Pre-Bleaching Coral Microbiome Is Enriched in Beneficial Taxa and Functions

Area of Science:

• Marine Biology
• Microbial Ecology
• Coral Reef Science

Background:

• Coral reef health relies on the coral holobiont, a symbiosis between coral and its microbiome.
• Microbial services like nutrient cycling are crucial but vulnerable to environmental changes, especially thermal stress.
• Warming oceans and thermal stress can disrupt coral microbiomes, leading to bleaching and widespread coral loss.

Purpose of the Study:

• To investigate how elevated temperatures affect the taxonomic and functional profiles of coral surface mucous layer (SML) microbiomes.
• To understand the relationship between SML microbiome dynamics and coral-algal physiology under heat stress.
• To identify potential microbial contributions to coral thermal tolerance.

Main Methods:

• Shotgun metagenomics was employed to analyze the SML microbiome of *Pseudodiploria strigosa* corals under experimental heat treatment.
• Microbial taxa and gene functions in the SML were profiled to assess changes in response to increased temperature.
• Coral-algal physiology was measured to correlate with microbiome variations.

Main Results:

• Heat-exposed corals exhibited stable bacterial genera and functional genes related to nitrogen and sulfur metabolism and stress response.
• The SML microbiome shifted under heat, with increased abundance of potentially probiotic taxa and genes for nutrient acquisition.
• Coral-algal physiology was a significant factor explaining variations in both taxonomic and functional microbiome profiles.

Conclusions:

• The coral SML microbiome demonstrates specific and consistent responses to thermal stress, with an increase in potentially beneficial microbes and functions.
• These microbial shifts suggest a role for the SML microbiome in enhancing coral health and thermal resistance.
• Understanding these microbial dynamics is crucial for predicting and mitigating coral reef decline in a warming climate.