Functional traits are direct measures of plant responses and adaptations to environmental changes. In this study, we quantified the photosynthetic and hydraulic traits of five plant species (Scaevola taccada, Ipomoea pescaprae, Casuarina equisetifolia, Arachis hypogaea, and Cocos nucifera), which were either grown in a nursery in Wenchang, Hainan Province, China, or transplanted to a coral island that has harsh habitats, such as high solar radiation and low fresh water availability. The maximum photosynthetic rate (A_max) of S. taccada, I. pescaprae, and C. equisetifolia growing on the coral island increased significantly compared to the plants growing in Wenchang nursery. Except for C. nucifera, the other four species on the island had lower specific leaf areas (SLA) and higher long-term water use efficiencies. The leaf carbon content (LC) of the five species on the coral island all decreased. In addition, the leaf hydraulic conductivity (K_leaf) of I. pescaprae, C. equisetifolia, and C. nucifera increased and the leaf turgor loss point (Ψ_tlp) for I. pescaprae, and A. hypogaea decreased significantly. However, the stomatal conductance (g_s) of I. pescaprae and C. equisetifolia significantly increased. Our results demonstrated that S. taccada, A. hypogaea, and C. nucifera adapted to the island environment through non-stomatal regulation, (i.e., an increase in K_leaf, but a decrease in Ψ_tlp and SLA). In contrast, I. pescaprae and C. equisetifolia employed both stomatal regulation (i.e., an decrease in g_s) and non-stomatal regulation (an increase in K_leaf, but a decrease in Ψ_tlp, and SLA) to promote plant carbon assimilation. In conclusion, S. taccada, I. pescaprae, and C. equisetifolia had higher photosynthetic rates and water use efficiencies, which enabled them to cope better with the harsh environmental conditions. Therefore, they are recommended as suitable species for vegetation restoration on tropical coral islands.