The Effects of Global Warming on Pearl Oysters

Warming waters, changes in weather patterns, and increases in storm activity may all affect the future success of pearl farms, both freshwater and ocean-based. Precisely what impact they will have is a little harder to determine: Relatively little research has been done into oyster husbandry.

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By Suzanne WadeMore from this author

As the world gets warmer, pearl oysters are on the front lines of the ocean's early warning system.

In February 2007, the United Nations Intergovernmental Panel on Climate Change released a report that confirmed what most people intimately connected with the environment already knew — the planet is getting warmer, and its oceans are changing as a result.

In March, the pearl industry responded by drawing up a resolution during the annual World Jewellery Confederation (CIBJO) conference supporting the Kyoto Protocol. The Kyoto Protocol is thus far the world's most important treaty addressing global warming; its goal is to reduce the carbon emissions thought to be contributing to the warming trend.

Oysters of all types are particularly susceptible to the effects of warming oceans.

"Oysters are very much the canaries of the ocean system," says Joseph Taylor, manager of Atlas South Sea Pearls in Indonesia. "The first animals to be affected by changes in pollutants or climates are bivalves, because they can't move [away] and they're cold blooded."

Warming waters, changes in weather patterns, and increases in storm activity may all affect the future success of pearl farms, both freshwater and ocean-based. Precisely what impact they will have is a little harder to determine: Relatively little research has been done into oyster husbandry.

"In the past, pearling companies haven't had to invest much into research and development," says Dean Jerry, senior lecturer and the leader of the Aquaculture Genetics Program at James Cook University's School of Marine and Tropical Biology in Townsville, Australia. "The solution [to most problems] was just to put more oysters in the water."

Anecdotally, though, there are reasons for the pearl industry to be concerned. From the struggles of the Japanese akoya industry to overcome the effects of pollution and disease to high levels of South Sea pearl oyster mortality during El Nino years, there are signs that widespread changes in the environment could permanently change the ways and the places where pearls are grown.

One of the signature symptoms of climate change is increased ocean surface temperatures. A study published in the Proceedings of the National Academy of Sciences in the United States notes that tropical ocean temperatures have risen between 0.37C and 0.67C in the last century. Some scientists predict that temperatures could rise several degrees more in the coming decades.

Warmer waters are a concern to pearl growers because excessively high temperatures are known to result in higher oyster mortality. Research done by Naama Britt at the University of Haifa in Israel showed that Pinctada radiata oysters in the eastern Mediterranean thrived best in water temperatures lower than 26 C, while at 31 C the survival rate decreased, dropping to just 6 percent after four months.

Although these pearl oysters are a different variety from those commonly used to culture pearls, pearl growers in the South Pacific have also observed that the higher water temperatures associated with an El Nino weather pattern can lead to significant die-offs.

"Every five to seven years, we have an El Nino year, with the warming of the Pacific Ocean driving more torrid weather. When we have those effects, the survivability of any group of oysters tends to be much lower," says Taylor.

Recent studies have also shown that higher water temperatures make oysters more susceptible to pollution. Research by a team of University of North Carolina scientists on nonpearl-producing oysters demonstrated that relatively low levels of heavy metal pollution interfered with the shellfish's metabolic processes, which, combined with higher seasonal water temperatures, could lead to disease and death.

There are also questions about whether higher water temperatures will affect the quality of the pearls produced. "The quality of a pearl tends to be dependent on how fast the pearl grows," observes Jerry. "As water temperature increases, the growth of the oyster increases and they lay down nacre faster, which is believed to reduce the quality of the pearl."

Storm Watch

Changes in global temperatures are expected to change weather patterns worldwide, resulting in drought in some areas, floods in others, and possibly more frequent and more intense tropical storms. None are good news for pearl growers. Drought would have an obvious negative impact on freshwater pearl cultivation. "During prolonged dry periods, some mussel beds are at risk of drying out," observe the authors of a study of Scottish mussels published in AMBIO, the journal of the Royal Swedish Academy of Sciences. "Furthermore, the amount of silt deposits, algal growth, and organic debris on the riverbed may increase considerably as a result of reduced [water] flows. This process is detrimental to newly- settled mussels."

Increased rainfall may not be better news. Although greater water flow appeared in the AMBIO study to increase reproduction and spreading of mussel beds, serious flooding posed a danger to many mussel populations. "When exceptionally large floods occur, the ecological effects can be catastrophic," the researchers reported, noting numerous examples of mussel beds being severely damaged or destroyed by heavy flooding. More frequent, heavy rainstorms can also result in increased water pollution, points out Ian Hart, director of communications of the Pacific Institute, an environmental think tank based in California. "One likely consequence of climate change is extreme weather events in the form of more powerful rainstorms," he explains. "Powerful storms overpower the soil's ability to absorb rainfall as groundwater, and in developed areas are likely to overpower storm water treatment systems. The resulting runoff finds its way into our rivers, streams, and eventually oceans, and contains a host of pollutants, including sediment, fertilizers, chemicals, trash, and bacteria."

For South Sea and other saltwater pearl growers, another danger may be more frequent and more severe tropical storms. "The oysters themselves live in an ocean environment and have a degree of adaptability to storms," says Taylor. "But the way we farm is different than a natural habitat. The oysters are more exposed on a farm than if they're on rock or coral. Storms also bring in a lot of sediment, and that changes the sea chemistry, which will affect their health directly."

