A first monitoring in the bay of Bizerta during July 1992, based upon seven sampling stations, indicated a refinery and tankers, berthing at proximity, to be the cause of high amounts of hydrocarbon noted in the region. The nematodes, omnipresent, show a statistically significant decrease in densities, biomasses and specific diversity, in relation to the concentrations of hydrocarbon deposited in the sediments. After an apparent improvement of the quality of waste waters discharged by the refinery, a similar study was repeated in July 1996. The results indicate an increasing amount of hydrocarbons in the sediments in 1996 to which the nematodes have responded by a quantitative and qualitative impoverishment of their community. |