Light Pollution Disrupts Coral Reproduction

Light pollution can prevent coral from spawning. Pawel Papis/Shutterstock

We’re losing our coral reefs. Global warming, fishing, acidification, dumping waste, and reckless tourism all have detrimental impacts on coral and the ecosystems in which they live. Unfortunately, this list of stressors does not seem to end there, though. According to new research, light pollution can disrupt their moonlight-sensing systems, preventing them from spawning.

“We have known for years that moonlight is very important for coral spawning,” lead researcher Oren Levy from Bar-Ilan University told IFLScience. “All corals synchronize spawning in one way or another with the Moon. Whether that is a full Moon, half Moon – year after year each species uses the same cue.”

And in an area as vast as the Great Barrier Reef (GBR), it’s no surprise that these annual occurrences are the Earth’s biggest reproduction event. A finely orchestrated process, following the detection of changes in moonlight intensity vast numbers of coral and invertebrate species release egg and sperm into the water. Failure to synchronize this annual event will significantly reduce the likelihood of successful fertilization.

While numerous environmental factors play a role in spawning, such as temperature, which drives egg and sperm maturation, it seems that the phase of the Moon is crucial to coordinate the timing of this event. But how precisely is this annual harmony achieved?

To find out, scientists from Bar-Ilan and the University of Queensland looked at the expression of genes, basically which ones were switched on and off, in stony coral colonies sampled at different times. Results were obtained before, during, and after spawning to look for any changes in gene expression patterns.

Image credit: Study samples were taken from the Great Barrier Reef. JC Photo/Shutterstock

They found that many genes known to be involved in rhythmic processes like the biological, or circadian, clock showed ramped up gene expression at midnight on full Moon days. Other genes that showed heightened gene expression were those related to the detection of environmental cues – more specifically, those that are involved in so-called “G-protein” signaling pathways. G-proteins sit on the surface of the cell and help pick up things like changes in light intensity or chemical levels. All in all, these genes act in one way or another to drive the coordinated release of gametes – egg and sperm cells.

The team then examined whether it would be possible to manipulate this event by altering the ambient conditions. Using the same coral species, four colonies were measured in the field, on the GBR, and a further 16 were taken back to the lab. Here, they were exposed to either natural day/night cycles, abnormally light nights that mimic light pollution levels experienced at sample sites, or abnormally dark nights that represented a lack of moonlight.

While those in the first condition spawned at the same time as those back on the reef, colonies whose light levels were altered failed to spawn. Importantly, the researchers discovered that those in the light manipulation groups demonstrated mismatched patterns of gene expression. The light pollution condition, for example, resulted in the premature expression of genes involved in gamete release.

“This is the first paper ever dealing with light pollution on spawning behavior and gene expression,” said Levy. “We’re going to continue this and conduct long-term studies on more and less light-polluted areas, but we need to start protecting our corals. More sophisticated lighting can be used in coastal areas to not disrupt the environment.”

The work has been published in the journal eLife, alongside an accompanying editorial

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