1 - Cochin University of Science and Technology

Chapter i. introduction
species of sea grasses have been recorded, representing 12 genera and 2
monocotyledonous water plants throughout the world, of which 37 are
tropical and rest are temperate species. Importance of seagrasses as the
primary producers in coastal environments, for instance, in sustaining
fisheries, was proposed as far back as the turn of the last century (Peterson,
1913, 1918). Seagrass beds are also common along coastal lagoons
(Balasubramaniam and Khan, 2001) and sandy seas around the bases of
shallow fringing and patch reefs. Throughout the western Indian Ocean
seagrass beds are a common feature of intertidal mud and sand flats
(Richmond, 1997). They represent a unique flora of angiosperms adapted
to rigorous salinity, immersion, occasional desiccation, and hydrophilic
pollination (Schwarz et al., 2004).
Productivity of seagrasses is often enhanced by encrusting algal
epiphytes (Sheppard et aI., 1992). A dense vegetation of seagrass produces
a great quantity of organic material by itself and also offers a good
substrate for epiphytic micro and macro algae and sessile fauna. The
vegetation plays the role of sediment trap and minute suspended particles
both organic and inorganic are deposited in this biotype (Mc Roy and Mc
Millan, 1977; Walker, 1988). By trapping sediments, seagrasses play a
vital role in stabilising mobile sand and protect shores from erosion. It also
creates unique microhabitats for small animals (Kirkman, 1985, 1995;
Gosliner et aI., 1996). Encrustations on seagrass blades include fauna such
as sessile, often colonial invertebrates such as hydroids, bryozoans,
sponges, barnacles and tunicates. These In turn attract other fauna
(polychaetes, crustaceans like isopods, amphipods, mollusks and
echinoderms), which form the basis of food chains within the seagrass
ecosystems. Many amphipods, isopods, and tanaeids feed on the mixture of
microflora and detritus. Numerous fish species feed on the leaves and use
the seagrass beds as shelter from predators (Stoner, 1983). As there are few
seagrass grazers, most of the plant materials are utilized by animals as semi
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