The Legendary Slug Formerly Known as Discodoris

The tide has turned and I am reluctantly preparing to leave one of best rock pooling beaches in Cornwall after a fabulous few hours in perfect conditions in the company of great friends. As you’d expect, the day has been full of interesting finds, from sponge-covered spider crabs to golden clutches of clingfish eggs. My camera batteries are running low and my hair is dripping with seawater from all the time I’ve spent poking my head under seaweed-festooned overhangs. The kids migrated up the beach a while back to investigate the picnic bag but us adults can’t bear to leave the pools. As the water creeps up my wellies, I gently turn one last rock, and then another for luck.

This small species of spider crab (Inachus sp.) was so completely covered in sponges that I couldn't see her shell at all.
This small species of spider crab (Inachus sp.) was so completely covered in sponges that I couldn’t see her shell at all.

I let out gasp so loud that it would make most people think I’d just broken a bone, but my friend knows better. She moves closer to ask what I’ve discovered, but I’m so overwhelmed with excitement that I can only babble about having, “finally found one”.

I point a trembling finger at the rock. “It’s a Disco…a Discodoris planata,” I stutter, before launching into a garbled explanation of how it used to be a Discodoris has been renamed Geitodoris, but I use Discodoris because I love that name and…

I take a few photos of the cause of my breathless wonder, straighten up and fling my arms over my head and shout at the top of my lungs to attract the children’s attention. It takes me a minute to realise that the distant child I have in my sights is not mine, but  Junior has noticed my flailing and comes scrambling across the rocks with his friends.

We crowd in the fast-filling pool and peer down at my rock. Even Junior is a bit confused by my excitement over the small, brown lump I’m indicating.

Not just a brown lump... Geitodoris planata (the slug formerly known as Discodoris planata)
Not just a brown lump… Geitodoris planata (the slug formerly known as Discodoris planata)

“It’s Discodoris,” I explain, breathlessly. Instantly, he joins my paroxysms of delight, shrieking out the great news to his friends and going through the same Geitodoris speech as me, for this unassuming slug has become something of a legend in our household.

This isn’t the first time I’ve ever seen one, but it’s the first time I’ve had a working camera with me and it’s the first “Discodoris” that Junior has seen. He is especially impressed with the white star patches on the slug’s back. These are glands which secrete a powerful acid, ideal for seeing off predators.

The white patches are powerful acid glands.
The white patches are powerful acid glands.

On close inspection, there’s a pale-yellow blob alongside our “Discodoris” (Geitodoris planata): another slug. At first, I assume from its colour that it must be a Jorunna tomentosa, a slug I often see on this shore. Indeed, there is another Jorunna tomentosa on the same rock. However, this one seems to be getting very cosy with Discodoris. In fact, it looks to me as though they are mating. The yellow slug also has a far flatter profile than any Jorunna tomentosa I’ve seen before.

Our brown Geitodoris planata and its much paler yellow mate getting friendly in the Cornish rock pools!
Our brown Geitodoris planata and its much paler yellow mate getting friendly in the Cornish rock pools!

If the tide wasn’t coming in, and if I wasn’t called away by someone further up the beach finding a giant goby, I might have been able to check the slug’s underside. If I’d done that I could have seen without doubt that this was a second “Discodoris”, a two-for-one package. The underside of Geitodoris planata is fringed in brown spots, unlike the very similar sea lemon, which is all one colour.

The fish found by some holidaymakers was indeed a giant goby. These fish are a protected species so must not be caught or disturbed without a licence. We left it hiding in its surprisingly small pool.
The fish found by some holidaymakers was indeed a giant goby. These fish are a protected species so must not be caught or disturbed without a licence. We left it hiding in its surprisingly small pool.

Fortunately, social media now enables geeks like me to swap photos with other slug-loving types and sure enough, Geitodoris planata, though usually brown with distinct white acid glands, can sometimes be pale.

