More experimental evidence is needed to understand the role of propagules in macroalgal biology. There are no reports in the literature on the comparative physiology (e.g. photosynthesis) of sporelings and adults. In this paper we report on the variation in photosynthetic parameters (maximum photosynthesis, P(max), and efficiency, alpha, and dark respiration (R(d)) of cultivated young sporelings of the red alga Grateloupia doryphora (Montagne) Howe under normal conditions and after a short-term incubation at different salinities and temperatures. The results are compared to those for adult Stage III thalli obtained in laboratory culture from the same population of sporelings. The pigment composition of sporelings (more chlorophyll a and less phycoerthryn and phycocyanin than adults) promotes a better photosynthetic performance (higher P(max) and alpha and lower R(d) under chlorophyll a excitation. The younger sporelings were also more tolerant to variations in salinity and temperature than Stage III, in which the highest variation in maximum photosynthesis and dark respiration was observed.