BREAKTHROUGHS IN GROWTH STUDIES ON LARGER BENTHIC FORAMINFERA

Symbiont-bearing Larger Benthic Foraminifera (LBF) are marine mixotrophic protists that partly depend on the photosynthetic energy generated by their symbiotic microalgae. They are therefore restricted to photic tropic and warm temperate marine environments, where they are important carbonate producers. Due to their long geological history, starting in the Late Paleozoic, and their complex morphology they are extensively used for biostratigraphic purposes as well as for precise palaeoenvironmental analyses as their species specific distribution depends on temperature, water energy, light intensity, substrate, calcium carbonate and nutrients availability. During this project, growth-patterns and -strategies of these protists will be investigated to gain information on their evolutionary development and on growth deviations they may undergo under different environmental scenarios. In situ analyses by monthly scuba diving in the deeper photic zone West off Sesoko-Island, Okinawa, where LBF abundantly live, will be performed to obtain reproduction periods and longevity of the species based on population dynamics. This kind of investigations is named herein `natural laboratory` and their results will be compared with culture experiments at the laboratory of Sesoko Marine Station, one of the best labs for culturing tropical organisms in the Northwest Pacific. The use of Computed Tomography on the compartmented shell allows insights on their ontogeny, biology and time specific environmental adaptations by linking growth patters, bauplans, growth deviations and environmental parameters. The discovery of such links will be pivotal to use LBF in recent as well as in fossil environment for ecologic monitoring and to potentially estimate life cycles and reproduction strategies, which are mostly consequences of stressed scenarios. The variation of shell characters with water depth on the species Heterostegina depressa (which is the only living LBF species occurring from 10 meters to 90 meters water depth) will give more insights on speciation, reproduction strategies and on characters maintenance with changing environmental conditions.

This project concentrated on the understanding of the life cycles and reproduction strategies of one of the most important carbonate producers in the tropical shallow water ecosystems. We concentrate on small protists, which occur abundantly in modern reef systems and, most importantly, were dominant in the fossil record of the Earth history. Such little organisms called Foraminifera built a shell made of calcium carbonate, which has to be in equilibrium with the ocean chemistry. Todays ocean temperature rise can lead to major problems to these carbonate producers. We studied these group of organisms because there are still many open questions regarding their life span (i.e., how long do they live) and how they reproduce. Answering such questions is very important for three reasons: it give us the possibility to quantify the amount of carbonate produced by such organisms in a specific time interval, it tells us how and when they switch from meiosis to mitosis during their lifecycles to better understand their behavior in the fossil record, and lastly it gives us a much better insight into the past geological periods when such organisms fully colonized reefs ecosystems overpassing corals and sponges. Among the most important results we have discovered that the reproduction strategy changes with water depth and that such organisms have a life span that last no more than 2 years, thus their modern contribution to carbonate producers has been greatly underestimated in both recent and the past.