Monday, March 23, 2009

Rottnest Island - Bickley Bay (5) - Aplysia gigantea

One interesting natural phenomenon I observed during my short stay on the Rottnest Island was the mass stranding of the sea hare Aplysia gigantea.

I remember seeing so many of them when I took a walk on the beach at Bickley Bay one morning - I stopped counting at 20. In fact, when I snorkelled at Green Island, I saw many dead sea hares, probably of the same species, in shallow water too.


This one was about 40 cm long. I didn't try to lift it but it looked heavy.


Another big one that was washed ashore.



I noticed that that they got decolorized after a day or two on the shore.

According to The Sea Slug forum, mass mortality or mass stranding is a natural event for many sea hare species. And the reason could be as simple or natural as the animals reaching the end of their life cycle. For this species, the annual mass stranding and mortality occurs every summer.

The Sea Slug Forum Aplysia gigantea fact sheet
The Sea Slug Forum - Mass mortality
The Sea Slug Forum - Big sea slug from Western Australia

2 comments:

Steve Reynolds said...

Thanks Chai
That's amazing. I didn't realize that they grew so big.
Cheers
Steve

Tsun-Thai Chai said...

They sure are big! I read that they could grow to 60 cm long.

Chai

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