INTRODUCTION 



Biological investigations in the Gulf of Mexico have a long 

 history, beginning in earnest during the period 1877 to 1880 (Agassiz 

 1888) and continuing to the present. In contrast to other marine areas, 

 offshore oil and gas exploration and production activities in the open 

 gulf also have a long history, dating from March 1938 when a well was 

 drilled 2.4 km from the coastline of Louisiana (Bedinger et al. 1980). 

 Danenberger (1976) reported that during the period 1947-75, some 13,000 

 wells had been drilled in Federal waters of the Gulf of Mexico and, 

 during 1971-75, production from the gulf accounted for more than 10 $ of 

 the Nation's domestic crude oil production, and approximately 15 $ of 

 the natural gas production. Danenberger (1976) further noted that at 

 the end of 1975, there were approximately 65 mobile drilling units 

 operating in the Gulf of Mexico in water depths as great as 541 m; that 

 a total of 2,079 platforms were in operation in gulf waters up to 114 m 

 deep; and that one platform was being constructed in the gulf in water 

 deeper than 305 m. 



More recently, Jackson (1979) reported that there were 3»342 

 petroleum platforms operating in the gulf, some as much as 220 km from 

 shore and in waters up to 525 m deep. Based upon figures provided by 

 the United States Geological Survey (USGS), some 2,437 of these 

 platforms were in place in Federal waters as of March 1980, and that, 

 within this area, 17,407 wells had been completed. By 1985, 14.5$ of 

 the domestic crude oil demand and 33.4$ of the domestic gas demand will 

 be supplied by Gulf of Mexico production (U.S. Army Corps of Engineers 

 1973). 



If petroleum development activities constitute a real threat to 

 marine ecosystems, the Gulf of Mexico could be among the first places in 

 the Western Hemisphere to experience degradation of its biological 

 resources (Sharp 1979). This should be especially true for the region 

 of the Texas-Louisiana continental shelf lying between the Mississippi 

 River Delta and Matagorda Bay, Texas, because (1) the area has been 

 intensively developed (Figure 1), and (2) in a general sense, it is 

 relatively isolated from eastern gulf water masses by the overall 

 circulation patterns described in a later section. 



Although ecological investigations generally intensified in the 

 gulf from the early 1900's through the 1970's (see Pequegnat 1976 for a 

 recent review) , most studies were, by design, of a survey and 

 descriptive nature. Although some early studies addressed the effects 

 of oil and gas development on estuarine systems of the gulf (see Mackin 



