Test malformation or deformity in foraminifera is exceptionally rare in geological samples but is more frequently recorded in modern (often estuarine) samples from less than optimal environments. On 16
th January 1992 an accidental release of acidic water from a flooded mine into the Carnon River in Cornwall (UK), caused extensive contamination of Restronguet Creek (estuarine area) and the Fal Roads (marine area). The water entering Restronguet creek was rich in metals (Cu, Zn, Sn, Fe, etc.) and with a pH of 3.2. The short-term impact was a loss of all benthic foraminifera for a period of almost two years. Mitigation measures to normalize the pH of the water entering Restronguet Creek was in place by 1994. The living benthic foraminifera (mainly
Ammonia aberdoveyensis,
Elphidium williamsoni and
Haynesina germanica) were re-established by 1993, but with relatively high (<22.5% of the standing crop) levels of coiling deformation, malformed and additional chambers. Despite some improvement, deformed tests are still being recorded (0.06%–15.4% of the standing crop) as the estuarine muds and silts remain contaminated by metals. Some of this contamination was delivered by the 1992 flood, but much of it dates from the mid-19
th century mining activity.The pH of the water entering the estuarine system is, however, normal.
In the Mediterranean Sea around Ischia (pH 8.17 to 6.70) and in the Wagner basin (Gulf of California), where a sea floor pH of 7.40 to 7.80 is recorded, there are living (= stained by rose Bengal) assemblages of forminifera but almost no record of test deformation. In both areas there are post-mortem dissolution effects (surface pitting and fragmentation) and this is a problem for those assessing the impact of acidification in the geological record.
These studies indicate that metal pollution will cause on-going evidence of deformed tests while a drop in pH restricts the species content of the living assemblage but appears not to result in many deformed tests. In laboratory cultures, where foraminifera are living in reduced pH conditions, the recorded levels of test deformation may be more related to the culture environment than the effects of the lowered pH and results may have to be treated with caution. Foraminifera studied in naturally lowered pH environments do not appear to record the same levels of test deformation.
