By Barış Özdinç
A recent interview in the Scientific American highlights Darwin’s reef paradox; it observes that coral reefs are teeming with lush life in an otherwise nutrient-poor ocean. According to Dr. Christian Voolstra, the trick is the symbiosis between sessile animals, reefs, and the photosynthetic micro algae residing within the reefs. The micro algae produce sugars as a result of photosynthesis, which is consumed by reef animals. However, coral reefs are under great threat from climate change, with 14% experiencing bleaching in the last decade due to increased temperature, sunlight and pollutants. Coral reef bleaching is a result of the micro algae dying, as these organisms contain pigments responsible for the reefs’ color. Essentially, corals starve to death if environmental factors killing their algae persist. To investigate possible solutions to the coral bleaching problem, Dr. Voolstra and colleagues looked to the coral microbiome. They drew parallels between fecal microbiome transplants (FMT) and coral bleaching; they reason that if microbiome transfer from a healthy person to a sick person can improve health, why couldn’t the same be true of coral reefs? To identify healthy corals with resilience to climate change, Dr. Voolstra and colleagues cultured multiple types of corals in aquariums that simulated ocean warming conditions experienced by wild corals over 75 days. In their study, they collected probiotic bacteria from resilient corals, treated a subset of genetically identical corals with probiotics and placebo-treated the rest of the corals. Interestingly, all the corals under warming conditions started to bleach, but the probiotic treated ones recovered faster and had an increased survival rate of 40%. This seemed to be due to variation in the probiotic-treated corals’ microbiome which induced repair, immunity and stress response gene expression in the coral hosts. Although 40% survivorship is an immense improvement, Dr. Voolstra notes that how long probiotic induction of gene expression would remain is not known. Given this fact, combined with the 300,000 square kilometers of coral reefs worldwide, the application of probiotics to heal corals becomes unmanageable. No organism makes a living in isolation, says Dr. Voolstra, and highlights that understanding the interactions of corals within their ecosystem may be key to solving the coral bleaching issue.