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Physiological responses of two species of articulated coralline algae during a simulated tidal cycle Guenther, Rebecca


Intertidal macroalgae endure stresses associated with submerged and emerged conditions on a daily basis. Differences in physiology at high tide, low tide, and during recovery underlie spatial separation of species along the shore. Tidepools provide refugia from physical stresses associated with the low tide, and species with low stress tolerance may be restricted to these habitats. Species that survive emergence employ physiological and morphological strategies to survive exposure to pseudo-terrestrial conditions. I explored how tidepool and non-tidepool macroalgae respond to and recover from intertidal stressors, such as light, temperature, and desiccation. I investigated whether differences in physiology could explain differences in habitat distributions. To answer these questions, I explored the physiological responses of the coralline algae, Calliarthron tuberculosum (Postels and Ruprecht) E.Y. Dawson and Corallina vancouveriensis Yendo, to simulated tidal conditions. Calliarthron is restricted to tidepools, while Corallina can survive emersion during low tide. First, I documented physiological differences between the two species at high tide. Corallina performed similar to a high light adapted plant, while Calliarthron’s performance resembled that of a low light adapted plant. Surprisingly, their pigment composition did not differ, suggesting that both species are able to harvest light similarly but that other metabolic processes are at play. Second, I compared morphological and physiological strategies employed by Calliarthron and Corallina to resist stress during low tide. I found differences in the physiological responses of the two species to increased light and temperature, two chief stressors present in the tidepool microhabitat. Unlike Calliarthron, Corallina exhibited high tolerance to increasing water temperatures and was more effective at resisting desiccation via morphology. However, neither species photosynthesized in the air, regardless of hydration level. Finally, I quantified recovery upon the return of the tide. Both species recovered from warm tidepool temperatures. However, only Corallina recovered from the combination of temperature and desiccation stress associated with emergence. This study describes the variation in physiological performance of two intertidal macroalgal species during the tidal cycle, and documents several morphological and physiological strategies employed by species to survive stresses associated with low tide. Results help to explain the habitat differences between the two species.

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