Beach of Microstars (Foraminifera), Timor-Leste: Life Habitats and Environmental Influences

Baculogypsina sphaerulata and Schlumbergerella floresiana (Calcarinidae) are two large benthic foraminifera that are ecologically significant carbonate producers across Indo-Pacific reef environments. While their broader distribution has been mapped, the northern coastline of Timor-Leste situated at the southern margin of the Coral Triangle has remained unstudied with respect to its living calcarinid fauna. This study provides an initial explorative survey of the distribution, habitat associations, and sedimentological significance of both species at One Dollar Beach, and at other beaches along the Dili–Manatuto coastline. Schlumbergerella floresiana has orange-coloured tests, even in the death assemblage. These form the major grain component of the dominant 1–2 mm fraction of the beach sand. The related Baculogypsina sphaerulata with smaller, more delicate tests, is not present as recognizable grains in the beach sediment but is a major sediment contributor to sand at some adjacent subtidal sites. Both species live prolifically as epibionts on a variety of reef-flat microhabitats ranging from seagrass and filamentous algal mats to corals and high stand macrophytes. They were not observed living on mobile sand. Loss of the subtidal microhabitats would greatly alter the character and colour of the beach. Along the north coast of Timor-Leste the abundance of these species is likely driven by substrate type, currents, and proximity to large river outflows bringing terrigenous sediment to the inner neritic zone. In beaches observed during this study, the highest Schlumbergerella cover is at One Dollar Beach and at Fatubika near Hera Bay and lowest near the Comoro River mouth. These findings establish an opportunity for incorporating foraminiferal monitoring into Timorese coastal management. Future work should address other ecological aspects including thermal tolerance of the foraminifera and their living hosts and molecular identification of cryptic diversity.