Giants of the Cornish rock pools

Last week I shared with you the miniature world of the sea slugs, so this week I’ll super-size things and bring you some big fish. Silly-season reports of Great-white sharks often hit the headlines in Cornwall, but I prefer rock-pool giants; they’re not made up, and you can get close to them without having your leg bitten off!

Cornwall is brilliant in all sorts of ways, our network of local, grassroots marine conservation groups being just one of them. The public launch, last week, of the new Three Bays Wildlife Group brought experts and volunteers together and gave me a chance to explore some new beaches in the St Austell area.

Judging by the squeals of excitement from the children and adults alike, the crabs, pipefish, prawns and anemones we found at the main rockpool ramble on Portmellon beach near Mevagissey went down well. By the end of the day, the local group had recruited lots of potential new volunteers.

Green shore urchin at Portmellon beach - adorned in seaweed
Green shore urchin adorned in seaweed. Portmellon beach.

At the end of an event I’d usually relax and enjoy my sandwiches, but the group was keen to survey another local beach. The walk to Colona was like something out of an Enid Blyton adventure. Cresting the hill out of Portmellon, we passed a disused cattle grid filled with nettles, beyond which the view opened out to sheep-grazed pasture plunging down to the bay. The whitewashed house on Chapel Point, to the east of the beach, perches over azure waters and would be any rockpooler’s dream pad.

Walking down to Colona bay
Skipping down to Colona bay

Matt Slater from Cornwall Wildlife Trust was straight out on the rocks setting fish traps in the deep pools. Matt, of course, is a fully-licensed professional giant catcher.

After just half an hour of mooching about the pools looking at anemones and some fine lugworms, we clambered across to check the traps. The first looked successful. At the back of the yellow-mesh cage, several creatures wriggled while Matt hoisted them onto the rocks and eased them into an awaiting bucket.

Once the greedy shore crabs that had been feasting on fish-bait had been picked out, there were three fish left. Every one of them was large by goby standards. One in particular was what Junior would describe as “a whopper”. Matt’s face said it all. From the fishes’ fleshy lips that could out-pout Mick Jagger to the beady eyes, it was clear that all three were Giant gobies (Gobius cobitus).

Three giant gobies from the first trap.
Three Giant gobies from the first trap.

These fish have special protection under the Wildlife and Countryside Act and are at the northernmost point of their range around south west England. They’re not well recorded because they’re elusive and can be mistaken for the much more common Rock goby.

Giant gobies have huge lips, small eyes and lack the yellow band at the top of their first dorsal fin (distinguishing them from the Rock goby)
Giant gobies have huge lips, small eyes and lack the yellow band at the top of their first dorsal fin (distinguishing them from the Rock goby)
Another feature of the Giant goby is the fleshy lobe on their adapted pelvic fin - this helps them to sucker onto rocks
Another feature of the Giant goby is the fleshy lobe on their adapted ventral fin – this helps them to sucker onto rocks

To round off our week of giants, Junior and I took a stroll around a sheltered lagoon in Looe, after a Fox Club event and came across a fish even larger than a Giant goby. In fact, I was so busy examining tiny hydroids on seaweed looking for sea slugs that I practically tripped over the young catshark.

Greater spotted cat shark (Scyliorhinus stellaris) in a Cornish rock pool, Looe
Greater spotted cat shark (Scyliorhinus stellaris) in a Cornish rock pool, Looe

The Greater-spotted catshark goes by many different names (bull huss, nursehound, dogfish, etc.) and is far larger than a Giant goby, growing to around one and a half metres long when mature. The one I nearly stepped on in my neoprene beach shoes was just a baby, but still an impressive fish.

Catsharks tend to lie still for camouflage, so they’re easily approached to take photographs. If you touch one, as Junior did at the first opportunity, you’ll also notice that their skin is like sandpaper. Rough sharkskin is remarkably hydrodynamic, so much so that engineers are looking at ways to copy its structure to make swimmers faster and ships more fuel efficient, among other things.

This close-up of the catshark's skin shows how rough it is. You can also see the dark and white spots that are characteristic of this species.
This close-up of the catshark’s skin shows how rough it is. You can also see the dark and white spots that are characteristic of this species.

