Fusing a Healthy Coral to a Bleached One Helped the Sick Coral Regain Its Color in Lab Tests
All 52 pairs of Great Barrier Reef coral fragments fused, and the bleached partners recovered faster where the two tissues met, Australian researchers report.
Joining a healthy coral to a bleached one helped the bleached coral recover in laboratory experiments, according to a team at the Australian Institute of Marine Science that is looking for new ways to rescue overheated reefs. The work, led by Bede G. Johnston, appears in Environmental Microbiology Reports.
Corals bleach when pollution, high water temperatures or other stresses push them to lose the microscopic algae that live inside them and supply most of their food. Bleached corals do not die at once, but they can starve if the stress lasts. Rising ocean temperatures are now killing corals quickly, and they often cannot recover on their own.
Johnston's team asked whether tissue fusion could help. The idea is that two joined corals might share resources and algae. The study, titled "Stronger Together: Isograft Fusion Accelerates Recovery and May Facilitate Heat-Evolved Symbiont Transmission in Bleached Adult Corals," used two Great Barrier Reef species, Galaxea fascicularis and Psammocora columna.
The researchers first bleached small coral fragments with chemicals, stripping out their natural algae. Some were then inoculated with SS8, a laboratory-evolved, heat-tolerant strain of the alga Cladocopium proliferum. Those fragments recovered and served as donors. Each donor was paired with a bleached recipient of the same species, and their living tissues were placed in contact.
The pairings worked. All 52 donor-recipient pairs fused. Fusion began as early as three days after setup in G. fascicularis and nine days in P. columna. The recipients regained their color and the photosynthetic efficiency of their algae, and recovery was faster at the junction than in tissue farther away.
One result complicates the story. After about 50 days, genetic testing found the SS8 strain at low levels in 15 of 19 fused G. fascicularis. It also turned up in 13 of 18 unfused corals that shared the same tank. That means the heat-tolerant algae can spread through the surrounding water, not only through fused tissue, and the researchers could not tell whether any algae passed directly across the joined tissue.
The authors concluded that adult coral tissue fusion can support localized recovery after bleaching, and that it may contribute to the movement of symbionts between fragments. They stressed that the study was done in the lab on small fragments, and that much more work is needed before anyone tries it on a wild reef. They called for controlled dose-response experiments, longer-term monitoring and later heat-stress assays to test whether heat-evolved symbionts can meaningfully improve recovery or heat tolerance.
The paper arrives amid a wave of coral research aimed at buying reefs time as oceans warm. Even if fusion proves practical, it would be a tool for restoration projects rather than a fix for the underlying heat. Phys.org's Paul Arnold reported the findings on October 15.
