Ecomorphology of a recent largeforaminifer, Operculina ammonoides

Abstract

In order to understand rules of construction of the larger foraminiferal shell and their environmental constraints, extant Operculina ammonoides from the Gulf of Aqaba (Red Sea) were studied by computerized biometry of digitized high resolution equatorial and axial X-ray micrographs. More than 100 000 biometrical data were analyzed in terms of shell size, shape and ontogeny in their relations to depth and substrate. It allowed a search to identify the basic life processes. On one hand, light through symbiosis, controls the growth rate, the fecundity and the phenotypic involute-evolute morphology. Chamber partition obeys simple rules, probably dependent on symbiont metabolism. Gross photosynthesis flux is roughly equal to biocalcification, whatever is the shell size and shape. On the other hand, abundance, determined by interspecific competition, controls the size of the embryo and of the adult and indirectly other morphological features, such as chamber irregularity, as well as the distribution of large and small, previously overlooked, microspheric specimens.