I have written a lot about the natural variations in oyster shells belonging to the British Native, Flat, or European Oyster, Ostrea edulis Linnaeus. However variable these shells may be, it is always possible to identify the shells as belonging to that species, and to distinguish them from other species.
In Australia and the Far East, the oysters that grow wild and naturally on the tropical shores include several species of Saccostrea which can be difficult to differentiate from one another because of the diversity of their outward appearance. The morphologies of Saccostrea glomerata, Saccostrea cucullata, Saccostrea kegaki, and Saccostrea mordax, are so variable and overlapping that is not always possible to tell them apart by eye. As with so many other groups of organism currently being investigated (marine algae for example), it is only by use of mitochondrial-DNA analysis that true identities and relationships can be established (Lam and Morton 2006).
Which brings me to a discussion of the Rock Oysters that I photographed in several locations on the Queensland Coast. The images shown in this Posting were taken at Cape Tribulation in tropical Far North Queensland. Just going by the external characteristics, I suggest that they may be Saccostrea glomerata – also called the Sydney Rock Oyster. However, the differentiation of that species from Saccostrea cucullata is so problematic at times even for experts that oysters like this are frequently given both names, S. glomerata cucculata.
In following Posts I’ll show oysters growing in Yawarra Bay, Trinity Bay, and Port Douglas for comparison with these from Cape Tribulation. The shells from the rocks at the northern end of Three Mile Bay at Port Douglas look very different from the others and I think that they may be Saccostrea mordax. I’ll also refer in more detail to the Lam and Morton paper:
Lam, K. and Morton B. (2006) Morphological and mitochondrial-DNA analysis of Indo-West Pacific Rock Oysters (Ostreidae: Saccostrea species), Journal of Molluscan Studies (2006) 72: 235 -245, Oxford University Press on behalf of The Malacological Society of London.
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