ABSTRACT: Carbon and nitrogen stable isotopes were used to determine the main food sources of the 4 tropical Caribbean thalassinidean shrimps Glypturus acanthochirus, Corallianassa longiventris, Axiopsis serratifrons and Neocallichirus grandimana. By using the isotopic signatures of 5 to 6 potential food items, the signatures of the shrimps were modelled to determine feasible combinations of these sources. For G. acanthochirus, microalgae mats on the sediment surface, dominated by cyanobacteria and to a lesser degree by diatoms, were the most important food item. C. longiventris and A. serratifrons (2 isotopically almost identical species which both capture drifting plant debris) relied mainly on the detrital leaves of the dominant seagrasses Thalassia testudinum and Syringodium filiforme (and also on drifting brown algae). The wall lining of C. longiventris’ burrows also had some relevance as a dietary source. The diet of N. grandimana was less clear: no combination of potential food sources sampled could model this shrimp’s isotopic signature. For this species, the smallest organic particles in the ambient sediment around the burrows, together with the burrow wall lining, may serve as a nitrogen source; the main carbon source of this species remains unknown. For the 3 species with conclusive diets, the low organic content of tropical littoral sediments may help explain their predominant reliance on more nutritious food sources foraged from the sediment surface. With regard to nutrition, the subsurface areas of the burrows function only as places where food is processed rather than acquired.