sea squirt | Cornish Rock Pools

After the summer rush, Cornwall is starting to breathe again. Our usual autumn trip to Brittany was cancelled months ago, but we’re making up for that with an exotic adventure to visit friends on the Lizard. Junior disappears off to play leaving some of us adults to our own devices. Rockpooling it is then!

We’re unsure how productive this session will be; there is a definite change in the air this week. Huge ships are still lurking in the shelter of the bay after the recent storms and kelp is starting to pile up on the strandline. The stiff breeze makes it hard to see into the pools at times and I’m glad of my waders to keep me warm and dry.

In the distance there is a small group, perhaps from Falmouth University or the Rock Pool Project. It’s an unusual sight this year. So many events have been cancelled. It makes me think of how my Wildlife Watch groups and how much the children have missed out on. I’m not ready for close contact with groups just yet, but perhaps it won’t be long now.

This is the season of blue-rayed limpets. They will soon grow and move down into the holdfasts of the kelp but for now they glitter against the seaweed on which they feed. Some fronds of kelp are pockmarked with holes that these tiny molluscs have carved out.

Not all the blue-rayed limpets are on kelp. This one is tucking into seaweed on a rock.

Things may be winding down for the winter but the intensity of colours on the shore is as strong as ever. Even the sand is a treasure trove, a kaleidoscope of shell fragments interspersed with pieces of the knobbly skeletons of calcareous algae. The closer I look the more I see.

‘Maerl’ sand at Prisk Cove – made from the skeletons of dead calcareous algae.

There are three species of red seaweed that form beds of these loose pieces, collectively known as maerl. The top layer of live algae exposed to the light is a deep pink, while underneath the dead layers bleach to look like pale pretzel fragments. Offshore, these seaweed can form deep beds, which provide endless hiding places for small marine creatures.

Deep pink ‘maerl’ type calcareous algae.

This beach is always rich in brightly coloured worms, sea squirts, sponges and other animals that I tend to unscientifically group together as squidgy things. They aren’t all easy to identify – especially the sponges, which often require a microscope – but some creatures, like this strawberry worm (Eupolymnia nebulosa), are easy to recognise.

Unafraid to mix spots and stripes, this lipstick pink terebellid is one of the most glamorous worms on the shore. It sports a fringe of stylish bristles and crowns its unique look with an expansive mop of tentacles and bushy red gills.

Elsewhere, some of the rocks and seaweeds are covered in a layer of squidgy things.

The eye-catching collage of flower shapes created by colonies of star ascidian sea squirts seem like they have been painted onto every surface. I can’t help taking photos of each new colour scheme.

Scroll through this slideshow to see some of the different star ascidian colours…

Looking at one thing leads to another. Next to a patch of star ascidian, my friend notices an odd-looking brown blob. It is plant-like: brown, stumpy and gnarled like an old stem.

Styela clava sea squirt with star ascidian in the background – spot the flatworm!

Despite appearances, this is a distant cousin of the star ascidian. Styela clava, sometimes known as the leathery sea squirt or the clubbed tunicate, is a single animal rather than a colony of zooids. It arrived in the UK 1950s. Originally from the North West Pacific region, it is known to sometimes cause problems by growing in huge numbers on mussel farming ropes.

A movement draws my attention back to the star ascidian.

I sometimes spot the sea squirts opening and closing their siphons, but this is a larger shift. There is another squidgy animal at work here.

A flatworm is flowing across the surface of the sea squirt, moulding its body to the ridges and slopes as it goes. The worm is a fabulous midnight blue, flecked with yellow, yet it blends so perfectly with the colours of the star ascidian that I can’t make out its edges.

There are several flatworms on the sea squirt, but it is only when one ventures onto the rock that I can see it properly.

More blobby treasures abound on this shore: gem anemones, red speckled anemones, yellow-ringed sea squirts, golf ball sponges and more.

Anthopleura ballii – the red-speckled anemone

Yellow-ringed sea squirt (Ciona intestinalis) with a photo-bombing brittle star.

There is never enough time to see everything before the tide returns, so I focus on looking for all my favourite squidgy creatures of all – sea slugs.

Elysia viridis, the solar powered sea slug chomping on green seaweed.

The autumn isn’t the best time of year for sea slugs, however my friend, Other Half and I are the most dedicated little gang of slug-finders you could hope to meet. With great shrieks of delight, we uncover a few in the course of our explorations.

Slugs don’t have an especially cuddly reputation, but the Jorunna tomentosa is covered in tiny hair-like structures that make it look like a teddy bear to my eye. Even its rhinophores have a fuzzy look about them. There is a good reason for this sea slug’s appearance: all that fluffiness is perfect for hiding on the sponges that it eats.

Jorunna tomentosa’s rhinophores close-up… looking like teddy bear ears!

