We studied the effect of the ectomycorrhizal (ECM) fungus Scleroderma bermudense on growth, photosynthesis and transpiration rates, chlorophyll fluorescence and content, K/Na and Ca/Na homeostasis, and water status of two provenances of Coccoloba uvifera L. (named also seagrape) seedlings exposed to four levels of salinity (0.0, 54.7, 164.1 and 273.5 mM NaCl equivalent to 0.02, 5, 15 and 25 dS m−1, respectively). The results indicated that S. bermudense improved the salt tolerance in seagrape seedlings. There were no differences in terms of growth performance, nutritional and physiological functions between the two ECM seagrape provenances in response to salt stress. The reduction of the Na concentration and the increase of K and Ca favored a higher K/Na and Ca/Na ratio, respectively, in the tissues of the ECM seedlings. Furthermore, the beneficial effects of ECM symbiosis on the photosynthetic and transpiration rates, chlorophyll fluorescence and content, stomatal conductance and water status resulted in the improved growth performance of the seagrape provenances exposed to salt stress. From an ecological point of view, seagrape in symbiosis with S. bermudense may be used in the development of ornamental plantings and coastal windbreaks along beaches and roadsides in Cuba.