FOOD PATHWAYS ASSOCIATED WITH PENAEID SHRIMPS IN 

 A MANGROVEFRINGED ESTUARY 



Allan W. Stoneri and Roger J. Zimmerman^ 



ABSTRACT 



High abundance and production of juvenile Penaeus spp. in tropical estuaries has been attributed to high 

 concentrations of mangrove-derived detritus in the nursery habitats. Examination of the diets o{ Penaeus 

 notialis, P. subtilis, and P. brasiliensis in the mangrove-fringed Laguna Joyuda, Puerto Rico showed 

 that even the smallest juveniles are predators consuming capitellid polychaetes (20-38% of diets) and 

 amphipods (20-76%). Less than 25% of the diets was detritus. Ontogenetic variation in diets was greater 

 than interspecific variation, and there was no evidence for dietary separation among the sympatric species. 

 Seasonal shifts in foods reflected abundance patterns of macrobenthic prey species. Despite the con- 

 sumption of prey organisms generally classified as detritivorous, stable carbon isotope ratios in the 

 penaeids (-18.1 to -15.0"/oo), their food items (-18.8 to -17.7''/oo), and primary producers indicated 

 that shrimps and the majority of sediment dwellers in Laguna Joyuda obtain most of their carbon from 

 benthic algae (-14.4°/oo) and not from mangrove detritus (-25.0 to -22.9°/oo). 



The juveniles of penaeid shrimps are abundant in 

 many tropical and subtropical estuaries of the world, 

 particularly where wetland habitats such as marsh 

 grasses or mangroves are prominent coastal fea- 

 tures (Edwards 1978; Staples 1980; Stoner 1988). 

 The relationship between wetlands and commercial 

 shrimp has been attributed to at least two factors: 

 high food abundance and shelter from predators, the 

 relative importance of which is still debated (Boesch 

 and Turner 1984). Early wetland studies (Odum and 

 Heald 1972, 1975) suggested that a large variety of 

 fishes and invertebrates including Penaeus spp. 

 were directly dependent upon detritus from the 

 vascular wetland plants. More specific studies of 

 penaeid diets have since revealed that the shrimps 

 are omnivorous or carnivorous in many shallow- 

 water habitats (Moriarty 1976, 1977; Chong and 

 Sasekumar 1981; Moriarty and Barclay 1981) and 

 that some species may have a direct influence on 

 the abundance of small macrofauna (Leber 1983, 

 1985). 



The most important commercial shrimp species 

 in the Caribbean Sea and along the north coast of 

 South America are Penaeus notialis, P. subtilis, P. 

 brasiliensis, and P. schmitti, all of which have 

 nurseries in coastal wetland habitats (Stoner 1988). 



'Center for Energy and Environment Research, University of 

 Puerto Rico, Mayaguez, Puerto Rico 00708; present address; Carib- 

 bean Marine Research Center, 100 E. 17th Street, Riviera Beach, 

 FL 33404 and Lee Stocking Island, Exuma Cays, Bahamas. 



^Southeast Fisheries Center Galveston Laboratory, National 

 Marine Fisheries Service, NOAA, 2700 Avenue U, Galveston, TX 

 77550. 



Although the biology of tropical Atlantic penaeids 

 has been studied in a few localities (Neiva 1969; 

 Nikolic and Ruiz 1969; Lindner 1971; Garcia 1974; 

 Garcia et al. 1985), we have found no information 

 on their diets. 



Examinations of shrimp diets reported here were 

 conducted in a small coastal lagoon in Puerto Rico 

 where Penaeus populations are large and where four 

 species coexist (Stoner 1988). In this report, diets 

 of the three most abundant Penaeus species are 

 described with particular reference to ontogenetic 

 variation, similarities among the species, the sig- 

 nificance of detritus, and seasonality in diets as 

 related to the abundance of foods in the field. 



Because foods are retained and assimilated differ- 

 entially in the gut, examination of gut contents does 

 not necessarily give a true indication of the relative 

 importance of foods. For example, detritus has been 

 reported as a significant component of the gut con- 

 tents of Penaeus spp. (Odum and Heald 1972), but 

 detritus is known to be indigestible compared with 

 soft-bodied prey organisms such as polychaetes. 

 Furthermore, in the case of predators, the primary 

 source of carbon is not revealed through gut anal- 

 ysis. For these reasons, stable carbon isotope ratios 

 were measured for Penaeus spp. and most other 

 organisms common in the lagoon. 



METHODS AND MATERIALS 



Shrimps were collected in Laguna Joyuda on the 

 west coast of Puerto Rico Gat. 18°07'N, long. 



Manuscript accepted March 1988. 



FISHERY BULLETIN: VOL. 86, NO. 3, 1988, ^t^^-ST ) 



543 



