Pigment concentration of red algae, Kappaphycus alvarezii (Doty) Doty ex Silva during the cultivation in the coastal waters of Nain Island, North Sulawesi, Indonesia

Cultivation of brownish red algae Kappaphycus alvarezii in controled conditions was conducted in order to obtain informations about the growth and concentration of chlorophyll and carotenoid pigments. The cultivation was carried out for 9 weeks namely from March to April 2020 in coastal waters of Nain Island that was quite far from the mainland of Manado City. Pigment concentrations were obtained through extraction based on different polarity in the total pigment extract in petroleum ether added with methanol, KOH in methanol and diethyl ether. Red algae as much as 17 thalli with an initial weight of 100 g were cultured using floating method. The distance between thallus was 25 cm. A total of three thalli was taken every two weeks, namely at week 3, 5, 7, and 9 and grouped into 3 periods. After measuring the weight gain, the algae were then exposed to pigment extraction. K. alvarezii experienced weight gain, but the relative growth rate showed a decrease in the 3 period. The pattern of algae relative growth was identical with the pattern of temperature fluctuation during cultivation. Pigments obtained from the separation using different solvents were chlorophyll a, chlorophyll d, ß-carotene and xanthophyll. It was found that the concentration of chlorophyll a and d increased as the weight gain increased. Likewise, the concentration and quantity of ß-carotene and xanthophyll pigments were in line with the growth rate pattern of K. alvarezii.