Large oil spill3 in the gulf undoubtedly kill many individuals of 

 some susceptible species and may result in tissue contamination of many 

 individuals which are exposed to elevated but sub-lethal concentrations. 

 Both are seemingly short-term effects, but to extrapolate from a single 

 event impacting a population that may be poorly known itself to a 

 long-term prediction regarding that population's and the system's 

 response is not possible given the kinds of data that are typically 

 available (e.g. relative abundance, hydrocarbon levels, bioassay) . 



CUMULATIVE IMPACTS ON THE SYSTEM 



As described above, most studies which have been performed with the 

 goal of delineating oil and gas development activities on the shelf 

 ecosystem have essentially been conventional baseline studies of the 

 relative abundance of ecosystem components. Generally, these studies 

 have attempted to relate observed biological differences to 

 environmental variables, particularly specific contaminants such as 

 hydrocarbons which can be toxic at elevated levels. Two important 

 lessons have emerged from these studies. First, the ecosystem 

 components have been found to be highly variable and difficult to 

 measure; and, for assessment purposes, it has been, and is, exceedingly 

 difficult to establish adequate controls. Second, even when biological 

 differences have been determined and experimentally related to 

 contaminant discharges, the significance of the findings has been 

 difficult to evaluate at the population or system level as very little 

 is known about the physical and biological processes which govern or 

 regulate the nearshore, continental shelf ecosystem. 



It would appear that the impacts of offshore oil and gas 

 development activities on the shelf ecosystem per se have been minimal. 

 Hydrocarbon loadings from these activities are small in comparison to 

 other sources, and concentrations of discharged contaminants at toxic 

 levels have been seldomly observed in the environment, except perhaps at 

 the "end of the pipe" or in the cases of accidental, massive spills of 

 hydrocarbons. Even in the case of a large spill, physical and microbial 

 processes serve to quickly dissipate and reduce or change the nature and 

 toxicity of hydrocarbons and other contaminants. Apparent recovery of 

 affected areas is rapid, usually within a year. 



The Texas-Louisiana shelf environment is highly variable and one 

 which has long been exposed to hydrocarbon inputs through natural oil 

 and gas seeps. The marked variability of the shelf environment has 

 probably served to "temper" the system, resulting in a high degree of 

 biological resiliency. Typical life cycles of system components are 

 short and sexual maturity is attained rapidly. Characteristically, 

 adults produce young in excessive numbers, and few adults are required 

 to re-establish populations. Descriptions of species and size 

 compositions of shrimp ground faunal assemblages provided by Gunter 

 (1938, 19^5) and Hildebrand (1954) are remarkably similar to more recent 



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