EFFECTS OF SHADING ON GROWTH, BIOMASS AND POPULATION MAINTENANCE OF THE INTERTIDAL SEAGRASS ZOSTERA-NOLTII HORNEM IN THE DUTCH WADDEN SEA

Effects of low light levels on growth rates, biomass and population ma intenance of Zostera noltii were examined on tidal flats off the islan d of Terschelling in the Dutch Wadden Sea. Various levels of periphyto n density were simulated by placing nets of different mesh width above the seagrass vegetation from May to October 1989. Shading effected a 30% decrease in the leaf growth rate, a 3-fold increase in the leaf lo ss rate, and a 80% reduction in the total biomass of Z, noltii. The we ight of generative shoots and turion rhizome internodes was considerab ly reduced, 75 and 66%, respectively. Most changes in growth, biomass and maintenance of Z. noltii were linearly related with the level of a rtificial shading imposed.