Octocorals in Turbid Waters – An Untapped Source of Potential Bioactive Molecules

Discovering new secondary metabolites is an especially urgent task due to the rapid spread of bacterial resistance and the emergence of multi-resistant pathogenic strains of infectious diseases. Octocorals (soft corals and gorgonians) are a highly diverse group of marine organisms, which are known to contain a rich variety of rare and unusual secondary metabolites. These substances show not only great significance in chemical ecology but also various biological activities. Despite the intense interest in the isolation of novel compounds from octocorals, little is known about within and between-habitat variability in the levels and types of compounds in these species. Marine organisms living in extreme environments evolve unique strategies by biosynthesizing more diverse compounds than their counterparts living in moderate environments. Coral reefs of the Gulf of Mannar in India have a more moderate environment (with a sedimentation rate of 12.31 mg.cm-2day-1); whereas the Gulf of Kachchh is a marginal reef experiencing arid climate and heavy sedimentation rate (upto119.60 mg.cm-2d -1). In a preliminary cytotoxicity assay, carried out to evaluate the bioactivity of selected soft corals from the Gulf of Mannar and the Gulf of Kachchh, the highest cytotoxicity was exhibited by Mannar soft corals, Sinularia leptoclados (LC50=25.15μg/ml) followed by Sarcophyton ehrenbergi (LC50=43.76μg/ml). Whereas soft corals collected from the Gulf of Kachchh exhibited higher cytotoxicity than the Mannar samples (Si. leptoclados (LC50=19.24μg/ml) followed by Si. polydactyla (LC50=24.50μg/ml). Extreme physico-chemical and biological conditions in the Kachchh are the drive for the production of variant molecules with specific adaptations. Hence, soft corals inhabited in extreme waters may yield more effective compounds that may potentially be useful in drug development for existing and emerging human ailments. 

Keywords: Adaptation, Chemical ecology, Extreme environment, Marginal reefs, Marine natural products, Octocoral, Sarcophyton, Sinularia, Soft coral, Turbid water.