LONG-TERM CHANGES OF EPIBENTHIC MACROFAUNA COMMUNITIES IN A CLOSED LAGOON (TAIARO ATOLL, FRENCH-POLYNESIA) - 1972-1994

Epibenthic macrofauna communities (species composition and densities o f the dominant species) were investigated at Taiaro Atoll, Tuamotu Arc hipelago, 22 years after a previous survey. This small atoll is comple tely closed, has no permanent functional hoa, and is not affected by d irect anthropogenic disturbances since it is a Biosphere Reserve. Ten species were identified in 1994 (5 molluscs, 4 corals, and 1 echinoder m). With the 14 species identified in 1972 (12 molluscs, 1 coral, and I echinoderm), a total of 17 species (12 molluscs, 4 corals, and 1 ech inoderm) has been recorded for the lagoon. There has been a shift in d ominance away from the bivalve Crassostrea cucullata (in 1972) to Pinc tada maculata (in 1994). A high mortality of the epibenthic macrofauna affected the central part of the lagoon shortly before 1972 and reach ed the inner reef flat afterwards. The distance of Taiaro from sources of colonizers, its small size, and the isolation of its lagoonal wate rs posing a physical barrier to colonization by organisms and leading to harsh environmental conditions (e.g. very high salinities: 42.5-43 psu), are likely to be the major causes of the exceptionally low diver sity observed.