Although I will record the slug as Geitodoris planata and there are important scientific reasons for the name change, this little animal will always conjure up glitter balls and platform shoes in my mind. To take photos of the fabled Discodoris, and a mating pair at that, has to be the perfect end to a perfect day.

Geitodoris planata pair
Geitodoris planata pair
Shining like pure gold - the eggs of the Cornish clingfish (Lepadogaster purpurea).
Shining like pure gold – the eggs of the Cornish clingfish (Lepadogaster purpurea).
Jorunna tomentosa slug
Jorunna tomentosa slug
One pool on the mid-shore was home to scores of colourful St Piran's hermit crabs.
One pool on the mid-shore was home to scores of colourful St Piran’s hermit crabs.
Another species of hermit crab - the tiny Anapagurus hyndmanni
Another species of hermit crab – the tiny Anapagurus hyndmanni
Sarah's common eel - our last find of the day before my wellies overtopped!
Sarah’s common eel – our last find of the day before my wellies overtopped!

“The slug formerly known as Discodoris” and a host of other rock pool creatures feature in my book Rock Pool: Extraordinary Encounters Between the Tides. Out now online and in book shops nationwide from September Publishing. If only I’d found one in time to include a photo in the book…

An Outbreak of Starfish – Wildlife Watch Explores Readymoney Cove

Before I’ve found the time to upload all of last year’s records, the rock pooling event season is upon me again. Junior comes along to help at my first Wildlife Watch event of the year for Cornwall Wildlife Trust at Readymoney Cove, undeterred by the bone-chilling wind.

A crowd of hardy young rock poolers, kitted out from head to toe in weatherproof gear, is gathered at the top of the beach and I am joined by Liz, a lovely volunteer assistant. Half the group have their hands up before I’ve even asked a question and these keen kids are practically bursting with stories and facts about crabs, blennies, pipefish and killer jellyfish. They also have high expectations of what we might find – seahorses and cuttlefish are among the requests – but most of all they want to see starfish.

Starfish of some sort are almost guaranteed on all our local beaches, especially cushion stars, which like to hide under rocks and overhangs. If we are lucky we might also find brittle stars, that walk on their five feathery arms, or even a gargantuan spiny starfish, so I am hopeful that we will be successful on our mission.

As the group spreads across the shore, the finds soon rush in. We turn shiny top shells in our fingers, hold chunky-clawed Xantho hydrophilus crabs, and to the immense joy of one young seahorse enthusiast, we find the next best thing to a seahorse: a male worm pipefish with eggs on his belly.

Xantho hydrophilus - the 'furrowed crab'.
Xantho hydrophilus – the ‘furrowed crab’.
Male worm pipefish with eggs
Male worm pipefish with eggs

Pipefish are close relatives of the seahorse and the male takes care of the female’s eggs, storing them in a special groove on his belly until they hatch. Coincidentally this pipefish has taken up residence next to an old pipe.

It only takes a minute for the children to discover a common starfish. I often find one or two on this beach, even though they’re not so common intertidally as offshore. The deep-water harbour alongside this beach is probably packed with them and sometimes young common starfish make their way into these sheltered pools. Today, however, there is something unusual going on.

One of the common starfish found - photo courtesy of Liz Barker
One of the common starfish found – photo courtesy of Liz Barker

Under the first stone I turn, I see two baby common starfish. As I look I notice a third, a fourth and then a fifth. On the side of the rock, there is yet another starfish. The adjacent rock has four more.

Common starfish at Readymoney Cove near Fowey
Common starfish at Readymoney Cove near Fowey

Everywhere on the beach, children are shrieking with excitement as they find more starfish. There are scores of them among the rocks I look at.

We could easily collect the starfish by the bucket-load, but these children know not to disturb the animals. We keep just a few for our trays so that we can watch them and all those who want to can have a go at holding a starfish before they are returned to their rocky homes.

While the children are caught up in the magic of starfish, I take a moment to explore the rocks at the sea’s edge and discover this wonderful yellow clubbed sea slug, Limacia clavigera.

