by Goutham K
Estuaries can be defined as partially enclosed bodies of water found in the coastal areas, where the freshwater from rivers, lakes or streams mixes with the saline water from the ocean. Brackish water formed by the mixing of saline and freshwater is a peculiarity of estuaries. Estuaries are delicate ecosystems where diverse varieties of flora and fauna which are adapted to live in brackish water are seen. Moreover, many species rely on estuaries for food, breeding and various other purposes. Hence, they are considered living laboratories for bioscientists around the world.
Due to the geographical peculiarities of Kerala, with its long coastal stretch with numerous rivers draining to the sea is home to 27 different estuaries in its 589 Km coastline. Vembanad is the largest Estuary in the state followed by Ashtamudi, Korapuzha, Paravoor and Beypore. The estuarian ecosystem of Kerala is much important in the context of diverse and rare vegetation present in these geographical zones.
Mangroves are one of the most important species that are seen mostly in the estuarine regions. Due to their salt-tolerant nature, mangroves of Kerala are usually situated in the coastal river mouths and estuaries. 18 different species of Mangroves are present in Kerala, among which Avicennia officinalis and Rhizophora mucronata are the dominant species whereas Ceriops tagal, Avicennia alba and Sonneratia alba are rare. Not only do mangroves provide better habitat structure to diverse vegetation, but also offers various ecosystem services such as protection of topsoil, coastal protection, nutrient cycling etc.
Apart from this, estuarine ecosystems in Kerala are also home to various rare aquatic fauna. The abundant distribution of zooplanktons in these ecosystems plays a pivotal role in maintaining the balance of marine food chains. Zooplanktons are the intermediate link between Phytoplanktons and fishes in the marine food chain. According to the latest study conducted by a group of researchers from the Kerala University of Fisheries and Ocean Studies (KUFOS), Kochi, 90 different fish species belonging to 17 orders and 48 species were reported to be found in the estuarine ecosystem of Vembanad estuary, the largest in Kerala. This figure points out a steep 40% decrease in fauna diversity compared to the figures of the 1980s. Similarly, the Kadalundi estuary in the state reported the presence of 34 different fish species of 24 families belonging to 8 orders. Likewise, each of the 27 estuaries in the state is home to varied aquatic species and vegetation that are of high ecological significance.
Similarly, due to the delicate ecological system in the estuaries, its nearby areas are suitable habitats for various traditional and migratory birds. Kumarakom and Kadalundi bird sanctuaries which are close to Vembanad and Kadalundi estuaries respectively are concrete examples of this. 170 different species of birds have been observed to date in the Kadalundi sanctuary whereas the Kumarakom sanctuary has the presence of local birds like waterfowl, koel, owl, egret, heron, cormorant, moorhen, darter, and brahminy kite, as well as the migratory gull, teal, tern, flycatcher etc. many migratory birds from Serbia, The Himalayas, reach here during seasons.
Some of the estuaries in Kerala are also famous tourist destinations due to their aesthetic importance. The Ashtamudi estuary and lake is one of the most visited destinations in the state along with the Vembanad lake and estuary. Backwaters coming from these locations are one of the unique specialities of Kerala tourism. Moreover, these estuaries contribute highly to the livelihood and economy of local communities residing in proximity due to the abundant resources present here. But aftereffects some anthropological interventions in these estuarine habitats like change in shoreline, sedimentation, improper engineering constructions etc. are causing the estuaries to shrunk, both geographically and biologically. According to a recently published report, the Vembanad estuary is shrinking by an area of 0.288 square km per year which is concerning from an ecological point of view. The Paravur estuary, which faced a shrunk in flood plain deposit from 4.95 to 2.12 km square as a consequence of land-use changes is another example of the same. Moreover, the ecological diversity and environmental degradation of the ecosystem is another example of the threats faced by estuaries of Kerala.