larger foraminifera as important Calcium-carbonate producers in coral reef environments and constituting the main components of carbonate beach sands; examples from the ryuKyu archipelago.

Hohenegger, J., Institut für Paläontologie, Universität Wien, Althanstraße 14, A-1090 Wien, Österreich (Austria), johann.hohenegger@univie.ac.at

High salinity and pH, as found in shallow tropical and subtropical marine environments, enriches the amount of carbonate-ions () in seawater, which is used by various organisms for the production of calcium-carbonate (CaCO₃) shells and skeletons. Three organism groups are responsible for the construction of coral reefs. Beside stony-corals and corallinacean algae, a group of single celled organisms related to amoebas, the Foraminifera, are extremely abundant in coral reef environments. They protect their protoplasm by calcium carbonate tests, microscopically working as greenhouses for symbiotic microalgae. In housing symbiotic microalgae, they are independent of food in nutrition-depleted environments like coral reefs. Although they consist of a single cell, these organisms can get large sizes, sometimes reaching a few centimeters. Similar to stony corals, all larger foraminifera depend on light that is essential for photosynthesis of their algal symbionts.

Near-shore areas of the tropical and subtropical Northwest Pacific are characterized by high production rates in a special group of larger Foraminifera with star-shaped tests growing up to 3 mm (Hoshisuna) and becoming extremely abundant on the crest of coral reefs. They cling with their spines to the substrate to resist the high water energy at the reef front. Empty tests are transported by waves to the beach and accumulate there. The main component (> 50 %) of beach sands in the Ryukyus is thus represented by abraded tests of these star-shaped larger Foraminifera. Therefore, the protection of larger Foraminifera in healthy reef environments is important to remain the white sandy beaches.