subdivide the northern gulf into faunal provinces, ranging from two 

 divisions by Deevey (1950) to 27 by Pequegnat (1973) which, in turn, are 

 usually subdivided into depth zones (Parker 1960; Defenbaugh 1976). 

 Pulley (1952) divided the Texas-Louisiana shelf into two provinces based 

 upon bivalve distributions (Figure 16); Parker (1960), using a broader 

 array of macroinvertebrates obtained mostly by grabs, separated the area 

 into four provinces, also subdivided by depth zones (Figure 17). Parker 

 (1960) and Gunter (1967) pointed out that the nearshore gulf between the 

 delta and Sabine, Texas, is particularly notable because estuarine 

 conditions extend offshore. 



Basing his conclusions largely upon macroinvertebrates taken by 

 trawling and using historical data, Defenbaugh (1976) determined that 

 the Texas-Louisiana shelf was characterized by five faunal assemblages 

 primarily zoned by depth (Figure 18). The primary depth zones were from 

 4 to 20 m, 20 to 60 m, and from 60 to 120 m. In his treatment of the 

 shelf, Defenbaugh (1976) also included submarine bank assemblages (20 to 

 100 m) and a pro-delta fan assemblage (4 to 20 m) . 



Chittenden and McEachran (1976) described the zonation of the 

 demersal fish assemblages of the Gulf of Mexico, noting that 

 characteristic communities were associated with each of the major shrimp 

 species, which, on a gulfwide basis, have distributions closely matching 

 the major classes of sediment. White and brown shrimp ( Penaeus 

 setiferus and 2*. azteoua , respectively) occupy terrigenous muds which 

 predominate in the western gulf while pink shrimp ( £*_ duorarum ) occur 

 on calcareous sediments characteristic of the eastern gulf (Springer and 

 Bullis 1954; Hildebrand 1954, 1955; Osborne et al. 1969). Williams 

 (1958) showed that shrimp actively select these substrates, and similar 

 sediment-associated distribution has been demonstrated for many demersal 

 fish species (e.g. Hildebrand 1955; Miller 1959; Dawson 1964; Topp and 

 Hoff 1972). 



Chittenden and McEachran (1976) divided the white and brown shrimp 

 ground demersal fish communities of the northwestern gulf 

 bathymetrically, observing that the white shrimp ground assemblage 

 extended from about 3 to 22 m and the brown shrimp ground fish 

 assemblage was characteristic from 22 to 110 m. They noted that, 

 inshore, the bathymetric distribution of the white and brown shrimp 

 communities was not constant throughout, but was apparently affected by 

 salinity and/or associated factors. The white shrimp assemblage was 

 noted to be most developed and abundant offshore of Louisiana where 

 estuarine conditions extend into the gulf and least developed and 

 abundant west of the central Texas coast where climatic conditions 

 become more arid (Chittenden and McEachran 1976 and references therein). 



Although the pink shrimp community is best developed in the eastern 

 gulf which is predominantly characterized by calcareous sediments, 

 disjunct pink shrimp communities are scattered throughout the 

 Texas-Louisiana shelf at depths of 45 to 64 m where appropriate 



29 



