Coral reefs in the Gulf of Eilat (commonly called the Gulf of Aqaba) are highly resistant to global warming, rising sea temperatures and bleaching episodes, which are taking a toll on their counterparts throughout the world.
However, the findings of long-term research published recently in the journal Global Change Biology by an international team of coastal and data specialists show a new threat to this coral habitat in southern Israel: The surrounding maritime ecology is suffering as a result of an extensive urban expansion near the Gulf coast.
Scientists invested a year in examining how and whether urbanization is affecting normal biorhythms in corals, as well as if urbanization is an underrated contribution to the worldwide coral loss. Coral metabolism, development and reproduction cycles are all governed by natural biorhythms.
The research was directed by Dr. Yaeli Rosenberg and Prof. Oren Levy, Director of the Marine Lab at Bar-Ilan University’s Mina and Everard Goodman Faculty of Life Sciences.
The research was headed by the group, which also 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 (University of Konstanz, Germany) (ARC Centre of Excellence for James Cook University in Queensland, Australia).
Two locations in the Gulf of Eilat, at the northern edge of the Red Sea, were sampled: one near Eilat and the other further away. Eilat, like any other metropolis, releases a variety of chemical, light, hormonal and noise pollutants that can impact marine ecosystems.
The crew tested the reefs throughout the year at various times of day and moon phases, encompassing daily, monthly and annual biological cycles. To figure out how urbanization affects biorhythm, researchers employed a variety of methodologies, including RNA expression, physiological tests, stable isotope measurements and microbiome study.
Given the fact that the corals appeared to be in good condition, the researchers revealed that normal biorhythms and environmental sensing systems were seriously affected in corals residing near Eilat. The urban environment disrupted diel and lunar cycles associated with coral metabolism, predator, microbial functional diversity and circadian clock activities.
The microbiomes of the urban coral community showed altered seasonality patterns, indicating that urban has an influence on the holobiont (the complete organism) rather than just the coral host.
On the surface, the corals seem healthy, but when looking deeper than the naked eye, we saw the strong effect of urbanization very conclusively.
Dr. Yaeli Rosenberg, Director, Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University
Professor Levy notes, “The disruption of the daily and monthly cycles resulted in lower physiological performances and reproduction cycles that disappeared in the urban corals.” Corals in the non-urban location, on the other hand, appeared healthy, and their biorhythms cycled normally across the sample periods.
Before municipal development choices are made, researchers, according to Levy, must analyze the possible impact of urbanization on maritime regions.
Levy is now working on an evaluation of the worldwide impact of light pollution on marine habitats, as part of his research on biological cycles in marine creatures. With evidence that urbanization is a role in worldwide coral loss, he aims to investigate the effects of a mix of sensory pollutants (chemical, light pollution, hormone and noise) on coral reefs to see what pollution levels they can tolerate.
The Israeli Science Foundation supported Levy with funding for this research.
Rosenberg, Y., et al. (2022) Urbanization comprehensively impairs biological rhythms in coral holobionts. Global Change Biology. doi.org/10.1111/gcb.16144.