Community structure and coral health status across the depth gradients of Grande Island, Central west coast of India

- Grande Island is less explored for its biological diversity and this study provides the first comprehensive report on the coral community structure.
- Live coral cover and its diversity were high in the mid-shelf zone (5-8 m) compared to the shallow (<5 m) and deep zones (>8 m).
- Competition posed by turf algae and sponges was the predominant stressor affecting the live coral colonies.
- Coral diseases such as white plaque disease and trematodiosis were common among the live coral colonies.

The Grande Island, located at the central west coast of India is one of the less studied coral reef systems in India. In this study, we provide a comprehensive description of the coral community structure and health status of corals across the spatial scales at different depths in Grande Island. Such descriptions provide a baseline for evaluating future community changes and effective conservation in the face of changing climate scenario. Individual benthic components and the coral health were quantified using line-intercept transects and belt transects respectively along three depth zones: shallow (<5 m); mid-shelf (5-8 m) and deep zone (>8 m). Average live coral cover was high in the mid-shelf zone (8.05 ± 3.98%) compared to the shallow (1.92 ± 2.01%) and deep zones (2.12 ± 0.05%). In total, 15 genera of corals were recorded in Grande Island of which 14 genera were present in the mid-shelf and shallow zone and six genera in the deep zone. Turbinaria and Goniopora spp. were dominant in the mid-shelf zone. Whereas, Pseudosiderastrea and Porites spp. were dominant in the shallow and deep zones. Potential threats to the corals in Grande Island include diseases and competition posed by algal turf and boring sponges. An average of 53.2% of the live corals was affected by algal turf intrusion; 2.7% by boring sponges and 2.6% by diseases that include white plaque disease and trematodiosis. Understanding the physical processes around Grande Island will reveal more about the distribution and colonization of coral communities and their vulnerability to changes in the future.