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Nighttime Light Pollution Disrupting Corals’ Reproductive Cycles

A worldwide deluge of evening light pollution from artificial sources, coupled with rapidly expanding development in coastal communities, is contributing to disturbances in the reproductive cycles of coral reef populations, according to a new study.

(CN) — A worldwide deluge of evening light pollution from artificial sources, coupled with rapidly expanding development in coastal communities, is contributing to disturbances in the reproductive cycles of coral reef populations, according to a new study.

The increased use of LED light and illumination from other artificial sources has surged as economies become ever more globalized, work days extend into the evening hours and societies stray further from syncing activity with the Earth’s natural light cycles. 

Artificial light at night emanates powerfully from street lamps, hotels, sport stadiums, office buildings and other infrastructure, creating the skyglow effect, glare and over-illumination.

Light emitted from LED sources tends to be in smaller wavelength form and travels along the blue portion of the light spectrum, which can more easily penetrate deep ocean waters, according to a study published Thursday in the journal Current Biology.

The Earth’s natural light and dark cycles are based on the planet’s rotation and are a critical factor in the reproduction cycles of many marine organisms.

Many organisms in the ocean, including coral reefs, have spawning cycles that are synced with the natural solar and lunar illumination periods, which trigger the development of sperm and eggs and their synchronized release into the water for external fertilization, the study said.

Coral reefs’ reproductive processes are only active a few months of the year when conditions are right and successful development of viable offspring is critical to replenishing degraded reefs, the study states.

Researchers in Israel set out to examine the impact that light pollution from coastal communities around the world has on coral reefs’ gametogenic process. 

Two coral species, acropora millepora and acropora digitifera, were collected from the Indo-Pacific Ocean and monitored by researchers. 

The colonies were held in outdoor tanks at the Bolinao Marine Laboratory in the Philippines and exposed only to natural light and seawater.

After being divided later into three groups, including one control group, the colonies were exposed to LED lamps with both cold (yellowish with less blue light) and warm (white with more blue light) spectra.

The LED exposure went on for three months and was activated daily from sundown until sunrise, except for the control group, which received no light exposure after sundown. 

To measure colony health, researchers measured chlorophyll fluorescence yield.

The study’s lead author, Oren Levy of Bar-Ilan University in Israel, said in a statement the results show light pollution clearly delayed gametogenesis and unsynchronized gamete release, critical spawning components typically triggered by natural illumination cycles. 

"Both key coral species were affected by ecological light pollution. They exhibited asynchrony in the reproductive state which was reflected in the number of oocytes per polyp, gametogenesis, and gamete maturation," Levy said. "This was further reflected at the population level where only corals exposed to natural light cycles succeeded in spawning synchronization. Light treatment with both cold and warm LEDs had a similar impact on the gametogenesis cycle.”

To demonstrate the relevancy of their findings on a worldwide scale, researchers constructed a digital global map showing the impact of light pollution in bodies of water including the Caribbean Sea and both the Pacific and Indian Oceans.

A stark example of negative impact is in the Gulf of Aqaba — near Israel and Egypt in the northern Red Sea — where light pollution is illuminating the sky to a point that is 47% to 60% brighter than the natural night sky, the study said.

Researchers said in the statement the global “spectral shift” to artificial light must be taken into account when crafting conservation plans for coral reefs near human communities. 

Levy said in the statement further research is needed to determine what coral species have adapted to light pollution and what mechanism they have developed to do so.Contributors to the study include researchers from the University of the Philippines, the GFZ German Research Centre for Geosciences, and Tel Aviv University and the Interuniversity Institute for Marine Sciences in Israel.

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