The harmful alga Aureococcus anophagefferens utilizes 19′-butanoyloxyfucoxanthin as well as xanthophyll cycle carotenoids in acclimating to higher light intensities

► We studied the acclimation of the "brown tide" alga Aureococcus anophagefferens to high light. ► Its acclimation processes utilize two different carotenoid-based strategies. ► One involves the xanthophyll cycle carotenoids; the other involves fucoxanthin derivatives. ► Up to 50% of fucoxanthin is converted to 19'-butanoyloxyfucoxanthin during growth at high light. ► Hypothesis: This is a photoprotective conversion which decreases energy transfer efficiency.