Re: Giant Sea Hare poisoning dogs!

February 21, 2003
From: Sharon Wood

I have just read about "Sea Hares" killing dogs at Geraldton, Western Australia. This was on the news several months ago. We have seen quite a lot of these washed up on the beach in Jurien Bay W.A (about 160kms south of Geraldton) since hearing about the affect this species may have on dogs we have kept an eye out. Yesterday [18 Feb 2003] whilst walking the dog a "sea hare" (I think) was washed up and concealed amongst the seaweed, my partner made a lunge for the dog as it was about to walk on the black mass. His wrist touched the animal and today he has red, raised welts on his wrist. Is there any information on these animals being toxic to humans as well as dogs?
Sharon Wood

Dear Sharon,
The first report on the Forum of dogs being poisoned by these 'washed up' Sea Hares was from Peter Taylor in June last year. Kim Trotter's message yesterday, suggests that this is either another mass mortality event or perhaps these deaths have been going on for 8 months.

The first difficulty in answering your question is not being sure of the identity of your 'black mass'. I guess it is reasonable to assume it one of these Sea Hares, but there is a possibility it is something else. Your description of it being washed up with sea weed suggests you have had rough weather, and plants and animals have been dislodged from the sea bed and washed ashore. If so, it is possible that your black mass is a sponge, some of which are quite nasty to touch and would cause red welts and stinging. It could also be some sort of jelly fish. Why I am suggesting some alternatives is that I have never heard of humans being affected by Sea Hares in this way - mind you it is also very unusual for dogs to be poisoned.

If your black mass was a Sea Hare, the only suggestion I can make is that there are some toxic dinoflagellates in the water which are on the skin of the Sea Hares. Dinoflagellates are small single-celled plants. They are very common in the sea and are usually a very important food for many filter feeding animals. Sometimes however there are 'blooms', or population explosions, of very poisonous, toxic forms of dinoflagellates. They can kill sea life directly, but in some cases they are eaten by animals such as fish, or oysters, which are not themselves affected, but can make people who eat them very sick.

In this case I am only guessing as I am not sure if your black mass was a Sea Hare. If it was, this is a most unusual phenomenon and I guess somewhat disturbing for anyone swimming in the vicinity. While mass deaths of Sea Hares is a natural part of their life cycle, poisoning mammals who touch their bodies is definitely unusual. This would seem to be an on-going phenomenon in the Geraldton area. It would be interesting to know if anyone elsewhere has experienced, or heard of Sea Hares being such a problem.
Best wishes,
Bill Rudman

Rudman, W.B., 2003 (Feb 21). Comment on Re: Giant Sea Hare poisoning dogs! by Sharon Wood. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Aplysia gigantea

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