Species of the week

Learn more about Seagrasses, plants that have significant importance for coastal protection

Enhalus acoroides

Common Name: Broad-leaved seaweed

Scientific name: Enhalus acoroides

Class: Liliopsida

Oder: Hydrocharitales

Family: Hydrocharitaceae

Genus: Enhalus

Conservation Status: Least Concern

Size: The leaves thickness of Enhalus acoroides varies from 12.5 to 20 mm and has a height of 10 – 40 cm. Its rhizomes are up to 1.5 cm in diameter.

Description

Seagrasses are the only marine angiosperm plants that live their entire life cycle submerged in intertidal and subtidal and / or estuarine coastal waters. These plants form a polyphyletic group of vascular plants that are found in colonies of varying sizes, usually called meadows.

There are about 60 species of seagrasses described, of which Enhalus acoroides is one of them. This is a slow-growing species, found mostly in the persistent subtidal zone, with poor resistance to disturbance. It is characterized by a slow production of new shoots through its rhizomes, but produces high biomass, being a very large marine grass.

Distribution

Enhalus acoroides is a widespread species with a wide distribution in the Indo-Pacific waters. In the Indian Ocean, it is found from Roebuck Bay in northern Australia, extending across the Timor Sea, the southern coast of Indonesia, and across the Andaman Sea and northern Myanmar. It occurs in South India, Sri Lanka and the Lakshadweep Islands. It also occurs in the Red Sea to northern Mozambique, and in the Seychelles.

Reproduction

Seagrasses usually propagate vegetatively by the rhizomes. An entire meadow may be a single clone resulting from a seedling. Both sexual reproduction and vegetative growth are crucial for the propagation and maintenance of meadow. Enhalus acoroides is a species composed of dioic individuals, being the only species of all seagrasses that pollination is occur on the surface of the sea water.

Seagrasses of this species have pedunculated inflorescence, and in relation to the other species, these herbs produce probably the largest ovoid fruits with about 5-7 cm in length. Its seeds range from 1-1.5 cm in length.

The male of Enhalus acoroides has a single pedunculated inflorescence, containing numerous flowers and each flower is more reduced in the form of a small free floating device, and the female shows unifloral inflorescence, but with long peduncle.

Ecological Importance

Seagrasses plays an important role in marine ecosystems. These, provide ecosystem services that rank among the highest of all Earth’s ecosystems, providing shelter and food for various marine species (from fish to marine mammals).

Seagrasses contribute to the stabilization of sediments, avoiding erosion through their rhizomes, contributing substantially to the resilience of the coastal environment, and the leaves serve as filter of suspended nutrient and sediment in the water column. They are also useful for the maintenance of genetic variability, with potential biochemical utility (carbon sequestration, removing atmospheric carbon dioxide for the synthesis of organic matter).

The species Enhalus acoroides, in particular, contributes substantially to the understanding of the effects of environmental changes on seagrass meadows.

Social Importance

Seagrasses are generally considered to be high-value ecosystems, since highly prized commercial catches, such as shrimp and fish and other beings with cultural values, depend on these systems.

Enhalus acoroides, is used in some coastal communities as food, has a certain degree of importance in animal medicine, is used for the production of fiber and building materials and for handicrafts. It is also used as fertilizer in India.

Threats

This species presents numerous threats, such as coastal development, dredging and marine developments, minor damage caused by shipping activities, coastal outflow, eutrophization, climate change and aquaculture.

Conservation actions

This species is currently integrated in several programs and plans of conservation and management developed in several countries with its occurrence as well as the marine herbs in general.

Curiosities

  • Enhalus acoroides is the only species that releases pollen on the water during sexual reproduction, which restricts its distribution to intertidal and subtidal areas.
  • Enhalus acoroides is the highest species of all marine grasses found in tropical areas.

References

IUCN

Björk, M., Short, F., Mcleod, E., & Beer, S. (2008). Managing seagrasses for resilience to climate change (No. 3). IUCN.

Short, F., Carruthers, T., Dennison, W., &Waycott, M. (2007). Global seagrass distribution and diversity: a bioregional model. Journalof Experimental Marine BiologyandEcology350(1), 3-20.

Gullström, M., Lyimo, T. J., Eklöf, J. S., Björk, M., Semesi, I. S., & de la Torre-Castro, M. (2012). Seagrass meadows in Chwaka Bay: Socio-ecological and management aspects.

Rollon, R. N. (1998). Spatial variation and seasonality in growth and reproduction of Enhalus acoroides (Lf) royle populations in the coastal waters off Cape Bolinao, NW Philippines (p. 135). [sn].

Vichkovitten, T. (1998). Biomass, Growth and Productivity of Seagrass; Enhalus acoroides (Linn, f) in KhungKraben Bay, Chanthaburi, Thailand. WitthayasanKasetsart (SakhaWitthayasat).