Resources partitioning among co-existing suspension-feeding bivalves - Cyclina sinensis, Gafrarium tumidum, Katelysia japonica, Psammotaea elongata and Semele carnicolor on Tomigusuku intertidal flat, Okinawa was investigated using fatty acid (FA) biomarkers during the cold (January 2001) and warm seasons (July 2001). P. elongata is the most dominant infaunal species. Other species are semi-infaunal and minority on the tidal flat. The total FA methyl esters (FAMEs) content during both seasons was significantly higher in the tissues of P. elongata and S. carnicolor than in C. sinensis, G. tumidum and K. japonica. P. elongata showed most unique fatty acid characteristics compared to other species during the cold–season: low percentage of w3 and w6 polyunsaturated FAs (PUFA; 11.5% of total FAMEs) compared to others (23.6 to 37.3%), highest percentage of odd-numbered branched FAs (odd-BrFAs; 5.7 %), the revelation of even-numbered long-chain FAs (0.7%), and the lowest value of PUFA/saturated FA (SAFA), PUFA/monounsaturated FA (MUFA), 16:1w7/16:0 and w3/w6 PUFA ratios. Analysis of specific FA markers (irrespective to their mean percentage) showed a significant contribution of diatom (16:1w7 and 20:5w3), dinoflagellates (18:4w3 and 22:6w3), bacterial (odd-BrFAs and 18:1w7) and green macroalgal (18:2w6 and 18:3w3) markers in all bivalves during the cold-warm seasons. These indicate that the coexisting bivalves on Tomigusuku tidal flat utilize the same food sources, originating from phytoplankton, benthic microalgae, macroalgae detritus and bacteria. However, with references to the concentration of total FAMEs in all species, the level of most FAs (SAFA, MUFA, PUFA) and FA markers of food sources was significantly higher in P. elongata and S. carnicolor, suggesting that these bivalve species accumulate food more than other species. Because P. elongata is a deep burrower, this behaviour might have increased its survival rate and therefore its greater abundance on Tomigusuku tidal flat compared to other suspension-feeding bivalves.