The Malacologist | The Malacological Society of London The Malacological Society of London The Malacologist

Volume 47

Thursday 9 March 2006 in the Flett Theatre, Natural History Museum, London

At a SPECIAL LECTURE organised for The Malacological Society of London and the Zoology Department, Natural History Museum, Professor Philippe Bouchet
of the Muséum National d’Histoire Naturelle, Paris, talked about the intensive surveys of molluscs from coral reef habitats around New Caledonia and Philippines conducted by his team from the MNHN. The surveys involved large teams of collectors, sorters and taxonomists using a wide variety of sampling methods. Unprecedented huge diversities of molluscs were revealed by these methods and Philippe outlined the results and their ecological and taxonomic implications.


Lessons from a massive collecting effort on coral reefs

The seas occupy 67% of the Earth’s surface but contribute only 15% of its species biodiversity. Coral reefs occupy only 0.1% of the planet, but concentrate as much as 5% of global biodiversity. Because of the taxonomic impediment, the species-rich taxa (molluscs, crustaceans, polychaetes) are “carefully” avoided during most surveys because of problems with sampling, sorting and identifying them. Inventories and monitoring focus instead on a few “indicator” taxa that are used as proxies for marine fauna and flora in general. Species of fishes, corals, seashells, and seagrasses are the more frequently used proxies. But what exactly do these proxies measure? A massive collecting, sorting and processing effort involving 25 persons for 30 days, with stations chosen as representative of bottom type, was carried out at three New Caledonia sites, each covering 50-300 sq. km of a mosaic of coastal habitats. ‘Smart collecting techniques’ involved suction through a 2 m tube into a fine mesh bag and scrubbing coral into baskets, followed by a veritable sampling factory workshop. This reveals that 2,700-3,000 species of molluscs per site is the norm, and extrapolations from the cumulation curve indicate a range of 3,200-4,000 species potentially present at each site. This is comparable to the species richness for the whole European seas. Habitat heterogeneity is high at all spatial scales, with only 22% of the total species shared by all three New Caledonia sites. In terms of conservation, the consequence is that at regional level even a 30,000 hectares site cannot be considered "representative". Twenty per cent of the species are represented by single specimens and make up 0.4% of all catches. One-third of the species have adult sizes under 4 mm, while only 10% are larger than 40 mm and would rank as “seashells”. Many of the molluscs are under-represented in shell books because they are too small or too specialized - the five most diverse groups are, in fact, the turrids, triphorids, eulimids, pyramidellids and cerithiopsids. Such a fractal composition of the species guild is shared by insects in the canopy of rainforests. “Keystone” species, “indicator” species, and other “flagship” species may be adequate for biodiversity studies that focus on ecosystem function and habitat conservation, but they do not address one apparently fundamental property of complex tropical ecosystems: most species are rare and small.