Year 9 students of Shelford Girls’ College conducted shoreline shell and litter surveys at Middle Brighton today. Shells found were typical of the species gathered by Boon Wurrung (traditional owners) from shore platforms along the east coast of the Bay. They included abalone, turbos, and several species of limpets. But the most notable find was a large cart-rut shell (Thais orbita).
rare find at Brighton
This species is known to be affected by Tributyltin (TBT), the active chemical in some boat hull anti-fouling paints. Use of anti-fouling paints containing TBT were banned in Victoria in 1989 for use on recreational boats, but still permitted on commercial ships. Baykeeper shoreline surveys conducted around the Bay over the past 4 years have found only a handful of these shells. Thais orbita is a predator of other molluscs known to inhabit rocky shores to 10m deep.
So do you think this shell shows signs of TBT damage? Or is it just a very rare shell in these parts?
The effects of tributyltin aren’t seen on the shell. TBT causes the condition of imposex, where females of many species of gastropod grow male sex organs, eventually making them unable to breed. This can be bad news for whole populations.
This species is widely distributed in Australia and New Zealand, but was one of the reasons why TBT was banned in 1989. Unfortunately there appears to be no baseline data which might be used to measure population change of cart-rut shells in the Bay. They didn’t get listed in the 1968-71 Port Phillip Bay Study, which only recorded species living on or in sandy and silty sediments (cart-rut shells live on rocky shores).