Pinctada radiata is most notorious as one of the greatest sources of natural pearls. Historically, P.radiata pearls from the Ceylon region constituted the majority of pearls available. This particular variety has almost entirely white nacre that produces predominantly silver and yellow pearls. The lip of the pale yellow shells is slightly pinkish. Seven-eight brownish radial bands encircle the shell. The Persian variety is larger and darker with a reddish lip.
Habitat and Ecology
P. radiata is characteristic of hard surfaces and has been discovered attached to rocks and hard sandy plateaus, 10-20 meters deep. The oysters attach in clusters of several to many through byssal threads (tough organic fibers created by the oysters). Over years assemblages form consisting of dead pearl oyster shells, worm tubes, calcareous algal clumps and dead coral. These structures act as a landing dock for the veligers (free-swimming larvae) to metamorphose into juvenile pearl oysters that will maintain the reproductive cycle. Storms and predators are major threats to the continued health of this thriving habitat.
The Pearls of Pinctada radiata
Pinctada radiata is mostly known for producing seed pearls and some medium sized pearls. A seed pearl is a commercial term describing a pearl less than 2mm in diameter (<.25 grain). Due to the thinness of their shells, P. radiata provides the cheapest Mother of Pearl. Until the 1920's, P. radiata (mainly those from the Ceylon region of Sri Lanka) fueled the world's demand for both Mother of Pearl and pearls. The Ceylon oyster is Akoya-like, but is not used in pearl culture in the way that Akoya pearl oysters are. This is due to a few factors:
- Since the 1930's, Petroleum dominates the economics of countries in the Persian Gulf and Red Sea, which account for the bulk of the P. radiata shells. The discovery of oil in the 1930's ended pearl harvesting and diving is only a pastime.
- Bahrain, Sri Lanka and India have each tried to developed cultured pearl industries, but tradition favors natural pearls
- Through years of aquaculture, the Japanese have created farms of the fittest Akoya oysters in order to culture favorable pearls: large, round, lustrous and milky white.
Pearls from P.radiata were historically used for decoration and in jewelry. Most of the pearls were exported from Bahrein and then shipped to London. The shells were assigned symbolic meaning and some have been recovered from ancient tombs of the Hellenistic-Roman period.
Originally thought to be P. radiata, P. anomioides are now designated a separate species.