I think Junior would like it even better if we could stumble across a giant squid circling the pools, but for now, a shark will certainly do. The giants of the Cornish rock pools aren’t as easy to spot as you might imagine, but it’s well worth the effort.

 

 

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For the love of sea slugs…

I love sea slugs a bit more than is probably usual. My other half even made sure I have the t-shirt, which I wear with pride in the Cornish rock pools despite the odd looks it gets me.

Trend setting in my waterlogged wellies and 'I love sea slugs' t-shirt.
Trend setting in my waterlogged wellies and ‘I love sea slugs’ t-shirt. Hannafore beach, Looe.

If you don’t already have your own t-shirt, it might be that you haven’t yet met these amazing little creatures. Unlike land slugs, sea slugs come in a mind-boggling variety of colours and shapes and have cool super-powers.

So, this week I’ve been braving the traditional British summer-holiday weather to find top slugs to convert you to the cause. My lucky t-shirt worked its wonders…

If you follow my blog, you might remember my excitement earlier in the year at finding the rare Calma gobioophaga sea slug, which feeds on the eggs of gobies (fish).

It’s probably fair to say that a woman in an ‘I love sea slugs’ t-shirt has never been so excited as I was when I turned a stone this week in Looe, to find three sea slugs with some clingfish eggs. This was another new species to me – the equally rare Calma glaucoides.

Calma glaucoides and its eggs. See how pretty sea slugs are!
Calma glaucoides and its eggs. See how pretty sea slugs are!

This slug has striking long wavy cerrata (tentacles) down both sides of its back, with blueish glands running through them. The pattern of white circles on its back (part of its reproductive organs) help it to blend in among the white scribble-patterns of its egg strands.

The clingfish eggs on which Calma glaucoides feeds - there weren't many left under this rock.
The clingfish eggs on which Calma glaucoides feeds – there weren’t many left under this rock.
Calma glaucoides sea slugs
Calma glaucoides sea slugs – I have no idea what the collective noun would be.

Most sea slugs are ruthless carnivores, but not the Elysia viridis, which feeds on codium seaweed. For some reason up until now, I’ve tended to find blandly coloured brown specimens which don’t show their magic trick very well.

This week, I’m delighted to bring you an Elysia viridis in its finest regalia of green with vivid blue-green spots.

The photosynthesising sea slug - Elysia viridis, grazing on Codium tomentosum seaweed.
The photosynthesising sea slug – Elysia viridis, grazing on Codium tomentosum seaweed.
Elysia viridis showng the green colours and turquoise spots of the chromatophores it stores
Elysia viridis showng the green colours and turquoise spots of the chromatophores it stores

These colours contain chromatophores from the seaweed that the slug has eaten. In other words, it manages to retain the photosynthesising cells from plants and store them in their bodies where they continue to produce energy for the slug.

I almost popped with excitement when, after finding so many fabulous slugs, yet another one turned up during a rock pool event with Looe Marine Conservation Group. Rummaging on the lower shore for exciting crabs, starfish or squat lobsters to show the kids, I spotted some eggs belonging to a slug, the Sea lemon.

Next to a big clump of Sea lemon eggs (left) is a much smaller spiral of eggs
Next to a big clump of Sea lemon eggs (left) is a much smaller spiral of eggs

This egg spiral, in itself, was fairly commonplace but in its midst and alongside it, I noticed two more tiny spirals of spawn laid by something else that I didn’t recognise. After another minute of staring at the rock I spotted the slug.

A pale-coloured Favorinus branchialis sea slug
A pale-coloured Favorinus branchialis sea slug

This slug, the Favorinus branchialis, has two pretty groups of red-ish cerata along its back and a distinctive bulge in its rhinophores (the tentacles on top of its head). It is variable in colour and it took me another minute to spot the second slug, which was much paler, but with the same body form.

The darker of the two Favorinus branchialis sea slugs, showing the bulge in its rhinophores (the antennae on top of its head)
The darker of the two Favorinus branchialis sea slugs, showing the bulge in its rhinophores (the antennae on top of its head)
Favorinus branchialis swimming upside down because it can
Favorinus branchialis swimming upside down because it can

Cute and pretty though it is, this slug has a rather gruesome habit; it likes feeding on the eggs of other slugs. It was no accident that these slugs had laid their eggs right next to those of the sea lemon.

