Question

Patterns in the abundance of fish and snail corallivores associated with an outbreak of acute tissue loss disease on the reefs of vaan island in the gulf of mannar, india

Answer 1

Explanation:

Outbreaks of tissue loss diseases in corals, commonly known as white syndromes on Indo-Pacific reefs, are becoming more common resulting in direct colony mortality and also affecting the animals that depend on corals for food and shelter. Following observations of widespread acute tissue loss affecting the coral Montipora digitata on a reef in the Gulf of Mannar, India, we compared the density of fish and snail corallivores and abundance of tissue loss lesions between the affected area and an adjacent control area. In the affected area, an average of 50% of the Montipora digitata cover had acute tissue loss as compared to 0.33% in the control area. This is the first report of a widespread tissue loss disease for corals on the reefs in the Gulf of Mannar. The site was resurveyed four months later and no signs of tissue loss lesions were evident. Coral-feeding butterflyfish were observed feeding directly on coral lesions in the affected area but belt transects found the density of butterflyfishes to be similar between the affected and control areas and between the two time periods (outbreak and non-outbreak). In contrast, drupellid snails were also observed feeding on lesion margins but abundance was higher in the affected area (95 snails) compared to the control area (2 snails). In the follow-up survey, the densities of drupellids in the affected area had declined and were similar to those within the control site. Drupellids are attracted to damaged coral tissue and it is possible that snails actively migrated into the affected reef area and were taking advantage of the dying coral tissue. Alternatively, a Drupella outbreak could have initiated the disease outbreak. Our observations add further evidence to the potential importance of corallivores on disease processes.

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