When we sail through a canal in mangrove forests, we cannot find any coral reef; this is because the low salinity and high sedimentation environment is not appropriate for coral to survive. We may found small colonies of corals along rocky coast if we reach to estuary where the water becomes more salty and transparent. However, only some corals can adapt to live and be patchy distributed within this environment. The true coral reefs can be found beyond esturies and rivermoths where the environmental conditions are appropriate including high transparency, enough sunlight penetration, availability of hard substrates for coral recruitment, without freshwater run-off and strong waves.
It is known that monsoon causes the waves in the sea which are the key factors controlling the distribution of coral reefs along the islands. The Southern Gulf of Thailand was affected from northeast monsoon so coral reefs are distributed along the western and southern coast of the islands. In the northern and eastern parts of the islands, most areas are rocky shore without coral reefs because of the impact of waves, but coral reefs can also be found in the sheltered bays. Conversely, the Andaman Sea was influenced by southwest monsoon causing the coral reefs are only distributed on eastern and northern coast of the islands. The exposed rocky shores with coral patches are generally found in western and southern parts of the islands
Gulf of Thailand, the coral reefs can be found in the upper gulf including Chonburi, Rayong, Chantaburi and Trat Province; in the central gulf including Prachuap Khiri Khan, Chumporn and Surat Thani Province; in the lower gulf including Surat Thani to southern areas and some small coral reefs were found along the islands of Songkhla, Nakhon Si Thammarat and Pattani Province.
Andaman sea, the coral reefs were found in every province, i.e., Ranong, Phang Nga, Phuket, Krabi and Satun Province.