North-south gradient of incidence, distribution and variations of coral reef communities in the Andaman and Nicobar Islands, India

The current biophysical status of the coral reef ecosystems along the Andaman and Nicobar Islands was studied between July 2009 and March 2014 at 48 sites belonging to eight groups of Islands. The nature of the benthic environment and the distribution pattern of eleven different life-form categories and coral species diversity of the coral reef ecosystems studied are presented with their latitudinal variations. Principal component analysis indicated the increasing pattern of live coral (LC) cover towards the south in both the Andaman (Port Blair group) and the Nicobar (Nancowry group) Islands. De-trended correspondence analysis indicated that the contribution of coral species diversity was also more towards Port Blair followed by Nancowry group of Islands. Based on life-form categories, Metric multidimensional scaling analysis revealed seven major clusters with 85% similarity between the Islands. For species diversity studies, all the study sites were categorized into ten major clusters with 80% similarity. Among them, the first cluster covered the Digilipur group, the second cluster comprised areas from Mayabunder group, the third and fourth clusters comprised areas between Port Blair group and Nancowry group, the fifth and sixth clusters comprised areas of Car Nicobar group and the final four clusters formed from Havelock group. A significant negative correlation was observed between algal assemblage and LC cover. In conclusion, this study demonstrates that the algal cover acts as an important negative indicator for LC categories.