Matt Slater
Maerl beds
Beth yw o?
Maerl beds are special underwater habitats found in shallow seas. They’re made by rare types of red seaweeds that grow into hard, twig-like lumps called Rhodoliths, which means red stones. These pink or purple lumps can be as small as a pea or as big as a small stone. Maerl beds are rare in the UK and are full of marine life.
Pam fod o fel hyn?
Like plants, maerl uses sunlight to grow through photosynthesis. But it also takes minerals from seawater, which helps it build a hard, coral-like surface.
Over time, as millions of these tiny, hard seaweed lumps grow and tangle together, they form large, complex beds on the seabed creating an important and unique marine habitat.
Maerl beds are rare in the UK and are full of marine life. Their tangled, twig-like structure makes a perfect home for juvenile crabs, shellfish, worms, sponges, seaweeds, and many tiny creatures like bacteria and microbes.
Because they support so much life, maerl beds are recognised as a UK Biodiversity Action Plan habitat and are legally protected in areas like the South Arran Nature Conservation Marine Protected Area.
How old are maerl beds?
Maerl grows very slowly (just 0.5 to 1.0 mm per year) and it takes hundreds of years for maerl beds – accumulations of dead and live maerl – to develop. The maerl bed at St Mawes Bank, Falmouth is estimated to be 4000 years old! Because of their extremely slow growth, maerl beds are considered irreplaceable habitats. It’s essential we protect them as it’s impossible to restore and create them once they’re lost.
Dosbarthiad yn y DU
Maerl beds grow in shallow, fairly sheltered waters and can be found along the west coasts of Scotland, Ireland, Wales and around the Isle of Man. In England, they are only known to exist in a few places - the Carrick Roads bed, in the Fal Estuary in Cornwall, is the best example in England.
Beth i edrych am
A seabed which appears as though it has a rugged pink carpet. In amongst the pink, look out for scallops, starfish, crabs and juvenile fish that use these reefs as a nursery area.
Cadwraeth
Physical disturbance from activities such as dredging, using bottom-towed fishing gears, heavy anchors and mooring chains, and construction at sea has a significant effect on the health of maerl. These activities can cause physical damage and disturb sediment, which impacts the amount of light reaching maerl and its ability to photosynthesise.
Waters with high nutrient levels due to agricultural run-off and sewage pollution can also cause excess algae to grow on the maerl, smothering the beds.
Maerl is also expected to be affected by rising sea temperatures and ocean acidification caused by climate change.
Maerls absorb carbon dioxide from the water as they grow. They store this carbon in their hard, chalky skeletons made of calcium carbonate. Their tangled structure also traps bits of organic matter like mud, dead plants and species which get stored between the maerl lumps. This rich material stays protected from waves and currents because the living maerl layer holds it in place, stopping it from being washed away.
