Food resources of postlarval brown shrimp (Penaeus aztecus) in a Texas salt marsh

Field and laboratory experiments were conducted to identify the sources of food in the natural diet of postlarval brown shrimp (Penaeus aztecus Ives). A series of enclosures placed in East Lagoon (29°20N; 94°45W) on Galveston Island, Texas, USA, in May 1985, were used to evaluate the individual and combined contribution of Spartina alterniflora detritus, epiphytes of S. alterniflora, plankton, and demersal fauna in terms of differences in shrimp growth and carbon assimilation (stable carbon-isotope analysis). Demersal fauna (harpacticoid copepods, amphipods, tanaids and polychaete annelids), and plankton (>0.095 mm) accounted for approximately 53 and 47% of the growth of the postlarvae (11 to 22 mm rostrum-telson length), respectively, while the autochthonous plant substrates, S. alterniflora detritus and epiphytes, contributed little. Laboratory experiments confirm that a mixed diet consisting of both animal protein and phytoplankton promotes maximum growth. Our results indicate that plankton may be an important allochthonous source of carbon contributing to the growth and development of shrimp in the salt marsh.