Whilst diving at the old Rapid Bay Jetty on 25th October I saw the first decent aggregation of the Great Spider Crab, Leptomithrax gaimardii that I’ve seen for some years now. There were probably more than 200 crabs seen by us today, and there would have been more outside our fields of view.

I have posted my photos of the crabs to iNaturalist at https://www.inaturalist.org/observations/139943462

There may possibly have been some mating activity, although I cannot be certain of that. I did see some crabs heaped on each other as numbers of around 1 dozen or so in a few smaller areas of about a metre square.

We had rather expected to find the spider crab aggregation on this dive because we’d just heard of it by word of mouth.

I passed this information on to Dr Elodie Camprasse whose team at Deakin University has an iNaturalist project called Spider Crab Watch running. “It will allow us to gather more data on this iconic yet understudied species,” says Dr Camprasse. “If you log spider crab information in the future, could you please add them to the Spider Crab Watch program (https://www.inaturalist.org/projects/spider-crab-watch )? This would be super useful. Thank you! Elodie.”

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