Photo-physiological thermal stress responses of Echinopora forskaliana from shaded and light-exposed environments around Rodrigues Island, Western Indian Ocean

Abstract

Abstract. Jeetun S, Ricot M, Jogee SY, Taleb-Hossenkhan N, Ramah S, Perrine JS, Kaullysing D, Bhagooli R. 2025. Photo-physiological thermal stress responses of Echinopora forskaliana from shaded and light-exposed environments around Rodrigues Island, Western Indian Ocean. Indo Pac J Ocean Life 9: 111-123. Corals in shaded and exposed habitats experience variable heat and light stresses, impacting their photosynthetic performance and resilience to thermal stress. This study examined bleaching, photosynthetic performance, and growth patterns of Echinopora forskaliana (Milne Edwards & Haime, 1849) in shaded and exposed environments at St. François, Rodrigues Island. Bleaching prevalence and colony sizes were recorded using three belt transects. Field observations in 2018 revealed healthy-looking colonies in shaded habitats, while colonies in exposed habitats showed bleaching. Responses of healthy-looking E. forskaliana colonies from both habitats were assessed under exposure to 29 and 32°C. Effective quantum yield at Photosystem II (?_PSII), maximum relative electron transport rate (rETR_max), and maximum non-photochemical quenching (NPQ_max) were measured at the start, and after 3 and 12 hours of exposure. Field bleaching surveys showed that 93.3% of exposed colonies were pale/bleached, while shaded ones remained unaffected and were significantly larger (42.1±9.0 cm). Thermal stress at 32°C and 206.5±27.0 Lux caused steep declines in ?_PSII (99.7%), rETR_max (93.5%), and NPQ_max (97.37%) in exposed colonies after 12 hours, while shaded colonies maintained their photosynthetic performance. These findings suggest that shaded habitats may act as refugia for corals under climate-induced thermal stress, highlighting the need for adaptive conservation and management approaches. The urgency of adaptive conservation and management approaches is underscored, as these findings highlight the need for immediate action to protect these crucial habitats.