Haifa and Jerusalem U.: Scientists Reveal the Microbial Pulse of a Coral Reef in the Gulf of Aqaba
University of Haifa’s Dr. Derya Akkaynak calls the study “a critical baseline” that will enable future research to better detect shifts associated with environmental stress. A new joint study by researchers from University of Haifa and the Hebrew University of Jerusalem reveals that coral reefs in the Gulf of Aqaba drive dramatic daily and seasonal changes in the microscopic organisms living in surrounding waters—organisms that are essential to reef health and resilience.
The study offers the most detailed picture to date of how reefs shape the invisible microbial world around them. Researchers examined microbial communities in reef-adjacent waters across two distinct seasons and at high temporal resolution throughout the day–night cycle.
“This study provides a critical baseline,” said Dr. Derya Akkaynak, co-senior author of the study, and a member of the Hatter Department of Marine Technologies at University of Haifa’s Leon H. Charney School of Marine Sciences. “By documenting natural daily and seasonal variability, future research will be better equipped to detect shifts associated with environmental stress.”
While previous studies documented the reef’s impact on plankton levels, this study is the first to capture these dynamics at such fine time scales and to include single-celled eukaryotes, known as protists, in the analysis.
“Coral reef ecosystems are highly dynamic, but the role of microorganisms living at the coral-ocean interface is poorly understood,” said Herdís G. R. Steinsdóttir, postdoctoral researcher at University of Haifa and lead author of the study. “They shift fundamentally between day and night, and those shifts strongly shape the microbial communities in the surrounding water.”
During daylight hours, shallow coral reefs rely on the sunlight as a primary energy source, and photosynthesis is a dominant metabolism. At night, heterotrophic processes start to dominate. The researchers observed indicators of this metabolic shift in the surrounding microbial ecosystem, including a strong decline in phytoplankton and bacteria numbers at dusk and a marked nighttime increase in heterotrophic protists—organisms that feed on other microbes.
“The strength of the daily cycle surprised us,” Steinsdóttir added. “It highlights that the time of day at which reef waters are sampled can significantly influence scientific observations and conclusions.”
Microorganisms play essential roles in coral reef ecosystems, recycling nutrients, breaking down organic matter released by corals, and serving as food for reef organisms. The study also found microbial species typically associated with coral interiors present in the surrounding water, raising new questions about how corals acquire and maintain their symbiotic partners.
“Just as the human microbiome is essential to our health, microbial communities are fundamental to coral reef health,” said Dr. Miguel Frada from the Hebrew University of Jerusalem, co-senior author of the study. “Yet they are often overlooked because they are invisible and difficult to quantify.”
The findings come amid growing concern over climate change, ocean warming, acidification, and pollution on coral reefs worldwide. While many studies focus on coral organisms themselves, this research emphasizes the importance of understanding the broader reef ecosystem—including microbial communities that respond rapidly to environmental change.
Beyond advancing scientific understanding, the researchers note that microbial communities may eventually serve as sensitive indicators of reef health, offering early insights into ecosystem change through water-based monitoring.
