Ocean Literacy · Marine Taxonomy

One Name, Two Oysters: DNA Settles a 176-Year Indo-Pacific Question

A Curtin-led team combined museum specimens with gene sequencing to confirm that two rock oysters from opposite ends of the Indo-Pacific are separate species. Along the way, they recorded something nobody had documented before: a reef built by one of them on the Western Australian coast.

By SEVENSEAS Media | Ocean Literacy

Oysters are difficult animals to name. Their shells warp to fit whatever rock they settle on, thicken where the surf is heavy, and crowd into strange geometries where they grow shoulder to shoulder. That plasticity has made the genus Saccostrea one of the more stubborn problems in Indo-Pacific marine biology, and it is the reason a question first raised in 1850 has taken until now to get a firm answer.

The question is straightforward to state. In 1807, French naturalists working the Western Australian coast described Saccostrea scyphophilla from Bernier Island in Shark Bay. In 1850, a second rock oyster, Saccostrea mordax, was described from Fiji, roughly 6,000 kilometres east. The two looked similar enough that biologists have argued ever since over whether they were two species or one species wearing two outfits.

A study led by Curtin University, published in the taxonomic journal Zootaxa in April 2026 and publicised by the university this month, reports that they are two. The team sequenced DNA from historic museum material and from freshly collected specimens and found the two oysters to be genetically distinct.

What the shells could not say

Shell shape had always been the obvious place to look, and it had always been the least reliable witness.

Lukehurst, a senior research officer in Curtin’s School of Molecular and Life Sciences, said in a university statement that sequencing gave a definitive answer where morphology could not. The two species do not overlap neatly in range. According to the Curtin release, S. scyphophilla occurs along the Western Australian coast, across northern and eastern Australia and into the Indo-Pacific, while S. mordax sits further north and east, from Asia through to Fiji.

The paperwork behind the answer

Resolving a taxonomic dispute this old is partly a laboratory problem and partly an archival one. The team worked with historic specimens held at the Smithsonian Institution and the Museum of Comparative Zoology at Harvard University, alongside newly collected material from Bernier Island, the locality where S. scyphophilla was originally described.

They also did some housekeeping that will matter to anyone who works with these names. The paper designates a neotype for S. scyphophilla, now deposited at the Western Australian Museum. A neotype is a replacement reference specimen, designated when the original material behind a name is lost or too poor to settle arguments. It gives every future researcher a single physical object to measure their samples against. The paper also folds several long-floating names into the two species as synonyms, including Saxostrea amasa and Saccostrea mordoides.

Worth flagging for readers who use taxonomic databases: until now, several widely used references treated S. mordax as a synonym of S. scyphophilla, which is to say they treated the two as one. Those entries will need revising. Names in public databases lag behind the literature, and this is a good illustration of why a species list is a working document rather than a settled fact.

A reef nobody had recorded

The finding most likely to interest conservation practitioners is not the name change at all. In the course of the work, the team documented a tropical oyster reef at Point Quobba on the Western Australian coast, built by S. scyphophilla. The paper reports it as the first reef recorded as constructed by this species.

That is a modest sentence carrying a fair amount of weight. Reef-building oysters do work that is hard to replace.

Whether the Point Quobba reef is genuinely unusual or simply the first one somebody wrote up is a question the paper does not resolve, and it is a fair one to hold onto. Northern Western Australia is a long, thinly surveyed coastline. Adjunct Professor Fred Wells, a co-author also from Curtin’s School of Molecular and Life Sciences, noted in the university statement that many marine species along that coast remain poorly understood.

Why a name is a conservation tool

It is reasonable to ask why a taxonomic revision belongs in a conservation publication. The short answer is that almost every management instrument we use is keyed to a species name.

Protected area listings, fisheries and aquaculture regulations, biosecurity screening for introduced species, restoration targets, and biodiversity baselines all assume that the name on the form corresponds to a real and consistently identified organism. When two species travel under one name, a population can be considered secure because its lookalike is abundant elsewhere. When one species travels under two, effort gets split. Neither error is dramatic on the day it happens, and both are expensive to unwind later.

This paper does not, by itself, change any management decision. What it does is make future decisions about these oysters resolvable, and it gives anyone working on Indo-Pacific Saccostrea a fixed reference point to work from. The authors describe the study as a basis for further work on the genus, which remains only partly untangled.

Who did the work

The study brought together researchers from Curtin University, the Lee Kong Chian Natural History Museum and the Tropical Marine Science Institute at the National University of Singapore, the University of the South Pacific and the Pacific Community in Fiji, and the Field Museum of Natural History in Chicago. It was carried out under eDGES, the eDNA for Global Environment Studies program, a partnership between Curtin University and BHP. We note the industry funding for transparency; readers can weigh it as they see fit. The findings are published in a peer-reviewed taxonomic journal and rest on deposited specimens and sequence data that other researchers can check.

The paper, “Clarifying the identities of Saccostrea scyphophilla (Péron & Lesueur, 1807) and S. mordax (Gould, 1850) (Bivalvia: Ostreidae) from the Indo-Pacific” by Sherralee S. Lukehurst, Siong Kiat Tan, Koh Siang Tan, Jasha Dehm, Chinthaka Hewavitharane and Fred E. Wells, is published in Zootaxa 5799 (1), pages 1 to 31, and is available at doi.org/10.11646/zootaxa.5799.1.1. The Curtin University media release is available here.

SEVENSEAS Media · Conservation Journalism for the Ocean