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Research is paving the way for more profitable and environmentally friendly black pearl farming on the atolls of the South Pacific islands where production has taken a dive.
A recent special issue of Marine Pollution Bulletintook stock of the current knowledge and futureresearch needs for improving the sustainability of French Polynesia's black pearl trade.
Popularly known as 'Black Gold' or 'Tahitian Treasure', black pearls are French Polynesia's second largest economic resource after tourism.
- The price of black pearls plummeted to below US$5 per gram in 2010
- Farms have also been hit by unexplained pearl oyster deaths
- But research is uncovering the links between oysters, their habitat and the plankton they eat
The aquaculture of black pearls in French Polynesia boomed in the late 1980s and has "modified the livelihoods of thousands of islanders in the past 30 years", according to an editorial in the journal's special issue.
But since the turn of the century, the "black pearl industry has reached its climax, collapsed, and is now in a recovery stage".
Black pearl prices dropped from around US$100 per gram in 1985 to less than US$5 in 2010, primarily because of overproduction of low-quality pearls and commercial management of distribution to the Asian, European and US markets. This also means that fewer concessions have been given to smallholder farmers to develop new farms.
The global economic downturn also played a role, according to Jeremy Shepherd, founder and president of the US-based retailer Pearl Paradise.
"In 2008, the global economy took a serious hit. Over the next couple of years, prices for Tahitian pearls fell dramatically," Shepherd says. "It is impossible to stop harvesting pearls once the shells have already been implanted, so when people stop buying, it takes a couple of years before producers can stop producing."
Meanwhile, widespread deaths of pearl oysters remain poorly explained because of insufficient monitoring of environmental conditions given the remoteness of the atolls where the oysters live and monitoring costs. In addition, the pearl industry's exact ecological impact remains unknown.
"The success or failure of pearl farming relies heavily on the environment," says Lulu Tyers, founder and managing director of UK-based jewellery company Pearl-Lang.
"Water temperature and quality has a direct effect on the health of the oyster. Oysters feed by filtering tiny organisms called plankton from water. But an event called a red tide, when phytoplankton multiplies too quickly and becomes overabundant — often caused by pollution in water — is deadly for the oysters," she says.
Since 2008, researchers have been paying closer attention to water circulation, oyster dispersal and the plankton they eat in an attempt to better understand the relationship between oysters and their habitat.
Research carried out by on the Ahe atoll lagoon north of Tahiti has yielded new insights into how oysters feed; what environmental conditions influence the dispersion of their larvae — and thus why particular areas of the lagoon are better than others for collecting young oysters; and did not reveal any direct signs of environment contamination caused by the farms.
This understanding should aid efforts to improve the economic performance of Polynesian pearl farming, according to a press release by the French scientific organisation the Institute of Research for Development (IRD).
"Our goal now is to expand that information into how oyster larvae are dispersed and what conditions are optimal for their growth," IRD researcher Serge Andréfouët tells SciDev.Net.
But Josh Humbert, owner and manager of a pearl farm Kamoka Pearl, says that large-scale producers may be harming the ecosystem.
"The larger industrial farms often employ high-power water hoses to clean them and blast anemones off the oysters. But this practice causes numerous environmental problems. While the blasting kills most of the anemones, breaking them up with powerful jets of water causes them to disperse and provokes them to multiply upsetting the ecological balance of the lagoon. Many atolls in French Polynesia suffered because of this," he says.
Instead, Humbert suggest the holistic method of cleaning the oysters where natural fish populations feeds on the anemones.
"Farmers bring the oysters to shallow zones with existing fish populations and allow them to nibble on the anemones. But this method requires labour that we often can't afford now due to falling prices."