Sedimentation from agricultural practices is a major problem throughout the region. The problem is critical in Comoros and has also affected reefs off the Seychelles, Dar es Salaam, and Zanzibar. The northern Indian Ocean is divided by India, forming the Arabian Sea and the Bay of Bengal. The Bay of Bengal, the Sunderbans, and the Ganges delta support over 500,000 ha of mangrove. India supports about 100,000-700,000 ha.
Mangroves are economically very valuable in the area and are used heavily.
Since 1963 about 50 percent of India's mangroves have been destroyed. Extensive seagrass beds are found in southern India and in the many estuaries of Sri Lanka where they cover an area greater than that covered by mangroves and coral reefs, make the largest contribution to primary productivity in coastal waters, and support over 50 percent of the countries coastal fishery production. The degree of exposure and water turbidity limit the extent of seagrasses in western India and populations are negligible off Bangladesh because of seasonal fluctuations in salinity. Most coral reef growth is inhibited by fresh water and sedimentary deposits from rivers. Bangladesh and Pakistan lack reefs although there are isolated colonies.