Excretion of dissolved organic carbon by eelgrass (Zostera marina) and its epiphytes1

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Abstract
The release of dissolved organic carbon (DOC) by eelgrass (Zostera marina) and its epiphytic community was examined in a shallow estuarine system near Beaufort, North Carolina. Excretion by eelgrass alone, by epiphytes alone, and by heavily epiphytized eelgrass was determined by radiocarbon techniques. The percent of total photosynthate excreted was small in all cases: 0.9% for heavily colonized plants, 1.5% for Zostera alone, and 2.0% for the epiphytic community. The amount released by the eelgrass and epiphytes was proportional to the total amount of carbon fixed. Excretion rates in the dark were much lower than in the light. The rate of excretion increased after the plant underwent desiccation. The annual primary production and DOC excretion by phytoplankton, cordgrass (Spartina alterniflora), and the eelgrass community was estimated: 47% of the total annual primary production and 14% of the total excreted material was contributed by eelgrass and its epiphytes. Thus the eelgrass and epiphytes can play an important role in carbon cycling in estuarine systems.