Differential copper stress responses in populations of the golden kelp Ecklonia radiata

Urbanised coastal systems have a legacy of contaminants in sediments from historical industrial activities, compounded by ongoing contaminant inputs from agricultural and urban run-off. Sessile organisms, such as the habitat-forming golden kelp E. radiata are particularly vulnerable in these environments as they cannot avoid exposure to these contaminants. To survive these stressors, they must rely on mechanisms such as physiological modulation or genetic adaptations. Therefore, investigating how genetically distinct populations respond to contamination is essential for assessing ecological resilience and managing contaminant impacts. Through mesocosm environments, we investigated the physiological responses of two genetically distinct E. radiata populations to copper exposure and evaluated their potential for copper bioaccumulation. This represents one of the first studies to integrate prior genetic characterisation with experimental ecotoxicology to investigate differential stress tolerance in a marine foundation species. While both populations exhibited similar copper uptake, the population from the more urbanised area of the estuary ('inner harbour') demonstrated greater physiological tolerance to copper exposure compared to the population from the less urbanised area ('outer harbour'), which experienced greater weight loss (p = 0.022), and more severe tissue degradation (p = 0.002). These findings are suggestive of local adaptation or acclimation to contamination and warrant further investigation through transcriptomic and biochemical analyses to elucidate subcellular or molecular pathways underlying stress tolerance. By integrating genetic and physiological perspectives, this research advances our understanding of adaptation in urban marine environments and highlights the role of genetic differentiation in shaping ecological responses to anthropogenic stressors.