Maerl – an important ecosystem in Scotland’s Lochs

Diving into Loch Sween, the writhing arms of brittlestars welcome you with a bluish haze of movement.  Occasional slender peacock worms pop closed when they sense you pass.  Moon jellyfish feed and pulsate, their pink edges gleaming in the sunlight.  A circus of life on the seabed bustles together: crabs, gobies, sea cucumbers, spiny starfish, flat worms, so much tiny, fascinating life.  This incredible colony exists because of Maerl.

Maerl is a collective term for several species of very slow-growing red seaweed that form hard, chalky skeletons.  It is coral-like and grows into large reefs.  Maerl thrives in clean, fast-flowing water, sheltered from pounding seas, and is found in estuaries and Scottish Lochs.  Hedgehog maerl dominates the dive site at Caol Scotnish, Loch Sween.  It forms loose fist-shaped balls on the seabed with protruding branches, at times thickly covering the seabed.  Further down the Loch, at Taynish Narrows, another species that resembles Twiglets dominates the seabed.  This looks similar to the hedgehog maerl but without the fist-shaped base.  Both of these species have formed thick, loose beds with dead maerl beneath, turned white after it dies.

Maerl beds are fragile and are easily damaged and have declined in most areas.  Pressures on Maerl include scallop dredging, bottom trawling, fish farming, and pollution.  Maerl used to be dredged off Falmouth and used for fertilizer but this was stopped in 2005.  It is now recognized that Maerl forms an important ecosystem that was previously overlooked.  The nooks and cranies in these beds make them an ideal nursery.  The vibrancy of life they support make them a magical dive.

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Images by Andy, words by Jackie