A δ13C Study of the Feeding Habits in Four Mediterranean Leptomysis species (Crustacea: Mysidacea)

Abstract

Abstract. Mediterranean Leptomysis species are bentho‐nectonic shrimps living close to seagrass bed bottoms, forming swarms during the day and feeding on detritus and sedimentary organic matter during the night. As this matter is derived from different plant sources (phytoplankton, seagrasses, macro‐ and microalgae), assimilated carbon entering mysid tissues can hardly be identified on the basis of digestive tract analyses. Stable carbon isotope ratio measurements help to delineate food sources of the different studied Leptomysis species because plants are distinct isotopically. These 6°C measurements reinforce the view of the minor role of seagrass carbon in benthic food webs and of the importance of algae in the dynamics of these ecosystems.SummaryFour Leptomysis species inhabit three relatively closely adjoining biotopes in the Gulf of Calvi: L. lingvura near the surface, forming shoals within rock blocks, L. posidoniae in Posidonia seagrass beds, and the couple L. heterophila +L. gracilis at the lower border of the infralittoral zone. These three biotopes are characterized by different main plant food sources (namely macroalgae, seagrasses, and phy‐toplankton), which are C isotopically well separated. δ13C measurements of the different Leptomysis populations show that these shrimps do not feed preferentially on the carbon source prevailing in their own biotope, but rather have an isotope ratio (‐16.5 to ‐20%0) close to the algal ratio. These observations can either be explained by feeding selectivity or by a differential assimilation rate of ingested material; in any case, they corroborate the role of algae in the trophodynamics of Mediterranean seagrass ecosystems.