Black-lipped pearl oyster
Pinctada margaritifera
ORDER
Pterioida
FAMILY
Pteriidae
TAXONOMY
Pinctada margaritifera (Linnaeus, 1758), Indian Ocean. Recognized local varieties include P. m. var galtsoffi; Bartsch, 1931, of Hawaii, and P. m. var cumingii (Saville-Kent, 1890) of French Polynesia.
OTHER COMMON NAMES
English: Tahitian pearl oyster; French: Huître à lèvres noires, nacre; German: Schwarzlippigen Perlenauster; Arabic: Sadaf; Italian: Ostrica dalle labbra nere.
PHYSICAL CHARACTERISTICS
Shell is round in outline, compressed, with anterior and posterior auricles faintly delimited. It is ornamented with concentric, radially aligned rows of overlapping fragile lamellae, not gaping. Color is overall blackish with white to green mottling. Generally 6–10 in (15–25 cm) in diameter. Interior is thickly nacreous in a wide range of colors including gray, blue, pink, yellow, and green, but seldom black as common name implies. Soft body with a gray or black foot and expansive gills. The orange mantle margin is unfused. The pearl oyster secretes strong byssal threads that exit the shell through a byssal notch below the anterior auricle.
DISTRIBUTION
Widespread in Indian Ocean and western to central Pacific, including Hawaiian Islands. Raised in pearl cultivation ventures in French Polynesia, Cook Islands, Gilbert Islands, Marshall Islands, Solomon Islands, southern China, northern and western Australia, Seychelles, and the Sudan. Variety galtsoffi (Bartsch, 1931), is cultured in Hawaii for potential restocking of natural habitat.
HABITAT
Epibenthic, bysally attached to hard substrates in atoll lagoons and coral reefs with calm clear (nutrient-poor) waters at depths of 3–130 ft (1–40 m).
BEHAVIOR
Water currents associated with normal physiological processes (respiration, excretion) eliminate most nonconsumable particles and microfauna. Natural pearl formation often results when these processes and muscular movements cannot dislodge foreign particles. Such particles lodge between shell and mantle or within mantle tissue, and are subsequently coated with nacre. More often, natural pearls form around internal parasites.
FEEDING ECOLOGY AND DIET
REPRODUCTIVE BIOLOGY
Protandric hermaphrodite, broadcast spawner. Cultured pearl industries in South Pacific collect wild free-swimming larvae on spat collectors, subsequently raising juveniles to adult size for nucleation (insertion of a piece of mantle tissue and a pearl bead). Life span in wild is more than 30 years.
CONSERVATION STATUS
Not listed by the IUCN. Collection by diving has been illegal in French Polynesia since the collapse of the mother-of-pearl industry and the concurrent rise of the cultured pearl industry in the 1960s. Collecting has been illegal in Hawaii since 1930, where P. margaritifera was fished to near extinction for natural pearls at Pearl and Hermes Reef in a period of only three years (1927–1930). The population had still not recovered by the early 1990s.
SIGNIFICANCE TO HUMANS
Pinctada margaritifera is historically important as a primary source of mother-of-pearl for carving and inlay. The earliest cases from the Red Sea and Persian Gulf are from sites dating from ancient Sumeria (2300 B.C.) in Iraq and from the Greco-Roman era in Cyprus and Jerusalem. At present P. margaritifera is the source of black Tahitian pearls, both natural and cultured. The latter have been produced commercially and most extensively in French Polynesia and the Cook Islands since the 1960s.
