Better together? Coral fusion could throw bleached reefs a lifeline - Biology - Ecology - Cell & Microbiology

Conceptual diagram illustrating potential mechanisms of heat-evolved (HE) symbiont and nutrient transfer across coral fragments following tissue fusion. Credit: Environmental Microbiology Reports (2026). DOI: 10.1111/1758-2229.70418

When corals are stressed by pollution, high water temperatures or other environmental changes, they can lose the microscopic algae living inside them and on which they depend for food. As a result, they turn white, a phenomenon known as coral bleaching. They will not die straight away, but it will be game over if the stress continues long enough for them to starve.

Corals are dying at a rapid rate due to rising ocean temperatures and cannot always recover on their own when bleaching occurs. But a team of researchers led by Bede G. Johnston at the Australian Institute of Marine Science is testing a new way to help them bounce back.

And the big idea is surprisingly simple: fuse a healthy, algae-rich coral to a bleached one so they might share resources and algae.

Giving bleached corals a helping hand

To see if this living connection could work, the team tested the process in the lab using two Great Barrier Reef coral species, Galaxea fascicularis and Psammocora columna.

For each species, they chemically bleached small fragments to remove their natural algae and inoculated some with a laboratory-evolved, heat-tolerant algal strain named SS8 (Cladocopium proliferum). These were then allowed to recover and served as donors for the remaining bleached fragments.

Then, they placed donor and recipient pairs of the same species next to each other so their living tissues were touching and waited to see what would happen.

(A) Psammocora columna donor (pigmented) and recipient (bleached) fragments at 0 DPF (days post-fusion setup). (B) The same donor–recipient pair at 13 DPF and (C) 36 DPF. Credit: Environmental Microbiology Reports (2026). DOI: 10.1111/1758-2229.70418

When two become one

The results, published in the journal Environmental Microbiology Reports, revealed a rapid and intriguing response.

All 52 donor-recipient pairs fused successfully, beginning as early as three days in Galaxea fascicularis and nine days in Psammocora columna.

What's more, recipient corals recovered their color and the photosynthetic efficiency of their algae. This occurred faster at the spot where they joined the donor coral than it did in tissue farther away.

After about 50 days, genetic testing revealed that the heat-tolerant SS8 strain was present at low levels in 15 out of 19 fused Galaxea fascicularis. However, it was also detected in 13 out of 18 unfused corals sharing the same water tank. So while physical fusion clearly speeds up local recovery, SS8 can also spread through the surrounding water. The researchers could not establish whether any of the algae had passed directly through the fused tissues.

"These findings suggest that adult coral tissue fusion can support localized post-bleaching recovery and may contribute to symbiont movement between coral fragments," wrote the team in their paper.

While tissue fusion offers a promising new tool for restoring reefs, the scientists stress that more work is needed before it can be used in the wild.

"Controlled dose-response experiments, longer-term monitoring and subsequent heat-stress assays will be needed to test whether acquired HE [heat-evolved] symbionts can meaningfully alter post-bleaching recovery or thermal tolerance." 

by Paul Arnold, Phys.org

edited by Lisa Lock, reviewed by Robert Egan 

Source: Better together? Coral fusion could throw bleached reefs a lifeline