Shelled-Molluscs Fauna at Abrolhos Bank (Brazil): Assessment of Both Total Species Richness and the Completed Distribution of Species Frequencies by Numerical Extrapolation of a Partial Survey

Numerous anthropogenic threats to the exceptionally rich coral-reef ecosystem at Abrolhos Bank (Brazil) arguably require implementing drastic conservation policy and meanwhile, urge for the prior detailed assessment of species richness and the species distribution across the Bank. Due to their unavoidable incompleteness, the already implemented “Rapid Assessment Surveys” at Abrolhos Bank deserve being completed, at least numerically, by implementing an appropriate extrapolation procedure, to avoid serious bias precisely due to ignoring both the number and the frequency distribution of those species still remaining undetected after Rapid Assessment Surveys. Complying with this concern, I report on the results of a numerical extrapolation of a previously achieved partial survey of the soft-bottom shelled-mollusc fauna at Abrolhos Bank. This numerical extrapolation provides least-biased estimates regarding not only the number of species which have remained unrecorded but, moreover, additional information on the respective frequencies of these still unrecorded species. As a result, the extrapolated total species richness at Abrolhos Bank reaches at least 435 shelled-molluscs species (instead of only 293 species actually recorded by the Rapid Assessment Survey), out of which 30 species (instead of 19) are expected to be Brazilian endemics. Accordingly, the soft-bottom shelled-mollusc fauna – an admittedly fairly reliable indicator for the whole marine biodiversity – definitely demonstrate the major biological interest of the whole reef ecosystem at Abrolhos Bank and the imperative necessity of implementing truly efficient conservation programs of this ecosystem.