Relationship between Abundance and Morphology of Benthic Foraminifera Epistominella exigua: Paleoclimatic Implications

The relationship between abundance (relative as well as absolute abundance) and morphology (size of the shell, number of chambers and proloculus size) of benthic foraminifera Epistominella exigua has been studied in a core to understand the influence of changing environmental conditions on its morphology and distribution. A total of 50 samples from the top 100 cm section of a gravity core collected from the southern Bay of Bengal Fan were used. The changes in abundance of E. exigua match well with variation in average proloculus size of E. exigua. An opposite relationship however, is observed between the abundance and size of E. exigua shells. The higher abundance corresponds with smaller E. exigua shells. Similarly, the increased E. exigua abundance matches with a decrease in the number of chambers. The increased abundance of E. exigua shows favourable conditions for its growth and survival. Thus the study indicates that during favourable conditions, while the number of chambers in the shells and the size of the shells of E. exigua decreases, more number of specimens have a larger proloculus. Since asexual reproduction results in megalospheric specimens with larger proloculus, smaller size and less number of chambers, it is inferred that E. exigua prefers an asexual mode of reproduction during favorable conditions. The findings can be used to apply morphological characteristics of E. exigua as a proxy to infer past climatic conditions.