Ecotypic differentiation in populations of the giant kelp Macrocystis pyrifera from southern Chile: Implications for the species aquaculture development

Abstract

The giant kelp Macrocystis pyrifera is a foundation species with high ecological and economic importance, increasingly considered for aquaculture in southern Chile. However, populations experience strong environ- mental heterogeneity, particularly in fjord systems where salinity and temperature fluctuate due to freshwater inputs. Such conditions may drive ecotypic differentiation, influencing stress tolerance and cultivation potential. In the present study, physiological and biochemical responses of juvenile sporophytes from inner-sea (estuarine) and oceanic populations exposed to contrasting absolute salinity (SA 32 vs. SA 22) and temperature regimes (8, 11, and 16 ◦C) were compared. There were pronounced population-specific differences under hyposalinity. Inner-sea sporophytes maintained higher growth, photosynthetic rates, antioxidant capacity, and pigment sta- bility, indicating local adaptation to estuarine environments. By contrast, oceanic sporophytes exhibited reduced growth and photosynthetic performance, greater frond bleaching, and higher nitrogen accumulation under low salinity, suggesting osmotic stress and limited metabolic adjustment. Polyphenol levels were consistently higher in oceanic sporophytes but were not associated with enhanced antioxidant activity, highlighting differential biochemical strategies among populations. These findings provide evidence of ecotypic differentiation in M. pyrifera and underscore the importance of considering local adaptation in aquaculture development. Selecting tolerant genotypes, particularly from estuarine habitats, may improve resilience and productivity of kelp culti- vation under projected climate-driven increases in freshwater inputs