Stormy weather in the Cornish rock pools

Rockpooling in stormy winter weather can be a risky business here in Cornwall, so my advice is … don’t. At best you get blown over on the slippery rocks and soaked by rain that seems to come in horizontally and go right up your nose. At worst you could end up in the path of the fierce waves and currents. It’s not worth it.

When there’s a calm moment and a good tide (I’m hoping tomorrow will be such a day), there’s plenty to see in the rockpools. Between times, stick to the strandline, where the sea throws up all sorts of treasures and unexpected visitors.

Mauve stinger jellyfish (Pelagia noctiluca) at Mawgan Porth
Mauve stinger jellyfish (Pelagia noctiluca) at Mawgan Porth

One of my favourites this year was the swarm of mauve stinger jellyfish (Pelagia noctiluca). They look small and inoffensive, measuring up to 10cm across their bell. The spotted pattern that gives them their name is distinctive and rather pretty. They can also glow in the dark – noctiluca means night light.

However, they have powerful stinging cells (nematocysts) all over them, including on their fine, hair-like tentacles which can extend up to 3 metres. They often cause problems for swimmers at tourist beaches further south in Europe. This year they turned up in their thousands on Cornwall’s beaches.

I know they sting, but this didn’t stop me from plunging my hands into a freezing pool to take photos and video. The wind was so strong that it was hard to get a decent image through the ripples on the water’s surface and sea foam kept blowing back into my camera.

Mauve stinger jellies strewn across the shore - don't touch, they have a fierce sting!
Mauve stinger jellies strewn across the shore – don’t touch, they have a fierce sting!

The beach was strewn with them, and a few ‘By the wind sailor’ (Velella velella) jellies. They’re powerless against such strong winds and currents, but these strandings are part of their natural cycle and have little effect on populations.

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‘By the wind sailor’ (Velella velella). These tiny jellies float on the surface and follow the wind using the ‘sail’ you can see on top.
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When they die and dry out, ‘by the wind sailors’ (Velella velella) turn transparent and look like little pieces of cellophane, blowing around the shore.

There’s a fantastic little film about Velella velella on here on YouTube if you’d like to find out more.

Another winter favourite are the ‘mermaid’s purses’, the egg cases of small sharks and of rays from the skate family, which I often pick out from tangled bundles of seaweed that are heaped on the strand line.

'Mermaid's purses. Blonde ray eggcase (top) and Spotted ray eggcase (bottom) with a coin for scale.
‘Mermaid’s purses. Blonde ray eggcase (top) and spotted ray eggcase (bottom) with a coin for scale.

It’s surprisingly easy to identify what species the egg case belongs to, especially if you bring them home and soak them overnight as Cornish Rock Pools junior and I do.

We followed the Shark Trust’s excellent key to identify these two egg cases as a blonde ray (Raja brachyura) and spotted ray (Raja montagui). Junior enjoyed doing his bit for conservation by recording the finds into the database so that they help build up a picture of the populations of these fish, many species of which are endangered.

It’s well worth a stroll along the tide line this time of year when the tide’s out and the weather’s not too hideous. You never know what you might find. Unfortunately marine mammals can be affected by the storms too. It’s common for grey seal pups to be stranded and quick action may save them. If you find any marine animals (dead or alive) on the shore in Cornwall, please contact the Marine Strandings Network on 0345 201 2626.

Here are some more of this winter’s strandline treasures. If you’re interested in doing your own beachcombing, I’d highly recommend Steve Trewella and Julie Hatcher’s new book: The Essential Guide to Beachcombing and the Strandline.

Seagrass is the only marine flowering plant and grows as meadows in shallow waters. It is sometimes damaged by storms.
Seagrass is the only marine flowering plant and grows as meadows in shallow waters. It is sometimes damaged by storms.
Turnstones are hardy little birds that find food among debris on the strand line. Look out for them as you walk on the beaches all year round.
Turnstones are hardy little birds that find food among debris on the strand line. Look out for them as you walk on the beaches all year round.
Goose barnacle (Lepas antifera). These large barnacles attach to floating debris and are often washed in during storms.
Goose barnacle (Lepas anatifera). These large barnacles attach to floating debris and are often washed in during storms.
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4 thoughts on “Stormy weather in the Cornish rock pools”

  1. Thank you! I have a lot of fun writing it. The sun finally came out today, so I went rockpooling and found an amazing rock gully packed with interesting creatures that seem unruffled by the storms. I’ll have a new post up this weekend – hope you like it.

    Liked by 1 person

  2. Thanks Sean. They are a very strange animal and such a striking colour. I didn’t realise until I watched the video I linked that the blue colour gives them protection from the sun’s rays – they’re always at the surface so very exposed. They quite often get washed up in their thousands here because they have no control over where they go. I hope you manage to see them sometime.

    Like

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