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INTERNATIONAL JOURNAL OF ENGINEERING, SCIENCE AND - Volume 7, Issue 4 (2) , April 2018 (Special Issue FBSA)

Pages: 153-159
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ABUNDANCE AND DISTRIBUTION PATTERN OF INTERTIDAL SHORE CRABS ON EXPOSED SANDY BEACHES OF BAKHALI, SUNDARBANS

Author: Ranu Naskar*

Category: Engineering, Science and Mathematics

Abstract:

Ecological survey of inhabited shore crabs was carried out at exposed sandy beaches of Bakkhali island (21o33'48''N and 88o15'34''E), located at southern proximity of West Bengal falling within Sundarban mangrove ecosystem. The main objectives were to analyse the across-shore distribution pattern of interspecific crabs by means of burrow counts and diameter of their openings and to identify their preferable zones and spatial segregation. To achieve the aims, quantitative transect and quadrat sampling was done to access the habitat distribution, their abundance and the relative density. The present survey reported the considerable interspecific variability in across-shore distribution pattern showing dominance of three brachyuran crabs of family Ocypodidae and Dotillidae. Niche segregation among the species had also been reported with two species more widely distributed, while one had restricted distribution. The Red ghost crab, Ocypode macrocera and Horned Ghost crab, Ocypode cerathophthalmus are typical predators, scavengers and deposit feeders, leaving huge amount of characteristic pellets on sandflats. Juveniles dig simple and shallower burrows towards seaward, while adults create deeper and complex burrows towards landward with great variability. Data revealed that O. macrocera were relatively abundant with greater population density (0.8 individuals/ m2) preferring inhabiting almost dry supratidal, while O. cerathophthalmus only occurred at 0.3 individuals/ m2. Distribution pattern of O. macrocera also varied greatly with maturity showing predominance of small burrows (1.5-2.5 cm) in diameter along transect T1and T2, inhabited by juvenile ones and by adult group (3.5-6.0 cm) within supratidal. The tiny spherical Soldier crab, Dotilla blanfordi, measuring upto 1 cm body width were important members of intertidal community occuring abundantly in moist sand of lower intertidal, with juvenile dominating towards waterline. The burrowing behaviour of shore crabs has been considered as one of the major bioturbations affecting the physical and chemical characteristics of the substratum, thereby promoting sediment turnover and biogeochemical cycling

Keywords: Ocypode macrocera; Ocypode cerathophthalmus; Dotilla blanfordi; Distribution; Abundance.