Distinct biochemical profiles in Antarctic seaweeds reflect acclimation to polar and hydrothermal environments with implications for biomass nutritional value

Global change is driving ocean warming (OW) and acidification (OA), impacting marine ecosystems worldwide, including polar regions. Seaweeds, as key primary producers in coastal ecosystems, synthesize a wide range of biochemical compounds that support higher trophic levels. Their biochemical composition is conditioned by local environmental factors, including seawater temperature, pH, and nutrient availability. However, how polar seaweeds respond to ongoing global change remains poorly understood. In this study, we examined the influence of local environmental changes on the biochemical composition - including fatty acids (FA), pigments, carbon, and nitrogen - of nine Antarctic brown and red seaweed species. Specifically, we considered a latitudinal gradient from the South Shetland Islands (⁓62°S) to Yalour Island (⁓65°S), and the presence of active fumarole vents at Deception Island. Our results reveal species-specific and location-dependent biochemical shifts in most species. While chlorophyll a concentrations tended to increase with latitude, specimens collected from fumarole vents exhibited a reduction in total FA content, PUFA:SFA (polyunsaturated to saturated fatty acid) ratios, PUFA omega-3, and pigment concentrations. These shifts under hydrothermal influence are likely driven by elevated seawater temperatures and acidic conditions, suggesting a potential decline in nutritional value under future global change scenarios. Additionally, higher magnesium content was found in the skeletons of crustose coralline algae from shallow waters than in those at 22 m depth. Our results highlight the species-specific nature of biochemical responses to environmental stressors, underlining the complexity of predicting the impacts of global change on seaweed physiology and the potential cascading effects on Antarctic food webs.