A slug with some serious weaponry turned up on my next foray into the pools.

Berthella plumula sea slug
Berthella plumula sea slug

The Berthella plumula slug (or Feathered Bertha as I call it), resembles a sherbet lemon, but is far more squidgy. I’d never advise actually squidging one, mostly because it’d be cruel, but also because they can secrete sulphuric acid when attacked.

This sea slug has a feathery gill on its underside - unlike most slugs which have their gills in a tuft on their back or in their cerata.
The Berthella plumula sea slug has a feathery gill on its underside – unlike most slugs which have their gills in a tuft on their back or in their cerata.

Interesting defences are common in sea slugs. Many aeolid sea slugs store the stinging cells from the food they’ve eaten, such as anemones or hydroids. If they’re attacked, the stinging cells fire from the tips of the cerata on their backs into their prey. Sea hares, on the other hand, have a similar defence system to squid and cuttlefish, squirting a cloud of purple ink out their bottoms to ward off predators.

Last week, my lucky t-shirt did me proud, so I’m looking forward to getting it on again to explore the shore on next week’s big spring tides. If you’d like to meet these cool creatures for yourself, there are rock pooling events taking place all round Cornwall through the rest of the summer holidays.

Here's your bonus slug for reading to the end - a Rostanga rubra which eats red sponges and is perfectly camouflaged on them.
Here’s your bonus slug for reading to the end – a Rostanga rubra which eats red sponges and is perfectly camouflaged on them.
A charming view of a Favorinus branchialis's bottom. You're welcome!
A charming view of a Favorinus branchialis’s bottom.

The One That Got Away… Cuttlefish in a Cornish Rock Pool

If you’ve ever been rockpooling, you’ll know the feeling: you’re in the zone, bottom high, head down, lifting a rock or staring into the water when a movement catches your eye. While you’re registering that it’s some interesting creature you’ve never found before, said creature is darting away under an overhang or boulder never to be seen again.

My camera is full of “things that were there only a millisecond before”.

Not the most accomplished photo of a Greater pipefish as long as my arm!
Not the most accomplished photo of a Greater pipefish as long as my arm!

So, you’ll have to take my word for it that I finally encountered an animal I’ve been longing to find in a pool. After four decades of failure, my big moment came while I was taking some friends rock pooling this week.

At risk of overtopping my wellies, I was wading in the centre of a long pool, staring through a clump of Sargassum weed to the sand beneath.  Some baby dragonet fish were zipping from spot to spot and I, as usual, was failing to take a photo of them.

As I bent in close to tease aside some seaweed, a few small creatures shot out. I only had a second to clock that they seemed to be swimming backwards with jerky movements. It was hard to make them out given their sandy colouring, but in the moment it took me to turn towards them and realise what they were, they were gone.

From their shape they had to be either young common cuttlefish (Sepia officinalis) or, very likely, the little cuttlefish (Sepia atlantica). These amazing animals can adapt their camouflage to match their surroundings or to signal their mood. It’s difficult to believe that such mobile, intelligent creatures are a type of mollusc, making them distant relations of limpets and mussels.

Cuttlefish, like this one in an aquarium, are masters of disguise.
Cuttlefish, like this one in an aquarium, are masters of disguise.

Along with an octopus and a seahorse they’re the thing I’ve always wanted to find (in the case of seahorses, I almost definitely never will).

This photo of a cuttlefish was taken in aquarium
This photo of a cuttlefish was taken in an aquarium

Without photos of the cuttlefish or much likelihood of re-finding them in this pool, my excitement was tinged with disappointment. It was going to sound like a tall tale of “the one that got away”.

The second after the cuttlefish disappeared, my eye was drawn back to where they had been. In the water, tails spreading behind them like minuscule comets, were several black blobs.

During their escape from the giant wellies and the hand parting the seaweed, they had fired off their defensive ink. The way the ink formed little clumps suggested they had deliberately mixed the ink with mucus to make it look like little decoy cuttlefish.

With a yelp of delight, I scooped up some ink in a tub and proudly showed my friends and Junior.

