Year of Natural Scotland – Beneath the Waves
The wind is rising and the rain is hammering against the window. As high tide approaches the waves are pounding the ancient rocks creating fountains of spray. The grey sea merges with the low cloud, obscuring the horizon in the fading light. The very epitome of a winter afternoon on the edge of the north Atlantic – bleak, cold, gun-metal grey. However on a calm day, even in winter, the crystal clear waters will reveal a hidden landscape that is rich in wildlife and as colourful and mystical as any tropical reef.
The continental shelf extents westward from the Outer Hebrides until it meets the deep waters of the Rockall Trough. The complex topography of the sea floor and confluence of warm waters of the North Atlantic Drift (Gulf Stream) and cold polar currents bring nutrients to the surface creating an environment which supports a rich and diverse marine fauna and flora. These deep waters have yet to reveal all their secrets but on the continental shelf there are vast kelp forests which biologically are as important as any ancient terrestrial woodland. Where the sea bed shelves gently this diverse community of plants and animals extends up to 5 km offshore. The exceptionally clear Hebridean waters enable macro marine algae (seaweeds) to grow to depths of 20m and even as much as 40m.
You don’t need a boat or an Aqualung to explore these remarkable forests, you can see the stalks (stipes) sticking out of the water at low tide and the fronds gently undulating as the waves rise and fall. This is kelp (brown macro-algae – Laminariaceae) which has a tree-like structure and grows in vast congregations in shallow waters. As the water deepens and the light levels fall the forests give way to kelp parks where the plants are more scattered and other species begin to predominate. Do not be deceived by the dark brown tangles of slippery weed washed up on the beach; look closely it is a symphony in brown, ochreous yellow to rich mahogany with a hint of green and a touch of red.
These are not the dark tangled wild woods of a Grimm nightmare but refuges for a variety of small invertebrates and fish. No sinister monsters lurk here, except maybe a lobster or marauding starfish. Within the shelter of the forest sea anemones, sea squirts, sponges delicate seaweeds, small fish and a host of strange invertebrates all find protection from the force of the waves. Some like the anemones, sponges and encrusting red algae cling the to rocks and boulders within the forest, red and orange jewels glowing in the diffuse filtered sunlight. Filamentous red seaweeds adhere to the stipes like feathery lichens on a branch whilst bryozoans form mosaic mats on the fronds.
Throughout the winter mountains of kelp are washed onto the shore by the winter gales and as it rots it releases organic material into the food chain. This is used directly by small marine grazing animals whilst the detritus and dissolved nutrients are trapped by filter feeding animals which in turn are eaten by larger animals. This organic recycling is essentially the same as nutrient cycling in terrestrial ecosystems. After a while the mounds of kelp piled on the beach begin to heave with life, this is the perfect environment for larvae of seaweed flies which are enthusiastically hunted by flocks of starlings and small wading birds.
These hidden forests are important marine and coastal ecosystems in terms of their biodiversity and productivity, and in the Outer Hebrides and Northern Isles they are also of economic importance. In the same way that coral reefs protect low-lying tropical shores these vast areas of undulating kelp help to dampen impact of Atlantic waves on the sandy shores of many Scottish islands.
The storm cast kelp is collected from the beaches to be used as an organic fertiliser on the machair and inbye fields. Once gathered by women and children into creels and transported by pony it is now a modern mechanised operation involving tractors and agricultural trailers. In the 18th and 19th centuries the tangle was collected to extract the potash and soda for glass and soap manufacture and later for iodine extraction. This industry collapsed when cheaper alternatives were found with devastating effects on the local economy. It is still collected, on a small-scale, for the extraction of alginates for the pharmaceutical and food industry.
At present this complex habitat is safe and we can all enjoy the delights of slipping and sliding among the tangle looking for hidden animals. However if it s to be exploited let us hope that it’s biodiversity is not wrecked by uncontrolled, large-scale commercial harvesting.