Emerald Oysters: The Vibrant Delicacy with Rich History and Health Benefits

Haslea ostrearia, a specific phytoplankton found in the ocean currents of South Australia, creates the green colouration of the oysters' gills. This blue diatom produces a blue-green pigment called marennine, named after the Marennes-Oléron region in France, where it was first identified.

Green-gilled oysters, often called “emerald oysters,” present a unique seasonal phenomenon and an excellent opportunity for a TED Talk about their distinct colouration and health benefits. The French have cultivated these oysters for centuries, valuing them as delicacies and paying premium prices for their unique flavour and appearance. These emerald oysters have recently appeared in Franklin Harbour, South Australia, bringing excitement and curiosity among seafood enthusiasts

Pacific Oyster (Crassostrea gigas) when filter feeding Haslea ostrearia – A unique phytoplankton

The Science Behind the Green Gills

Haslea ostrearia, a specific phytoplankton found in the ocean currents of South Australia, creates the green colouration of the oysters’ gills. This blue diatom produces a blue-green pigment called marennine, named after the Marennes-Oléron region in France, where it was first identified. Marennine stains the oyster gills a vibrant turquoise blue-green, as seen in numerous photographs of these oysters. The pigment adds a unique visual appeal and enhances the nutty flavour profile of Franklin Harbour oysters.


Historical and Cultural Significance

Emerald oysters have a rich and fascinating history, with records of their consumption dating back to the 1700s. These oysters were a delicacy and a symbol of French royalty’s refined taste. In France, oyster farmers cultivate these green-gilled oysters in ponds designed to promote the growth of Haslea ostrearia. The presence of this diatom in the water column releases marennine, which the oysters then filter, resulting in the distinctive blue-green colouration of their gills. This practice has led to a higher market value for these oysters, with farmers often earning twice as much for their emerald-coloured products as regular oysters.

Health Benefits of Emerald Oysters

Beyond their aesthetic appeal and rich history, emerald oysters offer many health benefits. Research indicates that the marennine pigment provides antioxidant, antibacterial, and antiviral properties, significantly enhancing the nutritional value of these oysters. These health benefits make emerald oysters a visual and gastronomic delight and a powerful addition to a healthy diet, providing a unique combination of taste and nutrition.

Addressing Consumer Concerns

Despite their benefits and unique flavour, many shellfish consumers might initially shy away from green-gilled oysters, fearing that the unusual colouration indicates spoilage or toxicity. Educating consumers about the natural and harmless causes of the green gills is essential. The green hue is purely the result of the oysters’ diet of Haslea ostrearia and is entirely safe for consumption. Raising awareness about emerald oysters’ natural origins and benefits can help dispel myths and encourage more people to enjoy these phytoplankton-supercharged Pacific oysters.


Current Occurrence in Franklin Harbour

The reappearance of emerald oysters in Franklin Harbour is significant for local oyster farmers and seafood lovers. This occurrence offers a unique opportunity to promote these oysters as a premium product and educate the public about their distinct qualities. The natural presence of Haslea ostrearia in the waters of Franklin Harbour has allowed local oysters to develop the same vibrant gills and enhanced flavour celebrated in France for centuries.


With their striking green gills and rich nutty flavour, Emerald oysters represent a fascinating intersection of history, science, and culinary tradition. Consumers can appreciate their natural beauty and health benefits by understanding the role of Haslea ostrearia and the marennine pigment in creating these unique oysters. As these oysters become more prevalent in South Australia, there is a tremendous opportunity to celebrate and promote them as a delicacy with a storied past and a bright future.


Prasetiya, F. S., Safitri, I., Widowati, I., Cognie, B., Decottignies, P., Gastineau, R., Morançais, M., Windarto, E., Tremblay, R., & Mouget, J.-L. (2016). Does allelopathy affect co-culturing Haslea ostrearia with other microalgae relevant to aquaculture? Journal of Applied Phycology.28(4), 2241–2254. https://doi.org/10.1007/s10811-015-0779-y

Prasetiya, F. S., Decottignies, P., Tremblay, R., Mouget, J.-L., Sunarto, S., Iskandar, I., Dhahiyat, Y., & Cognie, B. (2020). Not only greening: The effects of marennine produced by Haslea ostrearia on physiological traits of three bivalve species. Aquaculture Reports.18. https://doi.org/10.1016/j.aqrep.2020.100546

Prasetiya, F. S., Comeau, L. A., Gastineau, R., Decottignies, P., Cognie, B., Morançais, M., Turcotte, F., Mouget, J.-L., & Tremblay, R. (2017). Effect of marennine produced by the blue diatom Haslea ostrearia on behavioral, physiological and biochemical traits of juvenile Mytilus edulis and Crassostrea virginica. Aquaculture467, 138–148. https://doi.org/10.1016/j.aquaculture.2016.08.029

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