Tropical Stromb found on Largs Bay Beach

May 3, 2018 | Posted in: Marine invertebrates, Molluscs

Steriyoula Thethes recently posted some photos of a couple of shells from Largs Bay beach on the SA Natureteers Facebook page, as follows: –

(Photos courtesy of Steriyoula Thethes)

“A new species of shell, Largs bay. And the last image of a shell that is becoming more common in the same area of Largs North”, said Steriyoula.

There were a few different suggestions about what the two shells might have been. I suggested that the Malacological Society of SA would know what they both were and passed the query on to Peter Hunt from that Society.

Here are a couple more photos of the first shell: –

(Photos courtesy of Steriyoula Thethes)

There were suggestions that this shell was a stromb. Ian Gibbins said, “The one beside the ruler is definitely a stromb. The notch at the anterior end of the outer lip is diagnostic. Strombs are a purely tropical group and are not found in South Australian waters.” Three MLSSA members had become involved in the conversation by this time.

Steriyoula Thethes commented, “I was thinking about the ballast water, and the very frequent international cruise ships at Outer Harbor. Perhaps spilled out with the ballast water. I am not an expert, but I sure wonder what they bring into our shores.”

Ian Gibbins commented, “Strombs are very athletic, at least for a gastropod mollusc. They have a kind of claw-like structure on the end of their foot which they use to quickly change direction, or to flip themselves over if they get up-turned, etc…”

Dan Monceaux thanked Ian, and he also thanked Steriyoula for sharing this sighting. He went on to say, “The Marine Life Society of South Australia would be interested in that. We’re discovering quite a few surprises in the Port River estuary of late, and yes, many are suspected to have been introduced via international shipping (ballast water or hull fouling).”

Steriyoula Thethes asked Dan if MLSSA would want the specimen. Dan’s reply was, “The South Australian museum would, Steriyoula. Contact Dr Andrea Crowther at the Museum – www.samuseum.sa.gov.au .

(Photo courtesy of Steriyoula Thethes)

By this time, Peter Hunt had told me, “The last image (shown above) is an example of the Mitra glabra or Smooth Southern Mitre. Our largest species in this group. It is common, and occasionally found on most local beaches. Up to 90mm. Live specimens have a black periostracum which is lost soon after mortality.

The other specimen (below) is a tropical shell very common and wide spread. From the Strombidae family which is not represented by any species here in SA.

(Photo courtesy of Steriyoula Thethes)

This one is most likely Strombus vomer most likely by colouration. A north WA specimen and would have been dropped on the beach by someone. Not possible to be found alive in our temperate waters. There is another similar from Qld called Strombus aurisdianae which this could be a faded specimen of. I hope this helps.”

Dan Monceaux weighed in with, “In the summertime, the Port River has pockets where tropical water temperatures are maintained, particularly those close to the thermal discharge from the Torrens Island power station.”

Ian Gibbins added, “I still don’t think a tropical species could live there… there is the whole ecosystem to consider, not just the water temperature…”

Steriyoula usually collects lots of shells during her weekly beach walks. Here is a photo showing a collection of them: –

(Photo courtesy of Steriyoula Thethes)

Many thanks go to Steriyoula Thethes, Peter Hunt, Dan Monceaux and Ian Gibbins for their assistance in this matter.

Steve Reynolds is the current President of MLSSA and is a long-standing member of the Society. Steve is a keen diver, underwater explorer, photographer and is chief author of the Society's extensive back catalogue of newsletters and journals.

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