When the tide is low, an unusual sight appears on the very sheltered shores of many of Scotland’s fjordic sealochs. A great shag-pile carpet of brown seaweed, made up of wig-like tufts, lies over the shore. Unlike most seaweeds, it is not attached to rocks, but just rolls with the gentle tides, like tumbleweeds in desert winds. Dense beds of this seaweed, golden-brown in summer, are one of the features that makes our sealochs such an attractive feature for visitors, and, because they are uniquely Scottish, they are a high priority for our care
What is wig wrack?
The loose driftweed is actually an unattached form of a much commoner seaweed called egg or knotted wrack Ascophyllum nodosum. ‘Wrack’ is the common name for a range of brown seashore algae, and egg wrack is typical of these, with a long, strap-shaped frond with single egg-shaped bladders. It grows anchored to rocks between the tides on the seashore, buoyed up to sunlight when the tide is in by its air-filled bladders. But when broken-off fragments of egg wrack arrive in these sheltered sealoch locations, they divide and multiply in a new form, spiky and branching, with only a few, small bladders. This only happens at places where a surface brackish layer, usually from a nearby stream, covers the seaweed fragments with alternate brackish water and seawater as the tides rise and fall. This ecological form – or ‘ecad’ – looks so unlike the parent seaweed that the original fragment came from, it is given an appropriately Scottish name: ecad mackaii. The big, round, detached tufts of the weed earn it the common name ‘wig wrack’.
Why is it important?
Wig wrack only forms in the special conditions of fjordic sealochs, so is a particular Scottish speciality. In recognition of this, wig wrack has been identified as a priority for action under the UK Biodiversity Action Plan , and this is now being taken forward by the Scottish Government as part of the Scottish Biodiversity Strategy , with SNH as a key partner.
The loose mats of ecad mackaii provide a sheltered and humid habitat for a range of mid-shore animals that otherwise might not be able to survive on an open shore of mud or fine shingle. Shore crabs, sea snails and little creatures called amphipods hide amongst the weed. These, in turn, are food for wading birds along the shore, and for fish when the tide comes in. So the carpets of wig wrack help provide a sealoch feeding station, from which many other animals benefit