The biological clock of corals can function even without the algae that nourish them
In the marine ecosystem, corals and algae maintain a symbiotic relationship such that corals provide algae with shelter and carbon dioxide, while algae, through photosynthesis, supply corals with food and nutrients vital to their survival. This give-and-take relationship is largely dependent upon synchronization and coordination, and likely requires "cross-talk" between the biological clock of the coral host and that of the symbiont algae.As rising sea temperatures and increasing bleaching events cause corals to lose their algae and die, researchers are seeking to decipher exactly how this biological mechanism works, and whether corals can survive without the presence of algae for a period of time. This is important in order to understand which species might be “winners or losers” in continued heat wave episodes. Researchers at Bar-Ilan University in Israel have now discovered one species of "winners". Photo: The coral species Euphyllia paradivisa in the Red Sea Gulf of Eilat. Credit: Dr. Gal Eyal

An organisms ability to gauge daily and seasonal signals and live in sync with nature is enabled by the internal and independent mechanism of the biological clock. Breaks down sugar and synthesizing fats is one of the things corals do.

In the marine environment, corals and algae have a symbiotic relationship in which the corals provide the algae with shelter and carbon dioxide and the algae provide the corals with food and nutrition. The give-and-take relationship is dependent on coordination and the biological clock of the coral host.

As rising sea temperatures cause corals to lose their algae and die, researchers are trying to understand how this biological mechanism works and whether corals can survive without the presence of algae for a period of time. In heat wave episodes, it's important to understand which species are winners and which arelosers. One species of "winners" has been discovered by researchers.

In previous studies, the coral species known as E. paradivisa has been shown to be able to survive in the dark. The biological clock of this species was documented for the first time in a paper recently published in the journal Science Advances.

A team of researchers from Bar-Ilan led by Dr. Mieka Rinsky transferred abundant E. paradivisa from their marine environment in Israel's Red Sea Gulf of Eilat to a laboratory. The corals were put in aquariums in which the water from their natural habitat was pumped. Half of the samples were kept under ambient light and dark cycles, while the other half was kept in complete darkness for a year, triggering a coral bleaching event.

The performance of the biological clock in a high number of replicates of healthy coral colonies was studied after a year. The bleached and unbleached corals were exposed to light and darkness for 48 hours. There is a biological clock that is guided by tidal cycles and influenced by symbioticalgae.

The corals have an independent biological clock that controls the timing of their metabolism. The clock operates on a 24 hour schedule similar to that of humans and functions independently.

The corals can survive in the "twilight zone", which is 65 meters underwater and in almost complete darkness.

Corals die once they're bleached, according to most research. Dr. Rinsky is from Bar-Ilan's laboratory for marine ecology.

The coral's biological clock can operate without daily changes in oxygen and nutrients in its tissues, which results from the presence of their symbiotic algae and, hence, photosynthesis. Corals have a certain "plasticity" that allows them to shift between different rhythms and survive adverse situations such as bleaching caused by changes in the environment.

Corals are able to deal with stress because the biological clock functions independently. The findings show that they can survive extreme heat.

Mieka Rinsky and her team show the complexity of biological clocks in the coral. There is a book titled "Sci Adv.abo6467."

Journal information: Science Advances