Abstract. Kaullysing D, Jogee SY, Mundil SP, Soondur M, Gopeechund A, Ricot M, Jeetun S, Chinta T, Chockalingum J, Mungur D, Kowal B, Kristnama L, Gunness V, Balgobin A, Fakun ZR, Munbodhe V, Nohur MB, Ramdhun D, Ramsurrun LK, Rase S, Seetohul TK, Mattan-Moorgawa S, Ramah S, Bhagooli R. 2023. Variations in photo-physiological responses of shaded and non-shaded mangrove, Rhizophora mucronata tree parts from Mauritius Island, western Indian Ocean. Indo Pac J Ocean Life 7: 71-78. This study assessed and compared the photo-physiological responses of the tree parts of juvenile and adult mangrove, Rhizophora mucronata, under shaded and non-shaded conditions in the northern coast of Mauritius Island. Chlorophyll a fluorescence of mature (dark) leaves, young and mature propagules, lichen, buds, and sepal of adult R. mucronata trees, and of mature and young (pale) leaves of juveniles under natural shaded and non-shaded conditions was measured using a field-portable Diving Pulse-Amplitude-Modulated (D-PAM) fluorometer. Commonly used chlorophyll fluorescence parameters such as Fv/Fm, rETRmax, NPQmax were calculated. The tree parts of adult and juvenile R. mucronata showed considerable variations in their photosynthetic responses. Fv/Fm of adult tree leaves was 30% higher in shaded condition as compared to non-shaded condition. The combined effect of mangrove tree parts and conditions (shaded; non-shaded) resulted in significant differences in mean values of Fv/Fm (three-way ANOVA, p<0.001). Leaves of adult trees had 52% higher rETRmax in shaded condition. While a significant difference (p<0.001) was noted in the mean rETRmax values of various tree parts, the shaded and non-shaded conditions did not have any significant effect on rETRmax (p>0.05). Non-shaded parts of R. mucronata, including the leaves, exhibited higher NPQmax values as compared to shaded conditions. Mean NPQmax varied significantly among mangrove parts (p<0.001), between tree stage (p<0.001) and between conditions (p<0.05). These findings revealed differences in the photosynthetic activities of various mangrove parts of juvenile and adult trees under shaded and non-shaded conditions, a first attempt for the tropical island of Mauritius.