65 



at least a one-year period, both before and after drilling commenced. Potential dose-response relationships 

 would be tested by assessing biological changes in benthic assemblages together with concurrent physical or 

 chemical changes in the sediments that were specifically linked to platform discharges. 



What specifically are the potential impacting agents or factors associated with offshore drilling that might alter 

 these hard bottom communities? Other than the obvious physical presence of the platform (i.e., an artificial reef) 

 biological communities at some variable distance around oil and gas development and production platforms are 

 exposed to a variety of platform-associated contaminants (Table 5). The most significant discharges, in terms 

 of volume and composition are drill muds and cuttings (Table 6). Produced waters may be important at some 

 installations, but have not, and will not, been discharged in the Platform Hidalgo region. 



Table 5. Permitted discharges and effluents associated with offshore oil development. 



Drill cutting 

 Drilling fluids 



Cooling water 

 Domestic sewage 

 Sacrificial anodes, 



anti-fouling paints, pipe dope 

 Produced water 



particles of sedimentary rock (up to 900 metric tons per well) 



primarily barium sulfate, clay, ligno-sulfonates, sodium hydroxide with 



some trace metals and hydrocarbons (up to 1000 metric tons per well) 



deck drainage, ballast water (treated) 



treated 



small amounts of Al, Cu, Hg, Pb, Sn, Zn 



saline "fossil water" (up to 1.5 million liters per day) 



Table 6. Ingredients of water-based drilling muds. 



Barite (barium sulfate) 



Bentonite clay 



Lignosulfonates 



Lignin 



Sodium hydroxide 



Sea Water 

 Total = 99 + % 

 Other Additives 



used as a weighting agent 



seals bore-hole and maintains gel strength 



organic polymers from wood lignin, used to control viscosity 



a soft coal used as a clay deflocculant 



maintains pH between 10 and 12, which is needed optimum 



deflocculation 



clay 



Studies at Platform Hidalgo that are dedicated to fishes will begin in the fall of 1989. Entitled "Effects of an 

 OCS Oil and Gas Platform on Rocky Reef Fishes and Fisheries," the project will supplement the CAMP project 

 by adding studies of spatial variation, sublethal effects, and ecological relationships of fishes. In planning for 

 these studies, we recognized that experimental design is limited by having to collect data at depths of 100 to 250 

 m, by the lack of unbiased sampling techniques, and by high sample variance. The mobility of fishes makes 

 the study problematical. For example, conclusions regarding the uptake (or lack of uptake) of contaminants from 

 a point source discharge are tenuous if the distributional history of the species under study is unknown. 

 Nevertheless, MMS is supporting these studies because the perception persists that commercially valuable finfish 

 may be at risk as a result of platform placement or routine platform discharges. 



We selected Platform Hidalgo and the adjacent reefs for the fish studies in part because fishes are known to 

 aggregate on or over rocky outcroppings and topographic features. Such behavior, i.e., a limited home range, 

 should provide the opportunity for tenable hypothesis testing on platform effects to reef associated species. We 



