NITROGEN AND PHOSPHORUS EXCRETION AND ITS ECOLOGICAL EFFECT BY SEVERAL BIVALVES AND FOULING ANIMALS

Nitrogen and phosphorus excretion by several filter feeding mollusks,including Chlamys farreri,Argopecten irradians,Mytilus edulis,Crassostrea gigas,Ruditapes philippinarum and fouling organisms (Styela clave,Ciona intestinalis,Balanus amphitrite and Trapezium liratum) collected from coastal culture areas,were studied.NH 4 N was the predominant nitrogenous excretory product,which accounted for more than 70% (mean 70 8%-80 1%)of TN excreted by these organisms.Amino acids are the second main nitrogenous component excreted by all of the studied organisms,which constituted 10%-25% of TN product.Other nitrogenous components excreted by the species were urea,nitrite and nitrate,but no significant amount of uric acid was measured in these bivalve species.Organic phosphorus constituted 15%-27% of the total phosphorus excreted by these organisms.The calculated everyday excretion rates of N and P of all raft cultured bivalves in Sishili Bay in summer could provide 44% and 40% respectively of N and P demands for pelagic primary production.The raft cultured bivalves played an important role in nutrient regeneration in a coastal aquaculture ecosysten.