Limacia clavigera - the yellow-clubbed sea slug
Limacia clavigera – the yellow-clubbed sea slug

There is never enough time to take many photos at these events as I am too caught up in the excitement of identifying finds and helping the children learn more about them. We also have plenty of discussions about the animals’ impressive defences and quirky eating habits.

The children do a perfect job of looking after the animals, returning them all safe and unharmed to their homes before the incoming tide floods back into the pools. Despite the chilly conditions, the kids are buzzing with happiness at finding so many starfish. A friend tells me her kids talked of nothing else all the way home.

Even Junior, who has seen most things before, is delighted with today’s finds and even more delighted when he secures the very last cheese and onion pasty from the beach shop for his lunch.

If you’d like to get involved with Wildlife Watch, book on to my rockpooling sessions or join any other Wildlife Watch events, check out the listings on the Cornwall Wildlife Trust pages.

Did you know that starfish can regrow their limbs? Find out more about the secrets of these iconic rock pool animals in my book Rock Pool: Extraordinary Encounters Between the Tides out on 2nd May with September Publishing and available through local and national bookshops and online.

West Cornwall Adventures

You’re never far from a beach in Cornwall, but the distances from one end of the county to the other mean I visit some beaches more often than others. I made the most of a recent trip ‘out west’ visiting friends to explore the Penzance area.

Although Mount’s Bay itself is a protected area and is best left undisturbed, there are plenty of fabulous rock pools to discover near the town and at nearby Mousehole.

The wealth of colourful seaweeds here makes the clear waters especially enticing. Stepping carefully among them, I found clingfish, shark egg cases and an abundance of stalked jellyfish.

A small species of clingfish hides among the coral weed near Penzance.
A small species of clingfish hides among the coral weed near Penzance.
A Calvadosia cruxmelitensis stalked jellyfish near Penzance. The diverse seaweeds of the Mounts Bay area provide a perfect habitat for a variety of stalked jellyfish species.
A Calvadosia cruxmelitensis stalked jellyfish near Penzance. The diverse seaweeds of the Mounts Bay area provide a perfect habitat for a variety of stalked jellyfish species.

Star ascidians formed a psychedelic wallpaper of turquoise and pastel blue petal patterns along some deep overhangs. Close by, another star ascidian colony painted the rocks in saffron yellow. 

The delicate colours of this star ascidian blew me away. It comes in so many colour morphs, but this one was new to me.
The delicate colours of this star ascidian blew me away. It comes in so many colour morphs, but this one was new to me.

 

More of the wonderful pastel-blue star ascidian, looking like an impressionist flower painting.
More of the wonderful pastel-blue star ascidian, looking like an impressionist flower painting.

Shouts carried across the shallow waters. My friends had found something exciting: a newly-hatched baby catshark. This young greater-spotted catshark, also known as a bull huss or nursehound, had spent many months incubating in an egg case before emerging. When fully grown it could be over one-and-a-half metres, but for now it lay quietly in the tub, taking in the world through half-closed eyes. We returned it quickly to the shelter of the dense seaweed where it would soon be covered by the rising tide.

A cat shark egg case with a young greater-spotted catshark developing inside
Egg case with a young greater-spotted catshark developing inside
Hatchling greater-spotted catshark, which we kept for a minute before returning it safely exactly where it was found.
Hatchling greater-spotted catshark, which we kept for a minute before returning it safely exactly where it was found.

As the days begin to lenthen noticeably I hope this is the first of many forays to new and more distant beaches over the course of the summer. No matter how many times I visit the rock pools, there is always something new.

If you’re looking for some summer reading, my book Rock Pool: Extraordinary Adventures Between the Tides is out on 2nd May with September Publishing and is available at local book shops, Waterstones and through NHBS as well as through online retailers.

