Mollusc mortuaries

This photo may not seem very spectacular, but there’s more information in it than you might suppose. If you are a bit of a beach detective (or intertidal itinerant), you can get an idea of what’s in or near the area and gauge the health and biodiversity of the local ecosystem.

Where have you all come from?

In fact, there have been several studies done on these collections of dead bits and pieces. One, published in 2009, is: ‘A state-wide assessment of marine, intertidal, molluscan death assemblages for NSW’, by Stephen D. A. Smith of the School of Environmental and Rural Science, National Marine Science Centre, University of New England. Other such studies are referenced in the report.

Fifty beach sites in NSW and one in south-east Queensland were investigated (trawling the entire coast of NSW’s beaches for shells – sounds awful, doesn’t it 🙂 )

Several collecting sites are local-ish to me. Skennar’s Head is just north of Flat Rock (collection site 5 in Table 1, and on the map in the report), which I’ve posted about a lot. Flat Rock is listed as having 127 molluscan species in the assemblages. Woody Head, which I’ve also posted about many times, is collection site no. 7.

Habitat diversity implies species diversity, as many species have specific habitats. Species common to all sites were Siphonaria denticulata and Cellana tramoserica  (limpets), Cabestana spengleri (Spengler’s triton), Austrocochlea porcata (a small herbivorous gastropod), Montfortula rugosa (a keyhole limpet); Saccostrea glomerata (the Sydney rock oyster), and Thais orbita (the cart-rut shell, Dicathais orbita in many reference books). You can see my photos of Thais orbita and Cabestana spengleri here.

Flat Rock has four species unique to itself, but which exact species aren’t mentioned, unfortunately.

The author points out that the composition of ‘death assemblages’ is likely to be biased towards those shells less likely to break, those that are readily transported onshore by currents (the author says he has observed that shell shapes have a lot to do with that) and the ones left over after shell collectors have been through ( I have to confess that I once took a load of shells I didn’t want to such an assemblage, and there were very likely interstate ones in the collection).

There is also no way to tell how recently or otherwise the shells have been deposited or exactly where they came from, as currents can bring them in from up to 150 kilometres away. I’d assumed that they would be very local, but that isn’t necessarily so.

There’s a lot more detail in the study that you can read for yourself if you’re so inclined. Fascinating stuff!

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2 Responses to Mollusc mortuaries

  1. Ha! Yes, it occurred to the researchers that beachcombers may have high-graded the best shells–but they didn’t take into consideration folks like you who BRING shells to the beach! LOL!

  2. Cath Clark says:

    Prettiest gravesite I ever did see

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