Thermal tolerance of Hypnea pseudomusciformis ecotypes (Cystocloniaceae, Rhodophyta) related to different floristic provinces along the Brazilian coast

Studies on the effects of temperature on physiological processes are essential to model macroalgae biogeographic distribution. Tetrasporophytes of Hypnea pseudomusciformis were collected from three floristic provinces (tropical, transition and warm temperate) along the Brazilian coast (~3.000 km), representing three ecotypes. Specimens were cultured under 20°C, 24°C, 28°C and 32°C for 21 days, then physiological parameters (growth rates, photosynthesis and pigments content) were analyzed. H. pseudomusciformis specimens tolerated a temperature variation from 20°C to 32°C. However, all ecotypes displayed a significant decrease in physiological performance at 32°C in all parameters analyzed. We hypothesized that the H. pseudomusciformis ecotype from the tropical province is already living at its thermal physiological limit, reaching its maximum growth only in the winter months (June to September), whereas a warm temperate ecotype reaches maximum growth in the summer months (December to March). This wide thermal optimum may be the reason for the widespread distribution of this species along the Brazilian coast, allowing it to occupy different thermal environments.