Factors Impelling the Shell Selection Patterns of Hermit Crabs:A Case Study from Mangrove Entangled Biosphere of Indian Sunderbans

Diverse anomuran hermit crab population inhabits the intertidal zone of the coastal regions of Sunderban Biosphere Reserve, South 24 Parganas, West Bengal. These decapods seek out and occupy empty molluscan shells of various species that provide optimal fit to protect their soft abdomen from erosion and desiccation and protect themselves from predation. This behavior of preferential shell choice by hermit crabs depends on various intrinsic factors of the shells to finally choose it as their microhabitat. The present study was done to understand the factors for optimal shell choice from a natural habitat of a part of Sunderban Biosphere Reserve (West Bengal, India). Random sampling of specimens was done from the intertidal zone of extended mud flats of Bakkhali and Frazergunj month-wise for a year that showed greater availability of one type of shell Telescopium telescopium relative to other species like Cerithidea obtusa, Pirenella cingulata, Indothias sp. etc. Twenty different molluscan shell types were chosen by two species of hermit crabs, Clibnarius infraspinatus and Clibnarius padavensis, among which latter shows greater affinity for Telescopium shells. A part of the laboratory analysis showed that the crab weight and shell weight are positively correlated at a significant level (p<0.01). The results suggested that the suite of shells used by each species was distinct and the diversity of shells chosen showed a preferential pattern. Microhabitat selection preference depends upon various factors like spatial distribution and availability of resource, durability of resource, shell weight, internal volume, shell morphometry-coiling and association of epibiotic covering of shells (scallops and barnacles).