In the recent years, the introduction of various pollutants into marine environments has increased and this is considered a serious threat to these environments. Therefore, their monitoring is especially important using bioindicators in these environments. Bioindicators are species that are used to monitor the health of an ecosystem or environment. Since sea cucumbers have close proximity to sediments, due to their relatively long life, they are a good bioindicator for determining the concentration of heavy metals. Chabahar Bay are considered as sensitive areas of the sea for various reasons namely the presence of rich natural resources and specific marine ecosystems. In order to determine the amount of heavy metals of Chabahar Bay contaminating sediments, water and also their accumulation in different tissues of sea cucumber ( Holothuria leucospilota ), four stations were established on the coast of ChabaharBay and where samples were collected. The concentrations of lead, cadmium, chromium and nickel heavy metals in samples were measured by flame atomic absorption spectrophotometer.The results showed that the average concentrations of lead, cadmium, chromium and nickel in sediments were lower than the USA and Canada's standard sediment quality andUnited States Environmental Protection Agency, but higher than the lower bound of these standards. The concentrations of lead (0.35mg/L) and chromium (0.18mg/L) were too high in normal water samples from seawater. The accumulation of heavy metals was observed in all tissues of sea cucumber, including the respiratory tract wall, gonad and gut, but in general, the most concentrated metals were respiratory tissue and sea cucumber. Also, calculating the bioconcentration factor showed to be more than one (1.50 mg/Kg) and indicates the effective accumulation of heavy metals in the respiratory tissue .Comparison of metal concentrations among different stations in Chabahar Bay identified that the most polluted sediment samples were from Tis and Lipar stations and the most polluted water samples belonged the Tis Station. The sea cucumber samples exhibited the largest aggregate of metals. In general, this study revealed that concentrations of Heavy metal substances in sediment, water and sea cucumber were significantly higher than previous studies and other bioindicators studied in the Chabahar region and could be problematic over a long period of time. Key words : Heavy metals,Bioindicator,sea cucumber, Sediment, Chabahar Bay.
