Eroding islands of Gulf of Mannar, Southeast India: a consequence of long-term impact of coral mining and climate change

A study was undertaken to assess the morphological variations during the period 1969-2018 in the twenty-one islands in Gulf of Mannar, southeast India, using Survey of India Toposheet, Google Earth images and field survey techniques. The results show that two of the islands have eroded and submerged, fifteen islands area cover has reduced and four have their area expanded during the last 49 years. Overall, the Tuticorin group of islands has experienced the highest percentage of land cover reduction (78.55%), followed by Keelakarai (43.49%), Vembar (36.21%) and Mandapam (21.84%) groups. The exceptions are the four islands of the Mandapam group viz. Hare, Manoli, Krusadai and Shingle, whose area covers have increased (16.44%). A small change in the area of an island induces a greater change in its morphology. From the Island Change Ratio plot, it is observed that islands with an area cover of 10-30 ha have suffered loss of more area cover and undergone mobility from the core area. The constant changes undergone and the mobility exhibited by these islands clearly indicate that they are dynamic. The main factors that are responsible for the current changes in their extent and position are coral mining and sea level rise. Thus, it is clear that the low-lying reef islands of Gulf of Mannar are very dynamic, and that their expansion, loss in area cover and mobility are mainly controlled by coral mining and climate change. Immediate conservation action is necessary to prevent the islands from submergence.