Down-regulation of carbon concentrating mechanisms and adjustments in fatty acid composition in response to ocean acidification and warming cannot compensate for negative effects of multiple stressors in a habitat-forming kelpBiology & Ecophysiology

Abby Gilson¹, Nessa O’Connor¹

¹Trinity College Dublin, Ireland

Habitat forming species are under threat from a range of anthropogenic stressors. Ocean warming and acidification are predicted to drive changes in the abundance and distribution of many macroalgal species and alter their ecosystem functioning. Compensatory mechanisms including changes to rates of physiological functioning or chemical composition may mitigate the negative impacts and prevent detrimental knock-on effects. The response of many macroalgal species, however, remain poorly understood, particularly for stressors that will not occur in isolation. We tested for the individual and interactive effects of ocean warming (ambient, +3C) and acidification (350 ppm,1000 ppm) on the productivity of the juvenile kelp Laminaria digitata. In addition, we aimed to identify potential compensatory mechanisms including down regulation of carbon concentrating mechanisms and changes to fatty acid composition. We identified a greater effect of CO2, compared to warming, on the fatty acid composition of L. digitata. In addition, biomass of L. digitata was greater under enriched CO2 but only under ambient temperatures. The photo-physiology of L. digitata, however, remained unaffected by both OA and warming.