seagrasses range from species with long flat blades that look like ribbons to fern or paddle-shaped leaves, cylindrical or spaghetti blades, or branching shoots. The tallest seagrass species—Zostera caulescens—was found growing to 7 meters in Japan. These distinct structures and growth forms affect how seagrass influence their environment and what species live in the habitats they create.
Key habitat requirements
Seagrass form meadows in subtidal and intertidal environments estuaries and shallow coastal waters with sandy or muddy bottoms. They need light to grow and this restricts the depth and extent of meadows. Seagrass also require nutrients, carbon dioxide, substrate for anchoring, alongside suitable salinity, temperature and salinity to survive.
Grow with rhizome buried in sediment
They grow in sediment on the sea floor with erect, elongate leaves and a buried root-like structure (rhizome). The rhizome anchor the plant, store carbohydrates and absorb nutrients.