MEPS 528:205-220 (2015)  -  DOI: https://doi.org/10.3354/meps11252

ABSTRACT: Previous estimates of nitrogen (N) removal from coastal systems by either assimilation into tissues and shells of oysters or stimulated through biogeochemical processes have not accounted for ontogenetic changes in N sequestration. To understand how N removal may change with ontogeny, we compared N in tissue, shell, and biodeposits between juvenile and adult oysters. Juvenile oysters assimilated 165 ± 8 mg (±SE) N oyster^-1 into soft tissues and shell, while adult oysters lost mass and returned N to the estuary (-48 ± 21 mg N oyster^-1). The percentage of N in soft tissues (11.80 ± 0.01) did not differ between age classes but was significantly higher than measured elsewhere. The percentage of N in shell averaged 0.46 ± 0.01 and 0.26 ± 0.01 in juveniles and adults, respectively, accounting for ≥50% of total N in oysters. N released in biodeposits was estimated at 0.21 ± 0.00 to 0.23 ± 0.00 mg N oyster^-1 d^-1 and did not differ between age classes. Accurate quantification of N removal by oysters, therefore, should account for age and location-specific variation by including direct measurements of N assimilated into tissues and shell, released in biodeposits, and removed by biogeochemical processes. Continuous N sequestration and removal from local waters for bioremediation may require balancing recruitment or planting of young actively growing oysters with harvest of larger animals to ensure net N removal by assimilation before growth declines. This strategy may be particularly useful where environmental conditions do not support significant N removal through biogeochemical processes.

KEY WORDS: Aquaculture · Eutrophication · Shellfish · Assimilation · Restoration