Seagrass
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Seagrass (or sea-grass in British English) are flowering plants from four plant families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae) that grow in the marine saline environment.
They are called seagrasses only because most species superficially resemble terrestrial grasses of the Family Poaceae. Because these plants must photosynthesize, they are limited to growing submerged in the photic zone, and most occur in shallow and sheltered coastal waters anchored in sand or mud bottoms. They undergo pollination while submerged and complete their entire life cycle underwater. There are about 60 species worldwide (although the taxonomy is still disputed).
Seagrasses form extensive beds or meadows, that can be either monospecific (made up of one species) or multispecific (where more than one species co-exist). In temperate areas, usually one or a few species dominate (for instance Eelgrass Zostera marina in the North Atlantic), whereas tropical beds usually are more diverse, with up to 13 species recorded in the Philippines.
Seagrass beds are highly diverse and productive ecosystems, and can harbor hundreds of associated species from all phyla, for example juvenile and adult fish, epiphytic and free-living macroalgae and microalgae, shellfish, bristle worms, and nematodes. Few species were originally considered to feed directly on seagrass leaves (partly because of their low nutritional content), but scientific reviews and improved working methods have shown that seagrass herbivory is a highly important link in the food chain, with hundreds of species feeding on seagrasses worldwide, including dugongs, manatees, fish, geese, swans, sea urchins and crabs.
Seagrasses are sometimes labelled ecosystem engineers, because they partly create their own habitat: the leaves slow down water-currents increasing sedimentation, and the seagrass roots and rhizomes stabilize the seabed. Their importance for associated species is mainly due to provision of shelter (through their three-dimensional structure in the water column), and for their extraordinary high rate of primary production. As a result, seagrasses provide coastal zones with a number of ecological goods and ecological services, for instance fishing grounds, wave protection, oxygen production and protection against coastal erosion. Seagrasses can also be collected to be used to fertilize sandy soil. This was an important activity in the Ria de Aveiro, Portugal, where the plants collected were named moliço.
Contents |
[edit] Genera of sea grasses
- Family Posidoniaceae
- Family Zosteraceae
- Zostera
- Heterozostera
- Phyllospadix
- Family Hydrocharitaceae (Frogbit family)
- Enhalus
- Halophila
- Thalassia
- Family Cymodoceaceae
- Amphibolis
- Cymodocea
- Halodule
- Syringodium
- Thalassodendron
[edit] See also
[edit] References
- den Hartog, C. 1970. The Sea-grasses of the World. Verhandl. der Koninklijke Nederlandse Akademie van Wetenschappen, Afd. Natuurkunde, No. 59(1).
- Hemminga, M.A. & Duarte, C. 2000. Seagrass Ecology. Cambridge University Press, Cambridge. 298 pp.
- Short, F.T. & Coles, R.G.(eds). 2001. Global Seagrass Research Methods. Elsevier Science, Amsterdam. 473 pp.
- Green, F.P. & Short, F.T.(eds). 2003. World Seagrass Atlas. UNEP, UCP, Berkely. 286 pp.
- A.W.D. Larkum, R.J. Orth, and C.M. Duarte (eds). Seagrass Biology: A Treatise. CRC Press, Boca Raton, FL, in press.
