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Microalgae are unicellular organisms and commonly present in the euphotic zone of marine ecosystems. From the western coast of Mauritius, three strains of <i>Prorocentrum</i> species were isolated from macrophytes and cultured under standard laboratory conditions. Morphologies were examined by light, fluorescence, and scanning electron microscopy, and phylogenetic analyses were based on partial large subunit LSU rDNA (D1-D2) and ITS1-5.8S-ITS2 (ITS) regions. Three <i>Prorocentrum</i> species, including the <i>P. fukuyoi</i> complex, <i>P. rhathymum</i>, and <i>P. lima</i> complex, were identified. The antimicrobial activities were assayed against potential human pathogenic bacterial strains. The highest zone of inhibition was recorded for intracellular and extracellular protein extracts of <i>Prorocentrum rhathymum</i> against <i>Vibrio parahaemolyticus</i>. The polysaccharide extracts of the <i>Prorocentrum fukuyoi</i> complex had a higher zone of inhibition (24 ± 0.4 mm) against MRSA at a minimum concentration of 0.625 μg/mL. The extracts from the three <i>Prorocentrum</i> species had different levels of activity against the pathogens used, and this can be of scientific interest in the search for antibiotics from natural marine sources.