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Stressful conditions, such as mechanical damage, can significantly compromise the survival of algal beds by reducing their biomass, reproductive output, and even altering their production of defensive chemical compounds. In the present work, the effect of different intensities of trampling (no trampling, low and high trampling intensities) on reproduction, morphology, and phenolic content of Sargassum species was studied in three sites along the southwestern Atlantic Coast, Brazil, from March to October 2015. The parameters were evaluated in distinct periods (0, 90, and 180 days) after trampling, using 40- × 40-cm quadrats along transects. Trampling reduced algal reproductive biomass in two of the three studied sites (Pernambuco and Fortaleza beaches) shortly after the experimental treatment (T0). The mean thallus length was higher in trampled plots in all study sites, and the dry biomass of the individuals were higher in Pernambuco and Cigarras beaches, which also presented lower phenolic levels after damage. These results suggest a probable trade-off in resource allocation, with an immediate compromise of the individuals' reproduction followed by a decrease in the production of defense compounds, probably due to an investment in damage repairing of vegetative portions, maximizing the individuals' survival in the long term. Although the individuals reach larger sizes, they reproduce less and are more susceptible to other sources of stress that can compromise Sargassum spp. fitness. [ABSTRACT FROM AUTHOR]