The effects of time-averaging and taphonomy on the identification of reefal sub-environments using larger Foraminifera; Apo Reef, Mindoro, Philippines

At Apo Reef, Mindoro, a small, isolated, moderate-energy platform reef in the central Philippines, foraminifera comprise a significant portion (c.40%) of the sediment. This study examines four assemlages of foraminifera: live foraminifera; dead, unabraded foraminifera; abraded and fragmented foraminifera; and the three data sets combined into a total assemblage in order to determine their relative usefulness in identifying reefal sub-environments. The time averaged assemblages, the product of taphonomic processes, prove to be much more effective in delineating reefal physiographic sub-environments than do the live assemblages. The abundance of live foraminifera, except for minute sediment-attached rotaliines, is strongly controlled by the distribution of algal turf and filamentous algal mat. Filamentous algae, with abundant live delicate species, occur in both high- and low-energy reef zones. The time-averaged assemblages are characterized by robust calcarinids in the shallow seaward zones; by free-living miliolids and small rotaliines in the leeward zones; and by planktonics and large thin rotaliines in the fore reef. This enhanced fidelity of the time-averaged assemblages in relation to physiographic zones reflects a combination of the ecological distribution of robust, abrasion-resistant species, the selective destruction of small, delicate tests in higher-energy zones, and the failure of storms and other mechanisms to homogenize the reefal sands.