Coral Reefs Believed to Be Resistant, Found Vulnerable in Israeli Study

Researchers at Bar-Ilan University, Israel, have found that massive urban development near the Gulf of Eilat (also known as the Gulf of Aqaba) is affecting the marine habitat. It was earlier believed that the coral reefs in the Gulf are resistant to rising water temperature, bleaching and global warming compared to their counterparts around the world.

The researchers investigated if urbanization is disturbing the natural biorhythms (a rhythmic biological pattern in the functioning of the organism that controls, metabolism, growth and reproduction) in corals. And if yes, then how? They also examined whether urbanization could be a factor resulting in the global decline of corals.

The research was led by 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.

The coral samples were collected from the two sites in the Gulf of Eilat, at the northern tip of the Red Sea. One of the sites was the nearby area of the city of Eilat, and the other was away from it.

These samples were tested during the day and at night. Also, daily, monthly and seasonal biological cycles of the reefs were noted by the researchers. They used various genetic sequencing techniques such as physiological studies, RNA expression, microbiome analysis and stable isotope measurements to find how urbanization has altered the biorhythms of the coral reefs.

Researchers discovered that the corals’ environmental sensory systems and natural biorhythms were extensively affected by the urbanization of Eilat despite their healthy appearance. The urbanization also disrupted the lunar and diel cycles linked to coral metabolism, microbial functional diversity, circadian clock functions and predation. The impact of urban conditions was seen on the entire organism (holobiont) rather than the coral host in the form of changed seasonality patterns.

“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. In contrast to the corals in urban sites, the corals of the non-urban sites looked healthy and their biorhythms were normal during the sampling period.

Levy stated that scientists must be indulged in determining the possible impact of urbanization on marine areas before making decisions on municipal development.

Levy’s research also points to the biorhythms in aquatic animals. Currently, he is preparing a write-up on the global impact of light pollution on marine life. In addition to the evidence that urbanization is a contributing factor to the decline of corals globally, he aims to study the effects of sensory pollutants such as hormonal, noise, chemical and light pollution on coral reefs to find what thresholds (limit above which certain condition comes into effect) of pollution they can resist.

The study results have been published in the journal Global Change Biology.

Contributed by: Sunaina Dolwani