Effect of light and temperature on photosynthesis of a cultivated brown alga,Saccharina sculpera(Laminariales), from Japan

Understanding the physiological responses of kelp to environmental parameters is essential for the conservation of natural kelp beds and increased cultivation yield. We investigated the effects of photosynthetically active radiation (PAR) and temperature on photosynthesis of a subarctic edible brown alga,Saccharina sculpera(Laminariales), using pulse amplitude modulation (PAM)-chlorophyll fluorometry and optical dissolved oxygen sensors. Photosynthesis-PAR experiments at 8 degrees C, 15 degrees C, and 22 degrees C revealed the highest net photosynthetic rates at 22 degrees C. Values for compensation (E-c) and saturation (E-k) indicated a high affinity for a light environment that reflected the natural vertical habitat of this alga. The photosynthetic response ofS. sculperato temperature indicated that the optimum temperature for oxygenic photosynthesis (KoptGP) was 22.9 degrees C, which was consistent with the highest seawater temperature in Japanese distribution range for this subarctic species. The alga survived for 168 h at 24 degrees C in darkness. Continuous 6 h exposure to PAR of 100 mu mol (low) and 1000 mu mol (high) photons m(-2)s(-1)at 8 degrees C, 15 degrees C, and 22 degrees C induced chronic photoinhibition in the alga, with greater declines in effective quantum yields of photosystem II (phi(PSII)). Failure to recover F-v/F(m)after dark acclimation at low and high PAR was observed, except for low PAR at 8 degrees C. The physiological performance ofS. sculperaindicates an affinity for a low light environment. We expect that our results will lead to an improvement in aquaculture techniques through the regulation of cultivation depth.