Carbon and nitrogen sources for shrimp postlarvae fed natural diets from a tropical mangrove system

Postlarvae of Penaeus vannamei were fed various diets in order to examine the importance of detritus and other possible prey items in supporting postlarval growth. Stable isotopes (C and N) were used to determine the carbon and nitrogen source of the prey in the various diets. The zooplankton diet contained mostly copepods. The subtidal detritus treatment consisted mostly of plant material whereas the diets from both intertidal sites contained a mixture of plant detritus and associated meiofauna. Postlarvae reared on zooplankton and detritus plus meiofauna diets more than tripled their weight during a 6-day period. In contrast, postlarvae fed the detritus diet barely doubled their weight. Based on isotopic composition, postlarvae appear to obtain their carbon and nitrogen from various food sources. Postlarvae were enriched by 0.4 parts per thousand in C-13 and 2.7 parts per thousand in N-15 relative to the zooplankton diet, which is consistent with isotopic fractionation between successive trophic levels. In rum, the isotopic signal of the zooplankton was consistent with phytoplankton being the initial source of organic matter. In contrast, mean delta(13)C values of the shrimp fed detritus plus meiofauna were significantly different from their respective diets. Isotopic ratios of the postlarvae fed the mixed diet from Chomes were two trophic levels above benthic algae suggesting that the shrimp preyed on organisms that derived their carbon and nitrogen from benthic algae and/or phytoplankton. (C) 1997 Academic Press Limited.