Coral reefs are not only a draw for marine tourism but also an indicator of damage to the environment. Surprisingly, coral reefs in the Gulf of Eilat have been resistant to global warming, rising water temperatures and bleaching events that are crippling their counterparts elsewhere around the world. 

However, according to a long-term study by an international team of marine and data scientists that included researchers at Bar-Ilan University (BIU) in Ramat Gan (near Tel Aviv), the University of Haifa and the Weizmann Institute of Science in Rehovot, these corals may look healthy but in fact be very sick. 

Dr. Yaeli Rosenberg with Prof. Oren Levy, director of the Marine Lab at Bar-Ilan University’s Mina and Everard Goodman Faculty of Life Sciences, led the team, which included Dr. Shahar Alon (Bar-Ilan University Faculty of Engineering); Prof. Aldo Shemesh’s lab (Weizmann Institute of Science), the Bioinformatic Services Unit (University of Haifa), Prof. Chris Voolstra’s lab (University of Konstanz, Germany), and Prof. David Miller’s lab (ARC Centre of Excellence for James Cook University in Queensland, Australia).

They published their worrisome findings in the journal Global Change Biology under the title “Coral reefs are in global decline due to climate change and anthropogenic influences.” Their results confirm a different threat to this coral refuge in southern Israel – massive urban development near the Gulf coastline is taking a devastating toll on the local marine environment.

For an entire year, the researchers examined how and if urbanization is disrupting natural biorhythms, which are responsible for coral metabolism, growth and reproduction cycles, and whether urbanization could be an overlooked contributing factor to global coral decline. 

Two sites in the Gulf of Eilat at the northern tip of the Red Sea (Sea of Reeds) were sampled – one in close vicinity to the city of Eilat and one further away. Like any city Eilat emits various forms of chemical, light, hormonal, and noise pollution that can be harmful to marine environments.

Throughout the year, the team sampled the reefs during different phases of the moon and different times of day, covering daily, monthly and seasonal biological cycles. Many techniques, such as RNA expression, physiological studies, stable Isotope measurements and microbiome (bacterial) analysis were used to understand how urbanization alters biorhythm. 

Despite the coral’ relatively healthy appearance, the researchers discovered that natural biorhythms and environmental sensory systems were widely disturbed in corals living in proximity to urban Eilat. Cycles every 24 hours and cycles of the moon cycles related to coral metabolism, predation, microbial functional diversity and circadian clock functions were disturbed by the urban conditions. Altered seasonality patterns were also observed in the microbiomes of the urban coral population, signifying the impact of urbanization on the hthe entire organism rather than the coral host alone. 

“Coastal ecosystems [near] urban centers in the tropics are likely to be among the most vulnerable, as they face not only climate change but unpredictable and fluctuating nutrient (nitrogen and phosphorus) and xenobiotic (hormones and other organic contaminants) local pollution, besides chronic exposure to noise and light pollution,” they wrote. “Thus, urbanization of coastal areas near coral reefs is a global issue and is gaining momentum; not only has there been continuous growth of cities such as Jakarta, Singapore, and Hong Kong, but also major new developments have occurred or are planned that are likely to directly impact coral reefs in the near future.”

“On the surface, the corals seem healthy, but when looking deeper than the naked eye, we saw the strong effect of urbanization very conclusively,” said Rosenberg. “The disruption of the daily and monthly cycles resulted in lower physiological performances and reproduction cycles that disappeared in the urban corals,” added Levy. By contrast, corals in the non-urban site looked healthy and their biorhythms showed normal cycling over the sampling periods.   

Levy, whose research also focuses on biological rhythms in marine animals, urged that scientists must be involved in assessing the potential impact of urbanization on marine areas before municipal development plans are finalized. 

She is currently preparing a review of the impact of light pollution on marine environments globally. With evidence that urbanization is a contributing factor to global coral decline, he plans to study the combination of sensory pollutants – chemical, light pollution, hormonal and noise – on coral reefs to determine what levels of pollution they can withstand.