An investigation of the effects of discharged drilling fluids from exploratory drilling on hard bottom communities in the Western Santa Barbara channel

A pioneering investigation of the effects of discharged drilling fluids on hard bottom communities was carried out at depths of 51.8 to 64 m using the manned submersible, Nekton GAMMA. We report here on the first three surveys conducted for: reconnaissance and site selection; documenting pre-drilling conditions; and post-drilling impacts. A dose-response design, utilizing 10 stations at varying distances from the well site was used to interpret post-drilling ecological changes - in order for observed changes to be attributed to drilling, they had to correlate with measured doses of drilling fluids, as determined by analysis of Barium in particle traps. The biological community at each station was assessed by point-contact analysis of numerous 35 mm photographs, and larval settling plates, which were removed after drilling and analyzed for settlement patterns. Concentrations of trace metals in invertebrate tissues were compared between surveys to determine if drilling fluid constituents were being bioaccumulated.