Substratum preferences of Ascidians in Natural and Artificial Reef Environment, Andaman and Nicobar Islands

Abstract

Ascidians are one of the significant bio-fouling organisms causes great economic loss, as they grow on offshore shellfish and finfish culture system, ship hulls, pontoons, jetties, buoys etc. This study carried out to estimate the fouling preferences of ascidians in variation with depth, season, and substrate at Pongibalu (natural reef) (11°30.958’N; 92°39.201’E) and North Bay (artificial reef) (11°43.006’N; 92°45.465’E) of Andaman and Nicobar Islands. Panels (concrete, glass, ceramic and metal) of 30 X 20 cm2 were placed at the depth of 10 m and 20 m from January 2015 to December 2015 by SCUBA diving. The data collection was made in every four months interval. Altogether 35 species of ascidians belonging to five families were settled on the panels including 12 species under the family Didemnidae. A total of 29 species of ascidians were recorded from Pongibalu whereas, only nine species were recorded from the North Bay during the study period. It is interesting to note that, Pyura lanka was found on the settlement panels only, instead of reef areas of Pongibalu; similarly, Symplegma brakenhielmi and Symplegma rubra were observed on the panels at North Bay although they were not observed in the reef areas of North Bay during the study period. Both P. lanka and S. brakenhielmi is considered as cryptogenic in nature and status of S. rubra is yet to be established. Among four types of settlement panels, concrete and ceramic panels showed significant coverage of ascidian settlement at both experimental stations. It was observed during the study that the panels of natural reef area showed the higher diversity, species richness, lesser dominance, and lesser coverage. Whereas, panels of artificial reef areas showed lesser diversity and species richness, and higher dominance (90.20%) of three species coverage which indicates an early sign of species invasion.