Effects of light, temperature and desiccation on the net emersed productivity of the intertidal macroalga Colpomenia peregrina Sauv. (Hamel)

Abstract

The brown saccate macroalga Colpomenia peregrina Sauv. (Hamel) was incubated in the laboratory under 27 combinations of light, temperature and desiccation and the emersed net photosynthetic ( P net) and respiratory ( R) responses measured using a non-dissolved gaseous oxygen analyzer. 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 combinations of physical factors to which algae were exposed and differences in their physiological responses. Results from a three-way analysis of variance (ANOVA) suggest that C. peregrina has a threshold of water loss, beyond which interactions between temperature and desiccation have a significant effect on net carbon gain. Interactions between individual factors can substantially increase the complexity of estimating net carbon gain during emersion. During winter, C. peregrina populations in southern California are subject to reductions in primary productivity as a result of shorter daylengths, lower seawater temperatures and desiccation stress. Emersion can compensate for these conditions only if rates of photosynthesis during emersion are higher than under submersion. Otherwise, emersed photosynthesis only ameliorates deterimental effects of desiccation caused by prolonged periods of daytime emersion.