Causes of the eelgrass wasting disease: Van der Werff's changing theories

The 1930's wasting disease among the North Atlantic population of eelgrass,Zostera marina, is still an ecological and historical enigma, despite several attractive theories. Van der Werff investigated the die-back of eelgrass in the thirties in the Dutch Wadden Sea, and he considered the micro-organismLabyrinthula as the possible cause of the disease. In 1980, Grevelingen lagoon, harbouring an extensive population ofZostera marina, experienced a major decline of the area covered by the submerged macrophyte. Speculations about the cause of this dramatic decline induced us to think that the wasting disease had struck again. Van der Werff investigated the Grevelingen population and found bothLabyrinthula and a Chaetophoracean endophytic alga to be presumably responsible for the decline. During the quest for the ultimate cause of the wasting disease the question remains whether both micro-organisms are the cause of the disease or simply an effect of decomposition processes triggered by other factors.