Carotenoids are yellow to reddish dyes that occur naturally in plants and certain microorganisms. They play an important role in the transfer of energy in photosynthesis. In addition, they protect these organisms against the harmful effects of sunlight. Astaxanthin, a very special carotenoid with a characteristic red color, is produced in nature by plankton, algae and some plants, fungi and bacteria. The highest concentration of astaxanthin is found in the green microalgae Haematococcus pluvialis (which is also the source of Astamax from Vitals).