nucleation, however, this is very rarely, if ever, the case. Bivalves are able to flush sand from their bodies extremely effectively, and studies of pearl nuclei have shown that the overwhelming majority form from parasitic incursion, other organic irritants, or even tissue damage. The oyster's release of the nacre serves as an adaptation of the immune system to isolate the invasive particle and irritation. P. margaritifera in particular produces gray or black pearls. The benthic ecology of the region is a significant factor in the rate of production and the quality of pearls. Rocky, gravelly bottoms and low silt concentrations are preferable, and currents are necessary to keep the water clean with fresh phytoplankton and removal of fecal matter. Stronger currents cause faster but lower quality pearl development. Notes Yukihara, H., et al. (1999). “Feeding Adaptations of the Pearl Oysters Pinctada margaritifera and P. maxima to variations in particulates”. Marine Ecological Progress Series. Retrieved 2014-2-19. Ciesm (2002). “Pinctada margaritifera”. Retrieved 2014-2-19. Tëmkin, I. (2013). “Pinctada margaritifera (Linnaeus, 1758)”. World Register of Marine Species. Retrieved 2014-2-19. Fishing and Aquaculture Department (1991). “Pearl Oyster Farming and Pearl Culture”. FAO Corporate Document Repository. Retrieved 2014-2-19 Richmond, Matthew D. (1997). A Guide to the Seashore of Eastern Africa and the Western Indian Ocean Islands. References External links Pteriidae Commercial molluscs Molluscs described in 1758 Taxa named by Carl Linnaeus Endemic fauna of Tahiti