Morphological variation of the kelp Ecklonia cava along the Korean coast in relation to local environmental conditions

Ecklonia cava Kjellman is a large perennial brown alga of the temperate northwest Pacific that exhibits marked intraspecific morphological variation linked to local environmental conditions. We investigated E. cava at 11 sites along Korea's southern and eastern coasts, including Jeju Island, to quantify how habitat characteristics co-vary with morphology. Ten morphological traits were measured in 397 individuals and analyzed against six environmental variables (temperature, salinity, dissolved inorganic nitrogen and phosphorus, turbidity, transparency). These variables are treated as long-term site descriptors rather than growth-season predictors. Regional differences in morphology were highly significant. Turbidity and transparency were the variables most strongly associated with this variation at the site level; after multiple-testing correction, only the lamina width × turbidity correlation remained significant. Populations in turbid habitats (e.g., Wando) showed wider laminas and laterals, consistent with compensatory light harvesting under reduced irradiance, whereas those in clear habitats (e.g., Ulleungdo) showed stipe elongation, consistent with vertical growth toward more favorable light within the canopy. Linear mixed-effects models on all 397 individuals corroborated these patterns and identified the underwater light environment as the most robust correlate of lamina width and number of laterals. Redundancy analysis aligned the sites with the lightenvironment gradient and is reported descriptively. Observed morphological variation in E. cava is therefore most closely linked to the underwater light environment, though reciprocal-transplant or common-garden experiments are needed to determine whether this reflects phenotypic plasticity, local adaptation, or both. These findings provide baseline data for kelp-forest health assessment and conservation and restoration.