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.

4 thoughts on “A Night Out In The Rock Pools”

  1. Hi David, Any UV torch should do the job. Mine aren’t anything special and can pick out anemones from a few metres away. You just need to be careful not to get the torch wet if (like me) you haven’t invested in a waterproof one. Heather

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