Quality Trait Signature at Archipelago Scale of the Cultured Pearls Produced by the Black-Lipped Pearl Oyster (Pinctada margaritiferaVar.cumingi) in French Polynesia

Abstract

In French Polynesia, the aquaculture of Pinctada margaritifera (Linnaeus, 1758) covers a large maritime exploitation area, spread over nearly 20 degrees latitude and longitude, with numerous pearl farms located in three archipelagos (Gambier, Society, and Tuamotu). As these archipelagos have specific seasonal temperature patterns each year, pearl oysters are subject to disparate and contrasting environmental regimes. This study aimed to examine the specificity of commercial pearl quality traits (n ¼ 2,236 samples) at the archipelago scale, in such a way as to provide preliminary data to design the most appropriate strategy for the distribution of hatchery-produced phenotypes. A large and standardized grafting experiment using the same donor phenotype was designed and carried out over six grow-out locations, covering the three archipelagos. Results revealed significant differences in commercial pearl quality traits among archipelagos, giving these groups of growing sites distinctive ''signatures'': (1) more color, less circles, and higher overall pearl grade in Gambier; (2) larger size with paler pearls in Tuamotu; and (3) darker pearls with intermediate size in Society. Characteristic differences in the environment and seasonal temperature ranges among the three archipelagos, corresponding to their distinct environmental conditions, can explain the specific variations between pearl quality traits among the sites. The strong disparities at archipelago scale should be taken into account in selective breeding programs for P. margaritifera so as to choose the most appropriate pearl oyster donor phenotype for use in each environment and thus enhance site-specific qualities for pearl production.

Variation in cultured pearl quality traits in relation to position of saibo cutting on the mantle of black-lipped pearl oyster Pinctada margaritifera

“…Inversely, it was in the GMR site, that the lowest amount of pearls with up to 10 surface defects was observed in comparison to RRR. This result was consistent with results found by Ky et al (2016b), and…”

“…This inter-mantle section amplitude of variation was less than the inter-site variation, which suggests that the RRR location is the most appropriate for pearl size improvement. This was consistent with another recent study (Ky et al, 2016b), which confirmed the growth potential in favour of Tuamotu archipelago (where RRR atoll was located) compared with Gambier archipelago (where the GMR island is located). Indeed, the nacre deposition rate was faster in RRR than in GMR, because the average temperature in lagoons of Tuamotu is warmer than in the lagoon of Gambier (Ky et al, 2016b).…”

“…Significant differences existed between the culture sites, with a higher average number of pearls with lustre in RRR than in GMR. This seems to contradict previous studies (Ky et al, 2016b;Le Pabic et al, 2016), where average water temperature, recorded through the seasons, did not favour lustre. Indeed, the recent studies revealed that in…”

“…originating from the anterior zone produced a significantly higher proportion of pale pearls in both culture sites. Darkness level of pearls produced with saibo from the middle section was consistent with the previous difference observed between Tuamotu and Gambier archipelago (Ky et al, 2016b): more pale pearls were found in RRR culture site. In parallel, the rates of the most attractive green, peacock and aubergine pearl colours decrease significantly when using saibo from the anterior section compared to the three other zones (posterior, connection and middle).…”

“…This study explored, for the first time, cultured pearl quality trait variation within common donor individuals along the entire mantle of P. margaritifera. Previous studies on the species have already been designed to examine differences in cultured pearl quality traits brought about by: 1) using different donors at the individual or family scale, originating from wild (Tayale et al, 2012) or farmed (Ky et al, 2013) stocks, or from other species of the Pinctada genus (McGinty et al, 2010), revealing evidence of family effect, even among halfsib progenies (Ky et al, 2016a); 2) rearing at different culture sites (Blay et al, 2016;Le Pabic et al, 2016), including at the archipelago scale (Ky et al, 2016b) way; to confirm that if the anterior section gave the palest pearls, it would be the case, whatever the culture site, or the animal age used.…”