Not necessarily GMO, but there is some research into seeding corals with more resilient Zooxanthellae - the algae that is symbiotic with the coral itself. Often

Not necessarily GMO, but there is some research into seeding corals with more resilient Zooxanthellae - the algae that is symbiotic with the coral itself. Often it's the Zooxanthellae that dies in the higher temperatures and that causes the coral to die because it derives nutrients from the algae.