Physiological responses to environmental variation in intertidal red algae: does thallus morphology matter?

Morphological variation within and among many species of algae show correlated life his- tory traits. The trade-offs of life history traits among different morphs are presumed to be determined by morphology Form-function hypotheses also predict that algae of different morphological groups exhibit different tolerances to physiological stress, whereas algae within a morphological group respond similarly to stress. We tested this hypothesis by comparing photosynthetic and respiratory responses to variation in season, light, temperature, desiccation and freezing among the morphologi- cally similar fronds of Chondrus crispus and Mastocarpus stellatus and the alternate stage crust of M stellatus. Physiological differences between fronds of the 2 species and crusts and fronds were con- sistent with their patterns of distribution and abundance in the intertidal zone. However, there was no clear relationship between algal morphology and physiological response to environmental variation These results suggest that among macroalgae the correlation between life history traits and morphol- ogy is not always causal. Rather, the link between life history traits and morphology is constrained by the extent to which physiological characteristics codetermme these features.