A coral colony releases sex cells during a mass spawning event on the Great Barrier Reef. Image Credit: Kaniewska, Alon et al. (CC BY 4.0)

Corals indulge in moonlight romance

Light affects the expression of certain genes in corals to synchronize spawning with the phases of the moon.

Sexual reproduction in corals is possibly the most important process for replenishing degraded coral reefs. Most corals are “broadcast spawners” that reproduce by releasing their egg cells and sperm cells into the sea water surface. To maximize their chances of reproductive success, most coral in the Great Barrier Reef — over 130 species — spawn on the same night, during a time window that is approximately 30–60 minutes long. This is the largest-scale mass spawning event of coral in the world, and is triggered by changes in sea water temperature, tides, sunrise and sunset and by the intensity of the moonlight.

How corals tune their spawning behavior with the phases of the moonlight was an unanswered question for decades. Now, Paulina Kaniewska, Shahar Alon and colleagues have exposed the coral Acropora millepora — which makes up part of the Great Barrier Reef — to different light treatments and sampled the corals before, during and after their spawning periods. This revealed that light causes changes to gene expression and signaling processes inside cells. These changes are specifically related to the release of egg and sperm cells, and occur only on the night of spawning.

Furthermore, by exposing corals to light conditions that mimic artificial urban “light pollution”, Kaniewska, Alon and colleagues caused a mismatch in certain cellular signaling processes that prevented the corals from spawning. Reducing the exposure of corals to artificial lighting could therefore help to protect and regenerate coral reefs.

Future work will involve comparing these results with information about a coral species from another part of the world to investigate whether there is a universal mechanism used by corals to control when they spawn.

To find out more

Read the eLife research paper on which this eLife digest is based: “Signaling cascades and the importance of moonlight in coral broadcast mass spawning” (December 15, 2015).
Read a commentary on this research paper: “Mass spawning: Sex under the moon”
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