Decalcification of benthic foraminifera due to “Hebei Spirit” oil spill, Korea

•The crude oil in the “Herbei Spirit” spilled on the west coast of Korea, 12, 2007.•Sogeunri tidal flat with a low pH (6.98) was acidified by the crude oil spilled.•A breakage of the chambers in benthic foraminifera had seriously progressed.•It may be not only decalcification but also the exposure duration of substrata. In order to determine the effects on foraminifera due to spilled crude oil in the “Herbei Spirit” incident, a study of benthic foraminiferal assemblages was carried out on sediment samples collected from the Sogeunri tidal flat, Taean Peninsula, Korea. Breakages of the chambers in the Ammonia beccarii and Elphidium subincertum species of the Sogeunri tidal flat with a low pH (6.98 on average) were marked. These chamber breakages occurred in 71.6% of A. beccarii and are thought to be caused by decalcification due to the fall in pH resulting from the “Hebei Spirit” oil spill. The factors that affect breakage of the chamber in benthic foraminifera under low pH condition may be not only deto decalcification but also to exposure duration of substrata in the tidal flat spilled crude oil.