Horseshoe Crab: A Keystone Species of Mangrove Forests of Coastal Belts of Sunderban

Abstract

The mangroves within the biosphere reserve of Sundarban and Mahanadi Delta at Bhitarkanika and Kendrapara along the coastal belt of Bay of Bengal have been under considerable human impingement especially over the last few decades. Land reclamation for settlements along with agriculture and unplanned aquaculture practices, mechanized fishing in addition to non sustainable tourism activities proved deterrent to the ecosystem. It effect not to mention the additional burdens of pollution and changes in hydrological regimes that in turn causing adverse influence on subsistence dwellers in and around north-east coastal belt of Bay of Bengal. The horseshoe crabs are the creature on this earth surviving for the past 450 million years or so. Most of the biogenic activities of the horseshoe crab occur in the open ocean at a deeper zone. They specifically migrate regularly towards the shore for the purpose of breeding. Among the two Indian horseshoe crab species namely, Tachypleus gigas and Carcinoscorpius rotundicauda, the later species prefers mangrove habitat for breeding along the north-east coast of India. However, in spite of all previous studies on T. gigas such as spawning migration, feeding behaviour, breeding biology and several other aspects, no concerted efforts have been made for C. rotundicauda to develop effective strategies in protecting and conserving both the habitat and population of this valuable species along the coastal areas of India. The depleting population and losing important biodiversity has prompted us to undertake such a novel project. The degradation and destruction of the ground in the mangrove ecosystem of this species by natural and anthropogenic activities have also resulted in mass depletion of the population of this species along the north-east coast of West Bengal and Odisha. A mature female of this species carries hundreds of eggs under its prosoma but releases only a few eggs in one spawning act in a nest on suitable muddy breeding grounds in mangrove areas. The total number of eggs laid varied from 18 to 258 in each nest. The nest of the horseshoe crab is a depression in mud made by the female for laying their gametes. After fertilization, most of the pairs migrate to their natural habitat.