Rainbow sea slug found in a rock pool!

rainbow sea slug

Since joining The Rock Pool Project as a volunteer on our monthly Beach Days, and most recently as one of our safari guides, I have seen some amazing wildlife. However, this weekend’s discovery was extra special.

Another great Blue Recovery Beach day

We had just wrapped up our Beach Day activities, tallied up the points, and announced the winners of our bioblitz competition. In the summer months we run a ‘See Our Shore’ session, complete with a mobile rock pool so that the general public can view some of the wildlife we have found. I decided to hang behind in hopes of finding a Spider Crab to add to the collection. We often come across these magnificent creatures in the low shore pools.

With a low tide height of 0.57m it was a great tide to be out on and I soon found a large Edible Crab, a Green Sea Urchin and multiple Cushion Stars. Aware that there was a pasty and a cold drink waiting for me back at base, I scanned a few more of the larger pools, right on the edge of the sublittoral zone.

Rock Pool Bioblitz team

Something special

When you have been rock pooling as much as I have been in the last year, you start to get an eye for which rocks are most likely to have something interesting underneath. The last rock I picked up was exactly one of these. It was quite a large, heavy rock, covered in various seaweeds, and once lifted something extremely bright and unusual caught my eye. Having been reading up on nudibranchs a lot recently I knew exactly what the colourful blob in front of me was! The extremely rare Rainbow Sea Slug! Once delicately placed in a pot to view, the beautiful animal unfurled and revealed itself in full technicolour.

A rainbow sea slug

The rainbow sea slug, or Babakina anadoni, is a member of the aeolid nudibranch family, which are characterised by their bright colours and unusual shapes. It is usually found in warm sea waters, originally off the west coast of Spain, and also Portugal and France but has recently been found by divers around the UK. The first sighting was in August 2022 and there have been a handful of sightings since by divers and snorkelers since but, as far as we can tell, this is the first time this species has been found by a rock pooler in the UK!

rainbow sea slug

A few fellow nudibranch enthusiasts from our community soon rushed over and we all watched the creature navigate the pot in complete awe. Like most nudibranchs it had quite the personality, rearing up to get a better look at its surroundings, and using its tentacle-like ‘cerata’ along its back to make itself appear bigger if one of our hands got too close.

A permanent record

Once everyone had taken some photographs and spent a bit of time watching it, we took this very small, but very hardy, critter back to the pools that it has made its new home. I included one of the new rainbow sea slug images when we uploaded our BioBlitz data to the Rock Pool Project’s database. These records are shared via IRecord and the National Biodiversity Network and therefore will be freely available to researchers, conservationists and the general public. There are currently no records for this species on the National Biodiversity Network and therefore this should be the first one!

It is absolutely amazing what you can find on our rocky shores, and today was a perfect example of the incredible wildlife we have on our doorstep here in Cornwall. I have recently joined our team of safari guides and to have found this beautiful animal on only the second week of running them hopefully bodes well for future discoveries!

Images from the day:

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