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Water en land

Mens en Milieu

Primary production   Photosynthesis   
Several seaweeds, Foto Fitis, www.fotofitis.nl

Seaweeds

Seaweeds have two requirements in order to live: salt or brackish water and sufficient sunlight. They look like plants, but since recently they are no longer categorized as one because their internal structure is much simpler. They have no leaves, stems, roots or flowers. Biologists speak of a 'thallus' instead of a 'plant'. Seaweeds also have a different manner of reproducing. They form vegetations in shallow coastal waters, usually on rocky coasts and dikes. The thallus is tough yet flexible,capable of withstanding surf. Seaweeds can be used for all kinds of applications. One of the new up and coming types of farming in the Netherlands in the 21st century is seaweed aquaculture.

On Texel


, Sytske Dijksen, www.fotofitis.nl

Try walking along the slippery waterline on the wadden dikes or on the breakwaters on the North Sea side, you can't miss the seaweed. You find most seaweed particularly in those areas where there is no sand or mud, such as by 't Horntje since mud makes the water too murky and sand scours the plants. Several unusual seaweeds which only grow on pontons are found on the jetties in the Oudeschild marina. Some species of green and red seaweeds are able to grow on the mud flats in the summer, such as sea lettuce, gutweed and Gracilaria verrucosa. The dikes on either side of the Marsdiep by 't Horntje and Den Helder are the only locations in the wadden region where oarweed grows.
The huge bundles of torn off seaweed lying on the beach usually contain species from coasts along the English Channel. We know that because thery are often species which don't grow in the Netherlands.

  • Categories

    Seaweed can be divided into a number of large groups: green seaweed, brown seaweed and red seaweed. 'Blue-green' algae, also known as cyanobacteria, is sometimes considered a seaweed but it is more like a bacteria. The color of the seaweed is determined by the coloring material with the highest concentration which is present for photosynthesis. The color also says something about the depth where the seaweed grows. Green seaweeds generally grow closest to the surface, brown seaweed a little deeper and red seaweeds grow in the deepest water.

    Seaweed comes in all kinds of shapes: stringy species such as green hair algae and hair pen, branched species such as banded weed, leafy seaweeds such as ulva and purple laver, and more complicated shapes such as toothed wrack and sea belt. Some species such as knotted wrack and bladder wrack have floating bladders, allowing them to float up straight. Seaweeds that are exposed during low tide produce slime to prevent dehydration and protect them from sun and wind.

    Too much nitrogen in the water allows green seaweeds to grow so much that they form blankets on the tidal flats, sufficating life underneath.

  • Where is it found?

    Rich seaweed flora grows along the rocky coasts of England, Scotland and Norway. In the Netherlands, there are only artificial rocky coasts, such as dikes, breakwaters and harbor heads. The delta region probably has the richest seaweed flora in the country.

    Dike slopes have obvious zones of seaweed growth. You also find seaweed on the pontoons in harbors, on sheet-piling and in saltwater regions where no tides exist, such as the Grevelingen. Sandy coasts are not suitable for seaweed to establish itself. Sand moves about too much, offering no foothold. Only on tidal flats with little current are types such as sea lettuce and gutweed present. Seaweed species found on salt marshes are specially bonded to this environment. One example is scorpion wrack (Bostrychia scorpioides).

    Not all seaweed are indigenous. Japweed, also known as Japanese sargassum, is an example of a sort which has travelled from afar, yet survives very well in the North Sea waters. Many seaweed species lying on the beach originate from the coasts along the English Channel or French coast. They have had a long sea voyage lasting many months before landing on the beach. Sea thong is one such species.

  • Farming seaweeds

    Farming seaweed is one of the newest crops in the Netherlands. Since the early 21st century, several companies in the Netherlands together with various research institutes have been experimenting with cultivating seaweed for all kinds of applications, from food and power supplies to purifying water. Species that are used or being investigated include sea lettuce, sea belt, winged kelp, oarweed and dulse.

    Because oil and gas are growing scarce, more expensive alternative energy sources have become attractive. And using seaweed as a bio-fuel is just one of its applications. Seaweed is also used in fish farms. Not only does it serve as food for the fish, it can also help to purify the water. Sea lettuce in particular is known for regulating the acidity in seawater.

    Seaweeds are also very edible for humans and contain lots of protein. You can eat seaweed straight or extract the protein for use as a supplement. The new marine farmers hope to contribute to solving the world food problem with their new product. And according to researchers, there are no known negative effects for the environment.