Holothurian spatial variability and substratum preference in the intertidal habitats of the Andaman Sea

Abstract

Holothurians in the Indian waters are protected under the Wildlife (Protection) Act, 1972, yet poaching still threatens several species. Understanding species population and distribution trends is crucial to developing holothurian conservation and management directives. We examined the spatial variability in holothurian species assemblages from four intertidal habitats in the South Andaman (Burmanallah, Shaheed Dweep) and Great Nicobar Islands (B-Quarry, Shastri Nagar), India. Using multivariate statistical tools, we established trends between biological variables (Holothuroidea species) and environmental predictors viz., substratum, vegetation, pH, Sea Surface Temperature (SST), salinity, and water depth. We profiled the substratum into five types viz., dead coral with algae, sand, rock, rubble, and live coral. Seagrass and macroalgal cover contributed to the habitat vegetation. We documented five holothurian species in the present study and observed the most diverse assemblage at Shaheed Dweep, South Andaman (H’ = 0.9936; D = 0.4058). The overall relative species abundance was the highest for Shaheed Dweep (104 ind. 200 m−2), followed by Burmanallah (36 ind. 200 m−2), Shastri Nagar (26 ind. 200 m−2), and B-quarry (3 ind. 200 m−2). Species abundance positively correlated with water depth and SST. Principal component analysis (PC1 39.2% and PC2 23.8%) combined with Bray–Curtis cluster analysis revealed significant spatial variability in the holothurian assemblages. Substratum type, vegetation, and micro-habitat availability limited species distribution and abundance. The present study suggests species distribution and abundance be a function of habitat heterogeneity and water depth from the sampled regions.