Another species of stalked jellyfish - Haliclystus octoradiatus - near Penzance
Another species of stalked jellyfish – Haliclystus octoradiatus – near Penzance
A beautifully marked pheasant shell near Penzance, Cornwall
A beautifully marked pheasant shell near Penzance, Cornwall

Birthday Rock Pooling

It’s that time of year again. Amazing spring tides, ideal conditions and, of course, it coincides with Other Half’s birthday. Lucky him! What else could he possibly want to do but come rock pooling? To be fair, he needs no persuading that it beats a day in the office and, as a birthday treat, I offer him an evening out afterwards – watching me give a talk at the Cornwall Marine Recorders’ event in Gwithian (with a bar and nibbles).

We pile into the car ridiculously early in the morning to make sure we make it to Prisk Cove in time to meet our lovely friends and their twins to explore as the tide rolls out.

This beach is a little off the beaten track, but worth the walk. We find it empty of people and the tide so far out that the kelp hangs limply in shallow pockets of water in the bay.

The beach’s sheltered position between the Helford and Falmouth Bay, combined with the huge numbers of loose boulders, makes this habitat perfect for many marine species. Despite his initial certainty that he won’t find anything, Junior’s friend is first to find a spiny starfish. Its long tapering arms set with thick spines have an attractive purple hue.

Spiny starfish at Prisk Cove near Falmouth
Spiny starfish at Prisk Cove near Falmouth

We watch its many tentacle feet reaching out to explore the rocks.

Spiny starfish arm in action
Spiny starfish arm in action

The asymmetric heads of flat fish always intrigue me, so I am delighted when we find the first little topknot, then more and more of them. Some are sticking to the rocks, even clinging on when completely upside down, using their fringing fins to mould themselves to bumps and imperfections in the surface. Their mottled patterns can make them hard to spot and they stay completely still to avoid detection.

Topknot flatfish resting on a rock
Topknot flatfish resting on a rock
Flatfish like this topknot have their mouth set on one side of their head.
Flatfish like this topknot have their mouth set on one side of their head.

Under a large rock we find a large edible crab that makes the other twin shriek. She soon overcomes her nerves when I move it out of the way so that we can look at the fish, which are also sheltering here.

Everyone crowds round to see the stunning colours and impressive headgear of the tompot blenny, and the kids are amazed by the smoothness of the rockling’s eel-like skin.

Tompot blenny
Tompot blenny

Other Half holds the edible crab for a quick birthday photo before we pop everything back where we found it.

Edible crab at Prisk Cove
Edible crab at Prisk Cove

Out among the furthest accessible rocks, the twins’ mum is not being outdone. She brings some fish over to show me, among them a beautiful goldsinny wrasse. It’s not a fish I often see on the shore, but it is easily identified by its two dark spots, one at the front of its dorsal fin and the other at the top of its tail.

Goldsinny wrasse at Prisk Cove
Goldsinny wrasse at Prisk Cove

It has wide orange eyes with a flash of blue and the wonderful pouting lips of the wrasse family.

Goldsinny wrasse - a beautifully coloured fish
Goldsinny wrasse – a beautifully coloured fish

The finds flood in and I struggle to keep up with taking photos of everything to ensure that I can submit records afterwards. On one area of the shore I find a large patch of Wakame.

This invasive non-native seaweed is easily identified by its corrugated-looking stipe and thin, floppy fronds. Originating from China, Japan and Korea, it has spread widely in Europe and can out-compete native seaweeds.

White painted top shells, an improbably hairy purse sponge and an interesting anemone all catch my eye before the tide turns.

An especialy hairy purse sponge - presumably just a variant of Sycon ciliatum
An especialy hairy purse sponge – presumably just a variant of Sycon ciliatum
Painted top shells are usually pink, but this beach had many of the white variety
Painted top shells are usually pink, but this beach had many of the white variety

I also discover half a dozen shark eggcases of the Greater spotted catshark (Scyliorhinus stellaris) attached to the rainbow wrack of the lower shore pools.

