The occurrence of Phycocalidia tanegashimensis (Bangiaceae) in the splash zone may be related to the tolerance of photochemical efficiency to temperature, irradiance, desiccation, and salinity

Abstract

The combined effects of temperature and irradiance and the influences of desiccation and salinity on the photochemical efficiency in a subtropical red alga, Phycocalidia tanegashimensis (=\u2009Pyropia tanegashimensis, Bangiaceae) from Tanegashima Island, Japan, were determined to reveal how this species has adapted to its habitat in the splash zone. Continuous 6-h exposure to irradiance of 200 (low) and 1000 (high) µmol photons m−2\xa0s−1 at 12, 20, and 28\xa0°C showed a decline in the effective quantum yields (ΔF/Fm′) of photosystem II (PSII) during the exposures; nevertheless, the maximum quantum yields (Fv/Fm) of PSII measured in subsequent 14-h dim-light acclimation almost returned to initial values at 20 and 28\xa0°C, revealing its high capacity to recovery. In contrast, those under both low and high irradiances at 12\xa0°C did not recover to initial values even after 14-h dim-light acclimation, signifying enhanced inhibition under irradiance at low temperature. The response to continuous desiccation (~\u2009480\xa0min) under 50% humidity at 24\xa0°C showed that the ΔF/Fm′ decreased with decreasing absolute water content (AWC). However, for the samples with an AWC above 10%, ΔF/Fm′ mostly recovered to initial levels after subsequent 1-day rehydration in seawater, suggesting relatively strong tolerance to desiccation. This alga also tolerated a broad range of salinity (i.e., 10–60 psu) under 3-day exposures. The adaptations of P. tanegashimensis to relatively high irradiance, warm temperature, and a strong osmotic (desiccation and salinity) tolerance may explain its high capacity to flourish in the splash zone in the subtropical environment of Japan.