Hierarchical physiological sensitivity of the coral, Orbicella faveolata, to suspended sediment and elevated temperature

Coral reefs are increasingly exposed to multiple environmental stressors, including ocean warming and elevated turbidity from coastal development, dredging, and sediment resuspension. Understanding how these stressors affect coral physiology is essential for improving sediment management and protecting reef ecosystems. We investigated the short-term physiological responses of the Caribbean reef-building coral, Orbicella faveolata, to suspended sediment and elevated temperature during controlled 72-h laboratory experiments. Coral fragments were first exposed in independent chamber-sump systems to a gradient of target turbidity levels consisting of a control with no added sediment and treatments of 15, 29, and 50 NTU, followed by a factorial experiment evaluating suspended sediment (control or 29 NTU) and temperature (27°C or 30°C). Metabolic oxygen flux was quantified using intermittent-flow respirometry; photophysiological performance was assessed using pulse-amplitude-modulated fluorometry, and tissue and skeletal condition were evaluated using biological and calcification endpoints. Elevated temperature produced the most consistent responses, decreasing maximum photochemical efficiency (Fv/Fm), increasing regulated non-photochemical energy dissipation (YNPQ), and altering respiration. Suspended sediment elicited comparatively limited responses, primarily affecting photophysiological metrics, with modest effects on respiration in the highest-turbidity treatment. No suspended sediment × temperature interaction was detected. Net calcification, symbiont density, chlorophyll concentration, and host protein content remained largely unchanged across treatments, while genotype accounted for significant variation in multiple physiological responses. Collectively, these findings support a hierarchy of short-term physiological sensitivity, with photophysiological metrics showing the most consistent responses, metabolic responses being more limited, and biomass-related and skeletal-growth endpoints remaining largely stable over the 72-h exposure. Integrating photophysiological measurements into monitoring programs may improve early detection of sublethal coral stress during coastal and climate-related disturbances.