Estuaries are characterized by large amounts of nutrient loads, wide intertidal sand flats, and a high biomass of buried filter-feeding bivalves. A field study was designed to determine the role of the buried bivalves in the estuarine nutrient cycle. The biodeposition, respiration, and excretion rates of a dominant surf clam (Mactra veneriformis) in the Shuangtaizi estuary, Bohai Sea of China, were determined seasonally using a sediment trap and a closed respirator. The carbon (C), nitrogen (N), and phosphorus (P) budgets of M. veneriformis for 4 seasons were also modeled. The results showed an obvious seasonality in the physiological rates for the studied clam. The lowest biodeposition rates occurred in winter (0.008 g/individual/day), whereas the highest appeared in summer (0.309 g/individual/day), and were mainly attributed to the effects of water temperature and seston concentration. The maximum respiration rate occurred in summer (30.65 mg/individual/day), whereas the minimum occurred in winter (0.54 mg/individual/day). The excretion rates for ammonium and phosphate also fluctuated seasonally, with the highest value in spring and the lowest in winter. The results also showed that the C, N, and P budgets were in the following order: C loss from respiration > C loss from fecal production > C loss from growth; N loss from growth >N loss from fecal production > N loss from excretion; and P loss from growth > P loss from fecal production > P from excretion. The C, N, and P budgets illustrate that the M. veneriformis population used relatively more N and P than C for growth, and efficiently transferred the pelagic primary production to a higher trophic level. This study suggests that M. veneriformis may play a key role in the nutrient cycle of the estuarine ecosystem and should be considered an important component of the ecology of estuaries.
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Vol. 32 • No. 2