Cuvie, Sugar Kelp and Oar Weed form forests in the North Sea and Baltic Sea
Seaweeds belonging to the genus Laminaria grow in extensive underwater forests in the cooler oceans of the northern hemisphere. For example, three common species grow in the North Sea and the Baltic Sea , Cuvie (Laminaria hyperborea), the Sugar Kelp (Laminaria saccharina; new name: Saccharina latissima) and Oar Weed or Tangle Kelp (Laminaria digitata). They anchor on rocky outcrops on the seafloor and grow towards the sea surface to reach the light. Similar to land plants, the multicelluar large brown algae have developed specialised structures for attachment (holdfast), a stem-like structure for support (stipe) and a leaf-like blade.
"Rainforest of the sea"
Together with other large macroalgae, Laminaria species form unique ecosystems called kelp forests which seem to be like the "rainforests of the sea". These forests represent important habitats and nursery grounds for a large range of marine animals such as crustaceans and fish. Sea urchins, gastropods (slugs and snails) and marine isopods depend on kelps as their food source. Small, broken-off pieces of algal biomass are decomposed by microbes and serve as food for planktonic animals that filter tiny particles out of the water. Off Helgoland kelp forests grow in depths up to 10 m, and in the Mediterranean as deep as 120 m. On the Norwegian coast they extend over many thousands square kilometres, several times the size of the Saarland.
Kelps under threat
In recent years a number of alarming reports have been published, suggesting that natural kelps stocks have decreased drastically. It is possible that this is closely linked to the warming of the oceans: kelps can survive and grow only in cool water.
Multiple uses of the kelp product alginic acid
Alginic acid is a constituent of kelp cell walls and is constructed of long-chained molecules which can form gels. A range of different gels, with very particular viscosities, can be produced by simple chemical processes from alginates, the salts of alginic acid. Because of its unique properties, the natural ingredient alginic acid is used as a stabiliser in the food, cosmetic and pharmaceutical industries: instant-desserts, tomato ketchup and yoghurts, as well as ice-creams and cream cakes maintain their stability with the help of alginic acid. Alginic acid more and more replaces bovine-derived gelatine which has been suspected to transmit BSE. Since alginic acids can not be metabolised by humans, they are contained in many dietary and slimming products. Alginic acid also has applications in biotechnology, for example the separation of substances. Alginic acid is used as a stabilising agent and emulsifier in crèmes, lotions, toothpaste, massage gels and shampoos in the cosmetics and pharmaceutical industries. Calcium alginate is used as a wound-healing agent because it helps to stop bleeding. Also, imprints of dentures are made from alginic acid.
To fullfil the ever-increasing demand of alginic acid, in France alone about 75 000 tons of kelp are currently harvested annually from natural stocks using small boats. Some additional tonnage is harvested after cultivation in kelp farms in the sea. Because of the ongoing destruction of marine habitats due to the increasing exploitation of our coastlines and oceans, land-based kelp cultivation systems are currently being developed.
Whereas microscopically small, floating algae (phytoplankton) occur in open waters, macroalgae (seaweeds), up to 50 m-long, grow on rocky shores. The three Laminaria species mentioned above grow mainly in late winter and spring, at a time of year when only small amounts of light can penetrate through the water column. This means that the algae are strongly light-limited when they grow – but why have such an unusual growth pattern? For example, Laminaria hyperborea produces a new blade every year in its growth region which is located between the stipe and the existing, old blade produced the previous year: the young blade slowly pushes the old blade towards the tip of the plant. The ‘building blocks’ (e.g. reserve carbohydrates) necessary for growth have been accumulated by the old blade during the previous year and are transported in metabolic ‘pipelines’ (so-called trumpet cells) to the growth region at the base of the old blade. It appears that these species are adapted to grow at the end of winter because this allows the new blade to be ready to soak up the spring sun: it can start immediately to capture energy by absorbing light.
Why choosing an alga of the year?
This year, for the first time, algal researchers from the Phycology Section have voted for an ‘alga of the year’. They believe it is important to raise public awareness of this significant group of plant-like organisms, since algae are the most important oxygen producers in the world. To do this, algae absorb the greenhouse gas carbon dioxide. One group of algae alone, the diatoms (small, single-celled organisms that may form colonies), are responsible for 25 % of the primary productivity worldwide, on land and in water. This means that diatoms produce one in four oxygen molecules in the atmosphere. This may not be surprising since two thirds of the earth’s surface are covered by oceans or lakes, and algae live in the upper layers of all water bodies where enough light is available. In addition to their ecological significance, algae are important because of their position in evolution since all land plants and animals have their origin in the sea!