Effect of temperature on growth and nitrate and phosphate uptake kinetics of juvenile Saccharina latissima sporophytes (Phaeophyceae)

Kelp forests play a vital role in marine ecosystems by contributing to nutrient cycling and providing habitat for marine organisms. However, the impacts of rising ocean temperatures threaten the survival and growth of kelp species, with implications for ecosystem resilience. The aim of this study was to assess the effect of temperature on growth and nutrient uptake kinetics of young Saccharina latissima sporophytes. Growth and uptake rates of nitrate (NO₃^-) and phosphate (PO₄^3-) were examined under 5 temperature treatments ranging from 7.6 °C to 24.5 °C. Our findings revealed that NO₃^- uptake significantly decreased when temperature was at or above 15.7 °C, while high temperatures had no effect on PO₄^3- uptake rates. Nitrate uptake significantly correlated with growth only at lower temperatures of 7.6 °C and 12.6 °C. In contrast, PO₄^3- uptake was significantly correlated with growth across all temperature treatments except the highest (24.5 °C). Interestingly, at high temperatures (20.9 °C and 24.5 °C), we observed NO₃^- release, while PO₄^3- uptake consistently showed positive values, suggesting distinct regulatory mechanisms for N (nitrogen) and P (phosphorus). These findings highlight potential disruptions in nutrient cycling under climate change and underscore the importance of optimizing nutrient availability in kelp aquaculture.