Preliminary investigation: platform removal and associated biota

Abstract

Platforms are long-term, high profile structures of pilings and conductors that pass from beneath the seafloor to above the sea surface. They are built to remain stable and safe for a minimum of 20 years. Since the majority of GOM platforms are hundreds of miles from natural reefs, they function as de facto artificial reefs and have increased habitat by 28 percent. Sessile animals settle and develop on the subsea surfaces and depth limited and reef-related fishes locate to a platform and remain structurally faithful. Complex communities evolve and eventually over 10,000 individual fish may affiliate with a single platform. Federal law mandates that the entire structure be removed within a year after hydrocarbon production ceases. The use of explosives 16 ft below the seafloor is the only reliable method of piling and conductor severance. Quantitative surveys and photo documentation were performed before and after explosive severance at three removal sites to evaluate effects on the platform communities. Preliminary data indicate that death is related to distance from seafloor and explosive mechanics; the first detonation(s) kilUs) the most fish; and total fish killed cannot be estimated from those that float. There is little discernable effect on motile invertebrates able to maintain contact with the platform surface during detonation.