Functional traits and diversity of macrobenthic communities under organic and heavy-metal pollution in South Korean bays

Macrobenthic communities are used as indicators of coastal environmental quality because of their sensitivity to sediment disturbance. This study integrated taxonomic composition, functional traits, and functional diversity to evaluate macrobenthic responses to multiple sediment stressors across four bays in South Korea. Sediment properties and heavy metal concentrations were measured, and trait–environment relationships were examined using RLQ and fourth-corner analyses. Sediment characteristics and metal contamination differed among bays, accompanied by variation in macrobenthic abundance, species richness, and community composition. Assemblages were dominated by Annelida and functionally characterized by vermiform, small-bodied, infaunal, burrowing, and deposit-feeding taxa, with tolerant and indifferent ecological groups prevailing. Functional richness differed among bays and tended to decline at sites with organic enrichment and sediment-associated stress, whereas other functional diversity indices showed less consistent patterns. Functional entity analysis identified 95 entities among 183 species, with low functional redundancy (FRed = 1.926) and high functional vulnerability (FVuln = 0.600), indicating that single species supported many functional roles. RLQ analysis suggested a multivariate gradient associated with Cd, AVS, COD, ignition loss, mean grain size, As, and Pb. Deposit feeding, larger body size, and opportunistic strategies were more common toward the stressed end of this gradient, whereas mobility, omnivory, and sensitivity were associated with less-disturbed conditions. However, Model 4 was not significant, and fourth-corner associations did not remain significant after false discovery rate correction. These patterns should therefore be interpreted as exploratory rather than confirmed trait–environment relationships. Overall, sediment stressors may be associated with shifts in macrobenthic functional structure.