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 (= Pyropia 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 s−1 at 12, 20, and 28 °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 °C, revealing its high capacity to recovery. In contrast, those under both low and high irradiances at 12 °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 (~ 480 min) under 50% humidity at 24 °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.