Catshark egg case among the seaweed
Catshark egg case among the seaweed
When it is in the water, Rainbow wrack is wonderfully iridescent
When it is in the water, Rainbow wrack is wonderfully iridescent

All too soon it seems, the tide is flowing in. At first it is a faint current, but it turns quickly into a churning river through the tight gullies and we retreat to enjoy a birthday picnic.

A lovely little Lamellaria snail, likely Lamellaria latens
A lovely little Lamellaria snail, likely Lamellaria latens
Limacia clavigera sea slug at Prisk Cove
Limacia clavigera sea slug at Prisk Cove
An especially small anemone growing on rainbow wrack.
An especially small anemone growing on rainbow wrack.

Blustery Rock Pooling in North Cornwall

When the tides are perfect, I always hope that the weather will be perfect too, but this is Cornwall in late winter and strong southerlies are whipping up the waves. I plan my rock pooling accordingly, choosing Porth Mear, a north-facing beach between Newquay and Padstow to avoid the worst of the storms, accompanied by Junior and a new friend and fellow rock pool enthusiast.

Whatever the conditions may be, it’s a welcome chance to grab some fresh air after months of writing my new book Rock Pool: Extraordinary Encounters Between the Tides, which is out on 2nd May with September Publishing.

Junior hones his photography skills
Junior hones his photography skills

I give Junior a camera to use and he’s straight on the case, trying out the settings and attempting to capture a blenny at the back of a hole in the rock. He spots some jelly nearby; the eggs of a sea lemon slug and we soon find the animal itself. We place it in water to watch its gills and ringed rhinophores (head tentacles) emerge.

In the water the sea lemon's rhinophores and frilly gills emerge and we can see its wonderful colours
In the water the sea lemon’s rhinophores and frilly gills emerge and we can see its wonderful colours

We edge further down the beach, keeping a nervous watch on the swell that is breaking over the rocks and exploding through the gullies. Junior takes photos of everything and is entranced by the blue-rayed limpets, manoeuvring himself through every possible angle as he tries to capture the iridescent turquoise lines on their tiny shells.

Blue-rayed limpet. Photo by Cornish Rock Pools Junior
Blue-rayed limpet. Photo by Cornish Rock Pools Junior

We find two thriving colonies of St Piran’s hermit crabs, with dozens of shells of all sizes in and around one pool, all occupied by these hermits. They are immediately recognisable by their red antennae and blue-tinged claws, but they stay firmly tucked away in the recesses of their borrowed shells.

A brief glimpse of a St Piran's hermit crab.
A brief glimpse of a St Piran’s hermit crab.

Junior is keen to show our new friend a gully where we often make interesting finds, but even as the tide dips to its lowest point, we are unsure whether it will be accessible. We climb to a high vantage point to look down at our favourite spot, but with foaming waves crashing over the rock face on one side, we admit defeat.

I lead the way over the rocks to another sheltered inlet and we clamber down into a deep cleft in the blue slates. The wet rocks are so steep and slippery that after sliding to the bottom I briefly wonder if I will be able to haul myself out again, but I am soon distracted by the richness of the rocks here. Three-spot cowries abound and a large edible crab is resting under an overhang.

The European 3-spot cowrie (Trivia monacha)
The European 3-spot cowrie (Trivia monacha)

Our friend carries on over a huge boulder to look at the pool on the other side. We discover cup corals at the same time; there is just a scattering of them on our side, but many dozens in the pool out friend has found.

Junior and I cross to take a look and balance precariously on the edge of a deep pool, leaning under a steep shelf of rock to try to take photos of the corals that are tucked away there. Most of the scarlet and gold cup corals are a deep, warm orange, but some are bright yellow like tiny suns.

Scarlet and gold cup corals at Porth Mear - showing both the yellow and the orange varieties.
Scarlet and gold cup corals at Porth Mear – showing both the yellow and the orange varieties.

Within a couple of minutes, we can feel a shift in the sea and the waves are breaking harder and closer to us, so we abandon our efforts to take photos and slip and scramble our way out of the gully.

