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first disappear in upper estuaries where nutrient loading is highest, 

 and at the deep edges of beds where light limits growth (Orth and Moore, 

 1983b) . 



Along a nutrient gradient in a Danish estuary, biomass of eelgrass 

 algal epiphytes increased 50-100 fold, and phytoplankton abundance 

 increased 5-10 fold (Borum, 1985) . Light attenuation by epiphytes on 

 eelgrass shoots was 90% on older leaves in these enriched areas (Sand- 

 Jensen and Borum, 1983). Besides shading, algal epiphytes slow 

 photosynthesis by forming a barrier to carbon uptake (Sand-Jensen, 

 1977) . In Buttermilk Bay, the depth of eelgrass growth decreased by 9 

 cm for every 1 uM increase in dissolved inorganic nitrogen in the water 

 column (Costa, 1988). 



The loss of eelgrass in enriched environments is not unique and 

 has been reported for other submerged macrophytes in freshwater lakes 

 and ponds (Moss, 1976; Sand-Jensen and Sondergaard, 1981; Phillips, et. 

 al, 1978), artificial freshwater ponds (Mulligan et al., 1976), tidal 

 estuaries (Haramis and Carter, 1983), artificial estuarine ponds 

 (Twilley, et. al., 1985), and marine embayments (Brush and Davis, 1984; 

 Cambridge, 1979, Cambridge and McComb, 1984; Kautsky et al., 1986; 



Kindig and Littler, 1980; Orth and Moore, 1983b) . Experiments on marine 

 ponds containing eelgrass are now in progress in Rhode Island (S. Nixon, 

 pers. comm. ) . 



Alternate explanations have been offered for some eelgrass 

 declines. For example, Nienhuis (1983) suggested that the recent 

 disappearance of eelgrass in a Danish coastal pond was not due to 

 epiphyte abundance, but "toxif ication" of the sediments from decomposing 



