Light and temperature effects on photosynthetic activity of Eucheuma denticulatum and Kappaphycus alvarezii (brown and green color morphotypes) from Sulawesi Utara, Indonesia

Knowledge concerning the effects of several abiotic factors on the physiology of carrageenophytes is essential both in ecological and economic standpoints, to ensure their sufficient supply for the sustainability of seaweed-based industries. This paper presents the photosynthetic characteristics of farmed carrageenophytes, Eucheuma denticulatum and Kappaphycus alvarezii [brown (BRN) and green (GRN) color morphotypes] from Sulawesi Utara (Sulawesi Island), Indonesia, as determined by examining their photosynthetic response across different temperatures and irradiances using dissolved oxygen measurements and pulse-amplitude modulated fluorometer. Net photosynthesis-irradiance (P-E) curves at 26 degrees C revealed that net photosynthetic rates of the three seaweeds gradually increased until the estimated saturation irradiances (E-k) of 58 mu mol photons m(-2) s(-1) (49-68 mu mol photons m(-2) s(-1), 95% Bayesian prediction intervals; BPI) for E. denticulatum, and 158 and 143 mu mol photons m(-2) s(-1) (134-185 and 99-203 mu mol photons m(-2) s(-1), 95% BPI) for BRN and GRN K. alvarezii, respectively; and that no photoinhibition was observed at the highest irradiance of 1000 mu mol photons m(-2) s(-1). All seaweed samples exhibited photosynthetic tolerance to high PAR as shown by their recovery in maximum quantum yields (F-v/F-m) following chronic exposures; as well as tolerance over a broad range of temperature, which is from 19 to 33 degrees C for E. denticulatum, 20-29 degrees C for BRN K. alvarezii, and 17-32 degrees C for GRN K. alvarezii. Temperature responses of these carrageenophytes indicated that they were well-adapted to the annual seawater temperatures in the cultivation site; however, they are also likely close to threshold levels for thermal inhibition, given the decline in F-v/F-m above 30 degrees C.