Functional responses of juvenile kelps, Laminaria ochroleuca and Saccorhiza polyschides, to increasing temperatures

• We tested the ability of juvenile kelps to adjust their metabolism to increasing temperature.
• L. ochroleuca is more susceptible to ocean warming than S. polyschides, due to larger acclimatization capacity of the latter.
• Productivity optimum temperatures were found to differ between inter- and subtidal kelps.

We tested the ability of juvenile sporophytes of two coexisting kelps native to Portugal, Laminaria ochroleuca and Saccorhiza polyschides, to adjust their photosynthesis and respiration to increasing sea water temperatures. These responses were measured for S. polyschides from both the subtidal and the intertidal habitat, and for L. ochroleuca from the intertidal habitat. L. ochroleuca showed a reduced ability to acclimatize to changing conditions, whereas S. polyschides demonstrated a larger physiological flexibility. These findings are connected with the life-history traits of these species. Additionally, optimum temperatures for the primary production of kelps were assessed, indicating higher values for inter- than subtidal S. polyschides. Significant physiological differences between inter- and subtidal S. polyschides were observed, based on metabolic rates of primary production and dark respiration. This study suggests that, under a warming climate scenario, responses can significantly vary for each species, and that L. ochroleuca is more susceptible to ocean warming than S. polyschides, due to larger acclimatization capacity of the latter.