Carbon Sink Capacity Assessment of Marine Shellfish and Macroalgae in Dalian in 2022

Dalian boasts deep-water coastline and fishery resources and is rich in offshore biological resources. Regarding carbon sink fisheries, as the city with the longest coastline in China, Dalian has blue-carbon resources such as marine shellfish and macroalgae and is uniquely positioned to develop the natural conditions required for a blue-carbon economy. The seawater aquaculture industry in Dalian has formed a diversified aquaculture system with diversified modes and species. The aquaculture of scallops, Undaria pinnatifida, and mussels holds the leading position in China, and the production scale and output of scallops and U. pinnatifida account for more than 95% of the total output from the country. Dalian has become an outstanding representative of China's sea ranch construction. By the end of 2020, Dalian had 22 state-level sea ranch demonstration zones, which is the largest number of sea ranches in the country at the municipal level. Dalian's green ecological aquaculture industry is an important offshore sink-boosting resource, with the industrial foundation and capacity necessary for the development of a blue-carbon economy. In 2022, Dalian's mariculture area was 4.57×105 hm2 its mariculture production was 2.08 million tons, and the total economic output value of its fishery industry was 76.60 billion yuan, which makes Dalian's mariculture production the highest in the country. However, no report assesses the carbon sink capacity of marine shellfish and macroalgae in Dalian. Therefore, this study selected the main aquaculture shellfish species (scallop, oyster, clam, blood clam, mussel, Saccharina japonica, and U. pinnatifida) in Dalian in 2022 as the research object and calculated carbon sink capacity. The aim of this analysis was to provide a scientific basis for the contribution to and capacity of shellfish aquaculture in Dalian and provide a theoretical foundation and technological support for the development of carbon-sink fisheries in Liaoning Province. The results show that in 2022, the total carbon sink capacity of marine shellfish and macroalgae in Dalian reached 826, 900 t, of which the net carbon sink represented 538, 400 t and the removed carbon represented 261, 500 t, which is equivalent to a reduction in carbon dioxide emissions of 1, 974, 300 t and has a value of carbon aggregation equal to 79, 447, 100 yuan. Shellfish aquaculture production in Dalian accounted for approximately 64.48% of the province's total aquaculture production, with a carbon sink contribution rate of 55.58%; macroalgae production accounted for 94.75% of the province's total, with a carbon sink contribution rate as high as 94.68%. Among algae and shellfish in Dalian, kelp and clams had the highest carbon sinks, representing 66.12% and 31.37%, respectively, of the entire carbon sinks of algae and shellfish in Liaoning Province. Mussels, as a fishery shellfish with high carbon content, represented only 0.72% of the total carbon sink in Dalian due to factors such as small farming areas and low production. Additionally, it is recommended to strengthen the aquaculture of algae and mussels with high carbon sink contribution rates and to promote the integrated multi-trophic aquaculture (IMTA) of shellfish and macroalgae to optimize the structure of the aquaculture industry (aquaculture species, spatial layout) in Dalian while realizing the effective expansion of carbon sinks of marine organisms, changing the pattern of carbon circulation in the aquaculture industry, and promoting the healthy development of aquaculture in Dalian.