New research reveals that coral reefs actively shape the daily cycles of microscopic life in surrounding waters, with microbial populations fluctuating sharply over a single day. Led by researchers from Israeli universities, the study highlights how processes like predation and coral metabolism drive these patterns in the Gulf of Aqaba. These findings could help monitor reef health amid environmental changes.
Coral reefs, renowned for their biodiversity, play a more dynamic role in regulating nearby microbial communities than previously understood. A study published in Science Advances demonstrates that reefs impose distinct daily rhythms on bacteria, microalgae, and microscopic predators in the waters above them. Researchers collected samples every six hours from a reef in the northern Gulf of Aqaba, Red Sea, comparing them to open waters during winter and summer seasons.
The team, including postdoctoral researcher Dr. Herdís G. R. Steinsdóttir, Dr. Miguel J. Frada from the Hebrew University of Jerusalem, and Dr. Derya Akkaynak from the University of Haifa, used genetic sequencing, flow cytometry, imaging, and biogeochemical analysis to track these shifts. Waters over the reef showed consistently lower levels of bacteria and microalgae compared to open areas, indicating active removal by reef organisms through grazing and predation.
Notably, heterotrophic protists—tiny predators that consume bacteria—surged at night, sometimes increasing by up to 80 percent. Meanwhile, Symbiodiniaceae, dinoflagellates symbiotic with corals, peaked around midday, likely tied to light and coral metabolic cycles. "We found that the reef is not just passively surrounded by microbes," Dr. Frada explained. "It actively structures microbial life in time, creating daily patterns that repeat across seasons and influence how energy and nutrients move through the ecosystem."
These diel cycles proved as pronounced as seasonal variations. "These daily microbial rhythms were as strong as, and sometimes stronger than, seasonal differences," Dr. Steinsdóttir noted. "This shows that time of day is a critical factor when studying reef-associated microbial communities."
The interdisciplinary approach offers a detailed temporal view of reef microbiomes, suggesting these rhythms could serve as indicators of reef function and health in a changing ocean.