Ten mature colonies of Acropora digitifera (measuring >50 cm in diameter) were collected from Sesoko Island, Okinawa, Japan (26°38028" North, 127°51035" East) on June 25th, 2015 (Fig 1A). Corals colonies were kept in running sea water and divided into two groups, the first group was kept under natural light cycles and moon phase conditions (AMB) while the second group was under constant dim light (LL) treatment from a fluorescent lamp (1.5-2 µmol quanta m-2 s-1 at coral height, light was measured using a LI-COR underwater quantum sensor LI-193). As corals were maintained in experimental condition for a period of over a month we wanted to ensure that there was no physiological degradation that could impact our results. In order to examine the colonies health, immediately after coral collection, all ten colonies were dark acclimated for ten minutes and photosystem II (PSII) maximal quantum yield (Fv /Fm) was measured for each colony, using a diving PAM fluorometer (Walz GmbH, Germany). After one month, at the end of the experiment, all colonies from the light treatment were evaluated again. The tip of the instrument’s main optical fiber was placed five mm away from, and perpendicular to, the coral branch. All corals were acclimatized to their condition for a week prior to sampling. On July 2nd, the day of the full moon, sampling started at 12:00 followed by a second sampling at 21:00. Sampling continued throughout the month of July, returning every week according to the moon phase, sampling twice a day (Fig 1B experimental set up). At each sampling time a small branch from each colony, measuring an average of 5 cm in length, using pliers, was sampled. The sampled branch was placed in a small piece of aluminum foil with a tag containing the sample ID and was snap frozen in liquid nitrogen, then transferred to a -80 freezer.