Hydrobiologia 306: 1-6, 1995. 1 ( 1995 Kluwer Academic Publishers. Printed in Belgium. Particulate lipid class composition of three marine phytoplankters Chaetoceros gracilis, Isochrysis galbana (Tahiti) and Dunaliella tertiolecta grown in batch culture A. T. Lombardi' & P. J. Wangersky 2 Department of Oceanography, Dalhousie University, Halifax, N.S. B3H 4J1, Canada 'Present address: Universidade Estadual de Campinas, Instituto de Qumica, Depto. Qutmica Analitica, C.P 6154 Campinas - SP, 13081, Brazil 2 Present address: School of Earth and Ocean Sciences, University of Victoria, P.O. Box 1700, Victoria, BC, V8W 2Y2, Canada Received 12 October 1993; in revised form 15 March 1994; accepted 21 April 1994 Key words: Chaetoceros gracilis, Dunaliella tertiolecta, Isochrysis galbana, phytoplankton, lipids, algal culture Abstract The green algae D. tertiolecta, the flagellate I. galbana and the diatom C. gracilis were grown in batch cultures. The organisms were analysed for lipid class composition at the logarithmic and stationary growth phases using the Chromarod-Iatroscan thin layer chromatography with flame ionization detection (TLC-FID) system. There were major differences in lipid class production among the organisms investigated, but few differences in lipid class distribution between log phase and stationary phase cultures of D. tertiolecta and I. galbana. C. gra- cilis displayed the general trend exhibited in diatom metabolism, which can be characterized by an increase in triacylglycerol synthesis in situations of stress. Introduction Interest in algal production of economically important molecules such as lipids has increased in the past few decades, mainly due to applications in aquaculture, where various phytoplankton species are used as food for larval and adult molluscs (Chu & Dupuy, 1980). One of the more common food choices for American oyster larvae, the flagellate Isochrysis galbana, also produces high levels of the unsaturated fatty acid 22: 6w3 (Enright et al., 1986). The utilization of lipid- rich algae for commercial production of hydrocarbons may be viewed as a possible approach to the linked objectives of wastewater treatment and liquid fuel pro- duction (Shifrin & Chisholm, 1980). It has been shown that the production and stor- age of lipids by phytoplankton cells is regulated by environmental factors, such as light intensity, nutrient stress, and temperature (Morris et al., 1983; Parrish & Wangersky, 1987). Several marine and freshwater phy- toplankton species accumulate total lipids as a result of nitrogen, phosphorus, or silicon starvation (Collyer & Fogg, 1955; Shifrin & Chisholm, 1981; Roessler, 1988; Lombardi & Wangersky, 1991). Some species of the unicellular green alga Dunaliella have been studied because of their tolerance to a wide range of salinities, to which they adapt by the production of glycerol for osmoregulation (Ben-Amotz et al., 1982). In waters such as the Dead Sea, this production can become commercially viable. The screening of both commer- cially viable lipids and situations which favor such production in a microalga is promising if the present limitation of Earth's resources is considered. Most of the studies on lipid production by microal- gae have been concerned with total lipids or only with fatty acids. Considering that lipids are a heterogeneous group of compounds of various structures and func- tions, united only in their definition, which is based on organic solvent solubility, the measurement of total lipids may mask trends to be found in the individual lipids and lipid classes (Parrish & Wangersky, 1987). For physiological and ecological studies, analysis for