Depth-relations of recent larger foraminifera in the Gulf of Aqaba-Elat

Intensive research on the recent foraminifera in the Gulf of Aqaba- Elat and their physico-chemical environment is being carried out for the last decade by groups of specialists from the Universities of Jerusalem, Basel, and Copenhagen. The results obtained hitherto indicate that this part of the northern Red Sea may represent a model-area of prime interest for a better understanding of foraminiferal distribution and, therefore, for paleontological interpretations of fossil faunas. The involvement in the study of this model area of the Utrecht University group is based on the latter's participation in the International Geological Correlation Program, Project 73/1/1 "Accuracy in Time". Since many biostratigraphical correlations are based on the evolution of measurable parameters of larger foraminiferal species groups, an investigation of possibly environment-dependent morphological changes in living Foraminifera was urgently needed. A recently advanced theory that proloculus-size might increase at greater water-depth was one such topic. Since the thermo-, halo-, and pycnoclines in the Gulf of Elat are rather insignificant, changes with depth in morphology and distribution of foraminiferal species must be governed by depth-related factors other than temperature, salinity or density. Direct or indirect influence of light penetration and types of substrate are thought to control in the Gulf the depthdistribution of the Soritidae and of the investigated species of Borelis, Amphistegina, Planorbulinella, Operculina, Heterostegina, and Heterocylina. Light may equally influence the intraspecific variation in several of these groups. Major changes seem to take place in the uppermost 80 meters of the depth-profiles. For the LG.C.P. project satisfactory estimates can be made now of the range of variation that mean values of such "evolutionary" features as protoconch diameter and nepionic arrangement may show at one time level, as a consequence of environmental control. The volume summarizes the present-day knowledge on the distribution and morphology of the larger Foraminifera of the Gulf, on their reproduction cycles, symbionts, and their possibly symbiont- and depth-related variability in stable oxygen-isotope ratios.