Comparative distribution and habitat preference of the sea cucumber Holothuria atra Jaeger at protected and unprotected sites in Thoothukudi region of Gulf of Mannar, south-east coast of India

Abstract

The present study was conducted to understand the density, biomass, size distribution and habitat preference of the holothurian, Holothuria atra, at a protected and an unprotected site in Thoothukudi region of Gulf of Mannar.Water quality and sediment characteristics of these stations were also assessed. At the unprotected station (St.1), comparatively lower numerical density (mean 0.044±0.003 nos.m-2) as well as lower biomass (6.33±0.99 g m-2) of H. atra were observed, rubble constituted the dominant habitat and the population comprised entirely of adult specimens. At the protected station
(St. 2), the numerical density varied between 0.17 to 1.43 nos. m-2 and biomass between 12.9 to 161.7 g m-2. Sand
constituted the dominant habitat and the population comprised both adults and fission pieces. Significant difference was noticed in the numerical density and biomass between stations (p<0.001). Except for the pH and high nitrite concentration, other water quality parameters were within the desired limit at St. 2. The sediment quality criteria, especially in terms of organic carbon (1.46±0.22%), organic matter (2.50±0.4%) and nitrogen concentration (0.12 ±0.02%) were comparatively higher in the sediment at St. 2. Significant differences were observed in the variation of organic carbon, organic matter and N2 between stations (p<0.001).