Distribution of living benthic Foraminifera on the back-reef and outer slopes of a high island (Moorea French Polynesia)

Living foraminifera were examined on both sides of the barrier reef across a section situated on the north-west part of the high island of Moorea (Society Archipelago, French Polynesia). In all, 87 species were found: 62 in the back-reef area (fringing reef, channel and barrier reef) and 72 on the outer slope; 47 were common to both zones. This study points out the importance of substrates in the distribution pattern of foraminifera. The sediments are essentially inhabited by epipsammitic species, whereas algae are colonized mainly by free-living foraminifera: miliolids in the back-reef area; rotaliids in the outer slope. Free-living individuals are much less abundant in the fringing reef, channel and inner part of the barrier reef than in the other parts of the study area. The two major groups on the two sides of the barrier reef are very different in size, test building and probably nutritional modes. In the back-reef area, epipsammitic taxa, mainly composed of small agglutinated species, dominate the fauna; in the outer slope large calcareous symbiotic Amphistegina are the major components of the living association (50 to 70%).