Can Twilight Reefs Usher In A New Dawn For Depauperate Shallow Coral Reefs?

摘要

As shallow reefs continue to decline, scientists are searching for the key to their persistence; as it turns out, they may just need to look deeper. Below many shallow tropical reefs, there exist healthy and more stable mesophotic coral reef communities. The ability of these reefs to act as a refuge for declining shallow populations has garnered significant interest among the scientific community; however, the reproductive and larval aspects necessary for this to occur are unknown. This study assesses the ability of deep reefs to act as a reproductive refuge for shallow counterparts by examining gametic compatibility, viability and larval settlement preferences. Gametes from Orbicella franksi inhabiting the shallow (14-20m) and the upper mesophotic (27-32m) were introduced in a series of inter- and intra-depth crosses and found to be compatible. Larval settlement experiments found no natal depth preference, with deep larvae significantly preferring to settle on shallow conditioned substrate. Our findings support the plausibility of healthy mesophotic reefs acting as a refuge for depauperate shallow populations by (1) providing gametes to mix with limited shallow gametes resulting in increased fertilization and (2) providing larvae that recruit and repopulate shallow reefs. This is the first study to comprehensively evaluate the Deep Reef Refugia Hypothesis from a reproductive and larval settlement standpoint. Our results suggest a close coupling between shallow and mesophotic reefs through gamete and larval export and illustrate the current and future importance of these mesophotic reefs.