Why are coral reefs not found from West Bengal to Andhra Pradesh but found in Tamil Nadu on the east coast of India?

High salinity, optimal temperature and less siltation are essential to colonise corals. If siltation and freshwater inflow are very high, the corals don't colonise. In contrast, when the siltation and freshwater inflow by the rivers are very less, the coral do colonise.

High salinity, optimal temperature and less siltation are essential to colonise corals. If siltation and fresh water inflow are very high, the corals don’t colonise. In contrast when the siltation and fresh water in flow by the rivers are very less, the corals do colonise.