Research Product

Drilling mud, as used in exploratory drilling for oil offshore, affected the composition of estuarine communities that developed from planktonic larvae in aquaria containing sand and flowing estuarine water. Aquaria contained: sand only; a mixture (by volume) of 1 part mud and 10 parts sand; 1 part mud and 5 parts sand; or sand covered by 0.2 cm mud. For all environments, annelids, mollusks, arthropods, and coelenterates were the numerically dominant phyla collected in a 1 mm mesh sieve after eight weeks exposure; a total of 1,025 animals, representing 45 species, was collected. Annelids and coelenterates were significantly fewer (a=0.05) in aquaria containing drilling mud than in the control aquaria. Arthropods were significantly affected only by mud cover over sand; mollusks also were diminished in this environment, but not significantly. Exposure to concentrations of drilling mud reduced not only the number of individuals, but also the frequency of occurence of macrobenthic species. Thus, the average number of annelid species in 1 part mud: 5 parts sand aquaria or in mud-covered aquaria was significantly less than in control aquaria. The average number of arthropod species per aquarium was also significantly less in mud-cover exposure than in the control. Discharge of large quantities of drilling mud at levels tested in the laboratory could adversely affect the colonization of various substrata by benthic animals in nature.