AUTHOR=Liu Yi , Zhang Jihong , Wu Wenguang , Zhong Yi , Li Hongmei , Wang Xinmeng , Yang Jun , Zhang Yongyu 

TITLE=Effects of Shellfish and Macro-Algae IMTA in North China on the Environment, Inorganic Carbon System, Organic Carbon System, and Sea–Air CO2 Fluxes

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 9 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.864306

DOI=10.3389/fmars.2022.864306

ISSN=2296-7745

ABSTRACT=Shellfish and macro-algae integrated multi-trophic aquaculture (IMTA) greatly increases the sustainability of aquaculture. However, studies of the effects of large-scale shellfish–macro-algae aquaculture on the functions of the environment and the ocean carbon sink are lacking. In this study, spatiotemporal changes in environmental factors and inorganic and organic carbon in the seawater of Sanggou Bay, which is a key region for shellfish–macro-algae aquaculture in northern China, were studied over one year. Results confirmed that a large area of shellfish culture may aggravate ocean acidification and ocean hypoxia. When the macro-algae in the aquaculture zone are harvested in summer，the pH and dissolved oxygen concentration in the seawater of Sanggou Bay decreased by 0.39 units and 1.06 mg/L, respectively. Macro-algae culture can offset the impacts of shellfish respiration and calcification on the pH and DO. Both shellfish and macro-algae affect the seawater carbonate system. In summer，surface seawater DIC concentration and pCO2 in Sanggou bay were highest，while the lowest DIC and pCO2 were found in the winter. The surface seawater DIC concentration and pCO2 were highest in the shellfish culture zone. The control area did not significantly differ from that in the shellfish–macro-algae mixed-culture zone. Shellfish and macro-algae can also promote the migration and transformation of organic carbon. The DOC concentration in macro-algae culture zone was the highest, and the DOC concentration in the shellfish culture zone was the lowest. The POC concentration in the shellfish culture zone and macro-algae culture zone surface seawater was lower, and the POC concentration in the shellfish-macro-algae mixed culture zone and the control area was higher. In summer, the shellfish culture zone and shellfish–macro-algae polyculture zone were sources of atmospheric CO2. In autumn and winter, the entire bay was a strong sink of atmospheric CO2. In sum, large-scale aquaculture altered the carbon sink function and carbon cycle of the marine ecosystem. Although the CO2 released by shellfish respiration and calcification may be a potential source of atmospheric CO2, the shellfish and marco-algae IMTA promoted the absorption of atmospheric CO2 by the marine ecosystem, as well as the growth and survival of calcified organisms.