PHOSPHORUS BUDGET OF A MUSSEL POPULATION1

Abstract

The phosphorus budget of a Modiolus demissus population in a Georgia intertidal salt marsh was studied. Percentage phosphorus in mussel bodies decreased from 1% of the dry weight in small individuals to 0.6% in adults. There was also a seasonal variation in phosphorus content of adults; the maximum occurred during spawning early in September, the minimum in November. The standing crop of phosphorus in the population was 37.2 mg P/m 2 , the body fraction comprising 67%, the shell 30%, and the liquor 3%. Prorated losses and elimination rates ( µ g P/m 2 day) of the population were: mortality 21; gametes 11; dissolved organic 23; phosphate 260; and feces 460. Quantities of phosphorus present in natural marsh water (mg P/m 2 ) were: particulate 14; phosphate 19; and dissolved organic 6. The mussel population removed 5.4 mg P/m 2 of particulate phosphorus and 0.07 mg P/m 2 of phosphate daily, of which 0.78 mg P/m 2 was required as food and 4.7 mg P/m 2 was deposited as pseudofeces. The turnover time of phosphorus in the population was 115 days. The major effect of the population on the ecosystem was the removal of particulate matter from sea water; the turnover time of the particulate phosphorus in the water was 2.6 days under the supposition that the mussel population was the only agent involved. Mussels are more important as biogeochemical agents than as energy consumers. Determination of the participatory turnover time of a substance via any route in a system sets the maximum turnover time of that system. Determination of the turnover time of a substance for an entire system fixes the maximum flux rate via any one route in the system.