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The Community of Arran Seabed Trust (COAST) is running a year-long media campaign to raise awareness of the many exciting habitats and species to be found in Arran’s seas, many protected by the South Arran Marine Protected Area.
The November article is all about mud which is a far more immersive topic than it may first appear. There is more information on COAST’s social media or visit www.arrancoast.com
‘Mud, mud, glorious mud…’; the opening words of the comedy song by Flanders and Swann were not written in celebration of anything to do with the sea, but they are entirely appropriate for how we should view one of our less-well-known and probably least-celebrated marine habitats.
In the wake of COP26 and last month’s Banner article about the importance of blue carbon habitats in helping to tackle climate change, it is timely to be showcasing marine mud habitats.
As well as being home to a wealth of weird and fascinating marine life and having a vital role in the functioning of our seas, they are also one of our critical blue carbon habitats.
In areas where there is little water movement from currents and waves, fine sediment particles sink, settle and accumulate, forming mud.
Around the Clyde, marine mud can be found on the shore in estuaries and sheltered coastal areas, forming sometimes extensive areas of mudflats, home to many small marine creatures and consequently often a haven for feeding birds.
This sort of seashore habitat is limited on Arran as there are not that many large, sheltered, intertidal marine inlets around the island, Lochranza being the exception.
But there is a lot of mud in deeper water around the island’s coast and it is one of the particularly important habitats in the South Arran Marine Protected Area (MPA).
Mud habitats are widespread within the whole Clyde, generally in water deeper than 50m around open coasts, but extending into shallower water in the more sheltered basins of sea lochs.
Mud is composed of much finer sediment particles than the sand and gravel habitats described in the March Banner article.
As with sands and gravels, animal species dominate mud habitats because there is little hard material for marine plants to attach to, and it is also often too deep for there to be sufficient light for seaweeds to survive.
Although some animals are found living on or at the surface of mud, much of the marine life of mud habitats is hidden from view with large numbers of burrowing animals such as worms, brittlestars, crabs, shrimps, heart urchins and even fish that live within the mud itself.
Mud burrowing worms are very important and industrious ‘ecosystem engineers’, although their work goes on under the surface of the mud and is all too easily overlooked.
Often described as ‘burrowed mud’ because of the abundance of burrowing marine life that lives within it, mud plays a really important role in the marine environment.
The burrowing activities of mud creatures helps exchange and cycle oxygen, nutrients and minerals between the water and the sediment, making mud an extremely productive habitat that provides food and shelter for many species as well as feeding areas for commercial fish species such as cod, haddock and whiting.
One of the better known mud dwellers is the large and commercially important orange-coloured langoustine or prawn which lives in shallow burrows in marine mud.
There are many interactions between different marine species, and these prawns are sometimes seen sharing their burrows with small Fries’ gobies, an infrequently recorded fish species in UK waters.
Other crab and crustacean species such as the mud runner crab, with its distinctive stalked eyes and extraordinarily long arms, also create burrows, which can sometimes form surprisingly complex systems of tunnels, passages and side chambers beneath the seabed surface.
Some of Scotland’s most spectacular seabed marine life can be found living in mud.
The aptly named fireworks anemone is perhaps the best example.
Generally found in more sheltered parts of sea lochs, this large anemone lives in a long tube that is buried in the mud.
The long and numerous, predominantly white tentacles which can extend up to 30cm across, give the impression of a firework exploding out of the seabed, and they almost seem to glow when seen against the dark water and dull-coloured mud.
Unlike most anemones, if disturbed the tentacles curl up as they are pulled back to the main body, and in extreme situations the whole animal can withdraw completely into its tube.
Sea pens are another impressive and characteristic species of mud.
These are colonial animals related to sea anemones and so named because of their resemblance in shape to quill pens.
The slender sea pen tends to be the most common and is present within Lamlash Bay and elsewhere around Arran.
Although it lives within a mucous-lined burrow in the sediment, it sticks up above the seabed surface to feed, with rows of small anemone-like polyps that extend out from a central stem, enabling the animal to feed by capturing small particles of food from the surrounding water.
They can grow up to 60cm long but are not the largest sea pen in Scottish waters; this title goes to the tall sea pen, which can grow to over two metres tall and, if left undisturbed, can form extraordinarily dense sea pen forests.
Burrowed mud habitats are vulnerable to a number of human pressures but physical disturbance and pollution are particularly problematic.
High levels of nutrients or organic material can cause the mud to become very low in oxygen, to a point where the characteristic mud communities can no longer survive.
Many of the larger mud species are considered to be long-lived and slow growing and so can be severely affected by physical impacts from activities such as bottom trawling which also affects the overall abundance and diversity of the marine life communities.
While these impacts have been known for many years, there is now increasing focus on the impact of bottom trawling on blue carbon habitats such as mud, because the physical impact of trawling releases carbon from the seabed sediment.
Scotland has particular responsibilities for looking after mud habitats – it has some of the largest areas of burrowed mud in Europe and the majority of mud habitat that is found in UK waters.
While the South Arran MPA has an important role to play in helping look after our marine mud habitat, action is also needed on a much larger scale to ensure that our biologically rich and important blue carbon marine mud habitat is protected into the future.