Abstract
The rhodophytes Mastocarpus stellatus and Chondrus crispus occupy the lower intertidal zone of rocky shores along North Atlantic coastlines, with C. crispus generally occurring slightly deeper. Consequently, M. stellatus 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 M. stellatus and C. crispus 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, C. crispus 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 M. stellatus, so that this species is more competitive in the highly variable upper intertidal zone compared to C. crispus. Since the high-light tolerance in C. crispus 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.
Highlights
Mastocarpus stellatus ((Stackhouse) Guiry, 1984; Phyllophoraceae, Gigartinales, Rhodophyta) and Chondrus crispus (Stackhouse, 1797; Gigartinaceae, Gigartinales, Rhodophyta) are morphologically similar red macroalgal species, both approximately 10 cm in size with numerous dichotomously branching blades arising from a flattened stipe [1,2,3]
In some red algae, fatty acid unsaturation is stimulated by an increase in light intensity [23, 65]. Since those high-light conditions exist in shallower waters around Helgoland, we propose that they might contribute to the higher contents of monounsaturated fatty acids in this habitat, which we observed in M. stellatus
Our study on rhodophytes from Helgoland showed that local populations of M. stellatus have a higher tolerance towards high-light stress than those of C. crispus
Summary
Mastocarpus stellatus ((Stackhouse) Guiry, 1984; Phyllophoraceae, Gigartinales, Rhodophyta) and Chondrus crispus (Stackhouse, 1797; Gigartinaceae, Gigartinales, Rhodophyta) are morphologically similar red macroalgal species, both approximately 10 cm in size with numerous dichotomously branching blades arising from a flattened stipe [1,2,3]. Koch et al Helgol Mar Res (2017) 71:15 potentially stressful environmental conditions such as intense photosynthetically active and ultraviolet radiation (PAR and UV), high or low temperatures (e.g. changes of 10 to 20 °C compared to seawater temperature in the Gulf of Maine, USA) [10], desiccation, osmotic stress and nutrient limitation [11]. To prevail in their challenging, dynamic environment, intertidal macroalgae have generally developed effective ecophysiological acclimation mechanisms [e.g. 11]. Thereby, adjustments of fatty acid profiles can facilitate electron and ion transport across/within the thylakoid membranes [27] and enhance the stabilizing effect of lipids on the protein complexes during photosynthesis under variable light conditions [28, 29]
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