Cuttlefish ink in my tub
Cuttlefish ink in my tub

I’m not at all sure they were as impressed as I was.

But at least there’s a chance you’ll believe me that I really did finally see cuttlefish in a rock pool.  Perhaps next time I’ll capture some photos of an actual cuttlefish.

In the meantime enjoy your summer rockpooling adventures and don’t forget there are loads of holiday events for all the family that would love your support (and some decent weather for a change).

Here's one that didn't get away - a large edible crab which impressed my friends far more than my pot of ink.
Here’s one that didn’t get away – a large edible crab which impressed my friends far more than my pot of ink.
I also thought this Aplidium turbinatum sea squirt was rather lovely - and it doesn't move, which is always a bonus.
I also thought this Aplidium turbinatum sea squirt was rather lovely – and it doesn’t move, which is always a bonus.
This lobed sponge (Oscarella sp.) was a lovely yellow tinged with pink -
This lobed sponge (Oscarella sp.) was a lovely yellow tinged with pink –

Summer Holiday Rock Pooling Events in Cornwall – The Full List

Here it is… the 2017 list of summer rockpooling events in Cornwall during the holidays. It’s the best ever, with events to suit all the family!

Take a look below to see what’s on near you. There’s no better way to make the most of your rock pooling than to join the experts to find amazing marine creatures and learn all about them.

All you need are: some sturdy rockpooling shoes like wellies, neoprene beach shoes or wetsuit boot (not flip flops or crocs); a bucket, and sun protection.

Please check the organiser’s page carefully for the exact details and any alterations. You will need to book in advance for some of these events.

 Happy rockpooling! Maybe see you there?

FRIDAY 28TH JULY, 14.00-16.00, St Michael’s Mount. Rockpool Explorer with the National Trust https://www.nationaltrust.org.uk/events/795f56c8-54f5-4205-acde-482402421940/pages/details

SUNDAY 6TH AUGUST, 10.00 – 12.00, St Michael’s Mount. Rockpool Explorer with the National Trust (Scroll to the bottom of the following web page for this date) https://www.nationaltrust.org.uk/events/795f56c8-54f5-4205-acde-482402421940/pages/details

MONDAY 7TH AUGUST, 12.00 – 13.30, Northcott, Bude. Hurray for Honeycomb with Cornwall Wildlife Trust. Meet at Northcott Mouth National Trust car park, Bude http://www.cornwallwildlifetrust.org.uk/events/2017/01/06/hurray-honeycomb?instance=0

TUESDAY 8TH AUGUST, 11.30 – 13.30. Polzeath. Rockpool Ramble with Polzeath Marine Conservation Group and the National Trust, BOOKING ESSENTIAL https://www.nationaltrust.org.uk/events/4d6bf7a6-558b-4e53-b1c1-3929cec9591e/pages/details

WEDNESDAY 9TH AUGUST, 11.00 – 13.00. Mousehole. St Piran’s Crab Search with Cornwall Wildlife Trust, Mousehole (Meet in Car Park, The Parade, by The Rock Pool Café) http://www.cornwallwildlifetrust.org.uk/events/2017/01/06/st-pirans-crab-search?instance=0

THURSDAY 10TH AUGUST, 13.00 – 15.00. Falmouth Harbour. Horrible Beasts Up the Creek. With Cornwall Wildlife Trust. BOOKING ESSENTIAL – Falmouth – location provided on booking. http://www.cornwallwildlifetrust.org.uk/events/2017/01/06/horrible-beasts-creek?instance=0

THURSDAY 10TH AUGUST, 13.00 – 15.00 Lantivet Bay. Rockpooling with the National Trust. Free no booking required https://www.nationaltrust.org.uk/events/0916c2da-8026-4e5e-a507-5d6c413e46a0/pages/details

FRIDAY 11TH AUGUST, 13.00 – 15.00. Marazion. Strandline Scramble – looking for creatures washed up by the tide. With Cornwall Wildlife Trust. BOOKING ESSENTIAL http://www.cornwallwildlifetrust.org.uk/events/2017/01/06/strandline-scramble?instance=0

FRIDAY 11TH AUGUST, 14.00-16.00. St Michael’s Mount Causeway. Rockpool Explorer with the National Trust. (Scroll to the bottom of the following web page for this date) https://www.nationaltrust.org.uk/events/795f56c8-54f5-4205-acde-482402421940/pages/details