Back on the beach, all seems calm and fish huddle under many of the rocks, waiting for the tide’s return. As always, this shore abounds with Cornish clingfish and worm pipefish.

A Cornish clingfish. There was also a Rock goby and a pair of worm pipefish under the same rock.
A Cornish clingfish. There was also a Rock goby and a pair of worm pipefish under the same rock.

Under the rocks we find a host of crabs and a few Candelabrum cocksii hydroids, which are fascinatingly variable in colour and shape, extending and contracting their bodies and proboscises.

Candelabrum cocksii hydroids are limited to the far south west of the UK.
Candelabrum cocksii hydroids are limited to the far south west of the UK.

Junior is especially pleased to find a bright orange Lamellaria perspicua (Dalek snail, as he calls it). It looks like a slug, but keeps its shell hidden under its soft body, exploring the rocks with two small antennae and a tubular appendage like a Dalek’s gun held out in front of it.

Strange and colourful - the Lamellaria perspicua is one of our favourite finds of the day.
Strange and colourful – the Lamellaria perspicua is one of our favourite finds of the day.

A short, prettily marked white worm with chestnut banding catches my eye, but I have little time to take photos as the waves are roaring in.

This colourful worm, which I think is Oerstedia dorsalis, was only around 1cm long
This colourful worm, which I think is Oerstedia dorsalis, was only around 1cm long

We watch the sea reclaim the shore from the safety of the tideline while we munch our sandwiches and check through our photos. Beaches can be challenging this time of year, especially when it’s stormy, but the vivid colours and strange lives of the creatures we have seen today, together with the chilly temperatures, send us home with colour in our cheeks.

Spiny starfish at Porth Mear near Porthcothan
Spiny starfish at Porth Mear near Porthcothan
A fuzzy-looking Jorunna tomentosa sea slug
A fuzzy-looking Jorunna tomentosa sea slug
Fish eggs by Cornish Rock Pool Junior - these were floating in a pool, unattached to anything.
Fish eggs by Cornish Rock Pool Junior – these were floating in a pool, unattached to anything.

A Winter Walk to Millendreath

There are many advantages to home educating Junior, but one of our favourite things is being free to go outside whenever we like. During the winter months, good weather and daylight coincide so infrequently that we nearly always drop everything to make the most of it. Today, Junior wants to explore our local beach and dig in the sand, so we grab our wellies, spade and camera and set out with the low morning sun glimmering from behind the clouds.

Spring comes earlier in Cornwall than it does further north, and the signs are there even though the days are still cold. The herring gulls have already moved back onto the roof-tops in our neighbourhood, and some are sitting on empty nests to deter others from moving into their territories. Buds are tightly wrapped on the hedgerow plants, waiting to open and a few hardy wildflowers are already blooming.

We hear the fulmars honking to each other on the cliffside above Plaidy before we see them. When we stop at a viewspot to look across to the Eddystone lighthouse, a male fulmar glides towards us on stiff wings before circling back to land on a ledge and touch beaks with the female that is resting there.

In the rock pools, spring is even further ahead and I have been finding sea slug spawn for a few weeks already. ‘Sea mushrooms’, the holdfasts of seaweed are appearing on the rocks and beginning to sprout from their centres. Colourful colonies of star ascidian are budding and spreading across the rocks. On one a flatworm is grazing, while another young colony is being visited by a hungry 3-spot cowrie.

Star ascidian at Plaidy beach
Star ascidian at Plaidy beach
A 3-spot cowrie closes in on a small star ascidian colony.
A 3-spot cowrie closes in on a small star ascidian colony.

The tide is wonderfully low so we scramble out to the furthest rocks we can safely reach. Junior discovers anemones and sponges. A tall rocky gully is coated in every colour of sponge, sea squirt and bryozoan, and we peer closely at their strange forms.

The overhang is coated in animal life including sponges, sea squirts and barnacles.
The overhang is coated in animal life including sponges, sea squirts and barnacles.

