Seagrass-rafted large benthic foraminifera transported into the deep Red Sea.

Large shallow-marine foraminifera tests occur in deep-sea carbonate sediments of the northern Red Sea as a minor but recurring component among the remains of otherwise pelagic and deep-marine benthic biogenic assemblages. In this study of sediments recovered along the northern shore of Saudi Arabia, the symbiont-bearing taxa Sorites variabilis, S. orbiculus, Amphisorus hemprichii, Amphistegina lobifera, A. lessonii and A. radiata were identified in samples from between 430 to 1,000 m depth. These foraminifera are dwelling in shallow-water environments, associated with coral reefs and seagrass habitats. The seemingly erratic occurrence of photosymbiotic benthic organisms in deep-sea sediments was explained by the finding of such foraminifera tests along with seagrass (e.g., Halophila leaves) and macroalgae remains in pristine preservational states in the sediment of the Umluj brine pool below ~ 638 m depth. This indicates a passive transport process by rafting attached to floating macrophytes to these off-platform settings. The abundant seagrass and oceanographic conditions along the Arabian Peninsula may facilitate the transport of epiphytes and associated taxa offshore. Such long-distance transport mechanisms could further contribute to the rapid (co-)dispersal of some of these organisms into new habitats. Passive rafting should thus be considered in interpretation of sedimentary records and biogeographic patterns.