SATURDAY 12TH AUGUST, 14.30 – 16.00. Hannafore, Looe. Rock Pool Ramble with Looe Marine Conservation Group http://www.cornwallwildlifetrust.org.uk/events/2016/12/23/summer-holiday-rockpool-ramble?instance=0

MONDAY 14TH AUGUST, 15.00 – 17.00 Polzeath, Rock Pooling and Beach Games with Wild Thymes. BOOKING ESSENTIAL http://www.cornwallwildlifetrust.org.uk/events/2017/01/26/rock-pooling-and-beach-fun-wild-thymes?instance=0

SATURDAY 19TH AUGUST, 21.30 – 23.30. Durgan. Night Time Rock Pooling with Cornwall Wildlife Trust. BOOKING ESSENTIAL – No children under 12. http://www.cornwallwildlifetrust.org.uk/events/2017/01/06/night-rockpooling?instance=0

SUNDAY 20TH AUGUST, 10.00-12.00. St Michael’s Mount Causeway. Rockpool Explorer with the National Trust. (Scroll to the bottom of the following web page for this date) https://www.nationaltrust.org.uk/events/795f56c8-54f5-4205-acde-482402421940/pages/details

MONDAY 21ST AUGUST, 11.00-13.00. Polzeath. Rockpool Ramble with Polzeath Marine Conservation Group and National Trust. BOOKING ESSENTIAL (Scroll to the bottom of the page for this date) https://www.nationaltrust.org.uk/events/4d6bf7a6-558b-4e53-b1c1-3929cec9591e/pages/details

TUESDAY 22ND AUGUST, 11.00 – 13.00. Polzeath. Radical Rockpooling with the Cornwall Wildlife Trust and the Polzeath Marine Conservation Group. BOOKING ESSENTIAL – Children over 11 only. http://www.cornwallwildlifetrust.org.uk/events/2017/01/26/radical-rock-pooling?instance=0

WEDNESDAY 23RD AUGUST, 11.00 – 13.00. Hannafore, Looe. Rockpool Safari Time with Fox Club, Junior branch of Cornwall Wildlife Trust. BOOKING ESSENTIAL http://www.cornwallwildlifetrust.org.uk/events/2017/01/05/rockpool-safari-time?instance=0

WEDNESDAY 23RD AUGUST, 12.30 – 14.30. Camel (Location available on booking). Rockpool Ramble with Fox Club, Junior branch of Cornwall Wildlife Trust. BOOKING ESSENTIAL http://www.cornwallwildlifetrust.org.uk/events/2017/04/20/rockpool-ramble?instance=0

THURSDAY 24TH AUGUST, 13.00 – 15.00. Polzeath. Rock Pool Ramble with Polzeath Marine Conservation Group BOOKING ESSENTIAL  http://www.cornwallwildlifetrust.org.uk/events/2017/01/26/rock-pool-ramble?instance=4

FRIDAY 25TH AUGUST, 14.00-16.00. St Michael’s Mount Causeway. Rockpool Explorer with the National Trust. (Scroll to the bottom of the following web page for this date) https://www.nationaltrust.org.uk/events/795f56c8-54f5-4205-acde-482402421940/pages/details

Can’t see your event? Please let me know of any additions or alterations to this list and I’ll be delighted to share them.

Wrasse and wrack

The Cornish summers are anything but predictable. One day I’m sweltering in shorts and beach shoes and the next I’m shivering in waders and a thick jumper. Although the showers are back with a vengeance, there’s always something to be found if I can make it across the rocks without breaking an ankle.

Painted top shell, East Looe
Painted top shell, East Looe

My first outing is to the rocks beyond East Looe beach and I’m pleased to come across a new colony of St Piran’s hermit crabs on the mid-shore.

A St Piran's hermit crab starting to emerge from its shell.
A St Piran’s hermit crab starting to emerge from its shell.

They’re becoming a familiar sight around Cornwall and I’m starting to recognise them from the tips of their red legs, before their chequerboard eyes and equal-sized claws emerge from their shells.