It’s clearly a good day for ‘hairy’ slugs because my next find is a bright-white fluffy sheep of a slug, the Acanthodoris Pilosa. Nudibranch slugs are a likeable bunch, but this one is especially appealing with its floofed-up gills and those towering rhinophores balancing on its head like two leaning helter-skelters.

It won’t be long before the autumn gales rage through, bringing the darker winter days behind them. It is strange to think of these tiny squidgy things clinging on here through everything the Atlantic will throw at them. By the time the spring sunshine returns, I may be able to start leading Wildlife Watch groups again. It will be exciting to make up for lost time.

Bonus sea slug…. Polycera sp. with my fingertip for scale

Polycera sp. sea slug moving surprisingly quickly towards its bryozoan meal. The yellow speck on the right may be a second, even tinier slug.

And another squishy thing! Calvadosia campanulata stalked jellyfish.

Whatever the weather, always stay safe in the rock pools. Follow my rockpooling tips to look after yourself and the wildlife on the shore.

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Days like this don’t seem ideal for rock pooling; the tide is nowhere near low enough to expose my favourite pools and the weather is iffy. Despite this, I am convinced that there is plenty to see on the mid-shore. Cameras and rock pooling super-crew (Other Half and Junior) at the ready, we set out to uncover marine treasures.

One advantage of neap tides, when the sea doesn’t go out very far, is that it won’t rush back in either. We can take our time. Junior soon locates lots of gem anemones with their tentacles wide open.

Under a stone further down the shore, I spot a beautifully camouflaged anemone. It’s too small to see properly, so I have to wait until I get home to confirm that it’s a Sagartia troglodytes anemone.

The B shape at the base of the tentacles is a useful identifying feature, although I’ve always thought they look more like Scooby Doo ghost eyes than letters.

Other Half calls me over to look at a blob. He’s becoming quite an expert blob finder.

We look together at the tiny brown jelly-spot on the seaweed. At first, we think it is an anemone because it seems to have a circle of retracted tentacles. As soon as I dunk it in the water though, I can see the pale lumps of primary tentacles around the edge. It must be a stalked jellyfish.

Is it just me or does this stalked jelly not look pleased to see me? Haliclystus octoradiatus.

Gradually, the stalked jelly unfurls each arm until it looks much less blob-like.

Haliclystus octoradiatus -starting to look more like a stalked jellyfish than a blob.

The rain seems to be holding off now, and I make myself comfortable by a calm pool to watch the little world go by. My camera has barely entered the water before a bold prawn trots out of the seaweed, its legs working at top speed in its eagerness to check out what I’m up to.

Common prawn coming to take a look at my camera.

A head pops up between the fronds of saw wrack at the back of the pool. The young Montagu’s blenny swivels an eye back and forth beneath its jaunty headgear. I feel a larger blenny move through the seaweed near my hand and lift my camera out of the water before I get a nip from the territorial shanny.

Peek-a-boo! Montagu’s blenny taking a look above the serrated wrack.

A dinky starfish in the coral weed catches my eye. I see several species of starfish on this beach, but this is a mid-shore specialist: Asterina phylactica. The colours of the tiny pincers on its back (the pedicellariae) form an orange star shape. Under the camera, I can see its tube feet reaching out and exploring its surroundings as it glides along.

Other Half brings passes me a tiny shell he has found. He thinks it might be a wentletrap, a shell we sometimes find. I have never seen one so small and assume it is probably a different species. I take a look with the camera and realise he was right. The bold sculpture of ribs over the rounded whorls of the long spire are striking, even in this tiny juvenile. Best of all, the shell is occupied.

I watch the snail emerge and set off across the pool.

This makes me think of a unicorn and a rainbow – juvenile wentletrap.

Sea squirts are something of an enigma to me. They are hugely varied in their colours, shapes and sizes. Aplidium turbinatum, in particular, seems to me to look different every time I find it. When I first see this one, I am convinced that the white, spiky-looking set of openings under the coral weed is a bryozoan.

I know this looks familiar, but takes me a long time to work out that it is Aplidium turbinatum, a sea squirt.

Yet, after a while watching it, I realise it is opening and closing like a squirt, puffing water in and out. It bears little resemblance to the orange gelatinous Aplidium turbinatum I usually see further down this beach, but the jutting triangular crowns around the edge of each opening are the same.

Fortunately, I can turn to the incredible Aphotomarine website for confirmation and, sure enough, it has some photos of very similar specimens (thanks David!).

While the tide seeps back into the pools, we chat with a fellow rock pooler whose photos I have often seen online, and who I eventually realise I have met before in real life through another conservation group.

Chthamalus sp barnacles starting to open as the tide comes in.

By the time we leave, the sun is low in the sky. I am more than satisfied with all the wonderful creatures I have found on the neap tide, and it is high time I had some birthday cake.