This study aimed to assess the effect of aquaculture activity, especially the cultivation of large algae such as kelp, on the seasonal variation of and related parameters of the surface water were measured by the OceanPack_TM (SubCTech, Kiel, Germany) before and after kelp harvesting (May and August, 2015) in a typical polyculture area in Sanggou Bay, China. The variations of and its corresponding impact factors are discussed for different seasons and culture modes, and before and after kelp harvesting. The results showed that:(1) the mean values of in the surface seawater during the spring and summer seasons were (346.7±13.85) μatm(1 atm=101325 Pa) and (351.50±8.00) μatm in the inner bay, and those of the outer waters were (353.42±0.71) μatm and (358.05±2.01) μatm, respectively. All these values were lower than atmospheric decreased from the coast of the bay to the outside waters and rose at the reference outer region. The lowest values in both seasons appeared in the algal culture area and the highest values appeared in the shellfish culture area. (3) No significant correlation was found between CO₂ was significantly correlated with chlorophyll a and dissolved oxygen, indicating that organic activity had a great impact on and water temperature, dissolved inorganic carbon, chlorophyll a, and dissolved oxygen were significantly correlated. (4) The values of Sanggou Bay and the adjacent outer surface waters were lower than the atmospheric . The algal culture area was a strong carbon sink zone, because its value was much lower than that of the natural sea area. The shellfish culture area was a weak carbon sink zone, because its value was slightly higher than that of the natural sea area. The values in the algae-shellfish polyculture area were intermediate between the two monoculture areas. The photosynthetic activity of kelp in spring was a major factor affecting the surface water . The aquaculture activity in Sanggou Bay resulted in altered values compared with those of the natural sea area. The effects of physical factors on surface water became apparent in summer owing to a lack of aquaculture in that season.