Twice a day along the coast, the water level rises and falls. This is called the tide, and has a huge influence on the special environment of the seashore. Sandy and rocky beaches, like the ones found around Galway Atlantaquaria, are home to numerous species that are specially adapted to the intertidal zone – the zone between the high water mark and the low water mark. These species need to be able to cope with being covered by water some of the time and being out of the water for some of the time.

In addition to being home to many forms of life, the intertidal zone is also where you can find traces of life from deeper parts of the ocean. Exploring the intertidal zone, or beachcombing, is a fun and interesting way to spend an afternoon! Just remember to return any animals or plants you find to the beach before you leave – they won’t be able to survive if you take them home.

In the following, you can see some of the things you may find while beachcombing.

Seaweeds are water plants, and belong to a group of life called algae. They are similar to land plants in that they photosynthesise (that is, they produce their own food using sunlight and carbon dioxide), but they are different from land plants in that they have no roots. Instead, they have a holdfast, which helps them cling on to rocks.

Some seaweeds, like the Bladder Wrack, have air bladders that help keep them upright in the water. This allows them to better utilize the sun’s energy. Other seaweeds, such as the kelps, may have a stiff “stem” called a stipe, which helps them to stay upright under water.

Sea anemones are relatives of jellyfish, and just like jellyfish, they have stinging tentacles. Unlike the jellyfish, they do not swim around, but spend their entire adult lives attached to a solid surface such as a rock. This lifestyle, along with their beautiful colours and flower-like tentacles has given them the name sea anemones, even though they are animals!

You may see sea anemones clinging to rocks close to the low tide mark. When the water recedes, the anemones pull in their tentacles to avoid drying out, making them look like little blobs of jelly on the rocks.

Bivalves is the scientific term for the group of animals that includes clams, mussels, cockles, and their relatives. While beachcombing, you will find live bivalves as well as their empty shells. If you find a shell that is firmly shut you can be certain it contains a live mussel or clam. Take a good look at it, but remember to return it to where you found it.

All bivalves have a hard outer shell consisting of two halves (valves). The shell protects the soft animal from predators and from drying out when the water level is low. Most bivalves are filter feeders. They suck water into their shells and filter out the plankton, which they digest. The filtered water returns to the sea.

Crustaceans are a group of ocean animals with jointed legs and hard outer skeletons. While beachcombing, you may find several species of crustaceans such as shore crabs, barnacles, or sandhoppers.

Barnacles look nothing like the other crustaceans. They spend their entire adult life attached to rocks, and are able to shut their hard shells tight when the water level drops. When water-covered, they extend their legs out of their shell to catch food particles in the water. You can think of as a barnacle as a “lobster standing on its head”! The head of the barnacle attaches directly to the rock, and it is the tail which flaps in the water catching plankton.

Sandhoppers and shore crabs live among the rocks in the intertidal zone. Shore crabs are very common under rocks and in the seaweed, where their brownish colour helps them blend in. Sandhoppers are tiny crustaceans that look like shrimp. They can be found in the hundreds under larger rocks, where they gather to wait for nightfall. They are able to jump quite long distances.

As well as spotting live crustaceans, you will often find the moulted (cast-off) shells of crustaceans washed ashore on the beach. All crustaceans must moult to grow, and the old discarded shell sometimes stays intact as it drifts around in the sea. If you find an empty crab or prawn shell on the beach, it is almost certainly not a dead animal, but infact the moulted shell of a living creature. It is worth noting that you will never see the moulted shell of a Lobster washed up on the beach, as after a Lobster has cast off his shell, he eats it!

If you are lucky, you may find the egg cases of some of the ocean’s inhabitants on the beach. Common finds are the egg cases of dogfish, rays, or whelks.

Dogfish and rays are closely related animals with cartilage skeletons, while whelks are a type of mollusc, related to snails, octopus, and bivalves. When you find the egg cases, the baby animal will have already hatched, leaving the empty shell or egg case to wash ashore. It is perfectly all right to take the empty egg cases home with you.