Marine Plant Life

Although water covers about 75% of the surface of the world it only contains approximately 15% of the full range of different species of living organisms found on Earth. Most of these species live on or near the sea floor and only 2% live in the open oceans. There are representatives of every group of living organism found in the sea but animals are the group that contains the largest number of different species. There are also plenty of Algae since this group includes all the seaweeds and also many microscopic organisms. Some of these microscopic algae are red or brown algae, which grow and reproduce rapidly under certain sea conditions and create such rich algal blooms that the sea becomes coloured.

The algae are able to photosynthesise and are very similar to other groups of plants but because of their simple organisation they are often placed in a completely different “kingdom” called the Protoctista. The members of this kingdom generally seem to be characterised only by the fact that they don't seem to fit easily into the other kingdoms. Seaweeds are one of these organisms since they are able to photosynthesise and often look just like other plants. They have root-like holdfasts, which attach the seaweed to rocks, but unlike roots the holdfast lacks the fine root hairs, which absorb water and nutrients from the soil. Many seaweeds grow large, branching stems which serve the same function as leaves by creating a large flat surface in order to absorb the maximum sunlight for photosynthesis. This is very important since 10% or more of the sunlight is reflected or refracted from the surface of the sea and within a few metres, even in clear water, all the red light has been absorbed and the blue-green light penetrates only as far as 50metres.

Some of the seaweeds, such as the sea lettuce, Ulva lactuca, are green but many are brown like the wracks and kelps. Less obvious are the red algae which are generally small and not very conspicuous. The fern-like red seaweed, Corallina officinalis, is common throughout the Argyll Islands especially around rock pools and harbours. As this seaweed ages it loses its rich, reddish-plum colour and eventually becomes white. The fronds contain lots of calcium and the crisp, brittle remains are often found washed upon the shore like a delicate white coral. Irish moss or carragheen, Chondus crispus, is a delicate purple-red seaweed, very similar to some types of salad lettuce. It is used widely as a food and as a gelling agent. It is also a rich source of iron and of Vitamin C and it is delicious deep-fried!

Known as “Tang” throughout the Argyll Islands , the wracks are probably the best known of all the seaweeds. Particularly the Bladder wrack, Fucus vesiculosus, which has regularly branched, flattened blades up to 1 metre long with 2 or 3 bladders on each branch. These bladders lift the long, dark olive fronds up towards the surface and therefore the sunlight. The Toothed wrack, Fucus serratus, is very similar, with swollen reproductive organs at the blade tips but they lack bladders and have toothed blade edges. Knotted wrack, Ascophyllum nodosum, is also known as Egg wrack because of the egg shaped terminal gas bladders and the stalked reproductive bodies along its length. This wrack is olive green or yellowish and often grows several metres long. A small delicate red alga Polysiphonia lanosa is often found attached to its stalks.

Dulse or Duilseag, Palmaria palmatum, is a wrack which is recorded as having been collected by monks at the time of St Columbus in 600AD. It was used to produce a brown dye for textiles and was also used as a thickener for soups and stews. The popular soup called Cullen Skink was often served with Dulse and there is a soup in the islands known as Càl duilsg. In the 18 th century it was a very popular food and was collected and sent to the lowlands for sale. In the 19 th century it was common in Edinburgh to hear the street vendors cry of “Wha'll buy dulse and tang!”

Kelps are generally larger than the wracks and the most common, known as Tangle or Oarweed , Laminaria digitata, grows up to 3 – 4 metres long. It is very widespread around the Argyll Islands forming dense forests across the surface of rocky bays. These kelp forests provide an important habitat for many crustaceans, molluscs, fish, seals and other seaweeds. A similar kelp called Cuvie, Laminaria hyperborean, is also found all around the islands but this kelp is often covered in other smaller algae and is much tougher. The stems of both were once used to make knife handles and because of the content of sodium glutamate in their blades they are tasty when dried and are found very palatable by both cattle and humans. Laminaria saccharina , has a sweet taste like peanuts. It is also a good source of mannitol which is a white, sweet tasting, crystalline alcohol and appears as a white coating when the fronds are dried. The fronds are tough and slender. When hung to dry they become stiff in dry weather but become limp again in humid weather and have led to the name Poor man's weather glass.

In fact kelp has been a mainstay of many island communities, providing food, fodder for cows and sheep and also used on the “Lazy beds”. Lazy beds are raised beds, usually for growing potatoes, onto which the kelp was heaped to provide the necessary nutrients to the depleted soils, to cover the developing tubers and to keep down weeds.

Two shallow, parallel trenches are dug about a metre apart and the sod turned over and laid along the inside of each trench. The potatoes are placed in the centre and then covered with a dressing of manure or seaweed. This was not a lazy method of cultivation, rather it was the only feasible way to work the poor, shallow soils.

In the late 1600's a new use was found for seaweed, which provided a major industry for the Argyll Islands . The production of soda and potash from the island kelps allowed Britain greater independence from the European centres of production and this was very important during the Napoleonic and later wars. The extraction involved burning the kelp in large, often stone-lined, trenches and was a back-breaking and labour intensive process. It produced a very good financial return, though not for the islanders themselves but for their landlords. The industry died out when mineral deposits of potash were discovered in Germany .

Iodine was also extracted from kelp ash but cheaper sources were found in Chile . The loss of these industries created a considerable depression throughout the Argyll Islands . There was hope that the alginate industry, which began in Campbeltown in 1934, might revive the seaweed economy but although there is still an alginate factory at Girvan and despite a recent heightened interest in seaweeds by the general public, the industry is not expanding at present.

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