New Study Reveals the Surprising Role of Microbes in Coral Survivability

For the first time, scientists have identified a single-celled bacteria that can protect corals from ocean warming-related disasters like bleaching. Researchers at the University of Miami's Rosenstiel School of Marine, Atmospheric, and Earth Science and the Institute of Evolutionary Biology in Barcelona led the new study.

Also, it provides fresh insights into the potential role microbes may play in assisting corals in withstanding projections of global warming by the end of the century. They discovered that scientists could determine if a coral would withstand heat stress by looking at the number of specific protists within the coral microbiome, which is made up of a variety of microorganisms that dwell within corals.

With ocean warming events becoming more common, these discoveries have significant ramifications for corals worldwide, particularly those without zooxanthellae, the symbiotic algae that cause corals to bleach in warm water.

This is the first time that a non-algae microbe has been shown to influence the ability of corals to survive a heat-stress event; as corals face more and more heat-stress events due to climate change, a better understanding of all the microbes that may influence survivability can inform conservation practitioners as to which corals they should prioritize for intervention.

Javier Del Campo, Senior Author and Assistant Professor, The Rosenstiel School, University Pompeu Fabra

The multinational research team gathered coral samples from all around the Mediterranean to perform heat-stress tests and microbiome analyses as part of the project. Before putting the bacteria and protists in the microbiome of one species of soft coral, the violescent sea-whip (Paramuricea clavata), to a natural heat stress in the lab to search for signals of mortality, they amplified and sequenced two forms of rRNA.

Due to enormous mortality episodes linked to global warming, Paramuricea clavata, an essential builder of the Mediterranean temperate reefs, is currently in danger.

They discovered that whereas Corallicolids, a group of protists closely linked to the parasite that causes malaria in people, are more prevalent in corals that die from heat stress, Syndiniales, a group of parasitic single-celled protists, are more common in corals that survive heat stress.

The researchers found that although bacteria are more studied in most host organisms than protozoa or single-cell eukaryotes, protozoa may have a significant impact on the health of their coral host.

Javier Del Campo said, “The microbiome is a vital component of coral host health, and we should study all members of it, from the bacteria to the protists.”  

The research was released in the Environmental Microbiology journal. The authors of the study are Anthony Bonacolta and Javier del Campo from the Rosenstiel School and the Institute of Evolutionary Biology; Jordi Miravall, Paula López-Sendino, Joaquim Garrabou, and Ramon Massana from the Institut de Ciències del Mar-CSIC in Barcelona, Spain; Daniel Gómez-Gras from the University of Hawai‘i at Mānoa; and Jean-Baptiste Ledoux from the Universidade do Porto in Portugal.

The research was funded by grant from the University of Miami, Agencia Estatal de Investigación, Departament de Recerca i Universitats de la Generalitat de Catalunya (Project 2021 SGR 00420), Severo Ochoa Centre de Excellence, Ministério da Educação e Ciência, Fundação para a Ciência e a Tecnologia and European Union Futuremares.

Journal Reference

Bonacolta, A. M., et.al., (2023). Differential apicomplexan presence predicts thermal stress mortality in the Mediterranean coral Paramuricea clavata. Environmental Microbiology. doi.org/10.1111/1462-2920.16548