Macrobenthic Community Structure and Associated Carbon Stocks in Tidal Flats of South Korea

Tidal flats are ecologically important coastal ecosystems with significant carbon stocks; however, although taxon-specific carbon assessments have been conducted in other coastal systems, such data remain scarce for Korean tidal flats, where bivalve aquaculture is actively practiced. This study examined the macrobenthic community structure and carbon stock contributions in two tidal flats on the west coast of South Korea (Seosan and Seocheon) through field surveys conducted in May and August 2023. A total of 110 invertebrate species from five phyla were identified. Annelida showed the highest species richness at both sites (47.4–62.3% of total species), whereas Mollusca dominated biomass and carbon stocks. Two-way PERMANOVA confirmed significant differences in community structure between sites (Pseudo-F = 15.376, p < 0.001) and months (Pseudo-F = 9.489, p = 0.001), and a significant site × month interaction (Pseudo-F = 4.800, p = 0.028). Nonparametric ANCOVA revealed that Mollusca exhibited a significantly higher carbon mass conversion rate relative to wet weight than all the other taxa (p < 0.001). Rank abundance curves and principal coordinate analyses indicated that Ruditapes philippinarum accounted for 86.9% of total carbon mass in Seosan, whereas R. philippinarum and Mactra veneriformis together accounted for 73.5% in Seocheon, despite Annelida comprising the majority of species richness. These results indicate that the macrobenthic carbon stocks of Korean tidal flats are disproportionately concentrated in a few dominant calcifying Bivalvia species rather than across the overall community diversity, with implications for coastal ecosystem management.