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Seagrasses: Biology, Ecology and Conservation. Anthony W.D. Larkum, Robert J. Orth and Carlos M. Duarte [Eds]. 2006. 691 pp. Springer, Dordrecht, The Netherlands. euro89 [hardback: ISBN 10 1-4020-2942-X].
There are some 240,000 described species of flowering plant, of which more than 239,000 grow on land or, much less commonly, are emergent aquatics. There are only about 850 species of submerged freshwater flowering plants, but invariably completion of their sexual life-cycle involves contact with the atmosphere. The most completely aquatic flowering plants are the seagrasses, which live in the sea and can complete their life cycle when fully submerged. Only just over 50 species of seagrass are known, from about 12 genera; they are all monocotyledons. Seagrasses are clearly of great evolutionary interest, with the ability to grow, and reproduce, when completely submerged, and their occurrence at much greater depths in the sea than where submerged flowering plants are found in freshwaters.
In addition to these unique properties of the seagrasses as organisms, they have great ecological significance in many coastal ecosystems, mainly those with muddy or sandy substrata. The ecological significance extends to providing a range of ecosystem services for mankind. These ecosystem services, and the diversity of seagrasses, are under threat from local environmental changes, such as coastal 'development' and changed land use in the...