AbstractLamellibrachia luymesi is a long-lived vestimentiferan polychaete that produces biogenic habitat at hydrocarbon seeps on the upper Louisiana slope of the Gulf of Mexico. Lamellibrachia luymesi relies on endosymbiotic, chemoautotrophic bacteria for nutrition which are supplied with hydrogen sulphide acquired from seep sediments by the tube worms. In this study, an individual-based model is developed for L. luymesi aggregations. The results show that aggregations can persist for centuries because of extremely low mortality rates. Recruitment patterns reflect intraspecific competition for settlement space, with the recruitment period estimated between 11 and 68 years. Substantial hydrogen sulphide requirements are estimated for large aggregations of L. luymesi, exceeding 30 mmol h−1. In addition to modifying habitat through physical structure, L. luymesi may be considered to be an ecosystem engineer because of its profound effect on the chemical environment at hydrocarbon seep sites.