Pearl Farming

Nov 7
5 min read

Lagoon species tested as indicators of plastic pollution

For the past thirty years, pearl farming — the second-largest economic resource in French Polynesia — has relied on plasticbased equipment, which is more durable than natural materials. The consequences: an accumulation of waste, water pollution, and negative effects on the oyster and its pearl. Could the industry be hastening its own decline? That is the question marine biologist Maëva Goulais set out to explore. From 2021 to 2024, she conducted a PhD based on monitoring tropical species — most of which had never been studied before — to assess the impact of plastic pollution on the tropical marine ecosystem and its resilience. Her research also offers insights and potential solutions to this growing issue.

Texte : Doris Ramseyer - Photos : © Doris Ramseyer, Maëva Goulais (schémas et portrait), Tahitienne de Service public (TSP)

In 2021, Maëva Goulais, a PhD student in marine biology, began a groundbreaking thesis on the toxicity of plastics used in pearl farming. Her research is based on the larval development of several lagoon species native to French Polynesia. With a keen interest in the impact of human activity on ecosystems, she is determined to contribute meaningful insight to the field.

Her work is rooted in French Polynesia at the Pacific Ifremer Center (CIP) in Vairao — an ideal setting for studying tropical species that, unlike their temperate counterparts, have rarely been examined in this context. She is supervised by a microbiologist and a plastic pollution specialist and collaborates closely with the Department of Marine Resources (DRM).

Plastic Pollution in Three Forms

According to Maëva, plastic pollution acts on three simultaneous fronts. The first is physical: large visible debris that can suffocate marine animals, as well as microplastics resulting from degradation, which are ingested by many organisms. The second is chemical: plastics leach various additives into the environment — a form of contamination that is invisible yet deeply harmful. The third is biological: floating plastics are colonized by organisms, some invasive or pathogenic, which then travel long distances on these artificial rafts.

“All three forms of pollution act at once,” Maëva explains. “Visible plastic seems the most threatening, but the others are often far more insidious.”

Plastic pollution operates on three levels: chemical, biological, and physical

Identifying Bioindicator Species

Her thesis focuses on chemical pollution — still poorly understood in the context of pearl farming. The team immersed 50 grams of polyethylene (PE) and polypropylene (PP) rope, taken from 200-meter buoy lines, along with 50 grams of plastic spat collectors, in one liter of seawater for 24 hours. The mixture was then filtered to isolate the liquid: plastic leachate. This leachate was diluted to create a range of concentrations for testing. Chemical analysis conducted in mainland France revealed the presence of phthalates, hydrocarbons, and numerous pesticides — all potentially toxic to marine life.

Five tropical species were selected:

Litopenaeus stylirostris (blue shrimp)
Tripneustes gratilla (collector urchin)
Holothuria whitmaei (sea cucumber, or rori)
Pinctada margaritifera (black-lipped pearl oyster)
Saccostrea cucullata (rock oyster)

Fertilized eggs from each species were exposed to the leachate. After 24 hours, the researchers assessed how many larvae developed normally, how many displayed malformations, and what percentage had died. A median effective concentration (EC50) was calculated to determine species sensitivity. Sea cucumbers were the most sensitive, but none of the species tested were unaffected. “None resisted high plastic concentrations,” notes Maëva, “and all showed serious developmental disruption.”

In her conclusion, she recommends using Holothuria whitmaei as a bioindicator species, given its heightened sensitivity and its wide

distribution in tropical marine ecosystems. A Simple Tool for Monitoring Pollution. Due to a lack of facilities in Tahiti, water and leachate samples had to be shipped to Brest — a costly and logistically complex process.

Plastic pollution operates on three levels: chemical, biological, and physical

To simplify future assessments, Maëva advocates using tropical larvae as a bioassay tool to evaluate lagoon water quality. Healthy larval development would signal clean water, while deformities or high mortality rates would point to pollution and the need for further investigation. “It’s a low-cost, accessible tool,” she says.

Impacts on Pearl Oysters

In parallel with her larval testing, the research team monitored 1,200 pearl oysters over six months.

Divided into groups of 300, the oysters were placed across four atolls: two pearl-farming sites (Takapoto and Takaroa) and two without farming activity (Tikehau and Anaa).

While rori proved useful in detecting microplastic toxicity, studying the health of pearl oysters — central to French Polynesia’s economy — was just as critical. The results were unequivocal: all oysters and water samples contained plastic particles. Plastic pollution was detected even in the least populated atolls, showing that pearl farming is not the sole source of contamination. Laboratory tests further confirmed that exposure to microplastics affects the growth, reproduction, and immune function of Pinctada margaritifera.

To date, only two studies have found microplastic particles inside pearls, and the phenomenon remains rare. But if no action is taken, Maëva warns, the presence of plastics may become more common in oysters and pearls alike — potentially undermining the reputation and quality of Tahitian pearls.

Which Path Forward?

Most pearl farmers Maëva interviewed expressed a genuine interest in adopting more sustainable practices — but they lack the means to do so. For now, there is no viable alternative to plastic, although experimental research is underway into bio-based materials that could prove more durable and less polluting.

In her view, real change must come from political will. She proposes two priority actions:

Limit the number of collector lines in heavily saturated atolls, where they are often used for only 2 to 3 years — adding to waste and storage problems.
Ban plastics with toxic additives, or at least introduce protocols to reduce their impact, such as pre-soaking to remove leachable substances before immersion.

However, she notes, “manufacturers are not currently required to disclose the composition of their plastics, which makes regulation difficult.” A Scientific Contribution to Ecological Decision-Making Maëva Goulais’s rigorous and thoughtful work offers a valuable tool for managing pearl-farming lagoons. Maintaining the ecological health of these environments is essential — not only for the future

of the pearl industry, but for the preservation of marine biodiversity as a whole.