I posted details on iNaturalist regarding my sighting of what appeared to be Giant Chitons, Plaxiphora albida at Fishery Beach on 15th September 2023.

“These were quite common on this snorkel. Speculation only:- I often wonder if these large molluscs, so tasty for larger wrasse, are now far more common in Gulf St Vincent (GSV) than they would have been a century ago, when adult Western Blue Groper still occurred in lower GSV, and there were higher populations of large adult Bluethroat Wrasse. Surely a giant chiton would be a sitting duck for big wrasse, as they are often found on bare rock surfaces. I then ask myself whether a chiton species could evolve behaviourally so fast (natural selection favouring spending more time where the best food is, and less time hiding in crevices, safe from predators) that, within only decades of drastically reduced predation pressure, they could have learned that they are safe out in full view on bare rock?”

“After my speculation, I read the linked blurb about this species, and it makes no mention of wrasse among the list of potential predators, but includes starfish, etc. Their list is not intended to be complete, nor necessarily accurate, i.e. the science needs more scrutiny before anyone can rule larger wrasse out or in.

“And for what it’s worth anecdotally, I’ve watched mature Western Blue Groper greedily snatch smaller chitons than this species from beneath rocks I’ve turned. So they certainly like eating chitons. Whether Giant Chitons are fair game, or perhaps have an unpleasant taste, is another question in need of an answer.”

By David Muirhead

David is a long-serving member of the Marine Life Society of South Australia. He has dived and snorkeled in South Australian waters for around five decades and has a particular interest in bony fishes. David has made the greatest single contribution to the society's Photo Index of local marine species.

One thought on “Giant Chiton, Plaxiphora albida, sightings at Fishery Beach”
  1. PS: I forgot to mention that Giant Chitons have an estimated life span of 6 years but have almost reached their full size after 2 years.

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