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Deep waters (c. 4200m) around the Crozet Islands have localised and isolated seabed communities on sediments lying beneath highly productive waters to the north and east of the Islands. The restricted areas of primary productivity are stimulated by natural iron fertilization from the volcanic islands, in an otherwise low productivity HNLC (High Nutrient Low Chlorophyll) region, characteristic of much of the ocean in the southern hemisphere south of 40°S. Seabed communities under high productivity are radically different from those lying beneath HNLC waters. The most common seabed species at Crozet, the holothurian Peniagone crozeti, is superabundant and occurs almost exclusively at the high productivity site. This is highly unusual. Several other new genera and species also occur. Seabed communities under highly productive sites, where they are surrounded by an ocean of low productivity (e.g. HNLC regions), are potentially unique in the southern Indian Ocean and are therefore biologically significant.