Opinion: 'Grasses of the sea, best kept secret in the land', writes Jayshree Vencatesan

One such group is the seagrass, which is a unique group of flowering plants that has adapted to exist fully submerged in the coastal waters, acting as ecological engineers and providing numerous important ecological services to the marine environment. Seagrasses are found distributed across the globe but unlike other plants and animals with worldwide distribution, they exhibit low taxonomic diversity. In simpler words, there is not much variety in them!  They are found in a variety of coastal habitats and typically occur in shallow, sheltered soft-bottomed marine coastlines and estuaries, as believe it or not, meadows! 

The coastal landscape of Tamil Nadu is abundant with seagrasses. Tamil Nadu coast includes estuaries fed by five major rivers namely Palar, south Pennar, Kollidam, Cauvery and Thamiraparani. All these rivers play a major role in the growth of seagrass along the river mouths of the estuaries. 

Seagrass habitats within this zone are supported by sheltered bays, gulfs, straits, channels, lagoons, estuaries, salt water lakes and backwater ponds. Fourteen seagrass species are found in the Tamil Nadu and have been observed from intertidal to subtidal regions to a depth of 8 m. 

These submerged meadows are the early warning systems of the coastal/ marine health for exposure at low tide, wave action and associated turbidity. Low salinity from fresh water inflow determine their survival. They do well in inter tidal zones, especially if they are sheltered from wave action or where there is entrapment of water at low tide, protecting the seagrasses from exposure (to heat, drying) at low tide. 

The proximity of seagrass beds to other critical habitats, such as mangroves and coral reefs (in tropical regions), facilitates trophic  transfers and cross-habitat utilisation by fishes and invertebrates. All these systems exert a stabilizing effect on the environment, resulting in important physical and biological support for other communities. 

Seagrasses produce considerable biomass, provide habitat, and perform multiple ecosystem services. Seagrasses alter water flow, nutrient cycling, and food web structure. Seagrasses on reef flats and near estuaries act as nutrient sinks, buffering or filtering nutrient and chemical inputs into the marine environment. These plants support numerous herbivore based food chains and are a food source for mega-herbivores such as green sea turtles, dugongs, and provide a critical habitat for many animals, including commercially and recreationally important fishery species. They also stabilize sediments and produce large quantities of organic carbon. In addition, seagrasses are indicators of the status of the coastal zone which can be used in coastal management strategies aimed at preserving or improving the environmental quality of the coastal zone.  Seagrass meadows occupy less than 0.2% of the area of the world's oceans but are estimated to bury nearly 10% of  the yearly estimated Carbon burial in the oceans, according to Suganthi Devadason Marine Research Institute, which has extensive data on seagrass diversity in Tamil Nadu. Additionally, these meadows offer protection from larger predators to juvenile and small fish and larval shrimps, thereby contributing to increased fish stocks.  Securing the liveihoods of the traditional fishing communities in the Palk Bay and Gulf of Mannar region is inextricably linked to the protection and conservation of sea grasses – a fact that is little known, and often ignored.