Earlier studies in the tropical Indo‐Pacific have grossly underestimated the richness of macrofauna species at spatial scales relevant to conservation and management as a result of insufficient collecting and sorting effort. A massive collecting effort involving 400 day‐persons at 42 discrete stations on a 295‐km2 site on the west coast of New Caledonia, south‐west Pacific, revealed 2738 species of marine molluscs. This is several times the number of species recorded from any area of comparable extension anywhere in the world. Spatial and habitat heterogeneity is high with 32% of the species collected at a single station. With 20% of the species represented by single specimens (0.4% of all catches), rare species make up a considerable proportion of the fauna. This justifies the parallel drawn between coral reefs and rain forests in terms of species diversity. The real richness of many soft‐bodied marine taxa is probably underestimated, as evidenced by the fact that 28.5% of the mollusc species present at the study site are represented in the samples only by empty shells. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 75, 421–436.

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