M. Lesourd

LOW pH EFFECTS ON AMMONIA BECCARII TEST DEFORMATION: IMPLICATIONS FOR USING TEST DEFORMATIONS AS A POLLUTION INDICATOR

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.

Environmental Variation and Foraminiferal Test Abnormalities

Foraminifers are increasingly used as bioindicators of environments. Their community structure provides information on the general characteristics of the environment, especially in highly changing paralic environments (e.g., Hayward and Hollis, 1994), and some species are sensitive to specific environmental parameters. Test morphology may also be related to environmental characteristics and is sometimes used as a bioindicator. The size and the density of pores, e.g., have been considered as indicators of dissolved oxygen concentration (Sen Gupta and Machain-Castillo, 1993).

Origin of double and multiple tests in benthic foraminifera: observations in laboratory cultures

Abstract Many juvenile and adult double and multiple tests of benthic foraminifera were observed on specimens grown in laboratory cultures or collected in various natural environments. Our observations bring to light three possible causes for such abnormalities, each one referring to characteristic morphological features. Double tests may result: (1) from an anomaly in the development of a single juvenile, building two or three second chambers or two third chambers, each one possibly developing in an individual whorl; (2) from the early fusion of two juveniles, which both develop after their fusion; (3) from the attachment of a juvenile on a parental test after the schizogony followed by the youngs development.

Cristobalite inclusions in the Tatahouine achondrite: Implications for shock conditions

Abstract The mineralogy of the Tatahouine diogenite was investigated by optical microscopy, Raman micro-spectrometry, and scanning and transmission electron microscopies. Inclusions of α-cristobalite in orthopyroxenes, locally in symplectic association with chromites, or associated with metal, have been characterized for the first time in a diogenite. Mosaicism of the orthopyroxenes indicates shock effects in the meteorite. The shock history of the meteorite must be consistent with the presence of vein-like structures containing inclusions of well-crystallized cristobalite, a low-pressure, high-temperature phase. Several possible mechanisms to account for these observations are discussed. The simplest one, consistent with all observations, is that a shock event would have occurred in a hot orthopyroxenite, either before extensive cooling of the asteroid, or in materials heated by previous impacts and maintained hot under an ejecta blanket.