Differences in physiological responses between winter and summer Gracilaria tenuistipitata (Gigartinales, Rhodophyta) to varying temperature

Gracilaria tenuistipitata var. liui Zhang et Xia, which is farmed in brackish water ponds of southern Taiwan as a major food of sea abalone, produces poor yields in winter. This study investigated the effects of year, location (pond), and season on the physiological responses of G. tenuistipitata to varying temperature. Neither year nor pond affected the physiological parameters. Season significantly affected the specific growth rate, the recovery specific growth rate, and the levels of free proline. The specific growth rate was different between winter (January in 1996, 1997 and 1998) and summer (August in 1996, 1997 and 1998) plants, which grew in a range of 14.1–32.3°C and 11.8–37.3°C with the maximum at 23 and 24.5°C, respectively. The recovery specific growth rate after transferal to 25°C showed a similar trend. Free proline accumulated only in summer plants at both 20 and 35°C. Thus, the growth and free proline levels at varying temperature are season-dependent events in G. tenuistipitata.