Nine species of macroalgae are newly reported for the Caribbean International Biosphere Reserve Seaflwer. Of these taxa, Neosiphonia sphaerocarpa, Polysiphonia schneideri, Polysiphonia sertularioides, Cladosiphon occidentalis, and Phaeophila dendroides, have been previously reported from Colombian waters, whereas Ulothrix sp., Ulva flxuosa subsp. paradoxa, Chaetomorpha minima, and Cladophora liniformis represent new records for the country. All the algae were found growing epiphytically on Thalassia testudinum in shallow (<1 m) seagrass meadows around San Andrés Island. Their morphological features are discussed.