Large scale declines in the distribution of seagrass meadows around the globe have demanded international attention for the protection of these vital coastal habitats from human activity. However, despite an increase in research effort on the ecology of seagrasses, much of the information we need to ensure their survival still remains unstudied. In Australia, the majority of our knowledge concerning the recruitment of seagrasses comes from studies conducted on small spatial and temporal scales within seagrass meadows. This site focuses on one small scale study which was carried out at Bushland Beach, over the years 2005 and 2006. The project was directed at monitoring the seed banks in the area, in particular the distribution of Halodule uninervis and Halophila ovalis and the location of germinated Halodule uninervis seeds within the sediment. The aim of our research was to gain an insight into the trigger for the germination of Halodule uninervis seeds.

“Halo” what?

Halodule uninervis belongs to the Cymodoceaceae family and can be found in the intertidal zone of Indian and Pacific Oceans or in mud banks. It is a creeping Rhizome and possesses anywhere from 1-6 roots, with a short erect stem at each node. The species has a narrow leaf blade which ranges from 6-15 cm long. Halodule uninervis seeds are 2-2.5 mm in length.

Halophila ovalis is a member of the Hydrocharitaceae family, located in the intertidal to subtidal depths of the Indo-Pacific Ocean. It's leaves arise directly from the main stem, they are ovate and 1-5 cm long, with 10-25 pairs of cross veins. Halophila ovalis produce seeds that are generally less than 5 mm long.

Why is seagrass so special?

Seagrasses have colonised the oceans since the time of the dinosaurs. They grow on sediment on the seafloor with vertically extended leaves and a buried root-like structure. Seagrasses typically grow in shallow, sheltered coastal environments. Their growth is regulated by the temperature, pH level, salinity, waves, currents, depth, light, nutrients and disease.

Seagrasses are the only flowering plants or angiosperms that can exist underwater. All but one genus can live entirely immersed in seawater. Enhalus plants are the exception, as they must emerge for reproduction.

Seagrasses reproduce through both asexual and sexual methods. In sexual reproduction the plants produce flowers and pollen from a male flower is transferred to the ovary of a female flower. Most seagrasses use sexual recruitment only for the initial establishment of the population (initial seedling recruitment; ISR). Long term survival is commonly achieved through clones by a means of vegetative propagation (asexual reproduction).

This competitive ability and longevity of seagrass enables them to exist in a disturbed habitat, aiding the dynamic coexistence of multiple species of plants and marine organisms. Seagrasses together with mangroves and coral reefs stabilise sediment, preventing the smothering of flora. They also act as nutrient sinks, buffering and filtering chemical inputs. It has even been suggested that the seeds and fruits of seagrasses are ingested and redistributed by vertebrates, such as the green turtle and dugong.

As well as providing a staple diet for these marine organisms, seagrass meadows are also nursery grounds for commercially important fish and crustaceans, making them an important natural resource that deserves our protection.

How can I help to conserve seagrass?

Seagrass-Watch HQ is based at the Northern Fisheries Centre in Cairns, Australia and organises volunteer groups to participate in the monitoring of seagrass. For more information on the program and for the list of local coordinators in the area click on the hyperlink below. http://www.seagrasswatch.org/participate.html#CGF1