Sea Life in Louth
Even a cursory look around will reveal the abundance of wildlife on the beaches and foreshore here in Louth. Here are some of the invertebrates and other creatures and plants you will see along the shoreline.
The Common Shore Crab is usually green with a patterned shell, but young crabs can be a variety of colours. It feeds on molluscs and dead matter on the shore. It is found under algae and among rocks, and especially in the rock pools to the north of the promenade. Crabs shed (moult) their hard outer skin (their carapace) in summer and you will find their discarded “shells” on the beach.
The body of the Common (or Moon) Jellyfish is bell-shaped and is colourless except for four purple horseshoe-shaped markings in the centre of the disc. It feeds on plankton and other small marine organisms by directing them into its mouth with its tentacles. It generally just drifts with the currents, and that is why jellyfish are often washed up on to the beaches here in Louth. The tentacles contain venom and can cause a mild prickling or burning sensation to humans.
The Edible Cockle has a rounded heart-shaped shell, with radiating ribs. The cockle is a bi-valve mollusc, meaning it has two shell sections joined at one edge by a ligament. It lives just below the surface of the sand and is an important source of food for many of the wading birds seen on the shoreline. Cockles are particularly prevalent on the beaches, and you can see cockle shells everywhere.
The Common Mussel is also a bi-valve mollusc, like the cockle (above). Its shell is elongated and is blue-black in colour. It lives on exposed rocks along the shoreline and filters its food from the water passing over it. It attaches itself to the rock by strong threads and can withstand even the strongest waves. Like cockles, mussels are edible.
Like the cockle and mussel, the Razorshell is a bi-valve mollusc. Its shell is whitish is colour, and its elongated rectangular shape, with its similarity to the old cut-throat razor, gives it its name. It lives in the sand and can burrow faster than a human can dig. It is fished by specially equipped boats, and the dead razor shells found on Louth's beaches are mostly washed ashore from these boats.
This small bug-like creature lives on the shoreline, but not close enough to the sea to be submerged. It burrows into the sand during the day to keep moist, and it feeds at night on the washed-up seaweed and other dead plants. In doing so it performs a very useful function for the ecology of the area. In turn the Sandhopper itself is part of the diet for many of the wading birds seen here. It has large legs at the back which it uses to leap out of the way when in danger, and which give it its name.
The lugworm is a large marine worm, up to 20 cm long. It lives its life in a U-shaped burrow in the sand, with its head near one end and its tail at the other. Because of this it is seldom seen, but its casts are a familiar sight on the wet sand when the tide is out. Lugworms are an essential item on the diet of many of the wading birds in Louth.
Bladderwrack and other Seaweed
Seaweed is an essential part of the marine ecosystem. It prevents shore animals from drying out, harbours sandhoppers and insects for feeding birds, and when it breaks down it puts nutrients back into the water. Bladderwrack is the most common type of seaweed found at Blackrock. It was the original source of iodine, and was used in the saltwater baths located at the southern end of the promenade during the last century.
Sea Lettuce and other Algae
Sea Lettuce is the most common type of alga found on the Louth shoreline. Fish depend on the oxygen produced by algae which are also an important food source for microscopic marine animals on which fish and wading birds feed. While seaweed can be a nuisance when it is washed onto the beach and begins to decay, it is an important part of the delicate marine ecosystem. Without it the population of wading birds in Dundalk Bay would be significantly lower.