St Piran's hermit crab showing its distinctive red legs and chequerboard eyes
A St Piran’s hermit crab showing its distinctive red legs and chequerboard eyes
This hairy crab was also out an about enjoying the showers.
This hairy crab is also out and about enjoying the showers.

Dragging the family with me on my next expedition, I take a look at the other side of Looe.

Junior and Other-Half exploring Hannafore in the rain
Junior and Other-Half exploring Hannafore in the rain

At Hannafore, the rocks are hidden under a thick brown  tangle of wracks, sargassum weed, and kelp making my feet slither with every step. It’s hard to make out where the pools are much of the time, let alone what’s in them.

Low tide at Hannafore, West Looe
Low tide at Hannafore, West Looe

Still, with some patience and careful sweeping aside of the long strands of weed, some treasures are revealed. This heart-shaped daisy anemone is the pinkest one I’ve ever seen.

An unusually pink daisy anemone
An unusually pink daisy anemone

As we wade in a long, deep pool a large fish passes between the fronds of sargassum near my feet. Moving slowly, I herd it towards a shallow corner, and, holding a bucket behind it take one more step. Nine times out of ten, I fail and the fish darts away never to be seen again. This time, the colourful fish takes me by surprise and swims straight into the bucket.

Junior getting to know our wrasse-friend
Junior getting to know our wrasse-friend

Here it is – is the first adult corkwing wrasse I’ve found in a rock pool.

Male corkwing wrasse have beautiful markings - they look almost tropical
Male corkwing wrasse have beautiful markings – they look almost tropical

Cornish Rock Pools junior comes over to admire the fish, talks to it and gives it a stroke. We look at its pouting lips and the iridescent blue stripes on its cheek, the typical colouring of the male corkwing wrasse. The female is much more dowdy.

After a few minutes, Junior lowers the bucket into the drizzle-spattered pool and we watch the wrasse swim free among the weeds.

I can see why most people see rockpooling as a fair-weather activity, but I’ve always liked the heavy calm of an empty beach on a foggy, damp day, and the animals are as colourful as ever.

Happy rockpooling!

Dahlia anemone, Hannafore
Dahlia anemone, Hannafore

My First Fox Club Expedition To Porth Mear

It’s the middle of the night and I’m convinced there’s something wrong with my eyes. I’ve unplugged my phone, tried blinking several times but I’m still seeing flickering lights and flashes. Finally I twig what’s going on and open the curtains to reveal incessant sheet lightning.

My first thought is that it had better stop by the morning, else no-one will turn up to my first rock pooling event at Porth Mear with Fox Club, the junior branch of the Cornwall Wildlife Trust. As a child, I was a keen member myself so I’ve been looking forward to this for months.

By the morning the lightning storm has given way to wind and rain, but conditions are less than inspiring. It’s amazing anyone shows up for rock pooling, but a few hardy well-wrapped-up folk do, as does a lovely volunteer assistant. In the chill wind at Pentire Farm car park my faith in the weather wavers, but we’re here now. There’s nothing for it but to grab the buckets and set out.

As soon as I see the bay, I know it’s going to be fine. The cliffs are sheltering the pools and the waves are dashing themselves out against the rocks on the western side of the cove. The cloud thins, the temperature lifts. It’s a perfect day for rockpooling.

Within minutes of hitting the pools, a little girl brings over the first sea hare. We watch it unfolding its long ‘ears’ in the tub and she’s delighted with it, announcing it to be far nicer than garden slugs.

Sea hares (Aplysia punctata) graze on seaweeds and have antennae on their heads that look like big ears.
Sea hares (Aplysia punctata) graze on seaweeds and have antennae on their heads that look like big ears.

She’s barely returned to the pool before she’s back again with a gorgeous baby spiny starfish on some kelp. When I turn the seaweed over I realise she’s also brought me an even tinier baby cushion star. The kids squeal at its cuteness. It’s going to be a magical day!

A Xantho pilipes crab. These crabs have hairy back legs and vary a lot in colour. They often curl up like pebbles when you pick them up.
A Xantho pilipes crab. These crabs have hairy back legs and vary in colour. They often curl up like pebbles when you pick them up.

