Although most of the reefs and coral communities of the eastern Pacific have been well studied, there is still great ignorance regarding the occurrence, distribution and faunistic composition of those on the western coast of Mexico. Moreover, the coastal margin of this region is being subjected to great anthropogenic modifications that may irreversibly affect the local coral communities. The present study has the objective of describing the structure and distribution of the main coral reefs and coral communities in the coastal region of the state of Nayarit (20-21 degrees N). The results indicate that these zones are characterized by a high specific richness and a clear zonation, but with low diversity and uniformity, principally due to the dominance of Pocillopora damicornis (L.) in these localities. Because of the combined effects of the small continental shelf area that can be colonized by corals, the relatively low water transparency and the presence of a very shallow thermocline, all the coral reefs observed in southern Nayarit are narrow fringing reefs. The physiographic and hydrologic barriers in the region, such as river mouths and ample marsh areas to the north, and upwelling effects in the south, give place to a disjunct distribution of the zones of coral reef development on the Nayarit coast, limiting their distribution to a rocky coastal section of about 130 km in length.