I spot an overhang that plunges into a pool. Even though I can see it’s too deep for my wellies, I wade in, balancing from one submerged rock to another, feeling a cold trickle down my shin as the water overtops my boots. At the edge of the rock the water is still precariously high, but I have noticed some dark, frilly tentacles in the water. Several sea cucumbers are lodged in cracks in the rock here and are busy feeding with their extended fronds. Junior crawls over the rock to get a better view of this unusual sight.

Brown sea cucumbers (Aslia lefevrei) feeding in the pool.
Brown sea cucumbers (Aslia lefevrei) feeding in the pool.
Brown sea cucumber feeding tentacles
Brown sea cucumber feeding tentacles

Edging our way through the narrow rocks, we reach the very edge of the sea. We are sheltered a little from the waves by a rocky reef further out, but the waves are still surging back and forth. In a hollow I can see a young common starfish. I tease it out of its hiding place and Junior holds it on his hand while I take photos.

One of several young common starfish we find on Plaidy beach.
One of several young common starfish we find on Plaidy beach.

Despite its name, this starfish is nothing like as common on our beaches as the other species we see here, preferring the deeper offshore waters. Junior takes a good look at its colours and its tube feet before placing it back where we found it.

We cross the rocks to the next beach, where Junior begins his sand-mining excavations while I take a walk along an old sea wall in the hope of taking a photo of shanny. These fish hide in holes out of the water while the tide is out and there are usually plenty in this wall. Of course, there are none in accessible places now that I have come to look for them, so I carry on across the beach to take photos of the lugworm casts that litter the muddy sand here.

The cast and depression in the sand mark the two ends of the lugworm's burrow.
The cast and depression in the sand mark the two ends of the lugworm’s burrow.

I am about to go back to see Junior’s work, when I see movement in a shallow pool. It looks as though there’s a tiny geyser beneath the surface throwing the sand up in a constant jet. There are several animals that like to bury themselves here, including some quirky species of prawn, but this sandy pool near the low tide mark makes me think of something else. I crouch by the pool for a few minutes without moving, scanning the sand before I see what I’m looking for. A small, sand-coloured fish is sitting unmoving in the shelter of a rock. I know it will be a weever fish.

A weever fish lying in the sand at Millendreath.
A weever fish lying in the sand at Millendreath.

Trying not to scare the fish away, I cross to the other end of the pool. It sticks its ground, watching me through shining eyes set towards the top of its head. Even as I lower my camera into the pool, it stays perfectly still, so that I can see its gaping mouth and moving gills. The mouth is unlike that of most other fish: the opening is nearly as high as the fish’s eyes and is hinged at the bottom like a tall flap. Inside it, I can see some spindly, crooked teeth.

The weever fish lies still as I approach, watching me with shining green eyes.
The weever fish lies still as I approach, watching me with shining green eyes.

I have no bucket and this fish will bury itself in the sand in an instant if I disturb it, so I just watch, putting my camera as close as I dare to frame the fish’s remarkable metallic-green eyes. Although the dark fin on the fish’s back is folded down now, it is made of venomous spines that cause painful stings to bathers in the summer.

Weever fish with its spiny fin folded down.
Weever fish with its spiny fin folded down.

Junior emerges from the hole he’s dug to look at the photos and do a beach clean before we head for home in the last of the day’s pale sunshine.

Painted topshells and a sea slug laying eggs - spring arrives early in the Cornish rock pools.
Painted topshells and a sea slug laying eggs – spring arrives early in the Cornish rock pools.
Junior's top find of the day. The yellow circles on the rock are boring sponge. This sponge drills into calcareous rocks and mollusc shells making round holes.
Junior’s top find of the day. The yellow circles on the rock are boring sponge. This sponge drills into the calcareous rocks and mollusc shells making round holes.

Full Moon in the Cornish Rock Pools

Ever since we discovered gem anemones in the pools at Plaidy last week, Junior has been planning a night-time trip to see them fluorescing under ultraviolet light. Lots of anemones glow in UV due to special proteins they contain that absorb the ultraviolet light before re-transmitting it at a longer, visible wavelength.