The finds flood in. There are Green shore crabs, Xantho pilipes (hairy-legged ‘pebble’ crabs), including some females with eggs tucked under their tails. There are hermit crabs, brittle stars and lots more sea hares. The seaweed-packed pools are providing the perfect conditions  for sea hares to get fat and start spawning.

Sure enough, we find the pink spaghetti eggs of the sea hare in a pool.

Sea hares lay egg-strings that look like pink spaghetti.
Sea hares lay egg-strings that look like pink spaghetti.

Even more excitingly, when one of the mums rescues a sea hare that is stranded on a rock, drying out fast, it assumes it’s being attacked and squirts out purple ink. We gather round to watch the jet of ink in the tub which soon turns the water purple.

Sea hare on the defensive squirting out purple ink to confuse predators.
Sea hare on the defensive, squirting out purple ink to confuse predators.

We’re all looking out for the St Piran’s hermit crab (Clibanarius erythropus) and sure enough we find several large colonies of them. They first re-arrived here last year after an absence of around 40 years.

St Piran's hermit crab at Porth Mear
St Piran’s hermit crab at Porth Mear

There are plenty of the common hermit crabs (Pagurus bernhardus) too. The species are easy to tell apart, as the common hermit has yellow eyes and a right claw much bigger than the left, whereas the St Piran’s crab has black and white eyes, equal sized claws and red, hairy legs.

I keep asking if they’ve had enough, given that it’s past lunch time, but they’re keen to carry on. I’m impressed by how knowledgeable everyone is already and how good they all are at taking care of the animals they find. There might well be some future marine biologists in this group.

Light bulb sea squirts at Porth Mear
Light bulb sea squirts at Porth Mear

The finds keep flooding in. There’s a smart little Aeolidia papillosa ‘sheep’ slug, which has turned from white to browny-red after eating an anemone.

This Great grey sea slug (Aeolidia papillosa) has been eating an anemone and turned brown
This Great grey sea slug (Aeolidia papillosa) has been eating an anemone and turned brown

On the lowest part of the shore I find a yellow-clubbed sea slug (Limacia clavigera).

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

Best of all, among the many fish eggs I see under the rocks, there’s a sea slug feeding on a patch of goby eggs. It’s the rare Calma gobioophaga that I only recorded for the first time last week. It’s so impossibly small and well-camouflaged that the children need to view it on my camera to even see that it’s there.

A Calma gobioophaga sea slug feeding on goby eggs at Porth Mear
A Calma gobioophaga sea slug feeding on goby eggs at Porth Mear

By the time I return to our ‘shore laboratory’ to talk through our finds at the end of the session, it’s teeming with colourful anemones, painted top shells and many more lovely creatures. Everyone has done a good job of keeping the animals comfortable and safe, with crabs in separate buckets to prevent any injuries to the animals.

The kids show me their favourite finds and we talk about each of them and practice handling them safely. There are enough starfish for all the children to hold one at the same time. The fish are popular too and we have a good selection of species to look at; a shanny, rock goby, Cornish clingfish and a baby sea scorpion.

A juvenile scorpion fish.
A juvenile scorpion fish.

Before the tide turns, everyone helps out with carrying creatures back to the pools where we found them.

Trivia monacha - Three spot cowrie at Porth Mear
Trivia monacha – Three spot cowrie at Porth Mear

It must be getting on for 2pm by the time Junior and I reach the top of the bay and sit on the sand for a quick sandwich. It’s been a perfect day despite the iffy weather at the start and I hope that the children will remember it as well as I remember my own Fox Club trips. Who knows, perhaps Junior and his new friends will be back here leading an event some day?

A predator among the fish eggs: Calma gobioophaga sea slug

If you read this blog regularly, you’ve probably noticed a pattern: I bimble about the Cornish rock pools looking for an exciting creature, fail completely, then find something unexpected. Well, hopefully you like the format because this week is no exception. I go on a quest to find fish eggs and discover this rare sea slug.

Fish eggs are amazing. If you catch them just as they’re nearing hatching you can see each baby fish staring out, its tail curled tight around its head like a scarf.

So, when Junior announces he wants to go for a big walk, I suggest Port Nadler. This slightly exposed rocky bay is ideal for Cornish clingfish. Their distinctive yellow eggs usually carpet the underside of the rocks and their developing babies are especially beautiful.

