The use of foraminifers as bioindicators of pollution in coastal and paralic environments has undergone a very fast development. Among various criteria, morphological abnormalities are sometimes considered as pollution indicators. However, responses to pollutants have not always been distinguished from responses to natural environmental parameters. In particular, endopelic foraminifers often live in changing pH conditions that may induce test deformation.
To study pH effects, cultures with pH ranging from normal marine down to ph 7 were prepared using hydrochloric acid to lower the pH. Ammonia beccarii was collected and introduced into these different cultures. Under neutral pH (7.0) conditions, pseudopodial emission was reduced or stopped. Then the test became opaque as a result of superficial alteration, which is the first stage of test decalcification. Decalcification progressively extended over the whole test, first destroying the last chambers, which are thinner. After 15 days, only interlocular walls were preserved, giving the test a star-shape characteristic of an advanced stage of decalcification. If a specimen was maintained in low pH conditions, the test was sometimes entirely destroyed and only the cytoplasm, covered with the Inner Organic Layer, remained. On the other hand, if a specimen with a partially dissolved test was placed in a solution with normal pH, it was able to rebuild its test. Recalcification was somewhat different from the original calcification and was accompanied, in most cases, by morphological abnormalities (e.g., abnormal expansions, irregular chamber sizes, wall with concave form).
These observations show that temporary acidification of the environment, causing partial decalcification of the test, is able to induce morphological abnormalities of foraminiferal tests during recalcification. This acidification may be caused by anthropogenic impact or a natural cause. In both cases, deformation of foraminiferal tests yields information on environmental characteristics of the area.