Aquaculture of bivalve shellfish and algae offers significant ecological benefits, yet the complex interactions between these organisms can substantially impact local carbon dynamics. This study investigated the effects of co-culturing four intertidal bivalve species Pacific oysters (Crassostrea gigas), Manila clams (Ruditapes philippinarum), Chinese clams (Cyclina sinensis), and hard clams (Mercenaria mercenaria) with microalgae (Isochrysis galbana) on specific water quality parameters, including total particulate matter (TPM), total organic matter (TOM), dissolved inorganic carbon (DIC), dissolved carbon dioxide (dCO 2 ), dissolved oxygen (DO), and ammonium (NH 4 + ) concentrations. The bivalves were divided into smaller and larger groups and cultured under two conditions: with algae (WP) and without (NP), along with matched controls. Total particulate matter (TPM), total organic matter (TOM), dissolved oxygen (DO), ammonium nitrogen (NH 4 + ), dissolved inorganic carbon (DIC), and CO 2 (dCO 2 ) were measured before and after 3-h cultivation. Results revealed species-specific impacts on water chemistry. C. gigas, C. sinensis and R. philippinarum showed the strongest reduction in DIC and dCO 2 in WP groups, indicating synergistic bioremediation with algae. M. mercenaria notably reduced TPM, highlighting its particle carbon sequestration potential. DO concentrations decreased in most WP or NP groups, reflecting respiration of the cultured bivalves or microalgae. NH 4 + levels also declined for most species, indicating nitrogen assimilation by these creatures. Overall, the bivalve size significantly impacted carbon and nitrogen processing capacities. These findings reveal species-specific capabilities in regulating water carbon dynamics. Further research should explore integrating these bivalves in carbon-negative aquaculture systems to mitigate environmental impacts. This study provides valuable insights underlying local carbon dynamics in shallow marine ecosystems.