A Critically Endangered Industry

At the heart of every cultivated black pearl is a seed, its nucleus. This seed, when surgically implanted into the gonad of the black pearl oyster (Pinctada margaritifera), is used to irritate the oyster into producing a pearl and the seed’s shape determines the shape of the pearls produced.
After researching the source of these seeds, I made an alarming discovery.
These seeds actually come from an increasingly rare source, namely the shell of the flat pigtoe mussel (Pleurobema marshalli), found in the Mississippi River delta and endemic to the continental United States. According to The International Union for the Conservation of Nature and Natural Resources (IUCN), an internationally recognised authority on the conservation status of species, this mollusk is categorised as critically endangered. According to the definition assigned to this status, it means that the number of flat pigtoe mussels have decreased, or will decrease, by 80 per cent within three generations.
So why is such an endangered species used in the Cook Islands’ pearl industry?
The currently utilised technique for seeding pearl oysters is little changed from the method developed and patented in the early part of the 20th century by the pearl industry pioneer Kokichi Mikimoto in Japan. Today’s method generally involves the implantation of a nucleus made from the pigtoe shell chosen due to its similarity to the pearl producing oyster shells and because of the shells thickness.
Large seeds can be created as the shell of the pigtoe can be up to 2.4cm thick, therefore enabling large seeds to be made, up to 20 seeds from a single shell. In the early 20th century. the world’s pearl market was small, mainly focusing on natural pearls and not cultivated ones. Today, millions of cultivated pearls are produced annually and therefore the use of pigtoe shell has exponentially increased.
Another reason for the use of pigtoe shell seeds is that as the pearl oysters excrete their nacre, covering the foreign body introduced into them, it is important that the introduced seed does not expand and contract at different temperatures from the nacreous layer, as this would lead to cracks in the finished pearl product. Suffice to say, pigtoe mussel shell offers the almost exact and necessary properties.
As pearl production globally steps up, the availability of these martyred mollusks will dwindle – ultimately they will cease to exist. Will another shelled creature then take its place as the seed giver for each and every pearl? And how long until this species is also driven to extinction through over harvesting?
With pollution of the Mississippi River delta also taking its toll on the dwindling pigtoe population, alternatives need to be found and soon. As dependence on natural pearl production is seen as too unreliable, with the yield being too low for commercial exploitation, perhaps it will be in the form of an artificial shell that can provide these seeds in the pigtoes’ stead. As it stands, though, potentially causing the extinction of one mollusk species to fuel the commercial exploitation of another is ecologically immoral and economically unsound in the long term.
By Simon Spinola

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