urbanized coral reefs

Marine organisms live in a complex environment, governed by geophysical oscillations, influenced principally by the daily light dark 24h and monthly lunar cycles 29.53 days. Predicting such oscillations is of vital importance for survival, particularly for sessile organisms living in the sea, such as reef-building corals. As human populations grow and lighting technologies improve, artificial light gradually alters natural cycles of light and dark that have been consistent over long periods of geological and evolutionary time. The use of artificial lighting to illuminate the night has provided substantial benefits to humankind. It has also disrupted natural daily, seasonal, and lunar light cycles as experienced by a diversity of organisms, and therefore interrupts the ability to sense cues for timings of many biological activities.In this study, we used transcriptomic and physiological methods to differentiate the response of Acropora eurystoma corals from two separate sites to the daily, monthly, and yearly cycles. We conducted a yearlong experiment, sampling at all four seasons, in two separate sites in the Red Sea, a light-polluted site, and a dark at night site. The different cycles yield distinct transcriptomic responses, with interactions between day time, moon phase, and temperature.Here we show that natural light dark cycles and moon phases are an important external stimulus for initiating biological processes at an accurate and synchronous time. We identified two times fewer differentially expressed genes between day and night and four times fewer differentially expressed genes between lunar phases in corals under nighttime lighting compared to corals under dark night conditions, indicating a loss of monthly and daily rhythms under light pollution. Additionally, physiology results show variance between treatments regarding the photo- physiology parameters resulting in higher Chlorophyll concentration in light-polluted samples as opposed to dark at night samples.Using omics methods, we clearly show changes between corals from both sites with an impact of light at night on corals perception of daily, monthly and seasonal cycles, hence, the increase of artificial light in coastal areas is a growing anthropogenic stressor to coral reefs around the world. This study helps policymakers decisions on optimal levels of light in coastal and urbanized areas to support coral reefs persistent and resilient.