Clingfish eggs - with one newly-hatched fish (centre)
Clingfish eggs – with one newly-hatched fish (centre)

Only the tide today isn’t low enough to access the clingfishes’ favourite gully.

I look in the pools and lose count of how many rocks I lift. There don’t seem to be any fish eggs. As the tide drops a little further, I come across some Berthella plumula sea slugs and a sea hare.

A pair of Berthella plumula sea slugs
A pair of Berthella plumula sea slugs

There’s an anemone I don’t recognise. Translucent white all over with a base so wide it looks like a bowl. I later realise it must be the white form of Sagartia elegans (var. nivea).

Sagartia elegans (var nivea) anemone
Sagartia elegans (var. nivea) anemone

Junior finishes his digging in the sand at the top of the beach and wanders over to join me. We lift a rock together and finally here are some eggs. They’re not the yellow clingfish eggs I was looking for, they’re smaller goby eggs, forming black-specked carpet of grey. Under the camera, the specks become a sea of eyes looking up at me.

It takes me a long time to decide that the Calma gobioophaga sea slug (in the background here) is 'a thing'
It takes me a long time to decide that the Calma gobioophaga sea slug (in the background here) is ‘a thing’

I remember rockpool expert David Fenwick, who runs the fabulous Aphotomarine site, telling me a year or two back that there was a species of sea slug that specialises in eating these eggs. I peer into the greyness and see nothing, apart from a thin yellowish patch in the centre which looks like a piece of sponge or sea squirt.

I look some more. The eggs around the edge of the yellow patch look longer than the others.

I stare, stare some more then focus my camera on the patch and do yet more staring. Even then I’m not sure, but it could be…

It’s only when I see a tentacle move that I begin to see the slug properly. It’s over a centimetre long, but most of its body is covered in pointed cerrata the colour and shape of goby eggs, right down to the black dots that ressemble eyes.

Calma gobioophaga on its goby egg prey, its eyes showing through behind its long rhinophores.
Calma gobioophaga on its goby egg prey, its eyes showing through behind its long rhinophores.

This is the weirdly named Calma gobioophaga egg-eating sea slug. It’s the first I’ve seen and only the second record of this species in Cornwall.

The yellowish patch I thought was a sea squirt is the slug’s back. It’s covered in pale circles, which my books tell me afterwards are the mature gonads. Who’d have thought?

The books also tells me that the slug absorbs the fish eggs so well into its gut that it has no need of an anus. That’s right; it doesn’t poo. I’m not sure how that works, but it’s the sort of fact that gets Junior’s attention.

Calma gobioophaga - the cerrata (tentacles) on its back blend perfectly with the goby eggs. Only the pale circles on its back (gonads) stand out.
Calma gobioophaga – the cerrata (tentacles) on its back blend perfectly with the goby eggs. Only the pale circles on its back (gonads) stand out.

It’s not the easiest thing to photograph: a grey blob on a mat of grey eggs on a grey day in silty water. As I start to get my eye in to the outline of the slug, it glides towards me, feeling the eggs with its tentacles and swinging its long rhinophores forwards.

Tucked immediately behind each rhinophore is a distinct black eye, one of the characteristic features of this species.

Calma gobioophaga on goby eggs (probably the eggs of a rock goby) near Looe, Cornwall
Calma gobioophaga on goby eggs (probably the eggs of a rock goby) near Looe, Cornwall

The books suggest this species only eats the eggs of the black goby (Gobius niger), but slugs are not great readers and the other records from Cornwall and Brittany are, like this one, probably on rock goby (Gobius paganellus) eggs. In the Mediterranean this species has also been recorded on giant goby (Gobius cobitis) eggs. There’s another, closely related, species of sea slug, Calma glaucoides, that feeds on a wider range of eggs, including clingfish eggs and has been recorded in Cornwall too. Hopefully I’ll find that one soon!

The slug’s life cycle intigues me. As fish eggs are available for such a short period of the year, I’m not sure what happens to these slugs during the remaining months.

It comes on to rain heavily and as we’re already soaked from exploring the rock pools, we call it a day. I haven’t found a single clingfish egg, but, as is the way with rockpooling, I’ve discovered something even better.

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