When seawater becomes too warm, the coral begins to lose its color. But the whiteness is only the visible part of a much deeper crisis.
The alliance that supports reef life is breaking down. The coral loses its connection with microscopic algae and a complex community of bacteria — with those that provide it with energy, participate in metabolism, and help it withstand adverse conditions.
Left without a significant portion of its energy, the coral weakens. If the heat lasts too long, the risk of disease and death increases.
But what if we could help it preserve this alliance?
New research has shown that specially selected communities of beneficial microorganisms can support corals during a real marine heatwave — not only in a controlled aquarium, but directly in the open sea.
First aid in the open sea
On September 3, 2026 in the peer-reviewed journal Cell Reports an article was published Probiotic and postbiotic treatment improves coral health and promotes specific metabolic and microbiome changes in situ during a heatwave — "Probiotic and postbiotic treatment improves coral health and induces specific changes in their metabolism and microbiome directly in the natural environment during a heatwave."
The first authors of the study were Erika Peçanha Santoro and Inês Raimundo from the Marine Microbiomes Laboratory at KAUST — King Abdullah University of Science and Technology in Saudi Arabia.
The field experiment took place in the central Red Sea during a natural marine heatwave in the summer of 2022, and its results, after laboratory analysis and scientific peer review, were first published on September 3, 2026. Over 15 days, the average daily water temperature ranged from 30,9 to 31,9 °C.
The study focused on corals Acropora cf. valida, which were already showing the first signs of bleaching.
The scientists divided them into groups and applied:
- two communities of live beneficial bacteria — probiotics;
- heat-inactivated analogues of these communities — postbiotics;
- a control solution without active components.
Thus, for the first time in the field, the researchers were able to compare the effects of live bacterial communities and preparations based on the same but already inactivated microorganisms.
A coral is not a single organism
A coral colony may appear to be a single creature, but in reality it is an entire ecosystem in miniature.
Within the coral's tissues live microscopic algae that, through photosynthesis, provide it with a significant portion of its energy — by some estimates, up to 90%. Alongside them exist numerous bacteria involved in metabolism, nutrient cycling, and protection against pathogens.
The coral and its microscopic partners form a single functional whole — the holobiont. This is a complex living system whose resilience depends on the interactions of all its members.
When the water remains hot for too long, the finely tuned alliance breaks down. The coral loses its algae or their photosynthetic pigments and turns white.
But a white coral is not yet dead. If the heat stress subsides quickly enough, it can restore symbiosis and regain its color. Prolonged heat, on the other hand, leads to energy depletion and increases the risk of disease and death.
Therefore, the researchers attempted to support not only the coral itself but also its associated microbial system.
What the experiment showed
The condition of the corals was assessed primarily by the photosynthetic efficiency of the symbiotic algae — the ability to convert light into energy. The scientists also monitored the corals' coloration and examined changes in their bacterial communities and metabolism.
After 15 days, both probiotic mixtures and one of the two postbiotic formulas helped preserve photosynthetic efficiency. In the control group, this indicator noticeably declined under heat stress.
Previous work had already demonstrated the promise of coral probiotics in aquariums. The new study shows for the first time that microbial therapy can support corals in the far less predictable conditions of the open sea — during a natural heatwave.
However, the results depended on the composition of the preparation: one postbiotic formula helped the corals, while the other did not show a comparable effect. Consequently, not only the form of therapy but also the specific combination of microorganisms is of decisive importance.
This does not yet prove that every reef will necessarily require a unique mixture. But it shows that a universal preparation cannot be considered a guaranteed solution without further trials on different coral species and in various marine conditions.
When even non-living bacteria help
One of the most interesting results was the effect of the postbiotic.
The postbiotic formulations were bacterial communities inactivated by heat. They could not colonize the coral as living microorganisms, but the remaining cells and their components could influence the coral organism and its microbiome.
As if the microorganisms were no longer present in the system alive, but left behind a biological message.
After postbiotic treatment, the researchers found an increase in the relative abundance of bacteria of the genus Cobetia. Some representatives of this genus have previously been associated with coral resistance to heat stress. However, the new work does not yet prove that it was Cobetia that caused the improvement.
Probiotics and postbiotics altered the microbial and metabolic profiles of corals in different ways. This suggests that a similar positive outcome may be achieved through several biological pathways.
From a practical standpoint, postbiotics are particularly interesting: inactivated preparations are potentially easier to store and transport, may remain stable longer, and require lower costs than live cultures.
But before talking about widespread use, it is necessary to determine which components provide the effect, how long it lasts, and whether repeated intervention is safe for the natural microbiome of the reef.
Not a cure for climate change
The results of the study are encouraging, but they cannot be turned into a promise of rapid salvation for all coral reefs.
The experiment:
- lasted only 15 days;
- was conducted on one coral species;
- covered a limited area of the Red Sea;
- tested several specific bacterial compositions;
- assessed the condition of corals during a single heat wave.
The work does not prove that the treated corals received long-term protection or that the technology can already be applied on the scale of an entire reef.
Probiotics also do not eliminate the main cause of mass bleaching — climate change caused by human activity and the rise in ocean temperature. Microbial therapy may become an additional tool for reef protection, but it will not replace the reduction of greenhouse gas emissions, the protection of marine areas, and the reduction of local pollution.
Scientists still have to test the duration of the effect, select compositions for other corals, and assess the possible consequences of intervention in the microbiome of different ecosystems.
Restoration as the return of a union
We are used to imagining treatment as a struggle: find the enemy, suppress it, remove it from the body.
The story of corals offers a different image — restoration of harmony.
Beneficial bacteria do not build the coral anew or replace its natural defense mechanisms. They help support the system of connections through which the coral organism is able to maintain vital functions.
The reef does not exist as a collection of independent beings. The coral is connected to algae and bacteria, the colony to the surrounding community, and the entire reef to temperature, currents, light, and the chemical composition of the water.
Resilience here does not belong to a single organism. It is born from many interactions — in the space between them.
What did the ocean remind us of today?
That life reveals its strength in unity.
The coral reef is not a collection of separate organisms, but an integral system of interconnections. Coral, algae, bacteria, currents, light, and water each play their special role. No one exists on their own, and the resilience of the whole is born when each is in its place and supports the common union.
Perhaps human communities are also arranged this way. We may seem separate, but our strength manifests in interconnection — in the ability to hear each other, preserve our own uniqueness, and at the same time participate in creating a common space of life.
Unity does not require everyone to become the same. On the contrary, it arises when each brings to the whole exactly what only they can give.
Today the ocean reminded us: when each is in its place and all connections sound in harmony, a multitude of separate lives becomes a single living organism.
