SEASONAL-VARIATION IN C-BUDGETS, N-BUDGETS AND P-BUDGETS AND TISSUE COMPOSITION OF THE MUSSEL MYTILUS-EDULIS

Net C, N and P budgets of mussels were measured monthly in a field lab oratory for a year. The calculated scope for growth was compared with the observed growth rates per month, for each element. Assuming ambien t food, scope for growth was calculated and compared with changes in t he tissue composition of mussels from an estuarine field population. W hen total organic material was used as food, the calculated scope for growth overestimated the actual growth rates throughout the year. When phytoplankton was considered to be the main food source, the scope fo r growth provided by each element compared well with observed changes in tissue content, except during the spawning period. During spawning, the difference between growth and scope for growth indicated a consid erable loss of C, N and P. These losses exceeded estimated loss throug h gametes, indicating additional loss, ascribed to tissue damage. Good correspondence was found between the predicted and observed C:N:P sto ichiometry of mussels. Compared with phytoplankton, mussels contained relatively more N. The absorption efficiencies of C, N and P were not significantly different, but in most cases the excretion ratios of C:N and N:P showed that N accumulated more than C and P. Average annual n et growth efficiency was higher for P than for C and N. Elemental resi dence time in tissue, however, was highest for N. It is concluded that mussels are able to use N more efficiently than C and P, because they retain it better.