Seagrasses are submerged monocotyledonous flowering adapted to complet their life cycle belo\ the sea surface. Tftt fiarbour rich divers> of marine flora and fauna of commercia importance; and help prevent beacft erosion and siltatio- Seagrass meadows are facing numerou chaUenges and threats in the prese context and need urgent conservatiw strategies for increasina fish wea le Union Territory of Lakshadweep, located which nine can be found in the Andaman and on the Laccadive - Chagos i\rchipelago Nicobar Islands. During the 1950s locals trans­ is a unique, magnificent but very fragile planted the seagrass {Tliaiassia hemprichii) beds coral ecosystem. These Islands are believed to onto several northern islands of Lakshadweep to be formed on the submerged portions of Aravali promote beach stability and to check the erosion, momitain cliffs rising from 1500- 4000 m deep The seagrasses here are locally known as kavarat- ridges as a result of millions of years of reef tippiillu as it was introduced from the Kavaratti building process of a wide variety of corals and lagoon. A healthy seagrass ecosystcm has resulted due to the prolonged geological changes dimng in a short time extending 40 - 60 m %vide from the the period. The lagoons and the reef flats of tidal line to the deeper zone. Lakshadweep are ideal habitat for seagrasses - In all seven spccies of seagrasses - Cvmo- submerged monocotyledonous flowering plants, docea rotimdata, C serniiata, , adapted to complete their life cycle below the sea Halophila ovata, Swingodium isoetifolium and surface. In contrast to other submerged marine hemprichii and Halophila decipieiis plants (e.g. seaweeds), seagrasses do flower, bear were reported from nine atolls of Lakshadweep. fruit and produce seeds. They also have true roots, C serndata was found to be dominant whereas stem and leaves and generally grow in shallow Halophila decipiens was limited to Kalpeni Island. coastal water from the inter-tidal zone to depths Higher seagrass diversity was found around up to 10 m. In less turbid areas, such as the Carib­ Agatti. According to Z A Anzari et. al., 1991, in bean Sea and the Australian coast, seagrasses can a sUidy titled 'Seagriiss habitat complexity and be found at depths even beyond 50 m. macro invertebrate abundance in Lakshadweep coral reef lagoons, Arabian Sea published in Cora] ^A G R A S S DIVERSfTY Reefs, seagrass meadows of Lakshadweep coral Sea^^sses exhibit low taxonomic diversity (about lagoons are known to harbour a dense and rich 54 species worldwide, compared to 250,000 invertebrate assemblage. terrestrial Angiosperms). The three independent hneages of seagrass - , Pota- SEAGRASS ECOSYSTEM mogetonaceae, and Zosteraceae have evolved from Undersea meadows play a significant role in a single lineage of monocotyledonous flowering deciding the processes and resources of near­ plants between 70 million and 100 million years shore coastal ecosystems as they have physical, ago. This is in stark contrast to other groups chemical and biological effects on habitats. that have colonised the marine environment, Seagrass meadows are also involved in cycling of such as salt marsh plants, mangroves, and marine nutrients from water and sediments. The capacity algae, which have descended from multiple and of seagrasses to absorb dissolved CO2 is quite high diverse evolutionary lineages. Seagrasses have - one sq km of seagrass can absorb CO2 equivalent evolved into 12 genera spreading to the Pacific to 50 sq km by tropical forests. In a paper by C and Atlantic as continents drifted apart during Ilartog 1970, titled ‘The Sea Grasses of the Worid’, North-Holland Publication, it is highlighted that the Eocene period. In India, seagrass meadows can be found seagrass ecosystems are the one of the most on the eastern and western coast, in Lakshad­ productive ecosystems in the world and have weep as well as in the Andaman and Nicobar a very high rates of growth, producing organic Islands. They range from the strap-leafed Enhalus matter of about 300-600 g dry weight/sq m/yr. acoroides which grows to a lengtli of 30-150 cm Seagrasses have also shown a decisive role in the to the Halophilla ovalis, tiiat is 2-3 cm long. Large productivity and oxygen budget of coral atoUs as seagrass beds are present along the Palk Bay and o u tlin ed by various scientific studies. Gulf of Mannar, -vvith the latter harbouring the Thus, the disappearance of seagrass may lead highest concentration (11) of seagrass species to a more significant contribution to climate in India and six of the worlds 12 genera. Nearly change than coral reef destruction, as seagrasses 14 species are found around the Indian coast, of are vridely distributed across the oceans. The

26 ■ NOVEMBER UECEMBER 2012 • CEOCRAPHT AND YOU Vie capacity of sea passes to absorb dissolved carbon dioxide is very high -onesq km of seagrass can absorb carbon dioxide equivalent to 50 sq km by tropicalforests.

health of seagrass meadows is closely tied to that of 0.05 sq km in jfXgatti and 0.34 sq km in Kavaratti. mangrove and coral reef ecosystems, as many fish Subsequently in 199S, T GJagtap in his study tided migrate between these habitats for food, shelter ‘Structure of major seagrass beds from three coral and breeding. The recent Itirge scale coral mortali­ reef atolls of Lakshadweep’ published in Aquatic ties reported from Lakshadweep could in effect Botany, reported a seagrass vegetation cover of be due to the seagrass destruction and resultant 0.005 sq km in Agatti - a drastic decline. The case sedimentation. The excessive removal of seagrass is almost similar in Kavaratti, Minicoy, Kiltan etc. shoots lead to stirring up of sands and sediments. Herbivory (grazing), boat services and other Such sediment particles transported by the waves construction activities pose a threat to seagrass and current setde on live polyps, which instanta­ meadows. Turtles, a protected species since the neously kill them. The dead corals, particularly 1980s, has increased their population exponen­ the branching corals, broken in to small pieces tially. Lack of predators and low fishing mortality (shingles) get deposited in the relatively deeper has encouraged herbivory by the turtles - leading parts of the lagoons. This accretion and filling to large wipeouts of seagrass meadows. Opposed up of the lagoons reduces the depths, warming to this, octopus - one of the benthic predators up the lagoon, and worsening the conditions for and a sought after resource in Lakshadweep, is vulnerable communities, perpetuating the cycle rampantly harvested. Tliis has resulted in the of imbalance in the ecosystem. Till about two infestation of crabs due to the reduction of tlieir decades ago ahnost the entire fresh fish require­ predators. Crabs feed on modiolus, threatening ments of the islanders were met from the respec­ their population in many of the Lakshadweep tive lagoons. Presently, many lagoons have turned atolls resulting in an imbalance in the reef barren. It is believed that seagrass destruction is ecosystem. Once seagrass beds have been lost responsible for the reduction in fish availability. through environmental degradation, they are notoriously difficult to restore. Seagrasses are THREAT TO SEAGRASS ECOSTOTEM important in stabilising bottom sediments as they Although corals and sea turtles receive more slow water movement. They prevent erosion, trap attention, it is the seagrass meadows that are and bind sediment and organic detritus, provide amongst the most threatened ecosystems on a stable habitat for epiphytes and associated flora earth. A recent study by a group of seagrass and fauna. And due to its carbon sequestration experts supported by the National Centre for benefits the preservation of these ecosystems Ecologicjil Analysis and Synthesis, Chennai, found may prove essential in the global fight against that seagrass meadows have been disappearing climate change, osa ^ by about 7 per cent per ycEir since 1990, Anzaris The authors are Scientists at Central Marine Fisheries Research j 1991 study reported a seagrass vegetation cover of Institute (CMFRI), Cochin. [email protected] 3

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