Status and distribution of Trochus niloticus (Linnaeus 1767) in Andaman and Nicobar Islands

Abstract

Trochus niloticus (Linnaeus 1767) is a marine gastropod that belongs to the Order Archaeogastropoda and Family Trochidae. The present status survey on Trochus niloticus was carried out during August 2009 to March 2010 at 79 stations covering entire Andaman and Nicobar Islands to assess their distribution and standing stock on its natural beds parameters along with the primary and secondary productivities in their ambience. Extensive undersea and intertidal surveys revealed that the occurrence of Trochus niloticus throughout the sublittoral zone of continental shelf of Andaman and Nicobar Archipelago up to the depth of 20 m. The density of Trochus niloticus found in the depth ranges between 10 and 20 m at all the places of study. The mean density of Trochus niloticus varied from 6 shells/100 m 2 in the coastal waters of South Andaman to 15 shells/100 m 2 in Nancowry Islands. The abundance of Trochus niloticus was maximum in Nancowry group of Islands, and it recorded up to 20 shells/100 m 3, and also the larger specimen up to the maximum size of 13.62 cm has been observed at this region. The observations of the present study revealed that the density and size of the Trochus niloticus is comparatively higher in the Nicobar group of Islands than Andaman group. Apart from that, Middle and North Andaman were shown to have moderately high density of animals.