APPENDIX E 



Utilization of Estuarine Organic 

 Matter During Growth and Migration 

 by Juvenile Brown Shrimp Penaeus 

 aztecus in a South Texas Estuary 



p. Riera Centre de Recherche en Ecologie Marine et Aquaculture de L'Houmeaii, France 



P.A. Montagna University of Texas at Austin, Marine Science Institute 



R. D. Kalke University of Texas at Austin, Marine Science Institute 



P. Richard University of Texas at Austin, Marine Science Institute 



In Press in: Marine Eco/o^-Prvgress Series 



ABSTRACT: The trophic dynamic links of migratory juvenile brown shrimp Penaeus as^tecus were investigated 

 along the South Texas coast from the i\ransas Pass to Corpus Christi and Nueces Bay and to the nursery 

 ground in the Nueces Delta. Shrimps and their potential food sources were measured for 6'^C and 6'^N ratios 

 between December 1995 and July 1996. During this period, shrimp length increased from 10-11 mm when the 

 animals entered Corpus Christi Bay as larvae to 80-90 mm when they returned to Mexico Gulf as subadults. 

 Brown shrimp exhibited spatial and temporal 6'^C variation (from -25.2 to 12.5%o) indicating a high diversity of 

 food sources throughout their migration. From o"C values, the main sources used as food sources by juvenile 

 brown shrimp in the Rincon Bayou marsh, were Spartina altemiflora and Spartina spartinae detritus and benthic 

 diatoms. o'^C and o'^N values showed that organic matter inputs carried by the river inflow can also contribute 

 significandy to the feeding of migratory brown shrimp. In these marsh habitats, shrimp isotopic ratios changed 

 rapidly suggesting high tissue turnover rates. The study showed that coastal marshes after restoration through 

 the introduction of freshwater inflow may provide feeding habitats favorable for growth and development of 

 juvenile brown shrimp. 



KEY WORDS: Penaeus a^eats, food sources, migration, nursery area, 6"C and 6''N 



INTRODUCTION 



Many marine species utilize salt marshes, coastal lagoons and estuaries dixring part of their life cycle (Day et al. 

 1989). The brown shrimp, Penaeus aztecus Ives, is widely distributed along the Texas coastline where it is an 

 important commercial fishery. Like most penaeids, the life history of brown shrimp is complex (Dall et al. 

 1990). In the Gulf of Mexico, after offshore spawning, post-larval brown shrimps are carried by on-shore water 

 movement and enter bays and shallow estuarine waters where they generally find productive areas and are 

 protected from storms and predators (Day et al. 1989, Fry 1981). Following growth of juvenile shrimp in 

 nursery areas there is a subsequent offshore migration of subadults to complete their life cycle. More precisely, 

 throughout the Texas bay systems, most of the larval brown shrimp enter marine bays from late winter through 

 early spring, spend about 3-4 months in estuarine nursery grounds, and return to the offshore Gulf of Mexico 

 in eady summer (Moffett 1970). However, the shrimp fishery is an exploited resource in the Gulf of Mexico 

 (Parker et al. 1988). Restoration of coastal marshes, which act as nurseries, could contribute to increased brown 

 shrimp populations because the marshes provide habitats for juveniles. Enhancing freshwater inflow may have 

 at least two beneficial effects for restoring shrimp habitats: terrestrial inputs may be used as food sources 



Appendix E ♦ E-1 



