A black long-spined urchin that grazes kelp down to bare rock. It has spread south into Tasmania as the water has warmed, and the barrens it creates are one of the clearest visible effects of that.
Test to about 12 cm with long black spines. It sits in a rock crevice by day and grazes at night, and where it is abundant it removes the kelp entirely and leaves bare rock — the urchin barrens that are now a large part of the New South Wales coast and are spreading into Tasmania.
That spread is the interesting part and it is recent. The East Australian Current has strengthened and warmed, and the urchin’s larvae now survive as far south as Tasmania, where the kelp forests had never had to deal with it. It is one of the clearest and most visible effects of a warming current anywhere a diver can go and look. Fishery and restoration programmes are removing it in places.
The spines are long, brittle and go through a glove. They break off in the wound and are hard to remove; the injury is a puncture rather than a sting.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.