Benthic foraminiferal responses to water-based drill cuttings and natural sediment burial: Results from a mesocosm experiment

• Do water-based drill cuttings and natural sediment burial impact benthic fauna?
• Mesocosm experiment investigates responses in benthic foraminifera and macrofauna.
• Burial by a 24 mm layer of natural sediment impacts foraminifera, not macrofauna.
• Water-based drill cuttings affect foraminifera and macrofauna communities negatively.

Effects of burial by water-based drill cuttings and natural test sediment on living (stained) benthic foraminifera were investigated in a mesocosm experiment. After 193 days, the foraminiferal response in sediment covered with drill cuttings was compared to the response in sediment covered with defaunated natural test sediment. Increasing thickness of added material, independent of type of material, significantly reduced the benthic foraminiferal abundance and species richness. While most species managed to migrate through added sediments of up to 12 mm thickness, results indicate that a burial depth of 24 mm severely limits the migration capability of the foraminifera. Textularia earlandi and Bulimina marginata dominated the 0–1 cm of sediment (including added material) in most mesocosms but the former was most resistant to maximum burial (24 mm). The physical disturbance caused by the burial triggered reproduction in surviving populations of B. marginata and Nonionellina labradorica. Addition of water-based drill cuttings and defaunated natural test sediments impacted the microhabitat of N. labradorica differently. Stainforthia fusiformis seems to be the species most tolerant to the water-based drill cuttings. Results indicate that the foraminiferal faunal composition respond differently to the two different materials added, even if only agglutinated forms are considered. This agrees with earlier macrofaunal results from the same experiment which indicate that the water-based drill cuttings represent an additional stress factor for the benthic community.