Mesophotic coral-reef environments depress the reproduction of the coral <italic>Paramontastraea peresi</italic> in the Red Sea.

With more than 450 studied species, coral reproduction is a well-known research field. However, the vast majority of coral reproduction research has focused exclusively on shallow reefs. The incentive for the present study was: (1) the recent accelerated global degradation of coral reefs; (2) the growing interest in mesophotic coral ecosystems (MCEs; 30–120 m depth) and their potential to serve as a larval source for shallow reefs; and (3) the lack of information on MCE coral reproduction. Here, we compare the reproduction and ecology of the depth-generalist coral <italic>Paramontastraea peresi</italic> between shallow (5–10 m) and mesophotic (40–45 m) habitats in the Gulf of Eilat/Aqaba, Red Sea. Field surveys were conducted to assess the living cover, abundance, and size frequency distribution of <italic>P. peresi</italic>. Four to six colonies from each habitat were sampled monthly between April 2015 and January 2017, and the gametogenesis cycles, fecundity, and oocyte sizes were measured. The reproductive cycle in the MCEs was shorter than in the shallow reef. Despite having larger polyps, the mesophotic colonies contained significantly smaller and fewer oocytes per polyp. In spite of the relatively stable environmental conditions of the MCEs, which may contribute to coral survival, scarcity of sunlight is probably a major energetic impediment to investment in reproduction by <italic>P. peresi</italic> at mesophotic depths. Further intensive reproductive studies in mesophotic reefs are thus required to assess the ability of corals in this environment to reproduce and constitute a larval source for depleted shallow-water reefs. [ABSTRACT FROM AUTHOR]