sediments occur (Chittenden and McEachran 1976). These authors also 

 noted that areas of topographic relief in the northwestern gulf were 

 characterized by distinctive assemblages which, in the southern gulf, 

 corresponded (in part) to Robins' (1971) tropical insular fauna. 



Most of the above studies draw largely upon studies of soft-bottom 

 communities. However, hard bank communities are abundantly represented 

 along the Texas-Louisiana continental shelf and include both natural and 

 artificial habitats, the latter particularly dominated by petroleum 

 platforms (see Figure 1). The communities characteristically utilizing 

 these two classes of habitats consist of a sessile epifauna which 

 provide habitat and/or food for an intimately associated cryptic fauna 

 and food for an assemblage of fish which graze on epifauna. These 

 assemblages are complemented by large aggregations of (1) 

 plankton- feeding pelagic fishes and their predators, and (2) benthic 

 reef fish (particularly snappers, Lutjanidae; and groupers, Serranidae). 

 The latter two categories include both permanent residents and 

 short-term, seasonal residents. 



Results of studies performed offshore of Louisiana demonstrate that 

 there is faunal zona ti on of reef communities related to depth. Sonnier 

 et al. (1976) noted that a tropical fauna was characteristic of reefs 

 located in depths of 90 to 180 m, but inshore, temperate species were 

 characteristic. Gall away et al. (1980) determined that there were 

 three major platform or reef assemblages represented offshore 

 Louisiana — a coastal assemblage (to about 27 n), an offshore assemblage 

 (27 to 64 m) , and a blue water or tropical assemblage (>64 m) . 



Nearly all of the zoogeographic treatments described above and 

 references therein are in agreement that there is a distinct 

 northwestern Gulf of Mexico nearshore faunal assemblage of Carolinean 

 origin extending from the humid area of the delta towards the southwest 

 where it is ultimately replaced by the "Mexican Province" fauna (Pulley 

 1952). There is no general agreement with respect to placement of the 

 boundary between these two provinces, or how the transitional zone 

 between them should be defined. For the assessment purposes of this 

 paper, I follow the treatment by Pulley (1952), and define the 

 boundaries of the system of interest as being the Texas-Louisiana shelf 

 (out to 118 m) west of the delta to about Matagorda Bay (Figure 19). 

 This area includes the humid and wet, sub-humid climatic zones of Parker 

 (1960) and is greatly influenced by freshwater discharge from major 

 river (primarily the Mississippi and Atchafalaya system) and 

 low-salinity estuarine systems. South of this area, climatic conditions 

 grade from dry, sub-humid to semi-arid; and river discharge is minimal 

 which results in the estuaries becoming exceedingly more saline. The 

 defined system of interest also appears to be delimited by temperature, 

 and was classified by Parker (1960) as "Warm- temperate" in contrast to 

 most of the remainder of the shelf which he called "warm-subtropical." 

 Although the major faunal assemblages of the defined system extend 

 southward (and examples will be drawn from studies performed in this 

 area) , the region of about Matagorda Bay marks an area where species 



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