Lipid Contents and Fatty Acid Compositions of Idotea baltica andSphaeroma serratum (Crustacea: Isopoda) as Indicators of FoodSources

Lipid contents and fatty acid compositions of Idotea baltica and Sphaeroma serratum (Crustacea: Isopoda) as indicators of food sources. Zoological Studies 51(1): 38-50. The lipid and fatty acid (FA) compositions of Idotea baltica and Sphaeroma serratum, from Mar Piccolo basin at Taranto (Ionian Sea), Italy, were analyzed during winter and summer to assess their feeding habits. The 2 isopods showed strong similarities in total lipid contents. Phospholipids (PLs) were the major lipid class in both species, followed by triacylglycerols (TAGs). A low proportion of energystorage lipids suggested a regular food supply. Twenty-seven fatty acids were identified in the species studied. Unsaturated FAs (UFAs) represented the predominant proportion in both species in the seasons studied. Among them, monounsaturated FAs (MUFAs) showed higher levels. Regarding FAs corresponding to the potential food of the 2 isopods studied, I. baltica and S. serratum displayed different FA profiles. Large amounts of 18:2n-6 and18:3n-3 were found, especially in S. serratum suggesting a specific selection of phytodetritus from green algae or terrestrial material of neighboring vegetation. The FA marker for diatoms of I. baltica differed from that of S. serratum, although both species showed major consumption of diatoms during summer. Idotea baltica showed higher levels of 22:6n-3 and 20:4n-6 in winter suggesting a preference for dinoflagellates and macroalgae in this period. High levels of the carnivorous marker (the 18:1n-9/18:1n-7 ratio) reflected consumption of animal materials, especially in winter. Examination of trophic markers indicated that I. baltica and S. serratum consumed a mixed diet, showing that they have the ability to choose among available food sources.