Physiological activity of Porphyra in relation to eulittoral zonation

Eulittoral seaweeds at different tidal elevations are exposed to various frequencies and durations ofemergence. Their physiological activities (e.g. nutrient uptake) may be affected by water loss duringemersion. We used threePorphyraspecies from different tidal elevations to test whether species at differentvertical elevations on the shore respond differently to the increasingly non-marine environment, in terms oftheir physiological activities including nutrient uptake, tissue carbon, nitrogen and phycoerythrin contents.Simulated tidal cycles produced water losses of 0%, 40 ± 10% and 90 ± 5% tissue water. Emersion was stressfulfor all species regardless of their habitat. It was more stressful to nitrate and phosphate uptake for thesublittoral speciesP. yezoensisthan eulittoral species,P. umbilicalisandP. leucosticta. Interestingly, tissue Nfor thalli that had been emerged and then re-submerged was significantly higher than those of continuouslysubmerged individuals. During exposure, tissue N contents of all species declined but recovered quickly (e.g.within 30 min) after re-submergence. This result suggests that emersion-induced N release may constitutean undescribed biogeochemical pathway linking marine, terrestrial, and atmospheric N reservoirs.