Stable Carbon and Nitrogen Isotope Ratios of Penaeid Juveniles and Primary Producers in a Riverine Mangrove in Guimaras, Philippines

Stable carbon and nitrogen isotope ratios were analyzed for primary producers and juveniles of four penaeid species (Metapenaeus ensis, Penaeus indicus, P. merquiensis and P. monodon) in a riverine mangrove in Guimaras, central Philippines. δ¹³C values of shrimp (– 15.5 to – 19.6‰) were closer to phytoplankton (–23.8‰) and possibly epiphytic algae (–24.2‰) than to mangrove leaves (–26.9 to –30.0‰) or detritus (–28.0‰). Differences in δ¹⁵N values suggested 2–3 trophic shifts between phytoplankton (0.6‰) and shrimp (6.9‰), assuming a 2.4‰ enrichment per trophic level. There were no significant differences in δ¹³C and δ¹⁵N ratios between green and decomposing leaves, and among mangrove species, shrimp species and different size groups of shrimp.