Over the last few weeks I have had several conversations with fellow walkers as we stepped over hundreds of creatures that created brilliant purple stains upon the white sands of Callala Beach. Some of us tried to pick the slippery culprits up and toss them back out to sea, only to have our hands dyed violet. Others bent to observe their squishy little olive green bodies. None of us understood why there were so many. So, I decided to do a little Googling and found the Australian Museum and scientist Bill Rudman had a wealth of knowledge on these unusual little creatures with many curious qualities.
I confirmed that they were indeed Sea Hares and aptly named due to their long tentacles that certainly resemble the ears of a hare. They are in fact slugs and part of the mollusc family. They have an internal shell and ‘wings’ that help them swim gracefully through the water, unafraid of any known predators. For it is not known what will or can eat a Sea Hare. They love hanging out around rocks and the intertidal zone where they are cleverly camouflaged.
Being herbivores, their favourite food is algae and seaweed. It is believed that the purple dye is a result of the Sea Hare dining on red seaweed. Every resident of Callala Beach is aware that when the southerlies hit and the swells surge with ferocity, we often find the beach draped in a vibrant red coat of weed that is the colour of shiraz. Delicious to a Sea Hare!
And so why the purple dye? Bill Rudman’s research informs that the Sea Hare can store the noxious chemicals found in their algal food, especially from the red variety. Deposited in their skin, it is released when they feel threatened by predators. Apparently, it tastes horrible and a Western Australian species has even been known to poison dogs.
But, there is even more to reveal about this smooth secretive slug. Being a hermaphrodite, it has both male and female sex organs and when it is time to mate it revels in making this a very social affair! They invite their friends along and start a ‘mating chain’. The first slug will act as a female, then each other hare that joins in forms a link in the chain, acting as both a male and a female until the last one acts only as a male. The more the merrier they sometimes say!
Such a fascinating little marine mollusc that is rarely seen, has shown themselves in huge numbers, stranded and dying at low tide. I kept wondering why there were so many? Back to my trusty scientist who concludes that mass deaths of Sea Hares is fairly common. It seems that when conditions are favourable, and lots of shackling of Sea Hares has occurred there will be babies booming all over that red algae. Those juveniles will grow quickly and perhaps there were many chains connected and their life cycles just so happened that this mega population died at the same time. And then came the southerlies and washed them upon Callala Beach and we are left to wonder about what else goes on out there in the bay.