Effects of temperature and PAR on the photosynthesis of Kappaphycus sp (Solieriaceae, Rhodophyta) from Okinawa, Japan, at the northern limit of native Kappaphycus distribution in the western Pacific

The successful cultivation of the Japanese Kappaphycus sp. (K. striatus auctorum japonicorum) in Okinawa, Japan, requires the detailed understanding of its physiological response to environmental factors. The photosynthetic performance of this native red alga was investigated under a variety of temperature and photosynthetic active radiation (PAR) conditions by employing methods based on pulse amplitude modulation-chlorophyll fluorometry and dissolved oxygen sensors. The net photosynthesis-irradiance (P-E) curve at 24 degrees C revealed that the compensation (E-c) and saturation (E-k) irradiances were 26 [95% Bayesian prediction interval (BPI), 11-29 mu mol photons m(-2) s(-1)] and 140 (95% BPI, 98-192) mu mol photons m(-2) s(-1), respectively. No inhibition in oxygenic evolution and quantum yield was observed at the highest PAR of 1000 mu mol photons m(-2) s(-1). However, the ability of the seaweed to recover from photoinhibition was complicated following long-term PAR exposures at 18 degrees C but not at 28 degrees C. The Japanese Kappaphycus sp. showed photosynthetic optima at 17.4-29.1 degrees C, derived from the F-v/F-m and gross photosynthesis-temperature models, respectively. These characteristic results were closely related to the depth of its habitat and its northern limit of distribution in Okinawa as influenced primarily by seawater temperature. Findings of this study should be useful to the development of culture systems adapted for subtropical waters, whether for commercial purpose or for conservation of natural communities.