The effect of hydrocarbons and drilling fluids on the fecal pellet production of the deposit feeder Abra alba

Abstract The fccal pellet production of Abra alba was measured during exposure to different concentrations of diesel oil, drilling muds with different base fluids, oil-based cuttings and barite. For oil-based drilling muds a curvilinear regression ( y = ax + b log x + c ), gave a very good description of the relationship between fecal pellet production ( y ) and concentration of drilling mud in the sediment ( x ). EC 50 ) (5 days) values calculated from the regression equation ranged from 57 to >1000 mg kg −1 . The response was significantly correlated to the content of naphthenics in the mud. After 5 days of exposure to diesel oil and to two oil-based muds, no increase in the concentration of total hydrocarbons was found in the soft tissue of A. alba , and normal fecal pellet production was restored within 4–6 days in uncontaminated sediment. This suggests that the reduction in fecal pellet production may be due to a negative stimulus to feeding activity and ingestion, as well as to internal toxic effects on the organism. A reduction in feeding activity of A. alba may slow down the bioturbation of the sediments.