Inferences on Sediment Production and Transport at Carbonate Beaches Using Larger Foraminifera

In the tropical Central and West Pacific as well as in the East Indian Ocean the symbiont-bearing benthic foraminifera (single celled marine organisms getting size of a few millimeters) are the main producers of calcium-carbonate grains deposited at carbonate beaches. The proportion of larger foraminifera tests on sand grains ranges from 20 to 95 %. This amount depends on the two factors productivity and transport, since the larger foraminifers do not live on or in the sandy bottom near the beaches, but prefer firm substrate in high-energy environments close to the front of coral reefs. Therefore, foraminiferal tests are produced in extreme numbers on the reef crest that is covered by filamentous macroalgae or in the transition zone between the crest and the reef moat. After the release of the test by reproduction or death, empty tests are entrained through the high water energy acting at the reef crest and transported. This transport depends on the direction and intensity of currents connecting the production area (reef crest and transition to the moat) with the deposition area (central moat, lagoon, beach). Devastation of the production area and/or the interruption or diversion of water flow hinders the accumulation of larger foraminifera tests at the beach. Understanding the ecology of larger foraminifera in combination with the transport of empty tests is thus necessary to preserve the equilibrium between deposition and removal of sand at carbonate beaches.