[B-PT01] Biomineralization and Geochemistry of Proxies

[BPT01-11] Can Irregular Observations Provide the Next Clue for the Ecology of Foraminifera?

*Takashi Toyofuku^1,2, Yukiko Nagai^1,3 (1.Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2.Tokyo University of Marine Science and Technology (TUMSAT), 3.National Museum of Nature and Science,Tokyo)

Keywords:foraminifera, time-lapse microscopy, biomineralization, laboratory culture, fulorescnet obseervation, null negative

Calcareous foraminifera is major producers of carbonates in the ocean. By extracting foraminifera from sediments, analyzing their assemblages, and analyzing their elemental compositions, we can reconstruct the geologic time's past environment. The carbonate shells, called tests, deposited by foraminifera play a central role in paleoenvironmental reconstructions. Therefore, it is one of the centers of interest how the calcareous test is formed. This carbonate test is known to form intermittently as the foraminifera cell grows. As the foraminifera collect food and increase the volume of their cytoplasm, they repeatedly build the next chamber before the last one is full. In this process, new chambers are built using the existing chambers as footholds. The angle and size of the new chamber determine the overall shape of the test e.g., biserial, triserial, spiral, and others. Behind the scenes, the pseudopods, which control the foraminifera's locomotion, have been found to play a very diverse and important role in chamber formation. This is due to the repeated and detailed observation of the chamber formation process and the observation of its ultrastructure by electron microscopy. In our laboratory, we controlled the feeding conditions of foraminifera to derive the conditions that induce chamber formation. Therefore, we can control the timing of shell formation to some extent and prepare a system for reliable observation. The process of shell formation can be documented by, for example, time-lapse observation, recording foraminifera chamber formation, and the order in which they form (and sometimes reproduction to observe the birth of new offspring in detail). We can also use fluorescent indicators to label calcium, pH, and other intracellular organelles and observe how they are distributed during chamber formation and the rest of ecology.

On the other hand, if such observations are made for too long and too often, the observation may fail. For example, an individual may stop and run away when it seems to be forming a chamber, or it may return to a single cell even though it is dividing during reproduction. These observations are difficult to explain straight forward, so it is not easy to publish them in a paper very much. However, there are many interesting observations, and it would be a shame to keep them in storage, so we would like to introduce them to this opportunity.