Recolonization of reef flat by larger foraminifera, Funafuti, Tuvalu

Abstract. The ecology of the larger foraminifera is poorly known for western Pacific atolls, despite the importance of these species to the sediment budgets of the atolls. Many beaches and islets (motu) are composed largely of foraminiferal tests derived from reef flat communities; however, populations of larger foraminifera are often under threat or may even have been eliminated by the effects of pollution and development of the reef flats. It is therefore important to understand the rates of response of foraminiferal populations to natural and human changes to their environments.

This note reports some observations arising from studies of foraminifera and sedimentation on Funafuti Atoll in the south-central Tuvalu Group, west central Pacific Ocean, at latitude 8°30′S and longitude 179°12′E. The atoll consists of some 39 small islets surrounding a c. 200 km² lagoon up to 55 m deep (Smith & Woodward, 1992), with reef flats up to several hundred metres wide surrounding the islets on both ocean and lagoon sides.

Foraminiferal faunas in the lagoon and on the reef flats are diverse, and include some 8 species of larger foraminifera. Although they do not usually make up more than 40% of the reef flat sediments, because of various concentrating processes, tests of the larger foraminifera (particularly Baculogypsina sphaerulata and Amphistegina lobifera) comprise up to 80% of the sediments forming the main island Fongafale. This foraminiferal component may be even higher for the sands of other atolls, and its significance to the carbonate sediment budget and to problems of coastal erosion. . .