A COMPARATIVE STUDY ON THE DOMINANCE OF Alcyonaceans (Anthozoa: Octocorallia) IN THE REEF AREAS IN GULF OF MANNAR, INDIA

Corals constitute a dominant benthic community in the reef areas of the Gulf of Mannar. The decline of hard corals provides space for the dominance of other coral taxa, which helps in stabilizing the degraded reef ecosystems. We documented one such degraded patch reef area with abundant octocoral distribution. This site is located near Periyasamipuram, a coastal village on the mainland (outside Marine National Park). We made a comparative study to assess the significant difference in the distribution of octocorals between the patch reef and the main reef in Kariyachalli Island (inside Marine National Park). The study was conducted from January to March in 2017 and from January to March 2018. This study's underwater visual estimations reveal that the increase in the octocoral cover is significantly different in the patch reef and the island reef. A total of 19 species of octocorals were recorded, representing the families Alcyoniidae, Subergorgiidae, and Ellisellidae. Based on the external morphology and the presence of sclerites (calcareous structures), identification was done down to the possible level. Our preliminary study recorded a maximum of 15.53% of octocoral coverage in the patch reef area and total coverage of 1.51% in the reefs of Kariyachalli Island. Statistical analysis and non-parametric multivariate and univariate scaling reveal the difference in the octocoral distribution between the study sites. Long-term monitoring is required to assess their ecological role and formulate effective conservative reef ecosystem measures.