eng Science and Education Publishing Journal of Environment Pollution and Human Health 2334-3494 2025-05-13 13 1 18 22 10.12691/jephh-13-1-3 JEPHH20251313 article Konan Estelle S¨¦v¨¦rine estydekonan@yahoo.fr 1 Koffi Kouakou Urbain 2 N¡¯Guessan Benjamin Kouadio 2 Kouassi Kouam¨¦ Moise 2 Centre de Recherches Oc¨¦anologiques, 29 Rue des P¨ºcheurs, BP V18 Abidjan, C?te d¡¯Ivoire Ecole Normale Sup¨¦rieure (ENS) Abidjan, C?te d¡¯Ivoire, 08 BP 10 Abidjan 08, C?te d¡¯Ivoire No study relating to Harmful Algal Blooms (HABs) in the marine coastal waters of Côte d¡¯Ivoire has been carried out. Given their harmful effect, the aim of this study is to identify and quantify HABs in Ivorian waters and monitoring their temporal distribution. Weekly sampling was carried. Samples were fixed in formalin solution (5% final concentration) and afterward, were examined using a standard optic microscope equipped with a digital camera. The quantitative estimation of the HABs species was performed by counting with an inverted diavert microscope, using Utermöhl¡¯ method. Seventeen (17) HABs were determined using the species¡¯ identification detailed in the literature. They are divided into two groups, those which don¡¯t produce toxins like genus Ceratium, Dictyocha, and two species of Prorocentrum, P. micans, and P. gracile and those which produce toxins like genus Dinophysis, Pyrodinium and species Prorocentrum rhathymum. The lowest densities of HABs were observed during the long and short rainy seasons and the highest were recorded in september with a significant peak on september 11. The species responsible for these high densities are: Ceratium furca (8444000 Cells.L-1), Dinophysis caudata (4960000 Cells.L-1) and Protoperidium divergens (2000000 Cells.L-1). These high values are due to upwelling. The processes that develop during upwelling, in particular the rise of nutrients, are responsible of high biological productivity, hence the high values of HABs observed during this period. https://pubs.sciepub.com/jephh/13/1/3/jephh-13-1-3.pdf Harmful Algal Blooms marine coastal water C?te d¡¯Ivoire Gulf of Guinea