Today’s post features the Sea Hare of the class of Gastropoda and shows the sea hare Aplysia parvula.

I took these photographs in 2014 and 2015, with also seeing many at the end of 2019, at ERMS.

I have had some of my favourite times observing the gentle algae grazing action and interactions of families of sea hares in rock pools in Vic, TAS, SA and WA.

The name Sea Hare derives from their rounded shape and from the two long rhinophores that project upwards from their heads that were thought to somewhat resemble the ears of a hare. Those rhinophores are extremely sensitive chemoreceptors which gives the sea hares the ability to follow the faintest scent, like a super power. (The “scents” detected are chemicals dissolved in the sea water.)

Other identifiable physical traits are the oral tentacles at the front of the head, on either side of the mouth, and the large flaps (parapodia) on their backs that enclose the fragile shell. These large wing-like flaps protect the gills, and some species of sea hares use these flaps for swimming, but generally we see them gliding over rocks whilst feeding on algae.

Being herbivores, they live in seagrass beds, rock pools and other intertidal environments where there is a good amount of healthy algae. As they eat, they take up the pigments in the algae, which influences their colour. This is an effective way of ensuring they camouflage well with their habitat. Overall, they consist of 9 x genera, and size-wise, range from less than 2cm up to 70cm in length.

They tend to come closer to shore when it is time for them to breed. They are hermaphrodites and when it comes to breeding time, they congregate in shallow waters, forming a chain. In due course they lay yellow spaghetti-type eggs. In the intertidal zone they are more vulnerable as they’re prone to being effected by wind and wave action, and can therefore be stranded on the sand. As they have soft bodies, they oft look like a coloured blob of jelly, when unfortunate enough to be washed up onto the sand. Gently collecting them and returning them to the ocean, and watching them restore and take on their true shape, is very rewarding.

The neurophysiology of sea hares is unique and are being used by scientists to assist in research of human neurological diseases due to their observable 20,000 neurons.

They are sweet, very gentle, slow moving creatures, with a defence mechanism being to taste unpleasant, which would be an effective deterrant. They can have a semi-toxic slime layer over their bodies and toxins infused through their tissues (that are usually of no effect to humans). They are also able to emit a coloured dye when stressed to work as a distraction/smoke screen. The colour of the dye is dependant on the pigments in their algae food source. That said, of those I have seen beached in SA and WA, including those being collected by humans as food (in a Marine Sanctuary which made for good teaching material), even though in danger, they had not emitted the dye.

Whilst they have minimum predators due to the above their life cycle is very short.

Along the Surf Coast, I’ve only seen them under rocks at the Eagle Rock Marine Sanctuary, and once further along towards the Fairhaven Surf Club. I’d love to know if and where you’ve seen them along the Surf Coast. 

Happy sea hare day to you.


(I’ve included some other photos of those taken in Aireys Inlet, Robe and Beachport in SA, and Gnaraloo in WA, showing differences and similarities, on my photography page if interested.)