Tag Archives: night

A Night Out In The Rock Pools

It’s not often that you have the beach to yourself in Cornwall in July, but we want to show our friends the best Kernow has to offer. With this in mind, we meet Irys and her mum late in the evening to walk to our local shore and crunch across the sand to the rocks in the grey twilight.

Arriving at the empty beach before it is completely dark. (Photo by Other Half).

It doesn’t seem dark yet, but the birds are quiet, there are no other people about and it’s becoming hard to see where we’re putting our feet.

At night, it is especially important to put safety first so that you don’t find yourself in difficulty and have to get the Coastguard out of bed. We stick to a planned route on a beach we know well so that we will not be clambering over unfamiliar or slippery rocks. As always, an outgoing tide is safest and we arrive a full two hours before low tide so that we will leave before it turns. Sturdy boots and good torches are essential equipment, as are working phones and warm clothes. Our best-loved pieces of nighttime kit are our ultra-violet torches. Irys is trying hers out for the first time.

Testing the UV torch on some anemones. (Photo by Other Half)

The lack of predatory birds and drying sun makes life easier for rock pool inhabitants, so most of them are nocturnal. Creatures that we have to search for in daylight, such as prawns, crabs and fish, are all out and about looking for food.

Junior takes Irys straight to his favourite spot for seeing gem anemones. Under the UV torch they glow brightly, as does this snakelocks anemone. This fluorescence is caused by proteins that may help the anemone to survive in bright sunlight in shallow pools.

Snakelocks anemones

By scanning the torch across the pools it is possible to spot the anemones from some distance away.

Snakelocks anemones fluorescing. Seaweeds on the rock are also fluorescing red and pink.

We stand on the rocks and look into a large pool. Prawns, glowing blue under the UV torch, swim to and fro, intent on feeding. A common shrimp skitters across the sand. The green seaweeds glow bright red and the pink encrusting seaweed takes on a deeper pink-purple hue.

Exploring the pools as it gets dark.

We alternate between the normal torches and UV, finding sea scorpion fish, a rockling and even a young tompot blenny with its distinctive headgear. Irys finds a common blenny in a hole in the rock, lying still and breathing through its skin while it waits for the tide to return.

Sea scorpion fish – Taurus bubalis – hiding among the seaweed.

Hermit crabs run around the pools and some of the top shells glow pink under UV where their shell has worn away to reveal the mother of pearl layer below.

Taking a close look at an isopod at night. (Photo by Other Half).

Flying insects swarm around our head torches while bats dance in and out of the light. We tread carefully and stop still for long periods, looking into the water, enjoying the window into the animals’ lives while the waves splash against the rocks beyond us.

It’s fascinating to explore fluorescence. Anemones glow, stalked jellyfish not so much. Crabs and isopods stand out against the seaweeds in shades of blue and grey. A shell containing a hermit crab shines a bright orangey-red, probably due to micro-algae growing on it. In every pool, once you get your eye in, there are countless blue specks zipping about in dizzying circles, which must be copepods or similar small crustaceans that I would normally only see under the microscope.

At night, crabs often emerge from the water and cross the rocks. This green shore crab was carrying a limpet off to eat.

Green shore crab holding a limpet in its right pincer.

Normally it is the rising tide that brings an end to our rockpooling, but tonight it is tiredness that creeps up on us. Still buzzing from all that we have seen, we head home to bed. Behind us the rock pools seem quiet and deserted, but we know better; for the wildlife on the beach, the night is just beginning.

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.

A Night Out in the Rock Pools

Nights out tend to become a distant memory when you’re a parent. For the most part I don’t miss them. I have, however, been looking forward to Junior being old enough to join me for night time rock pooling. Towards the end of last year, we tried it for the first time and, although the conditions weren’t ideal, he’s been asking to go again ever since.

The best low tides always happen around the middle of the day, and the middle of the night, but we compromise for this first family expedition of the year, choosing a reasonable low tide at around 10.30pm. The warm, calm weather provides good opportunities for seeing nocturnal activity and tonight I’m trying out my ultraviolet (UV) torch.

It doesn’t disappoint.

Head torch at the ready - night time rock pooling is a perfect adventure
Head torch at the ready – night time rock pooling is a perfect adventure

I’ve always known that certain species glow under UV light, but I had no idea how much. We’ve barely taken ten paces out across the rocks when we see our first snakelocks anemone, shining from the darkness like an eerie green beacon. The colour is wonderfully alien.

Snakelocks anemone at night under UV light - a true alien of the Cornish rock pools
Snakelocks anemone at night under UV light – a true alien of the Cornish rock pools

This fluorescence is caused by certain proteins within the animals that take in light of one colour and emit it as another. Some deeper water species can use these properties to appear red, even though red light is filtered out as it passes through the water, meaning the only light available to underwater creatures is UV or blue.

It’s not clear why snakelocks anemones and other sea creatures might want to fluoresce in this way. It seems there may be some benefit in it for their symbiotic algae or it might give them sun protection. It may just be a by-product of a protein that’s useful in other ways. Whatever the reasons, it produces an incredible glow. Junior is already talking of coming back at Halloween.

A spooky night time rock pooling walk is definitely on the programme for this Halloweeen!
A spooky night-time rock pooling walk is definitely on the programme for this Halloweeen!

It’s not just the anemones that take our breath away. If you’re used to rock pooling in daylight when most animals are hiding away under rocks and seaweed, the sheer level of activity in after dark takes you by surprise.

A scratching, crackling sound stops us in our tracks. It’s coming from the rocks. I lift the seaweed to show Junior a group of limpets. Some are feeding, their strong radulas scouring seaweed off the rock and chipping bits of rock. Others are setting into their home scars, grinding their shells into their grooves to create a perfect fit. Close-up, their activities make a surprising amount of noise.

Limpets on their way home as the tide retreats
Limpets on their way home as the tide retreats

Most rockpool animals are largely nocturnal. Pools that seem empty in daytime become bustling cities of activity. We watch hermit crabs milling around in large numbers, crabs marauding through the pool and across the rocks, fish floating in plain sight. Prawns come towards the light and watch us before shooting away backwards.

A green shore crab looking blue in the UV light
A green shore crab looking blue in the UV light

Hermit crabs are more active at night, every pool is teeming with them
Hermit crabs are more active at night, every pool is teeming with them

Other Half spots a small species of spider crab (Macropodia sp.) decorated with long fronds of seaweed edging sideways across the pool. It’s moving too fast to take a clear photo in the poor light. The blurring makes it look even more alien.

A blurry small spider crab (Macropodia sp) moving across sand.
A blurry small spider crab (Macropodia sp) moving across sand.

A scorpion fish lies still on the sand, watching out for prey.

A scorpion fish (Taurus bubalis) hiding in plain sight.
A scorpion fish (Taurus bubalis) hiding in plain sight.

One surprise is the stunning colours of the seaweeds under the UV light. Some of the dark red seaweeds take on a far more intense, bright colour, glowing red, pink and orange. Where the top shells have worn spires, their tips glow pink.

A grey topshell on a red seaweed under UV light
A grey topshell on a red seaweed under UV light

After an hour, tiredness and cold begin to set in. We switch off our torches and take a moment to gaze at the stars before we head home to bed. Junior is already asking if we can come again the next night, and the next.

It looks like I’ll be having a few more nights out this summer.