Clark et al.: A habitat-use model for juvenile Farfantepenaeus aztecus in Galveston Bay 



271 



spring 



summer 



winter 



Predicted density (#/m 2 ) 



m 0-0.12 



0.13-1.51 

 1.52-2.72 

 2.73-5.46 

 ■I 5.47-14.85 



Figure 7 



Seasonal spatial distribution maps of predicted densities for brown shrimp (F. aztecus). 



in SAV and 858.7 million shrimp in SNB. We used marsh 

 edge densities to estimate 473.5 million shrimp in regu- 

 larly flooded vegetation or about 55,700 shrimp per hectare 

 of this habitat type. 



Discussion 



Various factors are considered important in defining 

 nursery areas for juvenile estuarine-dependent organ- 

 isms; however, the specific contributions of these factors 

 are poorly understood (Beck et al., 2001). Specific combi- 

 nations of physiochemical conditions and cyclic primary 

 production that are related to food availability, growth, 

 and sanctuary from predation often define optimal envi- 

 ronments (Miller and Dunn, 1980). Barry et al. (1999) 

 considered prey availability to be a necessary component 

 defining the nursery function of estuarine habitats. 



Shrimp and blue crab production has been correlated with 

 the availability of wetland habitat in estuaries (Turner, 

 1977; Zimmerman et al., 2000). In the present study, 

 brown shrimp were most abundant in the lower bay where 

 vegetated habitats were most abundant. Zimmerman et al. 

 ( 1990b) reported that benthic infauna are most abundant 

 in vegetated habitats within lower Galveston Bay and 

 are nutritionally important for penaeids (Zein-Eldin and 

 Renaud, 1986; McTigue and Zimmerman, 1991, 1998). 

 In addition, field and laboratory experiments have shown 

 that brown shrimp growth is positively correlated with 

 the abundance of marsh epiphytes and phytoplankton 

 (Gleason and Zimmerman, 1984). 



Most estuarine nekton are adaptable to the highly 

 dynamic environmental conditions exhibited within es- 

 tuaries (Gifford, 1962; Tagatz, 1971; Zimmerman et al., 

 1990b). These organisms are commonly found in a wide 

 range of salinities and temperatures and are most affected 

 by sudden changes in these environmental conditions 



