The three methods by which seagrass reproduce are seeds, propagules (plantlets) and spreading rhizomes. As with terrestrial flowering plants, the seeds are produced as a result of pollination between male and female parts of the flower. Some species like Halophila and Amphibolis have male and female plants and flowers.
Zostera and Herozostera have male and female flowers alternating in a swollen stem structure called a spandex. Pollination occurs in the spandex and the fruits mature prior to release. The seeds ripen to an advanced state within the spandex prior to their release.
When ripe, the seeds are released to the water and dispersed by tides and currents to form new plants at locations suitable for their establishment.
Reproduction can also occur via sprigs or propagules (small plantlets) that grow on the stems of mature pants. They eventually break free from the adult plants and float to new locations. Sprigs can survive for quite long periods enabling them to be transported considerable distances.
The final means of reproduction is vegetative expansion via lateral rhizomes that anchor the plants to sandy or muddy substrates.