An Assessment of Hard/Live Bottom Epifaunal Community Structure Post-Construction of the Gulfstream Natural Gas Pipeline

Gulfstream Natural Gas System, L.L.C. (Gulfstream) constructed a 36-inch-diameter pipeline in 2001 to transport natural gas from plants in Mississippi and Alabama to markets in central and southern Florida. The route of the marine portion of the pipeline originates from the shoreline of Mississippi and Alabama in Mississippi Sound and transverses a large portion of the Gulf of Mexico, making landfall in Tampa Bay. Activities such as the installation of the pipe on the seafloor and the mooring of construction vessels used in these processes were anticipated to disturb the seafloor and associated resources. Of particular concern during project permitting were areas of hard/live bottom habitat within the pipeline construction corridor. As part of the mitigation plan, Gulfstream has monitored post-construction disturbance and re-colonization of sessile epifauna into the disturbed pipeline, spoil mound, and anchor strike areas. Monitoring has been performed using ROV video and diver collected photograph transects. The mitigation plan defined impacted hard/live bottom recovery as achieving a metric of 80-percent similarity to unimpacted hard/live bottom areas (it was not stated if this similarity metric referred to percent cover or species composition). After completion of the 2005 monitoring effort, it was determined that percent cover and species composition recovery criteria have been achieved. Biotic cover was found to have been enhanced in the trench corridor, spoil mound, and visible anchor strike areas in comparison to unimpacted hard/live bottom areas. Although recruitment within impacted hard/live bottom areas was enhanced and a greater diversity of fauna was present, the actual community structure was not significantly different from undisturbed bottom. During project permitting, recovery of the biological community was predicted to take 100-years, however, it is evident that within less than five-years, the community structure has recovered in equivalence to unimpacted areas.