<div><div><div><p>The potential effects of the oil industry on the Sonda de Campeche (SC) marine ecosystem are of high relevance for our society due to the wealth of living and fossil fuel resources found in this sector of the Gulf of Mexico. An ecological or environmental risk analysis can be understood like an assessment procedure that allows determining the probability that adverse ecological effects exist or may occur, as a result of one or several stressor factors. The oil industry operations (PEMEX) constitute potential stressor factors acting upon a large marine ecosystem- Sonda de Campeche-, during the last 2.5 decades. PEMEX, like a chemical stressor factor, chronically or accidentally introduces organic and inorganic substances to the marine environment; similarly, as a physical stressor, causes further ecological disturbances due to the offshore oil rigs construction for exploration, extraction, services, etc., and by the installation of facilities on the coast for transport, pumping and storage of crude oil. In the marine ecosystem, each living subcomponent (plankton, benthos, and nekton) exhibits its own resilient (capacity) when is being exposed to stressor factors such as: drilling muds, trace metals, hydrocarbons, etc. Important boundaries or ecotones in the SC are the two sedimentary provinces in the study area (carbonate-terrigeneous) whose surface extends by more than 34.000 km2; the offshore area where most of the oil fields are located, known as exclusion zone (ca. 1250 km2), encompasses nearly 176 fixed drilling platforms, eight autoelevables and two submersibles. A physical stressor of moderate environmental impact is represented by the network of pipelines that radiate from this zone, towards Dos Bocas and to the large buoy anchored off Arcas Reef. The exploration and fossil hydrocarbon extraction operations in the SC cause two levels of ecological effects. Firstly, severe effects are observed on the adjacent costal ecosystem due to the reduction or permanent removal of aquatic vascular plants. This disturbance is evident and predictable. Substratum alterations caused by dredging, opening of channels, pipe lines and platforms in the coastal and marine environment, produce flora and fauna changes of different complexity. Secondly, in the marine ecosystem potential alterations derived from the oil industry are attenuated by the buffer capacity of the tropical system itself. In this system, normal patterns of variability are recognized in each living subcomponent; such patterns are somewhat compensated by internal homeostatic mechanisms which contribute to maintain the energy and organic matter flow equilibrium. A preliminary study of the organic carbon flow in the SC, shows a system subsidized by the input of organic materials of continental origin, whose final destiny is the shelf-benthic subcomponent and the adjacent deep-sea. Should this subsidizing process be disturbed by either natural or anthropogenic events, unfavorable ecological conditions at the system level can be expected to occur.</p><p>The attempt to identify the system response to chronic anthropogenic effects in the SC was precluded by the void of precise data on most of the marine ecosystem subcomponents. Potential signals of change or impact are mostly local or ill defined, with the exception of those of toxicity recorded at species level. Under conditions of disturbance caused by accidental fossil hydrocarbon spills, biodiversity and biomass of both phytoplankton and zooplankton are reduced; presumably, their attain equilibrium conditions after 40 days, when the adverse effect disappears. Marine nekton displays a highly predictable seasonal structure and its biomass is favored by the «sanctuary” effect provided by the complex of oil platform structures in the exclusion zone. Aromatic hydrocarbon concentrations in demersal fish tissues, under conditions of accidental spills do not exceed sublethal levels. Among benthic organisms, bioaccumulation of heavy metals and hydrocarbons in sentry species (bivalve mollusks) exist in the coastal zone. Such concentrations do not reach critical levels in species of commercial importance (peneid shrimps). The oil and fishing industries converge in strategic sites for their operations in the SC. Even though the fishing experts attribute the collapse of the shrimp production in the last two decades to overexploitation and to the absence of appropriate growth and recruitment regulations of shrimp stocks, it is considered of the utmost importance to promote an environmental developing program that insures the success and prevents conflicts in the long term of both activities in the southwestern sector of the Gulf of Mexico.</p></div></div></div
