Ebro Delta, Spain - Large Sea Hares

August 20, 2005
From: Jorge Jimenez

Dear Bill,
Today (18th August) we were on the Eucaliptus Beach at the Ebro Delta, near Amposta (Tarragona, Spain). There were literally hundreds of what we think were very large sea hares, in the shallow water and being washed up on the beach by the tide.

The sea hares were brown, around 15-20 cm in length, around 8-10 cm wide when washed up, but almost round in the water when their flaps were open. Some gave out a reddish liquid as they moved. Looking at your website we think they were probably from the Aplysia species (though we know nothing about this topic... we are only musicians!)

Locality: Eucaliptus beach, Delta del ebro, Tarragona, Spain. Depth: Shallow water/beach. Mediterranen Sea. Length: 150-200 mm. 18 August 2005

Could you let us know what these might have been, or what might have caused this sudden appearance? We were with a friend who has lived all his life there and had never seen them before. The sea was quite rough (there have been sorms in the area) and there was also quite a bit of red feathery seaweed in the water.

We would be very interested to hear your expert opinion!

Many thanks,
Jorge

inegalfiles@hotmail.com

Jimenez, J.M., 2005 (Aug 20) Ebro Delta, Spain - Large Sea Hares. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/14600

Dear Jorge,
Surely not only a musician! In the grand scheme of things I am sure musicians rank a lot higher than slug experts.

I would agree your animals sound like a species of Aplysia. Have a look at the earlier message [#3856] about a similar mass swarning of Aplysia fasciata in nearby Meditteranean France. There is a Fact Sheet on the Forum discussing mass swarmings and mass mortality in Sea Hares. Basically we are not sure, but it almost certainly a 'natural' phenomenon rather than a result of pollution. Most sea hares live for less than a year and the simplest theory is that there life cycle is fairly synchronised so at any one place, most animals will reach maturity about the same time. I don't know your Eucaliptus beach but I would suspect that there are algal beds just offshore where these animals were feeding and breeding. You mention a lot of red algae pieces in the water. This suggests there has been a storm recently that broke this algae off. It's possible the same storm washed the sea hares in to the beach at the same time
Best wishes,
Bill Rudman

Rudman, W.B., 2005 (Aug 20). Comment on Ebro Delta, Spain - Large Sea Hares by Jorge Jimenez. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/14600

Factsheet

Mass mortality

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