Harmful diatoms and dinoflagellates in the Indian Ocean: a study from Southern coast of Sri Lanka


D.A.S.J. Dissanayake, D.D. Wickramasinghe, P.M. Manage

Studies on Harmful Algae (HA) are rare in the Indian Ocean around Sri Lanka. The current study investigated diatoms and dinoflagellates in five Sri Lankan Southern coast locations, focusing on potentially harmful species. A total of twenty-seven diatom species and ten dinoflagellate species were identified during the study. Among them, eight diatom species (Asterionellopsis glacialis, Chaetoceros curvisetus, Chaetoceros lorenzianus, Guinardia flaccida, Leptocylindrus minimus, Nitzschia sp., Proboscia alata and Pseudonitzschia fraudulenta) and three dinoflagellate species (Ceratium fusus, Ceratium furca, and Dinophysis caudata) were identified as potentially harmful species. Specifically, P. fraudulenta related to producing domoic acid, causing Amnesic Shellfish Poisoning (ASP), was recorded in all sampling locations. Potentially harmful species showed a significant correlation with turbidity and total phosphorus levels (p < 0.05). Discerning the occurrence of these species in the region is vital, as the seascape under investigation is in anthropogenic pressure with many sea routes. Even though bloom conditions were not observable during the study period, the risk of transporting microalgae to many different locations and the possibility of bloom formations cannot be ignored. As a country surrounded by the ocean, the results demonstrated the importance of continuous monitoring of potentially HA and regulating maritime and land-based activities, covering a broader area to identify and manage potential threats to the Indian Ocean.

Keywords: Indian Ocean; Sri Lanka; coastal zone; harmful algae; diatoms; dinoflagellates; water quality


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