In addition, damage from more frequent storms could be costly. "The equipment we have in the water is meant to withstand storms, and it does, but each time you have a storm event there is a cost to ensure that everything is safe and protected, and if damaged, that it is repaired," says Taylor. "If you were suddenly faced by an increased amount of storms, it could get to a point where you couldn't sustain it. For example, [a West Australian] farm might expect to get hit with a cyclone one year out of four or five, but if it became every year, the viability of the operation would come into question." Many of the most significant impacts of climate change may still be decades away, and even climate experts are uncertain about the extent of the changes. As a result, it's difficult to say whether their impact on pearl growers will be minimal, devastating, or something in between. But there is no doubt that the health of the pearl industry is intimately entwined with the health of the ocean environment, and that pearl growers will have to learn to cope with changes global warming is almost certain to bring.

"I think [climate change] is almost unavoidable now. It's the severity we don't understand," says Taylor. "What we do know is when we have an obvious climactic event, such as El Nino, it does have an effect on survival. So as we move into a changing climate, and we see changes in temperatures, that will affect things."

"The only thing we can do is to assist in looking after the environment, and to remind people that the beautiful product they're wearing is something they can only have if the environment is protected," he concludes. "We do have a role in helping our consumers understand that our object will only exist while the ocean and the general environment is in good health."

Under Water

Warming waters and melting ice are also causing rising sea levels. The United Nations report noted that sea levels are now rising an average of 3 mm per year, with a total accumulated rise of 0.17 meters in the last century. That rise is small enough and gradual enough to have had only a small impact on most coastlines, but low-lying river deltas and South Pacific islands are particularly vulnerable to rising seas.

Studies of the impact of sea level rise on coastal areas in China, including the Pearl River Delta, have predicted economic losses in the billions of dollars due to flooded wetlands and contaminated groundwater. In addition, rising sea levels already threaten coastal communities on some Pacific islands, including Tuvalu — which saw the highest tides on record flood coastal communities last year - and Vanuatu, which in 2006 undertook the relocation of the village of Tegua because of repeated flooding due to high tides.

Such problems are unlikely to directly affect pearl farms. Unlike coral reefs, where rising sea levels interfere with the sunlight available to organisms dependent on it for their growth, pearl farms can adjust the depths pearl oysters are cultivated at to take into account changes in sea level and food supplies.

Pearl growers will have to contend with the effects of sea level rise on the island communities where their farms are located, however. "If you're operating in [these isolated areas], there is a high expectation that you are supporting the community," says Taylor, who notes that his company has built schools, provided medical care, and is often the only regular source of transport in remote areas. "If a village were greatly affected by a storm or rising sea levels near us, we would be the first port of call."

Another possible impact of climate change is an altered sea chemistry, particularly changes in salinity and acidity.

A study from the Woods Hole Oceanographic Institute noted that tropical ocean waters have become dramatically saltier in the last 40 years, a change which could accelerate if rising temperatures and increased melting of ice sheets results in slowing or shutting down of planet-wide circulation of fresh and salt water in Earth's oceans. Salinity has been shown in multiple studies to have a direct effect on the growth rate of pearl oysters, with salinity levels in excess of 40 parts per thousand shown to slow growth significantly.

Higher levels of atmospheric carbon dioxide may also make the oceans more acidic. A team of researchers from the National Oceanographic and Atmospheric Administration Pacific Marine Environmental Laboratory in Seattle found measurably lower pH levels in ocean waters from Tahiti to Alaska, as well as increases in dissolved inorganic carbon. Scientists predict that as levels of dissolved carbon dioxide in sea water rise, the skeletal growth rates of calcium-secreting organisms, such as corals, plankton, and shellfish, could be reduced.

Whether this greater acidity would harm pearl oysters has not yet been studied, and scientists disagree on how acidic the ocean may become. However, the potential loss of coral reef habitats and organisms that form the foundation of the marine food chain, as well as direct damage to oyster shells, could be yet another future source of trouble for pearl growers.

Building a Better Oyster

The effects of global warming are likely to be gradual, and pearl growers are optimistic that oysters can be bred to adapt to counter the environmental changes. Jerry and his colleagues at James Cook University are working to establish a selective breeding program they hope will breed oysters that produce higher-quality pearls and are able to survive under a variety of environmental conditions.

The research is still in the early stages, and data collected has yet to be analyzed to determine if some oyster "families" survive environmental stresses better than others. But Jerry is betting the answer will be yes. "I think there will be oysters which are better adapted to [changing] conditions and will survive and grow, while other families will be exterminated. Having that information will allow us to include it as a breeding objective."

Taylor also notes that pearl growers may also be able to move their operation to areas newly conducive to pearl farming. "Some areas might become more appropriate, while some areas might no longer support [pearl farms]," he says. "As it stands, we structure the program so that we do certain activities in certain areas where it suits a particular life stage of the oyster. For example, all our breeding work is in north Bali, because we've found that site best suits survival and growth of young oysters. It might be with changing conditions, areas formerly good for pearl growing might not be so any more, and we might have to restructure or move entirely."

By Suzanne Wade – © Colored Stone
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Suzanne Wade

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