Fathoming the diversity of foraminifers: how many species are there?

The assessment of the taxonomic diversity of marine protists is an important unresolved issue in the International Year of Biodiversity 2010 and its (paleo)biological implications are manifold. Estimates of the number of species of extant foraminifers are largely conjectural and range from a minimum of ~4,000 to a maximum of ~15,000 estimated species. The main aims of the present contributions are threefold. First, to provide a baseline for the number of nominal extant foraminiferal species-group taxa (including also planktonic and organic-walled taxa) that have been formally described as yet. To do so, different sources have been integrated, starting from the Ellis & Messina Catalogue of Foraminifera and the Zoological Record. The number of taxa counted by us is 6,281, including 103 presumably living taxa, for which insufficient data as to their exact type locality are given. This figure increases to 6,390, adding 109 taxa which were originally based on both fossil and recent material. However, many described extant species-group taxa are not yet included in the Catalogue: summing these ~2,175 missing taxa to those listed in the Catalogue (6,390), we obtain a minimum figure of 8,565. Second, to discuss the novel approach by Murray (2007), based on counts from rose Bengal-stained benthic assemblages, leading to an estimate of ~3210 to ~4280 species. We show with detailed data from various regions that this approach of making up global estimates by scaling up local studies fails to take into account a vast amount of available systematic evidence and does not lead to a realistic estimate of the number of extant species: most taxa are rare, many rare taxa occur at lower latitudes, and many regions and habitats are insufficiently sampled. Third, to provide an estimate of the number of extant foraminiferal species. Models hinge on different assumptions (e.g., different estimates of overall synonymy; endemicity; species as yet in open nomenclature; extant species first described as fossils; spatial scaling of species richness; genetic and molecular measures). Our models suggest that the total number of extant species has been generally underestimated by one order of magnitude, and that there are no shortcuts for this issue but basic taxonomic work. In contrast, there is an exponential decrease in new species-group taxa described from 1988 to 2007 (n=704).