ABSTRACT.Forty‐five axenically grown algal (sensu lato) species representing six divisions—that is. 13 Chlorophyceae, 14 Chrysophycophyta, five Dinophycophyta, seven Cryptophycophyta, two Rhodophycophyta, and four Cyanochloronta—were aseplicaily presented separately as potential food sources to the marine helerotrich ciliateFabrea salinaunder standardized algal number, medium, lighting, and temperature. The algae can be placed into three groups based on their effect on the intrinsic growth rate of the ciliate. Nutritious:Rhodomonas lens, cryptomonad LIS1,Dunaliella parva, Prasinodadus marinus, Chroomonas salina, D. tertiolecta, Chaeloceros galvestonensis, D. primolecta, Phaeodactylum tricornutum, D. salina, Isochrysis galbana, Cylindrothecaclosterium, cryptomonad strains M2, WH2&FSA,Chroomonas sp., P. lubricus, and Peridinium trochoideum.Maintamers: Cyanobacterium strain Tigriopus blue green,P. triquetum.Monochrysis lutheri, Exuviella gracilis, Platymonas tetrathele. Cyclotella caspa, Crypthecodinium cohnii, Prasinocladus C5strain,D. viridis, Nannochloris occulata, Tetraselmis gracilis, Anacystis marinum, Rhodosorus marinum, andThalassiosira pseudonana.Nonnutritious:Stichococcus immobilis, Hymenomonassp. strain 150,Syracosphaerasp. strain 181, Tetraselmis verrucosa, Thalassiosira fluviatilis, Microcoleus chthonoplastes, Synechococcus sp.,Pavlova gyrans, Prymnesium parvum, Coccolithus huxleyi, Olisthodiscus luteus, Amphidinium carterii, and Porphyridium aerugineum.There was no apparent relationship between a given taxon and the nutritional value of the group, with the possible exception of the Cryptophyco