Eelgrass

Eelgrass is a seed plant that can grow in the sea. It is not a seaweed. It grows in places that rarely lie above the water surface and where strong currents are absent. There used to be extensive eelgrass fields in the Zuiderzee and Wadden Sea. They were very important for the fauna as well as for human usage. Since the Middle Ages, pressed eelgrass was used for constructing steep sea dikes: the so-called seagrass dikes. However, impoldering and an infectious disease ended that. Nowadays, eelgrass is only found in a few places in the Wadden Sea and the delta area. Since 1993, experiments are being performed to re-introduce it.

Eelgrass is the only vascular plant found in the Netherlands. Long ago, there were extensive fields of eelgrass in the Zuiderzee and the Wadden Sea, which was very important for the tidal fauna and for the people who lived in the tidal region.

Biotope in itself

An eelgrass field is a biotope in itself. It is very important for many types of animals. Wigeon, brent geese, mute swans and coots graze the fields. But since the large eelgrass fields have disappeared, many of these birds now forage on the farmed grasslands on the other side of the dike. Baltic isopods also eat the large eelgrass. Pipefish thrive best in eelgrass fields. Furthermore those fields, which stay submerged during low tide, function as a nursery for young fish.

Eelgrass needs clear water in order to receive enough light for photosynthesis. Clear water is often poor in nutrients. To be sure it is able to obtain enough nutrients, the plant has an extensive root system to extract the necessary supplements from the sea bottom. Cloudy water caused by eutrophication or whirling particles from a changing water current can lead to the disappearance of the species in specific areas. When more nutrients are present in the water, algae and seaweed obtain a better competitive position in relation to the eelgrass since these species do not need to exert energy into a root system. More algae present in the water means less light available for the eelgrass. In addition when the nutrient supply is great, eelgrass will produce more leaves and relatively fewer roots, allowing heavy storms to pull the plant out of the bottom.

Seaweed fisheries in the Netherlands

Eelgrass was useful for man in several ways in earlier days. Therefore, the eelgrass fields were mowed and the floating material was fished up. This fishery was called seagrass fishing. The oldest reports of seagrass fishing date back to around 1300 A.D. For centuries, the seagrass fisheries was an important source of income for the inhabitants along the coastal tidal flats. The eelgrass was dried in special seagrass sheds. Lots of seagrass was processed in the Dutch region called Wieringen, which used to be an island bordering the Wadden Sea. The eelgrass was used in many ways.It served as compact piling material for constructing dikes. Whale hunters used bales of eelgrass as a means for plugging leaks. Furthermore, eelgrass was used as filling for mattresses and cushions. A pinch sea wormwood kept the fleas away. When the eelgrass disappeared from the Wadden Sea after 1932, the seagrass fisheries disappeared as a means of existence for the island inhabitants.

Re-introduction of eelgrass in the Wadden Sea

Experiments with planting eelgrass in the Wadden Sea have not yet brought any satisfactory results. One hopes that the Wadden Sea will continue to grow cleaner and clearer. The eutrophication level, the clarity of the water, the salinity and the fisheries are all factors which play a role in the existence of eelgrass.

At the research institute Alterra (now IMARES) on Texel, survival experiments were performed using eelgrass from various origins. The results showed that the strongest eelgrass came from the German Wadden Island Sylt. Therefore, tens of thousands of eelgrass shoots from the region of Sylt were planted in three areas of the Dutch Wadden Sea in 1993: on the Balgzand, near Texel and near Terschelling. The plants near Texel did not take root. The other two areas have been more successful, however the eelgrass did not appear all that healthy two years after planting.

In 2002 and 2003, there were more attempts made to reintroduce eelgrass by scientists from the Catholic University in Nijmegen. The experiment in 2002 was unsuccessful, partially due to planting the shoots too deep. A small eelgrass field was found on the Balgzand, which is probably a remnant from the 1993 experiment. In 2004, Rijkswaterstaat announced that a large number of plants (almost 800) were growing in 2003, all coming from an earlier experiment from 1999 on the Balgzand. This population survived all four seasons but had as of yet not spread out so much.

Names:
Dut: Groot zeegras
Lat: Zostera marina
Eng: Eel-grass, grass-wrack
Ger: Gemeines Seegras
Dan: Havgræs

Names:
Dut: Klein zeegras
Lat: Zostera noltii
Eng: Eel-grass
Ger: Zwerg-Seegras
Dan: Havgræs (Kleines Seegras)
Dan: Havgræs (dværg-bændeltang)