Fatty acid compositions associated with high-light tolerance in the intertidal rhodophytes <italic>Mastocarpus stellatus</italic> and <italic>Chondrus crispus</italic>.

The rhodophytes <italic>Mastocarpus stellatus</italic> and <italic>Chondrus crispus</italic> occupy the lower intertidal zone of rocky shores along North Atlantic coastlines, with <italic>C. crispus</italic> generally occurring slightly deeper. Consequently, <italic>M. stellatus</italic> is exposed to more variable environmental conditions, related to a generally higher stress tolerance of this species. In order to extend our understanding of seasonal modulation of stress tolerance, we subjected local populations of <italic>M. stellatus</italic> and <italic>C. crispus</italic> from Helgoland, North Sea, to short-term high-light stress experiments over the course of a year (October 2011, March, May and August 2012). Biochemical analyses (pigments, antioxidants, total lipids, fatty acid compositions) allowed to reveal mechanisms behind modulated high-light tolerances. Overall, <italic>C. crispus</italic> was particularly more susceptible to high-light at higher water temperatures (October 2011 and August 2012). Furthermore, species-specific differences in antioxidants, total lipid levels and the shorter-chain/longer-chain fatty acid ratio (C14 + C16/C18 + C20) were detected, which may enhance the tolerance to high-light and other abiotic stress factors in <italic>M. stellatus</italic>, so that this species is more competitive in the highly variable upper intertidal zone compared to <italic>C. crispus</italic>. Since the high-light tolerance in <italic>C. crispus</italic> seemed to be affected by water temperature, interactions between both species may be impacted in the future by rising mean annual sea surface temperature around the island of Helgoland. [ABSTRACT FROM AUTHOR]