Sand Dune Ecosystem
As one walks along the coast in Southern Chennai between Kovalam and Mamalapuram, one can’t miss the sand dunes that are characteristic of these areas. Sand dune vegetation occurs between the spring tide line and the littoral zone of the coastal ecosystem. I had the opportunity of studying an elusive reptile the sand skink (Eutropis bibronii) in the sand dunes adjoining Crocodile bank. It is basically a small mound of sand along with ground vegetation such as
1.Ravan’s moustache (Spinifex littoreus)
2.Crown flower (Calotropis gigantea)
3.Beach Morning Glory (Ipomoea pes-caprae)
4.Beach Casuarina (Casuarina equistifolia).
Ravan’s moustache that spreads itself on the sand is a creeper so called because of the needle shaped leaves that are stiff like a moustache. It is a soil binder that keeps the beach sand together from being blown away by wind and sea erosion. It has two methods of reproduction. Fruits are produced in the form of ball that travels rolling along with the wind to find areas suitable for growth. It also spreads along the sand by vegetative means by nodular vegetation thus binding the sand of the sand dune. This plant is not edible to goats and cattle hence making it an ideal binder of sand. Beach morning glory is a common plant that is seen mixed along with Ravan’s moustache vegetation. Flowers are pink like a rose in color. It has the ability to resist salt hence can proliferate in the sand dune vegetation. Crown flower is a poisonous shrub that plays host to many butterfly and insect species that lay their eggs in it. The leaves of these plants are poisonous hence the butterfly caterpillars that eat these leaves are also poisonous as adults. Beach casuarina is an exotic large tree that can resist the salt in the soil. It has needle shaped leaves and it absorbs the ground water hence doesn’t let other vegetation to grow. Due to its fast growth as a tree it is considered important as a fuel wood tree and for construction material.
Several species of fauna are found in these sand dunes. The most important of them all is the Olive Ridley sea turtle (Lepidochelys olivacea) that is an endangered reptile that come to nest and lay eggs in the sandy vegetation between sand dune and beach surf. The eggs are ping pong ball sized and close to 80 to 150 eggs are laid in a clutch. The eggs are buried in the sand by a flask shaped chamber dug by the gravid female with its hind legs. The eggs are incubated by solar radiation. After a period of about 45 days the hatchlings emerge and instinctively rush towards the sea. There are predators for hatchlings both at land and at sea. It is believed one in a thousand survive to adulthood.
There is a rare species of skink named the sand skink that inhabits these sand dune vegetation. It exploits the sand dunes thermal profile. It emerges out in the mornings to feed on its prey that is insects and retreats in to the sand when the temperature increases in the afternoon. It emerges again in the evening when the sand temperature cools down. There are several species of ground birds notable amongst them being Indian Stone Curlew (Burhinus indicus) Red wattled lapwing (Vanellus indicus) and Grey francolin (Francolinus pondicerianus). All these are ground birds.
During the dry season of March- April (2009) the ground vegetation in the stretch from Kovalam to Mamalapuram was burnt for a plantation of casuarinas. This World Bank project was stopped due to protests from sea turtle conservationists and the saplings were removed. Casuarina doesn’t provide an ideal habitat for nesting of sea turtles. Sea turtles avoid nesting in these areas. Of late there is lots of pressure on these ecosystems because of urbanization. Concrete structures cause of breaking of wind because of which the sand dune vegetation is disturbed.
The author is a Herpetologist with Care Earth Trust, Dr. J.Subramanean.