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ABSTRACT: Northern Gulf of Mexico Hydrocarbon Seep Communities: Implications to the Petroleum Industry

Robert M. Avent

Most animals consume organic food sources based on primary productivity at the base of the food web. Little food reaches deep-sea bottom animals, which are usually small, fragile, and sparsely distributed. Recent worldwide discoveries of chemosynthetic organisms have generated investigations into the taxonomy, ecology, biochemistry, and physiology of these forms.

The dominant animals in these communities, several large species of vestimentiferan tube worms and bivalve mollusks, energetically use dissolved gases (primarily methane and hydrogen sulfide) issuing from the bottom under certain geological conditions. Endosymbiotic bacteria aid metabolic pathways. The large chemosynthetic animals and their dense populations (orders of magnitude over background) are the exceptions that prove the rule that food is an important limiting factor in the deep sea. The discovery of relatively shallow, luxuriant gas-seep communities on the Louisiana upper slope raises concerns on the environmental effects of nearby petroleum operations. If there is geophysical evidence of seeps ("wipeout zones" or streams of bubbles), to protect these communities the Minerals Management Service requires photographic bottom surveys in depths from 400 to 900 m. If they are found near proposed well locations, high-density communities must be avoided to prevent physical damage from any structure. Deep-sea community surveys can be expensive and can result in alternative siting plans and development delays. However, Mineral Management Service's requirements should conserve these shallow communities, which have considerable value as natural laboratories accessible to academic study.

We know little about the permanence, dynamics, recruitment, recovery potential, and life requirements of chemosynthetic communities. Additional studies have been proposed.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990