St. Martin Island the only island in Bangladesh where coral formation occurred and the previously mentioned in various journals and books the island, as Coral Island has in fact no scientific base. The island supports the coral community associated with diverse animal and plant group and provides a unique marine environment. Based on the fringing reefs the “veneering coral communities” classification is best fit for the island since the status of the coral colonies are not extensive developed and so far reefs are formed. Here fringing reefs seem to have failed to become established due to high turbidity during a major period of the year as well as unstable substrate. Although the large rocks provide suitable substrate for coral settlement and a fair recruitment of juvenile corals was observed, the boulders are subject to frequent overturning by storm surges. During NCSIP-1 survey by coral biologist 66 species of corals have been identified under 22 genera including soft and sclerectinian hard corals. The major hard coral genera are; Porites, Favites, Goniopora, Cyphastrea and Goniastrea. The Porites was the most abundant in terms of coverage.
The live coral colonies are visible and can be seen along the lower portion of the intertidal zone particularly during low spring tide. The same continuation with greater forms is present in the sub tidal up to 400 meter to 1 kilometer.
The eastern and southern side of the Cheradia 6 genera of hard corals are present but surface area coverage was only 2 % during 1997 at the northern portion and 7-8 % at the Cheradia southeast zone at about 7-8 meter depth where Acropora is dominant. At the west of Cheradia coral bed observed 400-500 meter westward and density were 5-7 %. Further north near the Northwest rocky shoal (Bora Shiler Bandh) coral are more dense and diverse and occupy about 10 % of the area. In general sub tidal zone of the island up to 200 meters sea ward almost all rocky substrate areas supports diverse coral communities. Small coral colonies and recruitments growths are present in the intertidal rock pools at lower portion. The abundance of coral coverage is low in the whole marine area. The density measured as 1.3 colonies/square meter measures in some quadrate data in southeast Cheradia where the coral are more abundant.
In fact the coral communities and the coverage of the island areas has not been extensively surveyed due to facilities and time constraint. The entire boulder substrate may have coral growth but it has to be thoroughly investigated. The conservation actions need some fixed area as unit sample where timely systematic monitoring will occur to identify coral recruitment and growth in future after intervention. 10 – 15 sample plot monitoring would be valuable representative of the overall coral health of the island. The diverse coral associated fish and the associated invertebrates will also play as major indicator of coral habitat status. The coral bleaching has been observed during the 1998 while the whole world face the catastrophe. But the situation became normal later. The seawater temperature & salinity fluctuate in St. Martin Island between 24 –28oC and 33-38 PPT.