Characteristics of fouling organisms and carbon storage in Mytilus coruscus aquaculture areas, a case study at Gouqi Island, Zhejiang Province

Global warming is becoming increasingly severe, and the ocean plays an important role in mitigating climate change by absorbing CO₂ from the atmosphere. Mariculture of macroalgae and shellfish exhibits significant carbon sequestration potential. However, researches on the carbon fixation contributions of fouling organisms in perennial shellfish aquaculture areas remains limited. This study investigated the characteristics of fouling organisms and their carbon sequestration capacity in Mytilus coruscus aquaculture zones across four seasons (spring, summer, fall, and winter) in the coastal waters of Gouqi Island, Zhejiang Province. Results showed that the perennial M. coruscus aquaculture areas host diverse fouling organisms with high biodiversity. A total of 69 fouling animals including 8 phyla of Mollusca, Arthropoda, Cnidaria, Annelida, Porifera, Echinodermata, Bryozoa, and Chordata and 64 fouling algae including 3 phyla of Rhodophyta, Chlorophyta, and Phaeophyceae were identified. Seasonal variations of abundance in fouling animals were significant, exhibiting the order of autumn (46 species), summer (43 species), spring (36 species), and winter (26 species). Fouling algae presented in all seasons, with species richness ranked as spring (33 species), summer (30 species), autumn (29 species), and winter (16 species). The biomass of fouling animals increased with mussel age of M. coruscus, accounting for 31.36% and 21.80% in 3-year-old and 1-year-old mussel aquaculture areas, respectively. Fouling algal biomass varied markedly by season in consequence of winter (22 985.53±143.40) g/m², spring (7 107.95±193.37) g/m², summer (4 290.20±95.91) g/m², and fall (2 380.19±154.56) g/m². The fouling organisms in M. coruscus aquaculture areas demonstrated substantial carbon storage potential, with an annual carbon storage of approximately 0.983 t/hm². Specifically, fouling animals contributed 0.059 t/hm² (5.96% of total) and fouling algae accounted for 0.924 t/hm² (94.04% of total). Among all organisms, the brown alga Sargassum horneri exhibited the highest annual carbon storage of 0.668 t/hm². These findings highlight that the fouling organisms in perennial M. coruscus aquaculture zones significantly contribute to marine carbon sequestration, showing their ecological importance for marine ecosystem conservation and climate change mitigation.