The Gulf of Mannar lies between the SE coast of the Indian Peninsula and the W coast of Sri Lanka. Its S boundary lies between Cape Comorin, the S extremity of India, and Point de Galle, the SW point of Sri Lanka. The gulf is bounded N by Adam’s Bridge, a chain of islets and rocks extending from the E end of Pamban Island to Mannar Island, about 16 miles ESE.

The NW coast of the Gulf of Mannar is, with the exception of the mountains extending N from Cape Comorin, generally low and sandy, with the mountains lying about 55 miles inland.
This level plain has an average elevation of about 50m, and gradually rises toward Cape Comorin.

The W coast of Sri Lanka is low and planted with coconut trees. Inland, the foothills of the mountain district abreast Colombo begin about 20 miles from the coast.

Winds—Weather

The coast covered by this sector is, like the rest of Sri Lanka, predominantly in a region of the monsoon.
Of the four phases to be considered the Southwest Monsoon is the most important, followed by the Northeast Monsoon. Between these two monsoon are the spring and autumn transitions with their light and unsteady winds.

In the Gulf of Mannar, the Northeast Monsoon is steadiest in January and has much weakened by March. The wind becomes light and variable toward the end of April, and squally showers are common.

The Southwest Monsoon is usually established sometime in May and gains strength in June. From July to the end of September fresh SW winds prevail, with mainly fair weather at the end of the gulf. The wind usually moderates near the head of the gulf at night and in the early morning and freshens again in the afternoon as a result of land and sea breeze effect. In October the wind is more variable and there are heavy squalls with rain in the latter part of the month.

In November, the wind is normally between WNW and NE and the weather is very unsettled with frequent heavy squalls and rain; the Northeast Monsoon usually becomes established by about the end of the month.

Marine sanctuary

The Gulf of Mannar is known to harbour over 3,600 species of flora and fauna, making it one of the richest coastal regions in Asia.
In 1986, a group of 21 islets lying off the Tamil Nadu coast between Thoothukudi and Dhanushkodi were declared the Gulf of Mannar Marine National Park. The park and its 10 km buffer zone were declared a Biosphere Reserve in 1989.

The Gulf of Mannar Biosphere Reserve covers an area of 10,500 km² of ocean, islands and the adjoining coastline. The islets and coastal buffer zone includes beaches, estuaries, and tropical dry broadleaf forests, while the marine environments include seaweed communities, sea grass communities, coral reefs, salt marshes and mangrove forests.