If you’ve ever ventured down to Cornwall’s coastline, you’ll know that its rock pools are magical. These miniature, tidal ecosystems offer a peek into a hidden world brimming with life. Left behind by the retreating tide, Cornish rock pools teem with fascinating creatures and vibrant marine plants. Here are four amazing rock pool inhabitants you might find on, under and around the rocks.
Flat Periwinkles: Tiny shells with big appeal
Orange flat periwinkle feeding on bladderwrack seaweed. Credit: Cornish Rock Pools.
Among the small but fascinating residents of Cornwall’s rock pools are flat periwinkles (Littorina obtusata). These little snails are a common sight, their spiralled shells varying in colour from pale brown to green. Less common, are the bright yellow and orange periwinkles which stand out against the dark of their feeding ground. Typically found clinging to bladderwrack seaweed, they feed on algae and other microscopic plant life, using their rough tongue to scrape the surface.
Not only are flat periwinkles, with their black eyes and food-searching tentacles, fun to watch, they also play an important ecological role. As herbivores, they help to control algae growth, maintaining balance within this coastal ecosystem. If you’re trying to find a flat periwinkle feeding, try looking along the high tide line too.
Beadlet Anemones: From red blob to swaying flower
Beadlet anemone out of the water. Credit: Cornish Rock Pools
Another note-worthy inhabitant of the Cornish rock pool is the carnivorous beadlet anemone (Actinia equina). These creatures lead a double life. Attached to rocks by a sucker at the base of their body, they resemble a dark red glistening blob when out of the water. It’s only when they are submerged by the tide that they bloom into, what looks like, a swaying sea flower.
The Beadlet anemone below water. Credit: Cornish Rock Pools
The beadlet anemone then reveals its thick short tentacles which sting, catch passing prey, then move it to a mouth in the centre of their tentacles. As soon as they are disturbed or the tide retreats, these tentacles are retracted and it becomes a dark red blob once more.
These anemones are tough creatures, able to thrive in the harsh conditions of rock pools, where they can endure both drought and crashing waves.
Snakelocks Anemones: Silent but deadly
Snakelocks Anemone. Credit: Cornish Rock Pools
A bit more dramatic in appearance is the snakelocks anemone (Anemonia viridis). This anemone rarely retracts its tentacles so lives on the lower shore or in shallow seas to prevent itself from drying out at low tide. With its long, curly tentacles that resemble snakes, it’s easy to see how this anemone got its name. These tentacles can vary in colour from bright green to purplish and are covered with tiny stinging cells called nematocysts.
Like other anemones, they use their tentacles to immobilize small animals, such as shrimp or tiny fish but watch out – their sting is strong enough for humans to feel. Living in sunny spots, they have developed a clever relationship with the algae that live in them. The algae get a safe place to live and the anemone gets extra food, created from the process of photosynthesis (converting light into energy).
Shore Crabs: The unfussy eaters
Common Shore Crab
No exploration of Cornwall’s rock pools would be complete without mentioning the hardy shore crab (Carcinus maenas). Although often camouflaged, with a bit of patience, these greenish-brown creatures can be spotted scuttling across rocks, darting between seaweed, or hiding under stones. They are the least fussy rock pool creatures when it comes to food. Shore crabs are opportunistic feeders and will eat just about anything they can get their claws on, from algae and rotting fish to worms and other shore crabs. Always on the go, the shore crab also goes through a process of shedding its shell and growing a new one once or twice a year. Whilst this is happening, they are vulnerable and need to be alert to predators, like cod, bass and birds.
If you want to find out more about the amazing, resilient and sometimes strange-looking creatures in the Cornish rockpool, Cornish Rock Pools is a great website. It’s suitable for children and gives lots of tips on what to look for and how to search in an environmentally friendly way.
COMING SOON – 2025
Some of these creatures appear in my latest book, The Shell Secret, a fast-paced adventure story that sees Alice and Jasper race against time to solve a war-time crime and come to terms with a family tragedy.