Snakelocks anemones are well-known in rockpooling circles for glowing a vivid, eerie green in UV and we have seen those many times, but we’re intrigued to see if gem anemones are as spectacular by night as they are by day.

Gem anemone by day
Gem anemone by day

Other-Half joins our after-dark ramble. We wrap up and walk through the deserted lanes. In the light of the rising full moon, there’s no need for torches. The stars have been out for a while already and the Eddystone lighthouse is flashing away at the horizon.

It took us quite a while to spot the gem anemones by daylight. Despite their pretty colours, they are tiny and well camouflaged among the pink encrusting seaweed that lines the pools.

We cross the sand and the heap of seaweed that the tide has brought in to the far rocks and take our UV torch out. Junior scans it over the pool and within seconds we’ve found them. They seem to light up in patterns of green and orange.

Under UV the gem anemones are easy to spot
Under UV the gem anemones are easy to spot

We kneel down and look closely at the starburst of orange that radiates out from the turquoise and pink mouth at the anemone’s centre. The green fringes to the tentacles that are sometimes visible by day are unmissable now.

Gem anemone under UV light
Gem anemone under UV light

Junior is keen to look at the sponges and seaweeds to see what they do under UV and leads me on a precarious climb towards an overhang he knows. The rocks here glow insanely orange and though it’s hard to tell what is causing this effect in the dark, it feels like either a dense red seaweed or a sponge.

Junior's orange-glowing sponge or seaweed
Junior’s orange-glowing sponge or seaweed

As we scramble over the rocks, we find more fluorescing plants and animals. A brown seaweed glows green, possibly due to micro-algae that is growing on its fronds.

Brown seaweed glowing green in places - presumably coated in a microalgae
Brown seaweed glowing green in places – presumably coated in a microalgae

Grey topshells are easy to spot because the tip of their shell glows pink.

Grey topshell in UV light
Grey topshell in UV light

We are intrigued by thin bright-blue streaks among the seaweed. It takes a while for us to realise that these are man-made threads. They feel coarse and may well be fibres from a fishing net. Many seaweeds on the shore are so tangled in them that it is almost impossible to clear the plastic fibres without damaging the seaweed.

One of many plastic fibres found tangled in the seaweed
One of many plastic fibres we find tangled in the seaweed

In a shallow, rocky pool lined with sediment more anemones are glowing. These look nothing like the gem, snakelocks or daisy anemones I’ve seen so far.

Another anemone species that fluoresces - Sagartia troglodytes.
Another anemone species that fluoresces – Sagartia troglodytes.

I turn my normal torch on them to see what species they are and I can’t see them at all. By switching back between UV and normal light I manage to pinpoint them. They are at least as small as the gem anemone, but are flecked with a marble of brown, white and orange that blends perfectly into the sand and rock around them.

Under the camera I can make out dark ‘B’ shaped markings at the base of the tentacles and realise this is Sagartia troglodytes. I don’t remember seeing this anemone before, probably because it would be almost impossible to spot in daylight.

The same Sagartia troglodytes anemone under normal torchlight is much harder to see among the sediment.
The same Sagartia troglodytes anemone under normal torchlight is much harder to see among the sediment.

I touch one of the anemones gently with a finger and it retracts in a puff of sediment, disappearing without trace.

I take photos while Junior and Other Half climb onto a high rock to watch the stars. On nights like this it is hard to tell whether the sea or the sky is shining more brightly. With a last sweep of the torch over the glowing anemones we turn away and head home for hot drinks.

Gem anemone under UV
Gem anemone under UV
This daisy anemone glowed red under UV but was a dull brown under normal light.
This daisy anemone glows red under UV but is a dull brown under normal light.
Anemones weren't the only animals out in the moonlight - this green shore crab glowed blue under the UV torch.
Anemones aren’t the only animals out in the moonlight – this green shore crab glows blue under the UV torch.

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