WAX AND WANE OF EELGRASS ZOSTERA-MARINA AND WATER COLUMN SILICON LEVELS

Long-term observations in an enclosed estuarine branch in The Netherla nds showed a remarkably strong correlation between water column levels of dissolved silicon (DSi) and standing stock of eelgrass Zostera mar ina. Si levels in the leaves of Z. marina varied between 0.02 and 0.66 % of tissue dry weight; they were lower in the declining population th an in other populations in neighbouring areas. We hypothesize that dec reased concentrations of DSi, which may coincide with eutrophication o f coastal waters, may be a factor in the worldwide decline of estuarin e eelgrass populations whose significance has so far been ignored.