A. K. Jaiswar et al 119 Assessment of Coastal Pollution through Bioassay and Transplantation of Intertidal Clams A.K. JAISWAR*, B.G. KULKARNI** AND S. K. CHAKRABORTY* In the present study, a survey of Mahim creek and Bay area was undertaken that indicated absence of fauna, particularly molluscs from the area, which was a repository in the past. During bioassay experiments of Mahim creek water, the clams G. divaricatum and C. antiquata could not open their valves in 100% creek water and died within 12 hrs of exposure. The 96 hrs LC 50 values of Mahim creek water for G. divaricatum and C. antiquata were found to be 20% and 40% respectively during summer and 38% and 57% respectively during rainy season. When two sets of the clams were transplanted at Mahim creek, they died within 12 hrs. These experiments suggest the extreme level of pollution in the area. This level of pollution is responsible for transforming the area into barren locality in terms of fauna, specially the rich molluscan diversity. However, Gorai creek was found to be comparatively very less polluted and it still serves as breeding and nursery ground for various fishes and prawn species. Hence it must be protected and conserved. Key Words : Transplant, bioassay, clam, G. divaricatum, C. antiquate, pollution JOURNAL OF ENVIRON. SCIENCE & ENGG. VOL. 47, No. 4, P. 326-335, October 2005 JOURNAL OF ENVIRON. SCIENCE & ENGG. VOL. 48, No. 2, P. 119 - 122, April 2006 * Fisheries Resource Management Division, Central Institute of Fisheries Education (Deemed University), Fisheries University Road, Seven Bungalows, Mumbai - 400 061, India, ** Department of Zoology, The Institute of Science, 15, Madam Cama Road, Mumbai - 400 032, India. Introduction Chemical pollutants from different sources and sewage are discharged into coastal ecosystem in various forms and concentrations. They transform the ecosystem into toxic medium. In turn, this polluted water wipes away the fauna inhabiting in the coastal ecosystem demonstrating its toxic potential. Mahim creek and nearby shore area (Bay) is one such affected intertidal region of (Bombay) Mumbai, the most industrialized city of India. The same area was famous for its rich molluscan biodiversity in the past 1 from where 24 species of pelecypods and 90 species of gastropods were recorded 2,3 . During a recent survey, except S. radiata and P. bakeri, no other molluscan species were recorded from the area. However, noticeable number of molluscs were detected at other shore areas of Mumbai 4 . This is a clear indication of severity of pollution existing in Mahim creek and nearby shore areas. Furthermore, many investigators have assessed physico- chemical characteristics also and indicated the deteriorating condition of this habitat 5-7 . Generally, pollution of an aquatic ecosystem is assessed by analyzing physico-chemical parameters. However, living organisms like bivalves can also be used as indicators to predict effects and susceptibility due to presence of anthropogenic substances 8,9 . They can bio-accumulate a large variety of pollutants in levels higher than those present in sediment and their behaviour can be recorded in short periods of time 10,11 . Therefore, several organisms have been used to evaluate health conditions of aquatic system 12-14 . Many investigators have conducted bioassays on the clams, under laboratory conditions, using various pollutants 15 . Fernandes 16 evaluated the impact of pollution on selected gastropods of Bombay by detecting the concentration of various pollutants in the animals from polluted and non-polluted areas. However, barring few-investigations, data on toxicity potential of polluted water to the marine organisms, specially clam is limited 17,18 . These studies are directly useful for evaluation of the quality of water stressing on the sustainability of the aquatic biodiversity. Therefore, an attempt has been made to assess the toxicity level of polluted water of Mahim creek using bivalves G. divaricatum and C. antiquata through bioassay of creek water and transplantation of these clams in Mahim creek. At the same time, Gorai creek, a less polluted site, was also selected for comparison. This paper presents the relevant information regarding the pollution level in Mahim creek and toxicity potential to the aquatic organisms. Materials and methods The static bioassay test was conducted following the method of Sprauge 19 . The healthy and active G. divaricatum and C. antiquata were collected during low tide from Bandstand and Girgaon Chowpatty respectively and acclimatized in the laboratory for 24 hrs. Clams to be exposed to the Mahim creek water were kept in thoroughly cleaned glass aquaria (22 x 15 x 15 cm) each containing 2 L of sea water and 10 animals of uniform size (30 + 1 mm). Normal seawater collected from Nariman point coastal area was filtered and utilized for acclimatization and bioassay test. Polluted water of Mahim creek collected during low tide was utilized as 100% and the same was diluted to 10%, 25%, 40%, 50% and 75%