EFFECTS OF LIGHT, TEMPERATURE AND DESICCATION ON THE NET EMERSED PRODUCTIVITY OF THE INTERTIDAL MACROALGA COLPOMENIA-PEREGRINA SAUV (HAMEL)

The brown saccate macroalga Colpomenia peregrina Sauv. (Hamel) was inc ubated in the laboratory under 27 combinations of light, temperature a nd desiccation and the emersed net photosynthetic (P-net) and respirat ory (R) responses measured using a non-dissolved gaseous oxygen analyz er. Estimates of net emersed carbon gain were made based in the P-net: R ratio. These were highly variable (-0.02 to 2.86) depending on the c ombinations of physical factors to which algae were exposed and differ ences in their physiological responses. Results from a three-way analy sis of variance (ANOVA) suggest that C. peregrina has a threshold of w ater loss, beyond which interactions between temperature and desiccati on have a significant effect on net carbon gain. Interactions between individual factors can substantially increase the complexity of estima ting net carbon gain during emersion. During winter, C. peregrina popu lations in southern California are subject to reductions in primary pr oductivity as a result of shorter daylengths, lower seawater temperatu res and desiccation stress. Emersion can compensate for these conditio ns only if rates of photosynthesis during emersion are higher than und er submersion, Otherwise, emersed photosynthesis only ameliorates dete rimental effects of desiccation caused by prolonged periods of daytime emersion.