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The annual nitrogen budget of a mussel ( Geukensia demissa = Modiolus demissus ) population in a salt marsh was determined and compared to the nitrogen budget of the marsh. During each tidal cycle in summer, the mussels filter a volume of water in excess of the tidal volume of the marsh. Yearly, the mussels filter 1.8 times the particulate nitrogen exported from the marsh by tidal flushing. Half the nitrogen filtered is absorbed by the mussels and half deposited as feces and pseudofeces (biodeposition). Of the nitrogen absorbed, 55% is excreted as ammonia. As a result, the mussel population releases more ammonia into the marsh water than does any other population in the marsh. Four percent of the nitrogen absorbed by the mussels is secreted in byssal threads, 20% invested in growth, and 21% released in gametes. Gametes are the largest component of mussel production to enter the food web, because mortality of adult mussels is very low.
Jordan et al. (Fri,) studied this question.