THE ECOSYSTEM AS A RECIPIENT OF OIL 

 AND GAS DEVELOPMENT ACTIVITIES 

 AND EFFLUENTS 



In the preceding sections, the Mississippi River has been suggested 

 to be a dominant environmental factor acting on the Texas-Louisiana 

 shelf ecosystem. In effect, the river sets the limits for community 

 productivity and distributional patterns. The effects of man-made 

 physical alterations of the river and contaminant discharges into the 

 river have not been adequately addressed, but a case could easily be 

 made suggesting that such activities already have had overriding effects 

 on the Texas- Louisiana shelf ecosystem. For example, white shrimp 

 landings peaked in the early 19^0's at about 65,000 metric tons. The 

 fishery declined markedly in the late 1940's, and catches have 

 fluctuated erratically since that time (e.g. from 14,000 to 36,000 

 metric tons between 1957-65). The marked drop in white shrimp 

 production also corresponds with the general period during which the low 

 oxygen phenomenon offshore of Louisiana was first being discovered and 

 rediscovered. Further, the present distributional and relative 

 abundance patterns of white shrimp, based upon fishery landings (Klima, 

 undated manuscript), reflect a low abundance of white shrimp in the area 

 historically characterized by seasonal oxygen deficiencies (e.g. 

 compare Figures 13 and 22). In any assessment of the Texas-Louisiana 

 shelf, the effects of channelization and industrialization of the 

 Mississippi River cannot be taken lightly, and possibly overshadow all 

 other development activities. 



EFFECTS OF STRUCTURES 



One effect of oil and gas development activities on the shelf is 

 immediately obvious — the addition of hard substrate extending from the 

 bottom to above the water's surface. These substrates serve as focal 

 points for rich and diverse biofouling communities and a complex 

 assemblage of platform-associated macrobiota as described in preceding 

 sections. Fish which would normally be found scattered throughout a 

 large area are concentrated in the immediate vicinity of platforms, 

 attracted to the food and/or shelter they provide. Such concentrations 

 are commonly referred to in the literature as the "reef" or "artificial 

 reef effect of platforms. 



The red snapper is one of the more important species attracted to 

 petroleum platforms in that it supports sports and commercial fisheries. 

 The life history of red snapper follows the generalized pattern 



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