Discovering a winter rockpool

Discovering a winter rockpool


At first glance a beach in the middle of winter seems like a bleak, lifeless environment. However, when you look closer you will realise that life still thrives despite freezing air and stormy seas. In this blog Emma shares some of the different species of marine animals you are likely to see when rock pooling in the winter!

The idea of winter doesn’t create images of highly productive environments. On land it is the season where a lot of plants die back and many species of animals go into hibernation. Animals that live in the intertidal zone, between the high tide mark and low tide, do not have the ability to hibernate due to the constant changing environments brought about by the tidal cycle and ever-changing weather conditions. 

You would not be on a rocky shore if you didn’t see any barnacles. There are several species of barnacles found on our shores and between them they cover much of the intertidal zone on both exposed and sheltered shores. It is a common misconception that barnacles are related to molluscs, like mussels, who also attach themselves to rocky structures. In reality, barnacles are actually a crustacean like crabs and lobsters. 

Anemones come in all sizes and colours, and are found in many different habitats. The species you are most likely to find when searching through a rock pool around North Wales are the Beadlet anemone; the snake lock anemone; and if you are lucky gem anemones. Anemones belong to the group Cnidaria which also includes jelly fish and corals, all of which have stinging cells to protect from predators and to catch food. Small fish and shrimp will often be found associated with anemones as the stinging tentacles deter predators.

A trip to the rock pools wouldn’t be complete without the searching for different colour shells which brings me on to the periwinkle and top shells. These are two of the most common sea snails found on rocky shores and add a splash of colour to rock pools. Periwinkles can be found in a variety of colours and it is not unusual to see a dot of yellow moving along seaweed fronds. If you see a shell with a ‘mother of pearl’ effect then you have spotted one of the many species of top shells found in Wales.  Top shells are important grazers and eat algae growths on rocks.

various sea snails on Rhosneigr


Occasionally when searching though rocks you will come across yellow rice shaped capsules stuck to rocks. These are the eggs of another common gastropod found on our rocky shores, the dog whelk.  Dog whelks are important predators in the intertidal zone. They prey upon barnacles and bivalves such as mussels. There are two ways the dog whelks’ feed. The first is by forcing their proboscis between the two shells of the bivalves or plates of barnacles and removing the flesh. The second feeding method is by boring a hole into the shell of the prey and inserting its proboscis through the hole to get to the flesh. If you find a bivalve shell with a small round hole in it, its possible that it was the prey of a dog whelk. Dog whelks aggregate before spawning can occur. In winter they will aggregate in sheltered areas such as crevices where they will stay for up to 5 months and will not feed in this time. They will lay their eggs on the underside of rock or hidden beneath seaweed. Not all of the eggs will hatch. Juvenile dog whelks will use the unfertilised eggs as a food source when they first hatch.

a mix of marine life with dog whelk eggs


Keep an eye out for crabs as well! You can often find many different species of crabs when out rock pooling. Some crabs can be found hiding amongst periwinkle shells at the bottom of pools, hermit crabs, and others can be found under rocks.

Juvenile edible crabs live in the intertidal zone. When they mature they move to deeper waters so it is unlikely that you will find a crab large enough to eat when rock pooling. These crabs have a very distinctive carapace (shell) shape which is often compared to a pasty with their crimped sides. Despite having big claws, these crabs are quite timid and you are unlikely to be nipped by their pincers. Another crab you should keep an eye out for the Velvet swimming crab. These feisty animals are blue in colour with distinctive red eyes. You will want to watch your hands with these crabs as they are territorial and will stand their ground.

Keep an eye out for these animals plus more on your beach excursions. You never know what fascinating species you may find.